[meteorite-list] Many Questions Remain On Chesapeake Crater

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:48:56 2004
Message-ID: <200109051555.IAA06941_at_zagami.jpl.nasa.gov>

http://www.charlotte.com/observer/natwor/docs/crater0905.htm

Many questions remain on Chesapeake crater
By ROBERT S. BOYD
The Charlotte Observer
September 5, 2001

Meteor impact 35 million years ago

Scientists review collision that left 56-mile-wide depression in bay

BAVON, Va. -- It is so peaceful here - a flat green marsh bordering bay
waters, reeds, scrubby pines, gulls circling a distant lighthouse.

Only the clatter of a drilling rig breaks the spell, as scientists poke deep
below the ground. They are searching for traces of one of the greatest
catastrophes ever to hit the Earth.

Near this spot 35 million years ago, an enormous ball of ice or rock
screeched down from outer space in a blinding flash of light and blasted a
crater 56 miles across and almost a mile deep.

The meteor, the largest ever to strike what is now the United States, hurled
fragments as far as Antarctica and gouged a depression that lies under the
Chesapeake Bay, one of the East Coast's scenic wonders.

Today, a rough circle of low ridges in Virginia's coastal plain, near
historic Williamsburg and Jamestown, marks the outer rim of the ancient
crater, which is buried under thousands of feet of sand, silt and clay.

Other signs of the collision remain: Two million nearby residents face a
shortage of fresh water, because the searing heat of the long-ago impact
vaporized huge quantities of seawater, leaving the basin still filled with
salt that threatens their freshwater aquifers. Nearby rivers make a peculiar
sharp bend as they are diverted toward the sunken crater.

This summer, researchers from the U.S. Geological Survey are drilling holes
in and around the Chesapeake Bay Impact Crater, as it is known. They are
trying to understand what happened when the meteor hit and what it means for
people now and in the future.

Wylie Poag, a senior USGS scientist, pointed out that our planet is
constantly pummeled by extraterrestrial objects, around 25,000 of them each
year. Most are small and harmless. A little one bonked a boy on the head in
Uganda in 1992, injuring him slightly; another dented in a car fender in
Peekskill, N.Y., the same year.

But it's only a matter of time, experts say, before another "big one"
strikes, like the monster that rammed the Earth off the coast of Mexico 65
million years ago. Scientists think the long-lasting global climate change
that followed that collision wiped out the dinosaurs and thousands of other
species.

Speaking above the roar of the drill, Poag, who found and identified the
Chesapeake crater in 1994, shows off a box of cylindrical cores pulled up
from 2,000 feet below the ground. The muddy cylinders, each about the size
and shape of a child's baseball bat, show rock that was twisted, jumbled and
squeezed by the battering it endured long ago.

Scientists aren't certain whether the meteor was a comet, made mostly of
ice, or an asteroid, a lump of stone or iron. At 2 to 3 miles in diameter,
it was only a third the size of the Mexican dinosaur-killer. But when it
crashed into the ocean here at 60,000 mph, it did awesome damage.

The splash-down caused a massive tidal wave that surged far inland into the
Appalachian foothills. Such a wave, known as a super-tsunami, can tower more
than a thousand feet, Poag said, as it roars into shallow water near the
shore.

In addition, a hail of white-hot debris flung outward by the impact turned
the Eastern United States into a wasteland. A cloud of dust encircled the
globe, darkening the sky for months. The world's climate rapidly warmed and
then cooled, perhaps contributing to a mass extinction of sea creatures a
million years later.

"Life on Earth would have been shocked, vaporized, pulverized, barbecued,
blinded, irradiated, acidified, drowned, starved and frozen," Poag wrote in
his book, "Chesapeake Invader." "A similar strike in Chesapeake Bay today
would wipe out all the major East Coast cities, killing tens of millions.
The scale of annihilation is appalling to contemplate."

On the Web

http://woods hole.er.usgs.gov/epubs/bolide
Received on Wed 05 Sep 2001 11:55:47 AM PDT