Söderfjärden is a

polder A polder () is a low-lying tract of land that forms an artificial hydrological entity, enclosed by embankments known as dikes. The three types of polder are: # Land reclaimed from a body of water, such as a lake or the seabed # Flood plains s ...

in Ostrobothnia, western

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 ...

, 10 kilometres south of the town of

Vaasa Vaasa (; sv, Vasa, , Sweden ), in the years 1855–1917 as Nikolainkaupunki ( sv, Nikolajstad; literally meaning "city of Nicholas),

. The plain is 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 craters ...

which was made at least some 640 million years old (

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

, near the end of the

Cryogenian The Cryogenian (from grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by ...

). The crater's diameter is and its maximum depth is . It is filled with

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

s leaving only the outer rim visible. There is also a central uplift, which is buried. After rising from the sea due to

post-glacial rebound Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound a ...

, Söderfjärden was a wetland but was later drained with help of a pump station. It is currently cultivated and is clearly visible from air as a large circular field. This makes Söderfjärden unique among the other impact structures in Finland which are at least partially below sea level. The area of the basin is divided half and half between

Vaasa Vaasa (; sv, Vasa, , Sweden ), in the years 1855–1917 as Nikolainkaupunki ( sv, Nikolajstad; literally meaning "city of Nicholas),

and

Korsholm Korsholm (; fi, Mustasaari) is a municipality of Finland. The town of Vaasa was founded in Korsholm parish in 1606 and today the municipality completely surrounds the city. It is a coastal, mostly rural municipality, consisting of a rural landscap ...

, with a small corner belonging to

Malax Malax (; fi, Maalahti) is a municipality of Finland. It is located in the province of Western Finland and is part of the Ostrobothnia region. The municipality has a population of () and covers an area of of which is water. The population dens ...

References

External links

Sundom village
travel information page about Söderfjärden.

in Finnish impact structures homepage.
The homepage
of a local exhibition site, called ''Meteoria'', in Swedish, ''Meteoriihi'' in Finnish, describing the area. Ria (riihi) is a kind of

barn A barn is an agricultural building usually on farms and used for various purposes. In North America, a barn refers to structures that house livestock, including cattle and horses, as well as equipment and fodder, and often grain.Allen G. ...

, where crop is dried, and the building looks like one.
Google Earth view
Impact craters of Finland Proterozoic impact craters Landforms of Ostrobothnia (region) Polders {{WesternFinland-geo-stub

See also

References

External links