Panhole
Encyclopedia
A panhole is a depressed, erosional feature found on flat or gently sloping rock. Panholes are the result of long-term weathering and are generally seen on bedrock or very large blocks of rock. Similar terms are gnamma (Australia), opferkessel (German, roughly “sacrificial basin”), “armchair hollows”, weathering pans (or pits) and solution pans (or pits). Other German names include kamenitza and kamenica. In Spanish they are tinajita.
In Namaqualand
these features are called !gau
These shallow solution basins, or closed depressions, tend to form on bare limestone
or silicate rock. They are also found on granitic rock. 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 15 centimeters
In the Sierra Nevada, California these features were termed weathering pits by Francois 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. 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.
The Australian aboriginal term gnamma, in particular, implies a depression capable of holding water at times.
A related concept is a "swirlhole": A hole in rock in a streambed eroded by eddying water, with or without sand or pebble abrasives. Swirlholes typically form at the bottoms of waterfall
s.
In Namaqualand
Namaqualand
Namaqualand is an arid region of Namibia and South Africa, extending along the west coast over and covering a total area of 170,000 square miles/440,000 km². It is divided by the lower course of the Orange River into two portions - Little Namaqualand to the south and Great Namaqualand to the...
these features are called !gau
These shallow solution basins, or closed depressions, tend to form on bare limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
or silicate rock. They are also found on granitic rock. 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 15 centimeters
In the Sierra Nevada, California these features were termed weathering pits by Francois 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. 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.
The Australian aboriginal term gnamma, in particular, implies a depression capable of holding water at times.
A related concept is a "swirlhole": A hole in rock in a streambed eroded by eddying water, with or without sand or pebble abrasives. Swirlholes typically form at the bottoms of waterfall
Waterfall
A waterfall is a place where flowing water rapidly drops in elevation as it flows over a steep region or a cliff.-Formation:Waterfalls are commonly formed when a river is young. At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens...
s.
Locations where panholes may be seen
- Beam Rocks, Forbes State ForestForbes State ForestForbes State Forest is a Pennsylvania state forest in Pennsylvania Bureau of Forestry District #4. The main offices are located in Laughlintown in Westmoreland County, Pennsylvania in the United States. Mount Davis, the highest peak in Pennsylvania, is located in the forest.The forest was named...
, Pennsylvania, USA - Shenandoah National ParkShenandoah National ParkShenandoah National Park encompasses part of the Blue Ridge Mountains in the U.S. state of Virginia. This national park is long and narrow, with the broad Shenandoah River and valley on the west side, and the rolling hills of the Virginia Piedmont on the east...
, Virginia, USA - Glacier PointGlacier Pointthumb|right|upright|Glacier Point, as seen from [[Yosemite Valley]]. In springtime, this cliff face is covered with dozens of freshets and tiny waterfalls from the snowmelt, the largest being [[Staircase Falls]]....
, Yosemite National Park, California, USA