Geoscience Reference
In-Depth Information
Source
Tsunamis
Unknowns
Slides off
Puerto Rico
—
Aided by a
wealth of steep
slopes (Fig. 3-1b)
and by active
faults associated
with the nearby
plate boundary
48
The 1918 tsunami, which caused roughly
40 deaths, may have resulted from an
earthquake-induced slide.
49
The slide
extends from a headscarp at 1,200 m
depth to a terminus at 4,200 m in Mona
Passage, the strait between Puerto Rico
and Hispaniola. It likely displaced 10 km
3
of
water.
What slides are poised to generate
tsunamis elsewhere on the steep
submarine slopes off Puerto Rico?
50
Volcanic debris
lows
—Hot and
cold debris lows
into Cook Inlet
and Bristol Bay,
Alaska; debris
avalanche at
Mount St. Helens
A tsunami in Cook Inlet resulted from a
debris avalanche off erupting Augustine
Volcano in 1883. Sedimentary deposits
suggest that Augustine and Redoubt
Volcanoes triggered additional Cook Inlet
tsunamis in the last 4,000 years,
51
and that
a caldera-forming eruption of Aniakchak
Volcano generated a tsunami 3,500 years
ago in Bristol Bay.
52
The debris avalanche
at the outset of the May 1980 eruption of
Mount St. Helens, upon entering Spirit Lake,
set off a tsunami that reached heights of
250 m above the former lake level.
53
How many of Augustine's debris
avalanches, a dozen of which have
reached Cook Inlet in the last 2,000
years alone, sent tsunamis onto
now-populated parts of the Kenai
Peninsula?
54
Slides off
southern
California
—
Include the Palos
Verdes slide, of
0.8 km
3
with a
headscarp 5 km
off the coast
near Los Angeles
(Fig. 3-1c)
55
The Palos Verdes slide serves as a poster
child for southern California's near-ield
tsunami hazard. Other potential sources
include a submarine slide near Santa
Barbara and offshore faults with known
or inferred Quaternary displacement.
56-61
The Palos Verdes slide occurred close to
7,500 years ago.
55
How do southern California's nearby
sources of tsunamis compare, in
probability and size, with its distant
causes of lesser inundation?
