CH 7 Glaciers, Deserts, & Wind Ice Age – when much of earth’s land is covered in glaciers The last one ended 15,000 years ago Glacier – a thick mass of slow moving ice They cover ~ 10 % of earth today Form by compaction, melting, and recrystallization of snow Firn = blue ice (the glacier look) Snow line – lowest elevation that remains snow covered all year

2 Types of Glaciers Valley (alpine) – Alaska, Alps, Himalayas Smaller More common In high elevations (mountains) Sharpen features Ice sheet (continental) – Greenland, Antarctica Larger Only 2 At high latitudes (poles) Round features

Movement Plastic flow Basal slip Move fastest at top and middle…why?? Brittle on the surface but they flow underneath 50 m depth limit Basal slip Ice melts on bottom due to enormous pressure and friction Slides on the layer of water Will squish you big time Move fastest at top and middle…why?? Forms crevasses (cracks) & pressure ridges

Glacier Budget Is the balance or unbalance between the upper end accumulation and the lower end loss Advance – when accumulation exceeds loss Retreat – when loss exceeds accumulation Stationary – when loss = accumulation Calving – breaking off of ice chunks making iceberges Only 10 % is above water

Erosion by Valley Glaciers Plowing and plucking – bulldozing and picking up Glacial trough – “U” shaped valley Hanging valley – tributary/side valleys Cirque – bowl shape depression at top Tarn – cirque filled with water

Erosion by Valley Glaciers Pater noster – tarns connected by a stream Arete – narrow, sharp ridge Horn – pyramid shaped sharp peak Fiord – “U” shaped valley filled with water Col – saddle between 2 horns Nunatack – lonely rocks

Glacial Deposits Drift – any sediment of glacial origin Till = deposited directly by the glacier (unsorted) Stratified drift = deposited by glacial meltwater (sorted) Moraines – the most common type of till Lateral – sides Medial – middle Terminal - end

Glacial Deposits Outwash plain – ramplike sediment accumulation Erratic – rock that does not belong Kettle – depression in outwash plain Kame – rounded mounds Esker – sinuous/winding ridge of sediment Drumlin – tear dropped shaped hills Roche mountonnes – sheep rocks Rock flour – pulverized rock (silt) Glacial milk – rock flour added to water

Causes of Ice Ages Milankovitch Theory – variations in the earth – sun relationships Eccentricity – change orbital shape of earth Obliquity - change in earth’s tilt Precession – wobble of the earth Effects of ice ages Lakes, crustal rebounding, sea level changes

Deserts Less moisture = less weathering Most weathering is mechanical, (mostly water) Ephemeral streams = only flow after rains Alluvial fans = triangular, fan/cone shape Playa lakes = flat, shallow lake

Wind Erosion Deflation – blowing away of small sediments - forms desert pavement (big sediment left behind) Abrasion – sandblasting - forms ventifacts (polished rocks)

Wind Deposits Loess – blankets of silt Sand dunes – mounds of sand Glaciers and rivers Sand dunes – mounds of sand Shapes depend on wind speed and direction, and the amount of sand and vegetation Beaches and deserts Crescent shaped Cross section and cross bedding

Sand Dunes (page 206) Barchan Parabolic Barchanoid Star Transverse Longitudinal