ABOUT THE MATANUSKA GLACIER
The Matanuska Glacier is a large ice flow, 24 miles long and 4 miles wide at the terminus, averaging approximately 2 miles in width. This glacier is a valley glacier; it exists on a valley floor. The majority of glaciers in Alaska today are smaller alpine glaciers which hang off mountain slopes.
The Matanuska is an active glacier which advances at one foot per day. It takes approximately 250 years for the ice to form up-glacier and advance to the terminus. The ice of an active glacier always moves forward due to gravity; like water in a river, the ice will flow down valley. When ice melts at a higher rate than snow accumulates, the glacier margin 'recedes'. (The term 'receding' does not refer to the ice actually traveling back up the valley.)
A frequently asked question concerns the cause of the blue ice. The density of glacier ice allows the entire spectrum of light to be absorbed with the exception of the blue light which is reflected, and can therefore be seen by your eye.
Moraine: Debris (including large boulders, gravel and sand) that has been deposited by the glacier in various ways.
Lateral: Lining both sides of the glacier, lateral moraines run parallel to ice flow. Lateral moraines are generally created by two processes:
1) a build up of debris between the sides of the glacier and the bases of surrounding mountains from rock slides off mountain
2) the dumping of rocks and other debris off the sides of the ice.
Medial: Created as two ice flows merge. As the glaciers meet, a pile of debris is pushed up in between them. The medial moraine may be recognized as a 'ribbon' of black material running down the center of the glacier.
End or Recessional: The terminus (or end) of the glacier is marked by this moraine. Generally lying perpendicular to ice flow, the
end moraine is created as the ice melts and deposits rock and debris.
Vent: An opening in the ice through which water exits the glacier, draining the sub-glacier and en-glacial conduits. The sub-glacial water discharged from this vents is occasionally supercooled (in a liquid state although the temperature is below the freezing point), leading to 'Vrazil' ice growth, and formation of terraces and rims surrounding vents.
Basal Ice: The debris rich ice layer at the bottom of the glacier. This ice is easily visible in several places at the terminus. Most sediment comprising the moraines is first transported in the basal ice.
Debris Flow: A small scale avalanche of rock, debris, and water.
Moulin: A wide vertical shaft connecting the ice surface to the glacial conduit system. Moulins are created by melt water and can be hundreds of feet deep.
Crevasse: A large crack in the ice that may be up to several hundred feet deep and several feet wide, caused by differential speeds in the ice movement.
Serac: Large, towering blocks of ice. Also created by differential speed in ice movement.