Hummock

A hummock is a small knoll or mound above ground. They are typically less than 15 meters in height and tend to appear in groups or fields. It is difficult to make generalizations about hummocks because of the diversity in their morphology and sedimentology. An extremely irregular surface may be called hummocky.

An ice hummock is a boss or rounded knoll of ice rising above the general level of an ice-field. Hummocky ice is caused by slow and unequal pressure in the main body of the packed ice, and by unequal structure and temperature at a later period.

Hummocks in the shape of low ridges of drier peat moss typically form part of the structure of certain types of raised bog, such as plateau, kermi, palsa or string bog. The hummocks alternate with shallow wet depressions or flarks.

Swamp hummocks are mounds typically initiated as fallen trunks or branches covered with moss and rising above the swamp floor. The low-lying areas between hummocks are called hollows. A related term, used in the Southeastern United States, is "hammock".

Cryogenic earth hummocks go by many different names; in North America they are earth hummocks; thúfur in Greenland and Iceland; and pounus in Fennoscandia. These cold climate landforms appear in regions of permafrost and seasonally frozen ground. They usually develop in fine-grained soils with light to moderate vegetation in areas of low relief where there is adequate moisture to fuel cryogenic processes.

Cryogenic earth hummocks appear in a variety of cold-ground environments, making the story of their genesis complex. Geologists recognize that hummocks may be polygenetic and form by a combination of forces that are yet to be well understood.

Recent research on cryogenic hummocks has focused on their role as environmental indicators. Because hummocks can both form and disintegrate rapidly (well within a human lifetime) they are an ideal landform to monitor for medium range environmental change. There are several explanations of earth hummock formation.

Hummocks may form as a result of clasts migrating to the surface through frost push and pull mechanisms. As the clasts rise they push up on the ground above forming bulging mounds.

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