Wolfe Creek Crater, as seen from a satellite, stretches 880 m in diameter.
Credit: NASA
Travelling south from Halls Creek in Western Australia, the hilly country of the southeastern Kimberley quickly gives way to the flat sand plains of the Great Sandy Desert.
Some 90 km south of Halls Creek, we see on the horizon a break in the monotonous flat spinifex sand plain: an apparently flat-topped hill. In these endless plains it is hard to judge the height and distance of the hill, but after another 10 km we are almost there.
The fascinating story of the Wolfe Creek Crater begins to be revealed as we approach the slopes of the hill: the quartzite country rock becomes increasingly broken and disarranged. Areas of laterite, which cap the quartzite, become increasingly fragmented.
Then, curious objects begin to appear. Close to the top of the hill, on its western slopes, rusty balls of rock lie scattered on the ground, sometimes fused into the laterite and at other times lying loose.
Reaching the top of the hill we gasp from something other than shortness of breath, for before us lies one of the most startling geological features in Australia: Wolfe Creek Crater.
Australia is an ancient land. Some of the rocks in the Pilbara region of Western Australia, for instance, are 4.03 billion years old. Earth itself is about 4.56 billion years old.
Some rocks on the continent have lain undisturbed for almost a billion years, while others twice this age represent the roots of great mountain chains that once towered high into Earth's young atmosphere.
The Australian landscape has been gradually transformed by the agencies of weathering, but it is occasionally pitted by regular circular structures, often no more than faintly hinting at their existence. There are seven distinct craters, ranging in size from about 25 m to around one kilometre in diameter. Five of these are associated with meteorites.
One of these is Wolfe Creek, one of the best-studied meteor craters. Unfortunately, however, ideas on the origin of the crater, one of the most fascinating structures in Australia, rarely escape the scientific journals in which they're published.
There are another 30 very much larger but deeply eroded and enigmatic circular scars that present some evidence of an origin by impact. Among the largest are Woodleigh in Western Australia, Lake Acraman in South Australia and Tookoonooka in Queensland, which are probably 60-70 km, greater than 35 km and 50 km in diameter respectively.
Another 12 structures remain enigmatic; there is little or no evidence other than their circularity to prove they are of impact origin. Altogether, there are 49 structures that have been recognised in Australia, with varying degrees of certainty about their impact origins, ranging from authentic to doubtful.
