Arizona Meteor Crater
                         Student Papers in Geology
Cochise College                        

Geology Home Page                                   

Roger Weller, geology instructor

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 50,000 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:

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:

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.