What makes glaciers grow

Scientists refer to this global collection of about 40 glaciers as "climate reference" glaciers. After decades of negative mass balance, glaciers worldwide are shrinking, fragmenting, or disappearing. Photos courtesy of Luca Carturan, University of Padova. In the update to their annual Global Glacier Change Bulletin , experts at the World Glacier Monitoring Service reported that glaciers in the reference network lost more than 1.

Tallying up each year's losses or gains, reference network glaciers have lost the equivalent of nearly 25 meters 82 feet water equivalent relative to —roughly the same as slicing an average of In State of the Climate in , glacier expert Mauri Pelto reported that the pace of glacier loss has accelerated from millimeters 6.

In many parts of the world—including the western United States, South America, China, and India—glaciers are frozen reservoirs that provide a reliable water supply each summer to hundreds of millions of people and the natural ecosystems on which they depend. Their accelerating retreat poses major challenges for people and nature.

Pelto, M. Alpine glaciers [in State of the Climate in ]. Pfeffer, W. Tidewater glaciers move at their own pace. Nature, , — WGMS , updated, and earlier reports. Global Glacier Change Bulletin No. Zemp, M.

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Like huge bulldozers, they plow ahead year after year, crushing, grinding, and toppling almost everything in their paths. Forests, hills, and mountainsides are no match for glaciers. Sometimes, glaciers form on volcanoes. When these volcanoes erupt, they are especially dangerous.

They send floods of water, ice, and rocks over the land and into the atmosphere. Alpine glaciers begin to flow downhill from bowl-shaped mountain hollows called cirques. As the glaciers overflow the cirque , they move downward. They dig deep into the terrain , forming rugged, dramatic landscapes. As they move, glaciers erode or wear away the land beneath and around them.

Glaciers carry great amounts of soil, rock , and clay. Some of the boulders they carry are as big as houses. Rocks carried hundreds and even thousands of kilometers by glaciers are called glacial erratics.

Glacial erratics differ significantly from the landscape in which they were deposited. The Big Rock was deposited from what is now northern Alberta, about 1, kilometers miles away, during the last ice age. They dig long grooves, called striations, in the surface of the Earth. Geologists can tell in what direction an ancient glacier moved by studying striations left in rock. Glaciers eventually deposit their loads of rock, dirt, and gravel. These materials are called moraine.

Lateral moraine forms along the side of a glacier. Medial moraine appears as dark lines near the center of the glacier. Supraglacial moraine appears on the surface of the glacier—dirt, dust , leaves, and anything else that falls onto a glacier and sticks. When glaciers began their final retreat 10, years ago, they left behind many landscape features, such as lakes, valleys, and mountains. Many hollowed-out areas carved by glaciers became lakes.

Bowl-shaped cirques, where most alpine glaciers form, became mountain lakes. These alpine lakes are called tarns. Glaciers can also create lakes by leaving depressions in the earth. The Finger Lakes in the western part of the U. The lakes were once stream valleys. Along the streams, the glacier scooped out troughs that now contain deep lakes. Glacial retreat created other features of the landscape. Materials deposited by a glacier as it retreats are called ground moraines.

The jumble of rock, gravel, and dirt making up ground moraines is called till. Much of the fertile soil in the Great Plains of North America was formed from layers of till left by ancient ice sheets.

Glacial valleys exist on almost every continent. These valleys are scooped out as a glacier scrapes through them. There are no glaciers in Australia, but Mount Kosciuszko still has glacial valleys from the last Ice Age. Distinctive mountain formations called aretes and horns are the result of glacial activity. Glacier National Park in the U.

These tall, singular landforms are also called pyramidal peaks. Roche moutonnee is a smooth, rounded rock formation created as a glacier crushes and rearranges rocks in its path. Roche moutonnee is visible in many hilly areas as outcroppings of flat rock.

In contrast to alpine glaciers, ice sheets do not create landscape features as they spread. They tend to smooth out the land beneath them. Glaciers provide people with many useful resources. Glacial till provides fertile soil for growing crops. Deposits of sand and gravel are used to make concrete and asphalt.

The most important resource provided by glaciers is freshwater. Many rivers are fed by the melting ice of glaciers. The Ganges is the most important source of freshwater and electricity in India and Bangladesh. Electricity is created by dams and hydroelectric power plants along the Ganges. Some companies link glacial water to clean, fresh taste. Because water has been trapped in the glacier for so long, many people believe it has not been exposed to pollutants that liquid water is exposed to.

The dramatic, diverse landscape of Yosemite Valley, California, was sculpted entirely by glaciers during the last Ice Age. Threats to Glaciers The processes that remove snow, ice, and moraine from a glacier or ice sheet are called ablation. Ablation includes melting, evaporation, erosion, and calving. Glaciers melt when ice melts more quickly than firn can accumulate. Glaciers are important indicators of global warming and climate change in several ways.

Melting ice sheets contribute to rising sea levels. As ice sheets in Antarctica and Greenland melt, they raise the level of the ocean. Tons of fresh water are added to the ocean every day. Large icebergs created by such an event create hazards for shipping. Large additions of fresh water also change the ocean ecosystem. Organisms, such as many types of corals, depend on salt water for survival.

Some corals may not be able to adjust to a more freshwater habitat. The loss of glacial ice also reduces the amount of fresh water available for plants and animals that need fresh water to survive. Glaciers near the Equator , such as those on the tropical island of Papua or in South America, are especially at risk. The residents below Chacaltaya Glacier in Bolivia, for instance, depended on the glacier for almost all of their fresh water and electricity.

In , Chacaltaya Glacier melted entirely. A few glaciers may actually be benefiting from global warming. Glaciers are growing quickly there.