The Ice Age has created the basis for the landscape and biodiversity in Hossa. Glacial streams made the steep eskers and the kettle holes. The most significant esker range runs from the Julma-Ölkky canyon lake, via Lake Laukkujärvi, and via the Hakoharju and Huosiharju Eskers, to the western shore of Öllöri Pond. The esker soil consists of coarser gravel underneath and finer sand on the surface.
The wooded moraine hills piled up by the continental ice sheet, such as Moilasenvaara Hill on the western edge of the national park, consist of richer till that has not been washed away so much by the Ice Age waters. The spruce is the dominant tree on these wooded hills, as a large amount of snow piles up on tree branches in these high-lying areas. The long branches of the pine can’t carry so much snow.