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 (Ovibos moschatus) and polar bears (Ursus maritimus) 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 (Odobenus rosmarus), bowhead whales (Balaena mysticetus), 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 percent 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.