Tvären
Key facts
- Country
- Sweden
- Diameter
- 2 km
- Age
- about 455 million years
- Location
- 58.77° N, 17.42° E
A round bay about 2 km across in the Baltic Sea archipelago south of Stockholm, near Studsvik. The crater lies under the water.
Tvären is a round bay about 2 km across in the archipelago off the coast of Södermanland, south of Stockholm, Sweden. Beneath the water lies an impact crater, filled with Ordovician sediments.
What it hit. About 455 million years ago, an asteroid fell into a shallow sea and struck the crystalline basement of the Baltic Shield, mostly granite and gneiss. The crater was soon filled and buried by sea-floor sediments, including limestones.
Discovery and proof. The round bay stood out on maps, and geologists suspected it might be an impact crater. Seismic surveys of the bay floor and drilling in the 1990s revealed a buried crater with a bowl shape and a fill of breccia and sediment. Quartz grains in the breccia show planar deformation features, confirming an impact.
Why it matters. Tvären is one of several Swedish craters that formed during the Ordovician, when the Earth received far more meteorites than it does now, after an asteroid broke up in the asteroid belt. The impactor is unknown.
Visiting. The bay is part of a beautiful archipelago popular with sailors. There is nothing to see of the crater itself.
Did you know?
Tvären is a round bay in the Baltic Sea archipelago south of Stockholm.
The crater is filled with sea-floor sediments about 455 million years old.
Drilling in the 1990s confirmed it was an impact crater.