Kummakivi erratic boulder

Kummakivi is an erratic boulder which was glacially transported to rest on top of a rôche moutonnée. The boulder is special since only around 0.5m² of its surface area is in contact with the rock below it. The dimensions of the boulder itself are approx. 7m x 4m x 5m. Kummakivi is protected as a natural monument outlined in the Nature Conservation Act.

Near Kummakivi erratic there is a moss bridge or “sammalsilta” in Finnish, across Pitkäjärvi lake. The bridge was built by the Kaukas company in the 1930s and its original purpose was to shorten the distance of forest workers traveling from one side of Lake Pitkäjärvi to another. Today, the bridge serves Kummakivi erratic passers-by and other nature enthusiasts.

Kummakivi geology

Both the rôche moutonnée and the erratic boulder are mixed granite-cordierite-mica gneiss typical for the area, and the grooves and chatter marks tell of glacial erosion. The area emerged from underneath the continental ice sheet around 11,500 years ago, when the environment around Kummakivi differed drastically from that of today: instead of nestling in the shade of the forest, the boulder was perched on the shore of an ancient ice lake.

Also read the story of Kummakivi made in the Rural Explorer project. 

Image: goSaimaa