Geoscience Reference
In-Depth Information
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
Southeast
62
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 km
3
, 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
Mexico
—
Some
generated
by rise of salt
domes,
67
others
at scarps in
carbonate
rocks,
68
still
others by ice-age
lowering of sea
level
69
No conirmed tsunamis. Tsunami hazard
inferred from a slump with a volume of
50-60 km
3
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
luctuation
of the level
of a reservoir
in northeast
Washington
State
72
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
