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Karikkoselkä

2007 Schools Wikipedia Selection. Related subjects: European Geography

   Coordinates: 62°13′N 25°15′E
   Landsat 7 image of Karikkoselkä.
   Enlarge
   Landsat 7 image of 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. 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. In addition, samples collected from deep
   drillings into the lake bottom confirm the impact origin of the
   structure.

   The crater is 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, 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.

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