Sculpting the Earths Surface Glaciers Deserts and Wind

Sculpting the Earth’s Surface Glaciers, Deserts, and Wind

Glaciers • Glaciers are a part of both the hydrologic cycle and rock cycle • A thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow

Glaciers • Location – Occupy 10% of Earth’s surface • Primarily located in polar regions (Antarctica & Greenland) • But found on every continent – Form above the snow line

Glaciers • Formation – New layers form each year – Weigh of overlying layers compresses buried layers • Snow recrystallizes – looks like sugar • Snow begins to grow, air pockets decrease • compacts & becomes very dense • After 2 winters => FIRN

Glaciers • Formation (continued) – Firn • Generally 16 x the size of a snow crystal • ½ as dense as water • Increase in size as the overburden increases • Over time, grows to form even larger crystals • Forms glacial ice

Glaciers • Movement – When ice sheet thickness > 18 meters, the ice sheet: • Deforms • Flows – Movement slower at base than at top – Advance and retreat – Surge

Glaciers • Types of glacial movements – Plastic flow – Basal slip

Glaciers • Rates of movement – Average velocities vary considerably – Rates of up to several meters per day – Some glaciers exhibit extremely rapid movements called surges

Glaciers • Movement (continued) – Budget of a glacier • Accumulation + loss = glacial budget

If accumulation exceeds loss (called ablation), the glacial front advances

If ablation increases and/or accumulation decreases, the ice front will retreat

Glaciers Features – Crevasses – Moraines Barnard Glacier http: //nsidc. org/glaciers/questions/compo nents. html

Glaciers Types – Ice • • • Ice Sheets, Ice Shelves, Ice Caps, Ice Streams, and Ice fields – Glaciers • • • Mountain Glaciers, Valley Glaciers, Piedmont Glaciers, Cirque Glaciers, Hanging Glaciers, Tidewater Glaciers.

Types of Glaciers

Glaciers • Glaciers erode by – Plucking – lifting of rock blocks – Abrasion • Rock flour (pulverized rock) • Striations (grooves in the bedrock)

Glaciers • Glacial deposits – Glacial drift • All sediments of glacial origin • Types of glacial drift – Till – material that is deposited directly by ice – Stratified drift - sediment deposited by meltwater

Glaciers • Glacial deposits – Depositional features • Moraines – layers or ridges of till • Types of moraines – – Lateral Medial End Ground

Glaciers • Glacial deposits – Depositional features • Outwash plain, or valley train • Kettles • Drumlins • Eskers • Kames

Glacial depositional features

Glaciers • Ice Ages – Have occurred throughout Earth’s history

Glaciers • Ice Age – Began 2 to 3 million years ago – Division of geological time is called the Pleistocene epoch – Ice covered 30% of Earth's land area

Glaciers • Indirect effects of Ice Age glaciers – Migration of animals and plants – Rebounding upward of the crust – Worldwide change in sea level – Climatic changes

Glaciers • Causes of glaciation – Successful theory must account for • Cooling of Earth, as well as • Short-term climatic changes

Glaciers • Causes of glaciation – Proposed possible causes • Plate tectonics – Continents were arranged differently – Changes in oceanic circulation (Thermohaline Current)

Glaciers • Causes of glaciation – Proposed possible causes • Variations in Earth's orbit – The Milankovitch hypothesis » Shape (eccentricity) of Earth’s orbit varies » Angle of Earth’s axis (obliquity) changes » Earth’s axis wobbles (precession)

Desert • Definition : – A region so arid that it contains no permanent streams except for those that bring water in from elsewhere, and has very sparse vegetation cover. – NOT related to temperature! – Deserts can be • Hot (>35 °C) • Cold (< 20 °C)

Desert • Location – Dry regions cover 30% of Earth’s land surface

Desert • Types of deserts – Two climatic types are commonly recognized • Desert or arid • Steppe or semiarid

Deserts • Types of deserts – Classified by environment in which they are formed • subtropical: in the hot dry latitudes between 20 and 30°, both north and south • rain shadow: on the landward side of coastal mountain ranges • coastal: along coasts bordering cold ocean currents • continental interior: deep within continents, far from major water sources • polar: in the cold dry polar regions, both north and south

Location of Deserts

Earth’s dry regions coincide with the subtropical high pressure belts & solar heating

Deserts • Weathering and Erosion – Not as effective as in humid regions – Mechanical weathering forms unaltered rock and mineral fragments – Some chemical weathering does occur • Clay forms • Thin soil forms

Deserts • Weathering and Erosion – Water Erosion • Desert rainfall – Rain often occurs as heavy showers – Causes flash floods • Poorly integrated drainage • Most erosional work in a desert is done by running water

Deserts • Weathering and Erosion – Water Erosion • Streams are dry most of the time • Desert streams are said to be ephemeral – Flow only during periods of rainfall – Different names are used for desert streams including wash, arroyo, wadi, donga, and nullah

A dry stream channel in the desert

The same stream channel following heavy rainfall

Deserts • Weathering & Erosion – Wind erosion • Differs from that of running water in two ways – Wind is less capable of picking up and transporting coarse materials – Wind is not confined to channels and can spread sediment over large areas

Deserts • Weathering & Erosion – Wind erosion • Mechanisms of transport – Bedload » Saltation – skipping and bouncing along the surface – Suspended load » In the air as duststorms

Deserts • Weathering & Erosion – Wind erosion • Mechanisms of wind erosion – Deflation » Lifting of loose material » Produces Blowouts & Desert pavement

Deserts • Weathering & Erosion – Wind erosion • Mechanisms of wind erosion – Abrasion » Produces ventifacts (stones with flat faces) and yardangs (wind sculpted ridges) » Limited in vertical extent

Deserts • Depositional Environments – Water Deposits • • Talus Aprons Alluvial Fans Bajada Playas and Salt Lakes

Deserts • Depositional Environments – Wind deposits • Dunes – Mounds or ridges of sand – Often asymmetrically shaped – Characteristic features » Slip face » Cross beds

Types of Sand Dunes

Deserts • Depositional Environments – Wind deposits • Loess – Deposits of windblown silt – Extensive blanket deposits – Primary sources are deserts and glacial stratified drift

Deserts • Basin and Range: the evolution of a desert landscape – Uplifted crustal blocks – Interior drainage into basins produces • Alluvial fans and bajadas • Playas and playa lakes

Deserts • Basin and Range: the evolution of a desert landscape – Erosion of mountain mass causes local relief to continually diminish – Eventually mountains are reduced to a few large bedrock knobs called inselbergs projecting above a sediment filled basin

Landscape evolution in a mountainous desert – early stage

Landscape evolution in a mountainous desert – middle stage

Landscape evolution in a mountainous desert – late stage

Inselbergs in Southern California

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