Largest Glaciers in the World: Frozen Rivers of Ice That Dwarf Cities

The Lambert Glacier in East Antarctica is widely cited as the largest glacier in the world, at roughly 400 km long and up to about 100 km wide; outside the polar regions, the longest are the Fedchenko Glacier in Tajikistan (about 77 km) and the Siachen Glacier in the Karakoram (about 76 km).

That answer comes with a catch. The Antarctic and Greenland ice sheets are glaciers in the broadest sense, and each dwarfs anything else on Earth, so if they count, the contest is over before it starts. Most rankings therefore exclude them and compare the individual glaciers that drain them, alongside ice caps and mountain glaciers elsewhere. Beyond Antarctica, the biggest are Greenland's outlet glaciers such as Humboldt and Sermeq Kujalleq, the Bering and Malaspina glaciers of Alaska, the ice caps of Svalbard and Iceland, and the outlet glaciers of the Southern Patagonian Ice Field, led by Pío XI.

Length, Area or Volume: Why the Ranking Changes

Three choices decide which glacier comes out on top. The first is scale: whether continental ice sheets count, or only the glaciers flowing out of them. The second is the measure. Length favours long, narrow valley glaciers and Antarctic outlet streams; area favours broad ice caps and piedmont lobes; volume favours thick ice, which is how Iceland's Vatnajökull can be called Europe's largest glacier even when another ice cap covers slightly more ground. The third is where one glacier ends and the next begins. Where tributaries merge or an ice field feeds dozens of outlets, drawing the boundary is a judgement call.

The standard global reference, the Randolph Glacier Inventory (RGI), deliberately excludes the two ice sheets and maps the outlines of every other glacier: more than 200,000 of them, covering roughly 700,000 km² in recent versions. Figures below use commonly cited values; different surveys and years give different numbers, and nearly all of these glaciers are shrinking.

Antarctica: Lambert Glacier and the Great Ice Streams

The Lambert Glacier drains a large basin of the East Antarctic Ice Sheet, often estimated at around 8 percent of the ice sheet's area, into the Amery Ice Shelf on Prydz Bay. It was identified from Australian aerial photography in the 1950s and named after Bruce Lambert, then Australia's director of national mapping. Its roughly 400 km length is measured along the fast-flowing trunk; including the upstream catchment and the Amery Ice Shelf would give a much larger figure, which is one reason published sizes vary.

Byrd Glacier, around 135 km long and some 20–25 km wide, cuts through the Transantarctic Mountains to feed the Ross Ice Shelf and is among the fastest-moving glaciers on the continent. On the other side of Antarctica, Pine Island and Thwaites glaciers drain into the Amundsen Sea. Thwaites is not the longest, but its front is often put at about 120 km wide and its drainage basin at roughly the size of Great Britain. Because warm ocean water is melting it from below, it has earned the nickname "Doomsday Glacier" and is the focus of the joint US–UK International Thwaites Glacier Collaboration. Our guide to the Antarctic ice sheet explains how these outlets fit into the continent's ice budget.

Greenland, Svalbard and Iceland

Greenland's ice sheet discharges through dozens of outlet glaciers. Three stand out. Sermeq Kujalleq, also known as Jakobshavn Isbræ, drains roughly 6–7 percent of the ice sheet into Ilulissat Icefjord, a UNESCO World Heritage Site since 2004. Around 2012 it was measured flowing at up to about 17 km a year, among the fastest speeds recorded for any glacier. Humboldt Glacier in the northwest has the widest calving front in the Northern Hemisphere, generally given as around 100 km. Petermann Glacier in the north is known for its long floating tongue, which shed ice islands of roughly 250 km² in 2010 and about 130 km² in 2012.

Farther east, Austfonna on the island of Nordaustlandet in Svalbard is an ice cap of roughly 8,000 km² and is often named the largest in Europe by area, though the ice caps of Russia's Novaya Zemlya can outrank it depending on where Europe's Arctic boundary is drawn. Iceland's Vatnajökull covers about 7,700 km², down from roughly 8,100 km² a few decades ago, and holds around 3,000 km³ of ice, making it Europe's largest glacier by volume. Its ice reaches roughly 900 m thick in places and buries active volcanoes including Grímsvötn and Bárðarbunga, whose eruptions trigger glacial floods known as jökulhlaups. More on its outlet tongues and ice caves is in our Vatnajökull glacier guide.

Alaska and the Yukon: North America's Biggest Mountain Glaciers

The coastal ranges where Alaska meets Canada's Yukon trap moisture from the Gulf of Alaska and hold the largest non-polar ice masses in North America.

• Bering Glacier is the longest and largest glacier in North America, commonly given as about 180–190 km long and, with the Bagley Icefield that feeds it, around 5,000 km² in area. It surges periodically, advancing several kilometres in a few years before stagnating.
• Malaspina Glacier is the world's largest piedmont glacier, spreading out of the Saint Elias Mountains onto the coastal plain as a lobe roughly 65 km across and around 3,900 km² in area. Its rippled, folded moraines are clearly visible from space.
• Hubbard Glacier begins in the Yukon and runs about 120 km to Disenchantment Bay, where its calving face is roughly 10 km wide. Unlike most glaciers it has been advancing, and in 1986 and 2002 it briefly dammed Russell Fjord, turning it into a rising lake.

The Pamirs and Karakoram: Longest Glaciers Outside the Poles

Central Asia's high, cold mountains hold the world's longest valley glaciers. The Fedchenko Glacier in Tajikistan's Pamirs, named after the 19th-century Russian naturalist Alexei Fedchenko, runs about 77 km and is usually ranked the longest glacier outside the polar regions. Its ice has been measured at close to 1,000 m thick.

The Karakoram, which straddles Pakistan, India and China, follows close behind. Siachen, about 76 km long, lies in territory disputed between India and Pakistan and has been the site of military positions since 1984, making it the world's highest battlefield. In Pakistan's Gilgit-Baltistan, the Biafo Glacier (about 67 km) meets the Hispar Glacier at a high basin called Snow Lake, together forming one of the longest glacial routes outside the poles. The Baltoro Glacier (about 63 km) leads trekkers to Concordia, the junction beneath K2, Broad Peak and the Gasherbrums. The Karakoram also shows one of glaciology's puzzles: for decades many of its glaciers held steady or even grew, the so-called Karakoram anomaly, while glaciers across most of the Himalaya retreated.

Patagonia's Ice Fields

The Southern Patagonian Ice Field, shared by Chile and Argentina, is the largest body of ice in the Southern Hemisphere outside Antarctica. Estimates of its area range from about 12,000 to 16,000 km², reflecting both different mapping methods and real shrinkage; part of the border across it was still undefined after the two countries' 1998 agreement. Fed by storms off the Pacific, it sends dozens of outlet glaciers down into fjords on the Chilean side and lakes on the Argentine side.

Pío XI, also called Brüggen Glacier, is the largest of them at about 1,260 km² and around 64 km long, and unusually it advanced through much of the 20th century. Perito Moreno, about 30 km long, is famous for staying roughly stable and for periodically damming the Brazo Rico arm of Lago Argentino until the ice wall ruptures. Nearby Upsala, one of the longest in the ice field, has retreated by several kilometres since the 1990s. The Perito Moreno glacier guide covers its rupture cycle in more detail.

Across the world, glaciers outside the ice sheets have been losing mass on the order of 250–300 billion tonnes a year in the early 21st century according to satellite studies, so every figure in this article is a snapshot rather than a permanent record.

Glacier, Ice Cap or Ice Sheet?

Much of the confusion over "largest" comes from three overlapping terms, which differ mainly in size and in whether the ice follows the land beneath it.

• Glacier is the general term for any mass of ice that forms from compacted snow and flows under its own weight. Valley, piedmont, tidewater and outlet glaciers are all kinds of glacier, and their shape is controlled by the terrain.
• Ice cap refers to a dome of ice covering less than 50,000 km², thick enough to bury the landscape beneath it and flowing outward in all directions. Vatnajökull and Austfonna are ice caps.
• Ice sheet means a continental-scale mass larger than 50,000 km². Only two exist today: Antarctica, at around 14 million km², and Greenland, at roughly 1.7 million km².

An icefield, such as the Southern Patagonian Ice Field or Alaska's Bagley Icefield, is interconnected ice whose flow is still steered by mountains poking through it. So when a list names Lambert as the largest glacier, it is ranking an outlet stream of an ice sheet, not the ice sheet itself. The different shapes, and how snow becomes ice in the first place, are laid out in our explainer on the main types of glaciers.