Glacier

Key facts

Land covered by ice

≈ 10%Mostly the Antarctic and Greenland ice sheets

Share of fresh water

≈ 68–69%Stored in glaciers, ice caps and ice sheets

Antarctic Ice Sheet

≈ 14 million km²Up to about 4.8 km thick

Greenland Ice Sheet

≈ 1.7 million km²Up to about 3 km thick

Sea-level potential

≈ 58 m and ≈ 7 mIf all Antarctic and Greenland ice melted, respectively

Typical flow speed

Centimetres to metres a daySome outlet glaciers move tens of metres a day

Oldest continuous ice core

≈ 800,000 yearsEPICA Dome C; newer drilling aims to reach older ice

Largest Alpine glacier

Great AletschAbout 20 km long, in Switzerland

Ice formation

Snow → firn → iceCan take decades to centuries

Ice sheets, ice caps and valley glaciers

Glaciers come in many forms. Ice sheets are the largest: today only two exist, on Antarctica and Greenland. They are domes of ice so thick that they bury whole mountain ranges, and they drain towards the sea through fast-moving outlet glaciers and floating ice shelves. Smaller ice caps cover highlands such as those in Iceland and the Canadian Arctic.

Mountain glaciers are what most people picture. Cirque glaciers sit in bowl-shaped hollows high on peaks; valley glaciers flow down mountain valleys like slow rivers, as in the Alps, the Himalaya, Alaska and the Andes; piedmont glaciers spread out where a valley glacier reaches a plain; and tidewater glaciers end in the sea, where they break off, or calve, icebergs.

How ice forms and flows

Glaciers grow where more snow falls in winter than melts in summer. Year after year, buried snow is squeezed into a granular material called firn and eventually into solid ice, a process that can take from decades to centuries. A glacier gains mass in its upper accumulation zone and loses it in its lower ablation zone, through melting, evaporation and calving.

Once ice is thick enough, it flows. Deep in the glacier, the pressure makes ice crystals deform slowly, so the ice behaves like an extremely stiff fluid. Where the base is wet, the whole glacier can also slide over its bed on a film of meltwater. Ice usually moves fastest at the surface and the centre, and slowest at the bed and sides. Most mountain glaciers move a few centimetres to a few metres a day, while some Greenland outlet glaciers, such as Sermeq Kujalleq (Jakobshavn), have been measured moving tens of metres a day.

Crevasses, seracs and blue ice

The top layer of a glacier is brittle. Where the ice speeds up, bends over a bump or stretches as it spreads, this surface cracks into crevasses, which can be tens of metres deep and are often hidden beneath snow bridges, making them a serious hazard for travellers. Deeper down, the ice is under so much pressure that it flows rather than cracks, which limits how deep crevasses can go.

Where a glacier pours over a steep step in its bed, it breaks into an icefall, a chaotic jumble of crevasses and towering blocks called seracs. Seracs can collapse without warning; the Khumbu Icefall on the Everest route is a famous example. Dense glacier ice often looks strikingly blue because ice absorbs red light and transmits blue, an effect that becomes visible once most air bubbles have been squeezed out. In parts of Antarctica, wind strips away snow to expose bare blue ice fields, which are excellent places to find meteorites.

Moraines and the landscapes glaciers leave

Glaciers pluck and scrape rock from their beds and walls and carry it along. This debris is dropped as moraines: lateral moraines form ridges along the sides of a glacier, medial moraines form dark stripes down the middle where two glaciers merge, and terminal moraines pile up at the furthest point the ice reached.

When glaciers retreat they leave tell-tale landscapes: U-shaped valleys, sharp ridges called arêtes, pointed horn peaks like the Matterhorn, lakes dammed by moraines and erratic boulders stranded far from their source. Norway's fjords are valleys carved by glaciers and later flooded by the sea. Much of northern Europe and North America was shaped this way during the last ice age, which peaked roughly 20,000 years ago.

Ice cores: archives of past climate

Each year's snowfall is buried by the next, so ice sheets build up layers like the pages of a book. Scientists drill cores of ice, sometimes more than 3 km long, and study them. Tiny air bubbles trapped in the ice preserve samples of the ancient atmosphere, while the chemistry of the ice itself records past temperatures. Dust, volcanic ash and other particles mark eruptions and changes in wind.

The European EPICA core from Dome C in Antarctica reaches back about 800,000 years and shows that carbon dioxide and temperature have risen and fallen together through repeated ice ages. Today's carbon dioxide levels are well above anything in that record. A newer project, Beyond EPICA, reported in 2025 that it had drilled to bedrock through ice thought to be at least 1.2 million years old; analysis of the core is ongoing.

Glaciers and climate change

Most of the world's mountain glaciers are losing ice, and the losses have accelerated in recent decades. In the Alps, the record-breaking summers of 2022 and 2023 together removed roughly a tenth of Switzerland's remaining glacier volume, according to the Swiss glacier monitoring network. Many smaller glaciers are expected to disappear entirely this century.

The ice sheets are losing mass too. Satellite measurements show that Greenland and Antarctica together have lost several trillion tonnes of ice since the early 1990s, contributing to global sea-level rise. Melting glaciers also affect water supplies for hundreds of millions of people, particularly in Asia and South America, where rivers are fed by mountain ice. How fast the ice sheets will lose mass in future, especially in West Antarctica, is one of the biggest uncertainties in climate science.

Surprising facts about Glacier

• Glacier ice is not a static solid; it flows, and in places can move faster than a person can comfortably walk over a day.
• Air bubbles in Antarctic ice are genuine samples of the atmosphere from hundreds of thousands of years ago.
• Antarctica's ice is so heavy that it pushes the bedrock beneath it down by hundreds of metres; parts of the land surface lie well below sea level.
• Meteorites are easier to find on Antarctica's blue ice fields, where ice flow and wind bring them to the surface; tens of thousands have been collected there.
• Glaciers sometimes surge, suddenly speeding up to tens or even hundreds of times their usual pace for months or years.
• There are more than 200,000 glaciers on Earth outside the two great ice sheets.

Frequently asked questions

What is the difference between a glacier and an ice sheet?

An ice sheet is a glacier of continental size, covering more than about 50,000 km². Only two exist today, on Greenland and Antarctica. Smaller glaciers include ice caps, valley glaciers and cirque glaciers.

How do glaciers move?

Under their own weight. The ice slowly deforms internally, like a very stiff fluid, and where the base is wet the glacier can also slide over its bed on a layer of meltwater.

Why is glacier ice blue?

Ice absorbs red light slightly more than blue. In dense glacier ice with few air bubbles, light travels far enough through the ice for this to show, so the ice looks blue.

What can ice cores tell us?

Ice cores record past temperatures, greenhouse gas levels, volcanic eruptions and dust. The longest continuous record, from Antarctica, covers about 800,000 years.

Can I explore a glacier in the app?

Yes. You can land on a glacier and explore its crevasses, seracs and moraines in interactive 3D.

Keep exploring

• Land in the 3D glacier landscape and walk around
• The Quaternary: the ice ages
• Europa: an ice shell over a hidden ocean
• Jungle: layered rainforest, a muddy river and drifting spores
• Desert: wind-carved dunes with sharp crests and long shadows
• Volcano: black lava fields, a glowing lava lake and steaming vents
• Tropical beach & reef: white sand, leaning palms and a lagoon to dive into
• Ocean & underwater: dive the blue onto a reef-capped seamount full of life
• Savanna: golden grass, umbrella acacias, granite kopjes and herds
• Archipelago: ice-polished granite skerries and pine islets in calm baltic water
• Fjords: a deep glacial fjord between kilometre-high walls and waterfalls
• The Moon's surface: grey regolith, craters and earth in a black sky
• Mars surface: rust-red plains, an ancient river delta and dust devils
• Europa's ice: cracked ice ridges under a sky filled by jupiter
• Gas giant clouds: drifting cloud decks, lightning and a giant storm

The landscapes in Ember’s Universe are procedural 3D scenes modelled on real places. The landforms, plants and light follow the real thing, but the details are generated, not mapped.

Sources

• NSIDC — Glaciers
• NSIDC — Ice sheets
• USGS — Ice, snow and glaciers and the water cycle
• NASA — Vital Signs: Ice sheets
• British Antarctic Survey — Ice cores and climate change