Editing Basalt (section)

===== Columnar basalt =====
{{Main|Columnar jointing}}
{{See also|List of places with columnar basalt}}
[[File:Causeway-code poet-4.jpg|thumb|The [[Giant's Causeway]] in Northern Ireland]]
[[File:Boyabat.jpg|thumb|Columnar [[Joint (geology)|jointed]] basalt in [[Turkey]]]]
[[File:Мыс Столбчатый. После заката.jpg|thumb|Columnar basalt at [[Cape Stolbchaty]], Russia]]
During the cooling of a thick lava flow, contractional [[Joint (geology)|joints]] or fractures form.<ref>{{cite journal |last1=Smalley |first1=I. J. |title=Contraction Crack Networks in Basalt Flows |journal=Geological Magazine |date=April 1966 |volume=103 |issue=2 |pages=110–114 |doi=10.1017/S0016756800050482 |bibcode=1966GeoM..103..110S |s2cid=131237003 }}</ref> If a flow cools relatively rapidly, significant [[Thermal expansion#Contraction effects (negative expansion)|contraction]] forces build up. While a flow can shrink in the vertical dimension without fracturing, it cannot easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of [[Columnar jointing|column]]s. These structures, or [[basalt prism]]s, are predominantly hexagonal in cross-section, but polygons with three to twelve or more sides can be observed.<ref>{{cite journal |last1=Weaire |first1=D. |last2=Rivier |first2=N. |title=Soap, cells and statistics—random patterns in two dimensions |journal=Contemporary Physics |date=January 1984 |volume=25 |issue=1 |pages=59–99 |doi=10.1080/00107518408210979 |bibcode=1984ConPh..25...59W }}</ref> The size of the columns depends loosely on the rate of cooling; very rapid cooling may result in very small (<1&nbsp;cm diameter) columns, while slow cooling is more likely to produce large columns.<ref name="spry-1962">{{cite journal |last1=Spry |first1=Alan |title=The origin of columnar jointing, particularly in basalt flows |journal=Journal of the Geological Society of Australia |date=January 1962 |volume=8 |issue=2 |pages=191–216 |doi=10.1080/14400956208527873 |bibcode=1962AuJES...8..191S }}</ref>