From en.wikipedia.org:
[Polygonal stone columns] [date=July 2023] [List of places with columnar
jointed volcanics] thumbnail COLUMNAR JOINTING is a geological structure where
sets of intersecting closely spaced fractures, referred to as joints, result
in the formation of a regular array of polygonal prisms, or columns. Columnar
jointing occurs in many types of igneous rocks (e.g. basalt, andesite,
rhyolite, tuff), and forms as the rock cools and contracts. Columnar jointing
can occur in cooling lava flows and ashflow tuffs (ignimbrites), as well as in
some shallow intrusions.<ref name="Oregon" /> Columnar jointing also occurs
rarely in sedimentary rocks, due to a combination of dissolution and
reprecipitation of interstitial minerals (often quartz or cryptocrystalline
silica) by hot, hydrothermal fluids and the expansion and contraction of the
rock unit, both resulting from the presence of a nearby magmatic intrusion.[1]
The columns can vary from 3 meters to a few centimeters in diameter, and can
be as much as 30 meters tall.<ref name="Oregon" /> They are typically parallel
and straight, but can also be curved and vary in diameter.<ref name="Oregon"
/> An array of regular, straight, and larger-diameter columns is called a
colonnade; an irregular, less-straight, and smaller-diameter array is termed
an entablature.[2] The number of sides of the individual columns can vary from
3 to 8, with 6 sides being the most common.[3]
** Physics
When magma or lava cools into solid igneous rock, for example basalt, much
heat still remains. As it cools down further, the basalt contracts, and it
forms cracks to release the tensile energy. It then is cooled down further by
groundwater boiling and reflux.
When the cracks first form at the surface, the cracks are dominated by
T-junctions, like mudcracks, because they were formed individually. One crack
would form and move across the surface, until it hits upon a previous crack,
forming a T-junction.
Then, these cracks extend downwards in a moving front that is roughly planar
and parallel to the surface. As it moves, the crack pattern anneals to become
lower in energy. The speed _v_ at which the front moves is determined by the
groundwater flow rate. After the front moves a few meters deep, it would
evolve into a hexagonal grid with roughly equal width _L_. The width _L_ is
determined by the basalt's material properties, and the speed _v_ at which the
front moves.[4]
*** Scaling
Define Péclet number <math>Pe = \frac{Lv}{D}</math> where <math>D</math> is
the thermal diffusivity of the material. For all columnar jointing, the value
of _Pe_ is around 0.2, and thus the shape and speed of all columnar joints are
similar after scaling. A scaled model can be made by drying cornstarch a
centimeter thick, which creates columns about 1 mm wide.
For basalt, <math>Pe \approx 0.35</math>. For cornstarch, <math>Pe \approx
0.1</math>.<ref name=":0" />
** Places
[List of places with columnar jointed volcanics]
Some famous locations in the United States where columnar jointing can be
found are Devils Tower in Wyoming, Devils Postpile in California and the
Columbia River flood basalts in Oregon, Washington and Idaho. Other famous
places include the Giant's Causeway in Northern Ireland, Fingal's Cave on the
island of Staffa, Scotland and the Stuðlagil Canyon, Iceland.[5]
*** Devils Tower
[Devils Tower]
Devils Tower in Wyoming in the United States is about 40 million years old and
[382] high.<ref name="Oregon" /> Geologists agree that the rock forming Devils
Tower solidified from an intrusion, but it has not been established whether
the magma from this intrusion ever reached the surface. Most columns are
6-sided, but 4, 5, and 7-sided ones can also be found.[6]
*** Giant's Causeway
[Giant's Causeway] The Giant's Causeway (Irish: _Clochán An Aifir_) on the
north Antrim coast of Northern Ireland was created by volcanic activity 60
million years ago, and consists of over 40,000 columns.<ref name="Oregon"
/>[7] According to a legend, the giant Finn McCool created the Giant's
Causeway, as a causeway to Scotland.[8]
*** Sōunkyō Gorge
[Sōunkyō] Sōunkyō Gorge, a part of the town of Kamikawa, Hokkaido, Japan,
features a [24] stretch of columnar jointing, which is the result of an
eruption of the Daisetsuzan Volcanic Group 30,000 years ago.
*** Deccan Traps
[Deccan Traps] The late Cretaceous Deccan Traps of India constitute one of the
largest volcanic provinces of Earth, and examples of columnar jointing can be
found in St. Mary's Island in the state of Karnataka.[9]
*** High Island Reservoir
Formed in Cretaceous, the columnar rocks are found around the reservoir and
the islands nearby in Sai Kung, Hong Kong. It is special that the rocks are
not mafic, but felsic tuff instead.
*** Makhtesh Ramon
The columnar jointed sandstone of the _HaMinsara_ (Carpentry Shop) in the
makhtesh (erosion cirque) of Makhtesh Ramon, Negev desert, Israel.
*** Cerro Kõi
There are several examples of columnar jointed sandstones in the greater
Asunción region of Paraguay. The best known is Cerro Kõi in Areguá, but there
are also several quarries in Luque.
*** Mars
[Marte Vallis] Several exposures of columnar jointing have been discovered on
the planet Mars by the High Resolution Imaging Science Experiment (HiRISE)
camera, which is carried by the Mars Reconnaissance Orbiter (MRO).[10][11]
*** Sawn Rocks
Sawn Rocks, in Mount Kaputar National Park close to Narrabri, New South Wales,
Australia, features 40 meters of columnar jointing above the creek and 30
meters below the surface.[12]
*** Basaltic Prisms of Santa María Regla
[Basaltic Prisms of Santa María Regla] Alexander von Humboldt documented the
prisms located in Huasca de Ocampo, in the Mexican state of Hidalgo.
*** Columnar basalt of Tawau (Batu Bersusun)
At Kampung Balung Cocos, Tawau, Malaysia, the river flows through the area of
columnar basalt. One section is seen vertically high on river bank. The rest
lies on river bank. The water flows from the lowest area forming waterfall.
*** Gorge of Garni, Armenia
The Garni Gorge is situated 23 km east of Yerevan, Armenia, just below the
village of the same name. This portion of the Garni Gorge is typically
referred to as the "Symphony of the Stones." On a promontory above the gorge
the first-century AD Temple of Garni may be seen.
*** Stuðlagil Canyon, Iceland
[Stuðlagil]
The Stuðlagil Canyon, situated 45 miles west of Egilsstaðir, showing a view of
columnar joint basalts rock formations and the blue-green water that runs
through it.
*** Black Point, Australia
Black Point, situated in the D'Entrecasteaux National Park, in Western
Australia is an example of black columnar basalt.
*** Jusangjeolli, South Korea
The columnar jointing (_Jusangjeolli_ in Korean) on the southern coast near
Seogwipo on the island of Jeju is a popular tourist destination.
** See also
- Basalt fan structure
- Honeycomb conjecture
- Mudcrack
- Prism (geology)
- Syneresis crack
** References
References:
[1]. [last1=Velázquez]
[2]. [last1=Long ]
[3]. Oregon State University > Volcano World > ... > Columnar Jointing (see http://volcano.oregonstate.edu/columnar-jointing) . Accessed 29 December 2013.
[4]. [last1=Goehring ]
[5]. southernhebrides.com > Staffa - A Geological Marvel (see http://www.southernhebrides.com/staffa.html) . Accessed 29 December 2013.
[6]. U.S. National Park Service > Devils Tower > Geologic Formations (see https://home.nps.gov/deto/learn/nature/geologicformations.htm) . Accessed 29 December 2013.
[7]. National Trust > Giant's Causeway (see http://www.nationaltrust.org.uk/giants-causeway/history/) . Accessed 29 December 2013.
[8]. Northern Ireland Tourist Board > Causeway Coast & Glens > The Giant's Causeway > Folklore and Legend (see http://www.causewaycoastandglens.com/Myths-and-Legends.T1090.aspx) [url=https://web.archive.org/web/20150502071214/http://www.causewaycoastandglens.com/Myths-and-Legends.T1090.aspx ] . Accessed 29 December 2013.
[9]. Geological Survey of India > Columnar Basalt (see https://www.gsi.gov.in/webcenter/portal/OCBIS/page17/pageGEOTOURISM/page1155) Retrieved 17 April 2020.
[10]. [url=https://www.uahirise.org/ESP_029286_1885]
[11]. [last=Milazzo ]
[12]. Sawn Rocks walking track, Mount Kaputar National Park (see https://www.nationalparks.nsw.gov.au/things-to-do/walking-tracks/sawn-rocks-walking-track) NSW National Parks and Wildlife Service. Retrieved 3 January 2019.
[Columnar igneous rocks]
** External links
- Aydin, A., and J. Zhong (nda) Columnar Joints (see https://web.archive.org/web/20140713211646/http://rockfracture.com/html2/ColumnarJoint.html) , Multiple Joint Sets (see https://web.archive.org/web/20140713211202/http://rockfracture.com/html2/MultipleJointSet.html) , Rock Fracture Knolwedgebase (see https://web.archive.org/web/20140713211128/http://rockfracture.com/html2/Index.html) , Stanford University, Stanford, California.
[Structural geology]
Category:Igneous rocks Category:Geomorphology Category:Structural geology
Category:Metamorphic rocks