Editing Wabar craters

{{Short description|Impact craters in Saudi Arabia}}
{{Infobox terrestrial impact site
| name          = Wabar craters
| other_name    = 
| photo         = 
| photo_caption = 
| map           = Saudi Arabia
| map_caption   = Asteroid impact location in Saudi Arabia
| coordinates   = {{coord|21|30|09|N|50|28|27|E|region:SA_type:landmark|display=inline}}
| confidence    = Confirmed
| diameter      = {{cvt|64|to|116|m|||}}
| depth         = 
| age           =  under 250 yrs
| exposed       = 
| drilled       = 
| imp_size      = 
| bolide        =[[Iron meteorite]] 
| country       = [[Saudi Arabia]]
| state         = 
}}
[[File:Wabar craters.jpg|thumb|upright=1.1|Smaller of the Wabar craters visible on the surface. The crater on the left is about 11 m in diameter.]]

The '''Wabar craters''' are [[impact crater]]s located in [[Saudi Arabia]] first brought to the attention of Western scholars by British [[Arabist]], explorer, writer and [[Colonial Office]] intelligence officer [[St John Philby]], who discovered them while searching for the legendary city of [[Atlantis of the Sands|Ubar]] in Arabia's [[Rub' al Khali]] ("Empty Quarter") in 1932.<ref>{{cite Earth Impact DB | name = Wabar| accessdate = 2009-08-15}}</ref>

==The expeditions==
[[File:Harry St. John Bridger Philby.jpg|upright|thumb|[[St John Philby]] in Riyadh]]

===1932 Philby===
The vast desert wasteland of southern Saudi Arabia known as the Empty Quarter, or ''[[Rub' al Khali]]'' in Arabic, is one of the most desolate places on Earth. In 1932, Harry St John "Jack" Philby was hunting for a city named [[Iram of the Pillars|Ubar]], that the [[Quran]] describes as having been destroyed by God for defying the Prophet [[Hud (prophet)|Hud]]. Philby transliterated the name of the city as Wabar.

Philby had heard of [[Bedouin]] legends of an area called ''Al Hadida'' ("place of iron" in Arabic) with ruins of ancient habitations, and also an area where a piece of iron the size of a camel had been found, and so organized an expedition to visit the site.  After a month's journey through wastes so harsh that even some of the camels died, on 2 February 1932 Philby arrived at a patch of ground about {{Convert|1/2|km2|mi2|spell=in}} in size, littered with chunks of white [[sandstone]], black [[glass]], and chunks of [[iron meteorite]]. Philby identified two large circular depressions partially filled with sand, and three other features that he identified as possible "submerged craters".  He also mapped the area where the large iron block was reputed to have been found.  Philby thought that the area was a volcano, and it was only after bringing back samples to the UK that the site was identified as that of a meteorite impact by [[Leonard James Spencer]] of the [[British Museum]].<ref>Philby (1933), pp 1-26</ref><ref>{{cite journal |url=http://rruff.geo.arizona.edu/doclib/MinMag/Volume_23/23-142-387.pdf |title=Meteoric Iron and Silica-Glass from the Meteorite Craters of Henbury (Central Australia) and Wabar (Arabia) |author=L. J. Spencer |journal=Mineralogical Magazine |volume=23 |issue=142 |date=September 1933 |pages=387–404 |doi=10.1180/minmag.1933.023.142.01|bibcode=1933MinM...23..387S }}</ref><ref>{{cite journal |url=http://rruff.geo.arizona.edu/doclib/MinMag/Volume_29/29-211-256.pdf |title=L. J. Spencer's work at the British Museum |author=W. Campbell Smith |journal=Mineralogical Magazine |volume=29 |issue=211 |date=December 1950 |issn=0026-461X |page=269 |doi=10.1180/minmag.1950.029.211.02|bibcode=1950MinM...29..256C }}</ref>

<blockquote>A volcano in the midst of the Rub' al Khali!  And below me, as I stood on that hill-top transfixed, lay the twin craters, whose black walls stood up gauntly above the encroaching sand like the battlements and bastions of some great castle.  These craters were respectively about 100 and 50 yards in diameter, sunken in the middle but half choked with sand, while inside and outside their walls lay what I took to be lava in great circles where it seemed to have flowed out from the fiery furnace. Further examination revealed the fact that there were three similar craters close by, though these were surmounted by hills of sand and recognizable only by reason of the fringe of blackened slag round their edges.<ref>Philby (1933), p. 13</ref></blockquote>

Amongst the samples of iron, cindery material, and silica glass that Philby brought back from the site was a {{Convert|25|lb|adj=on}} chunk of iron. Analysis showed it to be about 90% iron and 5% nickel, with the rest consisting of various elements, including copper, cobalt, and an unusually high concentration of [[iridium]], at 6 [[Parts-per notation#Parts-per expressions|ppm]]. This [[Goldschmidt classification#Siderophile elements|siderophile]] element implied that the Wabar site was a [[meteorite]] impact area.

===1937 Aramco===
In 1937, [[Saudi Aramco|Aramco]] geologists T. F. Harriss and Walton Hoag, Jr., also investigated the site, but, like Philby, were unable to locate the large block of iron.<ref name="aramco">{{cite journal | journal=Saudi Aramco World | issue=6 | first1=Z | last1=Bilkadi | url=http://www.saudiaramcoworld.com/issue/198606/the.wabar.meteorite.htm | title=The Wabar Meteorite | year=1986 | volume=37 | pages=26–33 | access-date=2008-07-19 | archive-date=2013-03-30 | archive-url=https://web.archive.org/web/20130330140110/http://www.saudiaramcoworld.com/issue/198606/the.wabar.meteorite.htm | url-status=dead }}</ref>

===1966 National Geographic and Aramco===
In 1966, reports came that the sands had shifted and the large iron block was again visible. ''[[National Geographic (magazine)|National Geographic]]'' journalist [[Thomas J. Abercrombie]] visited the site and found the large meteorite: "rumor has become a reality; the biggest iron meteorite ever found in Arabia lay at our feet&nbsp;... shaped roughly like a saucer, it measured about four feet in diameter and two feet thick at center. A little quick geometry puts its weight at almost two and a half tons."<ref name=thomas>Thomas J. Abercrombie, 1966, "Beyond the Sands of Mecca" ''National Geographic Magazine'', January 1966.</ref>

Later in October 1966, a group headed by Aramco employee James Mandaville visited the site with heavy lifting equipment. They found two large uncovered meteorites. The largest, weighing {{Convert|2045|kg}}, had a pitted, but roughly level, top surface about {{Convert|1|m|spell=in}} in diameter with one end formed into a cone shape when the meteorite penetrated the atmosphere like a bullet; it was embedded in sand, which had drifted over the top. It was photographed ''in situ'', then overturned by a bulldozer and lifted on board a trailer where it and another, smaller meteorite were taken to [[Dhahran]].<ref name=aramco/>

===1982 Aramco===
Mandaville visited the site twice after his 1966 visit.  On his last visit, in 1982, he noted that the desert winds and resultant movement of the dune system were covering the site: "instead of two thirds of the crater rim (visible as before [in 1966, 16 years earlier]), less than a quarter of it showed."<ref name=aramco/>

===1994–1995 Zahid Tractors===
In 1994 and 1995, a total of three expeditions were undertaken, sponsored by the Zahid Tractor Corporation. A [[United States Geological Survey]] scientist, [[Jeffrey C. Wynn]], joined all three expeditions, and astronomer and geologist [[Eugene Merle Shoemaker|Gene Shoemaker]] joined at least one.<ref>{{cite journal | first1=J.C. | last1=Wynn | url=http://volcanoes.usgs.gov/jwynn/1998SciAm-Wabar.pdf | title=The Day the Sands Caught Fire | last2=Shoemaker | first2=E.M. | journal=Scientific American | year=1998 | volume=279 | issue=5 | pages=36–45| doi=10.1038/scientificamerican1198-64 | bibcode=1998SciAm.279e..64W }}</ref>  These expeditions were made with modern off-road vehicles, but even with modern technology, the trips were difficult ones. Not only were conditions harsh, but the Wabar site was tricky to find, as it sits in the midst of an enormous dune field that has no fixed landmarks.

==The site==
The Wabar site covers about {{convert|500|by|1000|m}}, and the most recent{{When|date=March 2025}} mapping shows three prominent, roughly circular craters. Five were reported by Philby in 1932, the largest of which measured {{convert|116|m}} and {{convert|64|m}}  wide.  Another was described by the second Zahid expedition and is {{Convert|11|m}} wide: this may be one of the other three originally described by Philby. They are all underlain by a hemispherical rim of "insta-Rock," so called because it was created from local sand by the impact shock wave, and all three are nearly full of sand.

The surface of the area partly consisted of "Insta-Rock" or "[[impactite]]", a bleached-white, coarsely-laminar sandstone lookalike, and was littered with black glass [[slag]] and pellets. The impactite featured a form of shocked [[quartz]] known as "[[coesite]]", and is thus clearly the product of an impact event. The impact did not penetrate to [[bedrock]], but was confined to local sand, making it particularly valuable as a research site.

[[File:Widmanstatten patterns 1.jpg|thumb|left|A Wabar meteorite: etched section showing the [[Widmanstätten pattern]].]]
The presence of iron fragments at the site also pointed to a meteorite impact, as there are no iron deposits in the region. The iron was in the form of buried fist-sized cracked balls and smooth, sand-blasted fragments found on the surface. The largest fragment was recovered in a 1966 visit to Wabar and weighs 2.2 tonnes.<ref name=thomas/> It is known as the "Camel's Hump" and was on display at the [[King Saud University]] in [[Riyadh]] until it was moved to the new [[National Museum of Saudi Arabia]] in Riyadh, where it is displayed in the entrance foyer.<ref name=aramco/>

The sand was turned into black glass near the craters, and pellets of the glass are scattered all over the area, decreasing in size with distance from the craters due to wind-sorting. The glass is about 90% local sand and 10% meteoric iron and nickel.

The layout of the impact area suggests that the body fell at a shallow angle, and was moving at typical (although slightly slow) meteorite entry speeds of 11–17&nbsp;km/s. Its total mass was more than 3,500 tonnes (which would give it a diameter of 16 meters at a density of 1.5 g/cm<sup>3</sup>). The shallow angle presented the body with more air resistance than it would have encountered at a steeper angle, and it broke up in the air into at least four pieces before impact. The biggest piece struck with an explosion roughly equivalent to the atom bomb that leveled [[Hiroshima]].

==Dating the impact event==
[[Fission track dating|Fission-track]] analysis of glass fragments by Storzer (1965) suggested the Wabar impact took place thousands of years ago, but delicate glass filigree, and the fact that the craters have been filled in considerably since Philby's 1932 visit, suggests that their origin is much more recent. [[Thermoluminescence dating]] by Prescott ''et al.'' (2004)<ref>{{cite journal | last1 = Prescott | first1 = J. R. | last2 = Robertson | first2 = G. B. | last3 = Shoemaker | first3 = C. | last4 = Shoemaker | first4 = E. M. | last5 = Wynn | first5 = J. | year = 2004 | title = Luminescence dating of the Wabar meteorite craters, Saudi Arabia | journal = Journal of Geophysical Research | volume = 109 | issue = E1| page = E01008 | doi = 10.1029/2003JE002136 | bibcode=2004JGRE..109.1008P| doi-access = free }}</ref> suggests the impact site is less than 250 years old. This is consistent with Arab reports of a fireball passing over [[Riyadh]], variously reported as occurring in 1863 or 1891 and heading southeast, reported in Philby's book ''Empty Quarter'' (1933). Fragments scattered from the path of this fireball at the Umm al-Hadidah site {{Convert|25|km}} northwest of Wabar, which contained fragments of a Type IIIA [[octahedrite]] identical to Wabar fragments, support this northwestern direction of arrival. Moreover, mapping done in 1995<ref>{{cite journal | last1=Wynn | first1 = Jeffrey C. | last2 = Shoemaker | first2 = Eugene M. | year = 1998 | title = The Day the Sands Caught Fire | journal = Scientific American | volume = 279 | issue = 5 | pages = 64–71 | doi = 10.1038/scientificamerican1198-64 | bibcode=1998SciAm.279e..36W }}</ref> show that there is an asymmetric distribution of "Insta-Rock", the coarsely-laminar sandstone created by the impact shock-wave, in the down-range (southeast) direction of the three main craters mapped.

==See also==
{{Portal|Saudi Arabia|Geology
}}
* [[Atlantis of the Sands]]
* [[List of impact craters on Earth]]

==References==

===Sources===
* {{cite journal |title=Rub' al Khali: An Account of Exploration in the Great Desert of Arabia under the auspices and patronage of His Majesty 'Abdul 'Aziz ibn Sa'ud, King of the Hejaz and Nejd and its Dependencies |author=H. St John Philby |authorlink=St John Philby |journal=The Geographical Journal |volume=81 |issue=1 |date=January 1933}}

===Notes===
{{Reflist}}

==External links==
* [http://volcanoes.usgs.gov/jwynn/3wabar.html US Geological Survey report. Jeff Wynn and Gene Shoemaker]
* [https://web.archive.org/web/20110116221642/http://www.planetarium.montreal.qc.ca/Information/Expo_Meteorites/Agrandissements/fiche_agrandissement_127_a.html The large meteorite fragment (The Camel's Hump') before its removal from the site. Photograph taken by James Mandaville, 1966]
* [https://web.archive.org/web/20110116224550/http://www.planetarium.montreal.qc.ca/Information/Expo_Meteorites/Agrandissements/fiche_agrandissement_130_a.html One of the large Wabar craters. Photograph taken by James Mandaville, 1966]
* [http://www.meteoritestudies.com/protected_WABAR.HTM Description of a piece from the meteor.]
* [http://www.wynn.org/EmptyQuarter/ Wynn expeditions] {{Webarchive|url=https://web.archive.org/web/20200816025848/http://www.wynn.org/EmptyQuarter/ |date=2020-08-16 }}
* [http://www.lpi.usra.edu/science/kring/epo_web/impact_cratering/World_Craters_web/africacraters/Wabar.html Photographs]
* [https://web.archive.org/web/20120204072914/http://rst.gsfc.nasa.gov/Sect18/Sect18_4.html Information and aerial photograph of one of the craters.  Scroll 1/4 of way down page]

{{coord|21|30|09|N|50|28|27|E|region:SA_type:landmark|display=title}}

{{Impact cratering on Earth}}

[[Category:1932 in science]]
[[Category:Impact craters of Saudi Arabia]]
[[Category:Holocene impact craters]]
[[Category:Iram of the Pillars]]