The crater was first discovered in July 2015 as the researchers inspected a new map of the topography beneath Greenland's ice-sheet. They noticed an enourmous, but previously undetected circular depression under Hiawatha Glacier, sitting at the very edge of the ice sheet in northern Greenland. "We immediately knew this was something special but at the same time it became clear that it would be difficult to confirm the origin of the depression," says Professor Kjær.
In the courtyard at the Geological Museum in Copenhagen just outside the windows of the Center for GeoGenetics sits a 20-tonne iron meteorite found in North Greenland not far from the Hiawatha Glacier. "It was therefore not such a leap to infer that the depression could be a previously undescribed meterorite crater, but initially we lacked the evidence," reflects Associate Professor Nicolaj K. Larsen from Aarhus University.
The crucial evidence
Their suspicion that the giant depression was a meteorite crater was reinforced when the team sent a German research plane from the Alfred Wegener Institute to fly over the Hiawatha Glacier and map the crater and the overlying ice with a new powerful ice radar. Previous radar measurements of Hiawatha Glacier were part of a long-term NASA effort to map Greenland’s changing ice cover. What the scientists needed to test their hypothesis was a dense and focused radar survey there.
“The next-generation radar system deployed with the AWI’s research aircraft Polar 6 is exactly the kind of instrument we needed for the measurements,” says Prof. Olaf Eisen, galaciologist at the Alfred Wegener Institute and co author of the study. “The radar system that colleagues from the University of Kansas developed costom-made for our purposes exceeded all expectations and imaged the depression in stunning detail. A distinctly circular rim, central uplift, disturbed and undisturbed ice layering, and basal debris. It’s all there,” Olaf Eisen reports enthusiastically.
In the summers of 2016 and 2017, the research team returned to the site to map tectonic structures in the rock near the foot of the glacier and collect samples of sediments washed out from the depression through a meltwater channel.
"Some of the quartz sand washed from the crater had planar deformation features indicative of a violent impact, and this is conclusive evidence that the depression beneath the Hiawatha Glacier is a meteorite crater, " says Professor Larsen.