A glacier is a persistent body of dense ice that forms on land and moves under its own weight and the force of gravity. These massive formations begin as layers of snow that compress over many years, transforming the snow into hard, dense glacial ice. The largest of these features are continental-scale systems that function as the planet’s largest freshwater reservoirs. Understanding the size and movement of these ice masses is fundamental to grasping their profound influence on Earth’s climate and geography.
How Glaciers Are Defined and Measured
The size of a glacier is measured in two primary ways: by surface area or by total volume of ice. Glaciologists categorize these features based on their scale and form to standardize measurement. Ice Sheets represent the largest category, defined as a mass of glacial land ice extending over 50,000 square kilometers. This size is large enough to bury underlying topography.
Ice Caps are similar dome-shaped masses of ice but are smaller than the 50,000 square kilometer threshold. Both Ice Sheets and Ice Caps are distinct from Valley Glaciers, which are constrained and shaped by mountain valleys. For the largest ice bodies, volume is often a more meaningful measure than area, as it indicates the sheer quantity of frozen water and its potential impact on sea level.
The Dominant Polar Ice Systems
The two largest ice masses on the planet are the Antarctic and Greenland Ice Sheets, which together hold more than 99% of the world’s land ice. The scale of these polar systems makes all other glaciers appear small in comparison.
The Antarctic Ice Sheet is the largest, covering nearly 14 million square kilometers, an area roughly equivalent to the contiguous United States and Mexico combined. This immense ice body contains an estimated 30 million cubic kilometers of ice, which is enough to raise global sea levels by approximately 58 meters if it were to melt completely. The ice can be almost five kilometers thick in some places. This continental ice mass flows outward through channels called ice streams and outlet glaciers.
The largest individual glacier system within this mass is the Lambert-Fisher Glacier in East Antarctica. Recognized as the world’s largest named glacier, this feature is over 400 kilometers long and up to 100 kilometers wide. It drains a significant portion of the East Antarctic Ice Sheet, feeding into the Amery Ice Shelf.
The second largest system is the Greenland Ice Sheet, covering about 1.7 million square kilometers. This area is approximately three times the size of Texas and holds about 2.9 million cubic kilometers of ice. Complete melting of the Greenland Ice Sheet would result in a global sea level rise of about 7.4 meters.
Largest Glaciers in Temperate Zones
Outside of the two massive polar ice sheets, the largest glacial features are found in high-latitude, non-polar regions or high-altitude mountain ranges. These include the ice caps and ice fields of Iceland, Alaska, and Patagonia.
North America’s largest glacier is the Bering Glacier in Alaska, which combines with the Bagley Icefield to cover approximately 5,000 square kilometers. This Alaskan glacier system is over 200 kilometers long. In Europe, the Vatnajökull Ice Cap in Iceland is the largest by volume and area, covering between 7,700 and 8,400 square kilometers. The ice cap has an average thickness of 380 meters.
To the south, the Patagonian Ice Fields in Chile and Argentina represent the largest mass of ice in the Southern Hemisphere outside of Antarctica. The Southern Patagonian Ice Field alone covers about 16,480 square kilometers. This field generates dozens of outlet glaciers, including the Pío XI Glacier, which, at 1,265 square kilometers, is the largest glacier in South America.
The Global Significance of Massive Ice Bodies
The meltwater from land-based ice sheets and glaciers directly adds volume to the oceans, influencing global sea level. The freshwater stored in these sheets and caps represents a significant portion of the planet’s total freshwater supply.
The influx of cold, fresh meltwater can also impact oceanic circulation patterns. This release of lighter, less dense water into the North Atlantic, for example, has the potential to slow down the large-scale current system known as the thermohaline circulation.
The bright white surface of the ice sheets reflects a large amount of solar radiation back into space, a process called albedo. This reflectivity helps regulate global temperatures. As ice melts and exposes darker land or ocean, more heat is absorbed, accelerating planetary warming.