Earth impact craters
Large meteorites and asteroids occasionally strike Earth, as they do
other worlds in the Solar System, and create impact
craters. However, intense erosion and tectonic processes on our planet
quickly (on geological timescales) take their toll of these structures,
wiping out all traces of them. Of those of which visible evidence remains,
the best-known, best-preserved, and mostly recently-formed is the Barringer
Crater. The largest, and one of the most important in terms of its biological
effects, is the Chicxulub Crater. Some others
are described below. See also astrobleme.
A group of three impact craters formed about 360 million years ago in the
Sahara Desert in northern Chad at 19° 6' N, 19° 15' E. The first to be found,
the 17-km-wide crater now known as Aorounga South, had been buried by sediments,
which were then partially eroded to reveal the current ring-like structure.
Two further circular features, both about 16 km across, known as Aorounga
North and Aorounga Central, were detected in radar images taken from the
Space Shuttle in 1994. The Aorounga craters are only the second suspected
crater chain known on Earth; the first consists of eight round depressions,
3 to 17 km wide, stretching along a 700-km line from southern Illinois to
An impact crater, 10.5 km in diameter and about 1.3 million years old, located
in Ghana in crystalline bedrocks of the West African Shield (6° 32' N, 1°
25' W); it is almost entirely filled by Lake Bosumtwi. Chemical, isotopic,
and age studies show that the crater is the most probable source of the
Ivory Coast tektites, which are found on land in central Africa and as microtektites
in nearby ocean sediments.
Clearwater Lakes Craters
Twin, lake-filled impact craters in crystalline bedrocks of the Canadian
shield in Quebec; they were formed simultaneously, about 290 million years
ago, by two separate but probably related meteorite impacts. The larger
crater, Clearwater Lake West (56° 13' N, 74° 30' W), with a diameter of
32 km, has a prominent ring of islands some 10 km across. These islands
comprise a central uplifted area and are covered with impact melts. The
central peak of the 22-km-wide Clearwater Lake East (56° 05' N, 74° 07'
W) is under water.
Deep Bay Crater
An impact crater in Saskatchewan, Canada (56° 24' N, 102° 59' W), formed
about 100 million years ago in Precambrian metamorphic crystalline rocks, that is visible as a near-circular bay, about
5 km wide and 220 m deep, in the otherwise shallow Reindeer Lake. The circular
shoreline, at a diameter of 11 km, is partially surrounded by a ridge with
heights to 100 m above the lake surface. The diameter of this ridge, about
13 km, is likely the outer rim of the impact structure. Although not obvious
from the surface, Deep Bay is a complex impact structure with a low, totally
submerged central uplift.
A spectacular impact crater, partly filled by the 25-km diameter Kara-Kul
Lake, almost 6,000 m above sea-level in the Pamir Mountain Range in Tajikstan,
near the Afghan border (38° 57' N, 73° 24' E). The crater, whose rim has
a diameter of 45 km, was formed less than 10 million years ago.
Manicouagan Impact Structure
One of the largest preserved impact craters on Earth, located in Quebec,
Canada, at 51° 23' N, 68° 42' W; it was formed about 212 million years ago.
An ice-covered annular lake, 70 km across, now lies within a ring of rock
showing clear signs of having been melted and altered by a violent collision.
The original rim of the crater, though now eroded away, is thought to have
had a diameter of about 100 km.
Wolfe Creek Crater
A relatively well-preserved meteorite crater, thought to be about 300,000
years old, that is partly buried under wind-blown sand in the flat desert
plains of north-central Australia at 19° 10' 19" S, 127° 47' 42"
E. Its rim is 875 m in diameter and rises 25 m above the surrounding plains
and 75 m above the crater floor. Oxidized remnants of iron meteoritic material,
as well as some impact glass, have been found
in the vicinity. [Coordinates from Google Earth, thanks to
J. De Landtsheer]
AND PLANETARY SCIENCE