Hogback (geology)

In geology and geomorphology, a hogback is a long narrow ridge or series of hills with a narrow crest and steep slopes of nearly equal inclination on both flanks. Typically, this term is restricted to a ridge created by the differential erosion of outcropping, steeply dipping (greater than 30° - 40°), homoclinal, typically sedimentary strata. One side, its backslope, of a hogback consists of the surface (bedding plane) of steeply dipping rock stratum, which is called a "dip slope." Its other side, its escarpment or "frontslope" or "scarp slope", is an erosion face that cuts through the dipping strata that comprises the hogback. The name for this landform refers to its resemblance in outline to the back of a hog. It was named after a hogback, Hog's Back, of the North Downs in Surrey, England. This term is also used for any ridge with a sharp summit and steep slopes of nearly equal inclination on both flanks. It is sometimes applied to drumlins and, in Maine, to both eskers and ridges known as "horsebacks".

Hogbacks are a typical regional topographic expression of outcrops of steeply dipping strata, commonly sedimentary strata, that consist of alternating beds of hard, well-lithified strata, i.e. sandstone and limestone, and either weak or loosely cemented strata, i.e. shale, mudstone, and marl. The surface of a hard, erosion-resistant layer forms the back slope (dip-slope) of the hogback where weaker strata have been preferentially stripped off of it by erosion. The opposite slope that forms the front of a hogback, which is its escarpment or scarp, consists of a slope that cuts across the bedding of the strata. Because of the steeply dipping nature of the strata that forms a hogback, a slight shift in location may take place as the landscape is lowered by erosion, but it will be a matter of feet rather than miles, as might happen with cuestas.

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