Jänisjärvi
Key facts
- Country
- Russia
- Diameter
- 14 km
- Age
- about 700 ± 5 million years
- Location
- 61.97° N, 30.92° E
Lake Jänisjärvi, a large, roughly round lake in Karelia, Russia, north of Lake Ladoga, with islands and shores of impact melt rock.
Jänisjärvi is an impact structure about 14 km across in the Republic of Karelia, north-western Russia, filled by Lake Jänisjärvi, north of Lake Ladoga and close to the border with Finland.
What it hit. The impactor struck ancient metamorphic rocks, mainly schists and other metamorphosed sediments, about 1.9 billion years old. The heat of the impact melted part of the target, forming a sheet of impact melt rock. This rock is exposed on islands in the lake.
Proof of impact. The impact origin was established in the 1970s, when geologists found shock features in minerals of the melt rock and breccia, including quartz with planar deformation features.
Age. Argon dating of the melt rock gives an age of about 700 million years, in the late Precambrian. Some studies have suggested a younger or older age, and the dating has been debated.
Why it matters. Jänisjärvi is one of the oldest impact structures in Europe with well-preserved melt rock, which has been used to study how ancient magnetism and radioactive clocks are reset by impacts. The impactor is unknown.
Visiting. The lake lies in a border zone; check rules on access before travelling.
Did you know?
Rock melted by the Jänisjärvi impact forms islands in the lake.
The lake lies north of Lake Ladoga, near the border with Finland.
It is about 700 million years old.