Boulder ridges in Sal Island, Cape Verde: imprint of tsunamis, modern storms, or Last Interglacial wave deposits?

The northwestern coast of Sal Island, Cape Verde Archipelago, features an almost continuous rocky shoreline, regularly impacted by powerful Atlantic waves exceeding 4 meters in height and 20 seconds in period. The most striking geomorphic feature of this coast is a prominent boulder ridge perched atop the rocky cliff, situated 10 to 15 meters above sea level and extending 80 to 100 meters inland. The ridge contains boulders with diameters exceeding two meters, raising intriguing questions about its origin: Is the boulder ridge a product of modern wave action? Was it formed during the Last Interglacial, when relative sea levels were 4–8 meters higher than today? Or does it record a single, catastrophic tsunami event? To address these questions, we conducted high-resolution topographic mapping using Unmanned Aerial Vehicles (UAVs). This topographic data was used as a base for hydrodynamic modeling with XBeach. The modeled flow velocities were compared against the location and elevation of the boulder ridge, while the highest flow velocities were cross-validated with empirical equations of incipient motion for the largest boulders in the area. 

This presentation is a contribution to the WARMCOASTS project, which has received funding from the European Research Council under the European Union's Horizon 2020 research and innovation programme (grant agreement n. 802414)