Abstract
Giant mass failures of oceanic shield volcanoes that generate tsunamis potentially represent a high-magnitude but low-frequency hazard, and it is actually difficult to infer the mechanisms and dynamics controlling them. Here we document tsunami deposits at high elevation (up to 132 m) on the north-western slopes of Tenerife, Canary Islands, as a new evidence of megatsunami generated by volcano flank failure. Analyses of the tsunami deposits demonstrate that two main tsunamis impacted the coasts of Tenerife 170 kyr ago. The first tsunami was generated during the submarine stage of a retrogressive failure of the northern flank of the island, whereas the second one followed the debris avalanche of the subaerial edifice and incorporated pumices from an on-going ignimbrite-forming eruption. Coupling between a massive retrogressive flank failure and a large explosive eruption represents a new type of volcano-tectonic event on oceanic shield volcanoes and a new hazard scenario.
Highlights
Giant mass failures of oceanic shield volcanoes that generate tsunamis potentially represent a high-magnitude but low-frequency hazard, and it is difficult to infer the mechanisms and dynamics controlling them
Marine conglomerates and megaclasts found at unusually high elevations in Hawaii, Cape Verde, Mauritius and Canary Islands were interpreted as being the result of tsunami waves generated by massive flank failures of oceanic shield volcanoes[14,15,16,17,18,19,20]
The stratigraphy of the tsunami deposits and characterization of pumice clasts found in these deposits allows us to distinguish at least two successive tsunamis, identify their possible source, and demonstrate the association between a massive flank failure (Icod collapse) and an explosive ignimbrite-forming eruption (El Abrigo) both about 170 kyr ago
Summary
Giant mass failures of oceanic shield volcanoes that generate tsunamis potentially represent a high-magnitude but low-frequency hazard, and it is difficult to infer the mechanisms and dynamics controlling them. Marine conglomerates and megaclasts found at unusually high elevations in Hawaii, Cape Verde, Mauritius and Canary Islands were interpreted as being the result of tsunami waves generated by massive flank failures of oceanic shield volcanoes[14,15,16,17,18,19,20]. These conglomerates are preserved at different elevations, often out of the range of marine highstand deposits. Apart for this example, such causal links remain speculative, especially for larger-scale flank failures[22]
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