An ice cap is a glacier, a thick layer of ice and snow, that covers fewer than 50,000 square kilometers (19,000 square miles). Glacial ice covering more than 50,000 square kilometers (19,000 square miles) is called an ice sheet.

An interconnected series of ice caps and glaciers is called an ice field. Ice caps and ice fields are often punctuated by nunataks. Nunataks are areas where just the summits of mountains penetrate the ice.

Ice caps form like other glaciers. Snow accumulates year after year, then melts. The slightly melted snow gets harder and compresses. It slowly changes texture from fluffy powder to a block of hard, round ice pellets. New snow falls and buries the grainy snow. The hard snow underneath gets even denser. It is known as firn.

As years go by, layers of firn build on top of each other. When the ice grows thick enough—about 50 meters (165 feet)—the firn grains fuse into a huge mass of solid ice. At this point, the glacier begins to move under its own weight.

Ice caps tend to be slightly dome-shaped and spread out from their center. They behave plastically, or like a liquid. An ice sheet flows, oozes, and slides over uneven surfaces until it covers everything in its path, including entire valleys, mountains, and plains.

Ice caps and ice fields exist all over the world. Ice caps in high-latitude regions are often called polar ice caps. Polar ice caps are made of different materials on different planets. Earth’s polar ice caps are mostly water-based ice. On Mars, polar ice caps are a combination of water ice and solid carbon dioxide.

Few organisms have adapted to life on an ice cap, although many plants and animals live on the cold periphery. Forests rim some ice caps in Iceland, Russia, and Canada. Mammals as large as musk ox and polar bears live around Arctic ice caps.

The marine ecosystem beneath Arctic ice caps can be rich in biodiversity. Seaweeds, krill, fish, and marine mammals such as whales and seals are indigenous to ice caps around the Arctic Circle.

Many indigenous people have adapted to life around ice caps. The Yupik people of Siberia live in coastal communities along the Chukchi Peninsula, Russia, and St. Lawrence Island, in the U.S. state of Alaska.

The Yupik take advantage of seasonal thawing of ice caps to harvest plants and berries, and the migration routes of caribou that sometimes are close to ice caps and ice fields.

They rely primarily on marine life to supply food and material goods, however. Seaweeds, walruses, bowhead whales, and fish provide food staples as well as material for dwellings and transportation such as sleds and kayaks.

Northern Europe is home to many ice caps. Vatnajökull, Iceland, is an ice cap that covers more than 8% of the island nation. Austfonna, in the Svalbard archipelago of Norway, is the largest of many ice caps in Scandinavia. The largest ice cap in the world is probably the Severny Island ice cap, part of the Novaya Zemlya archipelago in the Russian Arctic.

Ice caps and ice fields are found far beyond polar regions, however. Mountain ranges, such as the Himalayas, Rockies, Andes, and the Southern Alps of New Zealand are all home to many ice caps and ice fields.

One of the most unusual ice fields is Yolyn Am, Mongolia. Yolyn Am, a deep gorge in the Gurvan Saikhan mountain range, is part of the arid Gobi Desert. It experiences little precipitation. The ice field appears only seasonally, usually melting by early autumn.

Mount Kilimanjaro, Tanzania, the tallest mountain in Africa, used to have enormous ice caps on its summit. Today, the Furtwangler glacier is the mountain's only remaining ice cap, at 60,000 square kilometers (23,166 square miles). The Furtwangler glacier is melting at a very rapid pace, however, and Africa may lose its only remaining ice cap.

ice cap
Beneath the brim of Norway's largest ice cap.

Martian Ice Caps
Ice sheets are sometimes called polar ice caps. On Mars, the polar ice caps are called the Planum Australe (southern) and the Planum Boreum (northern). The Martian ice caps are made of water and carbon dioxide about 3 kilometers (1.9 miles) thick.

accumulate
Verb

to gather or collect.

adapt
Verb

to adjust to new surroundings or a new situation.

Noun

a group of closely scattered islands in a large body of water.

Noun

region at Earth's extreme north, encompassed by the Arctic Circle.

arid
Adjective

dry.

Noun

all the different kinds of living organisms within a given area.

compress
Verb

to press together in a smaller space.

firn
Noun

grainy ice that forms glaciers. Also called neve.

food staple
Noun

food that can be prepared, stored, and eaten throughout the year.

forest
Noun

ecosystem filled with trees and underbrush.

Noun

mass of ice that moves slowly over land.

Noun

deep, narrow valley with steep sides, usually smaller than a canyon.

Noun

area of fewer than 50,000 square kilometers (19,000 square miles) covered by ice.

ice field
Noun

area of fewer than 50,000 square kilometers (19,000 square miles) covered by interconnected ice caps.

ice pellet
Noun

rain that freezes as it falls to Earth. Also called sleet.

Noun

thick layer of glacial ice that covers a large area of land.

Adjective

characteristic to or of a specific place.

kayak
Noun

small canoe made watertight around the waist of the occupant and moved in the water with a single paddle.

Noun

distance north or south of the Equator, measured in degrees.

marine ecosystem
Noun

community of living and nonliving things in the ocean.

migration route
Noun

path followed by birds or other animals that migrate regularly.

mountain range
Noun

series or chain of mountains that are close together.

nunatak
Noun

mountain peak that is completely surrounded by a glacier.

periphery
Noun

outskirts or boundary.

plastically
Adverb

in a moldable, alterable manner.

Noun

all forms in which water falls to Earth from the atmosphere.

Scandinavia
Noun

region and name for some countries in Northern Europe: Iceland, Norway, Sweden, Finland, and Denmark.

Siberia
Noun

region of land stretching across Russia from the Ural Mountains to the Pacific Ocean.

summit
Noun

highest point of a mountain.

transportation
Noun

movement of people or goods from one place to another.

Yupik
adjective, noun

people and culture native to eastern Siberia and the U.S. state of Alaska.