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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 (basalt prisms), or columns. Columnar jointing occurs in many types of igneous rocks and forms as the rock cools and contracts.
Basalt columns seen on Porto Santo Island, Portugal. Columnar jointing of volcanic rocks exists in many places on Earth. Perhaps the most famous basalt lava flow in the world is the Giant's Causeway in Northern Ireland, in which the vertical joints form polygonal columns and give the impression of having been artificially constructed.
This type of jointing is typical of thick lava flows and shallow dikes and sills. [5] Columnar jointing is also known as either columnar structure, prismatic joints, or prismatic jointing. [6] Rare cases of columnar jointing have also been reported from sedimentary strata. [7]
Flood basalt commonly displays columnar jointing, formed as the rock cooled and contracted after solidifying from the lava.The rock fractures into columns, typically with five to six sides, parallel to the direction of heat flow out of the rock.
A solidified lava pond that consists of a massive gray basalt with weakly developed columnar jointing occupies the crater of Vulcan. Radial, sinuous lava tubes 8 to 20 inches (200 to 510 mm) across and 300 feet (91 m) long are preserved on the northeast and northwest flanks of Vulcan.
Valentine Cave, a lava tube in Lava Beds National Monument, California shows the classic tube shape; the grooves on the wall mark former flow levels. Thurston Lava Tube in Hawaii Volcanoes National Park, Hawaii. The step mark, more visible on the right wall, indicates the depth at which the lava flowed for a period of time.
It is named for jusangjeolli, the Korean term for columnar jointing. [1] The cliff was formed when the lava from the island's volcano Hallasan flowed into the sea of Jungmun. The lava formed many rocks that resemble columns of geometric shapes. It was designated as Natural Monument No. 443 [2] on January 6, 2005. [1]
It is the southernmost volcano in the Garibaldi Volcanic Belt, comprising about 0.02 km 3 (0.0048 cu mi) of hornblende, pyroxene and sparsely porphyritic dacite lava and breccia. The dacite is characterized by columnar joints, 5 to 40 cm (2.0 to 15.7 in) in diameter, and exhibiting locally