California Underground, Realms -- Fire and Ice


	Fire & Ice

	Erupting volcanoes send streams of lava flowing down their flanks. If the surface of the lava cools and hardens first, the lava beneath can drain out forming lava-tube caves.

	Step 1 -- Lava erupting from volcanoes flows like a river down the flanks of the volcano.			Step 2 -- Lava spilling or splattering over the banks of the lava river forms natural levees, further channeling the flow.

	Step 3 -- If the lava meets a downstream blockage, the lava slows, the surface cools and forms a solid crust.			Step 4 -- If the lava breaks through the downstream blockage, the lava will flow again. When the eruption slows, or if the flow is diverted elsewhere, the tube drains and a lava-tube cave is born.

	Some volcanoes erupt explosively like Mt. Saint Helens. Others, like Mauna Loa, have extended periods of very fluid lava erupting from calderas and fissures running down the flanks of the volcano. In California we have both types of volcanoes, but lava tubes only form in the flows of the very fluid lava. Once the lava cools the lava tube formation is complete. However, stalactites and stalagmites of ice may form later and spectacularly decorate many lava tubes in California.

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