Mushroom rocks
Encyclopedia
A mushroom rock, also called rock pedestal or a pedestal rock, is a naturally occurring rock whose shape, as its name implies, strikingly resembles a mushroom. The rocks are deformed in a number of different ways: the processing of erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
and weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
, glacial action or from a sudden disturbance. Mushroom rocks are related, but different to yardang
Yardang
A yardang is a streamlined hill carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion, dust and sand, and deflation. Yardangs become elongated features typically three or more times longer than wide, and when viewed from above, resemble the hull of...
and zeugen.
Erosion
Usually found in desertDesert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
areas, these rocks are formed over thousands of years when wind erosion of an isolated rocky outcrop progresses at a different rate at its bottom to that at its top. Abrasion by wind-borne grains of sand is most prevalent within the first 3 feet of the ground, causing the bases of outcrops to erode more rapidly than their tops. Running water can have the same effect. An example of this type of mushroom rock is the one in Timna Park, Israel (see photograph opposite).
Occasionally the chemical composition of the rocks can be an important factor; if the upper part of the rock is more resistant to erosion and weathering, it will erode more slowly than the base. Its formation has also been attributed to chemical weathering at the base of the rock due to the collection of dew near the surface.
A mushroom rock may ultimately form from a zeugen, an originally flat area of hard rock overlying soft rock, similar to the pattern of rocks which cause the formation of a 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...
. Weathering of the exposed hard rock layer eventually exposes the lower rock to erosion from wind, water, salt intrusion, etc., depending on local conditions. The layer of softer rock is more readily eroded, leading to the formation of a depression or blowout. The overlying harder rocks are resistant to this process, and may ultimately end up as isolated 'mushroom rocks' standing above the new, lower plain.
The nature of wind erosion is that it concentrates a few feet over the ground - wind speeds increase with height, but sediment load reduces. This means that the combination of highest sediment loads and fastest wind speed exist a few feet over the ground - leading to the characteristic narrowing of zeugen at this height.
Glacial action
In contrast to a mushroom rock formed by the process of erosion of a single rock, these mushrooms are a type of balancing rockBalancing rock
A balancing rock, also called balanced rock or precarious boulder, is a naturally occurring geological formation featuring a large rock or boulder, sometimes of substantial size, resting on other rocks, bedrock or on glacial till. Some formations known by this name only appear to be balancing but...
formed from two separate rocks, one of which has come to rest on the top of the other. Typically the uppermost rock has been transported and deposited by the very slow action of a glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
; the lower part of the rock formation might or might not have also undergone a degree of erosion to accentuate the mushroom shape. Examples of this type of rock are 'Mushroom Rock' in Signal Point National Park, Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...
, and Le Champignon in Huelgoat
Huelgoat
Huelgoat is a commune in the Finistère department of Brittany in northwestern France.-Population:Inhabitants of Huelgoat are called in French Huelgoatains.-Geography:...
, France.
Rock disturbance
This type of mushroom rock is formed from two rocks, one of which has come to rest on the top of the other, caused by a very sudden disturbance such as a rock fall or earthquakes.Examples
- Ciudad EncantadaCiudad EncantadaThe Ciudad Encantada is a geological site near the city of Cuenca, in Castile La Mancha, Spain in which the erosive forces of weather and the waters of the nearby Júcar river have formed rocks into distinctive and memorable shapes....
, CuencaCuenca, Spain-History:When the Iberian peninsula was part of the Roman Empire there were several important settlements in the province, such as Segóbriga, Ercávica and Gran Valeria...
, Spain - Mushroom Rock State ParkMushroom Rock State ParkMushroom Rock State Park, located in the Smoky Hills region of Kansas, is noted for its mushroom rock formations. These rocks were formed through a process of nonuniform erosion and weathering in which a hard mass of Dakota Sandstone resisted erosion while the underlying softer stone weathered...
, Kansas - The stone mushroomsThe stone mushroomsThe Stone Mushrooms is a rock phenomenon near Beli Plast village in Bulgaria, on the road between Haskovo and Kardzhali. They are about 2.5 metres tall. The 3 hectares area is declared as natural resource on May 13, 1974 according to №РД-552 bill of the Ministry of Environment and Water...
, Bulgaria