Glaciers

Geog 3251 Mountain Geography

summer 2006

Adina Racoviteanu

Glaciers

1. Glacier formation, type and motion

2. Glacial landforms

3. Glacier-related hazards

4. Glaciers and climate (Friday & Monday)

Why glaciers?

• 10% of earth

covered by ice– 85% Antarctica– 11% Greenland– 4% elsewhere

• Glaciers store about 75% of the world's freshwater•Distribution: found at various

latitudes and climates

What is a glacier?

• Mass of moving glacial ice created by the accumulation of snow

• glaciers always moving forward at terminus

The Norwegian Arctic Archipelago of

Svalbard is 60% covered by glaciers.

Arctic

East Antarctic Ice Sheet

Antarctica

Photo: MH

Nev. Piramide, Cordillera Blanca, Peruphoto: Michael Hambrey

Tropical glaciers

Mid-latitude glaciers: Nepal Himalaya

Photo: A. Racoviteanu

Is this a glacier?

No-Icebergs are NOT glaciers

What climatic conditions are needed for glaciers to form?

• cool summer temperatures in (< 0 deg. C) • high winter precipitation

Why don’t we have glaciers in Siberia or parts of Antarctica?

The glacier story:

1.glacier birth

• accumulation of snow

• compression of snow by weight of layers

• snow metamorphism: snow grains squashed together--> conversion to ice

Air bubbles

Glacial Ice formation

• SNOW: seasonal snow void spaces

• FIRN (névé): snow that has lasted more than one year less void space density ~ 550 kg/m3

• ICE: compacted, air pores not connected

density > 860 kg/m3

The glacier story: 2. glacier growth

Accumulation:

•snowfall•avalanches : e.g. Karakoram, Andes•wind re-deposition•superimposed ice (rain freezing)

Avalanche-fed glaciers

Nev. Chacraraju, Cordillera Blanca, Peru

Wind (re)deposition

Nev. Huascaran,Cordillera Blanca, Peruphoto:Jürg Alean

The glacier story (cont’d): 3. glacier decay

Ablation:•melting•evaporation/sublimation (only cold arid areas)•calving•wind erosion

Calving

Hubbard glacier, Alaskaphoto:Jürg Alean

Thermodynamic classification of glaciers:

•warm based•thawed from their bed

1) Warm glaciers

Qori Kalis, QuelcayaIce Cap, Peru

Warm glaciers

2) “Cold” glaciers

– frozen to their beds

– ice below pressure melting point

– remain well frozen; melting only at surface

Cold glaciers: Antarctica

Hughes Glacier,Dry Valley, Antarctica

photo: MH

Glacier movement

• When glacier gets >20m thick,

• flow occurs

• has to do with behavior of ice under pressure

Ice is solid but it flows!

Glaciers flow!! East Greenland

False-colour Landsat image

Malaspina Glacier, Alaska (NASA, 31.8.2000).

Compression

Two types of glacier movement

1) PLASTIC DEFORMATION

2) BASAL SLIDING

1. Internal deformation

• ALL glaciers move

by deformation

Factors controlling rate of deformation:

•depth of ice•slope

Stress: Compaction (weight)

Strain = amount of deformation

2. Basal sliding

• needs liquid water!• Warm-based glaciers

only• glacier slips over the

rock surface• less friction

-water acts as lubricator-sliding

What if the glacier encounters a bump????

Glacier flowSteady-state flow rates 5-500m/a

Fastest flow in upper/central parts

( less friction)

Glacier movement summary1. Temperature at base of glacier is key

WARM glaciers: sliding + deformationCOLD glaciers: deformation only

2. Gravity main driving force

gh*sin stress

strength

gravity

θ

compression

Benefits of glaciers

• provide a reliable water supply for hydro-electric power generation & agriculture

• Cordillera Blanca,

Peru

Canals

Agricultural terraces

Technological Technological advances of the advances of the IncasIncas

Agricultural terraces

Inca roads and trails

Architecture

Benefits of glaciers

• recreation (climbing)

• Scenic value

Pastoruri, Peru -major tourist attraction

Glacier hazards

• Glacier surges

• Glacier lake outburst floods (GLOF)

• Ice avalanches

• Falling ice

Glacier surges

Glacier surges = short-lived episodes involving a sudden increase in ice movement by at least one order of magnitude

Glacier surge areas: Alaska, and theYukon Territory, Canada; Svalbard; Iceland; Greenland; the Russian High Arctic;Asia (the Pamirs, theTien Shan and the Karakoram)

Variegated glacier, Alaska• velocities of 100m/day

• dramatic increase in flow rate, 10-100 hundred times faster than its normal rate

Himalayas: morraine-dammed lakes

After the glacier lake outburst….

Ice avalanches: May 30, 1970 Peru disaster

•A large mass of ice and rock slid from a vertical face on Nevado Huascaran

•Debris reached a velocity of 280 km/hr

•Buried 2 towns •death toll: 20,000.

Questions?

• Glaciers online

• NSIDC: All about glaciers