Submarine Landslides and Tsunamis
By Jason Chaytor (USGS)
The United States Geological Survey (USGS), in cooperation with other government agencies and academic partners, has been studying the continental margin along the U.S. east coast using an extensive set of seafloor maps in order to better understand submarine landslides and their role in tsunami generation, and how the development and evolution of submarine canyon systems controls the shape of the margin.
A recent assessment of tsunami hazards along the U.S. east coast, carried out by the USGS and funded by the U.S. Nuclear Regulatory Commission, has identified submarine landslides along the submerged continental margin as the primary potential source of dangerous tsunamis to this coast. The seriousness of this hazard was demonstrated by the 1929 Grand Banks submarine landslide, which produced a tsunami 3 to 8 m high that killed 28 people along the sparsely populated Newfoundland coast. Most submarine landslides on the continental margin occur on the continental slope and upper rise, but a limited amount of detailed seafloor mapping along shallower parts of the east coast has limited efforts to produce a quantitative assessment of tsunami hazards.
Submarine landslides and canyons are ubiquitous features along the continental margin adjacent to the U.S. Atlantic coast (Figure 1). Based on their characteristics (mostly determined from multibeam bathymetry maps), some of these submarine landslides would have the potential to cause a tsunami locally along the east coast of the United States. Seafloor mapping and other geological and geophysical investigations show that the largest submarine landslides are concentrated along the New England and Long Island sections of the margin, outward of major ancient rivers along the mid-Atlantic margin, and in the salt dome province off South Carolina.
Whether or not a submarine landslide will generate a tsunami and its resulting size are functions of the depth of the landslide, the amount of material that moves downslope (the landslide volume), the initial acceleration of the material and the speed at which it moves downslope, and the characteristics of the material (its strength, composition, etc.). While seafloor maps can directly provide information about the depth and size of a landslide, they are invaluable in pinpointing locations where additional studies can yield information about the properties of the seafloor within and around the landslides and the age of the landslides along the margin.