Evidence for a persistent uplifting of La Palma (Canary Islands), inferred from morphological and radiometric data

The morpho-structural evolution of La Palma (Canary Islands) is characterized by vertical movements responsible for/or favoring large landslides. In its northern part, conglomerate terraces, nowadays topographically hanged and reincised by the present-day 'Barranco de Las Angustias', reveal a recent ongoing uplift process. Lava flows covered by this geological unit have been sampled and dated by the K/Ar Cassignol technique at a mean age of 507 +/- 11 ka. The minimum rate of uplift inferred, of about 0.4 mm/yr, is similar to the one deduced from the abnormal elevation of the early submarine series [Staudigel and Schmincke, J. Geophys. Res. 89 (1984) 11195-11215]. This indicates that the northern shield may have experienced a global rise fairly constant throughout most of its geological history. It probably results from the combination of regional Atlas tectonic processes and the existence of a swell at the island scale. This global rise, together with the existence of a north-south fault in the basement, may have controlled triggering of the SW flank collapse of the northern shield and the subsequent concentration of magma along a southern, still active topographic ridge, the Cumbre Vieja (CV). Morphological asymmetry of this structure may result from the destabilization of its distal western part, favored by strong injections at the axis. Tilting processes along lateral listric faults can then explain the existence of slope break-ups, especially on the western side of the ridge. Such tectonic processes are likely responsible for local superimposed uplifting contributing to the genesis and development of huge western coastal cliffs, even in sub-historic and historic times. We show that, unlike many oceanic islands, La Palma Island has experienced important positive vertical movements rather than subsidence. (C) 2003 Elsevier Science B.V. All rights reserved.