NHESSDNatural Hazards and Earth System Sciences DiscussionsNHESSDNat. Hazards Earth Syst. Sci. Discuss.2195-9269Copernicus GmbHGöttingen, Germany10.5194/nhessd-3-2883-2015Point release wet snow avalanchesVera ValeroC.cesar.vera@slf.chBühlerY.https://orcid.org/0000-0002-0815-2717BarteltP.WSL Institute for Snow and Avalanche Research SLF, Flüelastrasse 11, 7260 Davos Dorf, SwitzerlandC. Vera Valero (cesar.vera@slf.ch)30April2015342883291217February201521March2015This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://nhess.copernicus.org/preprints/3/2883/2015/nhessd-3-2883-2015.htmlThe full text article is available as a PDF file from https://nhess.copernicus.org/preprints/3/2883/2015/nhessd-3-2883-2015.pdf
Wet snow avalanches can initiate from large fracture slabs or small
point releases. Point release wet snow avalanches can reach dangerous
proportions when they (1) initiate on steep and long avalanche paths
and (2) entrain warm moist snow. In this paper we investigate the
dynamics of point release wet snow avalanches by applying a numerical
model to simulate documented case studies on high altitude slopes in
the Chilean Andes (33∘ S). The model predicts avalanche flow
temperature as well as meltwater production, given the thermal initial
conditions of the release mass and snowcover entrainment. As the
release mass is small, avalanche velocity and runout are primarily
controlled by snowcover temperature and moisture content. We
demonstrate how the interaction between terrain and entrainment
processes influence the production of meltwater and therefore
lubrication processes leading to longer runout. This information is
useful to avalanche forecasters. An understanding of wet snow
avalanche dynamics is important to study how climate change scenarios
will influence land usage in mountain regions in the near future.
Introduction
The purpose of this paper is to document and discuss the application
of numerical avalanche dynamics models to simulate small, point
release, wet snow avalanches. The problem is motivated by the
increasing frequency of wet snow avalanche events in the central
Europe and North America and usually attributed to global warming
. Although we have no
avalanche statistics to verify this trend, we find ourselves
increasingly confronted with the problem of small, wet snow avalanches
that disrupt road and railway traffic. This, of course, is
a longstanding problem in many mountain regions with maritime climate,
e.g. Norway, Alaska, Japan and Chile
.
The simulation of wet snow avalanches is not the primary application
of existing avalanche dynamics models . Existing models do not consider snow
temperature as an initial condition; flow parameters are simply
modified to account for the changing mechanical properties of snow
with temperature . Furthermore point
releases either dry or wet have not been simulated before. For
example, the Swiss guidelines on avalanche dynamics calculation
recommend increasing the velocity dependent turbulent friction to
account for the observed lower terminal velocities of wet snow flows
. Experimental field measurements indicate wet snow
flows exhibit slower, plug-like velocity profiles where shearing is
concentrated at the avalanche base , providing
some experimental foundation for the suggested increase in turbulent
friction. Although it is well-known, that avalanche flow regime is
a function of snow cover temperature (see ), it is only recently that
a statistical connection between temperature and avalanche runout has
been established . The long runout distances of wet
avalanches suggest a decrease in Coulomb friction induced by
lubricated gliding at the basal boundary, which controls the simulated
reach of the avalanche .
Snow temperature has been explicitly introduced as a state variable in
avalanche dynamics models by . This requires
calculating the internal heat energy of the avalanche, which is
a function of both, the initial temperature of the snow as well as the
avalanche dissipation rate. The temperature of the flowing snow thus
varies from initiation to runout (in time) as well as with location in
the avalanche (in space). An important assumption of this work is
that the heat energy per unit flow area is calculated, but no
information can be extracted concerning the distribution of
temperature over the flow height. The total heat energy is collapsed
down to the basal area. This appears to be satisfactory for the
plug-like motion of wet snow flows where shearing is concentrated at
the basal layer. A notable result of the model simulations is that
the entrained snowcover plays an important role in determining the
flow temperature of the avalanche. The temperature of the snow in the
release zone is important, but the final flow temperature is
controlled by the snowcover density and temperature along the track.
The density of the entrained snowcover is significant, because it
essentially determines the heat energy input by entrainment into the
avalanche. For example, a factor two increase in snow density (say
from 100 to 200 kgm-3) will change the heat energy
content more than a slight change in snow temperature (say from 270 to
272 K).
The model results of indicate that to simulate wet snow
avalanches, accurate information concerning the state of the snowcover
is necessary. Snowcover properties determine the onset of meltwater
production and therefore the possibility of lubricated gliding. In
this paper we simulate four wet snow point release avalanches
documented during two winter field campaigns at the high altitude
“Cajon del rio Blanco” Valley of the Codelco Andina mine situated
100 km North East from Santiago in the Chilean Andes,
well-known for wet snow avalanche activity. To include the important
role of snowcover, the field studies are supplemented with SNOWPACK
simulations to determine snowpack density and temperature
. Point release avalanches are
modelled using small triangular shaped starting zones, often
containing only 100 m3 of mass. Avalanche growth by
entrainment is therefore critical to model the final deposition
volume. Avalanche runout, velocity and lateral spreading in complex
terrain are reproduced. Forecasting applications are possible in the
near future if accurate snow cover information can be coupled with
avalanche dynamics calculations to predict extreme avalanche runout.
ModelModel equations
To model avalanche flow in general three-dimensional terrain, we apply
depth-averaged model equations for mass, momentum and energy
conservation . The mathematical
description of mountain terrain is defined using a horizontal X-Y coordinate system. The elevation Z(X,Y) is specified for each
(X,Y) coordinate pair. We introduce a local surface (x,y,z)
coordinate system with the directions x and y parallel to the
metric geographic coordinates X and Y. The grid of geographic
coordinates defines inclined planes with known orientation; the
z direction is defined perpendicular to the local x-y plane. Avalanche flow is described by six state variables:
UΦ=(MΦ,MΦuΦ,MΦvΦ,RhΦ,EhΦ,Mw)T
where MΦ denote the total mass of the avalanche core (ice and
water). The water mass is tracked separately and denoted and Mw.
The total mass and water mass is defined per unit flow area. When
Mw=0, the avalanche is termed “dry”. The flow height of the
total avalanche mass is designated hΦ. The source of water
mass in the snowcover is from rain precipitation, warm temperatures or
solar radiation input, etc. This water is defined as an initial
condition in the avalanche simulation. Additional water mass can be
generated during the avalanche flow by frictional heating. The mass
of water always bonded to the moving snow which is moving in the slope
parallel direction with velocity uΦ=(uΦ,
vΦ)T. Therefore, there is no momentum exchange between the
snow ice and liquid phases. Two energy equations are contained in the
model formulation: the mechanical free energy R
and the internal heat energy E. These quantities are defined per
unit flow volume. The flow temperature of the avalanche T is
derived from the internal heat energy E, see .
The model equations can be conveniently written as a vector equation:
∂UΦ∂t+∂Φx∂x+∂Φy∂y=GΦ
where the flux components (Φx, Φy) are:
Φx=MΦuΦMΦuΦ2+12MΦg′hΦMΦuΦvΦRhΦuΦEhΦuΦMwuΦ,Φy=MΦvΦMΦuΦvΦMΦvΦ2+12MΦg′hΦRhΦvΦEhΦvΦMwvΦ.
The source terms GΦ are
GΦ=Q˙Σ→ΦGx-SΦx-(Q˙Σ→Φ)uΦGy-SΦy-(Q˙Σ→Φ)vΦαW˙Φ-βRhΦ(1-α)W˙Φ+βRhΦ+E˙Σ→ΦhΦ-Q˙wLfQ˙w.
The flowing avalanche is driven by the gravitational acceleration in
the tangential directions G=(Gx,Gy)=(MΦgx,MΦgy). The acceleration in the slope perpendicular direction
is denoted g′ and is composed of gravity gz and
centripetal accelerations fz.
Furthermore the friction and fluidization processes are function of
the liquid water content. The snow cover conditions (temperature,
density and snow water content) are among the model input parameters
and determine the avalanche regime, and run out .
Frictional resistance is given by the Voellmy-type shear stress
SΦ=(SΦx,SΦy)T, with
SΦ=uΦuΦμ(R)N+ρΦguΦ2ξ(R)
that is, the shear stress is a function of the avalanche velocity
uΦ, fluctuation energy R and total normal pressure N
in the z direction. The effect of meltwater is to lubricate sliding
surfaces, decreasing the dry friction . We apply the
function
μ(hw)=μwet+μ0exp-RR0-μwetexp-hwhm
where μwet is the sliding friction coefficient of wet
snow (μwet=0.12) and hm is a constant
defining the decrease of friction as a function of the meltwater
content (hm=0.01m). The functional
dependency of the friction parameters ξ on R is:
ξ(R)=ξ0expRR0.
Modeling point release areas
To start an avalanche simulation is necessary to define the
initial release volume, V0. The volume released is calculated
by estimating a release area and a mean fracture depth. In case of
point released avalanches the released area is reduced to a single
dot in the terrain with negligible surface. In this work, point
release avalanches are simulated by defining a triangular shaped
release area where the upper apex of the triangle is located at
the point release. The triangle together with the fracture height
defines the initial release volume (see Figs. and
).
Fracture depth and erosion depths along the avalanche paths were
estimated from snow cover and meteorological data. The Codelco
Andina mine has automatic weather stations (see Fig. )
which provide air temperature, snow surface temperature, pressure,
wind, precipitation and radiation measurements (see
Table ). The meteorological data was used to run SNOWPACK
simulations to define the release
temperature and initial snowcover water content. Coupled with the
field studies performed by the winter operation crew, provides
accurate snow cover information. The distance between the chosen
weather station and the avalanches paths varies between 0.5 and
almost 4.0 km, (see Fig. ). The release areas in
the cases studies were between 3085 and 3600 ma.s.l.;
the weather station is located at 3570 ma.s.l. The small
elevation distance between the release zones and automatic weather
stations ensures accuracy in snow and meteorological data.
However, snow surface temperature and surface energy fluxes might
be influenced by the slope exposition. SNOWPACK allows the user to
generate virtual slopes, specifying slope angle and exposition and
coupling the measured meteorological and snow data to the virtual
slopes . We found no significant
differences between the measured data at the weather station
location with the calculated values on the virtual
slopes. Meteorological data from the winter operation building at
the valley bottom (Lagunitas building 2700 m, see
Fig. ) is available. Thus, it was possible to estimate
the precipitation and temperature gradients existing between the
weather station location and the winter operation building and
therefore to estimate the snow cover conditions along the selected
avalanche paths.
To estimate the fracture and erosion depths for each case study we
considered snow cover temperature and snow water content. The
model erodes and releases all the snow cover close to
0 ∘C and with snow water content higher than
0 mmm-2. This includes moist, wet, very wet and
slush snow cover and excludes dry snow
cover. The remaining snow input parameters are snow temperature
and snow density. These were specified directly using SNOWPACK
simulations using the meteorological and snow data collected from
the automatic weather station. We compared the simulated
snowcover data with field observations to ensure correctness (see
Table ).
The avalanche simulations require the friction (μ0, ξ0)
and free energy (α, β, R0) parameters, see
and . The friction parameters were
chosen based on the experience simulating wet snow avalanches in
the European Alps, Chile and Alaska, . In the four
case studies the model parameters remained constant and only
slight changes were made in the random kinetic generation α
parameter, see . The extremely steep and rough
gullies fluidized the avalanche and led to higher generation
parameters. Simulation parameters for the four case studies are
summarized in Table .
The equations are solved using the same numerical schemes outlined in .
Case studies
We simulated four point release avalanches that occurred in
“Cajón del rio Blanco” valley in the Chilean Andes (see
Fig. ). The four cases where spontaneous wet loose point
release avalanches that released in periods of high temperature
after a recent snowfall (see Table ). The four avalanches
were selected because they reached the primary industrial road in
the mine, endangering workers or interrupting mine logistics and
communication. The avalanches were subsequently well documented
by mine staff (Table and Fig. ). High
resolution digital elevation models (1m) of the terrain are
available for the four avalanche tracks. The avalanches are
designated Caleta Chica North CCHN-3, Cobalto CG-1, Lagunitas West
LGW-2 and Barriga North BN-1.
Caleta Chica North, CCHN-3
The CCHN-3 is a long, narrow and steep avalanche path that starts
at a ridge located at an elevation of 3685 ma.s.l. The
path contains a steep gully that includes track segments with steep
inclinations of more than 60∘. The avalanche path ends
directly above the industrial road at 2700 ma.s.l.
Although the gully is narrow, the avalanche collects enough snow to
endanger the industrial road due to the long distance between the
release zone and the deposition area (see Fig. ).
On the 14 August 2013 between 17:15 and 17:30 LT
a point release avalanche released
from the top of the avalanche path reaching the industrial road
with a final volume of 2000 to 2500 m3 (estimated by
the winter operation crew, see Figs. a and
a). On the 12 August 0.15 m of new snow was
recorded at 3500 ma.s.l. A 24 h period of cloudy
weather followed the snowfall. The 14 August was the first clear
sky day after the snow fall from the 12 August. The air temperature
at the estimated release time was 3.7 ∘C at
3550 ma.s.l.
Cobalto, CG-1
The CG-1 avalanche path is located 2 km to the north (see
Fig. ) of the CCHN-3 with similar west exposition. The
track starts at 3465 ma.s.l. and ends at the industrial
road at 2450 ma.s.l. The release is located at a steep
point located below a ridge. The track is channelized between two
vertical rock pillars. The gully between the pillars has an
inclination between 60 and 70∘ for the first 500
vertical meters of drop. The track becomes progressively flatter
(about 40–45∘) and wider. For the last 300 m
elevation drop the gully is between 50 to 70 m wide and
the avalanche can entrain large amounts of snow. The deposition
area is a open and located on a cone shaped debris fan above the
industrial road (see Fig. ). The surface of the debris
fan contains large blocks.
On the 7 September 2013 at 17:30 LT a point release
avalanche started from the upper part of the gully, eroding the
upper new snow layer. The avalanche reached the valley bottom
stopping a few meters above the industrial road (see
Figs. b and a). The volume of the deposits was
estimated to be approximately 7000 m3. On the
6 September a 24 h storm left 0.40 new snow at
3500 ma.s.l. At 2700 ma.s.l., the storm began
as a rainfall event, placing 7 mm of water in the
snowcover. However, the air temperature dropped at 2700 m
and the rain precipitation turned to snow depositing
0.10 m of moist new snow on the wet snowcover. At
2400 m only liquid precipitation was measured. The winter
operation crew made two snow profiles at the morning of the
7 August and estimated that the rain reached 2900 m, above
this elevation all precipitation fell as snow.
Lagunitas West, LGW-2
The LGW-2 avalanche path starts at 3250 m below a rock band
and continues over an open slope with 40–45∘
inclination. The track contains two 5 m drops over rock
bands before it gets progressively flatter, reaching a inclination
of 30–35∘. The track finishes at 2800 m at
the industrial road with a 25∘ inclination (see
Fig. ).
At 14:30 LT on the 9 September 2013 a point avalanche
released below the upper rock band reaching the industrial road
(see Fig. ). The 9 September was the first clear sky day
after the three day storm and cloudy weather that started on the
6 September. The air temperature at the release time was
8.3 ∘C.
Barriga North, BN-1
The BN-1 avalanche path starts directly in front of the winter
operation building at 3100 ma.s.l. (see
Fig. ). The release area is south oriented and situated
below a wide ridge with 40–45∘ slope angle. The
avalanche path becomes flatter and at the point of maximum
steepness the track becomes west exposed, indicating significant
channel twist. The avalanche path ends on an industrial road at
2775 ma.s.l., (see Fig. ).
At 17:30 LT on the 9 September 2013, three hours after the
LGW-2 release, a point avalanche released below the wide ridge
eroding the new snow. The avalanche passed the channel turn and
reached the industrial road (see Fig. c). The winter
operation crew estimated the avalanche deposits to be
approximately 6000 m3. The air temperature at the
released time was 7.8 ∘C.
The LGW-2 and BN-1 avalanche paths are directly in front of the
“Lagunitas” winter operation building (see Fig. ). The
avalanches were observed by mine staff members. Low quality video
recordings from mobile phones are available.
Simulation results
In the four case studies the calculated temperature of the flowing
snow reached the snow melting temperature and therefore the model
predicted the generation of melt water during the flow. The snow
cover temperature at the time of release were close to T≈0∘. The snowcover was therefore moist (bonded
water) or even wet (containing free water), (see
Table ). The calculated avalanches dissipated enough heat
energy that the snow within the entire flow was at
0 ∘C, (see Fig. ). As meltwater
lubricates the avalanche flow, reduced μ values are obtained in
the simulations, as the friction parameter μ is function of the
water content . The calculated water content lowered
the friction value μ enough to the avalanches reach the valley
bottom eroding the existing warm and wet snow cover. With colder
and drier snow cover conditions the avalanche simulations show the
avalanches would stop immediately after the release.
The set of Figs. – compares the four run out
calculations with the field pictures obtained by the mine winter
operation crew. The run out distance were accurately calculated by
the model calculations, in the four cases the avalanche run out
distances and the deposits extension were correctly estimated. The
avalanche flowing height was not possible to measure in any of the
four cases. However the final calculations deposits heights (see
Figs. –) agree with the rough measurements
made by the winter operation crew at the field (see
Fig. ).
Figure shows the increase in avalanche volume over time
from the initial release t=0 until deposition for the four case
studies. The calculations are normalized with the initial release
volumes. The final calculated volumes reach values between twenty
and sixty times the initial release volume. The calculations also
reveal that in the examples CG-1 and CCHN-3 the avalanche
simulations did not entrained more snow after the avalanche reached
the track midpoint. In these two examples there was no snow cover
below 2900 m (see Figs. and ) and
therefore the final ratio between the final deposit volume and the
initial volume are the lowest, (between 20 and 30 times the initial
release volume). Figure depicts the avalanche volume
with the avalanche time for the 4 cases studies. At t=0 the plot
shows the initial release mass. For the examples CG-1 and CCHN-3
the volume increase flattens at the point the avalanche is no
longer eroding snow. The final calculated deposition volumes are in
agreement with the observations made by the winter operation crew.
The Fig. indicates maximum velocity calculations in the
LGW-2 and BN-1 case studies. Avalanches velocity could be roughly
estimated through mobile phone video recordings. The estimated
velocity measurements coincide with the velocity calculations made
by the model (about 10 ms-1). Unfortunately the
approximation techniques are not accurate enough to perform a more
precise analysis.
Discussion
The results presented in this paper are valid for mountain rock
faces with well defined flow channels and also open slopes. At
release the avalanche mass spreads depending on the terrain
features. In two of the four case studies, avalanche spreading
was inhibited by the steep sidewalls of mountain gullies,
a function of the topographic properties of the mountain. The
other two examples where open slopes where the spreading angle was
larger than in the channelized cases but controlled too by
topographic features. Avalanche movement is therefore not only
controlled by the thermal state of the snow, but also by the slope
geometry. High resolution digital elevation models that
accurately represent mountain ravines and channels are thus
necessary to apply avalanche dynamics models to simulate small
avalanches . In open terrain (BN-1, LGW-2), the
lateral spreading of the avalanche is modeled.
The position of all release zones was obtained from the eyewitness
reports and post-event surveys. Entrainment depths for the
simulations were also obtained from field studies and event
documentation. From automated weather stations good estimates of
snow temperature could be obtained. Because the avalanches
disrupted road traffic, road clearance crews could estimate
deposition depths allowing good estimates of avalanche mass
balance. The velocity measurements are not accurate enough to
assess the model performance. Nevertheless the data available
showed that the model's velocity output is accurate in first
approximation.
The model calculated the snow temperature from initiation to
runout. Due to the warm initial conditions the investigated
avalanches reached the melting point of snow-ice almost
immediately after release. The entrainment of warm, moist snow
enhanced the lubrication process. The decrease of Coulomb friction
due to lubrication effects is key for small point release
avalanches to develop into long-running wet snow avalanches. For
practical applications it is important that lubrication processes
due to the (1) initial snow water content, (2) snow melting by
frictional dissipation and (3) heat energy of entrained snow must
all be taken into account. The model includes a lubrication
relationship between meltwater content and the Coulomb friction
parameter μ. The lubrication model is an empirical necessity
that needs to be improved with additional mechanical tests.
To back-calculate the four case studies the same set of model
parameters used previously in was applied. The
model results emphasize that complete information of the snow
cover is necessary to achieve accurate representations of the
events. The model is sensible to variations in the initial snow
cover conditions (temperature and water content). For example,
when colder snow is specified at release, the avalanche
simulations stop immediately after the release without reaching
the valley bottom. However given accurate initial conditions the
model was able to back calculate accurately runout distances,
avalanche outline and avalanche volumes in the four case
studies. It is therefore only possible to obtain realistic runout
predictions with accurate snow cover data. The application of the
avalanche dynamics model should be restricted to cases where
accurate data is available.
The method used to simulate the avalanche point release requires
defining a small triangular area. The ratio between the eroded
snow volume and the initial snow volume is between 20 to 60 for
the four case studies we studied in this paper. The initial area
used to simulate the avalanche release does not affect the final
run-out, velocity and avalanche deposit calculations.
Conclusions
Avalanche dynamics models have been traditionally applied to
simulate large, dry, slab release avalanches. The starting volumes
of such avalanches are typically larger than V0>50 000m3. The primary application is to prepare
avalanche hazard maps which are based on extreme events with long
return periods. In this work we applied a snow avalanche model to
simulate small, wet, point release avalanches. Avalanche release
mass was modeled using small triangular shaped release zones
containing less than V0≈100m3 of snow. The
purpose of the simulations was to help avalanche warning experts
determine whether a logistically important road should remain open
or be closed. The application of an avalanche dynamics model to
simulate small, point release avalanches is novel and poses many
new challenges. Three preconditions for the simulation of such
small avalanche events are:
The availability of high resolution digital terrain models
Simulation of snow entrainment to model avalanche growth
Reliable snowcover information, including snow temperature
Finally, this work demonstrates that not only large, wet snow slab
avalanches can develop significant destructive power. Wet snow point
avalanches releasing from steep slopes and long avalanche paths
collect enough snow to disrupt and harm human activities. The
application of an avalanche dynamics model was tested for two winter
seasons in the Andina mine (Chile). After initial promising results,
the operational application of an avalanche dynamics model is
planned. Simulations coupled with accurate and continually updated
snow cover and meteorological information is required to predict
avalanche run outs and deposition volumes. The model does not
provide any indication whether the avalanche is going to release or
not, but if the avalanche releases the model gives a good indication
of the potential run out distances and deposition volumes.
Acknowledgements
Financial support for this project was provided by Codelco Mining,
Andina Division (Chile). The authors thank A. Ellena and L. Cornejo
for starting the project and their helpful insights into the wet
snow avalanche problem. In addition we thank all avalanche alert
center members: L. Gallardo, M. Didier and P. Cerda, not only for
their support, but also for their confidence, patience and enormous
help during the last three winters in the Andina mine.
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Summary of the snow and meteorological conditions in the four cases studies at the
estimated release time. Note the first data section corresponds to direct measurements from the automatic weather station (AT, New Snow, SST and ΔSST12h). The second section contains simulated data from SNOWPACK calculations .
ParameterBN-1LGW-2CG-1CCHN-3SimulationSimulationSimulationsSimulationAir temperature AT (∘C)7.88.3-3.03.7New snow72h (m)0.280.280.40Snow surface temperature SST (∘C)-0.2-0.08-1.1-2.1ΔSST12h (∘C)*9.25.211.816.17Snow release temperature (∘C)-0.9-0.9-0.5-0.8Net energy flux12h (W m-2)73.5571.5579.95324.22Snow water content SWC (mm m-2)0.90.851.070.12Snow density (kg m-3)240235185190
*ΔSST12h is the change in snow surface temperature in the last 12 h before the avalanche released.
Summary of input and simulation parameters for the four calculations examples.
* Parameters with the sub index “0” denote fields related with the release mass.
Parameters with the sub index “Σ” denote fields related with the eroded mass.
hΣ denotes the amount of eroded snow, the first quantity shows the eroded mass at the altitude of the release. The
quantity coming with Δ shows the decrease of eroded mass per 100 m of
altitude. h0 denotes the fracture height at the released.
Location overview from the four avalanche simulations. The red line notes the main
industrial road. The snow flake on the bottom right corner indicates the exact position
from the automatic weather station. “Lagunitas” meteo building is located at valley
bottom at 2700 ma.s.l. Image captured from Google Earth.
Avalanche deposits: (a) CCHN-3, (b) CG-1 and (c) BN-1.
The outline, height and volume of the deposits was measured by the winter operation
crew immediately after the industrial road was open.
(a) CCHN-3 avalanche picture taken from the helicopter the day after the release.
The point release was on the top the steep gully on a rock face. The avalanche crossed the
industrial road (see Fig. a). (b) Maximum flow height simulation. The
model estimated correctly the run out distance and the avalanche deposits.
(a) Avalanche path CG-1. Image taken from the helicopter the day after the release.
The avalanche stopped eroding snow at 2900 ma.s.l. but kept flowing till reaching
the valley bottom over a gravel surface. (b) Maximum flow height simulation. The
model estimated correctly the run out distance and avalanche outline and volume.
(a) Avalanche LGW-2 picture taken from the valley bottom. The avalanche
released below a rock band and spread over the slope flowing over two rock bands
before reaching a secondary road at the valley bottom. Top left shows a closer view
from the release point. (b) Flow height simulation. The model calculated
correctly the three avalanche arms getting an accurate avalanche outline simulation.
Avalanche run-out distance, avalanche outline and avalanche spreading angle were
correctly calculated by the model. On the top left a closer view with the calculated
release area (in red) is shown.
(a) Picture from the BN-1 avalanche taken from the “Lagunitas” meteo building
some minutes after it happened. The avalanche crossed a secondary industrial road reaching
the avalanche deposits 4 m of snow at the road (see Fig. 2c). On the
top left closer view from the point release. (b) Flow height simulations
from the BN-1 avalanche. The model calculated accurately the avalanche run out
distance, the avalanche outline including the curve done by the avalanche on half
way from the avalanche path and the avalanche spreading angle. On the top left the
calculated released area (in red) is shown.
Temperature and melt water production calculations for the four case studies. The
avalanches temperature keep close to 0 ∘C or constant equals zero
during the whole avalanche simulation. Release temperatures and entrainment
temperatures were close to zero in the four case studies, therefore the model immediately
started melting snow into water. The model calculated from 0.5 till 3 mmm-2
of melt water production in the four case studies.
Ratio between the avalanche flowing volume and the initial release
volume. The x axis show the avalanche time since the release till
the last mass unit stopped. In the four case studies the ratio between
the final volume and the initial released volume is between 20 and 60
times.
Avalanche volume calculations for the four case studies. The x axis show the avalanche
time since the release till the last unit of mass stopped. Flat curves show time when the
avalanches were not entrainning additional snow, (cases CG-1 and CCHN-3).
Calculated maximum velocities of the LGW-2 avalanche (a) and of the BN-1 avalanche (b).