Keurusselkä
Key facts
- Country
- Finland
- Diameter
- 30 km
- Age
- about 1.15 billion years
- Location
- 62.13° N, 24.60° E
No crater shape: the structure lies under and around the lake Keurusselkä in central Finland, where shatter cones can be found in shoreline outcrops.
Keurusselkä is a deeply eroded impact structure in central Finland, centred on the lake of the same name near the town of Keuruu. It is thought to have been up to about 30 km across.
Discovery. In 2003 amateur geologists found shatter cones, cone-shaped fractures with branching grooves that form only under the shock of an impact, in rocks along the shores and islands of the lake. Later study found them over an area about 11 km wide, probably the central uplift of the original crater. Quartz grains with planar deformation features confirmed the impact.
What it hit. The impactor struck granite of the Central Finland Granite Complex, about 1.88 billion years old. Since then, perhaps several kilometres of rock have been eroded away, leaving only the deep roots of the structure.
Age. Argon dating of dark, glassy breccia veins from the central uplift gives an age of about 1.15 billion years, in the Mesoproterozoic.
Why it matters. Keurusselkä is the largest known impact structure in Finland, and its discovery by amateurs shows how careful observation can still reveal major structures. The impactor is unknown.
Visiting. The lake is popular for boating and fishing. Do not hammer or remove shatter cones from shoreline outcrops.
Did you know?
Keurusselkä was discovered by amateur geologists in 2003.
Shatter cones are spread over an area about 11 km wide.
It is the largest known impact structure in Finland.