**1. Introduction**

Tailings are the material left after the valuable parts have been separated from the uneconomic or low-economic ore. A tailings dam is typically an earth-fill embankment dam which is usually designed for permanent containment by intercepting valleys or enclosing lands in order to form a tailings pond used to store metal or non-metal oreseparation and discharging tailings or other industrial waste residues. Consequently, the tailings dam is a dangerous source of man-made mudflow with high potential energy. The

**Citation:** Cheng, D.; Cui, Y.; Li, Z.; Iqbal, J. Watch Out for the Tailings Pond, a Sharp Edge Hanging over Our Heads: Lessons Learned and Perceptions from the Brumadinho Tailings Dam Failure Disaster. *Remote Sens.* **2021**, *13*, 1775. https://doi. org/10.3390/rs13091775

Academic Editors: Paolo Mazzanti and Saverio Romeo

Received: 18 January 2021 Accepted: 26 April 2021 Published: 2 May 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

failure of the tailings dam is one of the most dangerous disasters causing serious accidents. Tailings dams are considered more vulnerable than hydraulic dams due to the lack of regulations on specific design criteria, stability requirements regarding monitoring during the construction and maintenance process, and high potential of pollution due to its filled material (solid waste) [1].

The mining byproducts collected in tailings dams may damage the environment by releasing toxic metals and poisoning the aquatic wildlife that relies on clear water [2]. In past decades, many researchers have investigated tailings dam failures using different research methods, e.g., site investigation, numerical simulation, and remote sensing technology. A field investigation has been proven to be a good method to obtain first-hand data when accessibility is possible to the disaster site. For example, Macklin et al. [3] collected sediment samples affected by tailings dam failures to assess the long-term fate and environmental significance of contaminant metals. Porsani et al. [4] used Ground-Penetrating Radar (GPR) on an iron mining area after the collapse of the tailings dam I at the Córrego do Feijão Mine in Brumadinho-MG, Brazil to map bodies, structural buildings, and equipment buried in the mud. A numerical simulation is another effective means, which can help us understand the tailing flow characteristics and assess the possible extents of the affected areas [5,6]. With the advance in remote sensing technology, remote sensing has been becoming a more and more important means of information acquisition in disaster investigation [7–10]. Many scholars have applied remote sensing technology to the study of tailings dam failure disasters. For example, Silveira et al. [11] used semivariogram indices derived from NDVI images to obtain an object-based change detection caused by the Mariana dam disaster. Grenerczy and Wegmüller [12] performed a Persistent Scatterer InSAR (PSI) analysis to examine the embankment failure of a red mud reservoir. The tailings dam failure is a kind of disaster which could affect wide areas, especially those along rivers, and different disaster characteristics often appear in different regions. Therefore, different remote sensing techniques are usually requested to be employed to analyze a series of remote sensing images to reflect the whole disaster process. In this study, we attempt to make full use of the available remote sensing images to examine the Brumadinho tailings failure disaster in order to make people realize the great harm of tailings dam failures. In addition, this paper demonstrates how RS techniques can be used to characterize and monitor the evolution of such complex processes, which provides a reference for disaster prevention and mitigation.
