J is for (Columnar) Joint(ing)

From Isle Royale National Park:

J is for Joint

Holy hexagons! Who carved those perfectly geometric columns of rock on #IsleRoyale’s north shore cliffs?

When lava cools rapidly the newly-formed rock may contract and crack, often in a distinctive pattern of long six-sided vertical columns. The faster the cooling and the more fine-grained the rock, the more astonishing the symmetry. Check out this text book example of columnar jointing on the north side of Passage Island. #geologyrocks! 

#Geology #Michigan #MI 






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