Rooms Carved by Water: Cave Words

Rooms Carved by Water

1Imagine walking into a dark room deep under the ground. No person dug this room. Water made it! Many caves form in a kind of rock called limestone. Limestone is a fairly soft rock. Much of it formed from the shells of tiny sea creatures that piled up long ago.

2A cave starts with rainwater. As rain falls through the air and soaks into the soil, it picks up a gas called carbon dioxide. The gas turns the water into a weak acid. A weak acid is too mild to hurt your skin, but it can slowly dissolve limestone. When rock dissolves, it breaks into bits so tiny that they mix into the water and get carried away, the way sugar disappears into a cup of warm tea.

3The acid water seeps into the ground. To seep means to flow slowly through tiny holes or cracks. As the water trickles through cracks in the limestone, it dissolves a little rock at a time, so the cracks gradually grow wider. This process is very slow. It often takes many thousands of years for a crack to become a passage, a tunnel through the rock. Some passages open into a chamber, which is a large, open room inside a cave.

4Once the water drains away and air fills a cave, water starts to build instead of carve. Each drop that hangs from the ceiling leaves behind a tiny ring of calcite. Calcite is a mineral. A mineral is a solid material found in nature, such as salt or quartz, that is not alive. Drop after drop, the water deposits more calcite, and the ring slowly grows longer. In time, a stone icicle called a stalactite hangs down from the ceiling. Where the drops land on the floor, calcite piles up into a stone mound called a stalagmite. If a stalactite and a stalagmite grow until they meet, they form a column. A column looks like a pillar holding up the roof.

5Deep inside many caves is the dark zone, the part that sunlight never reaches. There is no light at all, and the temperature stays about the same all year. Some animals spend their whole lives in the dark zone. Certain cave fish and salamanders have no working eyes. Instead, they find food by sensing tiny movements in the water.

6Scientists who study caves are called speleologists. They map passages, test the water, and search for rare animals. Their work shows that a cave is not just an empty hole. It is a place that keeps changing, shaped by water one drop at a time.