Meteorite Craters

Meteorite Craters

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Arizona, not far from the town of Winslow, and you will come to what has been described as ‘the most interesting place on Earth’. It is a huge crater, 1265 metres (4150 feet) in diameter and 175 metres (575 feet) deep; it is well preserved, and has become a well-known tourist attraction, particularly as there is easy access from Highway 99.

 There is no doubt about its origin; it was formed by the impact of a meteorite which hit the Arizonan desert in prehistoric times. The date of its origin is not known with certainty, and earlier estimates of 22,000 years ago may be too low. White men have known about it since 1871. 

The crater is circular, even though the impactor came in at an angle. When the meteorite struck, its kinetic energy was converted into heat, and it became what was to all intents and purposes a very powerful bomb. What is left of the meteorite itself is very probably buried beneath the crater’s south wall. 

Incidentally, the popular name is wrong. It is called Meteor Crater, but this should really be ‘Meteorite’ Crater. A smaller but basically similar impact crater is Wolf Creek in Western Australia. There are various local legends about it.

The Kjaru Aborigines call it Kandimalal, and describe how two rainbow snakes made sinuous tracks across the desert, forming Wolf Creek and the adjacent Sturt Creek, while the crater marks the spot where one of the snakes emerged from below the ground. It is much younger than the Arizona crater; the age cannot be more than 15 million years, and 2 million years is a more likely value. 

Wolf Creek is more difficult to reach than Meteor Crater, and the road from the nearest settlement, Halls Creek, is usually open for only part of the year, but it has now been well studied since aerial surveys first identified it in 1947. 

The wall rises at an angle of 15 to 35 degrees, and the floor is flat, 55 metres (180 feet) below the rim and 25 metres (80 feet) below the level of the surrounding plain. The diameter is 675 metres (2200 feet). Meteoritic fragments found in the area leave no doubt that it really is of cosmic origin.

 Also in Australia there are other impact craters; one at Boxhole and a whole group at Henbury, both in Northern Territory. Equally intriguing is Gosse Bluff, which is at least 50,000 years old and very eroded, though there is the remnant of a central structure and indications of the old walls. 

Lists of impact craters include structures in America, Arabia, Argentina, Estonia and elsewhere, but one must be wary of jumping to conclusions; for example, unbiased geologists who have made careful studies of the Vredefort Ring, near Pretoria in South Africa, are unanimous in finding that it is of internal origin. It is linked with localgeology, and the form is not characteristic of collision.

 Note also that no crater is associated with the giant Hoba West Meteorite. It has often been suggested that the Earth was struck by a large missile 65 million years ago, and that this caused such a change in the Earth’s climate that many forms of life became extinct, including the dinosaurs.

 It has been claimed that the buried Chicxulub impact crater in the Yucatan Peninsula, Mexico, was the result of the meteorite fall which killed the dinosaurs. 

No doubt further craters will be formed in the future; there are plenty of potential impactors moving in the closer part of the Solar System.

Although the chances of a major collision are slight, they are not nil, which is partly why constant watch is now being kept to identify wandering bodies.

 It is even possible that if one of these bodies could be seen during approach, we might be able to divert it by nuclear warheads carried on ballistic missiles – though whether we would be given enough advance warning is problematical. In January 2000, the British government set up a special committee to look into the whole question of danger from asteroidal or cometary impact. If there is such an impact, let us hope that we cope with the situation better than the dinosaurs did.

Source: Atlas of the Universe - Sir Patrick Moore