A glacier is a large, enduring accumulation of crystalline ice, snow, rock, sediment, and liquid water that forms on land. These massive ice bodies move downslope due to their own weight and the force of gravity. Glaciers develop where annual snowfall exceeds snowmelt, allowing layers to build up over many years, often centuries. As snow accumulates, it compacts and recrystallizes into dense glacial ice. This process creates distinct features as the ice slowly flows and deforms under pressure.
Continental Glaciers
Continental glaciers, also known as ice sheets, are immense masses of glacial ice covering more than 50,000 square kilometers (about 20,000 square miles) of surrounding terrain. These vast ice bodies form in polar regions where snow accumulates over thousands of years, compacting into thick layers of ice. The immense weight of the accumulated ice triggers movement, causing the ice to spread out under its own weight in broad domes.
The Earth currently has two primary continental glaciers: the Antarctic Ice Sheet and the Greenland Ice Sheet. The Antarctic Ice Sheet spans nearly 14 million square kilometers (5.4 million square miles), covering about 98% of the Antarctic continent, and reaches a thickness of almost 4.9 kilometers (3 miles) at its deepest point. It contains approximately 61% of the Earth’s fresh water. The Greenland Ice Sheet, though smaller, covers about 80% of Greenland’s landmass, extending over 1.7 million square kilometers (656,000 square miles) and reaching over 3 kilometers (1.9 miles) in thickness. Historically, continental glaciers covered large portions of the Northern Hemisphere during past ice ages, profoundly shaping landscapes through erosion.
Alpine Glaciers
Alpine glaciers, also referred to as valley glaciers or mountain glaciers, originate in high mountain ranges. They typically form in bowl-shaped depressions called cirques, located high on mountain slopes. As snow accumulates and compacts in these cirques, the ice begins to flow down valleys, constrained by the surrounding topography. This movement resembles slow-moving rivers of ice, following the existing contours of the mountainous terrain.
These glaciers are generally much smaller in scale compared to continental glaciers, ranging from hundreds of meters to over 100 kilometers in length. As they flow, alpine glaciers significantly reshape the landscape, carving distinctive U-shaped valleys, sharp mountain peaks, and ridges. They are found in mountain ranges across every continent except mainland Australia, including the Himalayas, the Alps, and the Rockies.
Key Distinctions Between Glacier Types
The primary differences between continental and alpine glaciers lie in their scale, shape, impact on topography, and typical locations. Continental glaciers are colossal ice masses, covering more than 50,000 square kilometers, and obscure the underlying landscape beneath their vast expanse. They spread outward from a central dome, driven by their immense weight.
Alpine glaciers, in contrast, are considerably smaller and are confined within mountain valleys. Their movement actively carves and sculpts the mountainous terrain, creating features like U-shaped valleys, sharp mountain peaks, and ridges. While continental glaciers are found exclusively in polar regions like Antarctica and Greenland, alpine glaciers exist in high mountain ranges globally, even in tropical areas if elevations are sufficient.