Identification and Delineation of the Earth’s Large-Scale Closed Terrain Depressions and Their Fractal Size Distribution

Abstract

Closed terrain depressions are geomorphic features that show scale invariance over the wide range of scales on which they occur, from metres to thousands of kilometres. They are also global features that are present on all continents. Morphometric analyses of these depressions are now possible because of the availability of global digital elevation models and advances in methods for mapping closed depressions. Here, a simple and automatic but efficient method is proposed for mapping closed terrain depressions. The GTOPO30 global digital elevation model, with a spatial resolution of around 1 km, was used to map the closed depressions of eight large test sites sampled from all inhabited continents. The identified and delineated terrain depressions include lake watersheds together with many other terrain depressions including deserts, karst terrains and rift valleys. A fractal analysis shows that South America and Central Africa have similar, and also the largest, fractal dimensions; Central Europe and North Africa have intermediate fractal dimensions; and North America, Central Asia, the Near East and Australia have similar, low fractal dimensions. The methodology proposed in this paper can be used to identify areas of interest for which a more exhaustive analysis, using digital elevation models with better spatial resolution, can be conducted.