A stack is a geological landform consisting of a steep and
often vertical column or columns of rock in the sea near a coast, isolated by
erosion. Stacks are formed through processes
of coastal geomorphology, which are entirely natural. Time,
wind and water are the only factors involved in the formation of a stack. They are formed when part of a headland is
eroded by hydraulic action, which is the force of the sea or water crashing
against the rock. The force of the
water weakens cracks in the headland, causing them to later collapse, forming
free standing stacks and even a small island.
Without the constant presence of water, stacks also form when a natural
arch collapses under gravity, due to a sub-aerial processes like wind erosion.
fig 1
thanks to our friends at wikipedia.org
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