[meteorite-list] Secrets of the Wabar Craters - Part 2 of 2

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:32 2004
Message-ID: <3D94DE50.B94C3280_at_lehrer.uni-karlsruhe.de>

WYNN J.C. and SHOEMAKER E.M. (1997) Secrets of the Wabar Craters
– A team of geologists explores this enigmatic meteorite-impact site
in southern Saudi Arabia (Sky and Telescope, 1997, pp. 44-48, cont.:):


Secrets of the Camel's Hump

Analysis of the small meteorite samples we collected indicates that
the Wabar impacting body was a Type IIIA medium octahedrite made of
up to 94 percent iron, 3.5 to 7 percent nickel, and roughly 0.22 %
cobalt, with traces of iridium. The rest was primarily copper. As the
object plunged through the Earth's upper atmosphere at hypersonic speeds
it broke into several large pieces, producing the cluster of craters.
Studies of impactite samples in the 1960s gives an age of about 6,400
years for the craters, but we think that this is probably an order of
magnitude too high. It seems unlikely that the craters could have
survived for several thousand years in such an active desert
environment. Based on circumstantial evidence, we believe the impact
took place sometime between 100 and 600 years ago.
A huge fireball was reported to have passed over Riyadh in 1863 and
headed southeast toward Wabar. Whether or not this meteor was associated
with the impact, such an event would have been witnessed by Bedouin
tribes, and the "fire from heaven" connected with the story of the
destruction of the ancient city of 'Ubar apparently led to the name.
The impact, if an observer survived it, would have been spectacular
indeed. Based on the crater sizes we calculate the incoming object to
have been at least 4 meters wide, weighing more than 300 tons. The
impact released the kinetic-energy equivalent of at least 1,000 tons of
exploding TNT. The resulting flash and debris cloud would have been seen
from as far away as 500 kilometers. Most of the iron-nickel body
vaporized upon impact; the fraction that remained was shattered into
small pieces and a substantial part was melted and mixed with
shock-melted sand.
A two-ton, cone-shaped iron fragment, nicknamed the Camel's Hump, was
reported to Philby, but he never found it. Moving dunes exposed it in
1965, and it was recovered by ARAMCO, Saudi Arabia's national oil
company, about 200 meters southwest of Philby B. The Wabar site is
unique indeed - no wonder it's the stuff of local legend. But what we've
learned from those rocks sitting in the sand should be a great boon to
geologists who will soon pore over high-resolution views from Mars
Global Surveyor. It wouldn't be surprising at all for "Wabar-type"
craters to be found all over the red planet's desolate surface.

JEFFREY WYNN is a research geophysicist at the U.S. Geological Survey
(USGS) in Reston, Virginia. EUGENE SHOEMAKER, formerly with the USGS
and Lowell Observatory in Flagstaff, Arizotia, lost his life in an auto
accident last July.

The authors are gratefuld to Sheikh Walid Y Zahid, who supported and
encouraged the expeditions to the Wabar site, as well as to Bill
Chasteen, Wafa' Zawawi, Tino Fenech, Kevin Bullock, Robin De'ath, Zahid
T Zahid, Steve Butler, Taha Jaffrey, and Tim Cooley who accompanied us,
worked alongside us, and survived the heat, sand, and scorpions and
camel spiders that thrive in the deep desert.


pp. 44-45: Surrounded by a seemingly endless sea of sand, author Jeff
Wynn uses a magnetometer to locate hidden meteorite fragments buried
beneath the ejecta blanket around the crater named Philby 8. This
feature is part of the young Wabar impact-crater complex in Saudi
Arabia's Rub'al-Khali(Empty Quarter). Many of the geologic studies
at this harsh, desolate site had to be done at night since midday
temperatures here can reach a scorching 142° Fahrenheit (61°C) in
the shade!

p. 46: Dubbed the Camel’s Hump, this two-ton fragment of the great Wabar
iron-nickel meteorite was revealed when shifting sand dunes uncovered it
in 1965. It is now on display at King Sa'ud University in Riyadh.
Photograph by James P. Mandaville, courtesy Aramco World.

p. 46: Located 550 kilometers (340 miles) east of the capital city of
Riyadh, the Wabar crater complex lies within the shifting desert sands
of the Rub'al-Khali. Bedouin tribes in the region call the impact site
Al-Hadida, Arabic for 'the iron.'

p. 47: The 11 -meter-wide crater (left of center) and a portion of
Philby A at the Wabar complex. Note the size of the people at upper
right. The sensor in the foreground is part of the magnetometer used to
study the site.

p. 47: The Wabar site (21° 30.2' N and 050°' 28.4' E) consists of at
least three impact craters measuring 11 to 116 meters across.Two of
them, dubbed Philby A and B, are partly covered by encroaching sand
dunes. Owing to the soft, continuously shifting sand, the site can be
reached only with special four-wheel-drive vehicles; it is inaccessible
by planes or helicopters.

p. 48: A dense scattering of ejected material surrounds the Philby B
crater. The black glassy slag, called impactite, is mixed with white
chunks of 'instant rock' (shock-fused sand).


Goodnight,

Bernd
Received on Fri 27 Sep 2002 06:40:16 PM PDT