Thursday, April 30, 2009

Columnar Basalt cool lava

When a thick lava flow cools it contracts vertically but cracks
perpendicular to its directional flow with remarkable geometric
regularity - in most cases forming a regular grid of remarkable
hexagonal extrusions that almost appear to be made by man. The size of
the columns depends loosely on the rate of cooling; very rapid cooling
may result in very small (<1 cm diameter) columns, while slow

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