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![NRCS This Week mast head](https://webarchive.library.unt.edu/eot2008/20090111095421im_/http://www.nrcs.usda.gov/news/thisweek/images/mastheaddshadow3.jpg)
Supply Forecast Program Monitors Mount Saint Helens Snowpack
![Spirit Lake SNOTEL site in the state of Washington - photo by Melissa Clark](https://webarchive.library.unt.edu/eot2008/20090111095421im_/http://www.nrcs.usda.gov/news/thisweek/images/snotelspiritlake.jpg)
Spirit Lake SNOTEL site in the state of Washington - photo by
Melissa Clark |
In the interest of public safety, the National Weather Service Northwest River
Forecast Center has requested the
NRCS Snow Survey and Water Supply Program to resurrect a procedure developed
in May 1980 to estimate snowpack water content surrounding Mount Saint Helens.
After several decades of inactivity, Mount Saint Helens erupted in late
September 2004 with ash and steam coming from the crater dome. A series of
harmonic tremors also signaled the movement of lava upward into the crater and
brought concern that an eruption, and subsequent rapid snowmelt, could once
again flood the Toutle River valley.
Immediately following the 1980 eruption, the NRCS installed additional Snow
Telemetry (SNOWTEL) sites near Mount Saint Helens to monitor seasonal snowpacks.
Six SNOTEL sites still surround the mountain and provide observations every six
hours that are placed on the Oregon Snow Survey and
Water Supply
Forecasting Program webpage. The six SNOTEL sites are used to create a
weekly
Mount Saint Helens Snowpack Analysis. The Snowpack Report summarizes the
amount of water available from existing snowpacks in four quadrants, (north,
south, east, west) that surround the mountain. Area-elevation curves constructed
in 1980 are used to estimate the volume of water, in acre-feet, for each
quadrant in three vertical zones (3,330 to 4,101 ft., 4,100 to 4,900 ft., and
4,900 to 8,200 ft.). The water content can be used as input to flood routing
models that estimate peak flows and travel times to downstream points.
Cascade Mountain snowpacks generally peak in early April and by July most
snowpack has melted except for high elevation glaciers which were significantly
reduced in size when the mountain lost 1,314 feet during the 1980 eruption. The
post-1980 Mount Saint Helens landscape is greatly diminished in its ability to
capture and retain significant snowpacks on the north face which collapsed and
blew outward into Spirit Lake. Inside the crater, a glacier has formed between
the lava dome and the south side of the crater. The USGS estimates this glacier
contains 43,240 acre-feet of water that is affected by strength of eruptive
activities within the dome. The National Weather Service includes this volume
with the north quadrant snowpack to determine flood risk.
The USGS Cascades Volcano Observatory provides a wide variety of information
describing Cascade Volcano seismic activity.
Your contact is Jon Werner, Acting Director,
NRCS National Water and Climate Center,
at 202-720-0772, or jon.werner@usda.gov
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