Coastal retreat and sea-cliff dynamic on the North Atlantic coast (Gerra Beach, Cantabrian Coast, Spain)

Abstract

Gerra is small beach located at the foot of a cliff on the Western coast of Cantabria (North of Iberian Peninsula). It has a sandy distal part and a proximal part at the foot of the cliff made up of boulders, supported by rockfalls and landslides from the cliff. Claystones, limestones and marls of the Triassic and Cretaceous ages form the cliff. To study geomorphological processes, a geomorphological map was drawn up; analysis of the beach deposits as texture, granulometry and Atterberg limits; analysis of photogrammetric flights between 1957 and 2017; drone flights between 2017 and 2020; and geomatic monitoring of the cliff and the beach by means of a terrestrial laser scanner (TLS) between 2012 and 2019. The processes involved in the coastal dynamic and retreat of the cliff and beach have been established, as well as the rates of erosion and retreat, which coincide with other beaches on the Cantabrian Coast. The current dynamics are characterized by the moderate regression of the coastline and greater regression and dynamism at the cliff-top, which implies the gradual degradation of the cliff due to loss of verticality. Among the factors involved in the cliff degradation, the main changes in the present and future evolution of the sea cliff can only be ascribed to sea level rise.