{{short description| Depression or basin eroded into flat or gently sloping cohesive rock}} [[File:Panholes granite Corsica.jpg|thumbnail|Panholes on a granite surface near Corscia, Corsica]] A '''panhole''' or '''weathering pit''' is a depression or basin eroded into flat or gently sloping cohesive rock.<ref name=TwidaleOthers2018a>Twidale, C.R., and Bourne, J.A., 2018. [http://journals.openedition.org/geomorphologie/11880 ''Rock basins (gnammas) revisited. ''] Géomorphologie: Relief, Processus, Environnement, Articles sous presse, Varia, mis en ligne le 08 janvier 2018, consulté le 01 juillet 2018.</ref> Similar terms for this feature are '''gnamma'''<ref name=wam>{{cite web | title=Gnamma Holes | website=Western Australian Museum |date =2017| url=https://museum.wa.gov.au/explore/wa-goldfields/water-arid-land/gnamma-holes | access-date=5 November 2021}}</ref> or '''rock holes'''<ref name=hiltaba>{{cite web | last=Jonscher | first=Samantha | title=SA students take to the bush to connect with land and Indigenous culture | website=ABC News |publisher= Australian Broadcasting Corporation | date=3 June 2018 | url=https://www.abc.net.au/news/2018-06-04/outback-classroom-program-teaches-kids-about-culture/9821236 | access-date=9 January 2022}}</ref> (Australia), '''armchair hollows''', '''weathering pans''' and '''solution pans''' (or '''pits''').<ref name=TwidaleOthers2018a/><ref name="Hughes2012a">Hughes, Kebbi A., 2012. [http://ir.lib.uwo.ca/etd/543 ''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.</ref>
Some authors<ref name= Hughes2012a /> 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.<ref name="NeuendorfOthers2011a">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}}</ref>
==Description == [[File:Carn Brea Cup and Saucer Rock.jpg|thumb|Weathering pits on the "Cup and Saucer Rock" at Carn Brea.]] 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 granitic rocks and sandstone. They are generally characterized by flat bottoms and sometimes by overhanging sides. The initial form may be a closed hollow created by a patch of humus. Diameters are rarely greater than {{convert|6|ft|m|abbr=on}}.<ref name="Paradise">Paradise, T. R., 2013 '[https://www.researchgate.net/profile/Thomas_Paradise/publication/287831478_Tafoni_and_Other_Rock_Basins/links/5f6a184292851c14bc8e164f/Tafoni-and-Other-Rock-Basins.pdf Tafoni and Other Rock Basins]' in ''Treatise on Geomorphology'', V.4, 111-126 {{doi|10.1016/B978-0-12-374739-6.00068-3}}</ref> Some panholes were at one time thought to be man-made because their roundness was so perfect they were argued not be natural and must have been shaped by humans.<ref name=TwidaleOthers2018a/><ref name="Hughes2012a"/>
Panholes are most commonly found in desert environments such as the Colorado Plateau. A few well-known panholes are found developed in sandstone surfaces in Canyonlands National Park, Capitol Reef National Park, and Moab. Panholes are capable of collecting water when it rains, freezing over when the weather gets cold, dry out in hotter weather, and can even contain some species of bacteria, lichens, mosses, and blue-green algae.<ref name="Paradise" /> Panholes range in size from a few centimeters to many meters in diameter. The cavities can be shallow or more than {{convert|15|m|ft|sp=us}} deep, containing hundreds of liters of water.
The Australian Aboriginal term ''gnamma'', in particular, implies a depression capable of holding water in arid areas, forming an important water resource for Aboriginal people that needed to be carefully maintained.<ref name =wam/><ref>Timms, B.V., 2013. [https://www.rswa.org.au/publications/Journal/96(1)/ROY%20SOC%2096.1%20BV%20TIMMS%20P7-16.pdf Geomorphology of pit gnammas in southwestern Australia] ''Journal of the Royal Society of Western Australia'', 96: 7–16 Retrieved 2 November 2020.</ref> Although initially formed naturally, gnammas used for water capture were maintained, and some enlarged, by Aboriginal people; others were used to trap lizards for food.<ref>Jones, Rhys, and Kavanagh, Eliza (30 December 2025). [https://www.abc.net.au/news/2025-12-30/noongar-elders-say-sacred-site-warnings-were-ignored-before-burn/106086072 Noongar elders say WA prescribed burn went ahead despite warnings of cultural heritage sites], ''ABC News''. Retrieved 30 December 2025.</ref>
Within the panholes is a varied eco-system that contains bacteria such as cyanobacteria, fungi, and algae which can be referred to as biofilm.<ref name= Hughes2012a/> Diverse communities of invertebrates are also often present, with insect and crustacean filter-feeders contributing the majority of the eukaryote biomass.<ref name=":0">{{Cite journal |last=Hedges |first=Brock A. |last2=Beasley-Hall |first2=Perry G. |last3=Dorey |first3=James B. |last4=Weinstein |first4=Philip |last5=Austin |first5=Andrew D. |last6=Guzik |first6=Michelle T. |date=2025-12-23 |editor-last=Özkundakci |editor-first=Deniz |title=Environmental DNA reveals temporal and spatial variability of invertebrate communities in arid-lands ephemeral water bodies |url=https://connectsci.au/mf/article/76/18/MF24243/266028/Environmental-DNA-reveals-temporal-and-spatial |journal=Marine and Freshwater Research |language=en |volume=76 |issue=18 |doi=10.1071/MF24243 |issn=1323-1650|url-access=subscription }}</ref> Panholes do not contain predators like fish, though smaller predators, such as aquatic insects are often present.<ref name=":1">{{Cite journal |last=Hedges |first=Brock A. |last2=Austin |first2=Andy D. |last3=Conran |first3=John G. |last4=Taylor |first4=Gary S. |last5=Madden |first5=Chris P. |last6=Weinstein |first6=Philip |date=2021-07-03 |title=A likely association of damselflies with the habitat heterogeneity provided by the freshwater swamp lily, Ottelia ovalifolia, in Eyre Peninsula granite rock-holes, with a review of potential threats to this ephemeral habitat |journal=Transactions of the Royal Society of South Australia |volume=145 |issue=2 |pages=152–167 |doi=10.1080/03721426.2021.1996878 |issn=0372-1426}}</ref><ref name=Davis2013a>Davis, Jim, 2013. [http://geology.utah.gov/surveynotes/gladasked/gladpotholes.htm "What are "Potholes" and how are organisms able to live in them?."] Utah Geological Survey. N.p., n.d. Web. 9 Oct 2013.</ref> The biofilm breaks down some of the siliceous minerals in the panhole for nutrients resulting in furthering the weathering the panhole.<ref name=Davis2013a/> The organisms that live in the panholes have to tolerate rapid change in water temperature, pH, oxygen, carbon dioxide concentration, and ion concentration.<ref name= Hughes2012a/>
==Origin== [[File:Weathering pits - granitic rock - Glacier Point, Yosemite National Park, California.jpg|thumb|Panholes in granodiorite at Glacier Point, Yosemite National Park, California]] In the Sierra Nevada, California these features were termed '''weathering pits'''<ref>Matthes, Francois E. 1930. Geologic History of the Yosemite Valley. U.S. Geological Survey Professional Paper 160</ref> 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.<ref>Huber, N. King. 1989. The geological story of Yosemite National Park. U.S. Geological Survey Bulletin 1595.</ref> 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.<ref>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.</ref> 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.<ref name= Hughes2012a />
A 2020 study concluded that weathering pits are generally formed by standing water in depressions on a flat near-horizontal rock surface due to weathering actions involving water.
== Age == Several studies from various parts of the world have attempted to date the age of weathering pits using cosmogenic radionuclide dating and therefore ascertain the rate at which they form. It has been suggested that the rate of deepening of the pits follows a sigmoidal rate of change, similarly to other tafoni weathering structures,<ref name=":2">{{Cite journal |last=Hall |first=Adrian Malcom |last2=Phillips |first2=William Morton |date=2006 |title=Weathering pits as indicators of the relative age of granite surfaces in the cairngorm mountains, scotland |url=https://www.tandfonline.com/doi/full/10.1111/j.0435-3676.2006.00290.x |journal=Geografiska Annaler: Series A, Physical Geography |language=en |volume=88 |issue=2 |pages=135–150 |doi=10.1111/j.0435-3676.2006.00290.x |issn=0435-3676|url-access=subscription }}</ref> and that the rate of weathering is dependent on local climatic conditions.<ref name=":3">{{Cite journal |last=Wang |first=Wei |last2=Huang |first2=Rihui |last3=Feng |first3=Jing |date=April 2020 |title=A new method for determining weathering rates in weathering pits |url=https://onlinelibrary.wiley.com/doi/10.1002/esp.4803 |journal=Earth Surface Processes and Landforms |language=en |volume=45 |issue=5 |pages=1262–1272 |doi=10.1002/esp.4803 |issn=0197-9337|url-access=subscription }}</ref>
To ascertain the rate of weathering of the pits the rate of weathering of the surrounding rock surface must be controlled. For granite tors in the Cairngorms, one study estimated this to be 4.1 ± 0.2 mm/1000 years.<ref>{{Cite journal |last=Phillips |first=William M. |last2=Hall |first2=Adrian M. |last3=Mottram |first3=Ruth |last4=Fifield |first4=L. Keith |last5=Sugden |first5=David E. |date=2006-02-01 |title=Cosmogenic 10Be and 26Al exposure ages of tors and erratics, Cairngorm Mountains, Scotland: Timescales for the development of a classic landscape of selective linear glacial erosion |url=https://www.sciencedirect.com/science/article/pii/S0169555X05002618 |journal=Geomorphology |volume=73 |issue=3 |pages=222–245 |doi=10.1016/j.geomorph.2005.06.009 |issn=0169-555X|url-access=subscription }}</ref> {| class="wikitable" |+ ! rowspan="2" |Location ! rowspan="2" |Lithology ! colspan="2" |Rate (mm/1000 years) ! rowspan="2" |Source |- !Min !Max |- |Cairngorms | rowspan="4" |Granite |3.3 |8 |<ref name=":2" /> |- |Brittany |4 |30 |<ref>{{Cite journal |last=Lageat |first=Yannick |last2=Sellier |first2=Dominique |last3=Twidale |first3=Charles R. |date=2007-11-23 |title=Mégalithes et météorisation des granites en Bretagne littorale, France du nord-ouest |url=http://id.erudit.org/iderudit/032976ar |journal=Géographie physique et Quaternaire |volume=48 |issue=1 |pages=107–113 |doi=10.7202/032976ar |issn=1492-143X}}</ref> |- |Lapland |2 |3.5 |<ref>{{Cite journal |last=André |first=Marie-Françoise |date=2002 |title=Rates of Postglacial Rock Weathering on Glacially Scoured Outcrops (Abisko-Riksgränsen Area, 68°N) |url=https://www.jstor.org/stable/3566131 |journal=Geografiska Annaler. Series A, Physical Geography |volume=84 |issue=3/4 |pages=139–150 |issn=0435-3676}}</ref> |- |Shanxi |10.8 ± 0.49 |20.0 ± 9.06 |<ref name=":3" /> |}
==Terminology== [[File:Hiltaba rock hole.jpg|thumb|Rock hole in Hiltaba Nature Reserve, South Australia]] ===Australia=== In Australia, the terms "gnamma" and "rock hole" (or "rockhole") are used. Gnamma is an anglicization of a Nyoongar language word, used by the Aboriginal people of Western Australia to describe a naturally formed rock hole as well as its retained rainwater. The term "gnamma hole" is also widely used, but is incorrect, being a tautology.<ref>{{ cite journal| journal=Journal of the Royal Society of Western Australia| issue= 96|page= 7|date= 2013| author= Timms, B. V.| url=https://www.rswa.org.au/publications/Journal/96(1)/ROY%20SOC%2096.1%20BV%20TIMMS%20P7-16.pdf| title=Geomorphology of pit gnammas in southwestern Australia|access-date= 9 January 2022}}</ref><ref name=hiltaba/><ref name=wam/>
==Locations == ===Australia=== *Eyre Peninsula<ref name=":1" /> South Australia *Fraser Range,<ref>{{Cite journal |last=McDonald |first=Rupert |last2=Bateman |first2=Philip W. |last3=Cooper |first3=Christine |last4=van der Heyde |first4=Mieke |last5=Mousavi-Derazmahalleh |first5=Mahsa |last6=Hedges |first6=Brock A. |last7=Guzik |first7=Michelle T. |last8=Nevill |first8=Paul |date=2023 |title=Detection of vertebrates from natural and artificial inland water bodies in a semi-arid habitat using eDNA from filtered, swept, and sediment samples |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ece3.10014 |journal=Ecology and Evolution |language=en |volume=13 |issue=4 |article-number=e10014 |doi=10.1002/ece3.10014 |issn=2045-7758 |pmc=10126312 |pmid=37113520}}</ref> Western Australia *Hiltaba Nature Reserve,<ref name=":0" /> South 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
== See also ==
* Tafoni - general term for cavities in granular rock.
==References== {{reflist}}
Category:Landforms Category:Depressions (geology)