Search results
Results from the WOW.Com Content Network
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.
Learn more about WA volcanoes. Usually, the public is invited to Johnston Ridge Observatory on the anniversary of the disaster, for a view of the Mount St. Helens lava dome.
Subduction zones occur where an oceanic plate meets a continental plate and is pushed underneath it. Subduction zones are marked by oceanic trenches. The descending end of the oceanic plate melts and creates pressure in the mantle, causing volcanoes to form.
A volcano close to erupting in Iceland could explode like a “can of fizzy drink,” an expert has said. ... An eruption could happen anywhere along the magma dyke, Iceland’s civil defence ...
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.