Source

Tsunamis

Unknowns

Slides off the edge of the U.S. Atlantic continental shelf Cover one-third of the continental slope and rise off New England, one-sixth off the Middle Atlantic, and one-eighth off the Southeast62

Submarine slides are “considered the primary source of potential tsunamis along the U.S. Atlantic coast.”15 The Currituck slide, with an estimated volume of 165 km3, is among the largest of these.63 Its simulated tsunamis originate with peak-to-trough amplitudes of several tens of meters. The waves crest about 6 m above sea level as they overtop the sandy barrier between the Atlantic Ocean and Currituck Sound, North Carolina.64

How probable are these slides today? Most of the slides off the U.S. Atlantic coast occurred at least 5,000 years ago, the notable exception being Canada’s Grand Banks slide, which generated a tsunami that took 28 lives in Newfoundland in 1929.65 The Currituck slide dates to roughly 25,000-50,000 years ago.66 Probabilities aside, simulating slides like Currituck requires uncertain estimates of slide size, speed, and duration, all factors in the slide’s effectiveness at generating a tsunami.64

Slumps and slides beneath the Gulf of MexicoSome generated by rise of salt domes,67 others at scarps in carbonate rocks,68 still others by ice-age lowering of sea level69

No confirmed tsunamis. Tsunami hazard inferred from a slump with a volume of 50-60 km3 in the northwestern Gulf of Mexico.70

As with the slides off the U.S. Atlantic coast, are the Gulf of Mexico examples mainly relicts from times of lowered sea level?69

Slides ascribed to human activity Includes construction at Skagway, Alaska,71 and fluctuation of the level of a reservoir in northeast Washington State72

Skagway: Wave heights said 5-6 m high in inlet and 9-11 m high at shore; one fatality.71 Northeast Washington: Waves up to 20 m high from shores of the reservoir behind Grand Coulee Dam,72 smaller examples from summer 2009.73

Causes considered for the Skagway slide include natural failure as well as dock construction.71



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