Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
OBSERVATIONS ON THE DEVELOPMENT / DESTRUCTION OF POTENTIAL SLIDING
LAYERS IN A PATH CONTROLLED WITH LARGE AMOUNTS OF EXPLOSIVES AND
ARTILLERY:
Mike Stanford, Brandon Levy
Washington State Department of Transportation
ABSTRACT:
The Old Faithful slide area just west from the summit of Stevens Pass in central Washington State is a
time tested area for Avalanches. Thousands of rounds of Artillery and tens of thousands of pounds of
explosives have been used over the years to control the hazard to US Highway 2. The area receives an
average snowfall of 454” per year. Big snowfall events followed by rain events are a common scenario.
WSDOT Forecaster/Controllers employ a hazard mitigation philosophy of “no snow, no hazard” in this
area. If there is little or no snow in the starting zones, then the hazard to the highway can be greatly
reduced. Unlike ski area mitigation strategies, there is no reason for us to maintain “skiable” terrain. Large
explosive charges, 25-200 lbs. are the norm.
With Ski Area expansion, the increase in “side country” skiing and dawn patrolling, increasing numbers of
skiers and boarders are finding their way into controlled paths that affect the highway. The need to hone
forecasting skills with these paths is becoming more and more important. Depending on “Backcountry”
forecasts and observations or profiles done outside these areas may be dangerous as the snowpack in
these highway chutes is not like the snowpack outside the areas that are controlled for the simple reason
that it has been altered by the use of explosives.
This poster will examine the development/destruction of potential sliding layers within one of the main
chutes in the Old Faithful Area caused by the artillery and explosives used to control the hazard to the
highway. We will compare this information with a similar chute not affected by Artillery or Explosives.
Keywords:
Old Faithful, Highway, Forecasts
1. INTRODUCTION
We refer to the highway as an “auto feed”.
State Route 2, Stevens Pass, is one of three
main passages through the Cascade
Mountains of Washington State. Unlike other
areas such as Ski Areas, affected by
potential avalanches, the highway is open
24/7/365. The highway continually provides
us with potential hazards in the form of
traveling motorists. If there is no chance of
injury to person, or damage to property,
there is no Avalanche danger. Conversely, if
we have no snow in our starting zones, we
have significantly reduced the hazard.
Figure 1: Weekend ski traffic can turn the
highway into a parking lot dramatically
increasing exposure time to Avalanche
hazard.
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Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
This philosophy is called the “no snow, no
hazard” method.
would be controlling soon and thus,
changing it again. Now however, for
whatever reason, more and more people are
finding themselves hiking and skiing in
Avalanche Paths that affect the highway.
The number of skiers and boarders in these
paths is not to the point where they are
effectively providing skier compaction. They
are merely a potential trigger in an
avalanche path. Due to this increasingly
popular scenario, more diligence needs to
be taken when forecasting these paths.
Using explosives to control Avalanche
Hazard brings with it, its own considerations.
Potential sliding layers can be formed by the
very explosives we use to control the
hazard. The need to identify, examine and
understand this phenomenon is apparent.
Forecasters responsible for a highway have
very little off time during the winter. The auto
feed is always on. The more we understand
what is going on in our chutes, the better
forecasters we will be. This project will
hopefully aid in our efforts to learn more, ski
more and worry less. Also, as with so many
experiments, these observations are
ongoing and incomplete. Further digging will
be done this upcoming winter.
3. TEST SITES
The Old Faithful Area on Stevens Pass is
one of the most Avalanche prone sites in
Washington State. Two test sites were used.
2. FORECASTING
Our regional Avalanche Forecast Center
produces two products. They provide a
mountain weather forecast and they provide
a “backcountry” avalanche forecast.
Forecasting for controlled paths that affect a
highway is left to the Forecasters and
Controllers responsible for that highway. It
would be virtually impossible and impractical
for our Regional Avalanche Center to try to
forecast for the chutes we control. We also
have paths that affect the highway that we
control passively by closing the highway
when the hazard reaches a critical point.
These areas we treat the same way we treat
a backcountry area. Our Region Forecast
Center is a vital link in our operation for
these areas.
Figure 2: The Old Faithful area produces
several large slide cycles per winter.
The first site was in the starting zone of shot
#4 of the Old Faithful slide area. Site
number two was on a slope similar in aspect
and elevation to site one in an area called
Hunter Hill. Profiles were done at each
location on the same day after control had
been conducted on the highway. A total of
six profiles were done at each site. Three
profiles of each site are presented on this
poster. All of the data collected is available
upon request.
Using a backcountry forecast to forecast
hazard in a controlled area can be
dangerous. This is a fact that we have
known for years. In that respect, this poster
does have a certain amount of “duh” factor
to it. However, until recently, the one factor
we did not have to consider very often was
human triggers. We knew that the structure
of the snow in our chutes was different, but
we were able to live with it, knowing we
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Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
The winter of 2011-2012 provided us with a
very well developed surface hoar layer that
became buried in early February and
remained a distinct player in the pack well
into the spring. This layer acted as a good
marker for us to observe as time
progressed.
5. CONCLUSIONS / QUESTIONS
We have come away from this brief
encounter with one winter’s snowpack
asking more questions than when we began.
We did not and did not expect to, come
away with any one “light bulb” moment. The
fact that explosives disrupt the snow is
nothing new to any experienced practitioner.
4. EXPLOSIVES
WSDOT uses a variety of tools to control the
hazard on Highway 2 in the Old Faithful
Area. Bomb Trams with 50 lb. bags of ANFO
producing large air blasts combined with 25
lb. bags of ANFO placed in the snow ignited
simultaneously are common.
In the maritime snow climate faceting is
often observed adjacent to crusts. In our
shot #4 starting zone in particular we use
large amounts of ANFO, 125 lbs., regularly
during mitigation efforts. Is this large
amount of ANFO hot enough and large
enough to create a crust in the blast area?
If this is indeed the case as was observed
during this last winter of 2011-2012, are we
providing an opportunity for facet formation
around this localized crust?
Artillery is also used in the form of 105 mm
Howitzers and M60 Main Battle Tanks. The
ability to use large charges and employ the
“no snow, no hazard” method has worked
well for us here.
Another question concerns our “no snow, no
hazard” approach. From a practitioner’s
standpoint this mitigation technique has
proven its worth. However, it is clear from
our observations that the snowpack in the
path subjected to mitigation efforts using
explosives is shallower than the
“backcountry” snowpack. A thin snowpack
is weaker because it is subjected to greater
temperature gradients. One may argue that
temperature gradients are not important
factors in the maritime climate because most
of our avalanche problems center on directaction storm snow events. Stevens Pass
experiences cool easterly flow throughout
the winter season. During these periods the
temperature gradient causes weak layer
formation. Therefore, does the “no snow, no
hazard” approach actually allow facets to
form because the resultant thinner
snowpack is at times (e.g. cool east flow),
subjected to a greater temperature gradient
than a thicker un-controlled snowpack?
Although producing Avalanches is our
primary goal, there are times that we will use
these large charges to simply disrupt the
layering in the pack. This method has been
well tested since the days of Monty Atwater.
Depending on condition and atmospheric
events, simply “shaking up” the snowpack
can be very effective.
Figure 3: Large amounts of explosives and
Artillery are used to control the hazard in this
area.
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Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
Figure 4: Profiles were done at both
locations on the same day.
In presenting this poster, our hope is that
others will become more aware of the
somewhat obvious. As you can see, we
have come away with more questions that
need to be answered. We would like to
create a dialogue with other professionals
who may see something we do not or who
may have questions that we have not
thought about and can perhaps look to
answer.
If we had to pick the one thing we did bring
away from our time in the holes, it would be
a better sense of situational awareness of
the area we are tasked to monitor and
mitigate and what each new meteorological
event or control mission may do to it.
7. CONTACTS
If you would like more information or want to
contact either author.
[email protected]
[email protected]
We would encourage anyone with questions
or comments to contact us.
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