Mires (peatland) are one of the younger natural phenomena in Rokua Geopark. The area started to form peatwhen the land rose above the surface of the water and peat formed in damp depressions. Initially the mires formed slowly. However, around 6,000 years ago the climate became colder and wetter, and the process began to speed up. Mires are damp and nutrient-rich habitats for plants and animals. They also offer interesting but sometimes challenging terrain for outdoor recreation.
There are several types of mire in Rokua Geopark. In the esker area you will encounter deep peat covering small areas at the base of kettle holes. Between the ancient shorelines there are narrow strips of marsh kilometres long. The flat lands surrounding the ridges, on the other hand, have wide areas of aapa mire. The marshes below the shoreline sand in Lake Oulujärvi are another special feature in one particular area. They came about as the water level of Lake Oulujärvi gradually rose, covering several shoreline marshes over a period of thousands of years. The marshes were subsequently covered by the sand carried by the waves. In shallow bays, today they feel like soft, bubbling sand on the lake bed.
The deepest kettle hole mire in Finland
Literally “the Well of Deepness”, Syvyydenkaivo is Finland’s deepest kettle hole with a measured depth of more than 50 metres. A kettle hole is a hole, depression typically filled by a lake or peat, resulting from the melting of a mass of ice trapped in glacial deposits. In this particular kettle hole a mire has formed at the bottom, eight metres thick, which covers part of the actual depth of the kettle hole.