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ArizonaMeteor Crater
by John Roberts
Physical Geology
Fall 2017
  


 

Barringer Meteor Crater

 

Figure  SEQ Figure \* ARABIC 1 Meteor Crater, Photo Credit J. Roberts 2017

 

Meteor crater is an impact crater located in Coconino County, Arizona.  It has been known the Coon Mountain, Canyon Diablo Crater (from the nearby Canyon Diablo) and later named Barringer Meteor Crater, named for Daniel Barringer who suggested it was an impact crater in the beginning of the 20th century.  It is about ¾ of a mile in diameter and 550ft deep at the center.  It was caused by an iron meteorite that hit the earth at around 25000 mph around 50000 years ago.  It is a US National Natural Landmark and is open to the public.
 

Meteor Crater was initially misidentified as a volcano.  Late in the 19th century after its discovery there were differences in thought about what created the crater.  Grove Karl Gilbert concluded based on research that crater was the result of a volcanic explosion.  On the other hand, Daniel Barringer theorized that the crater was due to an impact due to the large amount of iron meteorite fragments found around the site.  It wasn’t until the 1960’s that the final determination as made about the origin of the crater.  
 

In the Late 19th/Early 20th Century, not much was known about crater impacts of meteors. Most visible craters on earth were the result of volcanoes.  Since an observable meteor impact is a rare phenomenon, it is difficult for scientists to observe an impact in order to study their effects.















Figure  SEQ Figure \* ARABIC 2 Grove Karl Gilbert Photo Credit:
 https://upload.wikimedia.org/wikipedia/commons/6/67/Grove_Karl_Gilbert_0129.jpg

Figure  SEQ Figure \* ARABIC 3 Volcanic Fields near Flagstaff in the distance which lead Gilbert
 to adopt a volcanic origin for the crater. Photo Credit: J.Roberts 2017

Grove Karl Gilbert was a geologist in the latter half of 19th Century.  He was well renown as an excellent geologist and was USGS’s (United States Geological Survey) first geologist at its formation.  Gilbert had two theories.  Based on observations of the moon, he felt that the crater could be caused by a meteor due to the similar shape of the crater and those on the moon.  His other theory that the crater was volcanic in origin.  He assumed that if it were an impact crater, he would find a large fragment of the meteor at the center.  He visited the site, but did not find a large fragment, and based on the other volcanos in the area, he concluded that instead of an impact site, it was in fact a maar volcano.  

 

 













Figure  SEQ Figure \* ARABIC 4 Maar volcano crater in Sanbernardino Valley Volcanic Field,
Cochise County, Arizona. Photo Credit: R. Weller, Cochise College.

A maar is a volcanic crater cause by a volcanic explosion.  As magma rises, if it comes in contact with groundwater, the steam results in a massive increase in pressure in the rock.  The pressure builds so quickly resulting in a massive explosion, leaving a large crater.



 



















Figure  SEQ Figure \* ARABIC 5 Daniel Barringer Photo Credit:
 https://upload.wikimedia.org/wikipedia/commons/5/5c/Daniel_Barringer.jpg
 

Daniel Barringer was a lawyer who, bored with law, pursued an occupation in mining and acquired a large fortune in that business.  In 1902 he was made aware of the crater and the iron fragments surrounding it.  Seeing the potential scientific impact and great fortune he could gain, he theorized that the crater was due to an impact.  He set forth to buy the land and created the Standard Iron Company in hopes of finding the large mass of iron he (and Gilbert) assumed would be at the bottom of an impact crater.  After many years and loss of his and investors’ money, he never found the large iron fragment he sought to find at the bottom of the crater.



















Figure  SEQ Figure \* ARABIC 6 Remains of Barringer’s Mine at the base of Meteor Crater.
Photo Credit: J.Roberts 2017

    Though Barringer’s endeavor turned to be a financial failure, some discoveries would help later confirm the impact hypothesis.   At the rim of the crater, the rock layers are peeled upward.  It was noted that outside the rim, these layers are reversed. Pure iron fragments were found scattered through all the rock surround the crater.  Signs were there that the meteorite was vaporized on impact.  Another discovery on the site was the unique sandstone in the area.  It was unusual due to the very fine  texture and almost powder like appearance.



Figure  SEQ Figure \* ARABIC 7 Noticable uplift seen at the rim of the crater.
Photo Credit: J.Roberts 2017

 

 

In the 1950’s and 60’s, Eugene Shoemaker was researching Meteor Crater.  He noted similarities between this crater and those caused by the Nuclear test detonations performed in the 50’s in Nevada.  In analyzing the Nuclear Test sites, he found something remarkable.  In both, he observed a very fine white silica sandstone.  On further study of the mineral, he found that this mineral could only be formed under intense heat and pressures not possible in a volcanic explosion.  The mineral was a shocked quartz sandstone called coesite, and could only form by instant heat and pressure.  This discovery was the final piece to finally support Barringer’s claim that the site was from and impact event.

 


Figure  SEQ Figure \* ARABIC 8 On Exhibit: Normal Sandstone. Photo Credit: J.Roberts 2017

Figure  SEQ Figure \* ARABIC 9 On Exhibit. Shocked Quartz Sandstone from Meteor Crater. Photo Credit: J.Roberts 2017
 



















Figure  SEQ Figure \* ARABIC 10 Illustration showing a cross section of crater on display at Meteor Crater Exhibit on site.
Photo Credit: J.Roberts 2017

Shoemaker’s observations were that toward the inside of the rim, rock layers were turned upward and that outside the rim, these layers were turned completely over.  These findings by Shoemaker put to rest all doubt and he concluded that the crater was due to a meteoritic impact.
 
















Figure  SEQ Figure \* ARABIC 11 Holsinger Meteorite. Largest Fragment discovered on display at Exhibit.
Photo Credit J.Roberts 2017

 

    One final assumption made by Gilbert and Barringer took until later in the 20th century to finally disprove.  In all the mining and drilling Barringer performed on the crater, he never found a large iron fragment.   What happened to the meteorite? Over the decades, scientists theorized that the meteorite was vaporized upon impact.  Evidence at the site showed iron fragments scatter through all layers of material.  It wasn’t until the availability of computer modeling technology that scientists were able to model the impact and prove that the original source meteor was vaporized.  This was a significant conclusion.
 
















Figure  SEQ Figure \* ARABIC 12 This fine textured sandstone is everywhere around the crater rim.
Photo Credit: J.Roberts 2017

Meteor Crater in person is an impressive site.  Little was known about meteor impacts when it was discovered, but it’s study has allowed the discovery and further study of other impacts on the planet.

 

 

 

Resources:

https://www.youtube.com/watch?v=g9MiJUb7nRc&list=WL&index=20

https://en.wikipedia.org/wiki/Meteor_Crater

https://en.wikipedia.org/wiki/Grove_Karl_Gilbert

https://en.wikipedia.org/wiki/Daniel_Barringer_(geologist)

https://en.wikipedia.org/wiki/Eugene_Merle_Shoemaker

https://en.wikipedia.org/wiki/Canyon_Diablo_(meteorite)

http://www.barringercrater.com/about/

https://www.earthmagazine.org/article/benchmarks-july-221960-mineral-discovery-ends-meteor-crater-debate

http://www.psi.edu/epo/explorecraters/barringertour1.htm