A deep scar in the flank of Tenerife (Canary Islands): Geophysical contribution to tsunami hazard assessment

Among the high-intensity on-Earth tsunami generating events, seismicity, submarine landslides, and volcano lateral collapses are the most important [Ward, S.H., 2001. Landslide tsunami. J. Geophy. Res. 106, 11201–11215; Holcomb, R.T., Searle, R.C., 1991. Large landslides from oceanic volcanoes. Mar. Geotech. 10, 19–32; Tinti, S., Bortolucci, E., Romagnoli, C., 2000. Computer simulations of tsunamis due to the sector collapse ar Stromboli, Italy. J. Volcano. Geotherm. Res. 96, 103–128; Ward, S.N., Day, S., 2003. Ritter Island Volcano — lateral collapse and the tsunami of 1888. Geophys. J. Int. 154, 891–902; MacGuire, W.J., 2003. Volcano instability and lateral collapse. Revista 1, 33–45]. Offshore bathymetry studies highlighted huge accumulations of large mass-waste flows (up to thousands cubic kilometres) inherited from past lateral collapses or submarine landslides [Le Friant, A., Boudon, G., Deplus, C., Villemant, B., 2003. Large-scale flank collapse events during the activity of Montagne Pelée, Martinique, Lesser Antilles. J. Geophys. Res. 108, ECV13; Moore, J.G. et al., 1989. Prodigious submarine Landslides on the Hawaiian ridge. J. Geophys. Res. 94, 17465–17484] which spread over more than 100 km off the northern Tenerife (Canary Islands) coastline [Watts, A.B., Masson, D.G., 1995. A giant landslide on the north flank of Tenerife, Canary Islands. J. Geophys. Res. 100, 24487–24498]. Although mechanics and dynamics triggering such catastrophic events follow from combined complex processes and interactions [Hürlimann, M., Garcia-Piera, J.-O., Ledesma, A., 2000. Causes and mobility of large volcanic landslides: application to Tenerife, Canary Islands. J. Volcano. Geotherm. Res. 103, 121–134; Masson, D.G. et al., 2002. Slope failures on the flanks of the western Canary Islands. Earth-Sci. Rev. 57, 1–35; Reid, M.E., Sisson, T.W., Brien, D.L., 2001. Volcano collapse promoted by hydrothermal alteration and edifice shape, Mount Rainier, Washington. Geology 29, 779–782], potential movable volume is an unavoidable parameter to quantify and constrain tsunamigenic hazard. Numerical modelling of a tsunami generated by the potential La Palma landslide concluded that high amplitude waves threaten North Atlantic shorelines [Ward, S.N., Day, S.J., 2001. Cumbre Vieja volcano — Potential collapse and tsunami at La Palma, Canary Islands. Geophys. Res. Lett. 28, 397–400]. New audiomagnetotelluric results provide for the first time a good estimation of the Icod Valley (Tenerife, Canary Islands) volume, a potential giant landslide threatening the same shorelines. Two profiles image its electrically conductive roots with a characteristic of a U-shaped cross-section thought to be the consequence of previous landslides. By this study, we show that North Atlantic Ocean shorelines might be exposed to a destructive tsunami generated by a subaerial lateral collapse of at least 120 km3 during the next strong felsic eruptive activity of the Teide–Pico Viejo complex.This article highlights the degree of urgency of carrying out geophysical investigations on the flanks of most volcanic islands prone to potential flank collapse. These investigations will contribute to the understanding of their structure — a key parameter in the sliding process. Finally, all results should be included in model, providing a global map of tsunami hazard assessment.