Types of glaciers
Types of glaciers are classifications of glaciers based on their size, shape, location, movement, and thermal characteristics, reflecting how they form, flow, and interact with the landscape.
Main article: Glacier
Types of glaciers are like different kinds of roads — some are narrow mountain paths (valley glaciers), some are sprawling highways across highlands (ice caps), and some are massive continental freeways (ice sheets), each moving ice in its own way.
Continental Glaciers
- Ice Sheets: Enormous, thick glaciers covering more than 50,000 km² of land. Today, they are found in Greenland and Antarctica.
- Ice Caps: Smaller than ice sheets, typically less than 50,000 km², covering highlands with outward-flowing ice.
- Outlet Glaciers: Fast-flowing glaciers that drain ice from an ice sheet or ice cap, often through mountain valleys.
Alpine Glaciers
- Valley Glaciers: Confined to a valley, carving it as they flow from higher elevations.
- Cirque Glaciers: Form in bowl-shaped depressions at the head of a valley on the side of a mountain.
- Piedmont Glaciers: Form when a valley glacier flows out and spreads onto a flat plain at the foot of the mountains.
- Ice Fields: A complex of merged mountain glaciers, usually less than 50,000 km².
Glaciers That Extend into Water
- Tidewater Glaciers: Glaciers that originate on land and flow into a body of water, like a bay or ocean.
- Ice Shelves: Portions of an ice sheet or ice cap that float on the ocean surface.
Classification of Glaciers
By Size, Shape, and Behavior
Glaciers can be understood through their form, internal temperature, and movement. Alpine glaciers form along mountain crests and slopes, gathering in valleys where gravity draws them downward. A glacier that completely fills a valley is called a valley glacier. When ice spreads broadly over a mountain or plateau, it becomes an ice cap or ice field, depending on size.
Glaciers larger than 50,000 km² become ice sheets — vast ice masses that cover entire continents, hiding the land beneath except for isolated peaks called nunataks. Today, Antarctica and Greenland host true ice sheets, holding enough freshwater to raise global sea levels by over 70 m if fully melted. At the edges, ice sheets can extend into the ocean as ice shelves. Fast-moving corridors, called ice streams, funnel ice toward the coast, sometimes projecting directly into the sea.
Tidewater glaciers — glaciers ending in the sea — are found in Greenland, Antarctica, Alaska, Baffin Island, Ellesmere, and Patagonia. As they reach saltwater, chunks break off in calving events, creating icebergs. Tidewater glaciers often follow long cycles of advance and retreat, less directly influenced by climate than land-bound glaciers.
By Thermal State
From a thermal perspective, glaciers can be classified by the temperature of their ice from surface to base:
- Temperate glaciers: Stay at the melting point throughout their depth, constantly cycling between freezing and thawing.
- Polar glaciers: Remain below freezing from top to bottom, though surface snow may soften seasonally.
- Subpolar glaciers: Contain pockets of temperate ice within predominantly cold ice layers.
The thermal condition at a glacier’s base affects its movement:
- Cold-based glaciers: Frozen to their bed, moving very slowly and causing minimal erosion.
- Warm-based glaciers: Rest at or near the melting point, allowing them to slide over their beds, eroding the landscape more actively.
- Polythermal glaciers: Combine both types, with some ice frozen to the bed and some free to move.
Summary Table of Glacier Types
For a quick overview, the main types of glaciers are summarized in the table below:
| Type | Size | Location | Notes |
|---|---|---|---|
| Ice Sheet | >50,000 km² | Greenland, Antarctica | Vast, continent-spanning ice; only nunataks visible |
| Ice Cap | <50,000 km² | Highland areas | Smaller than ice sheets; ice flows outward from center |
| Outlet Glacier | Variable | From ice sheets or caps | Fast-flowing corridors draining ice through valleys |
| Valley Glacier | Variable | Mountain valleys | Confined to valleys; carves the landscape |
| Cirque Glacier | Small | Mountain cirques | Forms in bowl-shaped depressions at valley heads |
| Piedmont Glacier | Variable | Mountain foothills | Spreads onto flat plains at valley exits |
| Ice Field | <50,000 km² | Mountain regions | Complex of merged mountain glaciers |
| Tidewater Glacier | Variable | Coastal areas | Flows into the ocean; prone to calving |
| Ice Shelf | Variable | Edges of ice sheets or caps | Floats on the ocean surface; fed by glaciers |
