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Meteor Crater

 

 

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Here's a description of Barringer Meteor Crater in Arizona.

This was my "focus region" for the trip.

 

 

Meteor Crater, Arizona

The name, Meteor Crater, is a misnomer. Meteors are extraterrestrial debris that enters Earth’s atmosphere but either skips back into space as though a flat stone on the surface of a pond, or completely burns up during entry. Meteorites are meteors that actually strike the Earth’s surface, be it water or land.

Though a small and simple crater, Meteor Crater is the world’s best-preserved impact structure and the first recognized as such a structure. The region’s arid climate and the crater’s young age (49,000 ± 3,000 years) are responsible for its excellent preservation.

Studies show that a meteorite’s size can be approximated at a 20:1 ratio of the crater’s diameter though this depends on the variables of the object’s mass, speed, trajectory, etc. Considering these factors, estimates indicate an object about 40 m (130 ft), traveling at 20 km/sec (12 mi/sec) -- the RMS encounter speed for Earth-crossing meteoroids. Total energy release at impact was equal to that produced by a 15-megaton nuclear device exploded at a depth of 20 m (67 ft) below the surface to produce the crater which is 1.2 km (.75 mi) diameter, and 180 m (594 ft) deep with its upturned rim rising 30 - 60 m (100 - 200 ft) above the surrounding plateau. Today, the structure is slightly rectangular due to a mutually perpendicular scissor-type vertical joint set residing in the target rock.

At time of impact, a shockwave expanded hemispherically into the target rock exceeding its dynamic yield strength by several orders of magnitude – usually equal to thousands of atmospheres of pressure. Following this intense compression, a rarefaction (decompression) wave moved through the rock in the same manner but completely unloaded the compression thereby ejecting target rock into the atmosphere as a consequence of Newton’s third law of motion – that of equal and opposite forces. In effect, the compressed rock blasted itself out of the ground as it was decompressed to form a rapidly expanding cavity that would become the crater itself.

In the process of decompression, target rock is upthrust into an expanding cone of ejecta. Remnants of the ejecta blanket still exist as inverted stratigraphy in various regions surrounding the crater though today, it is almost completely eroded away. Originally, deposited as a continuous bed out to a distance of 3 km (2 mi), the ejecta would have become discontinuous beyond that. Smaller, secondary impact structures, surround the crater having been caused by fallback of large target fragments in excess of 30 m (100 ft) across, and pieces of the meteorite are found throughout.

The crater formation process continues until the force of the expanding shockwave equals that of the target tock’s mechanical strength. The crater stops growing at this point, but the shockwave and rarefaction continue to expand into the rock causing further alteration.

A melt lens of suevite breccia (pronounced sway-vite) composed of fractured bedrock and meteoritic material extends to a depth of 180 m (600 ft) below the crater’s floor which itself is comprised of a fining upward unit of fallout 11 m (35 ft) thick. This unit is overlain by talus from the crater’s walls and alluvium that was washed in with water that occasionally formed a small lake in the basin. Note that suevite differs from igneous rock in that it is composed of melted target rock and the melted remnants of the impacting body.

Click to see an enlarged topographic map of the crater.

Township & range sections are 1 mi2

 

 

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This page was last updated on 04/03/01

To report problems, ask questions, etc., please contact

Reuben Johnson at: rcjohnson@students.wisc.edu