[meteorite-list] Satellite Image of Kebira Crater in Egypt

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Mar 10 14:44:44 2006
Message-ID: <200603101853.k2AIrJO01736_at_zagami.jpl.nasa.gov>

http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17208

NASA's Earth Observatory
Kebira Crater

No, satellite images do not show any craters in Egypt's Western Desert
that can account for the mysterious "Desert Glass" found there, Dr.
Farouk El-Baz had just finished telling filmmakers interested in
exploring the origins of the yellow-green glass fragments in late
February 2006. But the interview made him wonder: could satellite data
show him where the crater was after all? As a geologist who had spent
most of his career studying the Earth's major deserts, he knew that the
glass formed after a massive meteorite hit the desert with enough energy
to splatter chunks of melted sand across the extensive fields where
fragments are common today. But beyond the glass, no evidence of such an
impact had ever been found. Now the director of the Center for Remote
Sensing at Boston University, El-Baz decided to take another look at
satellite data of the Western Desert to see if he could find the elusive
crater.

After the cameras stopped rolling, El-Baz sorted through image after
image of the Western Desert when he came across a ring of rocks
surrounded by traces of an outer ring: the telltale markings of an
impact crater. He called Boston University research associate Eman
Ghoneim, and she agreed that the image revealed a crater. The massive
crater measured 31 kilometers across and was large enough to contain
70,000 football fields; the site was a very probable source of the
glass. This Landsat-7 image, taken on March 15, 2001, shows the crater
with pale fields of shifting sand surrounding the darker sandstone that
bears the impression of the impact. The outer rim of the crater, mostly
buried by sand, is outlined with a white dotted line.

El-Baz named the crater "Kebira," which means "large" in Arabic. Because
a crater is about twenty times larger than the meteorite that creates
it, the meteorite that hit the Western Desert was larger than the famous
Meteor (Barringer) Crater
<http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=4598>
in Arizona, which is 1.2 kilometers wide. By contrast, the Chicxulub
Crater
<http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=11268>
left on the Yucatan Peninsula by the meteorite believed to have caused
the extinction of the dinosaurs is ten times larger than Kebira,
measuring 150 to 300 kilometers wide.

But why had no one noticed the giant Kebira crater before? El-Baz
speculates that the crater's massive size hid it in plain view. "The
search for craters typically concentrates on small features, especially
those that can be identified on the ground. The advantage of a view from
space is that it allows us to see regional patterns and the big
picture," he said in a Boston University press release. Also, the
double-ringed crater sits in sandstone that is 100 million years old,
which means that the impact probably occurred around 100 million years
ago. In the intervening time, wind and water have worn features of the
crater away, making it hard to identify. For example, the beds of two
ancient rivers run from east to west across the crater, leaving two gaps
in the inner ring on the upper right side.

NASA image by Robert Simmon, based on Landsat-7 data provided by the
UMD Global Land Cover Facility.
Received on Fri 10 Mar 2006 01:53:18 PM PST