thumb|Earth hummocks in England
In geology, a hummock is a small knoll or mound above ground. They are typically less than in height and tend to appear in groups or fields. Large landslide avalanches that typically occur in volcanic areas are responsible for formation of hummocks. From the initiation of the landslide to the final formation, hummocks can be characterized by their evolution, spatial distribution, and internal structure. As the movement of the landslide begins, the extension faulting results in formation of hummocks, with smaller ones at the front of the landslide and larger ones in the back. The size of the hummocks is dependent on their position in the initial mass. As this mass spreads, the hummocks further modify to either break up or to merge and form larger structures. 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.
thumb|Ice hummocks
Bog hummocks
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
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
thumb|Cryogenic earth hummocks on [[Mount Kenya]]
Cryogenic earth hummocks go by various names; in North America they are known as earth hummocks; the Icelandic term (pl. ) is also used to describe them in Greenland and Iceland, and the Finnish term (pl. ) in Fennoscandia. These cold-climate landforms appear in regions of permafrost and seasonally frozen ground. 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.
Cellular circulation
Hummock excavation normally reveals a disturbed soil profile, often with irregular streaks of organic matter or other colorations suggesting fluidity at some point in the past. These events are fast-moving, gravity-driven currents of saturated debris that do not necessarily include juvenile material. Debris avalanche deposits are characterized by the debris-avalanche block (hummocks) and the debris-avalanche matrix. Debris avalanches are diagnosed for landscapes where the volcano has an amphitheater at the source with hummocky terrain downhill. In some cases, such as Mount Shasta in California, the amphitheater has been filled in by later volcanic activity and all that remains are the hummocks.
Debris avalanche blocks are identifiable because they keep their internal stratigraphy. The blocks simply break off the mountain and slide down, completely intact, identifiable because they differ from the surrounding landscape.