GEOGRAPHIC EXTREMES SOCIETY
AUSTRALIAN RECORDS
Impact Craters
Every year the Earth is bombarded with hundreds of thousands of meteoroids. NASA estimates that on average, over forty-four tonnes of celestial material is added to our planet every single day. Most meteoroids burn up in the atmosphere and only five percent of the larger rocks make it to Earth’s surface, whereupon impact, they become known as meteorites.
The largest known impact crater in our solar system is Utopia Planitia residing on Mars and measuring a staggering 3,300 kilometres in diameter. Even our moon has a massive meteorite impact crater that fills a large portion of the dark side of the moon. The American Luna 3 module first detected this thirteen-kilometre-deep crater, naming it the South Pole – Aitken Basin and it spans an incredible 2,500 kilometres in diameter. That’s the distance from Melbourne to Cooktown on Cape York Peninsula.
By far, the largest extra-terrestrial object to ever hit Earth is very familiar to us all. It was our own Moon, which collided with Earth some 4.5 billion years ago. The initial proponent of this theory was George Darwin, son of Charles Darwin. Popular amongst astronomers today, his theory has been refined and expanded to naming the mystical planet Theia. The basic premise is that a planet the size of Mars collided with Earth. The impact tore large chunks off our developing world and the fragments went on to coalesce and form today’s Moon. Not everyone subscribes to this hypothesis, and many unanswered questions surround this theory, but it is the best explanation we have thus far regarding the Moon’s formation. The largest so far confirmed on Earth is the 300-kilometre Vredefort Crater in South Africa but slowly geologists are discovering indications of craters which may be twice as large in Quebec in Canada and in Australia’s red centre.
Largest Impact Crater
There are two contenders for largest of Australia’s celestial impact sites, the Acraman Crater near South Australia’s Lake Gairdner, and the Woodleigh meteorite crater east of Shark Bay in Western Australia.
Centred on what is now the twenty-kilometre-wide Lake Acraman in the Gawler Ranges, the Acraman crater is estimated to be 580 million years. The age places the strike in the middle of the Ediacaran Age of life, which was at that time, blossoming nearby in the Flinders Ranges. The original crater is estimated to range in size from thirty-five to ninety kilometres, but weathering processes have removed over a kilometre of topsoil and reduced it to today’s smaller depression. Ejecta from the Acraman crater has been found in a wide area of the Flinders Ranges, over 300 kilometres away. The discovery of rocks in the Officer Basin in, what was at the time, shallow seas near the Flinders Ranges exhibits the typical iridium signature of asteroids.
Lake Acraman. Largest Meteorite Crater in Australia? Image: NASA
The Woodleigh crater is conservatively estimated to be sixty-seventy kilometres wide and over 360 million years old. However, a recent revision of the size has now estimated Woodleigh’s impact crater at over 100 kilometres wide [which would place it in the realm of impacts capable of causing mass extinctions worldwide. By contrast, the Chicxulub Crater that caused the most recent global extinction event is eighty kilometres wide.
Woodleigh Crater. Largest Meteorite Crater in Australia? Image: NASA
Most perfectly formed impact crater
Barringer Crater in Arizona is the textbook example of a meteorite impact crater, but it is closely followed by Wolfe Creek as the most perfectly formed crater,
Wolfe Creek. Australia’s most perfectly formed meteorite Crater. Image: Halls Creek Tourism
The most impressive of all impact craters in Australia is Gosse’s Bluff. Situated next to the West MacDonnell Ranges in Central Australia, this impact crater stands alone and prominent on Missionary Plain, a testament to the incredible forces that created it. The chief suspect for the creation of Gosse’s Bluff is a comet that slammed into Earth 142 million years ago. The comet is estimated to be 600 metres wide and comprised mainly of frozen carbon dioxide and ice. The impact with Earth formed a crater over 24 kilometres wide with walls over one kilometre high. These estimations contrast with the current measurements of Gosse’s Bluff, at just five kilometres across with walls 180 metres high. The original massive crater, along with the surface of the land, has long since eroded away, leaving a much smaller imprint of the original impact. The visible section we see today is the deep underground uplift created by the impact. The rocks we see today at Gosse’s Bluff, were two kilometres below the original crater level, situated in the deep impact zone.
Gosse’s Bluff. Largest Comet impact in Australia. Image: NASA
Smallest and youngest impact craters
Australia is home to approximately fifty impact structures resulting from meteorite strikes on the Earth. They range in age from a few thousand years old, like the one at Dalgaranga, to the billion-year-old Yarrabubba Crater, both in Western Australia near Meekatharra. The Dalgaranga meteorite crater is regarded as Australia’s smallest, at just twenty-four metres in diameter and three metres in depth.
Dalgaranga meteorite crater. Smallest and Youngest Meteorite Crater in Australia. Image: Yalgoo Tourism
Impact Crater Records
GES Record: Best formed crater in Australia – Wolfe Creek Crater. (Source: RJ Andrews)
GES Record: Largest Meteorite Crater in Australia – Woodleigh Crater. 60 – 100km diameter. (Source: RJ Andrews)
GES Record: Largest comet impact crater in Australia – Gosse’s Bluff. (Source: RJ Andrews)
GES Record: Oldest known impact crater in Australia – Yarrabubba Crater. 2.229 billion years old (Source: RJ Andrews)
GES Record: Smallest Meteorite Crater – Dalgaranga meteorite crater. 24 metres wide (Source: RJ Andrews)
GES Record: Youngest Meteorite Crater – Dalgaranga meteorite crater. 3,000-years-old (Source: RJ Andrews )
The Geographic Extremes Society welcomes any input as to the veracity of these records and we encourage everyone to contribute to these extreme records by contacting us to initiate the discussion