How Do Columnar Joints Form

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The Answer is In a lava flow, especially a mafic one, a distinctive pattern of columns bounded by fractures may form. This occurs when the lava flow stops moving, contracts as it cools, and produces forces that cause fractures to open. The fractures, called joints, appear as polygonal cracks that extend downward, forming parallel columns with their long axes perpendicular to the cooling surface.

How Do Columnar Joints Form

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