Glaciers as Natural Resources. Glacial Hazards

Glaciers. Glaciers are masses of ice that flow downhill. They form when snow remains on the ground through summers so that, over time, the weight of successive snow layers compacts the snow and eventually turns it to ice. Ice becomes a glacier after it begins to move internally (deform) and slide downhill, which generally requires an ice thickness of at least 35 meters.

Glaciers cover approximately 10 percent of the Earth's land surface, and glacial ice represents 80 percent of the world's freshwater. Antarctica contains 90 percent of the world's glacial ice, and Greenland contains 9 percent, leaving just 1 percent in all the world's other glaciers. Of course, glacial coverage changes through time: At the height of the last ice age twenty thousand years ago, glaciers covered as much as 30 percent of the Earth.

Glaciers as Natural Resources. Glaciers offer many benefits to people, including practical or economic resources. Glaciers are ideal for water storage: The ice melts when summer temperatures rise and people most need the water, whereas ice (and thus water) accumulates during cold, wet winters. People use glacial water to drink, to irrigate, and to provide hydroelectric power. Glacial ice has also been used to cool drinks and to refrigerate foods.

The use of mountain snow and glacial ice dates back thousands of years in China, the Middle East, north Africa, and Europe. By the sixteenth century Europeans used ice consistently, and major markets developed in London, Paris, Granada, and Florence. In the 1600s Spanish colonizers in the Andes Mountains of South America imposed an ice mita, a system of forced labor that sent indigenous people to collect glacial ice for wealthy Spaniards living on South America's coast.

In Europe, Norway was a leading exporter of glacial ice before the late 1800s, when mechanical refrigeration took over. Some Japanese still use Alaskan glacial ice to cool their drinks.

Glaciers and People. Glaciers have shaped cultures and guided people's spirituality. For at least two thousand years peoples of South America have venerated the life-giving glaciated peaks of the Andes. Today religious pilgrims annually climb to the glaciers of Mount Ausangate in Peru, where they collect sacred, healing, and purifying glacial ice.

Glaciers have also played a prominent role in the culture of Tlingit and Athapaskan peoples in northwestern Canada. Oral histories reveal that glaciers not only affected hunting patterns and trade routes for these people, but also influenced social behavior, language development, place naming, and spirituality.

Glaciers also lure recreationists. Since the late 1700s mountaineers have climbed glaciers to reach the world's highest peaks. The link between glacier study (glaciology) and mountaineering has deep roots: Early mountaineers carried scientific instruments and made geological investigations during their climbs. For example, Scottish physicist James Forbes—who in 1843 made the first attempts to explain physical dynamics of glacial ice motion—found that studying glaciers quenched his intellectual thirst and that hiking on glaciers fulfilled his emotional passions.

The appeal of glaciers has also driven people to the Earth's poles. Curious explorers have visited the Arctic since a Greek sailor, Pytheas, attempted a voyage there twenty-five hundred years ago. The first landing in Antarctica was in 1895, and the first visit to the South Pole (by Norwegians) was in 1911. Recreationists' interest in Antarctica increased after 1958, when New Zealander Sir Edmund Hillary made the first traverse of Antarctica by land.

Glacial Hazards. Glaciers can pose serious threats to people. During the Little Ice Age (c. 1350-1850) global temperatures fell by 1-2° C. In response, glaciers generally advanced worldwide, occasionally creating problems for nearby inhabitants when glaciers overtook their pastures, fields, irrigation systems, bridges, homes, and even entire villages.

In 1663 Alps residents below the Aletsch glaciers pleaded with nearby Jesuit priests to perform ceremonies that would turn back the wicked glaciers. When the Black Rapids glacier in Alaska surged in 1936-1937, a wall of ice began racing at 66 meters per day toward local residents; today a surge in this glacier could break the Alaskan Pipeline.

Catastrophes also occur when glaciers generate outburst floods. Advancing glaciers from side valleys often dammed main valleys during the Little Ice Age. In 1595 the Gietroz glacier dammed the Val de Bagnes in Switzerland; when the ice dam burst, it killed five hundred people. In Argentina's Mendoza region advancing glaciers have produced ice-dammed lakes and catastrophic floods since 1788, and a 1934 flood killed many people, destroyed bridges, and wrecked 13 kilometers of railway.

Retreating glaciers can also trigger outburst floods. A deadly example occurred in Huaraz, Peru, when a melting glacier formed a lake that, in 1941, burst its moraine dam and killed six thousand people. Efforts were made to drain these glacial lakes and prevent catastrophic flooding in the Alps during the Little Ice Age, the Andes from the 1940s to the present, and the Himalayas since the 1980s.

Ice avalanches pose additional threats. In 1970 fifteen thousand people perished when an earthquake triggered an avalanche in Peru's Cordillera Blanca. When glacier-covered volcanoes erupt, glacial ice melts quickly and creates mudflows called "lahars" (avalanches consisting of ice, mud, water, and other debris). One of the worst cases occurred in 1986 when Colombia's Nevado del Ruiz erupted and produced a lahar that killed thirty thousand residents.

Glaciers and Climate Change. Because temperature and precipitation determine their size, glaciers make excellent climatic indicators. Glacier advances in Europe around 1600-1610, 1690-1700, 1770s, 1820, and 1850 reveal the coolest periods of the Little Ice Age, whereas glacier retreats during the Medieval Warm Period (c. 800-1200) and during much of the twentieth century demonstrate warmer periods.

To understand climate history, glaciologists have drilled ice cores in glaciers, which store data about precipitation, temperature, atmospheric conditions, volcanic eruptions, and winds. Scientists have drilled cores worldwide—from Kilimanjaro in Tanzania to Huascarän in Peru to Everest on the Tibetan Plateau to Vostok in Antarctica. But results from Greenland, where drilling began in 1958, offer the most accurate and longest records, which extend back 110,000 years.

These records have become particularly important in recent debates about global warming. Glaciers that store climatic history may also hold the key to understanding global climate in the future.