Iso-Naakkima
Encyclopedia
Iso-Naakkima is a lake
in Southern Savonia
, Finland
, about 10 km south of the town of Pieksämäki
. It is notable having an eroded Impact crater
under the northwestern part of the lake. The crater is one of the oldest known, about 1200 million years old (900–1200 Ma, Mesoproterozoic
). At the time of the impact event the continent of Baltica
(modern northeastern Europe
) was located near the equator
. The crater is filled by recent (Quaternary
) sediment
s and is not visible to the surface. Its existence was revealed by strikingly circular geophysical
anomalies which are concentrated in a region 3 km in diameter; the actual remnant is about 2 km wide and 160 m deep. Its existence was later confirmed by drilling
results. The discovery was made in 1989 and therefore Iso-Naakkima is the fourth known impact structure in Finland.
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
in Southern Savonia
Southern Savonia
Southern Savonia is a region in the south-east of Finland. It borders to the regions Northern Savonia, North Karelia, South Karelia, Kymenlaakso, Päijänne Tavastia, and Central Finland...
, Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
, about 10 km south of the town of Pieksämäki
Pieksämäki
Pieksämäki is a town and municipality of Finland. Its original name was Haukivuori .It is located in the province of Eastern Finland and is part of the Southern Savonia region.The town has a population of and covers an area of of which is water...
. It is notable having an eroded Impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
under the northwestern part of the lake. The crater is one of the oldest known, about 1200 million years old (900–1200 Ma, Mesoproterozoic
Mesoproterozoic
The Mesoproterozoic Era is a geologic era that occurred between 1600 Ma and 1000 Ma . The Mesoproterozoic was the first period of Earth's history with a respectable geological record. Continents existed in the Paleoproterozoic, but we know little about them...
). At the time of the impact event the continent of Baltica
Baltica
Baltica is a name applied by geologists to a late-Proterozoic, early-Palaeozoic continent that now includes the East European craton of northwestern Eurasia. Baltica was created as an entity not earlier than 1.8 billion years ago. Before this time, the three segments/continents that now comprise...
(modern northeastern Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
) was located near the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
. The crater is filled by recent (Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
) sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s and is not visible to the surface. Its existence was revealed by strikingly circular geophysical
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
anomalies which are concentrated in a region 3 km in diameter; the actual remnant is about 2 km wide and 160 m deep. Its existence was later confirmed by drilling
Boring (earth)
Boring is drilling a hole, tunnel, or well in the earth.-Earth boring:Boring is used for a wide variety of applications in geology, agriculture, hydrology, civil engineering, and oil and natural gas industries...
results. The discovery was made in 1989 and therefore Iso-Naakkima is the fourth known impact structure in Finland.