Glacier mass balance in the context of "Columbia Glacier (Washington)"

The Antarctic ice sheet is a continental glacier covering 98% of the Antarctic continent, with an area of 14 million square kilometres (5.4 million square miles) and an average thickness of over 2 kilometres (1.2 mi). It is the largest of Earth's two current ice sheets, containing 26.5 million cubic kilometres (6,400,000 cubic miles) of ice, which is equivalent to 61% of all fresh water on Earth. Its surface is nearly continuous, and the only ice-free areas on the continent are the dry valleys, nunataks of the Antarctic mountain ranges, and sparse coastal bedrock. It is often subdivided into the Antarctic Peninsula (AP), the East Antarctic Ice Sheet (EAIS), and the West Antarctic Ice Sheet (WAIS), due to the large differences in glacier mass balance, ice flow, and topography between the three regions.

Because the East Antarctic Ice Sheet is over 10 times larger than the West Antarctic Ice Sheet and located at a higher elevation, it is less vulnerable to climate change than the WAIS. In the 20th century, EAIS had been one of the only places on Earth which displayed limited cooling instead of warming, even as the WAIS warmed by over 0.1 °C/decade from 1950s to 2000, with an average warming trend of >0.05 °C/decade since 1957 across the whole continent. As of early 2020s, there is still net mass gain over the EAIS (due to increased precipitation freezing on top of the ice sheet), yet the ice loss from the WAIS glaciers such as Thwaites and Pine Island Glacier is far greater.

Ablation zone or ablation area refers to the low-altitude area of a glacier or ice sheet below firn with a net loss in ice mass. This loss can result from melting, sublimation, evaporation, ice calving, aeolian processes like blowing snow, avalanche, and any other ablation. The equilibrium line altitude (ELA) or snow line separates the ablation zone from the higher-altitude accumulation zone. The ablation zone often contains meltwater features such as supraglacial lakes, englacial streams, and subglacial lakes. Sediments dropped in the ablation zone forming small mounds or hillocks are called kames. Kame and kettle hole topography is useful in identifying an ablation zone of a glacier. The seasonally melting glacier deposits much sediment at its fringes in the ablation area. Ablation constitutes a key part of the glacier mass balance.

The amount of snow and ice gained in the accumulation zone and the amount of snow and ice lost in the ablation zone determine glacier mass balance. Often mass balance measurements are made in the ablation zone using snow stakes.

A glacier terminus, toe, or snout, is the end of a glacier at any given point in time. Although glaciers seem motionless to the observer, in reality they are in endless motion and the glacier terminus is always either advancing or retreating. The location of the terminus is often directly related to glacier mass balance, which is based on the amount of snowfall which occurs in the accumulation zone of a glacier, as compared to the amount that is melted in the ablation zone. The position of a glacier terminus is also impacted by localized or regional temperature change over time.

Svartisen is a collective term for two glaciers located in Nordland county in northern Norway. It is part of Saltfjellet-Svartisen National Park, located in the Saltfjell mountain range. The glaciers are located in the municipalities of Beiarn, Meløy, Rana, and Rødøy. Svartisen consists of two separate glaciers that are separated by the 1-kilometre (0.62 mi) long Vesterdalen valley. The two glaciers are:

• Vestisen or Vestre Svartisen ("western Svartisen") has an area of 221 square kilometres (85 sq mi) which makes it the second largest glacier on the Norwegian mainland after the Jostedalsbreen glacier. (There are larger glaciers on Svalbard.)
• Østisen or Østre Svartisen ("eastern Svartisen") has an area of 148 square kilometres (57 sq mi) which makes it the country's fourth largest glacier.

There are also a number of minor glaciers in the area surrounding Svartisen, such as Glombreen in the northern part of Meløy Municipality, and Simlebreen in Beiarn Municipality. One of the outlet glaciers of Svartisen, Engabreen ends at the lowest point of any glacier on the European mainland, at 20 metres (66 ft) above sea level (in 2007). The Norwegian Water Resources and Energy Directorate has monitored the glacier mass balance of the glacier since 1970 and operates a sub-glacial laboratory beneath Engabreen.

Glacier ice accumulation occurs through accumulation of snow and other frozen precipitation, as well as through other means including rime ice (freezing of water vapor on the glacier surface), avalanching from hanging glaciers on cliffs and mountainsides above, and re-freezing of glacier meltwater as superimposed ice. Accumulation is one element in the glacier mass balance formula, with ablation counteracting. With successive years in which accumulation exceeds ablation, then a glacier will experience positive mass balance, and its terminus will advance.