finding topples theory
TSUNAMI: Submarine avalanche blamed for '46 wave didn't happen.
By DOUG O'HARRA
Anchorage Daily News
Published: December 25th, 2004
Last Modified: December 26th, 2004 at 02:33 AM
Scientists traveled to the Aleutian Chain last summer to check out a
colossal submarine landslide blamed for one of the most devastating
tsunamis of the 20th century.
They wanted to find out how sea-floor life responded to such a huge
disturbance and produce detailed charts.
What they got was a shock of seismic proportions.
Instead of a 12-mile-wide avalanche dropping 30 to 40 miles down the
continental slope into the abyss of the Aleutian Trench, sonar
surveys and the remotely operated underwater vehicle Jason II found
regular ocean bottom, eroded and crusty and largely undisturbed.
There was no slide.
And now no one knows what triggered the legendary tsunami of 1946,
which destroyed Scotch Cap lighthouse on Unimak Island and killed
159 people in Hawaii.
"Basically, we found sea floor evidence that will cause tsunami
modelers to rethink the cause and characteristics of the 1946
tsunami," wrote research associate Tony Rathburn and professor Lisa
Levin, principle investigators with the project at Scripps
Institution of Oceanography. "The sea floor landslide ... that
seemed to be evident from previous, low-resolution (charts) does not
A Hawaiian geophysicist working on the project now believes that an
underwater slide probably hit farther east along the Aleutian slope,
near a feature that might be the toe of a previously unknown
avalanche. Triggered by an earthquake, this slide would have created
a tsunami. When the wave rolled into shallow water, the theory goes,
it accelerated into a bore of incredible power, surging along the
shore of Unimak Island with hurricane force.
"You think of a 40-foot wave or a 50-foot-high wave traveling at 140
mph," said Gerard Fryer with the University of Hawaii at Manoa in an
interview earlier this month. "It's an astounding image. It's almost
beyond our comprehension."
The summer expedition also gathered unprecedented biological
information about the ocean off Alaska's coast. During seven dives
and several weeks of cruising, the team gathered hundreds of
samples, images and photos. Rathburn and Levin are spending the
winter analyzing what may be dozens of new species.
Along the way, they found a bizarre methane seep in pitch darkness
more than two miles down on a steep slope: fuzzy carbonate rocks
"weeping" with upside-down life, unknown worms, gigantic bacteria,
seas stars, octopuses, clams.
It was like an oasis fueled by gas, Levin said.
"It wasn't altogether clear why the animals were growing down," she
said. "There never has actually been a community of animals that
live on rocks but get their (energy) from methane. ... But when you
go someplace that nobody has ever been before, you see things you
don't expect. That's my experience of the deep ocean."
"We were excited, perplexed, fascinated," Rathburn added. "There are
some really strange things going on with the seeps there that seem
to be different from what's going on elsewhere in the Pacific
The new findings mark the third season of amazing discoveries along
the Aleutian Chain by scientists using subs and underwater vehicles.
Over the past few years, biologists and marine geologists have
documented coral gardens, new species of fish and invertebrates, and
Alaska's first submerged volcano rising to a coral-shrouded cone of
black rock deep in Amchitka Pass.
Details of this new fish-rich habitat have spurred intense debate at
the North Pacific Fishery Management Council about restricting
trawling and other bottom-contact commercial fishing gear.
This summer, four scientific teams took turns voyaging on the Scripps
research vessel Roger Revelle, using the Jason II to explore
seamounts, coral habitat, the Adak underwater canyon, and submarine
slides. The work was sponsored by the West Coast National Undersea
Research Program of the National Oceanic and Atmospheric
The group led by Rathburn and Levin focused on what Fryer had named
the Ugamak Slide, located south of Unimak Island. The slope of the
North American tectonic plate pitches into the Aleutian Trench,
where the Pacific plate gets subducted into the Earth.
It was there, about 1:30 a.m. on April 1, 1946, that an earthquake
originally measured as magnitude 7.3 struck with surprising effect.
A second quake hit 27 minutes later.
Within about 30 minutes of the second jolt, a huge wave smashed into
the Scotch Cap lighthouse on the tip of Unimak Island, reducing a
new structure of reinforced concrete to rubble and killing the five
"Terrific roaring from ocean heard, followed almost immediately by
terrific sea, top of which rose above cliff and struck station,
causing considerable damages," reads the 2:18 a.m. entry in the U.S.
Coast Guard log from the radio communications station on the cliff
At dawn, personnel found a beach littered with debris. Human body
parts were discovered too, some washed 115 feet above sea level to
the cliff top. The victims had basically been shredded.
The idea that this five-year-old lighthouse, built on a platform 30
feet above the sea, could be vulnerable to a 115-foot tsunami was
unimaginable, Fryer said.
"Nobody living had seen a tsunami like this," Fryer said.
Meanwhile, another tsunami was traveling across the Pacific at nearly
500 mph. Within five hours, a train of waves reached Hawaii and
rolled into settlements without warning, ultimately destroying 1,400
structures. One 30-footer inundated the Hilo waterfront, killing 96
The destruction prompted the U.S. Congress to establish the Pacific
Tsunami Warning Center in Ewa Beach, Hawaii, and create a
Pacificwide warning system. (The West Coast and Alaska Tsunami
Warning Center, located in Palmer, was added after the 1964 quake.)
For years, scientists argued about the source of the tsunami. How
could such a relatively small earthquake make the entire Pacific
Ocean slosh like bath water?
Even more inexplicable, how could it also have created such an
enormous wave at Scotch Cap?
Fryer has argued that a huge underwater slide must be the explanation
for both tsunamis, not the earthquake. He thought he had found the
culprit with a sonar image taken a few years ago. But now he
believes that the older sonar data didn't produce an accurate
picture of the bottom and that the Ugamak Slide doesn't exist.
But other tsunami modelers disagree with Fryer, saying that the
earthquake was large enough to trigger the Pacificwide tsunamis
while an as-yet unidentified submarine avalanche probably caused the
damage at Scotch Cap.
"The 1946 event is not a textbook earthquake. It's not an earthquake
that follows the rules," said professor Emile Okal, a tsunami expert
at Northwestern University. "It was a much larger earthquake (than
originally measured) because it was a very slow earthquake (that)
released much of its energy at very long periods."
Last summer's findings deepened the mystery, said Rathburn, also a
professor at Indiana State University.
"This is what happens when all of your highfallutin theories come to
grip with reality," he said. "It's like theorizing on the moon or
Mars, and then actually going there and looking at the place. Lots
of things change, and it actually makes things more exciting."