Geology and Climate Glaciers, Deserts, and Global Climate Trends

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Geology and ClimateGlaciers, Deserts, and
Global Climate Trends

• Chapter 9

• 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
• Global climate changes can occur significantly
  over a long term

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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
• 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 and 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

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Figure 9.2
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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 called firn
• Gravity will pull the thickened mass of ice down
  any slope
• Types of Glaciers based 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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Figure 9.3
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Figure 9.4
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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 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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Figure 9.5
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Figure 9.6
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Figure 9.7
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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 and outwash, is deposited
  at the terminus of a glacier

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Figure 9.8
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Figure 9.9
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Figures 9.10 a, b, and c
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Figures 9.12 a and b
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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
• 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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Figure 9.13
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Figures 9.14 a and b
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Figures 9.15 a and b
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Figure 9.16
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Figures 9.17 a and b
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Figures 9.18 a and b
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Figure 9.19
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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 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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Figure 9.20
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Figure 9.21
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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
• Air mass is cool and dry at maintain tops, it
  warms as it descends on leeward side of mountain
• Causes of Desertification
• Rapid development of desert-like conditions
  caused by human activity
• Major and repeated disturbance to vegetation
  without complete recovery
• Overuse of regional surface and ground water
  resources

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Figure 9.22
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Figure 9.23
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Figure 9.24
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Global ClimatePast and Present

• Evidence of Climates Past
• Study geologic (rock and sediment )record
• Recent changes in soil and vegetation
  distribution
• Oxygen isotopes (18O/16O) in shell material
• Ice Ages and their Possible Causes
• Changes in solar out put of energy
• Disruption to global wind or ocean circulation
  patterns
• Atmospheric phenomena blocking incoming solar
  radiation
• Volcanic eruptions of ash
• Increase in cloud cover
• Change in chemical composition of atmosphere

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Figures 9.25 a and b
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Figure 9.26
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Figure 9.27
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Figures 9.28 a, b, and c
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Figure 9.29
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Figure 9.30
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ClimatePresent and Future

• The Greenhouse Effect involves sun light (energy)
  entering the atmosphere and a component of the
  atmosphere (CO2) trapping radiant heat (infrared
  energy)
• The result is warming of the atmosphere and
  Global Warming
• Increases, or decreases, in the concentration of
  CO2 in the atmosphere will show a respective
  increase, or decrease, in global warming

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Figure 9.31
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Figure 9.32
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Figure 9.33
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Figure 9.36
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ClimatePresent and Future

• Several centuries ago human activity did not
  adversely affect the CO2 balance of the
  atmosphere
• The industrial revolution has placed about 30
  additional CO2 into the atmosphere
• Global warming has occurred
• This trend must be changed or we will suffer
  consequences
• Rise in sea level about 20 of current land
  area would be submerged
• Progressive expansion of marginal agricultural
  lands
• Increase in severity of storm distribution and
  activity

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Figure 9.37
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ClimatePresent and Future

• Other greenhouse gases include methane (CH4),
  nitrous oxide (NO2), CFCs, and plus others
• These gases are becoming more concentrated in our
  atmosphere also
• Global cooling apparently can be promoted by an
  increase of SO4 from volcanic eruptions (plus
  abundant ash and clouds)
• To achieve a balance in global warming and
  cooling a reduction to the input of greenhouse
  gases and increase in the concentration of
  volcanic SO4 would be necessary
• How can this be done? Should it be done?

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Figure 9.38
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Winds and CurrentsClimate and Commerce El Niño

• The interplay between atmosphere and oceans is
  complex
• Oceans are sinks for CO2
• Generally, only the upper most part (within
  100-200 meters of the surface) of the oceans
  interact with the atmosphere
• Directional shifts in wind direction will disrupt
  ocean circulation patterns
• Shifts in ocean circulation patterns will cause
  normal upwelling cold, deep, nutrient rich water
  to cease
• Shifts in the distribution of flora and fauna
  will occur
• Fishing industries must shift their operations
• El Niño (Southern Oscillation) is such a cyclic
  warm event occurring every four to seven years
  when warm waters from the western South Pacific
  extend eastward to South America
• La Niña (a cold event) is the opposite and cycles
  periodically also
• The Pacific Decadal Oscillation (PDO) is a cycle
  of fluctuation surface temperature patterns that
  occur over a 20-30 year period

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Figure 9.39
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Figures 9.40 a and b