Karikkoselkä is a

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

formed in an

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

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 ar ...

Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...

. Karikkoselkä is located 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 cone Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite impact craters or underground nuclear explosions. They are evidence that the rock has been subjected to a shock with pressures in the rang ...

s, 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 naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

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 ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

or earlier). Some sources give an unreasonably young age of 1.88 Ma, which is likely a

misquotation A quotation is the repetition of a sentence, phrase, or passage from speech or text that someone has said or written. In oral speech, it is the representation of an utterance (i.e. of something that a speaker actually said) that is introduced by ...

– the discovery

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distrib ...

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 The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions ( eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

era. There is evidence of a

neolithic The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several p ...

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