Geomorphologic Evidences of Great Flank Collapses in the Northwest of Gran Canaria (Canary Islands, Spain)

Abstract

This work provides geological observations that support the existence of several large rock slides in the northwest sector of the Gran Canaria Island, which are now covered by recent lavas. Some erosional forms has been identified: a paleo-relief developed in Pliocene volcanic materials which could be related to a large rock slide, a number of streams with strong incision and sharp diversions which are related to the flanks of the fractured rockmass, a clear topographical unconformity between the oldest erosion surfaces, as well as a prior secondary scarp near de coastal border. Moreover, we have identified some aggradational morphologies: a debris avalanche deposit covering the offshore area of the island, several scoria cones which are developed following the main scarp of the rock slide and a field of volcanoes which covers the foot of the slide in the onshore part of the island. These observations confirm the existence of some large rock slides that affect successively the NWflank of Gran Canaria during the Miocene to Pliocene. These flank instabilities suggest a NE-SW extensional regime, which could be related to a NW-SE fault zone that divides the island into two sectors. This hypothesis is in agreement with the spreading process which has been proposed for other volcanic islands.