Geological evolution of the volcanic island La Gomera, Canary Islands, from analysis of its geomorphology

Abstract

Erosion and landslide processes played an important role in shaping the geomorphology of the Canary Islands. But for the heavily eroded La Gomera Island, those processes have been unclear. We conducted an integrated study of its offshore extension, onshore geology, and links between them in order to determine the geomorphological evolution of the island relative to the rest of the archipelago. The characteristics of the island's barrancos and its interfluves have led us to differentiate four types of morphological areas whose fluvial networks are in different stages of evolution. Those barrancos offshore are interrupted by La Gomera's shelf, and its erosion has been much greater than for the rest of the Canary Islands. Such erosion is both a function of time and varied swell action. La Gomera's insular slope is carved by a system of submarine canyons and channels that have morphology indicative of turbidity current erosion. Many of the barrancos onshore and the canyons offshore have steps or knickpoints: some are the result of varied resistance to erosion, and others are explained by other mechanisms. A ridge whose crest is covered by cone-like shape structures is interpreted as of volcanic origin, with the particularity that it lacks onshore continuation, the opposite of what has been observed elsewhere in the Canary Islands. Also in contrast with the other islands of the archipelago, La Gomera's margin does not seem to have resulted from destructive mass wasting and the only offshore sign of catastrophic events are the presence of two embayments along La Gomera's northern shelf edge and a lobe structure on the insular apron at 3000 m depth. These features may be the remains of the catastrophic failures that took place on the island 9.4–8.7 Ma ago. Alternatively, they could be due to recent catastrophic failures on the upper slope due to sediment steeping. Since the conclusion of the main volcanic activity 4.0 Ma ago, La Gomera has been intensively eroded by gradual fluvial denudation and secondary failures. La Gomera's insular margin reveals much regarding its evolution, but more comprehensive studies including seismic and coring are needed to understand its whole geological history.