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Progress in Physical Geography, Vol. 29, No. 2, 139-155 (2005)
DOI: 10.1191/0309133305pp440ra

Aspects of the geomorphology, genesis and environmental significance of earth hummocks (thúfur, pounus): miniature cryogenic mounds

Stefan Grab

School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, P/Bag 3, WITS 2050, South Africa

Miniature varieties of cryogenic mounds that are capable of forming in seasonally frozen ground are commonly referred to as earth hummocks (e.g., North America), thúfur (e.g., Greenland and Iceland) and pounus (Fennoscandia). Over the past few decades there has been a consistent interest to study earth hummocks from a variety of environmental settings. This review summarizes the current knowledge of earth hummocks, highlighting aspects on the external and internal morphology, and thermal characteristics, which may assist to explain hummock formation. Several hypotheses have been proposed for the genesis of earth hummocks, including the ‘cryoexpulsion’ of clasts, hydrostatic and cryostatic pressure, cellular circulation, and differential frost heave. These hypotheses are critically evaluated and some research gaps identified. It emerges that considerable advances have been made towards an improved understanding of earth hummock development, modification and disintegration. Much progress has been made in the application of earth hummock studies to a variety of environmental research approaches such as palaeoenvironmental reconstructions and assessing their impact on hillslope drainage.

Key Words: earth hummocks • environmental significance • genesis • morphology • review


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