Are mountain glaciers, river ice and snow an important part of the cryosphere?

Most often, when we think about the cryosphere – we think about the polar regions. However, when scientists talk about the cryosphere, they are referring to all the places on Earth where water is in its solid form. This is where temperatures freeze water and turn it into ice.  

The cryosphere exists across the planet, including in places that are far from the poles. For example, there is snow on the top of Mount Kilimanjaro in Tanzania. The cryosphere expands in the cold winter months and seasonal areas of the cryosphere include any places where snow falls and where soil, river and lakes freeze.

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What is snow?

Snow is precipitation in the form of ice crystals. It forms in clouds when temperatures are below the freezing point and water vapour condenses without going through the liquid stage. These ice crystals freeze additional water vapour from surrounding air, it forms snow and falls to Earth. Scientists study snow, how it forms, where it falls and how the snowpack changes over time to better understand how snow affects the planet and our society.

Perennial snow is snow that persists on the ground year after year.

Seasonal snow is snow that accumulates during one season or snow that only lasts for one season.

Seasonal snow is the largest single component of the cryosphere. The mean winter maximum area covered by seasonal snow is 47 million square kilometres. This accounts for the largest difference between the Earth’s albedo from the summer to the winter.

As it exists on such a large scale, snow cover helps to regulate the exchange of heat between Earth’s surface and the atmosphere. Variations in snow cover can affect regional weather patterns, such as shifting the timing and lengths of monsoon seasons.

Snow can be measured in various ways – for example, the amount of snow that falls from the air, its depth on the ground, the amount of water in the snowpack and its total surface area.

Changes in climate can affect how much snow falls and the timing of the winter snow season. It is important for scientists to be able to understand changes in snow, to understand how climate change is causing patterns to shift.

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What is river ice?

River and lake ice is a sheet or stretch of ice that forms on top of a lake or a river when the temperature drops below freezing.

About half of surface waters in the Northern Hemisphere freeze annually. In some warmer areas, water may only freeze when it is exceptionally cold, but in other areas, such as Antarctica, lakes may have a permanent ice cover.

Most lake and river ice has a seasonal cycle – ice cover thickens in winter and melts in the spring. Generally, small lakes freeze more easily than rivers.

The appearance of ice on lakes and rivers requires prolonged periods with temperatures below 0⁰C. The deeper the lake, the more cold is needed to cool it down. Higher temperatures affect the duration of the ice cover, its freezing and thawing date and how thick the ice is.

Monitoring river and lake ice is important because its timing and break-up has a great ecological impact – for example, it affects the production and biodiversity of phytoplankton and the occurrence of winter fish kills.

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What are mountain glaciers?

Glaciers form when snow that has fallen over many years compresses into large, thickened ice masses. Glaciers are unique because, due to their sheer mass, they flow like very slow rivers.

Mountain glaciers are found in high mountains on every continent, except for Australia.

They form in places where more snow falls (accumulates) then melts (ablates) each year. After it falls, the snow compresses and changes from light, fluffy crystals to hard, round ice pellets. When more snow falls and buries this granular snow, the hard snow compresses even more and becomes a dense grainy ice called firn. The process of snow compacting into glacial firn is called firnification. When the ice grows to about 50 meters thick, the firn grains fuse into a mass of solid ice and the glacier starts to move under its own weight.

Gravity pulls mountain glaciers down valleys. Most glaciers will move very slowly, only a few centimetres a day, but some glaciers can move up to 50 meters a day. As they move, glaciers erode and wear away the land beneath and around them. They can create or deepens valleys by pushing dirt, soil and other materials out of their way.