Silverpit Crater confirmed as an asteroid impact that raised a 100-metre tsunami

A crater 700 metres under the seabed

The Silverpit Crater lies in the southern North Sea, roughly 700 metres beneath the seabed and about 80 miles off the coast of Yorkshire. The crater itself measures about three kilometres across. Around it sits a much larger, 20-kilometre-wide region of circular faults, fractures in the rock where movement has occurred.

Scientists first identified the structure in 2002. Its nearly circular outline, elevated central peak and rings of faults resembled other impact sites, and central peaks can form when rocks compressed by a collision rebound upward. The interpretation was contested nonetheless. Some geologists argued that moving underground salt deposits had deformed the rock layers above, while others proposed that volcanic activity caused part of the seabed to collapse. In 2009, geologists voted on the competing explanations, as documented in Geoscientist magazine, and most participants rejected the asteroid impact hypothesis.

Shocked minerals settle the argument

A team led by Dr Uisdean Nicholson of Heriot-Watt University in Edinburgh combined 3D seismic imaging, petrographic and biostratigraphic data, and numerical impact simulations. The seismic data image the whole structure, confirming a central uplift, an annular moat, a damage zone and numerous secondary craters on the contemporaneous seabed. The distribution of normal and reverse faults in the brim, and curved radial faults around the central uplift, suggest a low-angle impact from the west. A pitted, flat-topped central uplift at the top chalk horizon may indicate significant devolatilization of chalk immediately after the impact.

The decisive evidence came from rock cuttings collected from the nearby 43/25-1 well. The published study reports two grains with shock lamellae, indicating shock pressures of about 10 to 13 gigapascals, consistent with the results of the numerical models. The university's account describes rare shocked quartz and feldspar crystals at the same depth as the crater floor. Nicholson said: "These prove the impact crater hypothesis beyond doubt, because they have a fabric that can only be created by extreme shock pressures."

A 160-metre asteroid and a tsunami over 100 metres

Biostratigraphic data place the event in the middle Eocene, between 43 and 46 million years ago. The simulations suggest that an asteroid roughly 160 metres across approached from the west and struck the seabed at a shallow angle. The collision blasted a curtain of rock and water 1.5 kilometres into the air and triggered a tsunami more than 100 metres, or 330 feet, high. The object was far smaller than the asteroid associated with the extinction of the dinosaurs.

Why confirmed impact craters are rare

The study, published in Nature Communications, establishes Silverpit as one of the relatively few confirmed impact craters on Earth. The paper notes that only about 200 confirmed impact craters are known in the terrestrial record, and that marine-impact craters are rarer still, with only about 33 confirmed or probable examples identified despite more than 70 per cent of Earth's surface being covered by water. Impactors larger than about 100 metres in diameter can penetrate the atmosphere and strike the surface.

Buried craters tend to be better preserved than those exposed at the surface, which are modified by weathering, erosion and tectonic deformation, but they are difficult to investigate without high-resolution seismic imaging or drill cores. Before this work, the only impact crater on Earth fully imaged with 3D seismic was the roughly nine-kilometre Nadir Crater offshore West Africa. The authors describe Silverpit as an exceptionally preserved hypervelocity impact structure.