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Solution
& Decoration |
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Think
of a cave -- most people picture stalactites and stalagmites in
a typical limestone cave. Water flowing underground dissolves the
rock and forms passages. Later, water redeposits dissolved rock
forming stalactites. |
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Step 1. Rain falling on a limestone terrain reacts with carbon dioxide,
produced by the decay of plant material in the soil, forming a
weak acid.
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Step 2 -- The acidic groundwater
accumulates at the surface of the water table and begins to dissolve
the limestone forming flooded passages into the limestone bedrock.
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Step 3 -- The deepening river
valley drains away ground water, lowering the water table and
draining the caves. The valley intersects the cave passage, revealing
an entrance.
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Step 4 -- Once the cave is opened
to the atmosphere, carbon dioxide can escape from the cave. This
allows the groundwater seeping into the cave to release carbon
dioxide and redeposit the dissolved limestone it carries. This forms
calcite stalactites and stalagmites.
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In
California these caves form in limestone and marble, both forms
of calcite. Over thousands of years, groundwater and carbon dioxide
dissolve away the rock forming the cave passages. Later, water flowing
into the cave carries in dissolved calcite, which is redeposited
as stalactites and other flowstone formations. Many caves in California
have not evolved to the point of having stalactites and flowstone
deposited - they are simply passages through the rock. In contrast,
deposition alone can form caves around springs. Here dissolved calcite
is deposited as flowstone at the spring mouth, forming a new cave
underneath. These are called travertine caves. |
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View Slide Show
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Return
to California Underground Realms |
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