HUMANITIES YEAR 9: AVALANCHES

1. AVALANCHES YEAR 9 HUMANITIES

2. DEFINITION
Avalanches are masses
of snow, ice, and rocks
that fall rapidly down a
mountainside.
While avalanches are
sudden, the warning
signs are almost always
numerous before they
let loose.

3. THE TRIGGER
In 90% of avalanche incidents,
the snow slides are triggered
by the victim. Avalanches
kill more than 150 people
worldwide each year.
Most are
snowmobilers,
skiers, and
snowboarders.

4. THE SPEED
Disastrous avalanches occur when massive slabs of snow break
loose from a mountainside and shatter like broken glass as they
race downhill.
These moving masses can reach speeds of 130 km per hour
within about five seconds. Victims caught in these events
seldom escape.

5. THE WINTER ARCHIVE
Avalanches are most common during and in the 24
hours right after a storm that dumps 30 cm or more
of fresh snow. The pileup overloads the underlying
snowpack, which causes a weak layer beneath the
slab to fracture.
The layers are like an archive of winter weather: big
dumps, drought, rain, a hard freeze, and more snow.
How the layers bond often determines how easily
one will weaken and cause a slide.

6. FACTORS
INFLUENCING
AVALANCHES
Storminess,
temperature, wind,
slope steepness and
orientation (the
direction it faces),
terrain, vegetation,
and general snowpack
conditions are all
factors that influence
whether and how a
slope avalanches.
Different
combinations of these
factors create low,
moderate,
considerable, and high
avalanche hazards.

7. WHAT TO DO IN
AN AVALANCHE?
If caught in an avalanche, try to get off the slab. In most
instances, this is not easy.
Skiers and snowboarders can head straight downhill to gather
speed, then veer left or right out of the slide path. Snowmobilers
can punch the throttle to power out of harm's way.
No escape? Reach for a tree.
No tree? Swim hard. The human body is three times denser than
avalanche debris and will sink quickly. As the slide slows, clear
air space to breathe. Then punch a hand skyward.

8. CHANCES OF SURVIVAL
Once the avalanche stops, it settles like concrete. Bodily
movement is nearly impossible. Wait—and hope—for a rescue.
Statistics show that 93% of avalanche victims survive if dug out
within 15 minutes. Then the survival rates drop fast.
After 45 minutes, only 20 to 30% of victims are alive. After two
hours, very few people survive.