Transcript Unit 2x

Chapter 14
William P. Cunningham
University of Minnesota
Mary Ann Cunningham
Vassar College
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1
Geology and Earth Resources
2
Earth’s Cross Section
3
Tectonic Processes
•
Upper layer of mantle contains convection currents
that break overlying crust into a mosaic of tectonic
plates.
 Slide slowly across earth’s surface
- Ocean basins form where continents crack
and pull apart.
- Magma (molten rock) forced up through the
cracks forms new oceanic crust that piles up
underwater in mid-ocean ridges.
4
Tectonic Plates
5
Tectonic Plate Movement
6
Pangaea
7
Rocks and Minerals
•
A mineral is a naturally occurring, inorganic, solid
element or compound with a definite chemical
composition and regular internal crystal structure.
•
A rock is a solid, cohesive, aggregate of one or
more minerals.
 Each rock has a characteristic mixture of
minerals, grain sizes, and ways in which the
grains are held together.
8
Rock Types
•
Rock Cycle - cycle of creation, destruction, and
metamorphosis
 Three major rock classifications:
- Igneous
- Sedimentary
- Metamorphic
9
Rock Cycle
10
Cool Quick
Cool Slow
11
Rock Types and Examples
Igneous  Solidified from magma extruded onto the
surface from volcanic vents eg: Basalt (quick cool)
Granite (slow cool)
Metamorphic  Change existing rock, heat, pressure
Marble (from limestone)
Quartzite (from sandstone)
Slate (from mudstone and shale)
Sedimentary  Formed from deposits due to
Weatherization and Sedimentation
eg: shale, halite
12
Weathering and Sedimentation
•
•
•
Mechanical weathering – physical, no change
chemical composition
Chemical weathering - removal or alteration of
specific components, weakens and disintegration
 Oxidation
 Hydrolysis
Sedimentation - deposition of particles of rock
transported by wind, water, ice and gravity until
they come to rest in a new location
13
Coal
•
•
•
•
What types of coal are there? What type of
rock is it?
Lignite, Bituminous, Anthracite
Which type has the most energy?
Which is
Anthracite
has the
least
sulfur
content?
(pollution)
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Sedimentary Rock
•
The sedimentary rock
of Bryce Canyon
National Park has
been carved by
erosion into tall spires.
18
Geomorphology
•
•
study of the processes that shape the earth’s
surface and the structures they create.
Humans shape the Earth’s surface more
than any other single geomorphic process
except plate tectonics.
19
Geologic Hazards
•
•
•
Asteroid impact wiped out dinosaurs.
Floods take the greatest number of lives, while
wind causes the most property damage.
Earthquakes - sudden movements of the Earth’s
crust that occur along faults where one rock mass
slides past another
 Gradual movement - called creep or seismic slip
- When friction prevents creep, stress builds up
until eventually released with a sudden jerk.
- Point at which first movement occurs is called
the epicenter.
20
Earthquakes continued
•
•
•
•
Worst death tolls from earthquake occur when
construction is poor. Now buildings in earthquake
zones are reinforced.
Most seismically active region in U.S. is west coast,
but largest earthquake recorded was in New
Madrid, Missouri.
Earthquakes followed by aftershocks
Tsunami can be generated by earthquakes as we
saw in 2004. WHY live in areas that are
susceptible?
 U.S. has installed warning buoys in ocean.
21
Volcanoes
•
Volcanoes and undersea magma vents are the
sources of most of the Earth’s crust.
 Many of world’s fertile soils are weathered
volcanic material.
 500 million people live in danger zones. WHY?
 Nuees ardentes - deadly clouds of hot gas and
ash like those that destroyed Pompeii.
Temperatures exceed 1000 degrees C. and they
move at 60 mph. Kill in minutes.
 Mudslides often accompany eruptions.
 Volcanic dust and sulfur emissions reduce
sunlight and temperature around the globe.
22
Excerpt from “Life Without Oil” by Steve Hallet
and John Wright
23
Eruption of the Mayon Volcano in Philipines
24
Mt. Saint Helens, WA
25
Landslides
•
•
Landslides are examples of mass wasting, in which
geologic materials are moved downslope from one
place to another.
 Can be slow and subtle or swift as in rockslides
and avalanches
HUMAN IMPACT
Road construction, forest clearing, cultivation, and
building on steep, unstable slopes increase the
frequency and damage done by landslides. WHY?
26
Landslide in Pacific Palisades, California
27
Chapter 15
William P. Cunningham
University of Minnesota
Mary Ann Cunningham
Vassar College
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
28
Air, Weather, and Climate
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The Atmosphere is a Complex System
•
•
•
Weather – short-lived, local patterns temperature
and precipitation.
Climate – long term patterns of temperature and
precipitation.
The atmosphere is composed of:
 Nitrogen gas
 Oxygen gas
 Water vapor
 Aerosols-minute, suspended particles & droplets
31
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39
Energy Balance
40
Absorbed vs. Reflected Solar Energy
•
Surfaces that reflect energy have a high albedo
(reflectivity).
 Fresh clean snow
80-85%
•
Surfaces that absorb energy have low albedo.
 Dark soil
3%
•
Overall net average albedo of earth = 30%
•
Absorbed energy evaporates water and runs
photosynthesis. Absorbed energy released as heat.
41
Energy and the Greenhouse Effect
•
Most solar energy reaching the Earth is near
infrared (short wavelength).
 Energy reemitted by the earth is mainly far
infrared radiation (long wavelength, heat)
- Longer wavelengths are absorbed in the
lower atmosphere, trapping heat close to the
earth’s surface.
 Greenhouse Effect
 The atmosphere transmits sunlight while
trapping heat.
42
Convection Currents
43
Weather
44
45
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47
Climate
49
The Coriolis Effect Makes Winds Curve
•
As air warms at the equator, rises, and moves
northward, it sinks and rises in several intermediate
bands, forming circulation cells.
 Surface flows do not move straight north and
south, but are deflected due to Coriolis effect.
 Winds and currents appear to move clockwise in
Northern Hemisphere and counterclockwise in
the Southern Hemisphere.
 These curving pattern results from the fact that
the earth rotates in an eastward direction as
winds move above it.
51
Circulation Patterns
52
Circulation Patterns
55
Jet Streams
•
Jet streams - hurricane
force winds at the top
of the trophosphere
which follow an
undulating path
57
Ocean Currents Modify Weather
•
Warm and cold ocean currents strongly influence
climate conditions on land.
 As surface water moves, deep water wells up to
replace it.
- Ocean circulation also driven by differences in
water density due to temperature and
saltiness of water
 Gyres - huge cycling currents carrying
water north and south
 Currents can shift abruptly.
58
Global Ocean Conveyor System
59
Billions of People Rely on Seasonal Rains
•
Monsoon - seasonal reversal of wind patterns
caused by differential heating and cooling rates of
oceans and continents
 Most prevalent in subtropical and tropical areas.
 Tilt of Earth’s axis changes location where the
Sun is most intense over the course of the year.
Places where the Sun shines most directly have
evaporation and convection currents which bring
thunderstorms.
 Seasonal rains support tropical forests and fill
great rivers such as Ganges and Amazon.
60
Summer Monsoons in India
61
Cyclonic Storms
•
When rising air is laden with water vapor, latent
energy released by condensation intensifies
convection currents and draws up more warm air
and water vapor.
- Hurricanes (Atlantic)
 Katrina in 2005 caused greatest natural
disaster in North American history.
- Typhoons (Western Pacific)
- Cyclones (Indian Ocean)
62
Cyclonic Storms
•
Tornadoes - swirling funnel clouds
 Generated by “supercell” frontal systems
where strong dry cold fronts collide with warm
humid air
- Greater air temperature differences in the
spring, thus more tornadoes
63
Cyclonic Storms
64
Hurricane Matthew Oct. 2016
65
Hurricane Matthew Oct. 2016
66
Natural Climate Variability
•
•
Climates shift on scales of decades, centuries or
millenia.
Ice cores - collected from glaciers, have
revolutionized our understanding of climate history.
 Cores reveal patterns of dark and light bands
caused by annual accumulations of snow.
 Gas bubbles can be analyzed for atmospheric
composition.
 Ash and sulfur deposits correlate with volcanic
eruptions.
 Vostok ice core gives us a record back 420,000
years.
67
Multi-Decade Ocean/Atmosphere Cycles
•
•
The ocean and the atmosphere have regular
patterns of flow or currents, but these may shift
from time to time.
Winds and rains may change as a consequence of
these shifts.
 Pacific Decadal Oscillation - very large pool of
warm water moving back and forth across the
North Pacific every 30 years.
- This affects salmon harvests in Alaska and the
Pacific Northwest.
68
El Nino Southern Oscillation (ENSO)




Most years, the pool is held in western Pacific by
steady equatorial trade winds.
Surface waters driven westward by trade winds
allow upwelling of cold, nutrient rich waters off
west coast of South America benefiting fisheries.
During intervening La Niña years, hot, dry
weather is often present. Resulting high sea
surface temperatures cause hurricanes to be
more violent.
Long term studies of coral reefs indicate that
ENSO events are becoming stronger and more
irregular due to global warming.
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Multi-Decade Ocean/Atmosphere Cycles

North Atlantic Oscillation, or NAO is another
oscillation which occurs between Canada and
Europe.
- Evidence for this phenomenon can be seen in
tree-ring growth records.
71
Historical Climate Changes
•
•
•
A historical climate change that had
disastrous effects on human populations was
the Little Ice Age that began in the 1400’s.
Temperatures dropped, crops failed, fish
migrations changed and shipping lanes were
blocked with ice.
Ice cores show drastic changes may have occurred
over short periods of time (years or decades rather
than centuries).
72
Earth’s Movements Explain Some Cycles

Milankovitch
Cycles - periodic
shifts in Earth’s
orbit and tilt which
change distribution
and intensity of
sunlight.
73
Global Climate
Change
74
Greenhouse Effect


Greenhouse Gases -Gases in the atmosphere,
especially carbon dioxide, water vapor, nitrous
oxides, methane and other substances that
retain heat.
Positive feedback loop - poles covered with ice
reflect solar radiation back into space. Now that
ice is melting, open water is absorbing more
heat, which in turn is melting more ice, leading to
more warming.
75
Major Climatic Changes
•
The data show that:
 There is a close correlation between carbon
dioxide concentration and temperature of the
atmosphere
 Gradual climate changes give species time to
adapt.
 Abrupt climatic changes have catastrophic
effects on living things as organisms are unable
to adjust before conditions exceed their
tolerance limits.
 These changes can cause species extinctions.
76
Vostok Ice Core Data
77
Recent Changes are Unusually Rapid
•
•
•
•
•
Many scientists believe that anthropogenic
climate change is the most important
environmental issue of our time.
The earliest data on came from an observatory
on Mauna Loa volcano in 1957.
Initial measurements showed carbon dioxide
levels increasing at 0.5% per year since data
collection began.
Levels have risen from 315 ppm in 1958 to 387
ppm in 2009.
If this trend continues, we could double
atmospheric CO2 levels by 2109.
78
CO2 Measurements from Mauna Loa
79
The IPCC Provides Data to Policy Makers
•
•
•
Intergovernmental Panel on Climate Change or
IPCC -an international group of scientists and
governmental representatives formed to review the
scientific evidence for climate change.
The 2007 report stated that there is a 90%
probability that the observed climate changes are
the result of human activities.
The report projects warming of 1-6 °C by 2100 with
the best estimate being 2 to 4°C (3.2 to 7.8°F)
 For perspective, there has only been a 5°C rise
since the last ice age 20,000 years ago.
80
Affects of Global Warming
•
•
•
•
People will experience more extreme weather
including droughts, floods, heat waves and
hurricanes.
These could have disastrous economic and human
costs.
Estimates published in 2009 project a sea level rise
of 1 meter by 2100.
This could flood low-lying coastal cities like New
Orleans, Miami, Boston, New York and London and
Mumbai.
81
Projected Sea Level Rises by 2100
82
LOOK AT ARTICLE SEA LEVEL COULD RISE
6 Meters
83
Climate Models vs. Observed Climate Change
85
CO2 is the Most Important Green House Gas
•
•
•
•
Carbon Dioxide – emissions have increased 80%
from 1970 to 2004
 fossil-fuel burning is the major human caused
source of carbon dioxide (constitutes 77%).
Methane (CH4) – ruminants and rice paddies are
sources
- Absorbs more infrared than CO2 .
Nitrous Oxide – vehicle engines, agriculture
processes are major sources.
- Highly effective at capturing heat energy.
The relative effects of each green house gas can
be seen by converting them to CO2 Equivalents.
86
Warming Ability of Various Green House Gases
87
Contributors to Global Warming
88
Climate Change Effects: Why Should I Care?
•
•
•
Evidence of climate change is overwhelming:
“As best as can be determined, the world is
now warmer than it has been at any point in
the last two millennia, and, if current trends
continue, by the end of the century it will
likely be hotter than at any point in the last
two million years.”
American Geophysical Union
89
Observations of Climate Change
•
Ave. global temperature climbed 0.6°C (1°F) in last
century.
 19 of 20 warmest years in the past 150 yrs have
occurred since 1980.
 Poles are warming fastest (4°C, 7°F over past 50
years). Permafrost is melting in Alaska and
Canada and houses, pipelines and trees are
being toppled.
Obama Article and $100 billion dollar Article
90
Observations of Climate Change
•
•
•
•
•
Arctic Sea ice is half as thick as it was 30 years
ago, and the ocean area covered by ice has
decreased by 1 million sq. km. in 30 yr.
 Polar bears are dying as they hunt on pack ice,
which is declining.
Antarctic ice shelves are disappearing.
 Penguins declined 50% in last 50 yrs.
Alpine glaciers are retreating all over the world.
The oceans are absorbing and storing more heat.
Sea level has risen 15 to 20 cm in last century.
91
Observations of Climate Change
•
•
•
•
•
Oceans are absorbing some of the extra CO2 but
that is acidifying the ocean and damaging corals.
Growing seasons are lengthening in Northern
hemisphere. Some animals are breeding earlier or
extending their range. Others are disappearing.
Droughts are more frequent and widespread and
storms more severe.
Animals breeding and migratory schedules are
changing.
Some species are declining or going extinct due to
warming temperatures and loss of habitat.
92
Observations of Climate Change
•
•
Corals are bleaching due to warming water
temperatures in the oceans.
Storms are becoming stronger and more
damaging.
 ie. Increased number of category 5
hurricanes in recent years.
93
Global Warming will be Expensive
•
•
•
At present, reducing greenhouse gas emissions
would cost 1% of world GDP according to Stern
report. (IPCC report says less than that.)
If we delay, it could cost as much as 20% of world
GDP.
Energy production will need to be 80%
decarbonized by 2050 to stabilize climate.
 Those in richer countries will be able to blunt the
effects of climate change.
 Those in poorer countries will suffer the most; at
least 200 million people in will become refugees
of floods or victims of drought.
94
4 Steps For Combating Climate Change
•
•
•
•
Implement emissions trading
Technology sharing with less developed countries
Reducing deforestation
Helping poorer countries adapt to climate change
95
Flooding, Storms and Disease
•
•
•
Melting of the glacial ice caps in Greenland and
Antarctica could raise global seal levels 100
meters flooding coastal areas where 1/3 of the
world’s population live.
Insurance companies have $2 trillion in insured
properties along U.S. coastlines at risk from
flooding or severe storms.
Infectious diseases will increase as insects that
spread them are able to move to places where
they could not live before.
96
Envisioning Solutions
•
Kyoto Protocol (1997)
 Called on nations to roll back carbon dioxide,
methane, and nitrous oxide emissions about 5%
below 1990 levels by 2012.
- Sets different limits for different countries,
depending on prior output
 China and India were both exempt from this
agreement.
 126 countries ratified the Protocol.
 The legislatures of both Australia and the
U.S. declined to ratify the agreement.
97
2 Main Options for Controlling Emissions
•
Cap and Trade Controls: legal limits on emissions
are set and countries that want to emit more must
purchase emissions credits from others.
 This approach is favored under Kyoto.
•
Voluntary Limits: governments, communities and
individuals voluntarily cut emissions for altruistic,
economic or conservation reasons.
 New local initiatives suggest this approach may
work.
98
Cap and Trade
•
•
•
•
A global market for trading carbon emissions
has already developed.
In 2006 700 million tons of carbon credits
were exchanged with a value of 3.5 billion
dollars.
This market may grow to 500 billion dollars a
year by 2050.
Some large businesses like BP America,
Dupont and GE are for this approach if the
rules are clear and fairly applied.
99
Stabilization Wedges Could Work Now
•
•
•
•
•
By utilizing Wedge Analysis, the problem of climate
stabilization can be broken down into smaller, bitesized peices.
To stabilize carbon emissions we would need to cut
7 GT (gigatons) over the next 50 years.
Doubling vehicle efficiency, and halving the miles
we drive would save up to 1.5 GT.
Installing energy efficient appliances, lighting and
insulating building could save another 2 GT.
Capturing and storing carbon emissions from
power plants and gas wells could save another GT.
100
Carbon Capture and Storage
103
Should We Focus on Methane Instead?
•
•
•
•
Methane is a more powerful absorber of heat
energy than carbon dioxide.
James Hansen of NASA believes that focusing on
reducing methane emissions might be the best
short-term strategy to slow global warming.
Reducing methane emissions from landfills, rice
paddies, oil wells and coal mines could reduce
warming.
Reducing the number of ruminants could help also.
104
Regional Initiatives Are Emerging
•
•
•
•
The U.K., New Zealand, Germany and many
other countries are working to reduce carbon
emissions voluntarily.
The United Kingdom has rolled back its CO2
emissions to 1990 levels and is aiming for a
60% reduction by 2050.
New Zealand has pledged to be the first
Carbon Neutral country-reducing green
house gas emissions to zero.
Germany has reduced CO2 by 10%.
105
Conservation and Renewable Energy
Offer the Best Solutions
•
•
•
•
Denmark gets 20% of its electricity from windmills,
and plans to increase that to 50%.
China reduced its emissions 20% between 1997
and 2005 by implementing more efficient burning
of coal in power plants and industry.
Individual cities like Copenhagen, Helsinki and
Toronto have pledged to reduce carbon emissions
by 20% by 2010.
Benefits: Conservation efforts save energy costs
and shifting to renewable energy frees us from
dependence on foreign oil.
106
Chapter 17
William P. Cunningham
University of Minnesota
Mary Ann Cunningham
Vassar College
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
107
Hydrologic Cycle
111
Average Annual Precipitation
112
Water Supplies are Unevenly Distributed
•
Three principal factors control global water deficits
and surpluses:
 Global atmospheric circulation
 Proximity to water sources
 Topography
 Rain Shadow
113
Rain Shadow
114
Major Water Compartments
•
•
The length of time water typically spends in a
compartment is called the Residence Time.
For example, the Average residence time of water
in the ocean is about 3,000 years before the water
evaporates and enters the hydrologic cycle.
116
The Oceans are a Major Water Compartment
•
•
•
The oceans hold 97% of all liquid water on
the earth.
90% of the earth’s biomass is found in the
oceans.
The oceans play a major role in moderating
earth’s climate.
117
Global Ocean Conveyor System
118
Easily Available Fresh Water is Scarce
119
Ground Water Compartments

Ground water is the second largest reservoir of
fresh water
 Infiltration - process of water percolating
through the soil and into fractures and
permeable rocks
 Zone of aeration - upper soil layers that
hold both air and water
 Zone of saturation - lower soil layers where
all spaces are filled with water
 Water table - top of zone of saturation
121
Infiltration
122
Groundwater Stores Large Water Resources
•
Aquifers - porous layers of sand, gravel, or rock
lying below the water table
 Artesian - Pressurized aquifer intersects the
surface (water flows without pumping).
•
Recharge zones - area where water infiltrates into
an aquifer
 Recharge rate is often very slow.
- Presently, groundwater is being removed
faster than it can be replenished in many
areas.
123
Groundwater
124
River & Streams Are Water Compartments
•
Rivers and Streams
 Precipitation that does not evaporate or infiltrate
into the ground runs off the surface, back toward
the sea.
- Best measure of water volume carried by a
river is discharge
 The amount of water that passes a fixed
point in a given amount of time
 Usually expressed as cubic feet per
second
125
Major Rivers of the World
126
Lakes and Ponds are Water Compartments
•
Lakes and Ponds
 Ponds are generally considered small bodies of
water shallow enough for rooted plants to grow
over most of the bottom.
 Lakes are inland depressions that hold standing
fresh water year-round.
- Both ponds and lakes will eventually fill with
sediment, or be emptied by an outlet stream.
127
Wetlands are Water Compartments
•
Wetlands
 Play a vital role in hydrologic cycle
- Lush plant growth stabilizes soil and retards
surface runoff, allowing more aquifer
infiltration.
 Disturbance reduces natural waterabsorbing capacity, resulting in floods
and erosion in wet periods, and less water
flow the rest of the year.
 Half of U.S. wetlands are gone.
128
The Atmosphere: A Small Water Compartment
•
The Atmosphere
 Among the smallest water reservoirs
- Contains < 0.001% of total water supply
- Has most rapid turnover rate
- Provides mechanism for distributing fresh
water over landmasses and replenishing
terrestrial reservoirs
129
Water Availability and Use
•
Renewable Water Supplies
 Made up of surface runoff plus infiltration into
accessible freshwater aquifers
- About two-thirds of water carried in rivers and
streams annually occurs in seasonal floods
too large or violent to be stored effectively for
human use.
 Readily accessible, renewable supplies are
only about 400,000 gal /person/year.
130
Water Consumption Is Less Than Withdrawal
•
•
Withdrawal - total amount of water taken from a
source
Consumption - fraction of withdrawn water made
unavailable for other purposes (not returned to its
source)
 Degradation - Change in water quality due to
contamination making it unsuitable for desired
use. Much water that is not consumed is
nevertheless polluted.
133
Water Withdrawal and Consumption
135
Agricultural Is the Greatest Water Consumer
•
Worldwide, agriculture claims about two-thirds of
total water withdrawal and 85% of consumption.
 Aral Sea, is a tragic example of this.
 The Aral Sea was once the fourth largest inland
body of water in world, but it has now lost 80% of
its volume since 1975 as the water was diverted
for irrigation of rice and cotton crops.
 Lake Chad is another example. Located in
northern Africa, this lake went from 400,000 sq.
km to less than 1,000 sq. km.
 Show Google Maps of Midwest
137
Aral Sea
138
Figure 17_14a
140
Figure 17_14b
141
Figure 17_14c
142
Domestic and Industrial Water Use
•
•
Worldwide, domestic water use accounts for about
one-fifth of water withdrawals.
 Only about 10% of consumption
- But where sewage treatment is unavailable,
water is degraded
Industry accounts for 20% of global freshwater
withdrawals.
 Range from 5% to 70% in various locations
- Small proportion is consumed, but
degradation is a problem
143
Typical Household Water Use in U.S.
144
Freshwater Shortages
•
•
•
U.N. estimates a billion people lack access to safe
drinking water.
 2.6 billion lack acceptable sanitation.
At least 50 countries, mostly in Africa and the
Middle East, are considered to have serious water
stress.
In many countries it is not access to water that is a
problem, it is access to clean water that is the
problem.
145
Many People Lack Access to Clean Water
•
•
•
More the 2/3 of the world’s population lack indoor
plumbing and must fetch water from outside the
home.
Where water is available in the home, it may be
expensive. In Lima Peru, a typical poor family uses
1/6 as much water as a typical middle class family
in the US and pays 3 times as much for the water
and they must boil the water before it is safe to
drink.
By 2025, the U.N. estimates that 2/3 of the word’s
population will be living in water stressed countries.
146
Groundwater is Being Depleted
•
•
Groundwater is the source of nearly 40% of fresh
water in the U.S.
50% of Americans (95% in rural areas)depend on
groundwater for drinking and domestic uses.
 Heavy pumping can deplete entire aquifers.
 Ogallala Aquifer underlies 8 states between
Texas and North Dakota.
 Heavy pumping has dried up wells and
whole towns are being abandoned
 It will take thousands of years to refill.
147
The Ogallala
Aquifer
148
Depleting Groundwater
•
Withdrawing large amounts of groundwater in a
small area causes porous formations to collapse,
resulting in subsidence (settling).
 Sinkholes form when an underground channel or
cavern collapses. Results in permanent loss of
aquifer.
 Saltwater intrusion can occur along coastlines
where overuse of freshwater reservoirs draws
the water table low enough to allow saltwater to
intrude.
149
Saltwater Intrusion
150
Dams and Diversions
•
Before 1900 there were 250 high dams in the
world; today there are more than 45,000.
•
In the U.S. dams are built by Army Corps of
Engineers and Bureau of Reclamation
 Provide cheap hydroelectric power
 Jobs
 Reduce flooding
 Allow farming on lands that would otherwise be
too dry
155
Dams and Diversions
•
On the downside, dams
 Drown free flowing rivers
 Submerge farmlands and towns
 Block fish migration e.g. salmon
 Change aquatic habitats for native species
 Can sometimes fail, causing catastrophe
- Johnstown flood (city just east of Pittsburgh,
PA) killed 2,200 people when dam broke.
- Dam failure in China killed 230,000.
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Figure 17_11
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Would You Fight for Water?
•
•
Nearly 40% of the world’s population live in river or
lake basins that are shared by 2 or more countries.
There have already been water skirmishes:
 Israel and its neighbors over the Jordan River.
 Turkey and Iraq over the Tigris and the
Euphrates Rivers.
 Nomadic tribes in Kenya have fought over
dwindling water resources.
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Trans-boundary River Basins
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Increasing Water Supplies
•
•
Seeding Clouds
 Condensation nuclei
Desalination - removing salt from ocean water or
brackish water to get fresh water
 Most common methods are distillation and
reverse osmosis.
- Three to four times more expensive than most
other sources
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Domestic Conservation
•
Estimates suggest we could save as much as half
of domestic water usage without change in lifestyle
 Largest domestic use is toilet flushing
- Can use low volume toilets or waterless
composting
- Anaerobic digesters use bacteria to produce
methane gas from waste
 Significant amounts of water can be reclaimed
and recycled.
 Purified sewage effluent
 San Diego pumps water from sewage
plant directly into drinking reservoir
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