I n s t r u m e n t s

a n d

M e t h o d s

the flow of largeravalanches. A profile radar installed in
thereleasezonebelowtheGAZ-EXmeasuressnow
accumulation,layering,settlingandfracturedepth and
therefore help to improve the control work and to reduce
residual risk at reducedclosure times. Alarm systems that
measure avalanche movements use Dopplerradar,force-
measurements in cables and measurements of the tremble
ofstructuresorinthegroundtotrafficlights.Special
attention has been given to reducethe time delay between
the recognition of an event and signaling the alarm to less
than 1 second. All systemsare powered by solarcells and
aredesignedto withstandharsh environmentalconditions.
Radio links connectthe remote systems to the public phone
systemand to the alarm relays.The systemsperform self
checksandtransmittheirstatusatregularintervalsto
controlcenters.Allsystemsusethe samevisualization
and control software runningunderMS WIN.

ASSESSMENT OF AVALANCHE DANGER BY REMOTE

MEASUREMENTS

Forlocalavalanche warningsystems,itisnecessaryto
supplementmeteorologicalandmanual observationsby
snowparametersmeasured automaticallyintherelease
zones and at representativelocations. The systems have to
supply reliabledataon thedevelopmentof dangerous snow
coverstratigraphiesbetweenandduringstorms.The
parameters measuredshould be closely relatedto the proc-
esses determining stability of the snow coverin potential
release zones (Gubler, 1992).These processes are: forma-
tion of weak layers as a necessary condition of slab forma-
tion,loading, variation of slab strength and viscosity, and
as the most direct stability indicators: initial fracturing and
avalanching.Withthe microwave snow stratigraphyradar
placeddirectly withinthe releasezone(Gubler, 1988, 1991)
snow accumulation (loading), settling (increaseof strength
andviscosity),stratigraphy(crusts,weaklayers,water
percolation,melting)butalsofractureheights andflow
heights of avalanches (partial unloading, future avalanche
size) canbe directlyobserved. Becausethe radarareburied
inthe ground lookingupwardsthrough the snowcover,
they are not endangered by creep,glide and avalanches.
Ultrasonicsnowdepthgauges, although theyhave been
significantly improved during the last years, measure only
total snow depth and cannot be located directly in release
zones.Usually they will be installed at representative but
safe sites,together with additional instrumentation:snow
temperature andIR-surface- temperature measurements,
combined withthe measurement of reflected short wave
radiation,airhumidity- andtemperaturemeasurements
that allow for direct modeling of weak layer formation. For
theassessmentofsnowdrift,windrecordingcanbe
combinedwithindexmeasurementsofsnowdriftflux
(opticalinstrumentsavailable,acousticalinstruments
under development atLEMA,EPFL).Geophones buried
intheground indicateavalanche flowsanddetonations
for artificial release (e.g. GAZ-EX). A typical installation is
shown in Fig. 1.
The informationis used toassess the actual danger. It
may be helpful to store these data together with avalanche
observations in a data base to allow comparisons between
similaractual and past situations.Expert systems can be
adaptedto support theassessment. At SFISAR, R. Bolognesi

130

(1994)hasdevelopedatooltosupportthemethodof
artificialreleaseofavalanchesingivenreleasezones.
NXLOGcombinesnearestneighbormethodswithrule
basedsymboliccalculation(artificialintelligencetech-
niques,A.I.) to arrive at a probabilityforan artificially or
naturally released avalanche in a given gully.

THE INTEGRATED AVALANCHE SAFETY SYSTEM

For experts in charge of avalanchesafety,it would be very
helpful to haveintegratedsystems at handthat allows them
tofollowup the developmentofsnowcoverstabilityin
given releasezones, to remotely initiate explosionsand to
check if an avalanchehasbeen released.Slabs are released
orstability is tested by applying additional stresses to the
snowcover.Detonationofexplosives,gasmixturesetc.
generate the additional stresses.Today only the GAZ-EX
system can be remote controlled any time, although firing
of projectiles, CATEX and pre-placeddynamite connected
to a remote firing control allow forlimited remote control
of avalanchestoo. Integratedsystems combine remote snow
and weather measurements,including snow stratigraphy
measurements within the release zone, with an improved
remote control of GAZ-EX exploders. Fig. 1 shows the basic
setupofthe system.Ifthe systemisconnected tothe
publicphone-systembyaradio-phonerelays,remote
access tothemeasuringand controlsystemsispossible
fromanyphonelineconnectorusinga PCornotebook
computerequipped with aphone modem.
The integrated system has several advantages:

• During stormsthedevelopmentofthe snowcoverin
  the release zone can beexamined 24 hours a day.
• Recording of natural releases.
• If the area isclosed and evacuated, remote controlof
  firingispossible24hoursadayindependent ofthe
  weather.
• Withina few minutes after the firing, fracture heightof
  a releasedavalanche can be estimated.
• Assessment of weak layer formation between storms.
• In spring the necessary conditions forreleases ofwet
  surface slabs can be assessed.

Allthese features help to reduce closure timesand to
increaseavalanchesafety, andto reducethe chancefor the
formation of large avalanches.

ALARM SYSTEMS

Avalancheandmud flow alarm systems measure avalanche
movementsinreleasezonesintheupperpartofthe
respectivetracks.Thetimebetweenrecognitionofa
dangerous movement and the time of impact of the flow
on a road or rail tracks is usually very short.In most cases
thistimeintervalislessthan60s.Thishastwoconse-
quences: the combined length of the endangered road or
track section andthe stopping distance of the traffic vehi-
cles has to be short becausea vehicle has either to be able
to pass before the flow reachesthe traffic line or has to be
stopped outside the endangered zone. To keep the alarm
time as large as possible,recognition of a dangerous flow
and transmission of the alarm to set the traffic lights have