Meteorite Craters
ATLAS OF THE UNIVERSE
G
o to 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▼ Site of the Siberian
impact of 1908, Tunguska;
photographed by Don
Trombino in 1991. No crater
was produced, so presumably
the projectile broke up
before landing, but the
results of the impact are
still very evident. ‘Saltpan’ near Pretoria,
South Africa, was identified
as an impact crater recently.
Larger than the Arizona
crater, the associated breccia
are clearly seen. The water
in the lake is salty. The
surrounding wall is uniform
in height. Photograph by
Dr Kelvin Kemm, 1994.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 rem-
nant 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 local▼ Wolf Creek Crater in
Western Australia; an aerial
photograph which I took
in 1993. This is a very
well-formed crater and
possibly the most perfect
example of an impact
structure on the Earth, apart
from the famous Meteor
Crater in Arizona, USA.D108-151 UNIVERSE UK 2003CB 7/4/03 5:20 pm Page 150