Sääksjärvi
Key facts
- Country
- Finland
- Diameter
- 6 km
- Age
- about 600 million years (poorly known)
- Location
- 61.40° N, 22.40° E
Lake Sääksjärvi, a round lake about 5 km across near Kokemäki in south-western Finland.
Sääksjärvi is an impact structure about 6 km across beneath a round lake of the same name near Kokemäki, south-western Finland.
Discovery. The structure was identified in the late 1960s, when geologists studying boulders in glacial deposits south of the lake found impact melt rock and breccia with shock features. Ice sheets had carried these rocks from the crater. Later geophysical surveys and drilling confirmed a buried structure under the lake.
What it hit. The impactor struck crystalline rocks of the Baltic Shield, gneiss and granite nearly 2 billion years old.
Age. The age is poorly known. Estimates range widely, but it is usually given as about 600 million years, in the late Precambrian.
Why it matters. Sääksjärvi was the first impact structure recognised in Finland, and it shows how boulders carried by glaciers can lead geologists back to a hidden crater. The impactor is unknown.
Visiting. The lake is surrounded by farmland and forest. Boulders of impact rock can sometimes be seen in fields; ask permission before entering private land.
Did you know?
Sääksjärvi was the first impact structure recognised in Finland.
It was found from boulders of melted rock carried by glaciers.
Its age is uncertain by many tens of millions of years.