Karikkoselkä

Karikkoselkä is a lake formed in an impact crater in Petäjävesi, Finland. Karikkoselkä is located approximately 30 km east from the centre of Keurusselkä, a much older and larger impact crater.[2] Most lakes in the region are elongated in northwest–southeast direction due to glaciation, but Karikkoselkä is strikingly round.

Karikkoselkä
Landsat 7 image of Karikkoselkä.
Karikkoselkä
The lake with the impact structure area in grey.
Location	Petäjävesi
Coordinates	62°13′N 25°15′E
Type	Impact crater lake
Primary inflows	Könkköjoki
Primary outflows	Autionsalmi
Basin countries	Finland
Max. depth	26 m (85 ft)[1]
Surface elevation	111.1 m (365 ft)[1]
References	[1]

Many shatter cones, rock formations that form under the extreme pressures of impact, have been found around the lake. Further evidence comes from aeromagnetic maps, which show a clear magnetic anomaly in the impact crater area.[3] In addition, samples collected from deep drillings into the lake bottom confirm the impact origin of the structure.

The crater is the smallest identified in Finland, 1.4 km diameter and 150 m deep. Due to sediments the lake has a maximum depth of 26m which is unusually deep for a lake in the region. Karikkoselkä is estimated to be between 230 Ma and 450 Ma (million years old), most likely near 240 Ma (Triassic or earlier).[3] Some sources give an unreasonably young age of 1.88 Ma,[4][5] which is likely a misquotation – the discovery paper mentions that the bedrock in the region (known as the Central Finland Granite Complex) formed about 1.88 Ga (thousand million years ago), in the late Paleoproterozoic era.[2][3]

There is evidence of a neolithic settlement on the southern shore of the lake.[6] According to a plate erected there no excavations have yet been conducted and the age of the settlement remains unknown.