Revised May 9, 1999 by W.W. Locke

First Edition by Adam N. Pedone Chandler

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Glacier Morphology:

Classification by Shape & Temperature

Shape Temperature
Confined Ice Unconfined Ice Surface Bed
Cirque Glaciers Continental Ice Sheets Temperate Glaciers Warm-based
Valley Glaciers Ice Caps Polar Glaciers Cold-based
Piedmont Glaciers Sub-Polar Glaciers

Glacier Classification by Shape:
Glaciers can be divided into two different basic categories: Confined (by topography) and Unconfined.

"Confined"

Ice masses in alpine environments are usually confined by valley walls. They are correctly termed "glaciers", and are commonly subdivided into cirque glaciers (localized within a semicircular basin at valley heads) and valley glaciers (which extend one to hundreds of km down valley). If a valley glacier empties onto an unconfining plain, the resulting pooled ice is termed a piedmont glacier.

Cirque Glacier:

Valley Glacier:
Cirque glacier, Wind River Range, Wyoming Cirque glaciers are the smallest of the alpine glaciers, they form in amphitheater like bowls and are confined to the basins they form in. A cirque glacier can be from a few hectares to square kilometers in area. Alaskan valley glacier A valley glacier usually originates as one or more cirque glaciers, then flows down valley as it accumulates mass,  grows, and joins others.

Piedmont Glacier:
Piedmont glacier (Malaspina) from space A piedmont glacier is a valley glacier that has spilled out onto adjacent flat land.  Here, a view from space at Alaska's Malaspina Glacier.
Cartoon of alpine glacier types

"Unconfined"

Unconfined glaciers are usually massive, they can be 1000's of square kilometers in area as well as 1000's of meters thick. They are subdivided into two categories: Ice Sheets and Ice Caps.  Ice caps are continental in scale (>50,000 km2), while ice caps are smaller.

Ice Sheets
South end of Greenland Ice Sheet from space Continental Ice Sheets:
A continental ice sheet (Greenland, to the left) is a vast expanse of ice which completely inundates all underlying terrain. They form in mountainous or non-mountainous regions and spread outward in all directions. The Continental Ice Sheet is the most significant of all the glacial agents because its immense size helps to cause climate change, as well as result from it.
Antarctica from space

The Antarctic Ice Sheet is the largest ice sheet on the planet, although it was matched by the combined Laurentide/Cordilleran Ice Sheet which covered North America north of about 45oN during the Pleistocene.

 South polar region
Ice Caps
Small ice caps, Ellesmere Island, Canada Ice Caps:
As shown at left on SW Ellesmere Island, Nunavut, arctic Canada, ice caps can be very small if a positive mass budget can be achieved on flat ground.  The problem is getting them to stop growing!

(Image courtesy Geological Survey of Canada, Terrain Sciences Division)

Transitional Ice Masses
Transection glacier - Baffin Island, Canada Naturally, Nature provides many other types of ice masses, including subdivisions of the major classes and forms transitional between them.  For example, mountain ice sheets are similar to continental ice sheets in that they cover relatively large areas.  However, they may not cover all of the underlying topography. Nunataks are unglaciated  islands of rock that stick up through the mountain ice sheet, as at left on Canada's Baffin Island, Nunavut.

Glacier Classification by Temperature:
Glacier temperature is an important factor when considering the glacial system: meltwater, erosion and deposition rates are directly related to the thermal characteristics of the glacier, especially its bed. The three classes of glaciers based on ice surface temperatures are TEMPERATE, POLAR, and SUB-POLAR.  The two classes based on bed temperatures are WARM- BASED and COLD- BASED.  An important consideration with respect to basal temperature is the pressure melting point.  Because ice is less dense than water (that's why it floats!), increasing pressure forces ice towards the more dense liquid phase, thus lowering the melting point slightly.

Temperate Glaciers:
In a temperate glacier the temperature is at the pressure melting point throughout the entire ice body except for the upper few meters of ice. This layer is subjected to annual temperature fluctuations.

Temperature on, in, and under glaciers

Warm-based Glaciers:
Warm based glaciers are at the pressure melting point at their bed.  Heat from the Earth and from basal friction provides energy to melt ice at the bed, thus facilitating slip and erosion.
Polar Glaciers:
Polar glaciers are always below the melting point at the surface. These glaciers produce no meltwater.  If they are thin and cold- based, ice movement is minimal. However, as in the case of the Antarctic Ice Sheet, they can be warm-based as well
Cold-based Glaciers:
Cold-based glaciers are below the pressure melting point at their beds.  They are thus frozen to the bed  Glacier movement is entirely by internal deformation above the bed, thus erosion is minimal
Sub-Polar Glaciers:
Sub-polar glaciers warm to the melting point at their surface in the summer time, thus produce meltwater.  They, too, may be warm- or cold- based.

Cold-based ice occurs where the rate of heat loss to the atmosphere (because of low average temperatures) requires a temperature gradient through the ice (determined by the insulating ability of ice) which maintains the bed at a temperature below the melting point (because of thin ice) despite the input of heat energy at the bed (from the warm Earth and local friction).   Similarly, warm-based ice reflects relatively high surface temperatures, thick ice, and/or high basal heat input.

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