DK - WOW! The Visual Encyclopedia of Everything

GLACIER CAVE

Near the end of a glacier, melting ice creates

streams of meltwater that often drain down

through crevasses to form vertical sinkholes.

When the water reaches the bottom of the

glacier, it flows between the ice and rock to

erode tunnels and caves in the ancient glacier

ice. At times when the melting rate is high

these can fill with water, which pours

through the ice in a torrent before finally

emerging at the glacier tip or snout. In

midwinter, however, these glacier caves

may be safe to explore.

Solidified lava forms the

roof of the lava tube

183

Ice covers the floor of this

glacier cave during a period

of reduced melting

Water is beautifully clear,

despite being full of calcite

LAVA TUBE

Now cold and empty, this cave was

once filled with a torrent of red-hot lava

erupting from a Hawaiian volcano. The

lava from such volcanoes is so hot and

liquid that it flows like water. As it pours

downhill, the top of the flow cools and

may become solid, forming the roof of

a lava tube. This keeps the heat in and

allows the lava inside to keep flowing.

When the eruption stops, the lava may

flow out to leave a long cave.

Water dripping into the Grotte

Casteret, in the Spanish Pyrenees

mountains, forms a frozen cascade

CALCITE BARRIERS

Water flowing through the

limestone cave of Akiyoshi-do

in Japan is saturated with

dissolved calcium carbonate,

or calcite. Where the water

flows over the sloping cave

floor, calcite has crystallized

to form a series of barriers.

The water overflows these

in a gentle cascade that falls

from one pool to the next.

ICE CAVE

In some mountain regions, the air inside

limestone caves can be so cold that water

seeping into the cave immediately freezes.

This creates glassy icicles and frozen cascades.

The temperature is critical to the

formation of these ice caves, so they

are quite rare. If the rock around

the cave is too cold, water freezes

solid before it can enter the cave.

If the cave is too warm, all the ice

melts and the water drains away

through the cave floor.

182_183_cave.indd 183 10/01/19 2:26 PM