Volcanic Island Drainage Divide Migration: Implications for Land Planning (Assomada Plateau, Santiago, Cape Verde)

Abstract

Volcanic landscapes during island formation are due to lava flows and their accumulation processes. However, erosive processes dominate landscape reshaping during periods of volcanic inactivity, posing unique and crucial land-use planning challenges. In the North Atlantic Ocean, the Cape Verde archipelago is an excellent area for assessing the implications of erosive processes on the definition of land planning strategies. Accordingly, this study focuses on the extensive Assomada Plateau (municipality of Santa Catarina), located on Santiago Island. The research uses the geomorphological index Chi (χ) to evaluate directional erosional trends of the drainage divides and relates them with the present and future (master plan) of urban occupation. This study aims to define problematic areas where it is expected that the erosion from drainage divide migration will likely cause severe problems for human occupation. For the Assomada settlements, the master plan establishes the consolidation of the existing urban area and expansion of its periphery close to the southern plateau edge. Furthermore, asymmetric Chi value patterns reveal areas of intense erosion from the movement of the drainage divide to the North and West. Watercourses have already eroded the plateau base, with erosion branching off in three directions. As a result, several cliff edge buildings are at risk, and any further expansion in these areas is questionable.