Glaciation Pack M

Question 1

What are GLOFs?

Answer 1

• Glacial lake outburst floods
• Powerful floods from the sudden and rapid release of water from glacial lakes
• There is a potential for a flood wherever meltwater collects/is ponded behind an ice or moraine obstruction (e.g. ice, moraine, landslide debris, bedrock)

Question 2

How are GLOFs caused?

Answer 2

• Sudden failure of the damming material or when water over tops the dam
• Increased flotation of ice as water levels rise
• Overflow and melting of an ice dam (more common with climate change)
• Breakdown of an ice dam due to tectonic activity
• Irreversible overtopping of a moraine dam by large tsunami-style waves (triggered by a snow or ice avalanche) or a landslide into a lake
• Failure of a moraine dam by slow melting of ice within it or removal of fine sediment from the moraine by underwater piping
• Enlargement of pre-existing tunnels beneath an ice dam due to increased water pressure

Question 3

What are the impacts of GLOFs?

Answer 3

• Damage to bridges, powerlines, roads, railway tracks and buildings
• Loss of life
• Impacts are intensifying due to climate change

Question 4

How can the risks of GLOFs be reduced?

Answer 4

• Identifying and monitoring the development of glacial lakes
• Modelling GLOFs
• Checking dam stability
• Reinforcing flood channels
• Installing warning systems
• Effectively communicating with those at risk

Question 5

What is an example of a GLOF?

Answer 5

Causes and background information:
- Luggye Tsho GLOF, Bhutan on October 6 1994
- Bhutan is home to 677 glaciers and 2674 glacial lakes (of which 20 are considered dangerous)
- Increased pressure resulting from an increase in the depth of the glacial lake due to melting ice caused the moraine dam to fail
- 18million cubic meters of water were released, which travelled at 12km/h

Impacts:
- Killed 21 people
- Flooded 700ha of agricultural land
- Washed away 12 houses, 5 watermills and 4 bridges
- Livestock was killed
- Fish died in the sediment choked water and fish stocks took 10 years to recover

Responses:
- Surveys were carried out to assess the risks of GLOFs
- The 1994 affected area was mapped for flood risk with building discouraged in high risk areas
- Escape route systems to higher ground were prepared
- Warning system with sirens was established and people were educated about what to do when there was a warning

Question 6

What are lahars?

Answer 6

• A hot or cold mix of water and volcanic debris (particularly ash) flowing down a volcano or river valley
• Spread out over the valley floor like a flood

Question 7

What are the impacts of lahars?

Answer 7

• People get trapped
• Destroy bridges and rods
• Economic, social and environmental damage

Question 8

What causes lahars?

Answer 8

• Associated with volcanoes that have a substantial cover of snow and ice
• Pyroclastic flows are the most common volcanic event that generate lahars as they quickly melt large quantities of snow and ice
• Lava eruption beneath a glacier can result in substantial ponding of water
• Lava flows moving slowly don’t melt snow and ice rapidly enough to form lahars

Question 9

What is an example of a lahar?

Answer 9

Causes and background information:
- Nevado del Ruiz 1985
- Volcano in the Andes
- 20% of its snow and ice cover was melted by pyroclastic flows
- Channels 100m wide and 4m deep were eroded into the ice caps
- Lahars were 50m thick and travelled at 60km/h

Impacts:
- Part of the icecap melted so rivers overflowed
- Natural dam burst
- 23,800 died

Question 10

What are avalanches?

Answer 10

• A mass of snow, rock, ice, soil and other material sliding swiftly down a mountainside

Question 11

What causes an avalanche?

Answer 11

• An unstable mass of snow breaks away from a slope
• Snow picks up speed as it moves downhill
• Moving mass picks up even more snow
• Happens as layers in a snowpack slide off
• A snowpack is layers of snow that build up
• Repeated snowfall in water build a thick snowpack with layers varying in thickness and texture
• Bonds between the layers in a snowpack may be weak
• Melted snow that refreezes may cause a slick coating of ice to form on the surface of a layer
• A new snowfall will not stick to this slippery layer so it will slide off
• During spring thaw, melted snow can seep through a snowpack, making the surface of a lower layer slippery
• Added weight or vibration can cause an avalanche as well