Columnar jointing
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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, or columns. Colu
Columnar jointing in Giant's Causeway in Northern Ireland
Columnar jointing in the Alcantara Gorge, Sicily
Devils Tower is an eroded laccolith in the Black Hills National Forest, Wyoming.
Hexagonal volcanic tuffs at East Dam of High Island Reservoir
Igneous rock
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Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava.
Columnar jointing
…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…
Volcanic eruptions of lava are major sources of igneous rocks. (Mayon volcano in the Philippines, erupting in 2009)
Natural columns of igneous rock separated from each other by columnar joints, in Madeira
Formation of igneous rock
Extrusive igneous rock is made from lava released by volcanoes