Reference work entry
Columnar joints are joints that divide the rock into column shapes. These joints form as a result of the rapid cooling and contraction of hot molten lava. They generally occur in the basic and acidic lava bodies. The columns are usually hexagonal or pentagonal, and most of the joint surfaces are straight and parallel to each other. The column diameter can vary from a few centimetres to several metres. Columnar joints and their associated landforms can be seen in many geoparks associated with volcanic rocks, such as the Zhangzhou Coastal Volcanic National Geopark (basalt) in Fujian Province and the Hong Kong Global Geopark (rhyolitic volcanic rock) (Fig. 42).
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