47
Humans as Trigger of the Trap
The steeper and more shaded the slope is, the
greater the likelihood of releasing a slab avalanche.
The likelihood increases with large groups without
spacing, frequent turns, and especially with falls or
jumps over cornices or other shock loading. Remote
triggering is possible starting with the danger level
CONSIDERABLE, i.e. the person triggering the ava-
lanche can be standing dozens of meters outside of
the fracture zone. This is fatal at the bottom of a
slope, because the entire slope above can be
released!
Note: Light forest (with trees far apart enough to ski
or ride through) will not protect you from slab ava-
lanches. Even rock outcroppings will not prevent the
release of slab avalanches.
8.3 Precautions
8.3.1 Standard Safety Precautions
The following standard safety precautions should
always be taken regardless of the danger level:
●
Avalanche transceiver on SEND,
along with a probe pole and shovel
●
Avoid fresh wind-deposited snow
●
Consider daily fluctuations in temperature,
especially in the spring
●
Constantly assess the conditions
throughout the trip
46
Introduction to Avalanche Theory
8. Introduction to Avalanche Theory
We would like to provide you with some basics on
this complex topic and recommend thorough initial
and ongoing advanced avalanche training.
The Slab Avalanche: The Set Trap
Most winter outdoor travelers trigger their own ava-
lanches. The snowpack is fragile. Slab avalanches
resemble set traps: If we trigger it, the trap snaps.
Remember that a small slab of 100m
3
weighs about
25 tons!
8.1 Hazard identification
Very critical weather situations
The avalanche danger increases rapidly after storms
with new snow, wind, and cold temperatures. Slopes
with wind-drifted snow are especially dangerous!
Snow can also be moved by wind during nice weath-
er. The first nice day after a snow event is particularly
dangerous. Most accidents occur when a cold front
with strong winds and snow moves in after days of
blue skies and cold temperatures! In this situation,
new snow amounts of 10 – 20 cm can constitute a
critical situation that can last several days.
Rapid and strong warming (downslope wind, rain) can
also cause an increase in avalanche danger, which
decreases again with falling temperatures. If the
snowpack is uneven and weak, the danger is hard to
perceive. This is often the case with shallow snow
packs in the beginning of winter or during periods of
little precipitation. In spring, the danger usually
increases as the day progresses: from low in the
morning following a clear night to considerable in the
afternoon.
8. 2 Risk Assessment
Critical amounts of new snow
With the following amounts of new snowfall within
1 – 3 days, the danger level is at least
CONSIDERABLE:
10–20 cm with adverse conditions
20–30 cm with average conditions
30–50 cm with favorable conditions
Adverse conditions
● Strong wind (> 50 km/h)
● Low temperatures (< -8° C)
● Slope seldom traveled
Favorable conditions
● Light wind
● Temperatures little below 0° C
● Slope traveled frequently
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