Mega-tsunami conglomerates and flank collapses of ocean island volcanoes

Abstract

International audienceMarine conglomerates at high elevation on the flanks of ocean islands are usually interpreted as evidence of mega-tsunamis generated by volcano flank collapses, although their origin is sometimes debated (elevated littorals vs. tsunami). In this review, we introduce case studies of well-documented examples of tsunami conglomerates in Hawaii (Pacific Ocean), the Canary and Cape Verde Islands (Atlantic Ocean), and Mauritius Island (Indian Ocean). Other less-documented marine conglomerates are also presented as tsunami candidates. Then, we build a comprehensive picture of the general characteristics of these conglomerates and the different methods that can be applied to date them. Different perspectives of research are proposed, especially on the use of tsunami conglomerates as proxies for better constraining numerical models of ocean island flank collapses and associated tsunamis. We also discuss the possible links between volcano growth, flank instability, and climate

Evidence on the Koseda coast of Yakushima Island of a tsunami during the 7.3 ka Kikai caldera eruption

“…The long‐axis orientations and composition of gravel clasts in Unit TG suggest that they were transported landward by a laminar flow, such as a tsunami run‐up flow (Figures a and ). Huge tsunamis are known to deposit run‐up gravel beds that resemble gravelly gravity‐flow deposits (A. L. Moor, ; J. G. Moor & Moore, ; Nanayama et al, ; Paris et al, ; Yagishita, ). Therefore, Unit TG is here interpreted to be a tsunami deposit resulting from a high‐particle‐concentration from ENE to WSW.…”

“…of a flank collapse) required to trigger a large tsunami (e.g. Kelfoun, Giachetti, & Labazuy, ; Paris et al, ). Moreover, even if a large and dense pyroclastic flow rapidly discharged into the sea, the results of numerical simulations (Maeno & Imamura, ) suggest that it is difficult to reproduce a tsunami large enough to explain far‐field evidence such as the deposition of Unit TG.…”

A geological record of multiple Pleistocene tsunami inundations in an oceanic island: The case of Maio, Cape Verde

“…A detailed analysis of the sedimentological criteria used for identifying tsunami conglomerates and gravel beds on oceanic islands can be found in the recent review by Paris et al . (). In general, tsunami deposits typically mantle the topography (even on steep slopes) and are usually preserved as patches (lenticular geometry) at different elevations (Moore & Moore, ; Moore, ; McMurtry et al ., ,b; Perez‐Torrado et al ., ; Paris et al ., , , ; Ramalho et al ., ).…”

“…(). In general, tsunami deposits typically mantle the topography (even on steep slopes) and are usually preserved as patches (lenticular geometry) at different elevations (Moore & Moore, ; Moore, ; McMurtry et al ., ,b; Perez‐Torrado et al ., ; Paris et al ., , , ; Ramalho et al ., ). Additionally, tsunami conglomerates and gravel beds almost invariably exhibit chaotic textures, being either clast or matrix‐supported but generally featuring a mixing of sediments from different sources redistributed both inland and offshore (i.e.…”

“…Additionally, tsunami conglomerates and gravel beds almost invariably exhibit chaotic textures, being either clast or matrix‐supported but generally featuring a mixing of sediments from different sources redistributed both inland and offshore (i.e. terrestrial and marine) (Perez‐Torrado et al ., ; Ramalho et al ., ; Paris et al ., , ). Grain‐size distribution is commonly highly heterogeneous, often including large boulders ‘floating’ in finer conglomeratic or sandy matrixes and frequently displaying a mixture of both well‐rounded and angular boulders/pebbles (Moore & Moore, ; Moore, ; McMurtry et al ., ,b; Perez‐Torrado et al ., ; Paris et al ., , , ).…”