Importance of glaciers
A glacier is a huge mass of ice that moves slowly over land. The term “glacier” comes from the French word glace (glah-SAY), which means ice. Glaciers are often called “rivers of ice.”
Glaciers slowly deform and flow due to stresses induced by their weight, creating crevasses, seracs, and other distinguishing features. They also abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glacial ice is the largest reservoir of freshwater on Earth.
On Earth, 99% of glacial ice is contained within vast ice sheets (also known as "continental glaciers") in the polar regions, but glaciers may be found in mountain ranges on every continent including Oceania's high-latitude oceanic island countries such as New Zealand and Papua New Guinea.
Between 35°N and 35°S, glaciers occur only in the Himalayas, Andes, Rocky Mountains, a few high mountains in East Africa, Mexico, New Guinea and on Zard Kuh in Iran.
Glaciers cover about 10 percent of Earth's land surface. Continental glaciers cover nearly 13 million km2 (5 million sq mi) or about 98 percent of Antarctica's 13.2 million km2 (5.1 million sq mi), with an average thickness of 2,100 m (7,000 ft). Greenland and Patagonia also have huge expanses of continental glaciers.
Types of Glaciers
Glaciers fall into two groups:
Alpine glaciers form on mountainsides and move downward through valleys. Sometimes, alpine glaciers create or deepen valleys by pushing dirt, soil, and other materials out of their way. Alpine glaciers are found in high mountains of every continent except Australia (although there are many in New Zealand). The Gorner Glacier in Switzerland and the Furtwangler Glacier in Tanzania are both typical alpine glaciers. Alpine glaciers are also called valley glaciers or mountain glaciers.
Ice sheets, unlike alpine glaciers, are not limited to mountainous areas. They form broad domes and spread out from their centers in all directions. As ice sheets spread, they cover everything around them with a thick blanket of ice, including valleys, plains, and even entire mountains. The largest ice sheets, called continental glaciers, spread over vast areas. Today, continental glaciers cover most of Antarctica and the island of Greenland.
Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that forms on the surface of bodies of water.
How do glaciers form?
Glaciers begin forming in places where more snow piles up each year than melts. Soon after falling, the snow begins to compress or become denser and tightly packed. It slowly changes from light, fluffy crystals to hard, round ice pellets. New snow falls and buries this granular snow. The hard snow becomes even more compressed. It becomes a block of dense, grainy ice called firn. The process of snow compacting into glacial firn is called firnification. As years go by, layers of firn build on top of each other. When the ice grows thick enough - about 50 meters (160 feet) - the firn grains fuse into a huge mass of solid ice.
The glacier begins to move under its own weight. The glacier is so heavy and exerts so much pressure that the firn and snowmelt without any increase in temperature.
The meltwater makes the bottom of the heavy glacier slicker and more able to spread across the landscape.
Why do glaciers matter?
Glaciers are also a natural resource, and people all over the world use the meltwater that glaciers produce.
Scientists and engineers in Norway, central Europe, Canada, New Zealand, and South America have worked together to tap into glacial resources, using electricity that has been generated in part by damming glacial meltwater.
Demand for glacier water has increased in other, perhaps less expected ways, too. Some beverage companies sell bottles of glacial meltwater, and ice cubes made of glacier ice are popular in some specialty drinks. In fact, a Chilean man was arrested in 2012 for stealing five tons of ice from the Jorge Montt Glacier.
Many of the rivers coursing through China, India, and other parts of the Asian continent are fed largely by snowmelt from the Himalaya, but in late summer a significant part of river flow comes from melting glaciers. In South America, residents of La Paz, Bolivia, rely on glacial melting from a nearby ice cap to provide water during the significant dry spells they sometimes experience.
Glacier melting has accelerated in the European Alps since 1980, and 10 to 20% of glacier ice in the Alps was lost in less than two decades. The vast majority of all Himalayan glaciers have been retreating and thinning over the past 30 years, with accelerated losses over the last decade. Greenland alone contains 12% of the world's ice; entire portions of the Greenland ice sheet appear to be sliding towards the sea.
A 4°C rise in temperature would cause nearly all of the world's glaciers to melt. The meltdown of the Greenland ice sheet could be triggered at a temperature increase of 2-3°C. Glacier melt is caused by rising global temperatures and climate change. Climate change is the result of anthropogenic impacts on the environment, primarily through greenhouse gas emissions
Causes of Glacier Melt. Continued and widespread melting of glaciers during this century will lead to floods and water shortages for millions of people. As sea levels rise, coastal communities and habitats will be destroyed.
Stock photo from BMJ