Karikkoselkä

Infobox_lake
lake_name = Karikkoselkä
image_lake = Karikkoselka-WorldWind.jpg
caption_lake = "Landsat 7" image of Karikkoselkä.
image_bathymetry = Karikkoselkä (kraatteri).pngcaption_bathymetry = The lake with the impact structure area in grey.
location = Petäjävesi
coords = coord|62|13|N|25|15|E|type:waterbody_region:FI|display=inline,title
type = impact crater lake
inflow = Könkköjoki
outflow = Autionsalmi
catchment =
basin_countries = Finland
length =
width =
area =
depth =
max-depth = 26 m
volume =
residence_time =
shore =
elevation = 111.1 m
islands =
cities =
reference = [http://kansalaisen.karttapaikka.fi/kartanhaku/paikannimihaku.html?query=hae&hakutapa=paikannimihaku&nimi=Karikkoselk%C3%A4&kunta=&cx=2565928&cy=6903695&scale=16000&tool=siirra&styles=normal&lang=en-GB Citizen's MapSite] ]

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.cite web | author=Moilanen, Jarmo | title=Karikkoselkä impact structure | work=Impact structures in Finland | url=http://www.somerikko.net/old/geo/imp/karik_e.htm | accessdate=2006-05-08] Most lakes in the region are elongated in northwest-southeast direction due to glaciation, 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 the impact crater area.cite journal | author=Lehtinen, M.; Pesonen, L. J.; Puranen, R.; Deutsch, A. | title=Karikkoselkä - A new impact structure in Finland | journal=Lunar and Planetary Science | volume=27 | issue=3 | year=1996 | pages=739–740 | url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996LPI....27..739L&db_key=AST&data_type=HTML&format=&high=4172e8435425195 ] 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). Some sources give an unreasonably young age of 1.88 Ma,cite web | title=Karikkoselkä | work=Earth Impact Database | url=http://www.unb.ca/passc/ImpactDatabase/images/karikkoselka.htm | accessdate=2006-05-08] 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.

There is evidence of a neolithic settlement on the southern shore of the lake.cite web | title=Petäjäveden kulttuuriympäristö | url=http://www.ymparisto.fi/default.asp?contentid=190501&lan=FI | date=2006-06-22 | accessdate=2007-08-30] According to a plate erected there no excavations have yet been conducted and the age of the settlement remains unknown.

References

External links

* [http://www.unb.ca/passc/ImpactDatabase/images/karikkoselka.htm Earth Impact Database]
* [http://www.somerikko.net/old/geo/imp/karik_e.htm Karikkoselkä impact structure]