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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.〔Huggett, JR (2011) ''Fundamentals of Geomorphology,'' 3rd ed., Routledge, New York. 516 pp. ISBN 978-0415567756〕〔Cotton, CA (1952) ''Geomorphology An Introduction to the Study of Landforms, 6th ed.'' John Wiley and Sons, New York. 505 pp.〕〔Fairbridge, RW (1968) ''Hogback and Flatiron.'' In RW Fairbridge, ed., pp. 524-525, ''The Encyclopedia of Geomorphology'' (Encyclopedia of Earth Sciences, Volume III), Reinhold, New York, 1296 pp. ISBN 978-0879331795〕〔Jackson, JA, J Mehl and K Neuendorf (2005) ''Glossary of Geology.'' American Geological Institute, Alexandria, Virginia. 800 pp. ISBN 0-922152-76-4〕 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.〔〔Thornbury, W. D., 1954, "Principles of Geomorphology'' New York, John Wiley & Sons, 618 pp.〕
All gradations occur between hogbacks, homoclinal ridges, and cuestas. The differences between these landforms are related to the steepness in dip of the resistant beds from which they have been eroded and to their geographic extent. Where hogback, homoclinal ridges, and cuestas occur depends upon whether the local rock attitudes are either nearly vertical, moderately dipping, or gently dipping. Because of their gradational nature, the exact angle of dip and slope that separates these landforms is arbitrary and some differences in the specific angles used to define these landforms can be found in the scientific literature. In addition, it also can be difficult to distinguish sharply immediately adjacent members of this series of landforms because of their gradational nature.〔〔
==Examples of Hogbacks==
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