Lake Summanen (Finnish: ''Summasjärvi, Summanen'') is a medium-sized lake of

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 ...

. It is located in Saarijärvi, in the region of Keski-Suomi. There is a Stone Age Museum in the island of Summassaari.

The Summanen crater

The 12th impact crater identified in Finland is located at the center of the lake. The crater is 2.6 kilometers wide, ~200 meters deep, and mostly buried under later sediments. The age of the crater is not known. It formed before the

Quaternary glaciation The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describe ...

, but on the other hand after the host rock which formed in the

Svecofennian orogeny The Svecofennian orogeny is a series of related orogenies that resulted in the formation of much of the continental crust in what is today Sweden and Finland plus some minor parts of Russia. The orogenies lasted from about 2000 to 1800 million y ...

1910 million years ago. (Plado et al. assume the impact was

Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period, when anima ...

, but give no evidence to support this.) The otherwise shallow lake (depth <10 m) has a 41 m central

deep Deep or The Deep may refer to: Places United States * Deep Creek (Appomattox River tributary), Virginia * Deep Creek (Great Salt Lake), Idaho and Utah * Deep Creek (Mahantango Creek tributary), Pennsylvania * Deep Creek (Mojave River tributary), C ...

or trench at the crater site. The location is also occupied by a significant, circular electromagnetic anomaly (with more conductive materials at the site). The anomaly is supposedly the result of a 100 to 200 m thick subsurface lens, presumably formed of fractured rock with saline liquids. The impact origin was inferred from the anomaly and the deep, and proven by identifying

shatter cones 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 ...

and

planar deformation features Planar deformation features, or PDFs, are optically recognizable microscopic features in grains of silicate minerals (usually quartz or feldspar), consisting of very narrow planes of glassy material arranged in parallel sets that have distinct orie ...

glacial erratics 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 betw ...

adjacent to the crater.

References

Finnish Environment Institute: Lakes in Finland

Etelä-Savon ympäristökeskus: Saimaa, nimet ja rajaukset

External links

Jarviwiki Summanen
{{DEFAULTSORT:Summasjarvi Impact craters of Finland Lakes of Saarijärvi

The Summanen crater

See also

References

External links