Download continental drift theory Now called PLATE TECTONICS

Geology: Processes, Hazards &
Soils
Chapter 10
35 km (21 mi.) avg., 1,200ūC
Crust
100 km (60 mi.)
200 km (120 mi.)
Low-velocity zone
Crust
Mantle
Lithosphere
Solid
10 to 65km
2,900km
(1,800 mi.)
3,700ūC
Outer core
(liquid)
Core
Inner
core
(solid)
100 km
Asthenosphere
(depth unknown)
200 km
5,200 km (3,100 mi.), 4,300ūC
Fig. 10.2, p. 212
Slide 2
Zones of earth’s sturcture
• Core – solid
• Mantle – thick solid zone
– Aesthenosphere – under the rigid outermost part of the
mantle – hot, partly melted rock that flows like plastic
• Crust – outermost and thinnest zone
– Contains:
• CONTINENTAL CRUST - lies under continents and
continental shelf
• OCEANIC CRUST – under ocean basins and covers 71% of
earth’s surface
Oceanic crust
(lithosphere)
Abyssal Oceanic
floor
ridge
Abyssal
floor
Abyssal plain
Abyssal
hills
Trench
Folded mountain belt
Craton
Volcanoes
Continental
shelf
Continental
slope
Continental
rise
Abyssal plain
Continental crust
(lithosphere)
Mantle (lithosphere)
Mantle
(lithosphere)
Mantle (asthenosphere )
Fig. 10.3, p. 213
Slide 3
GEOLOGIC PROCESSES
• CONSTANT CHANGES
• INTERNAL PROCESSES – build up the
planet’s surface
– Energy provided from heat in the interior
– Causes the mantle to deform and flow
– Two kinds of movements:
• CONVECTION CURRENTS
• MANTLE PLUMES – mantle flows upward in a
column
Plate Tectonics
• Movement of rigid plates called
TECTONIC PLATES caused by convection
currents and mantle plumes
• Plates are 60 miles thick and are made up of
continental and oceanic crust – called the
LITHOSPHERE
• Plates are constantly moving on the
asthenosphere at different speeds
Plate tectonics
• Concept accepted in early 1960’s was called
continental drift theory
• Now called PLATE TECTONICS
– PRODUCES:
• VOLCANOES and EARTHQUAKES – found at plate
boundaries
• OCEANIC RIDGE SYSTEM
• TRENCHES
Help explain patterns of biological evolution
Pangea
Reykjanes
Ridge
EURASIAN PLATE
JUAN DE
FUCA PLATE
CHINA
SUBPLATE
Transform
fault
PHILIPINE
PLATE
PACIFIC
PLATE
MidIndian
Ocean
Ridge
Transform
fault
INDIAN-AUSTRLIAN PLATE
Southeast Indian
Ocean Ridge
NORTH
AMERICAN
PLATE
COCOS
PLATE
East Pacific
Rise
MidAtlantic
Ocean
Ridge
EURASIAN
PLATE
ANATOLIAN
PLATE
CARIBBEAN
PLATE
ARABIAN
PLATE
AFRICAN
PLATE
SOUTH
AMERICAN
PLATE
Carlsberg
Ridge
AFRICAN
PLATE
Transform
fault
Southwest Indian
Ocean Ridge
ANTARCTIC PLATE
Convergent
plate boundaries
Plate motion
at convergent
plate boundaries
Divergent ( ) and
transform fault (
boundaries
)
Plate motion
at divergent
plate boundaries
Fig. 10.5b, p. 214
Slide 6
Volcanoes
Earthquakes
Fig. 10.5a, p. 214
Slide 5
TYPES OF BOUNDARIES
• DIVERGENT PLATE
BOUNDARIES plates move in
opposite directions
• Builds up the earth’s
crust
Lithosphere
Asthenosphere
Oceanic ridge at a divergent plate boundary
Fig. 10.6a, p. 215
Slide 7
Mid-Atlantic Ridge system
• Convergent plate
boundaries – plates are
pushed together by
internal forces
• Oceanic lithosphere is
subducted under the
continental at
subduction zones
• Trenches normally
form at the boundary
Trench
Volcanic island arc
Rising
m agm a
Subduction
zone
Lithosphere
Asthenosphere
Trench and volcanic island arc at a convergent
plate boundary
Fig. 10.6b, p. 215
Slide 8
Convergent Plate Boundary
• Transform faults –
occur when plates
slide past one another
along a fracture (fault)
in the lithosphere
Fracture zone
Transform
fault
– Most are on the ocean
floor
Lithosphere
Asthenosphere
Transform fault connecting two divergent plate boundaries
Fig. 10.6c, p. 215
Slide 9
External Geologic Processes
• Based directly or indirectly on energy from
the sun and gravity
• Tend to wear down the earth’s surface
• Two types:
– EROSION - material is dissolved, loosened, or
worn away at one part of the earth’s surface and
deposited somewhere else
• Caused by wind, water, and human activities
– WEATHERING – produces loosened material
that can be eroded
• MECHANICAL – large rock fragments broken into
smaller pieces
– One type called FROST WEDGING- caused by freezing,
expansion, and splitting of rock
• CHEMICAL – chemical reactions decompose a
mass of rock mainly reacts with oxygen, carbon
dioxide, and water in the atmosphere and ground
Minerals
• Either an ELEMENT or INORGANIC
COMPOUND – naturally occurring and a
solid
• Some are single elements – Au, Ag
• Most are compounds – mica, salt, quartz
ROCKS
• Any material that makes up a large natural
continuous part of the earth’s crust
• Can contain only one mineral but most
consist of two or more minerals
– Example: GRANITE – quartz, mica, and
feldspar
IGNEOUS ROCKS
• FORMS FROM MOLTEN ROCK MATERIAL
(MAGMA)
– Wells up from upper mantle or deep crust
– Cools
– Hardens into rock – EXAMPLE: GRANITE
• FORMS FROM LAVA
– Forms above ground when magma coold
– Main part of earth’s crust
– Source of many nonfuel mineral resources
The Rock Cycle
Transportation
Deposition
Sedimentary Rock
Slate, sandstone,
limestone
Erosion
Heat,
pressure,
stress
Weathering
EXTERNAL PROCESSES
INTERNAL PROCESSES
Igneous Rock
Granite, pumice,
basalt
Cooling
Heat, pressure
Magma
(molten rock)
Metamorphic Rock
Slate, marble,
quartzite
Melting
Fig. 10.8, p. 217
Slide 11
Natural Hazards
• Earthquakes caused by stress in crust which
deforms rock until it fractures producing
faults. This faulting or abrupt movement
causes EARTHQUAKES
CHARACTERISTICS OF
EARTHQUAKES:
• ENERGY IS RELEASED AS SHOCK WAVES WHICH MOVE
OUTWARD
– FOCUS - POINT OF INITIAL MOVEMENT
– EPICENTER – POINT ON EARTH’S SURFACE ABOVE THE FOCUS.
• MAGNITUDE – MEASURES SEVERITY OF EARTHQUAKE –
RICHTER SCALE- MEASURED ON A SEISMOGRAPH
– RANKED AS:
INSIGNIFICANT – LESS THAN 4
MINOR (4.0 – 4.9)
DAMAGING (5.0 – 5.9)
DESTRUCTIVE (6.0 – 6.9)
MAJOR (7.0 – 7.9)
GREAT (OVER 8.0)
*AMPLITUDE FOR EACH IS 10 X GREATER THAN THE NEXT
SMALLER UNIT
MORE …
AFTERSHOCK S– smaller earthquakes that follow
– often over a period of months
FORESHOCKS – seconds to weeks before the main
shock
PRIMARY EFFECTS - shaking, sometimes
permanent vertical or horizontal displacement of
earth
SECONDARY EFFECTS - rock slides, fires,
flooding, tsumanis,
REDUCING EARTHQUAKE
DAMAGE
• EXAMINE HISTORICAL RECORDS
AND MAKE GEOLOGICAL
MEASUREMENT
• MAP HIGH RISK AREAS
• ESTABLISH BUILDING CODES
• TRY TO PREDICT WHERE AND WHEN
EARTHQUAKES WILL OCCUR
VOLCANOES
• MAGMA REACHES THE EARTH’S SURFACE
THROUGH A VENT OF CRACK
– RELEASES:
• EJECTA – CHUNKS THROUGH ASH
• LIQUID LAVA –
• GASES – water vapor, carbon dioxide, sulfur dioxide
– USUALLY FOUND IN SAME AREAS AS
EARTHQUAKE ACTIVITY
– BENEFITS:
• FORM MOUNTAINS, LAKES, AND PRODUCE FERTILE
SOILS AS LAVA WEATHERS
REDUCE VOLCANIC HAZARDS
• LAND – USE PLANNING
• BETTER PREDICTION
• EFFECTIVE EVACUATION PLANS
Oak tree
Fern
Word
sorrel
Lords and
ladies
Dog v iolet
Earthworm
Millipede
Mole
Honey
f ungus
Grasses and
small shrubs
Organic debris
Builds up
Moss and
lichen
Rock
fragments
O horizon
Leaf litter
A horizon
Topsoil
Bedrock
B horizon
Subsoil
Immature soil
Regolith
Young soil
Pseudoscorpion
C horizon
Parent
material
Mite
Nematode
Actinomy cetes
Root system
Mature soil
Red earth
mite
Springtail
Fungus
Bacteria
Fig. 10.12, p. 220
Slide 15
Characteristics of soil
• TEXTURE
– DETERMINED BY SIZE AND TYPE OF
MINERAL PARTICLES
– CLAY - VERY FINE PARTICLES
– SILT - FINE PARTICLES
– SAND - LARGE PARTICLES
– LOAM = EQUAL MIXTURE OF CLAY,
SAND, SILT AND HUMUS
100%clay
0
80
clay
20
60
Increasing
percentage clay
40
silty
clay
sandy
clay
40
60
sandy clay
loam
20
clay
loam
silty clay
loam
loam
silty
loam
sandy
loam
0
sand
100%sand
Increasing
percentage silt
loamy
sand
80
80
silt
60
40
Increasing percentage sand
20
100%silt
Fig. 10.16, p. 224
Slide 20
Soil Porosity
• SIZE, SHAPE AND DEGREE OF CLUMPING
DETERMINE THE NUMBER AND VOLUME OF
SPACES FOR AIR AND WATER IN SOIL
• Called SOIL STURCTURE
–
–
–
–
How soil particles are “glued together”
Granular – large rounded clumps
Crumb – irregular clumps
Platy – thin horizontal plates
• MORE PORE SPACES, MORE AIR AND MORE
PERMEABLE TO WATER FLOW.
• Porosity determined by soil texture
PERMEABILITY &
STRUCTURE
AFFECTS MOVEMENT OF AIR AND
WATER THROUGH THE SOIL
PERMEABILITY – rate at which water and
air move from the surface down
PERCOLATION – Ability of water to soak
into the soil
CAPILLARY ACTION – movement of water
upward against the pull of gravity
Water
High pe rmeability
Water
Low pe rm eability
Fig. 10.17, p. 224
Slide 21
• TEXTURE, POROSITY, AND
PERMEABILITY DETERMINE THE
WATER HOLDING CAPACITY OF THE
SOIL , THE AERATION OF THE SOIL,
AND THE MOISTURE CONTENT OF
THE SOIL.
pH
• PLANTS CAN ONLY ABSORB WATER, ETC.
THROUGH ROOTS IF PH IS WITHIN A
CERTAIN RANGE
• MOST PLANTS PREFER 6.5 TO 7 – at this point
the minerals are fairly soluble.
• EAST COAST - ACIDIC - DUE TO MORE
RAINFALL - USE LIME TO NEUTRALIZE bue
must add manure or fertilizer.
• WEST COAST - ALKALINE - LESS
MOISTURE – reduces uptake off phosphorus and
zinc - USE SULFUR
• pH INFLUENCES THE RATE OF
NUTRIENT UPTAKE
• ACIDIC SOILS USUALLY LOW IN
NITROGEN & PHOSPHORUS – BELOW
5.5, BELOW 4.0 VERY LOW!
What causes soil erosion?
• Erosion - movement of soil components
from one place to another.
– Results in buildup of sediments and
sedimentary rock on land and in water.
• The two main agents:
– Wind and water
• Some is natural, other is caused by man
– Plant roots help to anchor the soil.
Main human causes of erosion
•
•
•
•
•
•
•
Farming
Logging
Construction
Overgrazing
Off-road vehicles
Burning of vegetation
MOST EROSION IS CAUSED BY MOVING
WATER!
Types of erosion
• Sheet erosion - movement of water across a slope
or field in a wide flow
• Rill erosion - water forms fast flowing rivulets that
cut small channels in the soil
• Gulley erosion - rivulets of fast moving water join
together and erode deeper and deeper until you
have ditches and gullies.
– Usually occurs on steep slopes where vegetation has
been removed.
Fig. 10.18, p. 225
Major harmful effects of erosion:
• Loss of soil fertility and it ability to hold water
• Runoff of sediment that pollutes water, kills fish,
and clogs irrigation ditches and builds-up in
waterways
• Increased use of fertilizer to keep soil fertile
• EROSION IS A SERIOUS WORLD PROBLEM!
– TOPSOIL IS ERODING FASTER THAN IT FORMS
ON ABOUT ONE-THIRD OF THE WORLD’S
CROPLAND.
Areas of serious concern
Areas of some concern
Stable or nonvegetative areas
What is Desertification?
• When the productive potential of arid or semiarid
land falls by 10% or more.
• Can be caused by climate or human activities
• Moderate - 10-25% drop in productivity
• Severe - 25 - 50% drop
• Very severe - drop of 50% - usually results in
gullies and sand dunes.
• A SERIOUS PROBLEM WORLDWIDE!
What causes Desertification?
•
•
•
•
•
•
Overgrazing
Deforestation without reforestation
Surface mining without land reclamation
Salinization and waterlogging of soil
Bad irrigation techniques
Farming on land with poor soil
Moderate
Severe
Very Severe
Fig. 10.21, p. 228
Consequences:
•
•
•
•
•
Worsening drought
Famine
Declining living standards
Economic losses
More environmental refugees
Major symptoms:
• Loss of native vegetation
• Increased erosion of dry soil - mainly by
wind
• Salinization
• Lowered water tables
• Reduced surface water as streams and
ponds dry up.
What can we do?
• Reduce overgrazing
• Reforestation programs
– Plant trees and grass
• Reduce the threat of global warming
What is Salinization?
• Accumulation of salts in topsoil due to
irrigation
• Most irrigation water is a dilute solution of
various salts picked up as the water flows
over the earth.
• Small quantities are essential but in large
amounts is toxic.
•
•
•
•
•
Stunts plant growth
Lowers crop yield
Eventually will kill plants
Ruins the land
Severe salinization has reduced the world’s
irrigated cropland by 21%.
• In U.S. it has reduced cropland by 23%.
What can we do?
• Flush salts with more water but this is
costly and wasteful
• Take land out of production for from 2-5
years
• Install an undergound network of perforated
pipes and flush soil with low-salt water
• All of this is expensive!
More…
• Reduce use of water in irrigation
• Switch to more salt tolerant plants
• Plant salt loving plants and convert the land
to grazing land.
• There is no cure for salinization.
Waterlogging
• Caused when large amounts of irrigation water
leach water deeper and deeper into the soil.
• Without drainage underground water rises higher
and higher.
• Eventually the salt water envelopes and kills the
deep roots of the plants.
• About 1/10 of all irrigated land suffers from water
logging.
Transpiration
Evaporation
Evaporation
Evaporation
Waterlogging
Less permeable
clay layer
Fig. 10.22, p. 229
SOIL CONSERVATION
• REDUCES SOIL EROSION AND
RESTORES SOIL FERTILITY
• CONVENTIONAL-TILLAGE –plow in fall
and plant in the spring – leaves soil bare
through winter and vulnerable to erosion
• CONSERVATION-TILLAGE – disturb the
soil as little as possible
OTHER SOLUTIONS
• TERRACING – use a
series of broad, nearly
level terraces – run
across the land’s
contours
– Retains water at each
level
– Reduces soil erosion
• CONTOUR FARMING –
plowing and planting in
rows across the contour of
gently sloped land – helps
to hold soil and slow
water run-off
• STRIP CROPPING –
planting alternating strips
such as corn & a legume –
traps soil, catches water
runoff, helps prevent
spread of pests and disease
• WINDBREAKS or
SHELTERBELTS –
trees planted – reduce
wind erosion, helps
retain soil moisture,
supplies wood for fuel,
provides animal
habitats
RESTORING SOIL FERTILITY
• ANIMAL MANURE – improves soil
structure, adds organic nitrogen, stimulates
beneficial soil bacteria
• GREEN MANURE - fresh or green
vegetation plowed into soil – increases
organic matter and humus
• COMPOST –
• INORGANIC FERTILIZER
– EASY TO TRANSPORT, STORE, AND APPLY
– DON’T ADD HUMUS TO SOIL
– REDUCE SOIL’S ORGANIC MATTER AND WATER
HOLDING ABILITY
– LOWERS OXYGEN CONTENT OF SOIL
– ONLY SUPPLY 2 0R 3 OF ESSENTIAL NUTRIENTS
– REQUIRE MUCH ENERGY TO PRODUCE
– RELEASE NITROUS OXIDE A GREENHOUSE GAS