BIG AL BERBY T AVALANCHES
Avalanches Presentation • This presentation contains information on the following aspects of Avalanches: • Causes of Avalanches. • Where avalanches happen and why they happen in these places. • The effects that avalanches have. • Two case study examples • How avalanches can be prevented.
What Causes An Avalanche? • 90% of all avalanches occur on moderate slopes, angle 30° to 45° as snow does not accumulate on steeper slopes. • An avalanche will occur when the force of the gravity pushing on the snow at the top of the slope is greater than the strength of the snow itself. • An avalanche can be triggered by both artificial and natural means: • Artificial • Skier • Snowboarder • Explosives • Cornice fall • Animals • Motorised vehicles • Natural • Snowfall • Wind-blown • Rain • Rapid temperature increase • Volcanoes
Types of Avalanche There are 5 main types of avalanche: • Loose snow avalanche • Ice fall avalanche • Roof avalanche • Cornice fall avalanche • Slab avalanche
Loose snow (sluff) avalanche The loose snow avalanche, or sluff, generally occurs at the surface in new snow or wet spring snow. This type of avalanche will generally spread out from its origin point. Sluffs seldom move enough snow to bury a person deeply and the chief danger to winter recreationists is being pushed over a cliff or rock band.
Ice fall avalanches Ice fall avalanches occur when a glacier encounters a steep drop. Chunks of ice "calf" off as the glacier slowly flows downhill under the force of gravity. Ice fall avalanches are unrelated to any abiotic or biotic factors and can happen at any time.
Roof avalanches Roof avalanches usually occur when the inside of the building is heated, melting base layers and causing snow to slip off the roof. They are more dangerous than you may think!
Cornice fall avalanche Cornice fall avalanches occur when cornices break loose from the lee side of ridges. Cornices are caused by prevailing winds blowing the snow and look like frozen ocean waves stretched along mountain ridges. The snow that forms cornices is very dense and hard, yet can be extremely fragile. It is often difficult to determine from the ridge top where the ground ends and the overhanging cornice is not supported. This type of avalanche is easily avoided by staying back from the peak of ridges, but can be deadly as the victim tumbles downhill amid massive, hard and heavy chunks of snow which often trigger secondary slab avalanches as they pass.
Slab avalanches The slab avalanche is the most dangerous of all. The slab is difficult to see and avoid and will often allow a person to travel well out onto it before it gives way.The forces that hold that snow slab in place include tension at the crown (top), compression at the stauchwall (bottom) and shear friction at the bed surface and flanks (sides). On the other side, the major force encouraging the slab to move is gravity. Snow is said to be a "visco-elastic" substance, basically meaning that it can behave as a liquid or a solid. It's choice of behavior is determined by the rate of strain--i.e.. the snow pack can withstand a much larger strain without avalanching if the load is applied slowly. Think of an elastic band or chewing gum on a cold day (other visco-elastic substances): they will stretch if pulled slowly, but will break if rushed.This theory helps to clarify the idea of ‘triggers’.
Parts of a slab avalanche • A force or event which initiates an avalanche. • The area near or at the top of an avalanche path where unstable snow breaks loose from the snow-cover and starts to slide. • The upper fracture surface of a slab avalanche. • The side boundary of a slab avalanche. • The surface on which a slab avalanche slides, usually the exposed surface after such an avalanche. • The bottom (down slope) boundary of a slab where it rides up over the snow below. • Within the track the highest speed will be attained. Deposition of debris will be minimal and typically limited to areas around trees, rocks, or other obstacles. The slope angle of the track does not need to be as great as that in the starting zone. • The part of an avalanche path where deceleration is rapid, debris is deposited, and the avalanche stops.
Where do Avalanches Occur? Avalanches obviously always occur in mountainous parts of the World. In the past avalanches have mainly occurred in the Alpine countries like France, Austria, Switzerland and Italy. These areas experience the greatest number of Avalanches and deaths annually. The United States also suffers from avalanches in mountainous states such as Colorado, Alaska and Utah. The United States ranks Fifth in World wide Avalanche danger.
Where Do Avalanches Occur? Alps Andes Himalayas
Why Do Avalanches occur in these areas? • Although avalanches can occur on any slope given the right conditions, in the United States certain times of the year and certain locations are naturally more dangerous than others. Wintertime, particularly from December to April, is when most avalanches will "run" (slide down a slope). However, avalanche fatalities have been recorded for every month of the year. • The highest number of fatalities occurs in January, February and March, when the snowfall amounts are highest in most mountain areas. A significant number of deaths occur in May and June, demonstrating the hidden danger behind spring snows and the melting season that catches many recreationists off-guard. During the summer months, it is often climbers who are caught in avalanches.
MEDC Case Study: Chamonix, France France is located in Northern Europe, south of the United Kingdom. It has the English Channel to the north, the Bay of Biscay to the west and the Mediterranean Sea to the south. It borders with Spain, Belgium, Luxembourg, Germany, Switzerland and Italy. Its two most famous mountain ranges lie across the borders with Spain (Pyrenees) and Switzerland and Italy (Alps). The resort of Chamonix is located on the Swiss border in the alps, below the towering Mount Blanc.
France: Social Impacts • 12 people killed (4 children) • 18 people rescued • 6 hospitalised • Shock and minor injuries • Loss of villages and towns • Death from various means: being buried (and suffocated) being knocked over a ledge • Lives ruined due to loss of homes • Rehousing, people need to be accommodated in hotels • Vehicles irreparably damaged
France: Demographic Impacts • In the 1980s and early 1990s, the victim demographic shifted to include snow-mobilers and snowboarders, who can cover more terrain in a shorter time than skiers can.
France: Economic Impacts Direct Costs • Maintenance • Restoration • Replacement • Property damage or loss • Loss of human life and productivity Indirect Costs • Reduced real estate value either due to impending avalanche hazard or zoning ordinances • Lower forest productivity • Decreased industrial productivity • Mitigation • Reduced access to recreational areas • Litigation • Loss of income from businesses forced to close • Less tourists into area when slopes are closed and due to danger warnings
France: Environmental Impacts • Trees destroyed (natural deforestation) • Air quality lowered from less photosynthesis • Air polluted from rescue vehicles
LEDC Case Study: Nepal Nepal lies in between the southern slope of Himalayas with eight of the highest peaks in the world. This region accounts for about 64% of total land area. It is formed by the Mahabharat range that soars up to 4,877m and the lower Churia range. The low-land Terai occupies about 17% of the total land area of the country.
Nepal: Social Impacts • Psychological damage to members of small mountainside communities • Potential for hundreds of deaths every year • People are unaware of when an avalanche may strike due to unavailability of early warning systems or preventative measures. This stems from a lack of government funds, spent more on tourism which can make more money for the country.
Nepal: Economic Impacts Direct Costs • Property damage or loss • Loss of human life and productivity i.e. farming Indirect Costs • Lower forest productivity • Mitigation • Tourism drops • Areas cannot be rebuilt due to lack of funds
How do people perceive and cope with Avalanches? Avalanches to some degree are a natural part of any human beings daily life. Avalanches affecting human life or property can be initiated by nature or the humans themselves. People consider most risks to be controlled by themselves, but some Avalanches are uncontrollable by humans. In general, people might feel safe in a dangerous place and unsafe in a safer place depending on their personal experience and knowledge of the risks. It is a question of risk perception.
How can Avalanches be Prevented? Automatic avalanche gun These Sheds are placed on the side of the highways and contain large guns, after a big snowfall these sheds open up and fire at a mountain side this causes a small controlled avalanche. This will hopefully stop decrease the potential for a large avalanche by removing some of the snow. A similar technique is also carried out by hand, using a small hand cannon.
How can Avalanches be Prevented? This system uses the combination of flexible nets and high yield anchors. The placement of the system on the mountainside is pre-engineered by avalanche experts, who pinpoint where the avalanches are most likely to strike and therefore where the system will be most useful. Engineers have made new barriers out of metal anchored in concrete. These are placed in breakaway zones above the first fence of trees. These avalanche snow fences can be made up to 12 feet high. However, it would be too expensive to make barriers on every slope. Snow avalanche barrier
How can Avalanches be Prevented? • Other preventative measures are: • Spatially Analyzing and Displaying Historical Avalanche Data. • Avalanche shelter • SnowMicroPen - A sensitive instrument used for collecting detailed snow profile which can aid in forecasting of likely avalanche sites • Aforestation
How can Avalanches be Prevented? Avalanches cannot be prevented, although in most cases can be managed effectively.