Pothole (landform)

For other uses, see Pothole (disambiguation).

In Earth science, a pothole is a smooth, bowl-shaped or cylindrical hollow, generally deeper than wide, found carved into the rocky bed of a watercourse. Other names used for riverine potholes are pot, (stream) kettle, giant's kettle, evorsion, hollow, rock mill, churn hole, eddy mill, and kolk.[1] Although somewhat related to a pothole in origin, a plunge pool (or plunge basin or waterfall lake) is the deep depression in a stream bed at the base of a waterfall. It is created by the erosional forces of turbulence generated by water falling on rocks at a waterfall's base where the water impacts.[2] Potholes are also sometimes referred to as swirlholes. This word was created to avoid confusion with an English term for a vertical or steeply inclined karstic shaft in limestone. However, given widespread usage of this term for a type of fluvial sculpted bedrock landform, pothole is preferred in usage to swirlhole.[3]

The term pothole is also used to refer to other types of depressions and basins that differ in origin.[1] For example, some authors[4][5] refer to panholes found in the Colorado Plateau also as potholes. Other terms used for panholes are gnamma (Australia), Opferkessel (German; “sacrificial cauldron”), armchair hollows, weathering pans (or pits) and solution pans or solution pits.[6] In another case, the term pothole is used to refer to a shallow depression, generally less than 10-acre (4.0 ha) in area that occurs between dunes or on subdued morainic relief on a prairie, as in Minnesota and the Dakotas, and often contains an intermittent pond or marsh that serves as a nesting place for waterfowl.[1]

Origin

The consensus of geomorphologists and sedimentologists is that fluvial potholes are created by the grinding action of either a stone or stones or coarse sediment (sand, gravel, pebbles, boulders), whirled around and kept in motion by eddies within and force of the stream current in a given spot. Being a spectacular feature of bedrock river channels, they have been and still are studied extensively and considered as a key factor in bedrock channel development and morphology and important factor in the incision of bedrock channels.[3][7][8]

References

  1. ^ a b c Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds., 2011. Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 800 pp. ISBN 0-922152-89-6
  2. ^ Marshak, Stephen, 2009. Essentials of Geology, W. W. Norton & Company, 3rd ed. ISBN 978-0393196566
  3. ^ a b Richardson, K. and Carling, P., 2005. A typology of sculpted forms in open bedrock channels. Special Paper 392. Boulder, Colorado: Geological Society of America. 108 pp. ISBN 0-813723-92-2
  4. ^ Chan, M.A., Moser, K., Davis, J.M., Southam, G., Hughes, K. and Graham, T., 2005. Desert potholes: ephemeral aquatic microsystems. Aquatic Geochemistry, 11(3), pp. 279-302.
  5. ^ Hughes, Kebbi A., 2012. Bacterial Communities and their Influence on the Formation and Development of Potholes in Sandstone Surfaces of the Semi-Arid Colorado Plateau University of Western Ontario - Electronic Thesis and Dissertation Repository. Paper 543.
  6. ^ Twidale, C.R., and Bourne, J.A., 2018. Rock basins (gnammas) revisited. Géomorphologie: Relief, Processus, Environnement, Articles sous presse, Varia, mis en ligne le 08 janvier 2018, consulté le 01 juillet 2018.
  7. ^ Das, B.C., 2018. Development of Streambed Potholes and the Role of Grinding Stones. Journal of Environmental Geography. 11 (1–2), 9–16.
  8. ^ Whipple, K.X., Hancock, G.S., and Anderson, R.S., 2000. River Incision Into Bedrock: Mechanics And Relative Efficacy Of Plucking, Abrasion And Cavitation. Geological Society Of America Bulletin. 112, 490–503.
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