*Article* **Vertical Land Motion as a Driver of Coastline Changes on a Deltaic System in the Colombian Caribbean**

**Juan Felipe Gómez 1,\*, Eva Kwoll 1, Ian J. Walker <sup>2</sup> and Manoochehr Shirzaei <sup>3</sup>**

<sup>1</sup> Department of Geography, University of Victoria, Victoria, BC V8P 5C2, Canada; ekwoll@uvic.ca

<sup>2</sup> Department of Geography, UC Santa Barbara, Santa Barbara, CA 93106, USA; ianjwalker@ucsb.edu

<sup>3</sup> Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA; shirzaei@vt.edu

**\*** Correspondence: jfgomez@uvic.ca

**Abstract:** To face and properly mitigate coastal changes at a local level, it is necessary to recognize and characterize the specific processes affecting a coastline. Some of these processes are local (e.g., sediment starvation), while others are regional (e.g., relative sea-level change) or global (e.g., eustatic sea-level rise). Long tide gauge records help establish sea-level trends for a region that accounts for global (eustatic, steric) and regional (isostatic) sea-level changes. Local sea-level changes are also the product of vertical land motion (VLM), varying depending on tectonic, sedimentological, and anthropogenic factors. We investigate the role of coastal land subsidence in the present-day dynamics of an abandoned delta in the Colombian Caribbean. Satellite images and synthetic aperture radar acquisitions are used to assess decadal-scale coastline changes and subsidence rates for the period 2007–2021. We found that subsidence rates are highly variable alongshore. Local subsidence rates of up to −1.0 cm/yr correspond with an area of erosion rates of up to −15 m/yr, but coastal erosion also occurs in sectors where subsidence was not detected. The results highlight that local coastline changes are influenced by multiple, interacting drivers, including sand supply, coastline orientation and engineering structures, and that subsidence alone does not explain the high rates of coastal erosion along the study area. By the end of the century, ongoing coastal erosion rates of up to −25 m/yr, annual rates of subsidence of about −1 cm/yr, and current trends of global sea-level rise are expected to increase flooding levels and jeopardize the existence of the deltaic barrier island.

**Keywords:** sea-level rise; InSAR; Magdalena River; coastal changes; subsidence; mangroves; sediment compaction
