Glaciers I mass balance and glacier motion Geog

Glaciers (I): mass balance and glacier motion Geog 1011 Landscape and Water Nov 28, 2005 Adina Racoviteanu

Glaciers (Part I) • • • Glacier formation Glacier mass balance Types of glaciers Glacier flow Major surface features of ice • Glacier fluctuations and climate (on Friday)

What is a glacier? • Mass of moving glacial ice created by the accumulation of snow • glaciers always moving forward at terminus • ice & water move forward

Why glaciers? • 10% of earth covered by ice – 85% Antarctica – 11% Greenland – 4% elsewhere • Distribution: found at various latitudes and climates • Glaciers store about 75% of the world's freshwater

Arctic The Norwegian Arctic Archipelago of Svalbard is 60% covered by glaciers.

Antarctica East Antarctic Ice Sheet Photo: MH

Tropical glaciers Nev. Piramide, Cordillera Blanca, Peru photo: Michael Hambrey

Mid-latitude glaciers: Nepal Himalaya Photo: A. Racoviteanu

Climatic conditions • cool temperatures in summer (average temperatures < O deg C) • high winter precipitation Moisture important!!! Eg: Siberia and parts of Antarctica: – low temperatures but – lack of adequate precipitation --> prevent glacier development

The glacier story: 1. glacier birth • accumulation of snow • compression of snow by weight of layers • snow metamorphosis snow grains squashed together--> conversion to ice

Glacial Ice formation • SNOW: seasonal snow void spaces • FIRN (névé): snow that has lasted more than one year less void space density ~ 550 kg/m 3 • ICE: compacted, air pores not connected density > 860 kg/m 3 Air bubbles

Transformation of SNOW --> ICE • Rate of transformation dependent on temperature and accumulation rate • Rate with load • Rate with Temperature (for a given load) – temperature determines size of crystals and amount of snowfall

The glacier story (cont’d): 2. glacier growth Accumulation: – snowfall – avalanches : e. g. Karakoram, Andes – wind deposition – superimposed ice (rain freezing)

Avalanche-fed glaciers Nev. Chacraraju, Cordillera Blanca, Peru

Wind (re)deposition Nev. Huascaran, Cordillera Blanca, Peru photo: Jürg Alean

The glacier story (cont’d): 3. glacier decay Ablation: – melting – evaporation/sublimation (only cold arid areas) – calving – wind erosion

Calving Hubbard glacier, Alaska photo: Jürg Alean

Glacier Mass Balance • area where ice accumulates area where ice melts Equilibrium line altitude (ELA) accumulation = ablation balance = 0

Mass balance • NEGATIVE: glacier gets smaller • POSITIVE: glacier gets larger • ZERO MASS BALANCE: – no change in glacier size (mass, volume) – GLACIER STILL MOVING FORWARD!!!

Where is the ELA?

Where is the ELA?

Classification of glaciers: thermodynamic 1) Warm glaciers • warm based • thawed from their bed • slide and flow

Warm glaciers Qori Kalis, Quelcaya Ice Cap, Peru

Cold glaciers: Antarctica Hughes Glacier, Dry Valley, Antarctica photo: MH

2) “Cold” glaciers – frozen to their beds – ice below pressure melting point – remain well frozen; melting only at surface

Glacier movement Ice is solid but it flows! • When glacier reaches critical mass (>20 m thick) • flow occurs

Glaciers flow!! East Greenland

Compression False-colour Landsat image Malaspina Glacier, Alaska (NASA, 31. 8. 2000).

Two types of glacier movement 1) PLASTIC DEFORMATION – COLD based glaciers 2) BASAL SLIDING – WARM based glacier Temperature main limiting factor as it dramatically alters the amount of water present!

1. Internal deformation • Ice > 60 m thick • specific for cold-based glaciers (frozen to bed) Stress: Compaction (weight) Factors controlling rate of deformation: • depth of ice • slope velocity Strain = amount of deformation

2. Basal sliding • needs melt water! • glacier slips over the rock surface • less friction Gravity main driving force, s = rgh* sina -water acts as lubricator -sliding What if the glacier encounters a bump? ?

Glacier flow Steady-state flow rates 5 -500 m/a Fastest flow in upper/central parts n. Area of least friction

Glacier travel: Major surface features 1) Crevasses: – deep, V-shaped structures found in the uppermost layer of the glacier. – form due to different velocities between center and edges of glacier – perpendicular to direction of flow

Accumulation area is often heavily crevassed Direction of flow New Zealand

2) Bergschrund: crevasse that separates flowing ice from stagnant ice at the head of a glacier Glacier on Shorong Yul-lha, Nepal

3. Icefall: steep, fast-flowing section of glacier with cracked and jumbled surface Khumbu Ice fall, Everest

4) Ogives : alternate bands of light and dark ice on a glacier (winter) (summer)

5) Séracs: towers of ice formed by • intersecting crevasses • rapid flow • steep slopes Glacier des Bossons, French Alps photo: MH

6) Penitentes: spiky columns of snow; formed in dry environments Nev. Coropuna, Peruvian Andes

7) Melt stream: on the glacier surface 8) Moulins Very slushy and slippery!! water

Glacier hazards • • Glacier surges Glacier lake outburst floods Ice avalanches Falling ice

Glacier surges = short-lived episodes involving a sudden increase in ice movement by at least one order of magnitude, sometimes two orders, compared to presurge, and post-surge behavior Glacier surge areas: · Alaska, and the. Yukon. Territory, Canada; · Svalbard; Iceland; Greenland; · the Russian High Arctic; · Asia (the Pamirs, the. Tien Shan and the Karakoram)

Variegated glacier, Alaska • velocities of 100 m/day • dramatic increase in flow rate, 10 -100 hundred times faster than its normal rate

Medial moraines (tear-drop shape)from past surges Bering glacier, Alaska

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.

Himalayas: morraine-dammed lakes

After the glacier lake outburst….

A strange feature in the ice: Glacier mummies 500 -year old mummy found in Peruvian Andes Otzi- 5, 000 year old mummy found in Tyrolean Alps, Italy Glacier retreat revealed mummy