How do Glaciers Form?
The large mass of a Glacier is a result of crystalline ice, snow, rock, sediment, and often liquid water buildup on land. Its immense weight is moved downslope due to the force of gravity acting on it. The United States Geological Survey agency outlines three instances where glaciers exist or can potentially be formed:
- mean annual temperatures are close to the freezing point
- winter precipitation produces significant accumulations of snow
- temperatures throughout the rest of the year do not result in the complete loss of the previous winter’s snow accumulation
If snow continues to accumulate past its ablation point for decades or centuries, the metamorphosis from snow to glacier ice can occur.
As the stress of gravity moves a glacier, its shape deforms. Crevasses, or breaches in the ice, fissure reactively. Intersecting crevasses often produce seracs, which are blocks or columns of glacial ice forced upright. Both glacial creations are known within the mountaineering community as objective dangers. A climber who successfully summited Denali, the tallest mountain in North America, slipped into a crevasse on his descent. It took rescuers 12-hours to chip away the ice and successfully save the mountaineer who had landed 40-feet down. K2, the second tallest mountain the world, requires passage up a couloir overhung with seracs. This segment, known as the Bottleneck, is located only 400 meters below the summit. In 2008, 11 climbers perished when the overhanging seracs loosened and crashed down onto the route.
Not only does a glaciers movement affect its form, but it also shapes the earth beneath it. Abrasion, a process of scraping or eroding away through friction or erosion, shakes up debris of substrate from the earth. This displaced substrate can leave landforms like cirques or moraines. A cirque is an arm-chair like valley formed by glacial erosion or other fluvial processes. Fluvial processes refer to rivers and streams and the geomorphology associated with them. When referring to geomorphology associated with glaciers, ice sheets, or ice caps, the accepted terms are glaciofluvial or fluvioglacial.
After fluvial or glaciofluvial processes shape an amphitheater-like landform, its inner hallow can fill with snow. Nivation (a group of processes that includes freeze-thaw activity, chemical weathering, and seasonal snow melt) then compacts snow into a glaciated state. The accumulated weight of the glaciated ice now abrades its enclosure. Simultaneously, the cirque’s glacier escapes down its only unobstructed course (also known as an overflow point). A moraine is any pile or accumulation of debris or glacial till resulting from glaciofluvial processes. Because of the looseness of its formation, compacting the vast range of processes into one definition is frivolous. Moraine creation depends the origin, movement, and shape of a glacier.
Glaciers only form on land, though their terminus often meets water.