Panhole
A panhole is a depression or basin eroded into flat or gently sloping cohesive rock.[1] Similar terms for this feature are gnamma[2] or rock holes[3] (Australia), armchair hollows, weathering pans (or pits) and solution pans (or pits).[1][4]
Some authors[4] refer to panholes also as potholes, which is a term typically used for similarly shaped riverine landforms. In fluvial geomorphology, the term pothole is typically used for a smooth, bowl-shaped or cylindrical hollow, generally deeper than wide, found developed in the rocky bed of a stream. This type of feature is created by the grinding action either of a stone or stones or of coarse sediment whirled around and kept in motion by eddies or the force of the stream current in a given spot.[5]
Description of panholes
Panholes are erosional or destructional features that are developed in a variety of climatic environments and in a wide range of rock types. These shallow basins, or closed depressions, are quite commonly well developed in surfaces of
Panholes are most commonly found in
Within the panholes is a varied eco-system that contains bacteria such as cyanobacteria, fungi, and algae which can be referred to as biofilm.[4] Panholes do not contain predators like fish or aquatic insects.[8] The biofilm breaks down some of the siliceous minerals in the panhole for nutrients resulting in furthering the weathering the panhole.[8] The organisms that live in the panholes have to tolerate rapid change in water temperature, pH, oxygen, carbon dioxide concentration, and ion concentration.[4]
Origin of panholes
In the Sierra Nevada, California these features were termed weathering pits[9] by François E. Matthes, where they are thought to indicate rock surfaces that are unglaciated or escaped more recent glaciations. In Sierra Nevada granitic rocks, these features have a characteristic shape such that they expand more rapidly in width than they grow in depth.[10] One explanation for their conformation is because the most active environment for weathering is the zone of alternate wetting and drying along the margins of the pools that collect in the pits, the margins tend to deepen and enlarge until all points of the bottom are equally wet or dry at the same time, thus producing their characteristic shape.[11] Panholes can expand from weathering and erosion but the main activity of how panholes expand is from biological weathering. At one time the belief was that the only agents involved with the expansion of panholes were physical weathering.[4]
Terminology
Australia
In Australia, the terms "gnamma" and "rock hole" (or "rockhole") are used. Gnamma is an anglicization of a
Locations
Australia
United States
- Beam Rocks, Forbes State Forest, Pennsylvania
- Canyonlands National Park, Utah
- Glacier Point, Yosemite National Park, California
- Navajo National Monument, Arizona
- Shenandoah National Park, Virginia
- Stone Mountain, Georgia
- Stone Mountain (North Carolina), North Carolina
References
- ^ a b c 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.
- ^ a b c "Gnamma Holes". Western Australian Museum. 2017. Retrieved 5 November 2021.
- ^ a b Jonscher, Samantha (3 June 2018). "SA students take to the bush to connect with land and Indigenous culture". ABC News. Australian Broadcasting Corporation. Retrieved 9 January 2022.
- ^ a b c d e f 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.
- ISBN 0-922152-89-6
- ^
- ^ Timms, B.V., 2013. Geomorphology of pit gnammas in southwestern Australia Journal of the Royal Society of Western Australia, 96: 7–16 Retrieved 2 November 2020.
- ^ a b Davis, Jim, 2013. "What are “Potholes” and how are organisms able to live in them?." Utah Geological Survey. N.p., n.d. Web. 9 Oct 2013.
- ^ Matthes, Francois E. 1930. Geologic History of the Yosemite Valley. U.S. Geological Survey Professional Paper 160
- ^ Huber, N. King. 1989. The geological story of Yosemite National Park. U.S. Geological Survey Bulletin 1595.
- ^ Clyde Warhaftig, attributed on page p. 63 in Huber, N. King. 1989. The geological story of Yosemite National Park. U.S. Geological Survey Bulletin 1595.
- ^ Timms, B. V. (2013). "Geomorphology of pit gnammas in southwestern Australia" (PDF). Journal of the Royal Society of Western Australia (96): 7. Retrieved 9 January 2022.