lecture 10 - avalanches

Question 1

Definition of a snow avalanche

Answer 1

a mass of snow many cubic meters in volume that separates from a snowpack and moves downslope

Question 2

what is the intensity of a avalanche depend on?

Answer 2

slope steepness, snowpack stability and weather

Question 3

two types of avalanches travelling

Answer 3

An avalanche travelling as a coherent block

An avalanche that becomes wider as it travels downslope

Question 4

are avalanches typically seen?

Answer 4

99% are not seen by anyone

Question 5

snow climatology

Answer 5

amount of snowfall depends on latitude, altitude, and proximity to bodies of water

temp decreases with altitude meaning high mountains have permanent snow cover

Question 6

2 types of avalanches

Answer 6

1. point release avalanche
2. slab avalanche

Question 7

point release avalanche

Answer 7

begins as an initial failure in snowpack after heavy fall

the sliding snow then causes more failures in adjacent snowpack causing the trough to widen

Question 8

slab avalanches

Answer 8

occurs when snowpack fractures along a week layer parallel to surface

move as cohesive blocks leaving behind a scarp

**most dangerous

Question 9

avalanche potential

Answer 9

new snow that has not been able to bond to the layer below is susceptible to sliding

wet, compacted snow is less likely to slide then dry powdery snow

mass of snow above vegetation level and larger boulder is more likely to slide

Question 10

slab avalanches require

Answer 10

a buried weak layer such a layer formed from wind or from hoar

Question 11

weak layers - wind

Answer 11

blowing snow can accumulate on the lee (downwind) slope of mountain (lee side = more risky side)

wind can deposit layers of ice crystals on layer of compacted snow

the boundary between two layers could become a horizon along which failure may occur

Question 12

weak layers - Hoar

Answer 12

layers composed of hoar have less strength than the rest of the snowpack

can form deep in the snowpack (in air pockets) or on snow surface

changes over time; overlying snow can leave the buried hoar as a weak layer

Question 13

avalanche motion

Answer 13

often generate clouds of powdered snow due to rapid movement

fastest have been measured 200km/h

some powerful enough to climb opposing slopes

Question 14

avalanche triggers

Answer 14

occur soon after snowstorms

may occur when daytime heating from the sin warms the upper part of the snowpack

avalanches that cause injuries or fatalities are often triggered by people

some triggered intentionally with explosives

Question 15

3 avalanche paths

Answer 15

start zone: area where the snowpack first fails

track: area of where avalanche accelerates and reaches maximum velocity

run out zone: area of deceleration and snow deposition

Question 16

most important factor that influences avalanche formation

Answer 16

the slope angle

Question 17

most avalanches occurs between what angles

Answer 17

25-60 degrees

Question 18

angles below _____ degrees does not slide easily

Answer 18

25 degrees

Question 19

angles above ___ degrees little snow accumulates on the slope

Answer 19

60

Question 20

the sweet spot of avalanches is between aka highest risk

Answer 20

30-45 degrees

Question 21

terrain factors

Answer 21

the orientation (direction slope faces)

snow on leeward slopes consist of inter-layered strong and weak layers

smoothness of slope, amount of vegetations and topography

Question 22

regions at risk

Answer 22

for an avalanche to form a snowpack of that at least 50cm is required

in north america, deep snowpack are most common in the rocky mountains

Question 23

effects of avalanches

Answer 23

most avalanche deaths occured between 18-1900s

in total 600 people have died (low)

have caused millions of dollars in losses in B.C. each year due to closed highways

damage of forests is evident each year but property damages are minor

Question 24

chilkoot avalanche

Answer 24

occured in 1898 and remains one of the worst in North American History

avalanche spread over chilkoot trail causing 60 deaths

trail was heavily used during the Klondike gold rush

this trail extends from Alaska to B.C. and is the easiest route through the mountains

Question 25

linkage with other disasters

Answer 25

can be caused by earthquakes

climate change may increase winter snowfall and increase severity of winter storms

some areas will experience more thaws in winter enhancing the instability of the snowpack

Question 26

natural service function (good things about it)

Answer 26

like landslides they act as an ecological disturbance

increase local plant and animal diversity

maintain open areas in otherwise forested regions

serve as an important habitat zone for certain plants and animals

Question 27

human interactions with avalanches

Answer 27

avalanches only become a hazard when humans encroach on areas that are prone to them

as tourism and recreation have increased in the Rockies and Alps, deaths have increased

Question 28

minimizing avalanche risk

Answer 28

risk is reduced when buildings, roads and infrastructure are located away from avalanche paths

hazard maps provide planners with locations of highest risk areas

building in these areas will need reinforced walls or deflection structures

mounds and beams can be used to slow and deflect avalanches

splitting wedges on sides of buildings can force avalanche to go around them

avalanche sheds** make avalanches go over roads, railways without disturbing traffic

control triggers (explosives)

Question 29

avalanche forecasting is based on

Answer 29

locations of past avalanches

strength and stability tests

snowpack observations

weather

Question 30

3 major strength and stability test for avalanches

Answer 30

compression test: vertical force placed on top of snowpack to detect weak layers

shovel test: column of snow is isolated and then force is applied on the uphill side

rutschblock test: a skier pushes and jumps on a column of snow to determine the cohesions of a snowpack

Question 31

avalanche safety; what should you do?

Answer 31

before travelling in a prone area, its important to check current danger levels as well an public bulletins

knowledge of slope angles are necessary

NEVER NO RISK

Question 32

avaluator

Answer 32

Canadian avalanche centre has developed the avaluator

chart is designed to warn traveler of the risk of an avalanche in an area

Question 33

avalanche rescue

Answer 33

motion of the snow itself kills about 25% of avalanche victims

survival depends on length and depth of burial

over 90% survive if rescues within 15 min, 30% within 35 min and 0% within 2 hours

die of suffocation and hypothermia

less then 10% survive when buried 1.5m in snow

Question 34

3 avalanche survival aids

Answer 34

avalanche cord: 10m rope that drags behind a person while skiing or snowboarding/shoeing

avalanche transceiver: portable device that emits a radio signal to assist in finding the location of a victim

avalanche dogs: detect human scent rising through snow and quickly cover large areas