Parts of the Water Cycle

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Ice, Snow, and Glaciers: The Water Cycle

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A stylized view from space of Greenland, showing the large extent of the icecap covering the country. Credit: NASA

NASA's Aqua satellite used microwaves to capture this snapshot of Arctic sea ice on September 3, 2010. The yearly minimum had not yet been reached, which normally occurs in mid-September.
Credit: NASA
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Stored water as part of the water cycle

The water cycle describes how water moves above, on, and through the Earth. But, in fact, much more water is "in storage" at any one time than is actually moving through the cycle. By storage, we mean water that is locked up in its present state for a relatively long period of time. Short-term storage might be days or weeks for water in a lake, but it could be thousands of years for deep groundwater storage or even longer for water at the bottom of an ice cap, such as in Greenland. In the grand scheme of things, this water is still part of the water cycle.

Ice caps around the world

Map of where glaciers and ice caps exist on Earth.
Credit: National Geographic

The white areas in this map show glaciers and ice sheets around the world (reproduced from National Geographic WORLD, February 1977, no. 18, p. 6, with permission). The vast majority, almost 90 percent, of Earth's ice mass is in Antarctica, while the Greenland ice cap contains 10 percent of the total global ice mass. The Greenland ice cap is an interesting part of the water cycle. The ice cap became so large over time (about 600,000 cubic miles (mi³) or 2.5 million cubic kilometers (km³)) because more snow fell than melted. Over the millennia, as the snow got deeper, it compressed and became ice. The ice cap averages about 5,000 feet (1,500 meters) in thickness, but can be as thick as 14,000 feet (4,300 meters). The ice is so heavy that the land below it has been pressed down into the shape of a bowl. In many places, glaciers on Greenland reach to the sea, and one estimate is that as much as 125 mi³ (517 km³) of ice "calves" into the ocean each year—one of Greenland's contributions to the global water cycle. Ocean-bound icebergs travel with the currents, melting along the way. Some icebergs have been seen, in much smaller form, as far south as the island of Bermuda.

Ice and glaciers come and go

The climate, on a global scale, is always changing, although usually not at a rate fast enough for people to notice. There have been many warm periods, such as when the dinosaurs lived (about 100 million years ago) and many cold periods, such as the last ice age of about 18,000 years ago. During the last ice age much of the northern hemisphere was covered in ice and glaciers, and, as this map from the University of Arizona shows, they covered nearly all of Canada, much of northern Asia and Europe, and extended well into the United States.

Map of the world showing the extent of glaciers about 18,000 years ago.

Glaciers are still around today; tens of thousands of them are in Alaska. Climatic factors still affect them today and during the current warmer climate, they can retreat in size at a rate easily measured on a yearly scale.

Ice caps influence the weather

Just because water in an ice cap or glacier is not moving does not mean that it does not have a direct effect on other aspects of the water cycle and the weather. Ice is very white, and since white reflects sunlight (and thus, heat), large ice fields can determine weather patterns. Air temperatures can be higher a mile above ice caps than at the surface, and wind patterns, which affect weather systems, can be dramatic around ice-covered landscapes.

Some glacier and ice cap facts

Bering Glacier in Alaska is the largest glacier in North America. This NASA satellite view shows how a glacier is similar to a river.
Credit: NASA Earth Observatory
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Glacial ice covers 10-11 percent of all land.
According to the National Snow and Ice Data Center (NSIDC), if all glaciers melted today the seas would rise about 230 feet (70 meters).
During the last ice age (when glaciers covered more land area than today) the sea level was about 400 feet (122 meters) lower than it is today. At that time, glaciers covered almost one-third of the land.
During the last warm spell, 125,000 years ago, the seas were about 18 feet (5.5 meters) higher than they are today. About three million years ago the seas could have been up to 165 feet (50.3 meters) higher.
Largest surface area of any glacier in the contiguous United States: Emmons Glacier, Washington (4.3 square miles or 11 square kilometers)

ice caps and global water distribution

Charts showing that 1.7 percent of Earth's water is ice and 68.7 percent of freshwater on Earth is ice. Even though the amount of water locked up in glaciers and ice caps is a small percentage of all water on (and in) the Earth, it represents a large percentage of the world's total freshwater. As these charts and the data table show, the amount of water locked up in ice and snow is only about 1.7 percent of all water on Earth, but the majority of total freshwater on Earth, about 68.7 percent, is held in ice caps and glaciers.

**One estimate of global water distribution**
Water source	Water volume, in cubic miles	Water volume, in cubic kilometers	Percent of total water	Percent of total freshwater
Ice caps, Glaciers, & Permanent snow	5,773,000	24,064,000	1.7%	68.7%
Total global freshwater	8,404,000	35,030,000	2.5%	--
Total global water	332,500,000	1,386,000,000	--	--
Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823.

Sources and more information

Glacier Studies - USGS Eastern Earth Surfaces Processes Team
Glaicer and Snow Program - USGS Water Resources of Alaska
The Ice Cap and the first Icebergs
Glacier Facts & Figures, National Park Service
Greatest Places Physical Geography:

Choose a water-cycle topic
	A - Storage in ice and snow B - Precipitation C - Snowmelt runoff to streams D - Infiltration E - Groundwater discharge F - Groundwater storage G - Water storage in oceans H - Evaporation	I - Condensation J - Water storage in the atmosphere K - Evapotranspiration L - Surface runoff M - Streamflow N - Springs O - Freshwater storage P - Sublimation