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Geology and Climate Glaciers, Deserts, and Global Climate Trends

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Title: Geology and Climate Glaciers, Deserts, and Global Climate Trends Author: ouimette Last modified by: eprice Created Date: 8/5/2004 10:51:10 PM – PowerPoint PPT presentation

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Title: Geology and Climate Glaciers, Deserts, and Global Climate Trends


1
  • Chapter 9

Ice and Glaciers, Wind and Deserts
  • Solar heat drives evaporation, makes
    precipitation, and generates glaciers.
    Differential solar heating of land, water, and
    thus air makes the winds
  • Glaciers shape our landscape and stand for a
    large reserve of fresh water
  • Wind is not a serious hazard except the winds
    during severe storms. Winds also shape the
    earths surface, but not so efficient

2
Glaciers and Glacial Features
  • Glaciers a 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

3
Glacier Formation Heat from the sun is generally
constant Climate factors may influence the global
temperature budget Global cooling ice will
accumulate and build ice sheets glaciers Global
warming ice sheet retreat and glaciers get
smaller Factors that change climate include
composition of the atmosphere, pollution or
particles suspended in the atmosphere, abnormal
heat retention (or loss) from the oceans
There must be sufficient moisture in the air,
and thus the necessary precipitation 1.The
amount of winter snowfall must exceed summer
melting 2. Snow accumulates during cold
periods 3. Snow transforms to ice 4. Overlying
ice will pack the ice tighter and thicker 5.
Packing causes the ice to re-crystallize into a
denser ice called firn 6. Gravity will pull the
thickened mass of ice down any slope
4
  • Types of Glaciers based on size and occurrence
  • 1. Alpine Glaciers (also known as mountain or
    valley glaciers) occur at high altitude (cooler
    temperatures)
  • 2. Continental Glaciers (also known as ice caps
    or ice sheets) occur near the poles (over land)
    they are larger and rarer

5
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
  • Faster Movement higher in the glacier
  • Glacier movement has a terminus
  • Glacier that encounter water will experience
    calving
  • Temperatures at the terminus are warm and
    evaporation, or melting, removes ice - ablation
    occurs
  • At one place on the glacier an equilibrium line
    is established
  • Above it snow accumulates
  • Below it ice ablation occurs
  • Overall glacial movement is slow and steady
  • (a few tens of meters per year)
  • surges are possible (several tens of meters per
    day)

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Glacial Erosion and Deposition
  • Glacier Erosion very effective process
  • Large mass and solidity of a glacier will shape
    the surface of the earth
  • Sediments are picked up and carried off
  • abrasions and striations are left behind
  • Carves its own valley. U shaped valleys mark
    locations where alpine glaciers once stood
  • Glacier Deposition abundant material is
    transported on or along the sides of glaciers a
    variety of moraines will form
  • Drift formed by till
  • Outwash is deposited at 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 having glaciers
  • Overall volume of glacial ice can be manipulated
  • Cloud seeding activities in glacial areas may
    cause accumulation of increased amounts of ice
  • Dusting glaciers with black coal 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 sediment
    erosion and transport but regionally it is very
    important
  • Wind erosion consists of abrasion, forming
    ventifacts,
  • or deflation, forming desert pavement
  • Vegetation is critical to reducing the effects of
    wind erosion
  • Wind Deposition principal feature of wind
    deposition
  • is the sand dune
  • Dune Migration will occur if wind blows from
    predominately a single direction

15
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 as loess
  • Loess can originate in either desert or glacial
    areas
  • 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 in foundations or structures
  • Structures may also settle unevenly or collapse

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Deserts and Desertification
  • Deserts regions with limited precipitation,
    people, and vegetation. (The features of wind
    processes are observed)
  • Causes of Natural Deserts
  • Found about 30o Latitude (north or south)
  • dry descending and warm air masses
  • Warm and dry air can hold abundant water
    evaporation rates are high
  • Topography and prevailing wind patterns establish
    rain shadow
  • moisture extracted on windward slopes of
    mountain ranges
  • Process Air mass is cool and dry at maintain
    tops,
  • it warms as it descends on leeward side of
    mountain
  • Causes of Desertification
  • 1. Rapid development of desert-like conditions
    caused by human activity
  • 2. Major and repeated disturbance to vegetation
    without complete recovery
  • 3. Overuse of regional surface and ground water
    resources

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