like surface water, can change the shape of the land. As water trickles
down through the soil can into the rock. Below, it may mix with
a gas called carbon dioxide, which is found naturally in the air
and the soil. When mixed with the carbon dioxide, water becomes
mildly acidic, which makes it possible to dissolve some types of
rock. The solution of water, dissolved rock, and carbon dioxide
is carried away to streams and gradually flows to the sea, where
it may combine with other solutions and form new rock material.
If a hole with an opening to the surface is left where the rock
dissolved, the hole is called a cave.Caves can be many shapes and
sizes. Large caves with connecting chambers are known as caverns.
They are cool, dark, and silent places, where the only sound may
be the steady dripping of water as it trickles on rock surfaces.This
water, which frequently carries dissolved rock material, can form
marvelous deposits. The most common of these are stalactites. Like
icicles made of stone, stalactites are formed when water rich in
dissolved rock material drips from cave ceilings. Stalagmites are
another deposit formed by water carrying dissolved rock material.
They resemble icicles that grow upward from the cave floor. If a
stalactite and a stalagmite join, they create a column.
Sinkholes, another land feature created by groundwater, are large
pits formed in much the same way as caves are-acidic groundwater
dissolves certain rock material. In fact, some sinkholes form when
the roofs of caves collapse. And many sinkholes drain into caves.