Avalanche

Question 1

Case study

Answer 1

• European avalanches on 1999
• avalanche that killed 75 people in the alps in February 1999 were the worst in the area for 100 years
• precautionary measures had been taken e.g. enormous avalanche wall to protect village of Taconnaz + second wall to stop the taconnaz glacier advancing onto the motorway
• but the villages if Montroc had no defences = thought to be a safe area but was heavily hit

Question 2

When are avalanches more likely

Answer 2

• slopes steeper than 30°
• a lot of new snow falls over a short period of time
• winds lead to drifts
• old snow melts + freezes, encouraging new snow to slide off

Question 3

Montroc avalanche

Answer 3

• 9 February 1999 a huge wave of snow 150m wide + 6m high crashes down into valley at 60 mph
• buries the village of Montroc = 10 people killed
• force of avalanche so great it sweeps through Montroc + travels 40m uphill to village of Le tour —> as far as 400m wide

Question 4

Could the avalanche have been prevented?

Answer 4

• nothing could have been done to prevent it
• warnings had been given the day before as the region had experienced up to 2m of snow in just 3 days
• however, buildings in Montroc were not considered to be at risk = in the ‘white zone’ supposedly completely free of danger
• due to belief that global warming will increase snowfall in the alps that are heavier it means the avalanche ‘safe zones’ need to be re-evaluated

Question 5

Slab avalanche

Answer 5

• most dangerous
• a large, cohesive slab of snow breaks away from the snowpack + slides down the slope as a single mass
• fast moving 100-300 km/h
• typically occurs on 35-45° slopes

Question 6

Causes of slab avalanches

Answer 6

• rapid snowfall adding weight
• warming temperatures melting a weaker layer
• human activity e,g, skiing

Question 7

Example of slab avalanche

Answer 7

1999 Galtur avalanche in Austria killing 31 people

Question 8

Loose snow avalache

Answer 8

• begins at single point + gathers snow as it descends = creates fan shaped path
• generally smaller + less destructive
• occurs on steep slopes greater than 40°

Question 9

Causes of loose snow avalanche

Answer 9

• fresh, unconsolidated snow
• overloading from new snow or a skier cutting through

Question 10

Wet avalanche

Answer 10

• occurs when snow becomes saturated with water due to rain
• moved slowly along the ground at 10-30 km/h
• often happens in late seasons (spring) or after heavy rain

Question 11

Dry avalanche

Answer 11

• fast moving flow of cold, dry, powdery snow that moves through the air downslope
• very fast = can exceed 300 km/h in steep terrain

Question 12

Unconfined avalanche

Answer 12

• spreads widely across open slope - not contained by landscape
• often associated with loose dry snow but can also occur in slab avalanches

Question 13

Channeled avalanche

Answer 13

• flows down a narrow, confined path e.g. gully or ravine
• the terrain directs + concentrates the movement of snow, making the avalanche more focused + powerful
• can be very fast due to confinement
• can involve slab or loose snow

Question 14

Causes of channeled avalanche

Answer 14

• heavy snowfall on steep, narrow slope
• collapse of a slab of snow into a gully
• wind loading in confined terrain
• human activity

Question 15

Where are channeled avalanches common?

Answer 15

Swiss alps