13.1 Glacier formation and types

Glaciers form when snow accumulates year-round in cold climates. They require specific conditions, including freezing temperatures, adequate precipitation, and suitable topography. Over time, snow compresses into dense glacial ice through a process of metamorphism.

There are two main types of glaciers: alpine and continental. Alpine glaciers form in mountainous areas, while continental glaciers cover vast land areas. Both types shape the landscape as they move, creating distinctive features like U-shaped valleys and ice sheets.

Glacier Formation and Types

Conditions for glacier formation

• Cold climate with average annual temperature below freezing fosters year-round snow accumulation (Arctic regions)
• Adequate precipitation ensures snowfall exceeds melting and sublimation rates (coastal mountain ranges)
• Topography allows snow accumulation in shaded areas (north-facing slopes in Northern Hemisphere)
• Time sustains conditions over many years or decades for glacier development

Alpine vs continental glaciers

• Alpine glaciers form in mountainous areas, smaller in size and confined by valley walls (Matterhorn Glacier)
• Alpine glaciers flow downslope due to gravity, sculpting U-shaped valleys (Yosemite Valley)
• Continental glaciers cover vast land areas, known as ice sheets (Greenland Ice Sheet)
• Continental glaciers flow outward from central accumulation areas, not confined by topography

Snow metamorphism in glaciers

1. Initial snowfall deposits light, fluffy snow with high air content
2. Compaction reduces air spaces between snow crystals due to weight of overlying layers
3. Recrystallization breaks down and reforms snow crystals into larger, more rounded grains
4. Firn formation creates an intermediate stage between snow and glacial ice, denser and more tightly packed
5. Glacial ice forms through further compression and recrystallization of firn, reducing air content to less than 20%

Key components of glaciers

• Accumulation zone in upper part experiences net gain of mass over time (snowfields)
• Ablation zone in lower part undergoes net loss of mass due to melting exceeding accumulation (glacier terminus)
• Equilibrium line marks boundary between accumulation and ablation zones, shifts seasonally with climate changes