Mjølnir
Key facts
- Country
- Norway (Barents Sea)
- Diameter
- 40 km
- Age
- about 142 million years
- Location
- 73.80° N, 29.67° E
Nothing: the crater lies beneath the floor of the Barents Sea, buried under younger sediments, and is known only from seismic surveys and drilling.
Mjølnir is a crater hidden beneath the sea. It lies under the floor of the Barents Sea, north of Norway, buried beneath younger sediments in waters a few hundred metres deep. It is named after Mjølnir, the hammer of Thor, the thunder god of Norse mythology.
The impact. About 142 million years ago, close to the boundary between the Jurassic and Cretaceous periods, an asteroid perhaps 1 to 2 km across fell into a shallow sea that covered the area. It formed a crater about 40 km wide in the soft sediments of the sea floor. The impact would have sent huge tsunamis across the surrounding seas and thrown debris over a wide area.
Discovery. Mjølnir was discovered in the 1990s by geologists studying seismic surveys, which use sound waves to map rock layers beneath the sea floor. The surveys revealed a circular structure with a central peak and ring-shaped faults, the classic form of a complex crater. Drill cores, including one drilled into the centre of the structure in 1998, have yielded shocked quartz and a layer enriched in iridium, a metal common in meteorites but rare in Earth's crust, confirming the impact.
Debris on land. Traces of the impact have been found in rocks on Svalbard, the Arctic islands to the north-west. A layer of sediment there, of the right age, contains iridium and other signs of an impact, and has been linked to Mjølnir. Studies of these layers suggest the impact disturbed sediments over a large area of the Barents Shelf.
A well-preserved marine crater. Most impacts on Earth fall into the oceans, but marine craters are hard to study. They are often destroyed by plate tectonics or buried and hidden. Mjølnir is one of the best-preserved and most studied marine craters. Because it formed in soft sediments under shallow water, it shows how such craters differ from those formed on land.
Oil and gas. The Barents Sea is an important region for oil and gas exploration, and seismic data gathered by the industry has been essential for studying Mjølnir. The crater's structure may affect how fluids move through the surrounding rocks.
Why it matters. Mjølnir helps scientists understand what happens when an asteroid strikes the sea, including the tsunamis and disturbances such impacts can cause. Because most of the Earth's surface is ocean, these events are the most common kind of impact, and understanding them is important for assessing hazards.
Did you know?
Mjølnir is named after Thor's hammer in Norse mythology.
The crater was found using seismic surveys that map rock layers beneath the sea floor.
Debris from the impact has been identified in rocks on Svalbard.