The hummocky peatlands are fairly common in Finland. Peatlands with hummock ridges are rare in southern Finland but become more common in northern parts of the country.
In the incompletely drained flark fens the development of the hummocks can be studied particularly well because they can be found in different development phases there. The phenomenon is more common in drained peatlands than in the peatland on their natural state.
The development of the hummock ridges is close related to development of the hummocks. The hummock ridges are formed only under certain circumstances.
Height increment of the hummock ridges is restricted by the same factors that prevent the unrestricted height increment of the hummocks. The hummock ridge may sink due to its own weight in unfrozen swamp, it may be eroded by frost, wind, flowing water or ice. Dead trees, shading or other detriments may prevent the growth of secondary peat.