The Link Between Upper-Slope Submarine Landslides and Mass Transport Deposits in the Hadal Trenchs

Abstract

Sediment gravity flow is a density current that moves down a slope due to the gravitational force. Submarine landslides are a trigger mechanism for sediment gravity flows, and the movement of a large amount of sediment mass has the potential for generating tsunami. An oceanic trench is a terminal depression in the hadal environment that receives mass transport deposits (MTDs) from the slope. Thick, acoustically transparent layers were found in small basins along the northern Japan Trench. Sediment cores obtained from these basins were composed of thick, homogeneous mud, suggesting the presence of distal MTDs. Radiocarbon dates obtained using bulk organic carbon from the sediment indicated that these MTDs were formed around 2000 years ago and were correlated with each other. Benthic foraminiferal assemblages in the MTDs contained upper-slope species. There are many submarine landslides distributed along the upper slope of the Hidaka Trough; thus, the upper slope of this trough is important not only as a sediment source but also as a source of carbon for the Japan Trench, which is an effective sink of organic carbon. However, the exact locations of the submarine landslide on the upper slope have not yet been determined. Furthermore, from the geohazard point of view, the upper slope is an area of large sediment movements, which should be considered in the context of tsunami hazard mitigation.