Lecture 13: Glacial Hazards in a warming world

Question 1

The cryosphere comprises

Answer 1

Snow
River/lake/sea ice
Glaciers
Ice shelves and ice sheets
Frozen ground

Question 2

Ice sheet

Answer 2

A mass of land ice of continental size, and thick enough to cover the underlying bedrock topography. Its shape is mainly determined by the dynamics of its outward flow.

Question 3

Ice shelf

Answer 3

A thick, floating slab of freshwater ice extending from the coast, nourished by land ice.

Question 4

Glacier

Answer 4

A mass of surface-ice on land which flows downhill under gravity and is constrained by internal stress and friction at the base and sides.

Question 5

Ice cap

Answer 5

Dome-shaped ice mass with radial flow, usually covering the underlying topography.

Question 6

A glacial hazard

Answer 6

Is any glacier or glacier-related feature or process that adversely affects human activities

Question 7

Ice avalanche

Answer 7

Sudden mass movement of ice down slope. Starting areas can be classified as ramp- or cliff-type.

Question 8

Rock avalanche

Answer 8

High velocity (~90-350 kph) transport of fractured rock mass, often starting as a rock fall or slide on step slopes. Can be triggered by freeze-thaw cycles (permafrost degradation), seismicity, or stress release following glacier retreat.

Question 9

Debris flow (Aluvión)

Answer 9

Typically a slurry of mixed grade soil and water. Commonly triggered by ice/rock avalanches and/or glacier/glacial lake floods.

Question 10

Glacier Mass Movements – Mitigation

Answer 10

Monitoring

Hazard map

Question 11

Glacier outburst

Answer 11

Catastrophic discharge of water from the subglacial and/or englacial system.
Often triggered by geothermal heating (jökulhlaup), opening of englacial channels at the start of the ablation season (spring events) or intense rainfall.

Question 12

Glacial Lake Outburst Flood (GLOF)

Answer 12

Catastrophic flood from the breaching of a moraine dam. Term used in Himalayan regions (synonymous with the French term dêbacle).

Question 13

Ice-dammed lake outburst

Answer 13

Catastrophic flood from the failure of an ice dam. Often occurs periodically from the same lake/glacier.

Question 14

Glacier outburst

Answer 14

The type of flood associated with a sub-glacial volcanic eruption.

Question 15

There are three recorded mechanisms by which glacier outbursts occur:

Answer 15

The rupture of an internal water pocket
The progressive enlargement of internal drainage channels
Catastrophic glacier buoyancy, or `jacking’, with sub-glacial discharge.

Question 16

If meltwater within the glacier is able to build up pressure to such a point that the hydrostatic pressure exceeds the constraining cryostatic pressure then…

Answer 16

A catastrophic burst through the ice may occur.

Question 17

Water may drain into the existing sub-glacial drainage from where it can discharge to the

Answer 17

glacier snout.

Question 18

The flood wave is dangerous as

Answer 18

it often quickly leaving little warning for communities downstream

Question 19

Eyjafjallajökull

Answer 19

Glaciated volcano in southern Iceland
Eruption on 13th April 2010
Ice cap melted
700 people evacuated 
Destroyed main road, 
20 farms destroyed

Question 20

Grimsvötn, Iceland – 1996

Answer 20

Eruption of subglacial volcano
Melting of the ice cap and draining of Lake Grimsvötn
3.2 km3 drained in 40 hours
Flow as high as 40,000 m3s-1
Was widely predicted and monitored in detail
No loss of life but damage to infrastructure

Question 21

Glacial Lake Outburst Floods (GLOFs)

Answer 21

Most destructive glacier flood events tend to be those associated with unexpected releases of stored glacier melt water and surface run off

Question 22

Formation and subsequent failure of ice- and moraine-dammed lakes.
Ice-dammed lakes

Answer 22

Developed when sub-glacial, en-glacial, supra-glacial or ice-marginal water bodies are impounded by ice.

Question 23

Such outburst or drainage events can occur regularly, on a near seasonal basis caused by changes

Answer 23

in ice thickness, lake bathymetry, sub-glacial water pressure, changes in meltwater production and =– water bodies impounded by terminal and lateral moraines left behind by retreating glacier snouts.

Question 24

Trigger Mechanisms

Avalanche Displacement wave

Answer 24

Ice avalanches
Glacier calving 
Collapse of hanging glaciers
Valley side rock falls 
Debris flows

Capacity of lakes to store water is reduced
Melting of ice-core within moraine
Seismic activity
60% of known GLOFs in the Himalayas caused by Avalanche Displacement Waves

Question 25

Glacial Lake Outburst Floods (GLOFs)

Hazards

Answer 25

Such outburst events carry significant amounts of debris downstream, altering the geomorphology of river basins, and can often transport large rocks and boulders for considerable distances.

Question 26

Glacial Lake Outburst Floods (GLOFs)

Destruction to property and infrastructure

Answer 26

Loss of essential power supplies due to failure of HEP schemes

Question 27

Glacial Lake Outburst Floods (GLOFs)

Death and injury

Answer 27

Some of the most deadly moraine-dammed outburst floods have occurred in the Peruvian Andes where local communities and cities exist in relative close proximity to potentially dangerous glacial lakes.
The most serious occurred in 1941 when an outburst flood originating from Lake Palcacocha destroyed a third of the city and killed 5000 people.

Question 28

Glacial Lake Outburst Floods (GLOFs)

Sabai Tsho GLOF

Answer 28

1998 warm wet monsoon increased lake depth, and increased velocity and destabilised glacier.
Then three small earthquakes, caused an ice avalanche into the lake, caused the displacement wave, collapse of moraine in 5-10 minutes, 25 million m3 water and lowered lake surface by 50m

Question 29

Glacial Floods - Mitigation

Hard measures (engineering)

At the lake site:

Answer 29

Drainage by syphon or pump
Cut drainage channels
Tunneling through bedrock
Early warning system at GLOF ste and along the downstream river channel

Question 30

Glacial Floods - Mitigation

Hard measures (engineering)

Downstream:

Answer 30

Early warning audio system adjacent to population centres
Flood control structures
Building reinforcement

Question 31

Glacial Floods - Mitigation

Soft measures (engineering)

Answer 31

Mapping of hazards and vulnerabilities
Computer modelling of potential GLOFs
Geophysical analysis of lake dames to determine structure and ice content
Observation and forecasting systems
Ground penetrating radar
Increase in community awareness and participation
Promotion of afforestation and conservation
Planning

Question 32

Tsho Rolpa, Nepal (Rana et al., 2000)

Answer 32

Largest moraine-dammed in Himalayas (ice –cored moraine)
Ground penetrating radar (GPR) studies of the moraine to locate ice-core
Tried to use syphon’s to lower lake level
Then cut a channel, installed a structure to regulate flow
Array of sensors and audio warnings

Question 33

What is an iceberg?

Answer 33

Anicebergis a large piece of freshwater ice that has broken off a glacier or an ice shelf and is floating freely in open water.

14th April 1912 Titanic, loss of 1517 lives – since then no iceberg impacts have come near the disaster in severity.

Question 34

Icebergs – Hazards

Answer 34

Direct impact with ships or installations – 3539 fatalities since 1800’s
Sea bed scour
Disruption of ecological systems

Question 35

Icebergs – Mitigation

Answer 35

Visual and satellite reconnaissance
RADARSAT -1 1995 and RADARSAT-2 in 2007
Immobile structures (e.g. oil rigs) need to divert the iceberg
Towing
Water cannons

Question 36

Glacier retreat

Answer 36

Increased risk of GLOFs due to glacier retreat creating more moraine dammed lakes which could fail
Debris flows are also a well-recorded consequence of glacier retreat (Ballantyne and Benn, 1994).
Existing moraine-dams may experience accelerated degradation through melting of ice cores
Lakes may increase in volume due to greater melt water input.
Steep hanging glaciers that are partially or entirely frozen to their beds may become prone to ice avalanching as their snouts become warm based

Question 37

Continued glacier mass-balance losses will result in

Answer 37

Water shortages after an initial period of increased discharge.

Question 38

The potential loss of glaciers as water resources is a greater source of anxiety to the people and industries that rely on glacial melt during dry seasons.
e.g.

Answer 38

HEP

Question 39

A further widespread problem that may develop with global warming is a shift in hazard zones

Answer 39

Glacial and related hazards may begin to affect areas with no history of such events, where regulatory and social aspects of preparedness will not exist.
Glacial retreat leading to increased volcanic activity.

Question 40

Sea Level Rise

Answer 40

Currently small glaciers and ice caps contributing most to sea level rise
In future Greenland and Antarctic have the potential to contribute large volumes

Question 41

Glaciers and Climate Change

Answer 41

Iceberg flux
Albedo
Ocean circulation

Question 42

Relationship between slope and volume can predict how far ice will travel

Answer 42

Tanα = 1.111 – 0.118 log (V)

α is the average slope, and V the volume of the ice avalanche in cubic metres.