The Tokositna Glacier in the Denali National
Park and Preserve was reported to be surging in an Associated Press
release dated April 22nd. Tokositna Glacier is a 23-miles long, medium
sized glacier, on the south flank of the Mount McKinley massif (see the
satellite image). The USGS has documented the behavior of the Tokositna
Glacier for more then four decades. Austin Post (USGS-retired)
identified the Tokositna Glacier as a possible surge-type glacier in an
article published in 1969 and began aerial photo documentation during
1957 while working with the University of Washington. USGS aerial-photo
documentation by Post, Krimmel, and Mayo contains 190 aerial photos of
Tokositna Glacier dating from 1966 through 1987. Since 1957, Tokositna
Glacier has had at least two notable events that displaced the lower
reaches of the glacier by about 2 kilometers (the 1971 aerial photo
shows the Tokositna in surge). These events failed to reactive all of
the stagnant ice at the terminus and produce an advance of the terminus.
In a 1978 paper, Larry Mayo (USGS - retired) identified the Tokositna as
a type example of "pulsing" glacier. A pulsing glacier
experiences flow-speed increases that are intermediate between the
10-fold increase that defines a surge-type glacier and the seasonal
speed changes associated with "normal" glacier flow. Guy Adema,
Denali National Park and Preserve glaciologist, has suggested the
current event will begin advancing the terminus into the Tokositna River
within a month. If this occurs, it will be an exciting exception to the
50-year history of Tokositna Glacier flow events and demonstrate that a
single glacier can undergo a broad range of flow instabilities. If the
current event is a full surge of the Tokositna Glacier, the outburst
flood that is associated with the culmination of a surge should be
larger than those associated with pulses. However, a 3-kilometer advance
of the terminus that could form a glacier dammed lake in the lower
Kanikuta valley, is very unlikely in light of the 50 year observational
history of Tokositna Glacier.
The surge of Tokositna Glacier is not
unique. On a short reconnaissance flight last summer, Austin Post
observed that the terminus of Hayes Glacier (on Mt. Spurr) was advancing
due to a surge, a small glacier was surging in the Boomerang Creek
drainage on the north flank of the Wrangell Mountains, and the Steller
Lobe (the western one-third of the Bering Glacier piedmont lobe) is
rapidly advancing into a glacier dammed lake (Berg Lake) from which it
has been retreating for decades. The Steller tributary to the Bering
system has not previously been considered a surge-type glacier. However,
the reported rapid advance into Berg Lake may reveal a previously
unrecognized aspect of its behavior. Other reported surge activity
include the Yentna Glacier (also on the south flank of the McKinley
massif) which was surging last summer and the Lacuna Glacier (a large
tributary to the lower Yentna) is surging at this time. See the
satellite image for the locations of the Yentna and Lacuna Glaciers. |
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March 19, 2001 LANDSAT 7 ETM+ browse image, path 71 row 16. The ongoing
ice flow instabilities of Tokositna and Lacuna Glaciers are not evident
in this low resolution image.
USGS oblique aerial photograph made July 29, 1971 by Larry Mayo. Shows
Tokositna Glacier during the beginning of its 1971-72 flow instability.
If you would like more information on glaciers in Alaska please visit: http://ak.water.usgs.gov/glaciology
You can also email Dennis Trabant
at dtrabant@usgs.gov or Rod
March at rsmarch@usgs.gov |
