1.88 Ga (Paleoproterozoic). Since the impact, 7–8 km of rock has eroded away, leaving no visible depressions (compare, in contrast, Iso-Naakkima, Lumparn). Sparse gravity data shows a negative anomaly (an area of lower gravity) in the area of the impact structure. However, there are other negative gravity anomalies nearby which are not believed to be related to the impact event. In addition, there are less dense felsic rocks in the western shore of the lake, which can contribute to the gravity low. The anomaly will be mapped in a much greater detail to determine if it is related to the impact event. Airborne magnetic data show a strikingly circular magnetic anomaly, but for a reason not yet known it is slightly east from the gravity low area as well as the region where the shatter cones are found. It is possible that the ring was created for example by a granitic intrusion instead of the impact event. No specific anomalies have been found from radiometric or electromagnetic data. Paleomagnetic data will be collected to define the age of the structure. Only some east from the centre of the Keurusselkä impact structure is Karikkoselkä, a much smaller and younger impact crater. See also Impact craters in Finland References External links Impact craters of Finland Kokemäenjoki basin Magnetic anomalies Proterozoic impact craters Lakes of Keuruu Impact crater lakes