begin quote from:
An
enormous landslide that spread rocky debris more than six miles across a
glacier in southeastern Alaska last week was not the first to occur in
the area, and certainly won’t be the …
An
enormous landslide that spread rocky debris more than six miles across a
glacier in southeastern Alaska last week was not the first to occur in
the area, and certainly will not be the last.
The slide, first noticed by Paul Swanstrom, a sightseeing pilot,
on June 28, occurred when part of a mountain gave way near Lamplugh
Glacier, in Glacier Bay National Park, about 100 miles northwest of
Juneau.
Photographs
taken by Mr. Swanstrom several hours after the slide showed a dark mass
spread over the glacier, which is about eight miles long and ends in
Johns Hopkins Inlet, part of Glacier Bay. A cloud of dust from the slide
was still visible.
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The slide caused seismic tremors that had a magnitude of 2.9, about as strong as a small earthquake, according to data from the Alaska Earthquake Center.
The
source of the slide appears to be a peak on the west side of the
glacier that was more than 6,500 feet high. It is unclear how much rock
broke away, but the Lamont-Doherty Earth Observatory estimated the slide
involved more than 165 million tons of material.
The Alaska Panhandle in and around Glacier Bay National Park has been the source of many large landslides in recent years.
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Scientists
say the slides will most likely continue as warming temperatures cause
more glacial melt. Glaciers buttress the mountainsides that surround
them; when the ice disappears, the slopes lose some of their support,
and erosion or earthquakes can cause them to collapse.
A mountainside next to Tyndall Glacier
gave way in October after heavy rains. The debris slid into an arm of
Icy Bay, causing a tsunami that struck a hillside across the water from
the slide, shearing off trees at an elevation of more than 500 feet.
This
part of Alaska was also the scene of what is thought to be the largest
tsunami ever measured, in Lituya Bay, a small inlet on the coast about
30 miles southwest of Lamplugh Glacier.
On the evening of July 9, 1958, a 7.7-magnitude earthquake
shook loose a huge mass of rock that fell 3,000 feet from atop a
mountain into the bay. The resulting wave scoured vegetation 1,720 feet
up on the opposite hillside. Three fishing boats were in the bay at the
time; two made it through the event safely but the third, with two
people onboard, was never seen again.
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