Barringer Meteorite Crater rises 150 feet above the Colorado
Plateau in northern Arizona. It is nearly a mile wide and 570 feet
deep. The nickel-iron meteorite is estimated to have been only 150
feet across and 300,000 tons. The meteorite traveled at 40,000
miles per hour when it struck the earth approximately 49,000 years
ago. The force of the impact was the equivalent of 20 million tons
of TNT, more than 1000 times the force of the blast at Hiroshima
and Nagasaki.
Approximately 175 million tons of rock was excavated by the
impact. Bedrock was ejected up to 1.2 miles away. The explosion
produced a shock wave and airblast which spread across the
landscape. Winds exceeding 1200 miles per hour scoured the terrain.
Parts of this meteorite may still be found scattered throughout
nearby Canyon Diablo.
Northern Arizona at that time was a forested terrain, with
mastodons, mammoths, giant ground sloths and bison. Plants and
animals within 6 miles would have been seared by the fireball
produced by the impact. All animals within 12 miles would have been
killed or severely injured by the airblast. Hurricane force winds
would have been felt as far as 24 miles away.
Barringer Crater is named after Daniel Barringer, a mining
engineer who concluded that the crater was the result of an iron
meteor, and worth mining. He presented his proofs that the crater
was the result of a meteorite encounter to the Academy of Natural
Sciences in Philadelphia in 1906 and 1909. Geologist George P
Merrill presented further evidence to support Barringers
theory.
In 1963, Eugene Shoemaker (of the Shoemaker-Levy comet fame)
analyzed the similarities between Barringer crater and the craters
left by nuclear tests in Nevada. Both Barringer crater and the
nuclear test explosion craters deposited ejected rocky material in
identical manner, proving the crater was the result of an impact
and not volcanic in origin. Shoemaker also discovered a new mineral
called coesite at the crater. This mineral is found only at impact
craters.
Barringer Meteorite Crater is the first proven meteorite crater
in the world. From this crater, criteria has been established that
aids in the identification of other meteorite craters in the world
today. The crater has been mined for iron, studied, and served as a
training ground for NASA astronauts in preparation for Apollo moon
landings.
Currently it is a privately owned attraction. A rim trail takes
you to 4 viewing locations along the edge of the crater.
There are over 150 identified meteorite impact craters in the
world. Specific criteria is used to identify such craters. The most
important criteria fall into 4 major categories: morphology,
evidence of shock metamorphism, geochemical evidence and presence
of geophysical anomalies.
Morphology is the study of landforms and topographical features
of the crater. Barringer crater is a simple crater. It is circular,
bowl shaped with a well defined rim. Ejecta deposits radiate
outward from the rim.
Coesite and stishovite, 2 mineral pseudomorphs of quartz that
form at extremely high pressures, are found only at impact craters.
These minerals provide evidence of shock metamorphism, proving that
the craters are the result of impact rather than having volcanic
origins. Another shock indicator is the presence of shattercones.
Shattercones are distinctive striated conical fragments of rock
along which fracturing has occurred.
Meteorites contain elements rarely found on earth. Most
meteorites vaporize on impact. Elements in the meteorites can
chemically interact with the surrounding rocks to produce
geochemical anomalies. Iridium in large quantities is one such
example.
Geophysical anomalies can be any unusual measurement of such
things as gravitational or magnetic properties, reflection or
refraction seismic activity, or electrical resistivity. Such
anomalies are often found at an impact crater.
When a meteorite hits the ground, several things occur. At first
there is the contact or compression stage. Material is pushed
downwards and out the sides of the impact area. This action of
pushing material out the sides is called jetting.
The next stage is the crater excavation stage. This is rapid
crater expansion. Material can leave either ballistically or
plastically. Surface material is thrown upwards, while deeper
material is shoved outwards. This results in a reverse stratigraphy
of ejecta than is evident in the untouched material in the ground.
Rock may be melted, partially melted, brecciated, or vaporized.
The final stage is post impact crater modification. Simple
craters, such as Barringer crater do not have much crater
modification. Complex craters may have raised centers or double
rings.
More than a hole in the ground visible from miles away,
Barringer Crater historically played a large role in our
understanding of the processes involved at impact craters. Today,
the crater is preserved and accessible to those who go there.
Somewhere along the way, my original proof of visit requirements
got dropped. A gps photo along the rim trail is required to log
this earthcache. In addition, you must email me how deep the crater
is or looks like it is from where you took the photo. 11/5/2011
Lately some folks are not emailing me the required answer to the
question above. Anyone not contacting me with said answer will have
their log deleted.