Glaciers (Part I) What is a glacier? Where are glaciers found? What is climate effect on glaciers?

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

Typical glacier system in Cordillera Blanca, Peru

Glacier landscape in Nepal Himalayas

Shorong Yul-lha glacier, Nepal Himalayas

How are glaciers formed? where average temperatures < O deg C. Snow accumulates and compressed by weight of layers buried layers slowly form a thickened mass of ice snow grains squashed together-- snow metamorphosis

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

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

Thermodynamic classification of glaciers “Cold” glaciers: –frozen to the rock of their beds –ice below pressure melting point –remain well frozen; melting only at surface “Warm” glaciers: –warm based –thawed from their bed –slide and flow

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

How does ice move? F faster

Two ways of glacier movement PLASTIC DEFORMATION BASAL SLIDING Gravity main driving force,  gh*  sin 

1. Internal deformation Ice > 60m thick specific for cold-based glaciers (frozen to bed) velocity Factors controlling rate of deformation: depth of ice temperature slope Compaction weight Pressure melting point

2.Basal sliding only “warm-based” glaciers glacier slips over the rock surface H2O as lubricator less friction velocities: 0-300m/day -water -sliding

Glacier surge velocities of 100m/day dramatic increase in flow rate, hundred times faster than its normal rate

Structures within glacial ice Crevasses: –cracks in the ice due to different velocities between center and edges of glacier –formed perpendicular to direction of flow

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

Crevasses

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

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

Geographical and Climatic conditions high snowfall in winter cool temperatures in summer Moisture important!!! –Eg: Siberia and parts of Antarctica: low temperatures meet glacier growth requirements, but lack of adequate precipitation prevents glacier development

Glacier distribution & importance 10% of earth covered by ice –85% Antarctica –11% Greenland –4% elsewhere Glaciers store about 75% of the world's freshwater

Glacier Mass Balance (Net)Accumulation zone = area where ice accumulates (Net) Ablation zone= area where glacial ice melts Equilibrium line where accumulation=ablation balance = 0 (at equilibrium)

Where is the ELA?

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

ELA and climate Cooling -- ELA lower Warming -- ELA higher Polar glaciers: ELA lower Tropical glaciers: ELA higher

How do glaciers reflect climate change? Climate change: –changes in temperature –changes in amount of moisture –Glaciers sensitive to temperature fluctuations climate change can cause glaciers to melt but the relationship is not straightforward, –eg. Antarctica:climate change-->warmer-->more evaporation from ocean ->more water vapor -> more snowfall!

Ice ages Ice ages return every 100,000 years approx. 20 ice ages Pleistocene = most recent ice age, that started about 2 million years ago and ended ~10,000 yrs ago 4 major advances of ice, most recent ones: –Laurentide: ended 20,000 yrs ago –Wisconsin: ended 100,000 yrs ago –Presently we are in an interglacial period

Causes of ice ages? Milankovic cycles long term variations in Earth’s orbit around the Sun:

Glacial ages During the last Ice Age, glaciers covered 32% of the total land area. Little Ice Age: –17th century - late 19th century –consistently cool temperatures –significant glacier advances.

Earth’s climate record

Glaciers sensitive to climate changes: a few facts strong warming over the last yrs increasing CO2 levels Alpine glaciers have been experiencing rapid retreat Ice cap on Mt. Kilimanjaro has been decreasing by 82% in the last 88 years Glaciers in the Alps decreased by 50% in volume

Ice-albedo (positive) feedback Global warming Glacial melt Decrease in albedo More energy absorbed Decrease in surface of ice

Climatic responses- scenarios winter temperature: –less, not more, snow –polar areas get little precip. (cold air) –if summer ablation same -- glacier retreats summer temperature: –more cloud cover –less summer ablation –if winter accumulation same -- glacier grows

Climatic response (cont’d) winter precipitation (snowfall) –if no change in temperature –some snow survives over summer –glacier advances –temperature crucial factor-

Glacier response -summary Alpine glaciers and N.Hem. Ice caps expected to retreat under global warming scenario NOTE: Antarctica expected to grow due to possible increase in humidity

Monitoring glaciers Field measurements Aerial photography Satellite images

Radar measurements - ice thickness

Aster image, Patagonia, Chile

ASTER Image courtesy of: NASA EROS Data Center, Sept. 9, 2001 Indian Himalayas : Glacier ablation at Gangotri, source of the holy Ganges glacier terminus retreated by glacier terminus retreated by 3km 3km

Climate reconstructions Ice core drilling Drilling tent on the summit of Cerro Tapado, Chile

Ice Core drilling, Coropuna, 2003

Having fun at high altitide.....trying to get the generator to work

Oxygen isotopes: 18 O and 16 O clues of temperature in the areas where ice formed Ratio of 18 O and 16 O indicator of temperature – 18 O/ 16 O > - warming signal – 18 O/ 16 O < - cooling signal

1.drilling the ice core 2. Taking the ice core out 3.measuring and storing the ice core

Isotope record

Glacier mummies: climate records? 500-year old mummy found in Peruvian Andes Otzi- 5,000 year old mummy found in Tyrolean Alps, Italy Glacier retreat revealed mummy