Lake Acraman

Acraman impact structure is a deeply eroded impact crater in the Gawler Ranges of South Australia. Its location is marked by Lake Acraman, a circular ephemeral playa lake about 20 kilometres in diameter. The discovery of the impact structure and independent discovery of its ejecta were first reported in the journal Science in 1986 by George E. Williams. The evidence for impact includes the presence of shatter cones and shocked quartz in shattered bedrock on islands within Lake Acraman.

The impact structure is deeply eroded, and its original size must be inferred by indirect means. Some authors estimate an original diameter of up to 85 to 90 kilometres, while other suggest a smaller size, perhaps only 35 to 40 kilometres, closer to that of the depression in which Lake Acraman is centred. The larger size estimate would imply an energy release of 5.2 × 106 megatons of TNT.