Defining a Glacier
A glacier is a persistent body of dense ice that is constantly moving under its own weight; it forms where the accumulation of snow exceeds its ablation (melting and sublimation) over many years. These colossal ice masses are distinct from sea ice or frozen lakes because they originate on land and flow like very slow rivers.
How Glaciers Form and Move
Glaciers begin when layers of snow compact over time, transforming into granular ice, then firn, and finally into dense, crystalline glacial ice. Once thick enough, the ice deforms and flows due to gravity and the pressure of overlying snow and ice. This movement, known as glacial flow, can happen internally (creeping) or by basal sliding, where meltwater at the base reduces friction.
Types of Glaciers and an Example
There are two main types: continental glaciers (or ice sheets), which are vast, unconfined ice masses covering large land areas, like those in Antarctica and Greenland; and valley (or alpine) glaciers, which are confined by mountain valleys, typically flowing from high elevations. A prominent example is the Athabasca Glacier in the Canadian Rockies, which is a valley glacier actively reshaping the landscape through which it flows.
Impact of Glaciers on Landscapes and Climate
Glaciers are powerful agents of erosion and deposition, sculpting V-shaped river valleys into U-shaped glacial valleys, carving out fjords, and leaving behind distinctive landforms like moraines, cirques, and drumlins. Globally, they are critical freshwater reservoirs and their melting contributes significantly to sea-level rise, making them vital indicators of ongoing climate change.