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31 The Changing Face of the Earth

Flooding of Mississippi & Illinois Rivers 1993

Before After

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According to plate tectonic theory, which of these should have the most violent earthquakes, on average?1. The midocean ridges2. Subduction zones near

continental margins3. Suture zones at collisions

of two continental plates4. Hot spots

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What is a Natural System?Group of natural, interdependent parts or componentsInteractions between parts forms the systemForces drive the systemAll systems tend toward a state of maximum disorder (entropy) called equilibriumEarth’s two major systems are:

Tectonic System Hydrologic System

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Hydrologic SystemSystem of moving water

RiversOceans, LakesGlaciersGroundwaterWater Vapor in Atmosphere

Effects of Hydrologic System

ErosionTransportation of SedimentDeposition of SedimentCreation of Numerous Landforms

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Hydrologic System

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Where is most of the water in Earth’s hydrologic system?1. In the atmosphere2. Locked up as glacial

ice3. In freshwater streams

and lakes4. In the oceans

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What Forces Drive this System?Solar Radiation

Average ~342 W/m2 = ~342 joules/sec m2

Causes evaporation

GravityPulls water down slopesCausing erosion, transportation of sediment

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Subsystems of Hydrologic SystemRiver SystemsGlacial SystemsGroundwater SystemsOcean/Shoreline SystemsDesert Systems

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RiversPrimary mechanism for erosionMove sediment from mountains to oceansAlso carry dissolved ions (salts)Can be easily disturbed by human activity

DamsPollutionIrrigation

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GlaciersRivers (or oceans) of iceVery effective agents of erosionCarve different topography than riversMany glaciers are currently shrinking

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Pasterze Glacier, Austria

1875

2004

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Continental GlaciersIceland

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GroundwaterNOT in underground lakes or rivers; in ROCKSRocks can hold a lot of water!

PorosityPermeability

Groundwater is a major source of drinking and irrigation waterGroundwater is often affected by human activity

OverpumpingPollutionIrrigation

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Water Table

PS 100 -- Chapter 31 18A spring in the Grand Canyon

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Sinking San JoaquinRemoval of ground water for agricultureLand subsiding

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Oceans & Shorelines

Beautiful, but changeableShorelines are places of active…

ErosionTransportationDeposition

Human activity can have a significant effect on shorelines

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Hurricane Katrina, 2005

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9th WardBreach in the Industrial Canal a day after Katrina passed over New Orleans. This neighborhood was built over a cypress swamp. Waves from Lake Ponchartrain and Lake Borgne broke the manmade levees.

Vincent LaforetNew York TimesNational Geographic

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PS 100 -- Chapter 31 25Smiley Pool, Dallas Morning News

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DesertsDominated by wind (Eolian system)

Carries light-weight particles (sand & dust)Leaves the rest behind

Human effectsDesertification

OvergrazingPoor Farming Practices

Destruction of SoilIrrigation adds salts

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Global WarmingIs Earth getting warmer?What have been trends in the past?

How do we know?What causes the changes?Should we do anything?

Year, A.D.

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What is Earth’s Past Climate History?How do we know?

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Past Temperatures and Atmospheric CO2 Levels Correlate

Cause or effect?

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Natural Climate Cycles: Solar RadiationOrbital eccentricity: 100ky

Axial inclination: 41ky

Axial precession: 23ky

According to these cycles, we should be entering a new ice age PS 100 -- Chapter 31 32

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Clouds, Ash, Pollution

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Greenhouse GasesCertain gases trap heat in the atmosphere (transmit visible light to ground, absorb infrared that ground emits)

Water vapor (H2O)Carbon dioxide (CO2)Methane (CH4)

Venus has a “runaway”greenhouse due to CO2

Surface temperatures hot enough to melt lead!

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What is the evidence that Earth is warming up?

Not only are we not entering an ice age, but we are also definitely seeing higher average temperatures.

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Recent Sea Level Changes

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Can you figure it out?Melting the continental glaciers on Greenland and Antarctica will cause a rise in sea level. Why won’t the north polar ice sheet do the same?

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Geologic record indicates that past sea level changes when polar glaciers melt have been hundreds of meters. The cost would be catastrophic.

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ICE CORE DATA

Atmospheric Methane Levels

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Possible Human Effects on Climate

Declining CO2 trend reversed 8000 years agoCorrelates with clearing of European forests & beginning of ricecultivation

Declining CH4 trend reversed 5000 years agoCorrelates with flooding of lowlands and beginning of rice cultivation

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Should we do anything?

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Risk, Cost, & BenefitCost of reducing greenhouse emissions will certainly be billions of dollarsCertainty of global warming is not 100%

Current predictions depend on imperfect modelsEnvironmental and economic consequences could be truly catastrophic

Some say global warming could cause the end of technological civilization

As voters & consumers, these are your issues

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Which best describes your opinion on global warming?

A. This is just political hype. No action is needed.B. We should wait until the models are better

before we do anything.C. I’d like beachfront property in Utah. Do nothing

and party on!D. We should invest the $billions needed to find

ways to reduce greenhouse gas emissions.E. We are already in danger. We should

immediately stop driving cars!

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