Söderfjärden

{{Short description|Impact crater in Ostrobothnia, Finland}}

{{Infobox terrestrial impact site

| name = Söderfjärden

| other_name =

| photo = Söderfjärden Landsat.jpg

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| photo_caption = Söderfjärden is visible as the hexagonal cultivated area in this Landsat image

| map = Finland

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| confidence = Confirmed

| diameter = {{convert|6.6|km}}

| depth = {{convert|300|m}}

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| age = 640 Ma

| exposed = No

| drilled = Yes

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| country = Finland

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| municipality = Vaasa

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File:Söderfjärden from Öjberget.jpg]]

Söderfjärden is a polder in Ostrobothnia, western Finland, 10 kilometres south of the town of Vaasa. The plain is in an impact crater dating back to more than 640 million years ago (Proterozoic, near the end of the Cryogenian). The crater's diameter is {{convert|6.6|km}} and its maximum depth is {{convert|300|m}}. It is filled with Cambrian sandstones 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, 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 hexagonal 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 and Korsholm, with a small corner belonging to Malax.{{cite Earth Impact DB | name = Söderfjärden|linkname = soderfjarden| accessdate = 16 August 2009}}{{Cite web |url=https://earthobservatory.nasa.gov/images/153774/the-many-facets-of-soderfjarden |title=The Many Facets of Söderfjärden |website=NASA Earth Observatory |date=19 September 2024 |access-date=3 January 2025}}