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Chapter 9

Solar heatdrives

evaporation, makes

precipitation, and generates

glaciers. Differential solarheating of land, water, and

thus air makes the winds

Glaciersshape our

landscape and stand for a

large reserve of fresh water

Windis not a serious hazard

except the winds during

severe storms. Winds also

shape the earths surface, but

not so efficient

Ice and Glaciers, Wind and Deserts

Death Valley, California. Photo

from NASA/Jet Propulsion Lab

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Glaciers and Glacial Features

Glaciersa mass of ice that moves over the

land under its own weight and shape the land Excellent indicator for global climate conditions (warm

or cool). Not be developed in a single winter

Glacier Formation

Heat from the sun is generally constant

Climate factors may influence the global temperaturebudget

Global cooling ice will accumulate and build ice sheets

and glaciers Global warming ice sheet retreat and glaciers getsmaller

Factors that change climate include composition of theatmosphere, pollution or particles suspended in theatmosphere, abnormal heat retention (or loss) from the

oceans

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Glacier Formation

There must be sufficient moisture in the air, and

thus the necessary precipitation The amount of winter snowfall must exceed

summer melting

Snow accumulates during cold periods Snow transforms to ice

Overlying ice will pack the ice tighter and thicker

Packing causes the ice to recrystallize into a denser ice calledf i rn

Gravity will pull the thickened mass of ice down any slope

Types of Glaciersbased on size and occurrence Alpine Glaciers (also known as mountain or valley glaciers)

occur at high altitude (cooler temperatures)

Continental Glaciers(also known as ice caps or ice sheets)

occur near the poles (over land); they are larger and rarer

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Movement and Change of Glaciers

Glaciers flow as plastic ice masses and at

different rates; overall movement is down slope Movement is slow at the base of a glacier where

it is in contact with and scrapes the valley walls

Movement higher in the glacier is faster

Glacier movement has a terminus Glacier that encounter water will experience calving

Temperatures at the terminus are warm andevaporation, or melting, removes ice - ablationoccurs

At one place on the glacier an equilibrium lineis

established Above it snow accumulates

Below it ice ablation occurs

Overall glacial movement is slow and steady (a fewtens of meters per year); surges are possible (several

tens of meters per day)

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Glacial Erosion and Deposition

Glacier Erosionvery effective process

Large mass and solidity of a glacier will shapethe surface of the earth

Sediments are picked up and carried off -

abrasionsand striationsare left behind Carves its own valley. U shaped valleys marklocations where alpine glaciers once stood

Glacier Depositionabundant material is

transported on or along the sides ofglaciersa variety of moraines will form

Drift, formed by till and outwash, is depositedat the terminus of a glacier

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Glaciers as a water source

Important freshwater source Approximately 75 % of fresh water is stored as glacial

ice

Glacial meltwater may be the principal source of

summer streamflow in the regions havingglaciers

Overall volume of glacial ice can be manipulated

Cloud seeding activities in glacial areas may causeaccumulation of increased amounts of ice

Dusting glaciers with blackcoal may cause an

increase melt of glacial ice to occur

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Wind and its Geologic Impacts Wind is moving air, air moves in response to

variations in air pressure

Wind accounts for a minor amount of sedimenterosion and transport; but regionally it is veryimportant

Wind erosionconsists of abrasion, formingventifacts, or deflation, forming desert pavement Vegetation is critical to reducing the effects of wind erosion

Wind Depositionprincipal feature of winddeposition is the sand dune

Dune Migrationwill occur if wind blows frompredominately a single direction Particles of sand will move by rolling, or saltation, up the

shallower windward dune face

Once at the dune top they fall down the steeper slip face

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Wind and its Geologic Impacts

Wind generally does not move sand or

coarser particles very rapidly Fine dust, or silt, can be carried off long

distances by the wind and is deposited asloess

Loess can originate in either desert or glacialareas

Loess, once deposited forms a porous and

open structure; holds abundant water Loess does not make a good foundation material

hydrocompaction may cause cracks to form infoundations or structures

Structures may also settle unevenly or collapse

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Deserts and Desertification

Desertsregions with limited precipitation, people, and

vegetation. The features of wind processes are observed Causes of Natural Deserts

Found about 30oLatitude (north or south); dry descending and warm air masses

Warm and dry air can hold abundant water; evaporation rates arehigh

Topography and prevailing wind patterns establish rainshadow; moisture extracted on windward slopes of mountainranges

Air mass is cool and dry at maintain tops, it warms as it descendson leeward side of mountain

Causesof Desertification Rapid development of desert-like conditions caused by human

activity

Major and repeated disturbance to vegetation without completerecovery

Overuse of regional surface and ground water resources

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