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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS002 Oral Presentation 1743
Tsunamigenic risk for North Atlantic shorelines
Mr. Nicolas Coppo
Institute of Geology and Hydrogeology University of Neuchtel - Switzerland IASPEI
Pierre-Andr Schnegg, Pierik Falco, Roberto Costa
Among the high-intensity on-Earth tsunami generating events, seismicity, submarine landslides, and
volcano lateral collapses are the most important (Holcomb and Searle, 1991; Ward, 2001). Recent off
shore bathymetry studies demonstrated the huge accumulation of debris flow deposits spreading over
more than 100 km off the northern Tenerife (Canary Islands) coast line, inherited from past lateral
collapses (Watts and Masson, 1995). Although mechanics and dynamics triggering such catastrophic
events follow from combined complex processes (vertical caldera collapse, flank destabilization,
hydrothermal pressurization, seismic events), potential movable volume is the unavoidable parameter to
quantify and constrain the tsunamigenic alea. In the same archipelago, mathematical modelling of the
La Palma potential landslide concluded that high amplitude waves may cross all the Atlantic Ocean with
harmful effects (Ward and Day, 2001) in few hours. However, because of often steep and inaccessible
volcano flanks, the geological and geophysical ignorance of lateral flank structures may lead to wrong
estimation of a potential movable volume. New geophysical results (audio-magnetotellurics recorded in
the 0.001-1 s period range) provide for the first time a good estimation of the volume of the Icod Valley
(Tenerife, Canary Islands) potential giant landslide threatening northern Atlantic Ocean shorelines. Two
profiles image its electrically conductive roots with a characteristic U-shaped morphology thought to be
the consequence of previous landslides. This conductive layer (20-70 m) corresponds to a plastic
breccia within a clayish matrix reached in some galleries that perforate the volcanic edifice for water
supply. It is overlaid by the recent resistive (200-2000 m) lavas from the Pico Teide Pico Viejo complex
with up to 1000 m thickness in the middle of the Icod Valley. Around 15 km separate two high
conductive bodies that delimit the lateral extension of the valley. Its length is estimated at 13 km.
Considering that the top conductive layer might be the sliding surface of the potential Icod Valley lateral
landslide, we show that northern Atlantic Ocean shorelines might be exposed to a destructive tsunami
generated by a subaerial lateral collapse of at least 120 km3 during a future strong volcanic activity of
the Teide-Pico Viejo complex.
Keywords: lateral collapse, tsunami, audio magnetotellurics