Geology

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Geology
Earth’s Structure
 Name the zones of the earth
Crust, mantle, core
 Now do it again with more detail
Crust, lithosphere, asthenosphere, mantle, outer
core, inner core
35 km (21 mi.) avg., 1,200˚C
Crust
100 km (60 mi.)
200 km (120 mi.)
Low-velocity zone
Crust
Mantle
Lithosphere
Solid
10 to 65km
2,900km
(1,800 mi.)
3,700˚C
Outer core
(liquid)
Core
Inner
core
(solid)
100 km
Asthenosphere
(depth unknown)
200 km
5,200 km (3,100 mi.), 4,300˚C
Fig. 10.2, p. 212
What is in each zone
 Core – mostly iron and a little nickel, inner solid
and outer is liquid
 Mantle – mostly iron, silicon, oxygen, and
magnesium, mostly rigid except near surface
which is plastic (asthenosphere)
 Crust – mostly oxygen, silicon, aluminum, and
iron (by weight)
Convection below
 Heat from the formation of the earth combined
with energy from radioactive decay gives way to
convection currents of rock (very slow) or mantle
plumes in which hot rock rises
Plate tectonics
 The lithosphere is broken into many large plates
which move due to convection currents within
the asthenosphere
 Remember continental drift (Pangaea)
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
Plate boundaries

Divergent – plates move apart, form mid ocean ridges

Convergent – plates slam together, form largest
mountains in the world
Subduction is a type of convergent where one plate dives
beneath another and usually creates trenches and volcanoes
nearby

Transverse – slide sideways past each other (San
Andreas Fault)
Trench
Volcanic island arc
Rising
magma
Subduction
zone
Lithosphere
Asthenosphere
Trench and volcanic island arc at a convergent
plate boundary
Fig. 10.6b, p. 215
Fracture zone
Transform
fault
Lithosphere
Asthenosphere
Transform fault connecting two divergent plate boundaries
Fig. 10.6c, p. 215
Lithosphere
Asthenosphere
Oceanic ridge at a divergent plate boundary
Fig. 10.6a, p. 215
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
Erosion and Weathering
 These are the external processes
 Erosion is the moving of rock material from one
place to another (deposition)
 Weathering is the breaking down of rock by
natural forces
Ice wedging, rain, wind, gravity
Chemical weathering, carbonic acid
Lake
Tidal
flat
Glacier
Spits
Stream
Lagoon
Dunes
Shallow marine
environment
Barrier
islands
Delta
Dunes
Beach
Shallow marine
environment
Volcanic
island
Coral reef
Continental shelf
Continental slope
Continental rise
Abyssal plain
Deep-sea fan
Fig. 10.7, p. 216
Rocks and minerals
 Mineral – an element or inorganic compound
that occurs naturally, is solid, and has a regular
crystalline internal structure
 Rock – type of music meant to be played loud,
also any material that makes up a large, natural,
continuous part of the earth’s crust
Types of rock
 Igneous
Granite, pumice, basalt
 Sedimentary
Shale, sandstone, limestone (coral reef)
 Metamorphic
Slate, marble, quartzite
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
Earthquake
Fault – break in the lithosphere
 Focus – where the earthquake took place
 Epicenter – location above focus at surface
 Richter scale – used to measure magnitude, less than 3
is not felt, logarithmic scale, so each increase of 1 is a
factor of 10
 Minor < 5, damaging 5-6, destructive 6-7, major 7-8,
great over 8
 Aftershock – reduced shaking after original movement

Volcano – it can happen here!
Volcano - Wherever magma reaches the surface
through a vent or fissure (also released are gases
carbon dioxide, water vapor, hydrogen sulfide, ash, and
other ejecta
 Mt. St. Helens – worst US volcano disaster


Ring of fire – other than a song by Social D, this is the
edge of the pacific plate where most volcanoes are
located
Soil
 Produced slowly (200-1000 years typically) by
weathering of rock, deposition of sediments, and
decomposition of organic matter
 Soil horizons – separate zones within soil
 Soil profile – cross-section view of soil
Horizons
 O horizon – surface litter
 A horizon – top soil, made up of inorganic
particles (clay, silt, sand) and humus (organic
particles from decomposed organisms)
Dark topsoil is richer in nutrients
Releases water and nutrients slowly
Provides aeration to roots
Healthy soil contains many nematodes and bacteria,
fungi, etc.
Oak tree
Fern
Word
sorrel
Lords and
ladies
Dog violet
Earthworm
Millipede
Mole
Honey
fungus
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
Actinomycetes
Root system
Red earth
Springtail
mite
Mature soil
Fungus
Bacteria
Fig. 10.12, p. 220
Poor topsoil
Grey, yellow and red are not the colors of healthy
topsoil
 Generally means that soil is lacking nutrients


Best soil is called loam with equal parts sand, silt, clay
and humus

Leaching – dissolving and carrying nutrients (or
pollutants) through soil into lower layers
B – horizon and C - horizon
 B – Subsoil mostly broken down rock with little
organic matter
 C- parent material broken down rock on top of
the bedrock
Soils
 Texture – relative amount of different sized
particles present (sand, silt, clay)
 Porosity – volume of pore space in the soil
 Permeability – the ability of water to flow through
the soil
Water
Water
High permeability
Low permeability
Sandy soil
Clay soil
Soils
 Clay – high porosity, low permeability
 Sand – high permeability, low porosity
 Acidity is another factor
 Where rain is low, calcium and other alkaline
compounds may build up (sulfur can be added –
turns to sulfuric acid by bacteria)
Forest litter
leaf mold
Acidic
lightcolored
humus
Humus-mineral
mixture
Light-colored
and acidic
Light, grayishbrown, silt loam
Iron and
aluminum
compounds
mixed with
clay
Tropical Rain Forest Soil
(humid, tropical climate)
Acid litter
and humus
Humus and
iron and
aluminum
compounds
Dark brown
Firm clay
Deciduous Forest Soil
(humid, mild climate)
Coniferous Forest Soil
(humid, cold climate)
Fig. 10.15b, p. 223
Mosaic
of closely
packed
pebbles,
boulders
Alkaline,
dark,
and rich
in humus
Weak humusmineral mixture
Dry, brown to
reddish-brown
with variable
accumulations
of clay, calcium
carbonate, and
soluble salts
Desert Soil
(hot, dry climate)
Clay,
calcium
compounds
Grassland Soil
(semiarid climate)
Fig. 10.15a, p. 223
Soil erosion
 Causes – mainly water and wind
 Human induced causes – farming, logging,
mining, construction, overgrazing by livestock,
off-road vehicles, burning, and more (go us!)
Soil erosion
 Types
 Sheet
Uniform loss of soil, usually when water crosses a
flat field
 Rill
Fast flowing water cuts small rivulets in soil
 Gully
Rivulets join to become larger, channel becomes
wider and deeper, usually on steeper slopes or
where water moves fast
Global soil loss
This is a major problem world wide
 Have lost about 15% of land for agriculture to soil
erosion

Overgrazing
Deforestation
Unsustainable farming

Also 40% of ag land is seriously degraded due to soil
erosion, salinization, water logging and compaction
Moderate
Severe
Desertification of arid and semiarid lands
Very Severe
Fig. 10.21, p. 228
Areas of serious concern
Areas of some concern
Stable or nonvegetative areas
Global soil erosion
Fig. 10.19, p. 226
Desertification
 Turning productive (fertile) soil into less
productive soil (10% loss or more)
Overgrazing
Deforestation
Surface mining
Poor irrigation techniques
Poor farming techniques
Soil compaction
Salinization
As water flows over the land, salts are leached out
 When water irrigates a field it is left to evaporate
typically
 This repeated process causes the dissolved salts to
accumulate and possibly severely reduce plant
productivity


Fields must be repeatedly flushed with fresh water to
remove salt build up
Waterlogging
 When fields are irrigated they allow water to sink
into the soil.
 Winds can dry the surface
 As more water is applied the root area of plants
is over saturated reducing yield
 As clay is brought to subsoil levels it can act as a
boundary for water infiltration
Evaporation
Transpiration
Evaporation
Evaporation
Waterlogging
Less permeable
clay layer
Fig. 10.22, p. 229
Soil conservation
 Conservation tillage – (no till farming) disturb the
soil as little as possible
 Reducing erosion also helps – save fuel, cut
costs, hold water, avoid compaction, allow more
crops to be grown, increase yields, reduce
release of carbon dioxide
Soil conservation
 Terracing – making flat growing areas on
hillsides
 Contour farming – planting crops perpendicular
to the hill slope, not parallel
 Strip cropping – planting alternating rows of
crops to replace lost soil nutrients (legumes)
 Alley cropping – planting crops between rows of
trees
Control planting and strip cropping
Fig. 10.24b, p. 230
Alley cropping
Fig. 10.24c, p. 230
Fig. 10.24a, p. 230
Terracing
Soil conservation

Gully reclamation – seeding with fast growing native
grasses, slows erosion or “reverses” it
Also building small dams traps sediments
Building channels to divert water or slow water

Windbreaks – trees planted around open land to
prevent erosion
Retains soil moisture (shade, less wind)
Habitats for birds, bees, etc.

Land classification – identify marginal land that should
not be farmed
Windbreaks
Fig. 10.24d, p. 230
Soil fertility
 Inorganic fertilizers – easily transported, stored,
and applied
Do not add humus – less water and air holding
ability, leads to compaction
Only supply about 3 of 20 needed nutrients
Requires large amount of energy for production
Releases nitrous oxide (N2O) during production, a
green house gas
Soil fertility
 Organic fertilizers – the odor is a problem
 Animal manure – difficult to collect and transfer
easily, hard to store
 Green manure – compost, aerates soil, improves
water retention, recycles nutrients
 Crop rotation – allows nutrients to return to soil,
otherwise same crop continually strips same
nutrient, keeps yields high, reduces erosion
See you on the farm!
 Remember without
farming we all starve
 But unless we change
our farming practice
we continue to
damage our
environment
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