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Chapter 15 • A is a large, permanent (non- seasonal) mass of that is formed on land and moves under the force of gravity. • Glaciers may form anywhere that accumulation exceeds seasonal melt. Glaciers and Glaciation

Types of Glaciers Glacier Dynamics • Alpine glaciers form in the • A typical glacier will add snow at its mountains. head and lose to melt at its foot. – A valley glacier is one that • The snow line is the line below which the occupies a valley, annual snow cover is lost in summer. – An iceice capcap is a mass of ice that • The region above the snowline is the zone occupies a high mountain area and of accumulation; the region below the zone flows outward in several of wastage (melting, sublimation, calving). directions. • If it gains more than it loses, its terminus • Continental glaciers (iceice will advance. sheets) may cover large • If it loses more than it gains, it will retreat. sections of continents as in Greenland and Antarctica.

Glacier Dynamics

1 , , and Ogives Properties of Ice • A is a fracture in the glacier surface. 3 • Ice has a density of 0.96 g/cm . (It – Crevasses form where the surface is in floats.) tension. • Ice is a weak solid and will not hold a – Crevasses are rarely more than about 40 vertical cliff higher than 40m (130ft). m deep. • Ice will flow under it own weight. – A is a crevasse at the head of a glacier. • Pressure can cause local melting. • A is a large, irregular block of ice formed by intersecting crevasses • An ogive is compressional wave in the glacier surface.

Crevasses Serac

Bergschrund

Ogives

2 • A is a deposit of unsorted (silt- to boulder-size) material (till) left by a glacier.

– Lateral moraines are left at the sides of glaciers – Medial moraines are left in the centers. – Terminal moraines are left at the ends.

Lateral Moraines Continental Glacial Landforms • A is a rounded, striated outcrop hill. • An is a low, sinuous hill of till left by a sub-glacial stream. • A kettlekettle is a depression in an left by a buried block of ice that has melted.

Mountain Glacial Landforms Mountain • Glacial valleys have a characteristic U- Glacial shape. Landforms: • A hanging valley is the valley of a tributary glacier. • A is a steep-walled bowl-shaped U-shaped & valley at the head of a glacier. • An arête is a narrow ridge between two Hanging . Valleys • A horn is a peak at the intersection of arêtes. • A fjordfjord is a glacial valley that opens to the sea.

3 Mountain Glacial Landforms: Mountain Horn Glacial Landforms:

Arête

Mountain Glacial Landforms: Mountain Glacial Landforms: Nunatak Cirque

Ice Ages • The last 1.8 million years of geologic time Mountain (Pleistocene) are the Ice Ages. • The last major ice advance in North Glacial America peaked about 18,000 years ago. Landforms: • Climate warmed abruptly at 14,500 years ago. • It cooled again and then warmed abruptly (~6ºC) at about 11,500 to near current Kangerluqsuaq levels. E. Greenland • The last remnants of the North American Ice sheets melted away less than 7000 years ago.

4 Previous Ice Ages Previous Ice Ages • Permian (300 million years) • Neo-Proterozoic (570 million years) Striations • Archaean-Proterozoic boundary? from Permian Glaciation in Namibia

Causes of Ice Ages • Milankovich Cycles – Eccentricity of orbit (100,000 y cycle). – Tilt of rotation axis (41,000 y cycle). – Precession of rotation axis (23,000 y cycle).

• CO2 variation. • Continental drift and polar continents. • Ocean Circulation patterns

Tilt Eccentricity

5 Precession Continental Drift

Continental Drift CO2 Variation • Carbon dioxide is a greenhouse gas. – It transmits visible and UV radiation – It blocks IR radiation.

• CO2 variation correlates with global temperature.

Glacial Terms

• Glacier • Snow Line • Drumlin • Alpine • Sublimation • Esker Glacier • Calving • • • Crevasse • Hanging • • Bergschrund Valley • Horn • Serac • Moraine – Terminal • Arête • Ogive – Lateral • Cirque • Till – Medial • Fjord

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