Blue Glacier set an ablation record on a summer day when it was cooler than normal at 8 degrees C with low thin clouds and fog, occasional showers, and a strong west wind. Glaciologists use the term ablation to describe the loss of material from a glacier through processes such as melting, evaporation, or calving. Sunshine is a highly effective means of melting snow and ice, but warm, wet, and windy weather can also quickly melt a glacier.

Both intensifying and reducing forces are always involved with solar radiation. For example, a dense cloud cover will reduce the amount of radiation reaching the snow but a thin layer of fog or clouds will actually increase melting. The incoming solar radiation bounces off the snow due to its high albedo, or reflectivity, and then is reflected again off the cloud layer. Solar radiation does not necessarily change snow to water, however. Often snow and ice evaporate directly into water vapor through a process called sublimation.

Water, through rain, condensation, or a supraglacial stream, is also an active means of ablation due to its high specific heat. A drop of rain just above freezing, or vapor condensing to the liquid state, contains enough heat energy to melt a significant amount of snow.

A thin layer of cold air, at or below freezing, insulates the glacier. Wind can disturb this layer so that it mixes with warmer air from above. The new air molecules on the glacier surface must lose their water vapor, condense, and in so doing cause melting. A glacier often creates its own wind. A katabatic wind forms when air cools over the ice surface and becomes heavier than the surrounding air. This cold mass sinks, flowing down slope or following a valley.

In order of importance, solar radiation, surface water, and vapor condensation cause ablation on Blue Glacier. Annually, the average melt is equal to a layer of water three to four meters thick over the entire glacier surface—roughly 4.5 billion gallons.



intro | terminology | accumulation | firn | blue | ablation | water | equilibrium | massbalance | movement | crevasse | structure | algae | moraine | debris | erosion
pdf version | glacier glossary | bibliography | about blue ice

Benjamin Drummond 2002