International Journal of Geoheritage and Parks (Dec 2021)
The mapping of closed depressions and its contribution to the geodiversity inventory
Abstract
In geoparks and other natural protected areas, a geodiversity inventory is essential for the identification, characterization, quantification, and management of geoheritage. The protection and preservation of geosites is essential for the sustainable development of geotourism. In this sense, geomorphological diversity is a significant component of a geodiversity inventory. In evaluating geomorphological diversity, one of the most ubiquitous key landforms that configurate the landscape are closed depressions. Closed depressions occur extensively across scales, lithologies, climates and a variety of origin processes. The unprecedented availability of digital elevation models with high spatial resolution has expanded the possibilities for the mapping and morphometric analysis of closed depressions in geodiversity studies. Until recently, the identification of closed depressions was based on topographical maps, aerial photographs and field work, all of which have inherent limitations such as the observable spatial resolution, difficulty in accessing some areas, coverage of large areas and the quantification of mapped depressions. The digital format of elevation models now provides the basis for a numerical approach to accurately identify and delineate closed depressions using the simple methodology of pit removal (i.e., pit filling) together with a map algebra operation. The result is a raster map of terrain depressions in which each pixel shows the depth of the depression with respect to the lowest altitude of its rim. Morphometric analyses of these raster maps of closed depressions are then straightforward. Closed depressions are scale-invariant, and their sizes range from millimetres or centimetres for a solution pan to hundreds of kilometres for a tectonic basin. Closed depressions are ubiquitous in all terrains and are not confined to karst terrains in which closed depressions are the most distinctive feature at the metric scale. This paper demonstrates the use of a digital elevation model for automatically mapping closed depressions. The resulting map of closed depressions can be directly integrated into a geomorphological map to evaluate geomorphological diversity. In addition, this paper reviews the rich realm of closed depressions that have been found in all types of lithologies, at all scales and for a wide range of genetic processes: dissolution, subsidence, collapse, meteorite impact, explosive volcanism, suffusion, ice melting, erosion, weathering, landslides and tectonic processes. The detailed identification, delineation and bathymetry of closed terrain depressions can be used in the management of geodiversity and in evaluating geoheritage and geosites and will contribute to the sustainable development of geotourim.
