Childrens Illustrated Encyclopedia

104

Caves

HOW CAVES FORM

Large cave systems lie

beneath the ground

in regions made of

limestone rock. For

thousands of years,

rainwater, which is

naturally acidic,

dissolved away the

limestone. Small

cracks formed, slowly

widening to create deep

holes, which became

underground caves and

rivers as water continued

to erode the rock.

STALACTITES
Slender stalactites
often hang from
a cave roof. Drops
of water seeping
down from above
dissolve a white
mineral called
calcite from the
rock. As the water
dries, small
amounts of calcite
are left behind.
These build up
to form stalactites.
This process is
usually very slow;
stalactites grow only
about 1 in (2.5 cm)
in 500 years.

STALAGMITES
Water dripping
from the roof or
from a stalactite
falls to the cave
floor, leaving layers
of calcite on the
floor. In this way,
a pillar called a
stalagmite slowly
builds upward.

BENEATH THE SURFACE of Earth lies a secret world. Caves run through the 

rock, opening out into huge chambers decorated with slender stone columns.

Underground rivers wind through deep passages, and waterfalls crash down

on hidden lakes. Caves such as these are many thousands of years old; they were

formed as water slowly dissolved limestone rocks. But not all caves are underground.

Sea cliffs contain caves that have been eroded by the waves. Caves also develop inside

glaciers and within the solidified lava around volcanoes.

Caves are damp, dark places. Some are only large enough

to contain one person; others, such as the network of caves

in Mammoth Cave National Park, in Kentucky, stretch for

hundreds of miles. One of the world’s deepest caves, in

France, lies almost 1 mile (1.5 km) below the ground.

Prehistoric peoples used caves for shelter. Caves at

Lascaux, France, contain wall paintings and ancient

tools that are perhaps 20,000 years old. A few cave

dwellers still live today in parts of Africa and Asia.

SPELUNKING

The sport of exploring caves is called

potholing or spelunking. Clambering

around in caves is a dirty and often

wet pastime, so spelunkers wear tough

clothing. Other important equipment

includes nylon ropes, a helmet with

a light, and ladders made of steel

cables. Spelunkers work in teams and

may stay in a cave for several days.

Spelunking can be dangerous; rain

can cause flooding, and spelunkers

can be trapped by sudden rockfalls.

Spelunkers marvel at the

fascinating rock formations

around an underground lake at

the mouth of a cave in France.

Groundwater

fills a previously

dry cavern to the

level of the water

table, which can rise

and fall over time.

Stalactites and stalagmites take

thousands of years to grow.

Sinkhole—point at which a

stream plunges underground

Sparse vegetation

Stream emerges via cave mouth

and flows along the valley bottom.

Later passage

eroded by

Underground lake stream.

Steep channel

carved by stream.

Water seeps through rock

joints; rock develops cracks,

which widen into potholes.

Ridges and grooves in

the limestone surface Steplike rock

formations

Stream emerges over waterfall.

Craggy limestone cliffs

Water drop
falls from tip
of stalactite.

A stalactite and stalagmite

may grow and meet to

form a column from floor

to roof.

Find out more

Bats

Geology

Prehistoric peoples

Rocks and minerals

Volcanoes