Neugrund
Key facts
- Country
- Estonia (Baltic Sea)
- Diameter
- 8 km
- Age
- about 535 million years
- Location
- 59.33° N, 23.67° E
Nothing above water: the crater lies on the floor of the Gulf of Finland, off north-western Estonia. Blocks of impact breccia lie on the shore of the nearby island of Osmussaar.
Neugrund is an impact crater about 8 km across on the floor of the Gulf of Finland, off the north-western coast of Estonia, near the island of Osmussaar. A wider ring of disturbed rock extends to about 20 km.
What it hit. About 535 million years ago, in the early Cambrian, an asteroid fell into a shallow sea. It struck soft sediments and the crystalline basement of gneiss and granite beneath. The crater was later filled and buried by sea-floor sediments.
Discovery. In the 1990s geologists studying the sea floor with echo-sounding and seismic surveys found a round structure with a raised rim. Divers and dredging recovered rock samples, and quartz grains with planar deformation features confirmed an impact.
Boulders on the shore. On Osmussaar, large boulders of impact breccia lie on the coast. During the last ice age, ice sheets scraped these blocks from the crater area and carried them to the island. They were known long before the crater was found, though nobody knew where they came from.
Age. The crater was once thought to be Ordovician, about 470 million years old. More recent work on the sediments filling it points to an age of about 535 million years.
Why it matters. Neugrund is one of the best-preserved impact craters on a sea floor anywhere. The impactor is unknown.
Did you know?
Neugrund lies on the floor of the Gulf of Finland.
Ice sheets carried blocks of its breccia to the island of Osmussaar.
It formed in a shallow sea about 535 million years ago.