SHEEPBACK IN SOLAMÄKI AND ORSILAMPI IN VIMPELI
Sheepback in Solamäki is a great place to discover the geology of the area and to have a swim!
On the edge of the pond, which was created in the old sandpit, there is a small sheepback, which, despite its small size, is one of the most diverse places on the Kraatterijärvi Georeitti. The rock shows clear signs of the multi-stage development of the bedrock and a power of the continental glacier.
Can you find these signs?
The relative age of the most common rock types in the area is clearly visible. The older type of stone is a fine-grained grey mica schist. It was originally made of clay deposited at the bottom of ancient sea that turned into mica schist around 1,900 million years ago.
Here and there, the mica schist shows couple of centimetres long ovals, formed by fine-grained and coarse-grained formations, called concretions. Formed as a result of limestone minerals crystallisation into clay layer. They wore off at different pace, creating the beautiful structure we see now.
Granite pegmatite - coarse-grained pink stone is younger than other main types of rocks in the area. It formed deep in the earth's crust as a result of crystallisation. Pegmatites often contain quite rare minerals. In this pegmatite there are black tourmaline crystals. Other colour tourmalines are regarded as gemstones.
Here and there, the pegmatite shows fragments of mica schists. Some pieces of pegmatite have bent and broke since the crystallisation in the final stages of the mountain range creation. These structures are beautiful.
Find traces of a continental glacier
The geological report of sheepback contains a gap of almost 1,900 million years. This is typical for Finland, because rocks have not preserved, with the exception of Lake Lappajärvi and several other impact craters.
The continental glacier of the last glacial period engulfed our country's soil, removing and crushing boulders and fine-grained rocks. Boulders and rocks at the bottom of the slowly moving glacier scratched the surface showing us direction the glacier moved. The gouges are also clearly visible on sweepback in Solamäki. They formed at the bottom of a continental glacier that flowed from northwest to southeast about 10,000 years ago. The sheepback's streamlined shape and smooth surface are also the result of the power of the continental glacier.
There may also be other signs of a passing glacier. Large mass of glacier fractured the rock surface, causing fragmentary curves and cracks transverse to the direction of the glacier's movement. You can also see crossover gouges caused by the movement of older glaciers.
Text and photos that will help you find the traces: Kraatterijärvi Georeitti destination 16
Location of the Solamäki sheepback: link to Google Maps
