Volcanic Landforms and Landscapes of the East Carpathians (Romania) and Their Geoheritage Values

Abstract

The Neogene–Quaternary volcanic range running along the East Carpathians in Romania, extends from the Oaș Mountains, in the north-west, to the South Harghita Mountains and the Perșani Mountains, in the south-east, as part of the broader volcanic province of the Carpathian–Pannonian Region. It resulted from intense volcanic activity during the 15–0.1 Ma time interval, generating huge volumes of effusive and explosive products and a variety of volcanic edifices and primary landforms from large composite volcanoes to small-sized domes/dome-coulées/lava flows and volcaniclastic plateaus around them. The present-day landforms were shaped by various syn-volcanic deformation processes (such as volcano spreading), post-volcanic erosion of various degrees and types (including glacial erosion on the highest-elevation parts and relief inversion in the peripheral areas) and modern anthropic intervention. Developed on this diverse volcanic substrate, the present-day landscape shows a large variety of aspects due to further factors (original topography, elevation, vegetation cover, distance from settlements, anthropic activities, and degradation processes). This volcanic range hosts many geoheritage-relevant sites of various spatial extent (from hundreds of km² to limited areas of a few 10 m²) and of protection status (from national parks, natural or scientific reserves, natural monuments, and protected areas to areas with no protection at all). Despite its high geoheritage potential, geoparks are still absent, geotrails are sparse, and geotourism is in its infancy in the East Carpathian volcanic range.

1. Introduction

Volcanic formations of various ages, from Palaeozoic to Quaternary (Geological map of Romania, scale 1:1,000,000; Geological Institute of Romania) occur on extended areas of Romania covering ca. 1/5 of its territory at surface (and much more if considering their buried counterparts).

The most widespread and long-lasting volcanic activity unfolded during the Neogene and the Quaternary times, starting at ca. 15 Ma ago and lasting until approximately ca. 0.03 Ma. Because of their relatively young age of formation, the original volcanic topography determining the present-day landform and landscape variability show the highest degree of conservation as compared to pre-Miocene volcanic formations.

The volcanic rocks of Neogene–Quaternary age crop out over large areas in the East Carpathians and the Apuseni Mountains. The Neogene–Quaternary volcanic formations of the East Carpathians occur along the western margin of the Carpathian fold-and-thrust belt, mostly at the contact with the Transylvanian Basin (Figure 1).

From NW to SE, the following volcanic segments are geographically individualized (Figure 1): Oaş, Gutâi, Călimani, Gurghiu, North Harghita, South Harghita, and Perșani. It is to note that the segment located between the Gutâi Mountains and the Călimani Mountains, including the Ţibleş, Toroiaga, Rodna, and Bârgău Mountains, traditionally named in the Romanian geological literature as ”the subvolcanic zone” [1], hosts shallow intrusive bodies piercing older sedimentary and metamorphic formations. It is not considered in this paper.

Prominent surface topographic features characterize the Neogene–Quaternary volcanic areas of the East Carpathians. They consist of specific landforms which, in combination with the adjacent non-volcanic topography (e.g., the presence of both volcanic and non-volcanic formations within a limited geographic area), determined the formation of particular landscapes, different from one segment of the range to another and, in cases, even within a particular segment.

Despite the fact that during the past few decades different parts of the range were subjected to geomorphological research for the Harghita Mountains [2,3], for the Oaş Mountains [4,5], and for the Gutâi Mountains [6], no modern synthetic work, combining volcanological and topographic observation, has been published so far. Therefore, this paper attempts to review the volcanic landforms and the landscapes of the East Carpathians, from the Oaş Mountains in the north-west to the Harghita and Perșani Mountains to the south-east.

While there is a strong focus on the geology and geomorphology of the volcanic terrains, we ultimately want to emphasize that this region may host a number of geoparks wherein various aspects of geological and geoheritage values are expressed. The reader should view the various sites described throughout this paper as geosites that illustrate volcanic and geomorphic features that have geoheritage significance. This paper also provides a presentation of the key features of geoheritage significance and attempts to highlight them in order to illustrate the volcanic/geological history of the region for later researchers and geotouristic planning and activities, as well as for educational purposes.

2. Geographic and Geologic Background

Geographically the study area belongs to the East Carpathians mountain range running along its western part, bordered by the Transylvanian Basin to the south and west and by different mountain units of the Carpathian fold-and thrust belt and a few Pliocene–Quaternary small intramountain basins to the East. The various segments of the volcanic range itself belong to various mountainous sub-units (from north-west to south-east): Oaş, Gutâi, Călimani, Gurghiu, North Harghita, South Harghita, and Perșani (Figure 1), showing distinct physiographic aspects, topographic features, areal extension, and elevation. The highest elevations are recorded in the Călimani Mountains (2102 m a.s.l.) and the North Harghita Mountains (1801 m a.s.l.), where glacial/periglacial features are present, lacking from the lower-elevation parts of the range. The areal extent of these mountains is largest in the Călimani Mountains and smallest in the South Harghita Mountains.

Unlike most other parts of East Carpathian volcanic range, where”mountain” denomination coincides with the respective volcanic segment entirely composed of volcanic formations (e.g., the Călimani Mountains, Gurghiu Mountains, and Harghita Mountains), in the case of the Perșani Mountains, its denomination refers to a geographically well individualized but geologically complex “mountain”. The volcanic formations cover just a small part of the area, contributing to just a small but locally relevant extent to its physiographic features and to its overall mountainous landscape.

From the geological point of view the Neogene–Quaternary volcanic area of the East Carpathians is part of the much wider Carpathian–Pannonian Region’s (CPR hereafter) magmatic province, which developed as a result of a complex geodynamic evolution of this East-European megastructure located at the junction between the huge Eurasian plate and an assemblage of smaller plates/lithospheric blocks involving large-scale processes, such as rotation and translation of those lithospheric blocks, subduction, and related orogenic processes (i.e., the formation of the arcuate Carpathian thrust-and-fold belt) and magmatism and an ever changing paleogeographic environment [7]. Magmatism occurred in the 21–<0.1 Ma time interval within CPR [8], with both intrusive and volcanic manifestations along the Carpathian fold-and-thrust belt (“Carpathian volcanism” acc. to [9]) and behind it (“intra-Carpathian volcanism” acc. to [9]). Three distinct chemical types of magma fed different types of surface volcanic activity: felsic calc-alkaline, intermediate calc-alkaline, and alkaline [10,11]—generating abundant volcanic material and covering areas of different extent and location within the CPR.

Most of the East Carpathian volcanic range, from the Oaş Mountains to the South Harghita Mountains, resulted from intermediate calc-alkaline magmatism. In contrast, volcanic activity in the Perșani Mountains was fed by alkaline magmas.

3. General Volcanic Evolution and Volcanic Structures

Miocene to Pleistocene volcanism unfolded in the East Carpathians during the 15–0.03 Ma time interval [8]. As a general trend, it started earlier in the north-western part and shifted gradually in space and time to the east and south-east, continuing the overall trend of eastward time–space migration of both Carpathian and intra-Carpathian volcanism of the wider CPR megastructure [8,9].

The volcanic evolution (i.e., local time–space pattern and trend, type of volcanic activity and resulted volcanic structures and edifices, related hydrothermalism and ore deposits, and type and degree of erosion) had particular features within different volcanic segments (Oaş, Gutâi, Călimani-Gurghiu-Harghita, and Perșani). Due to their age progression and different tectonic influences (e.g., uplift), preservation of the original volcanic topography as well as its modification by erosion is also variable: in general, pristine volcanic forms are well preserved in the south-east (the South Harghita, North-Harghita, and Perșani Mountains) and are progressively altered north-westward along the Călimani-Gurghiu-Harghita range to the Gutâi and the Oaş Mountains. Consequently, recognition and reconstruction of the original forms are more difficult to be achieved in the same direction.

Being generated by viscous magmas of prevailingly andesitic compositions, combined explosive and effusive volcanism in the study area resulted in volcanic landforms characteristic of intermediate calc-alkaline volcanic areas worldwide, where large composite volcanoes (with or without caldera) and smaller-sized volcanic domes (clustered or isolated) in various combinations dominate the landscape. However, factors such as spacing between eruption centers and the chemical variation and volume of the erupted magma, as well as eruption frequency and time distribution of volcanic events, differently modulated the local combination of the original volcanic landforms and their erosion from one segment to another, as presented in the following chapters in detail.

The volcanic landforms of the Perșani Mountains, where less viscous alkali basaltic magmas erupted by dry strombolian and wet phreatomagmatic events, are different, showing the typical features of monogenetic volcanic fields composed of lava fields, scoria cones, and maar depressions surrounded by tuff-rings or tuff-cones similar to other monogenetic volcanic fields in the CPR [12].

4. The Neogene Oaş–Gutâi Segment

4.1. Volcanic Evolution

Volcanic activity developed in the Oaş–Gutâi segment during Miocene, within a large time span of ca. 8 Myr, between 15.4 and 7.0 Ma [8].

In the Oaş Mountains, the volcanic activity lasted ca. 2.5 Myr (from 12.0 to 9.5 Ma [13]). In the 12.0–11.0 Ma time interval, a succession of rhyolitic to andesitic volcanic phases developed, the large-sized Oraşu Nou rhyolitic lava-dome being the most relevant volcanic structure built up in the southernmost part of the area (11.3–11.0 Ma) [14]. In the 10.9–10.5 Ma time interval, two andesitic composite volcanoes (Dealul Negru in the northern part and Poiana Şesu-Huta in the eastern part) and an isolated extrusive dome (Jeleznic dome) in the southern part of the area were formed. A major dome-building phase (10.5–9.5 Ma), generating isolated extrusive domes, dome-coulées, and dome complexes of dacite and high-silica andesite composition, ceased the volcanism in the Oaş Mountains [15].

In the Gutâi Mountains, the volcanism started by felsic (rhyolitic) caldera-related eruptions (approximately 15.4 Ma [16]) represented by ignimbrites and associated volcaniclastics, widespread in the southern part, mostly buried by younger volcanics. A complex intermediate (mostly andesitic) multiphase volcanism developed in the 13.4–7.0 Ma time interval, consisting of four volcanic stages [17]. The complex evolution of the intermediate volcanism reflects the intricate volcano plumbing systems recently constrained for some relevant volcanic structures [18]. The first two volcanic stages were the most voluminous, including numerous volcanic complexes with overlapping products of the coeval volcanic centers. The first volcanic stage developed between 13.4 and 12.1 Ma [19,20], mostly in a subaqueous environment, generating andesitic shield volcanoes, lava flows, and extrusive domes in the southeastern and southwestern part. The second stage (11.6–9.0 Ma) started with an acidic volcanic activity building up dacitic to rhyolitic domes, the most representative being the large-sized Dăneşti–Cetăţele composite dome in the southeastern part of the area. Paroxysmal volcanic events occurred between 11.0 and 9.0 Ma, during which many intermediate and acidic volcanic and intrusive rocks were emplaced [21]. The most voluminous volcanic activity developed in the central and the northern parts where composite volcanoes (Mogoşa, Igniş, Muntele Mic, Pietroasa, Rotundu, and Muntele Bradului), large-sized extrusive domes (Breze, Pleşca Mare, and Gutâi), and extended lava plateaus were formed. Numerous intrusive bodies (dykes, sills, and small-sized laccoliths) occur mainly in the southeastern part of the Gutâi Mountains (11.9–9.0 Ma) [22].

The third volcanic phase is represented by the Laleaua Albă (White Tulip) magmatic complex of small-sized composite andesitic–dacitic dykes emplaced in the southeastern part of the Gutâi Mountains (8.5–8.0 Ma [8]). Small mafic intrusions (Firiza basaltic complex, 8.1–7.0 Ma [23]), crosscutting the older volcanic formations in the central part of the area, represents the fourth stage, which ceased the volcanic activity in the Gutâi Mountains as well as in the whole Oaş–Gutâi segment.

4.2. General Volcanological Features

Volcanic activity in the Oaş–Gutâi segment took place simultaneously with major tectonic events, and it was influenced by the local paleogeography dominated by intra-volcanic and marginal sedimentary basins. The dominantly effusive volcanic products were emplaced in both subaerial and subaqueous conditions.

Large-scale, caldera-related explosive rhyolitic volcanism released a complex succession of ignimbrites and co-ignimbrite fallout tuffs in the southwestern part of the Gutâi Mountains, locally overlain by ignimbrite-related resedimented volcaniclastics interlayered with sedimentary deposits [16].

The andesitic volcanism displays specific features in the two areas where it took place. In the Oaş Mountains, dome-building phases developed mainly in a submarine environment. Extrusive domes, dome-coulées, and dome complexes are composed by coherent dacites and andesites. Volcaniclastic products-in situ and resedimented hyaloclastites, primary and reworked pyroclastic flow deposits often interbedded with sedimentary deposits, are associated to some of the domes [13].

In the Gutâi Mountains multiphase intermediate volcanism took place simultaneously with extensive tectonic events: a thick pile of volcanic products fills a series of volcano-tectonic depressions/grabens controlled by the major E-W trending Bogdan–Dragoş–Vodă fault system in the southern part of the volcanic area (e.g., the Baia Sprie graben with a ca. 700 m thick pile of volcanic products). In the northern part of the Gutâi Mountains, a more than 1000 m thick volcanic complex is also related to a volcano-tectonic depression. The origin of the thick succession of lavas and reworked volcaniclastic rocks interbedded with sedimentary deposits originated from fissure-fed eruptions in a submarine environment [11]. Overlapping of volcanic products belonging to coevally active volcanic centers hinders the identification and the reconstruction of individual edifices hence only a few composite volcanic structures were identified in the Gutâi Mountains: Mogoşa, Igniş, Muntele Mic, Pietroasa, Rotundu, and Muntele Bradului.

Lava flows of basaltic andesite and andesite composition represent the most voluminous volcanic products in the Gutâi Mountains, in places forming extended lava plateaus (e.g., in the northern part of the volcanic zone). Autoclastic breccias formed in the front of the subaerial lava flows, whereas hyaloclastite deposits formed as subaerial lava flows entered in a subaqueous environment. Scarce phreatomagmatic deposits with accretionary lapilli are related to explosive events. The widespread occurrence of mass flow type volcaniclastics, mainly by reworking of primary volcanic products, suggests erosional/denudation processes during and following volcanic activity.

Intrusive activity in the Gutâi Mountains is represented by intra-volcanic and shallow-level subvolcanic intrusions mainly developed in the southern part of the area.

4.3. Volcanic Landforms and Landscapes

The differences between the volcanic activity (duration, magnitude, surface, and volume) developed in the Oaş Mountains and Gutâi Mountains, respectively, are reflected in the specific features of the volcanic landforms and landscapes of the two areas.

The Oaş Mountains volcanic landforms show low elevations with altitudes ranging between 300 and 900 m a.s.l., the highest elevation being at 917 m a.s.l. The typical landforms are those of the extrusive domes representing the major and the most widespread volcanic structures. Being isolated and surrounded by Neogene–Quaternary sedimentary deposits, many of them show a typical dome morphology resembling the topography of the original volcanic edifices. The sizes of the individual domes vary from 300 m (e.g., Turulung dome, No. 7 in Figure 2a,b) to 5.5 km (e.g., Hatu Lung dome-coulée, No. 4 in Figure 2a,b), most commonly 1–2 km in length/diameter. Overall, the domes are of isometric or slightly elongated shape, conical or flat-topped, with steep or low angle slopes.

Some of the domes have a round shape with low angle slopes (e.g., Pleşcuţa dome of ca. 1 km diameter, No. 5 in Figure 2a,b and Figure 3a), others are subrounded with steep slopes (Jeleznic dome of ca. 4 km length, No. 8 in Figure 2a,b and Figure 3b). Other lava domes (e.g., Oraşu Nou large-sized lava-dome of ca. 5 km length, No. 9 in Figure 2a,b and Figure 3c) or dome-coulées (e.g., Hatu Lung dome-coulée of ca. 5.5 km length, Figure 3d) show more elongated forms with flat tops. The dome complexes show more complex morphologies (e.g., Batarci domes complex, whose lava flows and associated volcaniclastics are spread over a 6 × 8.5 km area, showing a strong relief fragmentation by the hydrographic network, No. 3 in Figure 2a,b).

The Oaş Mountains show a typical landscape imprinted by the isolated extrusive domes surrounded by Neogene–Quaternary sedimentary deposits of the Oaş Basin. This landscape characterizes the western, central, and southern part of the Oaş Mountains. A different landscape occurs in the northern and the eastern parts imprinted by the landforms related to two composite volcanoes: Dealul Negru (No. 1 in Figure 2a,b) and Poiana Şesu-Huta (No. 2 in Figure 2a). Overall, the high fragmentation level, enhanced by the presence of major valleys and of sediment-filled basins, interspersed within the volcanic area, led to the formation of this specific landscape.

In contrast, the Gutâi Mountains show an overall massiveness imprinted by the elevation difference (500–1000 m) of the volcanic area and the surrounding low-relief topography (Oaş, Baia Mare and Maramureş basins) [24]. Nevertheless, there is a significant geomorphological difference between the northern and the southern parts. Composite volcanoes, extrusive domes, and extended lava fields had imprinted a higher altitude (>1000 m a.s.l. elevations, with the highest point at 1443 m a.s.l. in Gutâiul Mare peak) and less fragmented topography in the northern part of the Gutâi Mountains. In the southern part, the lower altitude and more dissected volcanic relief can be assigned to higher erosion rates of the mainly subaqueous volcanic structures and their softer products.

The most specific volcanic landforms are associated to composite volcanoes, extrusive domes, lava plateaus, and exhumed intrusive bodies. The composite volcanoes (Mogoşa, Igniş, Muntele Mic, Pietroasa, Rotundu, and Muntele Bradului, Figure 4a) geomorphologically represent residual volcanic landforms resulting from erosional modeling of the original edifices. Their current morphology is a result of both constructional and erosional processes, including summit lowering and denudation processes related to the hydrographic systems formed after the edifice construction.

The most relevant landform features of the Gutai Mountains volcanic edifices are summarized in Table 1.

The exhumed intrusive bodies show a specific morphology consisting of positive landforms with irregular shapes, well individualized in contrast with the surrounding sedimentary deposits. The basaltic andesite sills in the northeastern (Agriş sills, No. 11 in Figure 4a) and northern (Cherec sills, No. 12 in Figure 4a) parts of the Gutâi Mountains, occurring outside of the contiguous volcanic area, display a topographically well-individualized scarp up to 6 km long and generally <50 m high.

Table 1. Major volcanic and landform features in the Gutâi Mountains.

Volcano (Name, Location and Figure Reference)	Volcanic Edifice Type	Morphometry (Extension, Elevation a.s.l.)	Major Landform Features
Mogoşa (Figure 4a,b and Figure 5a)	Composite volcano	8 km diameter 1246 m	Small peak plateau, elongated slopes toward S and W, much fragmented relief toward SW, impressive steep cliffs at the SE contact with sedimentary deposits
Igniş (2 in Figure 4a,b)	Composite volcano	9 × 4 km 1307 m	Asymmetric topography, wide summit plateau, big escarpment (>100 m high) toward S, residual landforms: rock pillars, towers, and tors (e.g., the ”Igniş Sphinx”)
Muntele Mic (3 in Figure 4a,b)	Composite Volcano	7 × 3 km 1012 m	Steep conical upper edifice, elongated slopes toward N, strongly fragmented relief toward SW and NW
Pietroasa (4 in Figure 4a,b)	Composite volcano	7 × 4 km 1200 m	Elongated shape, conical upper part, strongly fragmented to the N and S by two hydrographic systems, residual and periglacial landforms: cliffs and rock towers (e.g., the ”Oaş Sphinx”)
Rotundu (5 in Figure 4a,b)	Composite volcano	10 × 5 km 1241 m	Large remnant crater (ca. 3 km across) as a semicircular ridge open to the E [26] transformed into a hydrographic catchment area
Muntele Bradului (6 in Figure 4a,b)	Composite volcano	8–9 km diameter 1091 m	Strongly dissected by a hydrographic network developed around the edifice, parasitic remnant cone (Vârful Mare, 1032 m a.s.l.) in the upper part of the edifice
Dăneşti-Cetăţele (7 in Figure 4a,b)	Composite dome	7 × 5 km 675 m	Residual volcanic relief/skeleton-like landform (low-elevation hills with depressions between them), spectacular erosive landforms on volcaniclastic products
Breze (8 in Figure 4a,b)	Dome	3 × 1.5 km 1253 m	Topographically well-individualized, flat-topped, elongated (NE–SW) mountain
Pleşca Mare (9 in Figure 4a,b)	Composite dome	4.5 km diameter 1291 m	Cupola-like mountain of subrounded shape with low angle slopes
Gutâi (Figure 4a,b and Figure 5a)	Dome	4.5 × 2 km 1444 m	Topographically prominent mountain with a large summit plateau bordered by impressive steep cliffs and specific landforms of weathering origin at the NW and the SW edges

Table 1. Major volcanic and landform features in the Gutâi Mountains.

Volcano (Name, Location and Figure Reference)	Volcanic Edifice Type	Morphometry (Extension, Elevation a.s.l.)	Major Landform Features
Mogoşa (Figure 4a,b and Figure 5a)	Composite volcano	8 km diameter 1246 m	Small peak plateau, elongated slopes toward S and W, much fragmented relief toward SW, impressive steep cliffs at the SE contact with sedimentary deposits
Igniş (2 in Figure 4a,b)	Composite volcano	9 × 4 km 1307 m	Asymmetric topography, wide summit plateau, big escarpment (>100 m high) toward S, residual landforms: rock pillars, towers, and tors (e.g., the ”Igniş Sphinx”)
Muntele Mic (3 in Figure 4a,b)	Composite Volcano	7 × 3 km 1012 m	Steep conical upper edifice, elongated slopes toward N, strongly fragmented relief toward SW and NW
Pietroasa (4 in Figure 4a,b)	Composite volcano	7 × 4 km 1200 m	Elongated shape, conical upper part, strongly fragmented to the N and S by two hydrographic systems, residual and periglacial landforms: cliffs and rock towers (e.g., the ”Oaş Sphinx”)
Rotundu (5 in Figure 4a,b)	Composite volcano	10 × 5 km 1241 m	Large remnant crater (ca. 3 km across) as a semicircular ridge open to the E [26] transformed into a hydrographic catchment area
Muntele Bradului (6 in Figure 4a,b)	Composite volcano	8–9 km diameter 1091 m	Strongly dissected by a hydrographic network developed around the edifice, parasitic remnant cone (Vârful Mare, 1032 m a.s.l.) in the upper part of the edifice
Dăneşti-Cetăţele (7 in Figure 4a,b)	Composite dome	7 × 5 km 675 m	Residual volcanic relief/skeleton-like landform (low-elevation hills with depressions between them), spectacular erosive landforms on volcaniclastic products
Breze (8 in Figure 4a,b)	Dome	3 × 1.5 km 1253 m	Topographically well-individualized, flat-topped, elongated (NE–SW) mountain
Pleşca Mare (9 in Figure 4a,b)	Composite dome	4.5 km diameter 1291 m	Cupola-like mountain of subrounded shape with low angle slopes
Gutâi (Figure 4a,b and Figure 5a)	Dome	4.5 × 2 km 1444 m	Topographically prominent mountain with a large summit plateau bordered by impressive steep cliffs and specific landforms of weathering origin at the NW and the SW edges

Figure 5. View toward the eastern part of the Gutâi volcanic area from the Igniş Peak with well individualized volcanic structures of large-sized Gutâi extrusive dome, Mogoşa composite volcano, and Şatra dome (a). The northern zone of the Gutâi Mountains with typical landforms on the extended lava plateaus (b) (Photos credit: Péter Lengyel).

Figure 5. View toward the eastern part of the Gutâi volcanic area from the Igniş Peak with well individualized volcanic structures of large-sized Gutâi extrusive dome, Mogoşa composite volcano, and Şatra dome (a). The northern zone of the Gutâi Mountains with typical landforms on the extended lava plateaus (b) (Photos credit: Péter Lengyel).

In the southern part of the Gutâi Mountains, specific landforms formed on rocks subjected to intense hydrothermal alteration. The silicified ± adularized rocks display a ruin-like positive relief, commonly with vertical cliffs named by the local people ”Piatra” (i.e., ”Stone”), such as the ”Handal Stone” in the Nistru base metal ore deposits zone, the ”Malnaş Stone” in the Cavnic base metal ore deposits zone, and the ”Totoş Stone” in the Jereapăn base metal ore deposits zone.

The Gutâi Mountains display a large variety of landscapes related to the numerous and different volcanic landforms. The northern part of the volcanic area shows a specific landscape, resulting from the combination between composite volcanic landforms and extended lava plateaus, with steep slopes at the edges toward the Maramureş Basin. The impressive scars and escarpments of some volcanic structures (e.g., the Igniş volcano escarpment is more than 100 m high) form particular landscapes. Numerous local residual and periglacial landforms, such as rock pillars, rock towers, and individual tor-like forms (e.g., those from the upper part of the Igniş and Pietroasa volcanoes), isolated cliffs with spectacular erosional shapes (e.g., the “Igniş Sphinx”), and the residual crests/ridges resulting from selective erosional modeling (e.g., ”Creasta Cocoşului”/”Rooster’s Crest” of the Gutâi dome) imprinted a spectacular landscape in the area.

5. The Neogene–Quaternary Călimani–Gurghiu–Harghita Segment

5.1. Volcanic Evolution

The Călimani–Gurghiu–Harghita range (CGH), the south-eastern segment of the Carpathian volcanic range, is ca. 160 km long, roughly located at the boundary between the East Carpathian fold-and-trust belt and the Transylvanian Basin (Figure 1 and Figure 6a,b). It forms an uninterrupted area composed of a row of closely-spaced volcanic edifices of mostly stratovolcano/composite volcano type.

Along-range migration of volcanic activity from NNW to SSE in the 10.5–<0.1 Ma time interval [8,27] characterizes the volcanic evolution of this segment. Furthermore, this south-eastward migrating “transient volcanism” [9] of CGH shows gradually decreasing volumes and output rates of magma [27,28], resulting in systematic variation (i.e., decrease) of the sizes/volumes and heights of the volcanic edifices in the same direction [27]. Similarly, the duration of volcanic activity was, in general, gradually decreasing along the CGH range: the longest-lasting and therefore largest-volume volcanoes are those located in the Călimani Mountains, whereas the smallest are most frequent at the south-eastern end zone [27]. Erupted magma compositions are also variable along the CGH sub-segments, most significantly along the south-eastern South Harghita Mountains, which, in turn, influenced the style of volcanic activity, as summarized below following the papers of Pécskay et al. [8,29] and Szakács et al. [27,30].

The Neogene magmatic history of the Călimani Mountains unfolded over a time interval of >4 Myr (between 11.3–6.7 Ma [8,31]. Volcanism started after a time period (11.3–9.4 Ma) of pre-volcanic shallow intrusive magmatism in the southern extension of the “Subvolcanic Zone” (not addressed in this paper). The largest (ca. 300 km³) Rusca-Tihu composite volcano, mostly of basaltic andesite composition, was built up in the north-western and the central parts of the mountains, starting at ca. 10.2 Ma. Reaching impressive heights (probably >3000 m) and becoming unstable, this massive edifice collapsed at ca. 8 Ma, generating large volumes (ca. 26 km³) of debris avalanche deposits emplaced at its western and southern ring-plain part [31,32]. In the meantime, between 10.2–6.7 Ma scattered eruptions over most of the territory generated a number of small-volume structures such as the dacitic Drăgoiasa Formation (9.3–8.4 Ma), the andesitic Budacu (9.0–8.5 Ma) and Lomaș (8.6 Ma) Formations, a number of peripheral andesitic domes (8.7–7.1 Ma) (Figure 7), and the Sărmaș Basalts shield volcano (8.5–8.3 Ma) [31].

Rusca-Tihu continued erupting during its post-collapse stage, while the focus of activity and the major eruptive center slightly shifted to the East, building up the Călimani Caldera effusive volcano (No. 1 on Figure 6b) in the 7.5–6.7 Ma time interval. The most voluminous (ca. 10 km³) andesitic effusive eruption of this volcano resulted in caldera formation at ca. 7.1 Ma [31]. Post-caldera stage activity (7.1–6.7 Ma), both inside and outside the caldera, generated lava flows and a small-sized intra-caldera stratovolcano (Negoiu Românesc) and a few dacitic domes at the southern slopes of the volcano. A shallow multi-stage intrusion of a monzodioritic stock, now exposed in the caldera interior, formed in the 8.8–7.3 Ma time interval beneath the central part of the edifice [31].

In the Gurghiu Mountains, volcanic activity occurred in the 9.4–5.4 Ma time interval, as suggested by K-Ar radiometric data [33]. Mimicking the general CGH trend, eruption centers migrated along this sub-segment from North to South and built up a series of volcanic edifices of various sizes, complexities, and eruptive histories (Figure 8): Jirca, Fâncel-Lăpuşna (No. 2 in Figure 6b, Bacta, Seaca-Tătarca (No. 3 in Figure 6b), Borzont, Şumuleu (No. 4 in Figure 6b), and Ciumani-Fierăstraie (No. 5 in Figure 6b)).

The northernmost and the oldest Jirca volcanic center evolved in the 9.2–7.0 Ma time range.

The largest Fâncel-Lăpuşna volcano (No. 2 in Figure 6b and Figure 8) was active in the 9.4–6.0 Ma time interval, evolving to the caldera-forming stage as a consequence of a large-volume Plinian-type explosive eruption of amphibole–andesite magma at ca. 6.9 Ma. Seaca-Tătarca (No. 3 in Figure 6b and Figure 8) is the second largest volcano of the Gurghiu Mountains, and it built up between 7.3–5.4 Ma of a succession of lava flow eruptions of monotonous andesitic composition. The small-sized Borzont shield-like effusive center (Figure 8) was active at its southern edge apparently during a single-event phase at ca. 6.8 Ma. In contrast, the southernmost Ciumani-Fierăstraie volcano (No. 5 in Figure 6b and Figure 8) was built up by multiphase activity in the 7.1–6.3 Ma time interval, consisting of mostly effusive eruptions through two closely-spaced craters, similar to the neighboring and slightly younger (6.8–6.2 Ma) Şumuleu volcano (No. 4 in Figure 6b and Figure 8).

Volcanism was active in the North Harghita Mountains in the 6.3–3.9 Ma time period [8], consisting of mostly effusive eruptions of progressively southward-migrating and closely-spaced volcanic centers (Figure 9), partially overlapping in time: Răchitiş (Figure 9), Ostoroş, Ivo-Cocoizaş, and Vârghiş, from North to South. Of them, the Vârghiş volcano (No. 8 in Figure 6b and Figure 9) reached the largest volume and height becoming gravitationally unstable and collapsing at ca. 5.0 Ma, then resuming activity within its newly-created central depression left behind by the lateral collapse event [32]. Meanwhile, a lateral flank-located eruption center developed at the lower south-eastern slopes of the Vârghiş edifice. Effusive edifice building was interrupted by short episodes of explosive activity at two other North Harghita composite volcanoes: Ivo-Cocoizaș (No. 7 in Figure 6b and Figure 9) and Ostoroș (No. 6 in Figure 6b and Figure 9), whereas two isolated peripheral effusive centers of viscous magma generated the lava domes of Răchitiş (to the North) (Figure 9) and Şumuleu-Ciuc at the southeast).

The volcanic evolution of South Harghita Mountains is bracketed within the 4.6–<0.1 Ma time interval [8]. From North to South the following volcanic edifices were built up progressively during this time period: Luci-Lazu, Cucu, Pilișca, Ciomadul (Figure 6a,b and Figure 10), and a group of small-sized isolated domes at the southernmost peripheries. Eruptive activity evolved along this sub-segment, with decreasing intensity and erupted magma volumes and progressively changing magma composition from normal calk-alkaline to high-K calc-alkaline to shoshonitic. The eruptive history of individual volcanoes was largely determined by these compositional variations. Low-viscosity, low-silica andesite lavas were emitted at Luci-Lazu volcano in the northern extremity of the sub-segment (Figure 10a), whereas dome-building and explosive eruption phases of higher-silica andesitic–dacitic magma occurred at Ciomadul volcano (Figure 10d) [34], and purely extrusive dome-building activity at Murgul Mare (Figure 11), Murgul Mic and Luget monogenetic centers at its southern extremity). A combination of effusive eruptions of early low-viscosity andesitic–basaltic and of late higher viscosity andesitic–dacitic magmas took place at Cucu (Figure 10b) and Pilişca (Figure 10c) volcanoes in the middle part of the South Harghita Mountains.

In the south-westernmost part of the sub-segment, part of the reworked clastic volcanic products originating from South Harghita volcanoes were deposited inside the coeval Upper Pliocene to Pleistocene Baraolt Basin, interfingered with sediments of non-volcanic origin, including diatomites and coal seams.

Both during volcanic edifice construction and afterwards dynamic processes influencing the original volcanic topography took place. The volcano spreading phenomenon is best expressed in the present-day topography of the Gurghiu Mountains (Figure 12) along the whole CGH range, as revealed by Szakács and Krézsek [35].

5.2. General Volcanological Features

The major volcanic edifices along the CGH range that determine its dominating volcanological feature and its topographic expression are the following (from NW to SE): Rusca Tihu/Călimani, Fâncel-Lăpuşna, Seaca-Tătarca, Şumuleu, Ciumani-Fierăstraie, Ostoroş, Ivo-Cocoizaş, Vârghiş, Luci-Lazu, Cucu, Pilișca, and Ciomadul (Figure 6a,b).

Due to the progressive migration of volcanism and related edifices from NW to SE, the original volcanological features are gradually better preserved, and they can be recognized as so in the same direction.

The most relevant volcanological and landform features of the Călimani-Gurghiu-Harghita volcanic edifices are summarized in

Table 2. Major volcanic and landform features in the Călimani-Gurghiu-Harghita range.

Volcano (Name, Location and Figure Reference)	Volcanic Forms	Morphometry Aria/Diameter, Elevation a.s.l.	Major Landform Features
Călimani Mountains
Rusca-Tihu (Figure 7)	Collapsed composite volcano	~24 × 16 km 1925 m	Strongly eroded, high-mountain, steep-sloped remnants of the upper part of a tall (ca. 3000 m) collapsed composite volcano
Călimani caldera (Figure 6)	Andesitic caldera volcano	~15 km 2102 m	>8 km wide northward-open semicircular depression and gentle outer slopes diverging from its rim to the East and South
Sărmaș	Basaltic shield volcano	>3.5 km, 1398 m	Partially buried shield volcano with patchy outcrop areas
Gurghiu Mountains
Jirca	Andesitic composite volcano	>4 km 1480 m	Steep ruin-like remnants of a strongly eroded and partially covered volcanic edifice
Fâncel-Lăpușna (Figure 6 and Figure 8)	Andesitic composite volcano with caldera	~15 × 12 km 1684 m	Southward-open arcuate central despression of a half-caldera and gentle outer slopes to the North and the East;
Seaca-Tătarca (Figure 6 and Figure 8)	Shield-like andesitic volcano	~16 × 9 km, 1776 m	Upward-convex mountain with a large northward-open almost intact central crater depression with a centripetal hydrographic catchment area
Șumuleu (4 in Figure 6 and Figure 8)	Andesitic composite volcano	~12 × 6 km, 1576 m	Eastward-open central crater depression with centripetal hydrographic catchment area and gentle outer slopes
Borzont (Figure 8)	Andesitic lava dome	5 × 3.5 km	Upward-convex mountain with no central depression on top
Ciumani-Fierăstraie (Figure 6 and Figure 8)	Andesitic composite volcano	~9 × 6 km, 1694 m	Steep summit with two craters (opened to North and South, respectively) and moderate outer slopes
North Harghita Mountains
Răchitiș (Figure 9)	Aphanitic-andesite lava dome	3 km 1155 m	Isolated, cone-shaped mountain
Ostoroș (Figure 6 and Figure 9)	Andesitic composite volcano	~8 km 1384 m	Eastward-open central crater depression with centripetal hydrographic catchment area and gentle outer slopes
Ivo-Cocoizaș (Figure 6 and Figure 9)	Shield-like andesitic composite volcano	~11 × 8 km 1589 m	A large, semicircular summit depression opened to the South and drained by a bilaterally-divergent, hydrographic catchment area; gentle outer slopes
Vârghiș (Figure 6 and Figure 9)	Collapsed andesitic composite volcano	~18 km 1801 m	Southward-open, large, arcuate central depression bordered by 4 summit highs and gentle outer slopes; a second crater depression (Harghita-Băi) in the southern-eastern lower part
Șumuleu-Ciuc	Dacitic dome	2.5 km 1033 m	Roughly cone-shaped isolated mountain
South Harghita Mountains
Luci-Lazu (Figure 6 and Figure 10a)	Andesitic shield volcano	~15 × 12 km 1293 m	Low-angle, upward-convex mountain with a pit-bog hosting summit crater
Cucu (Figure 6, Figure 10b and Figure 11)	Domes-topped andesitic-dacitic composite volcano	~10 × 8 km 1558 m	Summit area with multiple craters opened in a paralellipipede-shaped common depression opened to SE and gentle outer slopes
Pilișca (Figure 6, Figure 10c and Figure 11)	Dome-topped andesitic-dacitic composite volcano	~8 km 1374 m	Upward-convex lower half and steep-sloped summit with a strongly eroded, steep crater remnant to the east
Ciomadul (Figure 6, Figure 10d and Figure 11)	Dacitic dome cluster with twin craters	10.5 × 7.5 km 1301 m	Assemblage of central, steep-sloped, tightly packed hills with two summit craters and a few isolated peripheral hills
Murgul Mare (Figure 11)	Dacitic lava dome	2.4 km 1016 m	Cone-shaped isolated mountain
Murgul Mic (Figure 11) and Luget	Two shoshonitic lava domes	2.7 × 2.3 and 2.2 × 1.8 km 821 m	Flat-topped hills partially removed by heavy quarrying in their eastern halves

.

The particular evolution and structural setting of the South Harghita Mountains (they cross the fold-and-thrust belt at the Carpathian’s bend interior) is reflected in the types and the structures of the volcanic edifices they host [30].

5.3. Volcanic Landforms and Landscapes

The volcanic landforms of the CGH range are dominated by the well-individualized, generally cone-shaped, lava-dominated volcanic edifices of stratovolcano/composite volcano type, located in its axial part rising up over the flat-lying “volcanic plateau” in the West (Figure 12), and over the Gheorgheni and Ciuc depressions to the East. Their massiveness, volume and height systematically decrease from NW to SE. A number of smaller-sized edifices, mostly of volcanic dome and dome-cluster type, are forming typical landforms at the eastern and southern peripheries of the range.

Transversal topographic asymmetry is the characteristic major physiographic feature of the CGH range, determining its overall landscape. The spatial distribution of the volcanic products (pyroclastic flow deposits, long-run lava flows, debris avalanche deposits, debris flow deposits) was strongly controlled by the pre-volcanic landform configuration: a westward-sloping paleo-topography at the junction between the mountainous East Carpathians to the East and the low-lying Transylvanian Basin to the West. As a consequence, wide ring-plains developed at the western feet of the volcanoes in contrast with a much narrower strip of volcaniclastic products deposited on their eastern peripheries. In addition, the classical axi-symmetrical development of the volcaniclastic ring-plains all around individual volcanoes was impeded by their tight spacing so that eruptive products had little depositional space in the along-range direction, rather they extended westward and merged together within a common flat-lying topographic feature bordering the whole CGH range (Figure 6a,b). This characteristic landform feature is called “volcanic plateau” by geographers (e.g., [24]) because its present-day higher elevation with respect the lower-lying topography of the pre-volcanic sedimentary deposits resulted by relief inversion. The presence of small syn- and post-volcanic Quaternary depressions developed at the contact between the volcanic range and the folded East Carpathians, such as the Bilbor, Borsec, Gheorgheni, and Ciuc basins (Figure 8 and Figure 9), further enhanced the transversal topographic asymmetry of CGH.

Mureş river is the only valley crosscutting the whole CGH from East to West connecting the Gheorgheni Basin with the Transylvanian basin. It forms a picturesque gorge, almost continuously exposing various volcanic formations originating from eruptive centers located both in the Călimani Mountains to the North and in the Gurghiu Mountains to the South [36]. Otherwise, the connection between the densely-populated Transylvanian Basin with the East Carpathian’s intra-mountain basins across the volcanic range is assured by a number of passes, such as Bucin (between the northern and the southern parts of the Gurghiu Mountains), Șicasău (between the Gurghiu and Harghita Mountains,), and Tolvaioș (between the North Harghita and the South Harghita mountains), actually representing topographic saddles between neighboring volcanoes.

The hydrographic network of CGH range displays a few different patterns: (1) a bilaterally divergent network (dominated by western and eastern flow directions) on the outer slopes of the composite volcanoes or a radially divergent pattern on isolated domes, (2) radially convergent (centripetal) networks developed in the interior of the central volcanic depressions (craters, calderas), and (3) irregular networks determined by other factors than the original, cone-shaped, volcanic topography (including the influence of topographic changes induced by volcano spreading).

Overall, interplay of edifice-building volcanic activity and the syn- and (mostly) post-volcanic erosional processes of various types (e.g., glacial or fluvial, areal or linear, etc.), rates and durations at different parts of the volcanic structures determined the sizes and the shapes of the present-day landforms in the CGH range. An average erosional lowering rate of ca. 30 m/Myr of the volcanic edifices in the whole Carpathian volcanic range was estimated by Karátson [37]. Erosion-induced modification of the original volcanic landforms is however variable along the CGH range, firstly due to the decreasing age of the volcanism: the younger edifices, hence their pristine landforms, are less modified than the older. Fragmentation and incision depth of the “volcanic plateau” by linear fluvial erosion is also variable along the range for the same reason. Syn- and post-volcanic deformation of the original volcanic topography by non-erosional processes, such as volcano spreading (Figure 12), further influenced the present-day landforms and landscapes along parts of the CGH range [35].

The following five categories of volcanic landforms, as seen today, can be distinguished:

• Inherited (i.e., non- or slightly modified) volcanic landforms preserving the most characteristic and easily recognizable features of the original volcanic topography such as the gentle outer slopes of most composite volcanoes, the youngest volcanic domes, a few central crater areas (e.g., those of Ciomadul volcano) and large parts of the western ring-plain of the Gurghiu and Harghita Mountains;
• Landforms modified by syn- and post-volcanic processes other than erosion, i.e., those related to volcano spreading;
• Landforms moderately modified by erosion, with roughly preserved and still recognizable original volcanic topography, such as the central depressions (craters and calderas) of large composite volcanoes (e.g., Călimani caldera, Seaca-Tătarca volcano in the Gurghiu Mountains);
• Landforms strongly modified by erosion, where the original volcanic topography is hardly (or not at all) recognizable: central areas of some of the large composite volcanoes that underwent syn-volcanic collapse events (e.g., Rusca-Tihu) and/or intense post-volcanic erosion (e.g., Jirca), as well as strongly dissected parts of the “volcanic plateau”;
• Anthropic landforms mostly related to mineral exploration/mining activities.

The Călimani Mountains display a typical above forest-limit high-mountain landscape at its highest reaches, with gentle outer (from the caldera rim) slopes on lava flow structural surfaces to the East and North, and steep slopes to the North, resulting from both the initial caldera collapse scarp and subsequent glacial erosion, as presented in the next section. The below 1800 m part of the mountains is, in general, heavily forested. Two types of contrasting landscape characterize the central and the peripheral (i.e., the western ring-plain “volcanic plateau”) parts of the Gurghiu Mountains, respectively. The central, composite cone part of the volcanic edifices show a typical heavily forested and medium-elevation (<1800 m a.s.l.) mountain landscape with centripetal radial hydrographic network in the steep-sided crater areas, and a centrifugal one on the gentler outer slopes developed on andesite lava flow surfaces. In contrast, the extensive western “plateau” (with 900–1200 m elevations) shows a roughly flat-lying topography with alternating forest and clearing patches, hosting a number of dispersed settlements in a much appreciated (by tourists) picturesque landscape, such as Vărșag village.

Of all the North Harghita volcanoes, only Vârghiş, with its highest point at Harghita Mădăraş (1801 m a.s.l.), shows a typical high-mountain (i.e., alpine) landscape, with its summit area rising above the forest limit, where small-scale periglacial cryonival features, such as cryoplanation terraces, block fields, and streams, formed of frost-shattered rock fragments are frequently and characteristically present [2]. Although sporadically taking place, such processes did not concur significantly to the configuration of the present-day landscape of Ostoroş and Ivo-Cocoizaş volcanoes. The general landscape of the western North Harghita “volcanic plateau” is similar to that described for the Gurghiu Mountains, but the flat- and lower-lying landscape is more fragmented and incised by fluvial erosion.

The South Harghita landscapes are diverse, too. Mountain landscape of moderate-elevation (<1600 m a.s.l., Cucu peak at 1558 m a.sl. is the highest topographic elevation), consisting of heavily forested areas alternating with clearings dominate the Luci-Lazu, Cucu, and Pilişca edifices. Ciomadul is much less elevated (maximum at 1301 m a.s.l. in the Ciomadul Mare peak), but still heavily forested on its western slopes and higher-elevation parts, as it is the Murgul Mare dome. The lower, ring-plain parts of the volcanoes with their low-angle, flat-lying topography, occasionally transiting into horizontal basin topography (such as the Baraolt Basin in the South-West and the Lower Ciuc basin in the East), display a completely different landscape with only patches of forest and hosting settlements and adjacent agricultural land (e.g., those at the southern slopes of Ciomadul belonging to the Bixad village).

6. The Perșani Pleistocene Alkali Basaltic Volcanic Field

The Na-alkali basaltic monogenetic volcanic field is relatively small-sized as compared with other similar volcanic fields of the CPR (e.g., [12]), covering a ca. 22 × 8 km (176 km²) area [38], located only ca. 40 km west from the southeasternmost part of the CGH range in the internal part of the Carpathian Bend Area (Figure 1).

6.1. Volcanic Evolution

The eruptive history of the Perșani monogenetic volcanic field is summarized here, following the most recent work of Seghedi et al. [38].

The volcanic evolution of this area unfolded within the 1.22–0.68 Ma time interval in the Pleistocene epoch, consisting of repeated eruptions of Na-alkaline basaltic magmas, involving a series of purely magmatic and phreatomagmatic eruptive events clustered in five major episodes. Its most recent manifestation at ca. 680 ka (i.e., 0.683 Ma) is the second youngest of this type in the whole CPR territory.

Eruptions in the Perșani alkali basaltic field include Strombolian and phreatomagmatic explosive events and lava-pouring effusive events in various combinations, most frequently with phreatomagmatic manifestations in the early phases due to explosive interaction of uprising basaltic magma with shallow ground-water. Strombolian, episodically Hawaiian activity at later stages accompanied, or followed by, lava flows of various duration and volume. However, explosive activity not followed by an effusive phase, and effusive activity not preceded by explosive activity also occurred.

The five eruptive episodes following each other occurred at 1220, 1142, 1060, 800, and 683 Ka, respectively, as resulted from radiometric dating and paleomagnetic study of their products. Seghedi et al. [38] suggested the occurrence of a sixth episode (not dated radiometrically) in the 1060–800 Ka time interval. These data suggest an average eruptive frequency of ca. 1 episode every ca. 100–120 Ka taking into account, based on historical examples that individual eruptions are of short duration (years at most). This means long time intervals (i.e., periods of dormancy) between eruptive episodes within this volcanic field. The erupted magma volumes are variable from one episode to another, and the largest volume is assigned to the 1060 Ka episode [38].

6.2. General Volcanological Features

Since each eruptive episode was short-lived and involved small magma volumes, as a typical manifestation of the so-called monogenetic volcanism worldwide, the volcanic features/edifices are also of small-volume, with characteristic topographic expressions according to the type of the generating eruption mechanism. Phreatomagmatic activity generated negative landforms of maar or tuff-ring type (with their bottom below or above the original land level, respectively) bordered by a relatively low-elevation rim (only tens of meters high) and an outer ring of outward dipping topography corresponding to the structural surface of the phreatomagmatic explosive products (i.e., pyroclastic deposits composed of alternating tuff and lapilli tuff beds). In contrast, “dry” Strombolian explosive activity generated steep-sided, cone-like edifices of several hundred meters high built up mostly of basaltic scoria fragments of various size (from bomb/block to lapilli), decreasing outwards, and with a steep-sided summit crater. In their near-crater parts, Hawaiian spatter deposits (agglutinated chunks of chilled coarse and tortuous magma pieces) and sporadically short lava tongues are also present in cases. The low-lying terrain at the feet of these prominent volcanic constructs were inundated by lava flows channelized along pre-existing valleys or ponded in depressions, including those generated by preceding phreatomagmatic events. The resulting volcanic features thus include elongated lava flows, extended lava-fields and maar-filling lava lakes.

A total of 21 monogenetic eruptive centers were recognized (Figure 13), listed, and summarily described in the Perșani Mountains by Seghedi et al. [38]. In total, 14 of them are clustered in the central zone of the field, 7 are found in a peripheral position (3 in the North, 4 in the South) with respect this central group (Figure 13). The largest cluster of eruptive centers includes nine volcanoes (Măguricea, Bârc, Fântâna, 636, Bogata, Dîlma-West, Pietrele, Gruiu, and Gruiu-Mic), all of them being isolated from each other (i.e., their products do not overlap).

6.3. Volcanic Landforms and Landscapes

The type of volcanic activity (eruptive mechanisms) and the resulting volcanic edifices, their constitutive products, and the intervening erosional processes determined the present-day observable volcanic landforms in the Perșani monogenetic volcanic field. Both positive and negative landforms were generated during eruptive activity with variable preservation potential. The scoria cones, modified by erosion at various extents, are the most prominent and, in general, easily recognizable, positive volcanic forms. The youngest of them, Gruiu, still almost entirely preserves its original cone topography, with a flat to gently concave (depending on the angle of view) summit area and steep (30–35°) outer slopes (Figure 14), as well as its almost intact original diameter and height. Older scoria cones, though prominent in relief, show altered (in general rounded) profiles, such as Măguricea Mare just on the opposite roadside with respect Gruiu (Figure 14). Still other cones are much more degraded, with only remnants of their original landform left (e.g., Trestia, Heghieș).

The negative landforms of original maar and tuff cone interiors were not preserved, so their location and size can only be intuitively inferred. One exception is the location of a vaguely outlined topographic expression of a maar or tuff ring depression that can be recognized (Figure 15). Other explosion-generated depressions can be inferred by considering their lava-lake fill with an isometric map outline. The surrounding tuff-ring- and maar-related topographic features are not recognizable anymore but can be roughly located by mapping and studying the phreatomagmatic pyroclastic deposits well exposed in outcrops, such as those in the Trestia valley in the central zone or those near Mateiaş locality in the northern part. Original, slightly modified flat lava flow surfaces are relatively well preserved around Gruiu scoria cone, for instance.

In contrast to the CGH range, the landscape of the Perșani Mountains as a whole is not dominated by volcanic landforms because their restricted occurrence areas, as compared to other formations building up these mountains, of horst-and-graben structure and with a mosaic of rocks of various age (from Pre-Cambrian to Miocene) and hardness on which an extremely diverse and rough topography was sculptured by erosion. This is true in particular for the northern and the southern parts of the volcanic field. In contrast, the western edge of the Perșani Mountains, at the junction with the Transylvanian Basin, shows a volcanic landscape characteristic for monogenetic volcanic fields, with prominent hills of a few hundred meters high (i.e., scoria cones) emerging above a low-lying terrain (Figure 14).

7. Discussion

7.1. Original Volcanic Landforms

The extent to which the original volcanic landforms can be recognized or, at least, reconstructed, is variable along the East Carpathian volcanic segments and areas, mostly because of a number of influencing factors, such as age of volcanic activity, local relief energy determined by relative height of the edifices, age-related climate changes, and tectonic movements (e.g., uplift), which individually and all together determined erosion type and intensity. The general trend is, however, a gradually better preservation of the progressively younger landforms from north-west to south-east along the East Carpathians.

In the Oaş–Gutâi segment, many of the original volcanic landforms are difficult to recognize, numerous older volcanic structures being partially destroyed and/or covered by younger volcanics, such as the 15.4 Ma rhyolitic ignimbrites-related caldera in the southwestern part of the Gutâi Mountains completely covered by later erupted volcanic products. The volcanic activity partially took place in a shallow marine environment involving a more advanced destruction of the volcanic structures and their original landforms.

The two main categories of volcanic structures whose original landforms can at least partially be recognized in the Oaş–Gutâi segment are:

• Volcanic structures emplaced outside the main volcanic area (generally isolated and surrounded by Neogene–Quaternary sedimentary deposits). The most relevant for this category are the andesitic to rhyolitic extrusive domes and dome-coulées at the western and the southern parts of the Oaş Mountains (Pusta Heghii, Pleşcuta, Turulung, Oraşu Nou, Hatu Lung, etc.). Although partially eroded, many of these domes consisting of erosion-resistant coherent lavas have kept their original overall morphology. Another example is the Şatra extrusive dome in the southeastern part of the Gutâi Mountains, located outside of the main volcanic area, which preserved quite well its original morphology despite the fact that it represents one of the oldest volcanic structures (13.2 Ma, Figure 5a);
• The volcanic structures belonging to the youngest eruptive events in their respective local areas. It is the case of some composite/effusive volcanoes of the latest major volcanic events in Gutâi Mountains (e.g., Mogoşa volcano whose activity ceased around 9.5 Ma or Igniş volcano ending his activity around 9.0 Ma). Some large-sized extrusive domes emplaced in the volcanic area of the Gutâi Mountains and surrounded by older volcanic products have partially preserved their original morphology (e.g., Gutâi andesitic dome dated at 9.3–9.0 Ma and Pleşca Mare composite/andesitic–dacitic dome built up at around 9.3 Ma).

In the Călimani-Gurghiu-Harghita segment, more-or-less well-preserved original volcanic landforms can be recognized in all four sub-segments.

The most obvious original volcanic landform of the Călimani Mountains is represented by the northward-open large caldera depression (Figure 6a), although somewhat enlarged by erosion, and its gently outward dipping lava-field surfaces largely preserving the original slopes, practically unmodified. A few isolated volcanic domes at the upper part of the Călimani Caldera volcano (e.g., Pietricelul and Drăgușul) and in the southern part of the mountains (e.g., Leul, Tarnița, and Băieșul) also preserved their slightly modified original morphologies (Figure 7).

The best preserved original volcanic landforms in the Gurghiu Mountains and the North Harghita Mountains are recognizable in the overall topography of the large composite volcanoes, some with their central crater depressions, although enlarged by erosion to some extent (Seaca-Tătarca, Șumuleu, and Ostoroș) and the almost intact outer lava-flow surfaces (10–12° slopes) of practically all of them (Figure 8 and Figure 9). Additionally, the original flat to very gentle slope ring-plain topography of the western lower parts of the volcanoes is generally well-preserved, even though locally inverted and/or dissected to various degrees by fluvial incision (Figure 12). Peripheral domes, such as the Şumuleu-Ciuc dome, also preserves their original morphological features.

The South Harghita Mountains host the best preserved original volcanic landforms in the whole CGH range, easily explained by their youngest ages. Subtle differences can, however, be observed between different volcanic edifices: the larger composite volcanoes Luci-Lazu and Cucu show intact outer lava-flow topography (Figure 10a,b), whereas their central parts are less well-preserved but still readily recognizable (more in the case of Luci-Lazu than Cucu). Smaller-scale original landform, such as volcanic domes as parts of the composite volcanic edifice, preserved their original overall morphology at the Cucu and the Pilişca volcanoes. Ciomadul practically displays an intact pristine volcanic landform with its typical steep-sided domes (Figure 11) and the two craters, except for two isolated peripheral domes (Bálványos and Puturosul). Similarly, almost intact original landforms are readily recognizable at the southernmost dacitic Murgul Mare dome (Figure 11) and the flat-topped shoshonitic Luget and Murgul Mic domes (although partially destroyed by surface mining).

The Perșani Mountains alkali basaltic volcanic field host a few scoria cones with their easily recognized and prominent original volcanic landforms of which Gruiu is the youngest and the most intact (Figure 14). In contrast, negative, maar-type (phreatomagmatic craters) volcanic landforms left behind difficult-to-recognize topographic features.

7.2. Erosion of the Original Volcanic Landforms

Erosional modification of the original volcanic landforms is variable along the East Carpathians, depending on a number of factors as enumerated in the previous section. This subject can be addressed at general as well as local (segment/subsegment-specific) scales. We try to combine the two.

7.2.1. Oaş–Gutâi Segment

No applied studies have been performed on the erosion rate of volcanic relief in the Oaş–Gutâi segment. It can be considered by extrapolating the data obtained for the whole Carpathian–Pannonian Region (CPR) volcanic zone or of some neighboring volcanic segments. Karátson [37] and Karátson and Timár [28] have constrained a 30 m/Myr average erosion rate for the entire volcanic zone of CPR and for the Călimani-Gurghiu-Harghita (CGH) and Slansky-Tokaj volcanic segments, respectively. An average erosion rate of 31.5 m/Myr was accounted for the Ciomadul volcano from South Harghita [39]. The smallest average erosion rate—20 m/Myr—was recently established for the CGH as a whole, with 28 m/Myr for the Southern Harghita volcanic zone [40]. Taking into consideration that the Oaş–Gutâi segment lies between the Slansky-Tokaj and the Călimani-Gurghiu-Harghita segments, we would tentatively consider a 20–30 m/Myr average erosion rate in this area.

In the Oaş Mountains, the erosion processes were directly influenced by the local environment in which the volcanic structures formed. In the northern and the northeastern part of the volcanic area, where the main volcanic activity took place on land, the erosion of the volcanic landforms was mainly associated to denudation processes related to streams/valleys formed after the construction of volcanic structures. The volcanic landforms are generally fragmented along these south-southeast oriented valleys toward the initial shallow marine gulfs of the Oaş Basin. In the western and the southwestern areas, the erosion of the volcanic structures resulted from a combination of destruction processes occurring immediately after their formation in a subaqueous environment and those of summit erosion after the retreat of the sea. Taking into account the 11.0–9.5 Ma time interval of volcanism in the Oaş Mountains [14] and an average erosion rate of 25 m/Myr, a total erosion of 235–275 m may be considered for the Oaş volcanic landforms. All the extrusive domes from the western and the southwestern part of the Oaş Mountains fall within the mentioned range (e.g., Oraşu Nou rhyolitic lava-dome, 11.3–11.0 Ma ca. 275 m, Hatu Lung andesitic dome-coulée, 9.7–9.6 Ma ca. 245 m, Pleşcuţa Hill andesitic–dacitic dome, 10.3 Ma ca. 250 m).

In the Gutâi Mountains, the volcanic activity took place in a much longer time interval, during a ca. 4.5 Myr time period (13.4–9.0 Ma [8]), as compared to those from the Oaş Mountains. A total erosion of 300–340 m for the volcanic structures of the first volcanic phase (13.4–12.1 Ma) and of 225–290 m for those of the second (11.6–9.0 Ma) can be considered. The erosion processes involved in the modeling of the volcanic landforms were different depending on the type, composition, and the environment in which the volcanic structures formed. In the case of the composite volcanoes built up on land, the erosion was a combination between summit erosion and denudation processes related to the hydrographic systems. Igniş volcano (9.5–9.0 Ma) has a typical radial-divergent hydrographic network developed as original barrancos which shaped the relief of the volcano, contributing also to the 225–235 m total erosion of the edifice. At the edge of the summit plateau, especially in the western part, many spectacular residual landforms, such as rock pillars, rock towers, tors (e.g., the amazing “Igniş Sphinx”), imprint a particular landscape for the volcano summit. A similar landscape assigned to residual landforms of weathering origin is found at Pietroasa volcano (“Oaş Sphinx”).

Rotundu volcano (9.9–9.7 Ma) has his initial large crater partially destroyed toward East by the present day upper Săpânţa valley hydrographic network, which continuously eroded the eastern slopes of the edifice, transforming them into a lower-elevation catchment area.

The large subaerially emplaced Gutâi extrusive dome, surrounded by older volcanics, is composed of coherent andesitic rocks. It displays a specific landform and landscape, with a large summit plateau bordered by steep cliffs of approximately 225–230 m in height. Impressive residual landforms of weathering origin occur at the northwestern edge of the dome and at Creasta Cocoşului (Rooster’s Crest) (Figure 16a). In contrast, the skeleton-like landform of the large Dăneşti–Cetăţele composite dome (11.6 Ma) is mainly the result of intense erosion (ca. 300 m) of the associated volcaniclastic rocks. Spectacular rock formations (e.g., Piatra Roşie/Red Stone escarpment with caves of erosional origin) and isolated rock towers with residual relief on the volcaniclastics, occur inside the area of the original dome. In the case of the older Şatra dome (13.2 Ma), the total erosion of 330–340 m contributed to the formation of large amounts of glacis-type products surrounding the isolated volcano. A special case of the erosion processes is that related to the exhumed intrusive bodies. An interesting example is the Biserica lui Vlaicu (Vlaicu’s Church) young composite dyke from the Laleaua Albă (White Tulip) magmatic complex (8.5–8.0 Ma) in the central-southern part of the Gutâi Mountains, with a spectacular residual relief (Figure 16b).

7.2.2. Călimani-Gurghiu-Harghita Segment

The volcanic areas of the CGH range are variously affected by erosional processes as reflected in their respective degrees of denudation: 30% in the Călimani Mountains, 25% in the Gurghiu Mountains, 20% in the North Harghita Mountains, and 15% in the South Harghita Mountains corresponding to erosion rates of 17, 11, 9, and 28 m/Ma, respectively [40]. In general, these processes consist of (1) overall lowering of the original topography which, however did not modify significantly the general volcanic landform’s profile of the volcanic edifices, in particular their summit region; (2) enlargement and deepening of the original central volcanic depressions (craters and calderas) by a radial hydrographic network draining these areas; (3) dissection of the peripheral ring-plain areas by deep radially diverging or structurally determined parallel valleys but leaving the original topographic surface almost intact at today interfluvial areas; and (4) specific locally developing erosional processes with minor impact on the larger-scale landforms, such as glacial and periglacial processes. These features are presented and detailed below for the four sub-segments of the CGH range.

The Rusca-Tihu volcano in the western part of the Călimani caldera (Figure 7), subjected to edifice collapse, did not preserve any of its genuine volcanic landforms, including the post-collapse depression, because it was strongly uplifted and eroded later on. In general, the western part of the Călimani Mountains is strongly dissected by erosion so that the pre-volcanic intrusions are largely exposed at the Bistricioru-Strunioru ridge, topographically almost equaling the elevations of the “volcanic” Călimani Mountains in its eastern half.

The highest elevation part of the Călimani Mountains (>1800 m a.s.l.) is the only area in the whole East Carpathian volcanic range significantly affected by glacial erosion. The landforms originating from glacial processes include well-preserved glacial cirques (Figure 17a) along the inner north-facing caldera rim, whereas periglacial processes generated minor features, such as block fields formed of frost-shattered rock fragments (Figure 17b), rock and block streams, rubble, slide rocks at the bottom of the slopes, and avalanche couloirs found all along the caldera rim [41,42].

According to Szakács and Chiriță [43], the lower topographic realm of the Călimani Mountains is characterized by intense fluvial erosion due to a dense hydrographic network with steep slopes, narrow gorges, waterfalls, and small erosional basins as well as colluvial and alluvial glacis and piedmont features. Incision and relief fragmentation is particularly intense on the “volcanic plateau” areas and on slopes with high relief energy inside the caldera. The average values of vertical fragmentation in the central part of Călimani Mountains are between 150 and 450 m on the southern and the eastern external slopes of the caldera, and over 400–650 m on the northern inner slopes of the caldera. Differential mechanical weathering and wind-generated corrasion locally resulted in spectacular rock formations and ruin-like landscape features in coarse volcaniclastic rocks, showing intricate irregular morphologies of residual relief (10 to 35 m high), such as those of the “12 Apostles” group (Figure 18).

Particular erosional features in the Gurghiu Mountains are present in its northern and oldest part, where the Jirca edifice is so strongly dissected, mostly by deeply incising fluvial erosion processes, that none of its original volcanic landforms can be recognized today. The internal area of the semicircular southward-open Fâncel-Lăpuşna ”half-caldera” is also strongly modified by erosion. Its present-day topography is lowered to such an extent (probably at least 300 m) that pre-volcanic intrusive rocks are exhumed and exposed here [33].

Closely-spaced composite volcanic cones along its axial part characterize the North Harghita Mountains, with central crater depressions enlarged by erosion and much less modified gentle outer slopes. Their merged common ring-plain, much more developed to the West, is moderately fragmented and deeply incised by a dense hydrographic network. Periglacial erosion features such as cryoplanation terraces, block fields, and streams formed of frost-shattered rock fragments are recognized on its highest elevation parts at, and in the vicinity of, the Harghita Mădăraş summit peak area (1801 m a.s.l.) [2].

The western ring-plain part of the South Harghita Mountains shows some particular features. Most of it is composed of debris avalanche and related debris-flow deposits originating from the Vârghiş volcano in the North Harghita Mountains channelized along the contemporaneous NNE-SSW-oriented valleys determined by the nearby Perșani Mountains horst-and-graben structure [32]. At present, these volcaniclastic deposits occur along the flat interfluvial summits, while the current hydrographic network is incised in the underlying Transylvanian Basin sedimentary rocks. Fluvial erosion-related relief inversion thus contributed significantly to the present-day landform and landscape picture of the south-western low-elevation parts of the Harghita Mountains. This is a relevant and a remarkable landscape evolution case of volcanic relief inversion among those listed and described recently by van Wyk de Vries et al. [44].

7.2.3. Perșani Mountains

Despite its young age (among the most recent in the East Carpathians), the Perșani Mountains alkali basaltic monogenetic volcanic field shows strong erosional features, in particular at its northern and southern extremities, where the volcanic landforms are the most isolated and, probably, of the lowest volume. In these areas, more in the South than in the North, the volcanic formations were emplaced on an originally highly fragmented rough erosional topography of much older metamorphic and sedimentary rocks, relief energy, hence erosional damage of the edifices was at the highest level. Therefore, only ruin-like remnants of the original volcanic landforms are found today.

The central, more compact part of the field, located on the western edge of the Perșani Mountains and located on a flatter and less fragmented pre-volcanic topography is less eroded with original landforms and volcanic features better preserved as presented in Section 6.3.

7.3. Anthropic Alteration of the Pristine Volcanic Landforms

In the Oaş–Gutâi volcanic segment, the anthropic alteration of the volcanic landforms consists of abandoned open-pits/quarries that exploited hydrothermal ore deposits and active or abandoned quarries extracting rocky materials for road-building and dam construction. Two abandoned quarries in the Mine Hill (Mons Medius, Figure 19a) and in the Şuior Hill in the south-central part of the Gutâi Mountains, wherein only decades ago gold, silver, lead, and zinc mineralization were exploited, substantially modified the volcanic landforms. Many quarries were opened in the entire Oaş–Gutâi segment, especially in the extrusive domes of the Oaş Mountains (e.g., Hatu Lung, Turulung, and Oraşu Nou) and in the intrusive bodies in the Gutâi Mountains. An abandoned quarry has modified the middle of the Laleaua Albă (White Tulip) composite dyke and an active quarry partially destroyed the morphologically well-individualized Cherec andesitic sill (Figure 19b). The present-day construction of the huge Runcu dam on the Runcu Valley (northern part of the Igniş volcano) already generated significant landscape alteration (many new roads and related quarries, the dam itself, Figure 19c) and in the near future it will cause more important modifications by the accumulation lake, which will cover a large area of the lava plateau, including the Tătaru Gorges protected area.

Anthropic influence on the natural landform features is significant inside the Călimani caldera, in particular at and around the Negoiu Românesc intra-caldera stratocone due to open-pit sulfur exploration and mining (now ceased), related waste deposition, and infrastructure developments (Figure 20c). The original and the recognizable landform of this post-caldera stratocone was radically spoiled by anthropic intervention [43].

In the southern Călimani Mountains, a dam was constructed on the Răstoliţa valley and the accumulation lake behind it; the new roads around the lake and related infrastructure, etc. resulted in partial deforestation of the area and a lot of environmental damage.

The anthropic imprint on landscape in the Gurghiu Mountains consist of patchy forest exploitation works and a few small-sized ski resort areas (e.g., at the Bucin Pass and on the southern slopes of the Ciumani (Délhegy) mountain). One large (Chilieni) and a number of small-sized local quarries extracting andesite for road-building and other technical purposes, spoil the otherwise attractive mountain landscape with bad-looking landscape wounds and air-polluting industrial activities.

Being lower in altitude and more accessible, the North Harghita landscape was a bit more affected by anthropic activities, as compared to the Gurghiu Mountains. Mining exploration and extraction works, for instance, affected quite large areas: “caoline” (in fact illite) mining at Harghita-Băi left behind a landscape-spoiling tailing pond (Figure 20b), and mineral exploration works resulted in smaller wounds within the larger central depression of the Vârghiş volcano. The Zetea dam, and the accumulation lake behind, at the northern junction with the Gurghiu Mountains significantly modified the local landscape. Ski resort areas at Harghita-Băi, Homorod-Băi, and, most significantly, high up on the Vârghiş volcano, close to its highest topographic elevation of the Harghita Mădăraş summit, with their infrastructures and tourist facilities, represent relevant examples of anthropically-modified/spoiled landscape in the North Harghita Mountains. The old health-spa area of Harghita-Băi is another typical example. The Şumuleu-Ciuc dome is located in a high-density anthropic environment and it (namely the saddle behind the smaller Şumuleu Mic dome) is the site of Christian cultic (i.e., the traditional late-spring pilgrimage) and other cultural events several times every year, resulting in a strong and evolving imprint on the local natural landscape.

The South Harghita Mountain landscape is even more intensely modified and modeled by anthropic activities, including remnants of more-or-less remediated mineral exploration works (e.g., quarries, such as the mercury-exploration quarry and related facilities at Sântimbru-Băi, Figure 20a), waste dumps, and ore-processing facilities of old iron ore extraction works along the Homorodul Mic valley at Vlăhiţa and Lueta. Other anthropic activities, such as health spa areas hosted or only partially overlapping with volcanic areas (e.g., part of Sântimbru-Băi, Tușnad-Băi, Bálványos, and Ozunca-Băi), frequently visited tourist spots and their local facilities (Mohoş–Sfânta Ana area of Ciomadul volcano, accessible by an asphalt road down to the shore of the Sfânta Ana Lake) partially modeled the landscape. The large-sized active quarries extracting road-building rock material from the shoshonitic domes and the lower-elevation part of the Pilișca volcano along the Olt Valley intensely modified the local volcanic landscape. Overall, South Harghita, with its smaller-sized, lowest-elevation, and most easily accessed volcanic areas, is the most anthropically influenced sector of the whole CGH range.

Landform and landscape modifying anthropic intervention is also present in the Perșani Mountains monogenetic volcanic field, mostly related to rock extraction activities. Due to its excellent mechanical properties, basalt lava rocks are largely extracted in a number of open-pits, some active and others abandoned today. In the western margin of the volcanic field, near Hoghiz town, along the picturesque Bogata valley, three large quarries extract basalt, spoiling the local landscape. Other smaller quarries, mostly abandoned today, dot the entire field where proper-quality basalt lava rocks are available and easily accessible. Scoria, as a high-quality, low-density building material, also attracted investors to extract them. The most eloquent example of scoria extraction activity, today ceased, affected the Hegheş scoria cone on the highest-elevation part of the volcanic area near Racoșul de Jos village, where the cone itself was literally eviscerated by mining activities in the near past (Figure 21). The sequence of phreatomagmatic deposits underlying the Heghieş scoria cone was also subjected to extraction activities, now abandoned but leaving behind a desolate landscape and an unesthetic artificial lake.

However, the positive side of the anthropic influence on the local landscape is that these anthropic modifications of the landscape near Racoșul de Jos left behind a plethora of large-scale artificial exposures of volcanic formations to be studied that would otherwise not be accessible for observation. Actually, profiting from the presence of these new exposures, scientists could improve their understanding of the volcanic evolution and the structure of the local area and, by extension, of the whole Perșani Mountain volcanic field.

8. Geoheritage Values

8.1. Sites of Geoheritage Relevance in the East Carpathian Volcanic Areas

The East Carpathian volcanic range of Romania is rich in geoheritage natural values, including well-preserved volcanic landforms, spectacular erosional features developed on volcanic formations and rocks, unique mountain landscapes at various topographic elevations, and specific natural environments and habitats for rare flora/fauna assemblages, all of them deserving to be protected, at various levels, from anthropic degradation as will be shortly presented in the following paragraphs.

Table 3. Relevant features of geosites with official protection status in the East Carpathian volcanic area. (significance and scale categories acc. to [47].

Geosite	Major Geoheritage Features	Significance	Scale (Size)	IUCN Category
Oaș–Gutâi Mountains
Ilba “Stone Rosette” (Gutâi Mountains, Figure 22a)	Impressive, radial columnar-jointing of lava dome andesite, unique in the East Carpathians; included in scientific and educational field trips	Local	Small scale (0.5 ha)	III
Limpedea Pillars (Gutâi Mountains)	Vertical columnar-jointing of andesite in an old quarry, a touristic attraction and a traditional rock climbing site	Local	Small scale (3.0 ha)	III
Tătaru Gorges (Gutâi Mountains, Figure 19c)	Spectacular gorges excavated in massive andesit plateau; a touristic attraction site	Regional	Small scale (15.0 ha)	IV
Lacul Albastru (Blue Lake) (Gutâi Mountains, Figure 22b)	Picturesque, mining-related anthropic lake with a changing blue-greenish-colored water imprinted by ore minerals, unique in Europe	National	Small scale (0.5 ha)	III
Chiuzbaia Fossiliferous Reserve (Gutâi Mountains)	One of the richest Upper Miocene fossil flora sites in Europe with species described for the first time in the world. Geosite of outstanding scientific value.	International	Mesoscale (50.0 ha)	IV
Creasta Cocoşului (Rooster’s Crest) (Gutâi Mountains, Figure 16a)	Impressive, crest-like landform at the edge of an andesite lava dome; a major touristic attraction site included in a very popular geotrail.	National	Mesoscale (50.0 ha)	IV
Călimani-Gurghiu-Harghita Mountains
Călimani National Park (Figure 7, Figure 17a,b, Figure 18 and Figure 20c)	High-mountain volcanic landscape hosting many geosites of high geoheritage value of geological, geographical, and botanical interest *; a very popular touristic destination, including the Maria Therezia Road	International	Macroscale (15,300 ha)	II
“12 Apostles” Science Reserve, Călimani Mountains (Figure 18) **	Spectacular, tens-of-meters high rock formations sculptured by wind erosion in volcaniclastic breccia; an outstanding geotouristic attraction site	National	Mesoscale (200 ha)	III
“Upper Mureș Gorge Natural Park” (Călimani and Gurghiu Mountains divide)	Almost continuous exposures of volcaniclastic rocks of various nature and sources along a picturesque ca. 25 km long valley sector; a picturesque easy-to-reach roadside touristic attraction site combining natural (geologic) and anthropic/cultural values hosting unique tree-mold caves	National	Macroscale (9156 ha)	IV
“Scaunul Domnului” (“God’s chair”) Nature reserve (Călimani Mountains)	Fragment of a lava plateau bordered by spectacular vertical cliffs; final destination of a very popular tourist trail offering a breathtaking panoramic view over the Transylvanian Basin	National	Mesoscale (71 ha)	IV
Toplița thermal water fall Natural reserve (Gurghiu Mountains)	Active deposition of calcareous tufa from thermal water on a steep vegetation-covered cliff facing the Mureș valley; a touristic attraction site near a thermal water spa area	Local	Small scale (0.5 ha)	III
“Dealul Melcului” (“Snail Hill”) Natural reserve (Corund, Gurghiu Mountains)	Three prominent mounds formed on thick veins of fracture filling aragonite covered by surface-deposited calcareous tufa; ongoing carbonate deposition from salty mineral water; remnants of historical aragonite extraction; geosite of scientific interest combined with cultural heritage (“Aragonite Museum” nearby) and a touristic attraction site	Local	Small scale (8 ha)	III
Tinovul Mohoș-Lacul Sfânta Ana Natura 2000 site (Harghita Mountains, Figure 25)	Two picturesque craters of Ciomadul volcano hosting a peatbog (Mohoș) and a lake (Sfânta Ana), respectively, unique in Eastern Europe; one of the most popular touristic destinations in Romania; outstanding scientific value	International	Mesoscale (240 ha)	IV
Sfânta Ana Lake protected area (Harghita Mountains, Figure 26) ***	A spectacular lake at the bottom of one of the Ciomadul volcano craters in a completely closed depression, unique in Eastern Europe and of outstanding scientific and geotouristic value	International	Mesoscale (120 ha)	IV
Piatra Șoimilor (“Eagle Rock”) Natural reserve (South Harghita Mountains)	Spectacular vertical rock cliff in andesitic clastic lava of Pilișca volcano; final destination of a steep tourist trail; panoramic view point over the Ciomadul volcano dome complex and the Băile Tușnad spa below	Local	Small scale (1.5 ha)	IV
Perșani Mountains
“Sculptured stone” basaltic columns (Comana)	Vertical columnar jointing of alkali basalts; difficult-to-find geosite of scientific value hidden in forrest	Local	Small scale (1 ha)	III
Racoșul de Jos Natural reserve (Figure 21 and Figure 27)	Various features of alkali basaltic volcanism: variously jointed lavas, phreatomagmatic deposits, and an eviscerated scoria cone exposing the internal structure of a small volcano; geosite of outstanding scientific value and of touristic attraction	National	Mesoscale (95 ha)	IV
“Racoș basalt columns” Natural monument ****	Spectacular vertical wall of columnar jointed alkali basalt lavas; one of the earliest protected geosites in Romania of great scientific value; also a touristic attraction site.	Local	Small scale (1.1 ha)	III
“Basaltic micro-canyon” of Hoghiz	Deep and narrow canyon with vertical walls exposing alkali basaltic lavas and a calcareous tufa mound on top; easy-to-reach geosite of scientific value	Local	Small scale (2 ha)	III
“Basaltic Rock of Rupea” natural monument (Figure 28)	Prominent isolated hill of basaltic andesite rising above Rupea town, with a medieval castle on top; unique site combining geological, cultural, and historical values; also a touristic attraction and a panoramic viewpoint over the surrounding landsacape and the Saxon-inhabited town below	National	Small scale (9 ha)	III

* Described in detail in [43]; ** Part of the Călimani National Park; *** Part of the Tinovul Mohoș-Lacul Sfânta Ana Natura 2000 site; **** Part of the Racoșul de Jos Natural reserve.

summarizes the major features of geosites of geoheritage interest in the East Carpathian volcanic range, including only those of geological-geographical type and having official protection status in Romania.

In the Oaş–Gutâi volcanic segment, there are numerous geosites with a significant geoheritage value, some of which have been declared protected areas: three nature monuments-Limpedea Pillars (southern part of the Gutâi Mountains, in the vicinity of the Baia Mare city), the Ilba Stone Rosette (southwestern part of the Gutâi Mountains, Figure 22a), and the Blue Lake (an anthropic mining-derived lake in the Mine Hill/Mons Medius, Figure 22b); two natural protected areas due to their impressive geologic-geomorphic landforms and landscapes—the Creasta Cocoşului (“Rooster’s Crest”) of the large-sized Gutâi dome (Figure 16a and Figure 23a) and Tătaru Gorges (in the lava plateau from the northern zone of the Gutâi Mountains); a scientific reserve—the Chiuzbaia paleontological scientific reserve, located at the foot of the Igniş volcano, unique in Romania and well-known in Europe by its impressive Upper Miocene fossil flora, some of its species described for the first time in the world [45].

Besides the above mentioned geosites, there are numerous other sites of geological and geomorphological interest that satisfy the criteria for being recognized as geoheritage sites: the Oraşu Nou lava-dome, with highly vesicular banded rhyolitic lavas and hyaloclastites with macro- and microperlites, unique in the Romanian volcanic chain; Laleaua Albă (White Tulip) and Biserica lui Vlaicu (Vlaicu Church) composite dykes (andesite envelope and dacite core), with numerous gabbroic enclaves and sanidine megacrystals (up to 5 cm) in the dacites [46], unique in the East Carpathian volcanic area; Piatra Roşie (Red Stone) Hill from the Dăneşti–Cetăţele composite dome, with its impressive escarpment in the in situ and resedimented hyaloclastites, with erosion caves in the upper part (Figure 23b); Săpânţa Stone, a big andesitic scar at the boundary of the volcanic zone and the Maramureş Basin in the northern part of the Gutâi Mountains. Other amazing erosional volcanic landforms/landscapes include the “Igniş Sphinx” at Igniş volcano (Figure 24) and the “Oaş Sphinx” at Pietroasa volcano.

Four European NATURA 2000 network sites—Gutâi Mountains (2800 ha), Igniş Plateau (19,598 ha), Gutâi Creasta Cocoşului/ Rooster’s Crest (684 ha), and the Baia Mare edible chestnut trees forest (2087 ha), including some of the geosites mentioned above, have also been designed in the Gutâi Mountains.

The most significant geosites of the Oaş–Gutâi volcanic area were proposed to be promoted through scientific field trips and geotrails of public interest [48] and to be included in a future Geological and Mining Geopark in the Gutâi Mountains, as proposed by Kovacs and Fülöp [49].

The CGH range also hosts many natural values of geoheritage relevance, but only part of them is considered, inventoried, presented, and protected as so.

The Călimani National Park, founded in 2000, is the largest (15,300 ha) and the only national park located entirely in a volcanic area in Romania. The natural values under protection here include the unique high-mountain volcanic landscape, hosting glacial and periglacial features, lakes, and marshes; spectacular rock formations; and unique floral elements [43]. Within the botanical Science Reserve of Juniperus with Pinus cembra (384.2 ha), the geographical Iezer Lake Science Reserve (322 ha) and the geological “12 Apostles” Science Reserve (Table 3), the latter with spectacular rock formations (Figure 18) resulting from interaction of erosional processes with a geological substrate of volcaniclastic rocks, are subject to the highest level of legal protection due to their outstanding scientific value. Damaged natural values of geoheritage importance are also present here. For instance, open-pit sulfur mining destroyed the original volcanic karst features first time described here in the world [50]. The high-mountain volcanic landscape was also catastrophically damaged by mining, although partially remediated today. The “Upper Mureș Gorge Natural Park” (Table 3), located along the Mureș valley between Deda and Toplița localities, follows the geographic boundary between the Călimani Mountains (to the North) and the Gurghiu Mountains (to the South). Its geological/volcanological geoheritage value, beyond its overall outstanding landscape value, consists of an almost continuous exposure of volcanic formations of various types (mostly volcaniclastic, primary, and reworked) originating from two different volcanic sources (Călimani and northern Gurghiu) interfingering with each other, uniquely displaying the internal architecture and composition of an inter-edifice volcanic ring-plain environment [32]. It hosts unique tree-mold caves, formed by erosional removal of large tree trunks engulfed in pyroclastic deposits that resulted from eruptions of the Rusca-Tihu volcano in the Călimani Mountains. The Scaunul Domnului (“God’s chair”) nature reserve (Table 3), a flat-topped lava plateau (1381 m a.s.l. at its highest point) bounded by spectacular > 40 m high vertical cliffs of platy-jointed andesite lava, is part of this Natural Park and of the NATURA 2000 site Călimani-Gurghiu. The thermal waterfall at Toplița, actively precipitating calcium carbonate from its 27 °C water on a steep rock cliff, is another highlight of the Upper Mureș gorges, having a status of natural reserve of geological and landscape type and a protected area of national interest (Table 3).

More reserve areas are located in the Harghita Mountains, most of them of flora/fauna type. Two of them are mentioned here because they are located in the central crater areas of their host volcanic edifices: the Tinovul Luci peatbog (273 ha) of the Luci-Lazu volcano, a protected area of national interest (of forest and flora type) and the Tinovul Mohoș peatbog (of 80 ha within the 240 ha protected area of flora and fauna type) of the Ciomadul volcano (Table 3), the NATURA 2000 site “Tinovul Mohoș-Lacul Sfânta Ana” (480 ha) includes both Tinovul Mohoș (i.e., Mohoș swamp) and Lacul Sfânta Ana (240 ha each) as protected areas (Figure 25). The latter, hosting the picturesque Sfânta Ana crater lake (Figure 26), unique in Eastern Europe, is declared a complex (i.e., geological, floristic, and faunal) natural reserve of national interest (Table 3). Piatra Șoimilor (“Eagle Rock”), a steep-sided rock cliff, developed on clastic andesite lavas on the eastern flank of the Pilișca volcano, offering a breathtaking panoramic view toward the East–over Băile Tușnad spa, the Olt River’s gorge, and the Ciomadul dome complex rising above it—is a protected area of national interest (Table 3), a natural reserve of geological and flora type.

The official list of protected areas of national interest related to the Perșani Mountains volcanic field includes four entries (Table 3): (1) the “Sculptured stone” basaltic columns in the Comana natural monument of geological type, (2) the “Racoș basalt columns” natural monument of geological type, (3) the “Racoșul de Jos geologic complex” nature reserve of geological type (Figure 27), including the “Racoș basalt columns” protected area and overlapping with the Dealurile Homoroadelor (the Homorod Hills) Natura 2000 site, and (4) the “Basaltic micro-canyon” of Hoghiz natural monument of geological type, all of them of outstanding scientific and societal interest. Of them, the most famous and the most frequently visited site is the “Racoș basaltic columns”. However, sadly enough, their officially “protected” status is in no way applied and reinforced in practice.

The “Basaltic Rock of Rupea” natural monument (Table 3) is a special case from the geological viewpoint. Although the prominent rock on top of which the picturesque tourist-highlight medieval castle was built and recently renovated, was traditionally described as “basalt”, it is actually composed of calc-alkaline basaltic andesite, different from the alkali basaltic rocks of the Perșani Mountains, and its age is much older (6.8 Ma), as revealed by more recent research [51]. This particular site combines geoheritage values (the rock) with cultural heritage (the castle) and that of a spectacular landscape (Figure 28).

The natural values of geoheritage relevance hosted by the Neogene–Quaternary volcanic range of the East Carpathians, summarily listed and characterized above, have various protection statuses and various accessibilities, and they are variously exposed to anthropic degradation by tourist and leisure activities, not always reflecting their intrinsic values. Given its uniqueness in terms of volcanic landforms, landscape, and complex geological–biological nature, the over-visited and anthropically stressed Mohoș peatbog-Sfânta Ana Lake area of Ciomadul volcano, for example, deserves the higher protection status of National Park or Geopark rank than the current one, which minimizes and mitigates the irreversible degradation hazard to which it is presently exposed.

8.2. Geoparks, Geotrails, and Geotourism

Despite its huge geoheritage potential, as sketched above, related only to its young volcanic areas, Romania has only two Geoparks (The “Hațeg Country Dinosaur Geopark” focused on dinosaur fossil findings and the “Buzău Land” Geopark with its world-famous mud volcanoes) today, none of them related to the East Carpathian volcanic range. The highest potential to gain Geopark status has the area hosting the most recently erupted Ciomadul volcano, with its unique crater-filling swamp (Mohoș) and lake (Sfânta Ana) and its environs rich in spectacular “post-volcanic” manifestations (bubbling grounds, dry CO₂ emanations (mofettes), and a plethora of CO₂-rich mineral water springs and pools. Purposefully designed geotrails, others than that hosted by the “Hațeg UNESCO Global Geopark” are extremely sparse in Romania. Ironically enough, a “House of Volcanoes” was established and can be visited by tourists at the “Hațeg UNESCO Global Geopark” (https://www.europarc.org/news/2018/10/the-house-of-volcanoes-a-community-based-initiative-in-romania/, accessed on 4 May 2022), whereas practically no volcanism-related displays, geotrails, or tourist-attracting shows are available at sites located within the huge territory, where volcanic activity was active for millions of years during the Neogene and the Quaternary. Consequently, geotourism is at its very infancy in Romania, in general, and in its volcanic areas, in particular.

There are, however, a few exceptions.

Geosites related to the over seven centuries old mining activity and related archeological features (e.g., the ”Smoke gallery” of the Dealul Crucii mine, as testimony of the Middle Age ”fire exploitation” of ores [48]) represent an important geotouristic potential prone to be capitalized in the Gutâi volcanic area. These sites of geoheritage significance are located within the four European NATURA 2000 network areas in the Gutâi Mountains in the close vicinity of UNESCO/World Heritage Patrimony cultural sites (such as the world-famous medieval wooden churches found inside or near the volcanic area).

After a long time during which the local authorities were not seriously involved in promoting geotourism in the Oaș–Gutâi Mountains, the first step was recently taken by establishing a geological mining park in the Mine Hill (Mons Medium) of Baia Sprie town, including the Blue Lake III IUCN geosite (Table 3) and a number of historical mining shafts and galleries.

One recent achievement related to the valuation of the natural volcanic landscape by tourism was the reconstruction of the old “Maria Thereza Road” in the Călimani Mountains, which, centuries ago, linked Transylvania and Bukovina, two provinces of the Austro-Hungarian Empire across the mountains, a picturesque high-mountain environment hosting a bike marathon organized on a regular basis. More educational and scientific activities within the Călimani National Park are also frequently taking place [43].

Sparse initiatives led by enthusiastic local people devised and realized a few local tourism-related objectives such as (1) the Dealul Melcului (Snail hill) in Corund (Gurghiu Mountains), displaying the remnants of an old aragonite excavation of three veins of beautifully-colored banded rock, a short trail with explanatory boards, and a small, nearby Aragonite museum exposing artistic artefacts obtained from this ornamental rock (Table 3), (2) the mineral water museum in Tușnad-Sat (South Harghita Mountains) located just near a high-output mineral spring, exposing the geological context of the CO₂-rich waters abundant in the area as a consequence of post-volcanic activity and the multisecular exploitation and trade history of local people.

Other local achievements of geotouristic relevance include the renovation of a number of traditional open-air cold mineral water baths and mofettes of a multisecular tradition in the area of dry and wet CO₂ emanations related to volcanism, used by local people for curative purposes. “Nádas Bath” at Lăzărești, the “Apor girls bath”, ”Bálványos baths”, all close to the Ciomadul volocano, are just a few of them. They are part of a quite poorly advertised Mineral Water Trail in Harghita and Covasna Counties, attracting numerous tourists. Most of them, however, were renewed and managed as a single-time effort using grant money, later progressively degrading due to a lack of maintenance resources and gradually losing their primary touristic attractivity.

Although not explicitly stated and recorded as so, geoeducational activities are traditionally conducted in the East Carpathian volcanic areas, in particular in the Gutâi Mountains, where mining-related geological features are commonly shown and explained to students by their teachers/professors and local geologists and occasionally other visitors and tourists without, however, being integrated in a coherent and well-advertized geoeducational strategy focused on geoheritage values.

As compared with most countries belonging to the same Carpathian–Pannonian Region mega-tectonic unit (Czech Republic, Poland, Hungary, and Austria), hosting Neogene volcanic areas, but covering much less widespread land areas [52,53], Romania is much delayed behind them in terms of geoheritage awareness, conservation and valuation. Therefore, sustained efforts are needed to fill this gap in knowledge, research, and valorization of the geoheritage values Romania undoubtedly hosts, including those located in its Neogene volcanic areas.

9. Conclusions

The East Carpathian Neogene–Quaternary volcanic areas, including the Oaș–Gutâi, Călimani-Gurghiu-Harghita calc-alkaline, and the Perșani Mountains alkali basaltic regions display a wide range of volcanic landforms of various genesis, types and sizes, and related landscapes due to a number of natural and anthropic factors. The following natural factors are considered:

• Primary volcanic topography (size, elevation, topography) depending on (1) the style (effusive, explosive, both) and (2) the duration of volcanic activity at individual volcanic centers, (3) syn-volcanic destruction events (e.g., caldera formation, sector collapse/edifice failure) operating during volcanic evolution, and (4) the spatial distribution of the volcanoes (isolated or clustered edifices of various shapes and sizes);
• Syn- and post-volcanic non-erosional deformation processes related to volcano spreading, as proved at the western peripheries of the largest Gurghiu and North Harghita edifices;
• Syn- and post-volcanic erosion of various intensity depending on (1) age of volcanism (decreasing from North-West to South-East along the Călimani-Gurghiu-Harghita segment), (2) contrast of erodibility between volcanic formations and the surrounding basement rocks and between various volcanic lithologies, and (3) varying relief energy (higher in the steeper proximal parts of the composite volcanic edifices as compared to their flatter peripheries).

The landscapes developed on various primary and erosion-modified volcanic landforms is also extremely diverse, including further determining factors, such as elevation (i.e., high-mountain landscapes, in cases influenced by glacial erosion, vs. low-lying landscapes), vegetation (partly determined by elevation), and proximity to human settlements. The anthropic influence on the landscapes is equally diverse: ancient or recent mining activities (many small quarries and a few large open-pit quarries), timber logging, dams and related accumulation lakes, access roads, and other infrastructure facilities. The anthropic influence is strongly detrimental leading to spoiling and degradation of the natural landscape.

All of the East Carpathian volcanic areas host a number of valuable geoheritage sites of various legal protection status and at various scales (from local small-scale objectives, such the “Stone Rosette” in the Gutâi Mountains or the “Racoș basalt columns” in the Perșani Mountains, to national parks, such as the Călimani National Park). Other potentially valuable values from the geoheritage perspective are not even inventoried and part of those legally protected, such as the Ciomadul volcano, are under-evaluated, hence under-rated. Some of them are over-exploited commercially (such as NATURA 2000 site “Tinovul Mohoș-Lacul Sfânta Ana” in the South Harghita Mountains, or the natural protected area Rooster’s Crest in the Gutâi Mountains) due to their accessibility, others, in contrast, are less visited (e.g., the 12 Apostles in the Călimani Mountains) due to more difficult access.

Despite its significant geoheritage potential, no Geopark related to the East Carpathian volcanic range, exists. Geotrails are almost entirely lacking, whereas geotourism is in its infancy in Romania, in general, and in the East Carpathian volcanic area, in particular.

As can be seen throughout the paper, there is much diversity of volcanic features through the presented region, and many of these have geoheritage significance. Ideally, each of the sites highlighted and listed in Table 3 are geosites of geoheritage significance and connecting them in a number of geotrails would form not only touristic attraction but also a valuable educational resource for the general public, students, and pupils alike. Moreover, the entire region of volcanic features, landforms, and landscapes would form a network of geoparks in the East Carpathian Neogene–Quaternary volcanic range from Oaș Mountains to South Harghita and Perșani Mountains, which in turn can be connected across the state border to volcano geoparks already existing in the broader Carpathian–Pannonian Region (such as those in Hungary) in an even wider regional network.