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 Image from http://pubs.usgs.gov/fs/fs133-99/

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 http://nsidc.org/glaciers/questions/formed.html

Glaciers Formation (continued) Firn Generally 16x 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 http://nsidc.org/glaciers/questions/formed.html

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/components.html

Glaciers Types Glaciers Ice Mountain Glaciers, Ice Sheets, Valley Glaciers, Piedmont Glaciers, Cirque Glaciers, Hanging Glaciers, Tidewater Glaciers. Ice Ice Sheets, Ice Shelves, Ice Caps, Ice Streams, and Ice fields http://nsidc.org/glaciers/questions/types.html

Types of Glaciers

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

Glaciers Landforms created by glacial erosion Glacial Valleys Fjords Pater noster lakes Cirques Tarns Arêtes Horns

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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