Karikkoselkä is a

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

formed in an

impact crater An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...

Petäjävesi Petäjävesi (; lit. "pine water") is a municipality of Finland. It is located in the province of Western Finland, next to the city of Jyväskylä, and is part of the Central Finland region. The municipality has a population of () and covers an a ...

Finland Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, ...

. Karikkoselkä is located in

Central Finland Central Finland (; ) is a Regions of Finland, region ( / ) in Finland. It borders the regions of Päijät-Häme, Pirkanmaa, South Ostrobothnia, Central Ostrobothnia, North Ostrobothnia, Northern Savonia, North Savo, and Southern Savonia, South S ...

approximately 30 km east from the centre of Keurusselkä, a much older and larger impact crater. Most lakes in the region are elongated in northwest–southeast direction due to

glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...

, but Karikkoselkä is strikingly round. 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 geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...

in the impact crater area. 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

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s 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 The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

or earlier). Some sources give an unreasonably young age of 1.88 Ma, which is likely a misquotation – the discovery paper mentions that the

bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...

in the region (known as the Central Finland Granite Complex) formed about 1.88 Ga (thousand million years ago), in the late

Paleoproterozoic The Paleoproterozoic Era (also spelled Palaeoproterozoic) is the first of the three sub-divisions ( eras) of the Proterozoic eon, and also the longest era of the Earth's geological history, spanning from (2.5–1.6 Ga). It is further sub ...

era. There is evidence of a

Neolithic The Neolithic or New Stone Age (from Ancient Greek, Greek 'new' and 'stone') is an archaeological period, the final division of the Stone Age in Mesopotamia, Asia, Europe and Africa (c. 10,000 BCE to c. 2,000 BCE). It saw the Neolithic Revo ...

settlement on the southern shore of the lake. According to a plate erected there, no excavations have yet been conducted and the age of the settlement remains unknown.

References

External links

Karikkoselkä impact structure
{{DEFAULTSORT:Karikkoselka Impact craters of Finland Kymi basin Magnetic anomalies Triassic impact craters Lakes of Petäjävesi Impact crater lakes

See also

References

External links