Huge Impact Crater Found Beneath Greenland's Ice

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Greenland is covered in 684,000 cubic miles of ice, 2,000 meters thick, spread over an area of 660,000 square miles. Beneath lies a vast, unexplored, preserved landscape, alien to every human alive on Earth. What could we find down there?

An international team of scientists has already turned up something fascinating. Using radar to penetrate Greenland's frozen shield, they discovered a giant impact crater more than 31 kilometers wide and 320 meters deep from rim to floor. This would make the crater one of the 25 largest on the planet.

The researchers detailed their discovery in a paper published in yesterday's issue of the journal Science Advances.

Close-up of the northwestern ice-sheet margin in Inglefield Land. The Hiawatha impact crater was discovered beneath the semi-circular ice margin.

The crater lies beneath the Hiawatha Glacier in the northwest corner of Greenland. This fortuitous placement right at the edge of the ice sheet allowed the scientists to probe glacial meltwater for sediments bearing signs of an explosive impact. They discovered grains of quartz apparently deformed by a powerful shock. Moreover, the meltwater itself contained elevated concentrations of nickel, cobalt, chromium and gold, evincing contamination by a rare iron meteorite.

As for the meteorite itself, the researchers estimated it had a diameter of 1.5 kilometers and slammed into Greenland at a speed of twenty kilometers per second. The strike would have melted and vaporized up to twenty cubic kilometers of rock! However, this scenario assumes that no ice was present at the moment of impact. If there was, the object would need to have been much larger or faster to produce the crater we see today.

Unable to access the impact site to carry out radiometric dating, the researchers could only guess at its age, placing the moment of impact roughly 11,700 to 1.9 million years before present time, during the Pleistocene Epoch. Owing to its size, the impact would almost certainly have affected climate regionally and possibly even globally.

The crater is unique, the researchers say, in that it is "the only known terrestrial crater of this size that retains aspects of its original surface topographic expression." So it would be nice to get a look at it without all that ice in the way. That double-edged wish might just come true in the near-future, as Greenland's ice sheet is melting surprisingly fast.

Source: K. H. Kjær, N. K. Larsen, T. Binder, A. A. Bjørk, O. Eisen, M. A. Fahnestock, S. Funder, A. A. Garde, H. Haack, V. Helm, M. Houmark-Nielsen, K. K. Kjeldsen, S. A. Khan, H. Machguth, I. McDonald, M. Morlighem, J. Mouginot, J. D. Paden, T. E. Waight, C. Weikusat, E. Willerslev, J. A. MacGregor, "A large impact crater beneath Hiawatha Glacier in northwest Greenland." Sci. Adv. 4, eaar8173 (2018). 10.1126/sciadv.aar8173

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