Glaciers Geog 3251 Mountain Geography summer 2006 Adina

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

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

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

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

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

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, 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

Thermodynamic classification of glaciers: 1) Warm glaciers • warm based • thawed from their bed

Warm glaciers Qori Kalis, Quelcaya Ice Cap, Peru

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 Ice is solid but it flows! • When glacier gets >20 m thick, • flow occurs • has to do with behavior of ice under pressure

Glaciers flow!! East Greenland

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

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 flow Steady-state flow rates 5 -500 m/a Fastest flow in upper/central parts ( less friction)

Glacier movement summary 1. Temperature at base of glacier is key WARM glaciers: sliding + deformation COLD glaciers: deformation only e str 2. Gravity main driving force s = rgh* sina th g n s s e str θ gravity compression

Benefits of glaciers • provide a reliable water supply for hydro-electric power generation & agriculture • Cordillera Blanca, Peru

Technological advances of the Incas Agricultural terraces Canals Inca roads and trails Agricultural terraces 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 = short-lived episodes involving a sudden increase in ice movement by at least one order of magnitude 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

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