Meteor Crater

Meteor Crater

Meteor Crater is a meteorite impact crater located approximately 43 miles east of Flagstaff, near Winslow in the northern Arizona desert of the United States. The site was formerly known as the Canyon Diablo Crater, and scientists generally refer to it as Barringer Crater in honor of Daniel Barringer who was first to suggest that it was produced by meteorite impact. The crater is privately owned by the Barringer family via their Barringer Crater Company.

The crater owners proclaim it to be "the first proven, best-preserved meteorite crater on earth.

Meteor Crater lies at an elevation of about 1740 m (5709 ft) above sea level. It is about 1,200 m (4,000 ft) in diameter, some 170 m deep (570 ft), and is surrounded by a rim that rises 45 m (150 ft) above the surrounding plains. The center of the crater is filled with 210-240 m (700-800 ft) of rubble lying above crater bedrock.

Formation of the crater

The crater was created about 50,000 years ago during the Pleistocene epoch when the local climate on the Colorado Plateau was much cooler and damper. At the time, the area was an open grassland dotted with woodlands inhabited by woolly mammoths, giant ground sloths, and camels; it was probably not inhabited by humans.

The object that excavated the crater was a nickel-iron meteorite about 50 meters (54 yards) across, which impacted the plain at a speed of several kilometers per second. The speed of the impact has been a subject of some debate. Modelling initially suggested that the meteorite struck at a speed of up to 20 kilometers per second (45,000 mph), but more recent research suggests the impact was substantially slower, at 12.8 kilometers per second (28,600 mph). It is believed that about half of the impactor's 300,000 tonnes (330,000 short tons) bulk was vaporized during its descent, before it hit the ground.

The meteor hit the ground at an 80 degree angle from the north, northeast and it is theorized that the bulk of the remaining unvaporized 150,000 tons of the meteorite is under the crater's south rim which show signs of uplift. The last major mining effort to recover the meteorite in that area was abandoned in 1929.

The impact produced a massive explosion equivalent to at least 2.5 megatons of TNT – equivalent to a large thermonuclear explosion and about 150 times the yield of the atomic bombs used at Hiroshima and Nagasaki. The explosion dug out 175 million tons of rock. The shock of impact propagated as a hemispherical shock wave that blasted the rock down and outward from the point of impact, forming the crater. Much more impact energy, equivalent to an estimated 6.5 megatons, was released into the atmosphere and generated a devastating above-ground shockwave. One of the interesting features of the crater is its squarish shape.

For a meteorite of its size, the impact melted surprisingly little rock, though it produced high enough temperatures and pressures to transform carbon minerals into diamonds and lonsdaleite, a form of diamond found near the crater in fragments of Arizona's Canyon Diablo meteorite. Limestone blocks as massive as 30 tons were tossed outside the crater's rim, and debris from the impact has been found over an area of 100 square miles (260 km²). The shock of the impact would have produced a localized earthquake of magnitude 5.5 or higher.

The blast and thermal energy released by the impact would certainly have been lethal to living creatures within a wide area. All life within a radius of three to four kilometers (1.9-2.5 miles) would have been killed immediately. The impact produced a fireball hot enough to cause severe flash burns at a range of up to 10 km (7 miles). A shock wave moving out at 2,000 km/h (1,200 mph) leveled everything within a radius of 14-22 km (8.5-13.5 miles), dissipating to hurricane-force winds that persisted to a radius of 40 km (25 miles).

Despite this destruction, the Barringer impact did not throw up enough dust to seriously affect the Earth's climate. The area was probably recolonized by the local flora and fauna within a century. This did not greatly affect the crater itself; its preservation was aided by the local climate's shift to its present-day arid conditions.

The meteorite itself was mostly vaporized. Relatively large chunks of nickel-iron fragments, ranging from gravel size to blocks weighing up to 640 kg (1,400 lb), have been recovered from the debris field surrounding the crater. Several thousand tons of tiny nickel-iron droplets, the size of sand grains, fell in and around the crater after condensing from the cloud of metallic vapour produced by the impact. Very little of the meteorite remained within the pit that it had excavated.

Discovery and investigation

Grove Karl Gilbert

Although the local Native American peoples would have known about the crater – the Ancient Pueblo Peoples lived relatively nearby at Wupatki – it was not until the 20th century that its origins were explained scientifically. The crater had come to the attention of scientists following its discovery by European settlers in the 19th century. Dubbed the Canyon Diablo crater, it had initially been ascribed to the actions of a volcano. This was not an unreasonable assumption, as the San Francisco volcanic field lies only about to the west.

In 1891 Grove Karl Gilbert, chief geologist for the U.S. Geological Survey, investigated the crater and ended up proclaiming that it was the result of a volcanic steam explosion. Gilbert had based his conclusions on a belief that if it was an impact crater then the volume of the crater including the meteorite should be more than the ejected material on the rim and also a belief that if it was a meteorite then iron should create magnetic anomalies. Gilbert's calculations showed that the volume of the crater and the debris on the rim were roughly equal. Further there were no magnetic anomalies. Gilbert argued that the meteorite fragments found on the rim were just "coincidence." Gilbert would publicize these conclusions in a series of lectures in 1895. Ironically, Gilbert in 1892 would be among the first to say that the moon's craters were caused by meteors rather than volcanos.

Maps at the time referred to it as Coon Butte.

Daniel Barringer

In 1903 a mining engineer and businessman named Daniel Moreau Barringer suggested that the crater had been produced by the impact of a large iron-metallic meteorite. Barringer's company, the Standard Iron Company, in July 1903 received a patent signed by Theodore Roosevelt for 640 acres around the center of the crater. The claim was divided into four quadrants coming from the center clockwise from northwest named Venus, Mars, Jupiter and Saturn. In 1906 Roosevelt authorized the establishment of a newly named Meteor, Arizona post office (the closest post office before was 30 miles away in Winslow, Arizona.

Standard Iron Company conducted research on its origins between 1903 and 1905. It was concluded that the crater had indeed been caused by a violent impact. Barringer and his partner, the mathematician and physicist Benjamin C. Tilghman, documented the evidence for the impact theory in papers presented to the U.S. Geological Survey in 1906 and published in the Proceedings of the Academy of Natural Sciences in Philadelphia.

Barringer's arguments met with skepticism, as there was a general reluctance at the time to consider the role of meteorites in terrestrial geology. He persisted nonetheless and sought to bolster his theory by uncovering the remains of the meteorite. At the time of first discovery by Europeans, the surrounding plains were covered with about 30 tons of large oxidized iron chunks from the meteorite. This led Barringer to believe that the bulk of the impactor could still be found under the crater floor. As impact physics were poorly understood at the time, Barringer was unaware that the meteorite had in fact vaporized on impact. He spent 27 years trying to mine the crater and find metallic iron, drilling to a depth of 419 m (1,376 ft), but no significant deposit was ever found.

Barringer, who in 1894 was one of the investors who made $15 million in the Commonwealth silver mine in Pearce, Arizona in Cochise County, Arizona, had ambitious plans for the iron ore. He estimated that given the size of the crater the meteorite had to be at least 100 million tons. The current estimate of 300,000 tons for the meteorite is only 3 percent of Barringer's estimate. Iron ore of the caliber found at the crater was valued at the time was $125/ton so the find could have potentially produced a lode worth more than a billion dollars.

Although many geologists remained skeptical of the crater's meteoritic origins until as late as the 1950s, it gained increasing acceptance as planetary science gained in maturity. Professor Herman Leroy Fairchild, an early promoter of the idea of meteorite impact cratering, argued Barringer's case in an article in Science in 1930.

Eugene M. Shoemaker

It was not until 1960 that later research by Eugene M. Shoemaker would confirm Barringer's hypothesis. The key discovery was the presence in the crater of the minerals coesite and stishovite, rare dense forms of silica found only where quartz-bearing rocks have been severely shocked by a large meteorite impact. They cannot be created by volcanic action; the only known mechanism of creating them is through an impact event (or artificially through a nuclear explosion).

Shoemaker's discovery caused a sensation in the geological world, as it was the first definitive proof of an extraterrestrial impact on the Earth's surface. Since then, numerous impact craters have been identified around the world.

Meteor Crater today

Meteor Crater is today a popular tourist attraction, easily reached via Meteor Crater Road (exit 233) off I-40. There is a $15 entrance fee to see the crater (adult rate). Despite its importance as a geological site, it is not protected as a national monument, a status that would require federal ownership. The crater is still privately owned by the Barringer family. The crater was designated a national natural landmark in November 1967.

A visitor center operated by the Barringer Crater Company stands on the north rim of the crater. The crater continues to be a focus for scientific research; during the 1960s, NASA astronauts trained there for missions to the Moon. The crater is a location in the 1984 film Starman.

On August 8, 1964, a pair of commercial pilots in a Cessna 150 flew into the crater for a closer look but were unable to climb out due to downdrafts. They ended up circling the interior until their fuel was exhausted and crash-landed. They survived their ordeal and a small portion of the wreckage not removed from the crash site remains visible to this day.

Canyon Diablo

The meteorite that struck the crater is officially called the Canyon Diablo Meteorite and all fragments of the meteorite that are officially labeled bear the Canyon Diablo name. The name comes from Canyon Diablo, Arizona which was the closest community to the crater when scientists began investigating in the late 1800s. At the time scientists were not sure if the crater was in fact a meteor crater and many of the fragments were found outside of the crater. The town was 12 miles northwest of crater and now is a ghost town. The town was the edge of Canyon Diablo (canyon) which at it closest point is about three miles west of the crater.

Geology

The impact created an Inverted topography so that the layers on the rim are in opposite order in which they formed. Specifically going from the top of the crater down:

In Fiction

  • Featured in the movie Starman. In this, a large spherical shaped UFO hovers over the crater.
  • Featured in the movie Damnation Alley (film). In this, it is featured as a nuclear blast crater.
  • Featured in a montage on the cover of the Midnight Oil album Red Sails in the Sunset. The crater is superimposed several times over Sydney Harbor suggesting the aftermath of a nuclear strike.

See also

References

External links

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