Lecture 9 - Snow Avalanches

- what part of avalanches kill 25% of people - what do survival times depend on - what % survive within 15, 30 mins, 2 hours - why can people survive in the beginning - what do people usually die of when buried - what % of victims survive burial in more than 1.5 m in snow - what is the best chance of survival dependant on

- The motion of the snow itself kills about 25% of avalanche victims. - Survival depends on the length of time the person is buried and the burial depth - Over 90% survive if rescued within 15 minutes, 30% within 35 minutes, and 0% within 2 hours. o Can survive in the beginning due to the high amount of oxygen in a snowpack -> air pockets - Buried victims die of a combination of suffocation and hypothermia o Very cold at these high altitudes - Less than 10% of victims survive burial in more than 1.5 m in snow. - The best chance of survival depends on an effective search by other members of the group rather than waiting for help. o Best to be in a group and not alone - Chances of finding a buried victim increase when everyone in the group carries standard avalanche survival aids

- what is the probability of a White Christmas calculated using - where is there a high chance and a low chance, how much in ON? - how often are snow cover maps updated - what is snow cover - what is used to measure this - how much does snow accumulate in ONT vs. the rockies

- The probability of a White Christmas takes into account average snow cover o Low chance on Vancouver Island, very high in Prairies, 60% in Ontario - Snow cover maps are updated daily o The maps show the snow on the ground o use satellites - when snow falls in Ontario, it melts away, comes back, then melts - eventually begins to stick as we get deeper into winter - but in Rockies, it never melts - accumulates, all winter long

terrain factors - what is the important terrain factor - what angles do nost avalanches occur at and why - what's the optimal angle - what are other factors of slopes that impacts avalanches (4) - what is the worst slope direction and why

- The slope angle is the most important terrain factor for avalanche formation. - Most avalanches occur at slope angles between 25° and 60° o Best is 35° to 45° - At angles below 25°, snow does not easily slide - At angles above 60°, little snow accumulates on the slope - The orientation of the slope can also be a factor o Deposits of snow on leeward (east - downwind) slopes can consist of interlayered strong and weak layers. o Slopes facing the Sun (south) are more prone to daytime avalanches during clear weather. o Worst slope faces south-east - Other factors include the smoothness of the slope, the amount of vegetation, and the topography of the slop itself

- what are the two types of avalanches - what % of avalanches aren't seen by anyone - how many avalanches large enough to kill a person occur annually in western canada

- There are two types: o 1. An avalanche travelling as a coherent block (most common) o 2. An avalanche that becomes wider as it travels downslope - It is estimated that 99% of avalanches are not seen by anyone - It is likely that over 1 million avalanches large enough to kill a person occur annually in western Canada alone. o BC, Alberta, Yukon - annually

where do we get most snow in Canada? what mountain range has a lot of avalanches and why

- higher north (higher altitude) and closer to bodies of water - think about Rocky Mountains - where we see most of our avalanches b/c of high altitudes

- how can hoar cause weak layers of snow - define hoar

- hoar: tiny and fine-grained ice crystals - Layers composed of hoar have less strength than the rest of the snowpack. - Hoar can form deep in the snowpack (in air pockets) or on the snow surface - Hoar changes little over time; therefore, overlying snow can leave the buried hoar as a weak layer.

6 ways to Minimize Avalanche Risk

- use of hazard maps when planning building things - reinforcing buildings, using deflection structures (i.e. splitting wedge) - mounds/berms to deflect snow from populated areas - controlled triggers using explosives - avalanche sheds over roads - fences to hold up snow pack at start zones

what was the worst avalanche in north american history

Chilkoot Avalanche

- how can wind cause weak layers of snow - what is lee slope - what direction does this impact in Canada - what boundary in the snow can a failure occur

Wind - Blowing snow can accumulate on the lee slope of mountains. o Lee = downwind o in Canada this is the east because wind blows from west to east - Wind can deposit a layer of light ice crystals (hoar) on a layer of more compacted snow - The boundary (called horizon) between the two layers could become a horizon along which failure could occur

what is a point-release avalanche

o These begin as an initial failure after a heavy snowfall. o The sliding snow then causes more failures in the adjacent snowpack causing the trough to widen - As it goes down, collects more snow and gets wider (upside-down V shape)

what is a Slab Avalanches how dangerous and common

o These occur when a snowpack fractures along a weak layer parallel to the surface o These avalanches move as cohesive blocks leaving behind a scarp o They are the most dangerous avalanches o More common

what is avalanche forecasting is based on: (4)

o occurrences of avalanches in the past § patterns on map o strength and stability tests § test for weak layers in snowpack o snowpack observations § trying to forecast based on dates of past events o weather

3 avalanche survival aids

- Avalanche Cord o A 10m rope that drags behind a person while skiing, snowboarding, or snowshoeing § Brightly coloured rope, with a yellow mark at each 1 m so it can be counted to see how deep a person is buried - Avalanche Transceiver o A portable device that emits a radio signal to assist in finding the location of a victim § Range of where the person might be o Transceiver is able to transmit through snow - Avalanche Dogs o They can detect human scent rising through the snow and can quickly cover large areas o Dogs can detect 4m deep, but often person is dead before dogs get there

- what other hazards can cause avalanches

- Avalanches can be caused by earthquakes. - Climate change may increase winter snowfall in some areas and increase severity of winter storms. - Some areas will experience more thaws in winter enhancing the instability of the slope

- when have avalanches become a hazard to humans - why has the death toll increased

- 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 the Alps, deaths from avalanches have increased. o w/snowboarding, skiing, since 1970's recreation causes most deaths

- how is the risk of an avalanche communicated to people - what is used to determine this - is there ever no risk?

- Before travelling in avalanche prone areas, it is important to check for any public bulletins as well as the current danger level. - danger level (low to extreme) with colours - Knowledge of slope angles and the terrain is also necessary - Only low risk, never no risk

what are the 3 major tests used to assess a snowpack - which is best

- Compression Test o A vertical force is placed on the top of the snowpack to detect weak layers. - Shovel Test o It assesses the strength by isolating a column of snow and applying force on the uphill side - Rutschblock Test o A skier pushes and jumps on a column of snow to detect cohesion of the snowpack, see if it triggers a failure o Best of the 3

- Define: snow avalanche - what else can move in a similar motion - what is the intensity of the hazard dependent on (3)

- Definition: A mass of snow many cubic meters in volume that separates from a snowpack and flows downslope - Rocks, soil, ice, and debris can travel in a similar motion; however, the term avalanche is generally reserved for snow. - The intensity of the hazard is dependent on slope steepness, snowpack stability and weather.

- what depth of snowpack is needed for an avalanche - what area in north america has the most deep snowpacks

- For an avalanche to form, a snowpack of at least 50 cm is typically required. - In North America, deep snow-packs are most common in the Rocky Mountains (B.C./Alberta border)

- what effect do these have on the environment

- Similar to landslides, avalanches act as an ecological disturbance. o Not an ecological hazard - This may increase local plant and animal diversity. o Avalanches maintain open areas in otherwise forested regions - This can serve as an important habitat zone for certain plants and animals o Animals like elk and deer that graze o Good to have varying habitat zones o Every summer, trees will try to grow back

Chilkoot Avalanche - when did this happen - what was this area being used for - where did the avalanche happen and how many people died - what is a mountain pass

- This disaster occurred in 1898 and remains one of the worst avalanches in North American history. o Height of the Gold Rush - An avalanche spread over the Chilkoot Trail causing 60 deaths (60/600 in Canada were here) - The trail was heavily used at that time by people heading to Yukon during the Klondike Gold Rush. - The Chilkoot Trail extends from Alaska to B.C and is the easiest route through the mountains o Mountain pass: trail was through mountains

- when did the most avalanche deaths occur in canada and why - how many people have died in total in canada - what losses do avalanches cause in B.C. - what damage occurs to the environment

- In Canadian history, most avalanche deaths occurred in the late 1800s and early 1900s. o b/c of building of the railroad in the west in 1800s o many of the people building were immigrants from China - In total, over 600 people have died from avalanches in Canada - Avalanches cause millions of dollars in economic losses in B.C. each year due to closed highways. o More of an economic hazard - don't cause that many deaths o Few roads connecting B.C. to Alberta - if they are snowed in, this is bad - Damage to forests is evident each year but property damage is relatively minor o Not really an environmental hazard, vegetation grows back

- when do most avalanches occur - another time they can occur - Avalanches that cause injuries or fatalities are often triggered by what - how can we control avalanches by triggering them

- Most avalanches occur soon after snowstorms. - Some may occur when daytime heating from the Sun warms the upper part of the snowpack. - Avalanches that cause injuries or fatalities are often triggered by people o Like by their movement - Some avalanches are triggered intentionally with explosives -> to control them

Avalanche Potential - what factor of new snow can impact avalanche potential - what location of snow is likely to slide

- New snow that has not been able to bond to the layer below is susceptible to sliding o The problem is when new snow doesn't bond to old snow - Wet, compacted snow is less likely to slide than dry, powdery snow. - A mass of snow that is above the vegetation level and above large boulders is more likely to slide

- what do rapidly moving avalanches generate, what speed is considered fast - how fast can avalanches get (max.) what needs to be happening for them to be really fast - how can fast avalanches climb opposing slopes?

- Rapidly moving avalanches (i.e. speeds of over 35 km/h) often generate clouds of powdered snow. - Fastest avalanches have been measured at speeds of 200km/h - To move really fast -> steep angle, all other conditions are perfect - Some avalanches are powerful enough to climb opposing slopes. o Goes down one side of a mountain and then up the side of an adjacent mountain o U-shaped valley

Minimizing Avalanche Risk - how are maps used - what cab buildings in hazard areas have - what can be put in start zones - what can be used to deflect snow from populated areas - what is built over roads - how can avalanches be triggered

- Risk is greatly reduced when buildings, roads, and other infrastructure are located outside dangerous areas. - Hazard maps provide planners with the locations of these areas o They fire guns to move snow and keep it away from highways - Buildings in hazardous areas within a specific recurrence interval may require special engineering. - This may include reinforced walls or deflection structures. - Splitting wedges on the sides of buildings can force an avalanche around the structure. - In avalanche start zones, fences or nets can be installed to support the snowpack - Mounds and berms can be used to slow and deflect avalanches away from populated areas - Avalanche sheds allow avalanches to travel over roads or railways without disruption to traffic. - Controlled triggers are used to force avalanches to occur in order to prevent build-up of the snowpack - This is performed through the use of explosives.

- what 2 things can cause weak layers in a snow pack

- Slab avalanches require a buried weak layer. Such a layer can form from wind or from hoar. - each layer represents a snowstorm, snow builds up every snowstorm

- what 3 factors impact snowfall accumulation - why do high mountains have permanent snow cover (and what angle are the slopes)

- Snowfall accumulation depends on latitude, altitude, and proximity to bodies of water. - Temperature decreases with altitude therefore high mountains have permanent snow cover. - Snow accumulation on mountain slopes that are at angles of less than 60 degrees

Avalanche Paths - what are the 3 areas of the path

- Start Zone o The area where the snowpack first fails. - Track o The area along which the avalanche accelerates and reaches maximum velocity - Run-out Zone o The area of deceleration and snow deposition o Snow begins to stick, angle is less steep

- what is the Avaluator - what factors are used

- The Canadian Avalanche Centre has developed the Avaluator. o took terrain score on x axis, avalanche condition score on y axis o wherever box fell, that's how they came up w/safety level - This is a chart designed to warn travellers of the risk of an avalanche in an area