Hiawatha

Key facts

Country

Greenland (Denmark)

Diameter

31 km

Age

57.99 ± 0.54 million years

Location

78.83° N, 67.30° W

Hiawatha is an impact crater about 31 km across hidden beneath the ice sheet of north-west Greenland. It is the first large impact crater found under a continental ice sheet, and one of the most surprising crater discoveries of the twenty-first century.

Discovery. In 2015 scientists studying Greenland's ice with airborne radar, which sends radio waves down through the ice and records the echoes from the rock below, noticed a round depression in the bedrock under Hiawatha Glacier. Further radar flights in 2016 mapped a bowl with a raised rim and a central uplift, buried under roughly 1 km of ice. The discovery was announced in 2018.

Proof of impact. Nobody has yet drilled through the ice to the crater floor. Instead, scientists sampled sand and gravel carried out of the crater by a meltwater river. These sediments contain shocked quartz, grains crossed by microscopic sets of planes produced only by an impact shock, along with pieces of glassy rock that had been melted. Chemical traces in the sediment suggest the impactor was an iron asteroid, perhaps about 1.5 km across.

Age. At first many scientists thought the crater might be very young, perhaps formed during the last ice age. In 2022, dating of grains of the minerals zircon and feldspar from the melted rock, using two different radioactive clocks, gave an age of about 58 million years, in the late Palaeocene. The crater formed long before the ice sheet existed and was later buried by it.

What it hit. The target was ancient crystalline rock of the Greenland Shield, more than a billion years old.

Why it matters. Hiawatha shows that large craters can still be found on Earth, even in places where nobody can see the ground. Drilling through the ice to sample the floor directly would answer many remaining questions.

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