Lockne
Key facts
- Country
- Sweden
- Diameter
- 7.5 km
- Age
- about 458 million years
- Location
- 63.00° N, 14.82° E
A subtle crater landscape of forests and farms near Lake Locknesjön in Jämtland, with outcrops of impact breccia and quarries of crater-filling limestone.
Lockne, in the province of Jämtland in central Sweden, is one of the best-studied examples of a crater formed in the sea. About 458 million years ago, in the Ordovician period, an asteroid fell into a sea several hundred metres deep, leaving a crater in the sea floor and a remarkable record of what happens when the ocean rushes back in.
The impact. The asteroid, perhaps around 600 m across, punched through the water and the soft sediments on the sea floor and into the hard crystalline rock beneath, forming an inner crater about 7.5 km across. Because the water and soft sediments behaved differently from the hard rock, a much wider, shallower crater formed in the upper layers, giving a total diameter of about 13 km.
The ocean returns. After the impact, the sea rushed back into the crater, carrying huge quantities of broken rock and sediment. This flood, called a resurge, carved channels in the crater rim and filled the crater with layers of breccia and sand. Studying these deposits at Lockne has helped scientists understand how marine craters form and fill, and how they differ from craters on land.
A double impact. About 16 km from Lockne lies a much smaller crater called Målingen, about 700 m across. It formed at the same time as Lockne, and scientists think the two were made by a binary asteroid, a pair of asteroids orbiting each other. Unlike the Clearwater Lakes in Canada, whose two craters turned out to have different ages, Lockne and Målingen appear to be a genuine pair.
A meteorite shower in the Ordovician. Lockne formed during a remarkable period in Earth's history. Around 466 million years ago, an asteroid broke apart in the asteroid belt, sending a huge number of fragments towards the inner Solar System. For millions of years afterwards, the Earth received far more meteorites than it does today. Fossil meteorites from this period have been found in limestone quarries in southern Sweden, and traces of the impactor at Lockne suggest it may have been part of the same event.
Why it matters. Lockne is a key site for understanding marine impacts, which are probably the most common type of impact on Earth because oceans cover most of the planet. Its well-preserved deposits show how the sea responds to a large impact.
Visiting. The Lockne area has trails and information signs, and some sites are part of a geological heritage programme. The rocks can be seen in outcrops and old quarries. As always, ask permission before entering private land, and do not collect from protected sites.
Did you know?
Lockne formed when an asteroid fell into a sea several hundred metres deep.
A smaller crater, Målingen, formed at the same time, probably from a binary asteroid.
It formed during a period when the Earth received many more meteorites than today.