Söderfjärden

Söderfjärden Impact Crater

Söderfjärden is a notable impact structure located in Ostrobothnia, western Finland, approximately 10 kilometers south of the city of Vaasa. This ancient crater, dating back over 640 million years to the Proterozoic Eon (near the end of the Cryogenian period), possesses a significant diameter of 6.6 kilometers and a maximum original depth of 300 meters. The geological history of Söderfjärden is marked by the deposition of Cambrian sandstones that have since filled the crater, obscuring most of its original form. Consequently, only the outer rim of the impact structure remains clearly visible today.

Geological Context and Visibility

Following its formation, post-glacial rebound caused the land to rise from the sea, transforming the basin into a wetland. This wetland was later drained with the assistance of a pump station. Currently, Söderfjärden is a cultivated area, and its unique geological history and subsequent land use have resulted in a distinct visual characteristic: it is clearly visible from the air as a large, roughly hexagonal field. This prominent surface visibility makes Söderfjärden stand out among other impact structures in Finland, many of which are situated below sea level and are therefore less apparent.

The area of the Söderfjärden basin is administratively divided among three municipalities: Vaasa, Korsholm, and Malax, with a small portion belonging to Malax. While the central uplift of the crater is buried, the remaining visible features and its distinct surface appearance continue to make Söderfjärden a site of geological interest.