The Giant's Cause...

 2004

… Most columns are straight with parallel sides and diameters from a few centimeters to 3 m. Some columns are curved and vary in width. Columns can reach heights of 30 m. …

Most columns tend to have 5 or 6 sides but have as few as 3 and as many as 7 sides.
1940s photo postcard of the Wishing Chair, Giants Causeway.
 


 

The columns may form sets. Straight, regular columns are called colonnade. Irregular, fractures columns are called entablature.


From Spry (1962).

 


The columns form due [sic] to stress as the lava cools (Mallet, 1875; Iddings, 1886, 1909; Spry, 1962). The lava contracts as it cools, forming cracks. Once the crack develops it continues to grow. The growth is perpendicular to the surface of the flow. Entablature is probably the result of cooling caused by fresh lava being covered by water. The flood basalts probably damned rivers. When the rivers returned the water seeped down the cracks in the cooling lava and caused rapid cooling from the surface downward (Long and Wood, 1986). The division of colonnade and entablature is the result of slow cooling from the base upward and rapid cooling from the top downward. from www.volcano.und.nodak.edu).

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