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 inCordillera 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 connectedAir bubblesdensity > 860 kg/m3

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?

Ffaster

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, 10-100 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 ShorongYul-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?

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 50-200 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 surfaceof 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 HimalayasIndian Himalayas::

Glacier ablation at Glacier ablation at Gangotri, source ofGangotri, source ofthe holy Gangesthe holy Ganges

• glacier terminus retreated by glacier terminus retreated by 3km3km

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 generatorto work

Oxygen isotopes: 18O and 16O

• clues of temperature in the areas where ice formed

• Ratio of 18O and 16O indicator of temperature– 18O/ 16O > - warming signal– 18O/ 16O < - 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, ItalyGlacier retreat revealed mummy