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| Measuring the snowpack in a snowpit on Gulkana Glacier. Photo by R. March. |
The largest seasonal snowpack in
37 years was measured on Gulkana Glacier on May 2, 2003.
The
2003 seasonal snowpack averaged 1.79 meters water equivalent for the
whole glacier. The snowpack was measured at three elevations on the
glacier and combined to estimate the average. At 1,836 meters
elevation, the snow depth was 4.46 meters and the snow water
equivalent was 2.14 meters. At 1,680 meters elevation, the snow
depth was 3.37 meters and the snow water equivalent was 1.47 meters.
At 1,356 meters elevation, the snow depth was 1.90 meters and the snow
water equivalent was 0.84 meters.
The 37-year average snowpack is 1.12 meters
water equivalent. Prior to this year's measurement, the largest snowpack was in 1968
when the snow water equivalent was 1.57 meters water equivalent for the whole
glacier.
A large seasonal snowpack; indeed, even a series of large
snowpacks, is not necessarily an indication of the end of the current
widespread glacier retreat and a change toward glacier growth. This is because
summer melt is about twice as variable as seasonal snowpacks at Gulkana Glacier
and is the dominant control over the annual mass balance. Hence,
while an exceptionally large seasonal snowpack has the potential for
producing an abnormally positive mass balance, the summer melt
commonly overrides any abnormality in the seasonal snowpack. The possible effect of
this year’s large snowpack on the annual mass balance will not be
known until the end of the summer. Visit the Gulkana
Glacier mass balance web page for updates (only once or twice a
year).
The
large snowpack measured on Gulkana Glacier (about 60 percent above
average) contrasts with USDA,
Natural Resources Conservation Service (NRCS) mountain snow water
equivalent
map
for May 1st that shows the snowpack in the area to be less than
50 percent of normal. The difference probably reflects real
variations with altitude. Nearby NRCS measurement sites are
lower than Gulkana Glacier.
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| Upper Gulkana Glacier on May
2, 2003. Photo
by R. March |
Gulkana
Glacier is located on the south side of the Alaska Range about 10
miles north of Paxson along the Richardson Highway (see
map). The USGS has
measured the mass balance on Gulkana Glacier since 1967 as part of a
program to document long-term glacier and climate trends. This
monitoring program includes automated recording of daily air
temperature, precipitation, wind speed, and runoff, as well as
surveying of surface elevation, velocities, and mass balance at
three sites on the glacier, two or three times a year. In general,
the long-term trend is for shrinkage of Gulkana Glacier.
See USGS News Release of June18, 2003
here.
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