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Background:
 

Location Map  

Location map of the Mapaspina Glacier on the Gulf of Alaska coast (click to enlarge)
(U. Texas, Austin Map Library
Physical Setting and Attributes

  • Malaspina Glacier (60º N latitude, 140º W longitude) is the largest glacier in Alaska and the largest piedmont glacier in the world. 

  • It covers nearly 4000 km2 (~1,600 mi2) of the coastal plain east of the Saint Elias Mountains, stretching between Yakutat Bay to the south and Icy Bay to the north.

  • Satellite photos clearly show that Seward Glacier is the largest ice contributor to the Malaspina, followed by the Agassiz Glacier further west.  The Seward flows through a narrow (~4 km wide) valley and fans out as the Malaspina Glacier to a width of ~65 km at the Sitkagi Bluffs along the Gulf of Alaska coast.  Agassiz Glacier is only ~5 km wide at the mouth of its valley where it becomes the Malaspina, and the distance from the Aassiz and Seward valley mouths to the Sitkagi Bluffs is ~45 km. 

  • Seismic investigations reveal that the Malaspina is ~600 m thick, and extends as much as ~300 m below sea level, although it is not a tidewater glacier at its present size and with present-day sea-level. 

NASA Photo
Space Shuttle visible photo (NASA, 1989)


LANDSAT 7 false-color composite image (NASA; click to enlarge)

Contoured Moraines and Surging Behavior

One of the most characteristic features of the Malaspina is its contoured moraines. Visible and false-color composite satellite images (made using infrared, near infrared, and green wavelengths of the LANDSAT 7 thematic mapper plus sensor) clearly show these features, which are most pronounced on the eastern margin of the main (Seward) lobe.

Early investigators of the Alaskan glaciers attributed the contoured moraines to surging behavior (Post, 1969).

What is a Surging Glacier?: A "surging" glacier has a repeating cycle of short intervals (months to a few years) of high-velocity flow separated by longer quiescent intervals (10-100 years) of low ice velocity. The majority of evidence suggests that basal hydrology is responsible for surging behavior. Increasing basal pore pressure due to the presence of basal water reduces the effective normal stress imposed by the weight of overlying ice, allowing the glacier to slide over the bed at high velocity. When the sub-glacial water channels become interconnected and basal pore pressure dramatically decreases, the surging phase ceases and the quiescent phase ensues (Raymond, 1987)

Visible Images of Contoured Moraines

Contoured moraines         contoured