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Mysterious Life of Caves

How Caves Form


Caves homepage

Cave-Making Agent: Lava

Lava, which is molten rock that has reached Earth's surface from deep underground, is able to form long and extensive cave networks. Instead of carving or eating away at existing rock, it creates caves within a lava flow as the flow slowly solidifies.

illustration: lava flows down slope

Lava flows down a slope in a shape that resembles a tongue.

Within this tongue is a channel of lava that flows faster than the surrounding lava, in the same way that a river or stream has a channel of faster-moving water, usually over its deepest point.

illustration: lava channel with lava flowing through center

The slower-moving lava along the sides of the flow cools first, leaving a stream of flowing lava near the center.

A crust then forms over the top of the lava as it cools further, first along the sides of the stream, then over the stream. The tube that now encases the flowing lava holds heat in, and the lava continues to flow.

illustration: lava flow with top of the channel begining to solidify, forming a tunnel

When the flow of lava from underground ends, most of the lava in the tube flows out, leaving an empty tube. Some molten rock clogs at the lower end of the tube.

Other lava flows may cover the new cave, burying it deeper and deeper.

illustration: cutaway of lava flow; with lava moving through tunnel

Openings to lava caves usually lie on the surface, where a thin part of the cave ceiling has collapsed.

Such caves are commonly found in places where lava has flowed recently (in geological terms), such as Hawaii and the western U.S. The longest lava cave is Kazumura Cave in Hawaii, a cave system that is almost 30 miles long.

Choose another way that caves can form.

illustration: lava flow present

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