Fissure

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Ground cracks at an east west segment of Kamoamoa after it's 2011 fissure eruption. Geologist is about 6 ft tall.[1]

A fissure is a long narrow crack opening along the surface of an affected area. It is from the Latin word fissura which means a cleft or crack. Fissures emerge in the Earth's crust, on ice sheets and glaciers, and on volcanoes.

Ground fissure[edit]

Aerial view of the Almannagja fissure in Thingvellir National Park, Iceland

A ground fissure, also called an earth fissure is a long, narrow crack or linear opening in the surface layer of the Earth's crust resulting from ground subsidence.[2][3] They appear in rock formations and compacted soils containing a high percentage of fine-grained material primarily covering arid valleys and valley floors and occur when the ground above the water table subsides. They are generally thought to be caused by the extensive withdrawal of groundwater and aggravated by a prevalence of torrential rain. They can be hazardous to people and livestock living on the affected surfaces as well as property and infrastructure, such as roads, canals, and dams.[4][5][6] Fissures are considered anthropogenic hazards,[7] although natural phenomena such as earthquakes and volcanic activity can contribute to their emergence.[8]

Crevasse[edit]

A crevasse in the Tangra Mountains, Antarctica.

A crevasse also called an ice fissure is a deep linear crack in an ice sheet or glacier resulting from the opposing force produced by their movement at different rates of speed. The force builds until their associated shear stress is sufficient to break the ice along the faces. The breakage often forms vertical or near-vertical walls, which can melt and create seracs, arches, and other ice formations.[9] A crevasse may be as deep as 45 metres and as wide as 20 metres.[10] A crevasse may be covered, but not necessarily filled, by a snow bridge made of the previous years' accumulation and snow drifts. The result is that crevasses are rendered invisible, and extremely dangerous to anyone attempting to traverse a glacier.

Types of crevasses[edit]

Transverse crevasses in Chugach State Park, Alaska.
  • Longitudinal crevasses form parallel to the ice flow where the glacier width is expanding.[11]
  • Splaying crevasses appear along the edges of a glacier.
  • Transverse crevasses form in a zone of longitudinal extension where the principal stresses are parallel to the direction of glacier flow.[11]

See also[edit]

References[edit]

  1. ^ "Volcano Watch — A recap of the Kamoamoa fissure eruption on its third anniversary". www.usgs.gov. Retrieved 25 September 2021.
  2. ^ Lund, W.R.; DuRoss, C.B.; Kirby, S.M.; McDonald, G.N.; Hunt, G.; Vice, G.S. (2005). The Origin and Extent of Earth Fissures in Escalante Valley, Southern Escalante Desert, Iron County, Utah. Special Study. Utah Geological Survey. ISBN 978-1-55791-730-0. Retrieved 21 September 2021.
  3. ^ Inkenbrandt, P.; Lund, W.; Lowe, M.; Knudsen, T.; Bowman, S. (2014). Investigation of land subsidence and earth fissures in Cedar Valley, Iron County, Utah. Special Study. Utah Geological Survey. ISBN 978-1-55791-891-8. Retrieved 21 September 2021.
  4. ^ "Earth Fissures, Subsidence & Karst in Arizona". AZGS. 12 July 2017. Retrieved 21 September 2021.
  5. ^ "USGS: Volcano Hazards Program Glossary - Fissure". volcanoes.usgs.gov. Retrieved 21 September 2021.
  6. ^ Star, Tony Davis Arizona Daily. "Record Pinal County fissure shows Arizona is still prone to shifting earth levels". Arizona Daily Star. Retrieved 22 September 2021.
  7. ^ Carlson, Grace; Carnes, Lorraine K.; Cook, Joseph P. (4 September 2019). "Exploring Arizona earth fissures: An anthropogenic geologic hazard". doi:10.1130/2019.0055(04). Retrieved 24 September 2021.
  8. ^ Berkeley, UC. "The Mystery about Earthquake Fissures". seismo.berkeley.edu.
  9. ^ van der Veen, C (1990). "Crevasses on Glaciers". Polar Geography. 23 (3): 213–245. doi:10.1080/10889379909377677.
  10. ^ Crevasse by National Geographic
  11. ^ a b Holdsworth, G (October 1956). "Primary Transverse Crevasses". Journal of Glaciology. 8 (52): 107–129. doi:10.1017/S0022143000020797.

External links[edit]