columnar jointing

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.{{Cite journal |last1=Goehring |first1=Lucas |last2=Morris |first2=Stephen W. |date=2014-11-01 |title=Cracking mud, freezing dirt, and breaking rocks |url=https://pubs.aip.org/physicstoday/article/67/11/39/414529/Cracking-mud-freezing-dirt-and-breaking-rocksThe |journal=Physics Today |language=en |volume=67 |issue=11 |pages=39–44 |doi=10.1063/PT.3.2584 |issn=0031-9228}}

Define Péclet number $Pe\; =\; \backslash frac\{Lv\}\{D\}$ where $D$ 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, $Pe\; \backslash approx\; 0.35$. For cornstarch, $Pe\; \backslash approx\; 0.1$.

{{main article|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.[http://www.southernhebrides.com/staffa.html southernhebrides.com > Staffa - A Geological Marvel]. Accessed 29 December 2013.

{{main article|Devils Tower}}

File:"This means something. This is important" (19967592275).jpg in the Black Hills National Forest, Wyoming.]]

Devils Tower in Wyoming in the United States is about 40 million years old and {{convert|382|m|ft|abbr=off|sp=us}} high. 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.[http://www.nps.gov/deto/naturescience/geologicformations.htm U.S. National Park Service > Devils Tower > Geologic Formations]. Accessed 29 December 2013.

{{main article|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.[http://www.nationaltrust.org.uk/giants-causeway/history/ National Trust > Giant's Causeway]. Accessed 29 December 2013. According to a legend, the giant Finn McCool created the Giant's Causeway, as a causeway to Scotland.[http://www.causewaycoastandglens.com/Myths-and-Legends.T1090.aspx Northern Ireland Tourist Board > Causeway Coast & Glens > The Giant's Causeway > Folklore and Legend] {{Webarchive|url=https://web.archive.org/web/20150502071214/http://www.causewaycoastandglens.com/Myths-and-Legends.T1090.aspx |date=2015-05-02 }}. Accessed 29 December 2013.

{{main article|Sōunkyō}}

Sōunkyō Gorge, a part of the town of Kamikawa, Hokkaido, Japan, features a {{convert|24|km|adj=on}} stretch of columnar jointing, which is the result of an eruption of the Daisetsuzan Volcanic Group 30,000 years ago.

{{main article|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.[https://www.gsi.gov.in/webcenter/portal/OCBIS/page17/pageGEOTOURISM/page1155 Geological Survey of India > Columnar Basalt] Retrieved 17 April 2020.

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.

File:Hexagonal volcanic tuffs at East Dam of High Island Reservoir 1.jpg

The columnar jointed sandstone of the HaMinsara (Carpentry Shop) in the makhtesh (erosion cirque) of Makhtesh Ramon, Negev desert, Israel.

File:Cerro Koi 6520 11.jpg

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.

{{main article|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).{{Cite web|url=https://www.uahirise.org/ESP_029286_1885|title = HiRISE | Columnar Jointing on Mars and Earth (ESP_029286_1885)}}{{Cite journal |last=Milazzo |first=Moses |date=2009 |title=Discovery of columnar jointing on Mars |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/37/2/171/519456/Discovery-of-columnar-jointing-on-Mars |journal=Geology |volume=37 |issue=2 |pages=171–174|doi=10.1130/G25187A.1 }}

File:Martevallis hir 2007304 lrgMod1.png region, Mars. Image courtesy of the High Resolution Imaging Science Experiment, University of Arizona.]]

File:Sawn Rocks.jpg

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.[https://www.nationalparks.nsw.gov.au/things-to-do/walking-tracks/sawn-rocks-walking-track Sawn Rocks walking track, Mount Kaputar National Park] NSW National Parks and Wildlife Service. Retrieved 3 January 2019.

{{main article|Basaltic Prisms of Santa María Regla}}

Alexander von Humboldt documented the prisms located in Huasca de Ocampo, in the Mexican state of Hidalgo.

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.

File:Garni Gorge Armenia axxp.JPG

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.

{{main article|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, situated in the D'Entrecasteaux National Park, in Western Australia is an example of black columnar basalt.

The columnar jointing (Jusangjeolli in Korean) on the southern coast near Seogwipo on the island of Jeju is a popular tourist destination.

• Basalt fan structure
• Honeycomb conjecture
• Mudcrack
• Prism (geology)
• Syneresis crack

{{commons category|Columnar igneous rocks}}

• Aydin, A., and J. Zhong (nda) [https://web.archive.org/web/20140713211646/http://rockfracture.com/html2/ColumnarJoint.html Columnar Joints], [https://web.archive.org/web/20140713211202/http://rockfracture.com/html2/MultipleJointSet.html Multiple Joint Sets], [https://web.archive.org/web/20140713211128/http://rockfracture.com/html2/Index.html Rock Fracture Knolwedgebase], Stanford University, Stanford, California.

{{Structural geology}}

Category:Igneous rocks

Category:Geomorphology

Category:Structural geology

Category:Metamorphic rocks