Kärdla
Key facts
- Country
- Estonia
- Diameter
- 4 km
- Age
- about 455 million years
- Location
- 59.02° N, 22.77° E
A low, round ridge about 4 km across around the town of Kärdla on the island of Hiiumaa, Estonia. The town is built inside the crater.
Kärdla is an impact crater about 4 km across on the island of Hiiumaa, off the west coast of Estonia. The island's main town, also called Kärdla, is built inside it.
What it hit. About 455 million years ago, in the Ordovician, an asteroid fell into a shallow sea. It punched through soft sea-floor sediments into the crystalline basement of granite and gneiss beneath. The crater was soon filled and buried by sediments, which protected it.
Proof of impact. Geologists noticed in the mid-twentieth century that the rocks under Kärdla were strongly disturbed. Many boreholes were drilled in the 1970s and 1980s. The cores contain impact breccia and quartz grains with planar deformation features, the microscopic fingerprint of shock, confirming an impact.
What can be seen. The crater rim forms a low, round ridge around the town, rising only a few metres above the surroundings. In the centre, a central uplift lies buried beneath the sediments.
Water. The broken rock of the crater holds water, and springs and wells in Kärdla draw on it.
Why it matters. Kärdla is one of the best-studied marine craters in Europe and one of several Ordovician craters in the Baltic region formed during the Ordovician meteorite shower. The impactor is unknown.
Visiting. A small exhibition in the town explains the crater.
Did you know?
The town of Kärdla is built inside an impact crater.
The crater rim forms a low ridge only a few metres high.
It formed in a shallow sea about 455 million years ago.