Undersea landslides: Extent and significance in the Pacific Ocean

Submarine slope failures have been identified in the Pacific Ocean by observing a) coastal evidence of shoreline disruption, b) damage to offshore structures such as communications cables, c) observed changes in sea-floor morphology over a short time span, and d) distinctive bottom and subbottom morphologic features. A review of twenty case studies of submarine landslides shows the range of scale and morphology of these landslides, mechanisms of failure initiation, and methods used to observe them. The floors of fjords, with steep slopes and rapidly deposited glacio-fluvial sediment, are the most susceptible to failure. Next most susceptible are active river deltas on the continental shelf, in which underconsolidation, gas charging and storm or earthquake loading can lead to instability. Other sites exist within canyon-fan systems and seemingly all areas of the open continental slope. Finally, some of the largest landslide deposits ever observed occur off Hawaii and involve major parts of the islands.