Glaciers Chapter 17. Why glaciers? 10% of earth covered by ice 85% Antarctica 11% Greenland 4%...

Glaciers

Chapter 17

Why glaciers?

10% of earth covered by ice

85% Antarctica11% Greenland4% elsewhere

Glaciers store about 75% of the world's freshwater

•Distribution: found at variouslatitudes 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

Nev. Piramide, Cordillera Blanca, Peruphoto: Michael Hambrey

Tropical

glaciers

Mid-latitude glaciers: Nepal Himalaya

Photo: A. Racoviteanu

Glacier birth

• accumulation

• snow metamorphism

• compression

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 connecteddensity > 860 kg/m3

Mass Balance

• Accumulation

• Ablation

Avalanche-fed glaciers

Nev. Chacraraju, Cordillera Blanca, Peru

Melting

Calving

Mass balance

• area where ice accumulates

area where ice melts

Equilibrium line altitude (ELA) accumulation = ablationbalance = 0

Austin Post photoSouth Cascade Glacier, Sept 20, 1966From NSIDC

Exit Glacier, Alaska

Bar graph showing winter, summer and net balance at Storbreen during 1949-2004.

www.nve.no

Movement of ICE

1. Internal deformation

• ALL glaciers moveby 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????

Regelation requires pressure-melting, transfer of water around the bump, and transfer of heat through it

Glacier movement summary

1. 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