Columnar jointing
Columnar jointingis a geological structure where sets of intersecting closely spaced fractures, referred to asjoints,result in the formation of a regular array of polygonalprisms(basalt prisms), or columns. Columnar jointing occurs in many types ofigneous rocksand forms as the rock cools and contracts. Columnar jointing can occur in coolinglava flowsand ashflowtuffs(ignimbrites), as well as in some shallowintrusions.[1]Columnar jointing also occurs rarely insedimentary rocks,due to a combination ofdissolutionandreprecipitationof interstitialminerals(oftenquartzorcryptocrystallinesilica) by hot,hydrothermalfluids and the expansion and contraction of the rock unit, both resulting from the presence of a nearbymagmatic intrusion.[2]
The columns can vary from 3 meters to a few centimeters in diameter, and can be as much as 30 meters tall.[1]They are typically parallel and straight, but can also be curved and vary in diameter.[1]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.[3]The number of sides of the individual columns can vary from 3 to 8, with 6 sides being the most common.[1]
Physics
[edit]When lava cools into 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 bygroundwaterboiling and reflux.
When the cracks first form at the surface, the cracks are dominated by T-junctions, likemudcracks,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 patternannealsto become lower in energy. The speedvat 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 widthL.The widthLis determined by the basalt'smaterial properties,and the speedvat which the front moves.[4]
Scaling
[edit]DefinePéclet numberwhereis thethermal diffusivityof the material. For all columnar jointing, the value ofPeis around 0.2, and thus the shape and speed of all columnar joints are similar after scaling. Ascaled modelcan be made by dryingcornstarcha centimeter thick, which creates columns about 1 mm wide.
For basalt,.For cornstarch,.[4]
Places
[edit]Some famous locations in the United States where columnar jointing can be found areDevils Towerin Wyoming,Devils Postpilein California and theColumbia Riverflood basaltsinOregon,WashingtonandIdaho.Other famous places include theGiant's CausewayinNorthern Ireland,Fingal's Caveon the island ofStaffa,Scotlandand theStuðlagilCanyon,Iceland.[5]
Devils Tower
[edit]
Devils Tower in Wyoming in the United States is about 40 million years old and 382 meters (1,253 feet) high.[1]Geologists agree that the rock forming Devils Tower solidified from an intrusion, but it has not been established whether themagmafrom 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
[edit]The Giant's Causeway (Irish:Clochán An Aifir) on thenorth Antrim coastof Northern Ireland was created by volcanic activity 60 million years ago, and consists of over 40,000 columns.[1][7]According to a legend, the giantFinn McCoolcreated the Giant's Causeway, as acausewayto Scotland.[8]
Sōunkyō Gorge
[edit]Sōunkyō Gorge, a part of the town ofKamikawa, Hokkaido,Japan, features a 24-kilometre (15 mi) stretch of columnar jointing, which is the result of an eruption of theDaisetsuzan Volcanic Group30,000 years ago.
Deccan Traps
[edit]The late CretaceousDeccan Trapsof India constitute one of the largest volcanic provinces of Earth, and examples of columnar jointing can be found inSt. Mary's Islandin the state of Karnataka.[9]
High Island Reservoir
[edit]Formed in Cretaceous, the columnar rocks are found around the reservoir and the islands nearby inSai Kung,Hong Kong.It is special that the rocks are not mafic, but felsictuffinstead.
Makhtesh Ramon
[edit]The columnar jointed sandstone of theHaMinsara(Carpentry Shop) in themakhtesh(erosioncirque) ofMakhtesh Ramon,Negev desert,Israel.
Cerro Kõi
[edit]There are several examples of columnar jointed sandstones in the greaterAsunciónregion ofParaguay.The best known is Cerro Kõi inAreguá,but there are also several quarries inLuque.
Mars
[edit]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 theMars Reconnaissance Orbiter(MRO).[10][11]
Sawn Rocks
[edit]
Sawn Rocks, inMount Kaputar National Parkclose toNarrabri,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
[edit]Alexander von Humboldt documented the prisms located in Huasca de Ocampo, in the Mexican state of Hidalgo.
Columnar basalt of Tawau (Batu Bersusun)
[edit]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
[edit]TheGarni Gorgeis 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
[edit]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.
See also
[edit]References
[edit]- ^abcdefOregon State University > Volcano World >... > Columnar Jointing.Accessed 29 December 2013.
- ^Velázquez, Victor F.; Giannini, Paolo C. F.; Riccomini, Claudio; Ernandes, Alethéa; Sallun, Martins; Hachiro, Jorge; de Barros Gomes, Celso (1 September 2008)."Columnar joints in the Patiño Formation sandstones, Eastern Paraguay: a dynamic interaction between dyke intrusion, quartz dissolution and cooling-induced fractures".Episodes.31(3). International Union of Geological Sciences: 302–308.doi:10.18814/epiiugs/2008/v31i3/003.ISSN2586-1298.
- ^Long, Philip E.; Wood, Bernard J. (1 September 1986)."Structures, textures, and cooling histories of Columbia River basalt flows".Geological Society of America Bulletin.97(9): 1144–1155.Bibcode:1986GSAB...97.1144L.doi:10.1130/0016-7606(1986)97<1144:STACHO>2.0.CO;2.
- ^abGoehring, Lucas; Morris, Stephen W. (1 November 2014)."Cracking mud, freezing dirt, and breaking rocks".Physics Today.67(11): 39–44.doi:10.1063/PT.3.2584.ISSN0031-9228.
- ^southernhebrides.com > Staffa - A Geological Marvel.Accessed 29 December 2013.
- ^U.S. National Park Service > Devils Tower > Geologic Formations.Accessed 29 December 2013.
- ^National Trust > Giant's Causeway.Accessed 29 December 2013.
- ^Northern Ireland Tourist Board > Causeway Coast & Glens > The Giant's Causeway > Folklore and LegendArchived2015-05-02 at theWayback Machine.Accessed 29 December 2013.
- ^Geological Survey of India > Columnar BasaltRetrieved 17 April 2020.
- ^"HiRISE | Columnar Jointing on Mars and Earth (ESP_029286_1885)".
- ^Milazzo, Moses (2009)."Discovery of columnar jointing on Mars".Geology.183(3): 171–174.doi:10.1016/S0012-821X(00)00307-1.
- ^Sawn Rocks walking track, Mount Kaputar National ParkNSW National Parks and Wildlife Service. Retrieved 3 January 2019.
External links
[edit]- Aydin, A., and J. Zhong (nda)Columnar Joints,Multiple Joint Sets,Rock Fracture Knolwedgebase,Stanford University, Stanford, California.
