[meteorite-list] Alaska's Deep Impact on the North Slope (Avak Crater)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Oct 12 13:59:00 2005
Message-ID: <200510121728.j9CHSkG03509_at_zagami.jpl.nasa.gov>


Alaska's Deep Impact on the North Slope
By Ned Rozell
www.sitenews.us (Alaska)
October 11, 2005

In the early 1950s, workers for the U.S. Navy drilled test wells in an
area of the North Slope known as the Naval Petroleum Reserve. The
drillers sent core samples of rock to Fairbanks, where Florence Weber
and Florence Collins, both geologists with the U.S. Geological Survey,
noticed something odd. The samples, taken from an area where the
surrounding rock was lying flat, were tilted upright. Some of the rocks
were shattered.

The strange rocks seemed vaguely familiar to Weber and Collins, two of
the first women geologists in Alaska. Both recently had attended a field
trip to Indiana to see an impact crater, the massive divot left behind
after a meteorite hit the ground. Looking at the pulverized rocks from
the petroleum reserve, they thought the Navy diggers may have tapped
into an impact crater on the North Slope. Weber and Collins followed
their hunch and wrote a USGS paper on what has become known as Avak, the
only impact crater confirmed in Alaska.

The Avak impact crater, located east of Barrow, measures about six miles
from rim to rim. Don't look for it from an airplane window, though.
Several hundred feet of sediment covered Avak in the last million years,
hiding the crater from view. Geologists know the crater exists because
it's revealed in the core samples and seismic and other geophysical surveys.

Avak was born when a meteorite or comet the diameter of downtown
Fairbanks crashed into northern Alaska millions of years ago. Buck
Sharpton, a University of Alaska professor who studies impact craters,
said the speeding celestial body struck the shallow ocean that covered
the North Slope with a shock 10,000 times as powerful as an atomic bomb.
The jolt triggered earthquakes, a tsunami, and sent earth flying in all
directions. Animals unfortunate enough to be grazing near ground zero
were vaporized. Sharpton said Avak was "extremely energetic," but it
didn't have anywhere near the effect of the impact in Chicxulub, Mexico
that probably caused the extinction of dinosaurs.

Avak provided a bit of energy for the people of Barrow. The concussion
that made the crater created folds in nearby rock that trapped natural
gas beneath a ceiling of impermeable rock. The Navy tapped one of the
gas traps to provide natural gas to heat buildings in Barrow.

Avak is one of just 139 discovered impact craters in the world. Despite
the rarity of known craters, Sharpton says Earth has absorbed thousands
of meteorites and comets over the millennia. He estimates Alaska should
be pocked with the indentations of about 250 meteorites and comets. Some
may show themselves as circular lakes, or chains of lakes that make a
circle. Most have been disguised by erosion, protruding mountains, or
the movement of Earth's plates. But the craters are out there, waiting
to be found by curious people like Florence Weber and Florence Collins.
Received on Wed 12 Oct 2005 01:28:44 PM PDT

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