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SCIENCEWednesday 3 February
Researchers find source of 1964 devastating Alaska tsunami
DAN JOLING either the size or location that occurred when this
of the landslide sources,” earthquake struck,” Broth-
Associated Press Plafker aid. ers said.
Researchers led by USGS The huge delta of unsta-
ANCHORAGE, Alaska (AP) geophysicist Danny Broth- ble sediment descended
ers mapped an underwa- down a steep escarpment
— Researchers from the ter landslide complex in into the third basin in a gi-
nearby Dangerous Pas- ant underwater landslide,
U.S. Geological Survey sage using multi-beam so- Brothers said. The “ava-
nar and ground-penetrat- lanche of sediment” cre-
have solved a 50-year ing tools that showed cross- ated the wave that struck
sectional views of sediment Chenega.
natural science mystery: layers, revealing a history of The 1964 quake and the
landslides. tsunamis played a role in
the undersea source of The study found three ba- the formation of the West
sins covering some 15 miles Coast and Alaska Tsunami
tsunami waves that devas- (25 kilometers) along Dan- Warning Center, renamed
gerous Passage, a fjord. the National Tsunami Warn-
tated a remote Alaska vil- Each basin was progres- ing Center, operated by
sively deeper. The basins the National Oceanic and
lage following the 1964 are bound by steep sides Atmospheric Administra-
and were carved by gla- tion. The center within min-
Great Alaska Earthquake. ciers when sea level was utes of a quake can put out
lower. Brothers said Mon- alerts to warn West Coast
Underwater landslides day the basins are like a and Hawaii communities
series of bowls setting on that a big wave is headed
at depths of up to 1,150 shelves at different heights. their way.
As glaciers retreated, sedi- Most Alaska communities
feet (350 meters)— much ment from rivers filled the vulnerable to local tsu-
underwater basins with un- namis have tsunami siren
deeper than caused tsu- stable sediment washed systems that can be acti-
from land. The earthquake vated by local emergency
namis affecting other spilled the second bowl. officials to warn residents to
“The intermediate basin head for high ground.
communities — sent killing filled up with sediment, The research has implica-
setting the stage for this tions for other communities
waves toward the Prince instability, and the trigger along deep-water fjords.q
William Sound community
of Chenega, where 23 of
75 residents died at all but In this March 29, 1964 file photo, a photographer looks over
wreckage as smoke rises in the background from burning oil
two buildings were de- storage tanks at Valdez, Alaska. On Monday, Feb. 1. 2016,
federal scientists say they’ve pinpointed the cause of tsunami
stroyed. waves following the 1964 Great Alaska Earthquake, the second-
largest ever recorded, at magnitude 9.2.
The villagers had little time
Associated Press
to get to high ground. The
epicenter of the magni-
tude 9.2 quake, which
shookAlaska for four and second largest in recorded ologist emeritus, one of the
history. Many more were first responders after the
a half minutes, was about killed by tsunamis. The ‘64 quake, said in a USGS
great quake rumpled the release that geologists sus-
56 miles (100 kilometers) ocean floor like a rug, cre- pected an underwater
ating a trans-ocean tsuna- landslide had led to devas-
away. Deadly waves hit mi that sent deadly waves tation at Chenega.
down the West Coast. “But we had no adequate
Chenega four minutes lat- George Plafker USGS ge- submarine data to define
er.
Nine people died in An-
chorage, Alaska’s largest
city, from the quake, the
