An ice field is a large mass of glacial ice that spreads across a mountainous area, connecting multiple individual glaciers. Its flow is dictated by the underlying peaks and valleys of the mountain range it occupies. Unlike some other large ice masses, an ice field does not completely overwhelm the landscape; the highest points of the mountains often poke through the ice surface. The ice mass accumulates in high-altitude basins and plateaus, acting as a reservoir that feeds numerous outflowing glaciers. This formation is found in cold, high-precipitation environments globally.
Formation and Structure
The development of an ice field begins with a sustained, high rate of snowfall where annual accumulation exceeds the rate of melt, known as the accumulation zone. As layers of snow build up, the weight of the overlying snow compresses the lower layers. This compression transforms the snow into firn, a denser, granular form that has survived at least one melt season.
Continued pressure and freezing cause the firn to recrystallize into solid, blue glacial ice, which then begins to flow under gravity. The ice field’s structure is fundamentally shaped by the pre-existing mountain topography, filling valleys and depressions. The flow is directed by the mountainous terrain, with the ice acting as a source area for multiple outlet glaciers that drain down the slopes.
The ice divide is the highest central ridge within the ice field, from which the ice flows outward in opposing directions. A distinctive feature is the presence of nunataks, isolated, rocky mountain peaks or ridges that protrude above the continuous expanse of ice. These exposed rock features confirm that the ice field has not grown deep enough to completely bury the underlying mountain range.
Differentiating Ice Fields from Ice Caps and Ice Sheets
Ice fields are classified differently from ice caps and ice sheets based on their size, shape, and relationship to the underlying land. An ice field is constrained by the mountainous topography; its shape is molded by the peaks and valleys beneath it. The ice flows through mountain passes and valleys, resulting in an irregular shape often featuring numerous nunataks.
In contrast, an ice cap is a dome-shaped mass of ice smaller than 50,000 square kilometers and is not constrained by the underlying terrain. An ice cap is thick enough to spread radially outward under its own weight, forming a distinct, high-domed profile that may partially bury the land beneath it. The ice field is defined by its compliance with the mountain structure, while the ice cap imposes its own shape.
An ice sheet represents the largest scale of glacial ice, covering an area greater than 50,000 square kilometers, such as those found on Greenland and Antarctica. These immense ice bodies completely bury the landscape, creating their own topography independent of the underlying rock. An ice field is also distinct from a simple glacier, as it is an interconnected system or source area from which multiple individual valley glaciers flow.
Major Global Examples
The world contains several ice fields, mostly situated in high-latitude or high-altitude mountain ranges. The largest contiguous ice mass outside of the polar regions is the Southern Patagonian Ice Field, shared between Chile and Argentina in the Andes Mountains. This feature covers approximately 16,800 square kilometers, acting as the source for famous glaciers like the Perito Moreno Glacier.
To the north, the Northern Patagonian Ice Field is a separate mass covering around 4,000 square kilometers, feeding numerous outlet glaciers down to the Pacific fjords and Atlantic lakes. North America hosts expansive ice fields, particularly in the St. Elias Mountains along the border of Alaska and the Yukon Territory. This area features the Kluane/Wrangell–St. Elias/Glacier Bay/Tatshenshini-Alsek Ice Field, spanning about 25,000 square kilometers.
The Columbia Icefield, located in the Canadian Rocky Mountains between Banff and Jasper National Parks, is a well-known example that is highly accessible. This ice field feeds six major outlet glaciers and is an important hydrological divide for North America. In Alaska, the Juneau Icefield spans about 3,800 square kilometers and feeds over 100 individual glaciers.