Transcript Soils - AaronFreeman

Geology:
Processes, Hazards, and Soils
Chapter 10
G. Tyler Miller’s
Living in the Environment
13th Edition
Geologic Structure
Earth’s
internal
structure
Fig. 10-2 p. 204
Structure of Earth
Structure of Earth
• Inner Core/Outer Core – magma/molten rock
with intensely hot metals, mostly Fe
• Mantle – pliable, hot enough to bend like
taffy, less dense than core as it contains
lighter elements (O2, Si, Mg)
• Crust – floats atop mantle, consisting of
oceanic and continental crust
Hard Boiled Egg
Eight Most Common
Chemical Elements (%)
WHOLE EARTH
CRUST
Iron 33.3
Oxygen 45.2
Oxygen 29.8
Silicon 27.2
Silicon 15.6
Aluminum 8.2
Magnesium 13.9
Iron 5.8
Nickel 2.0
Calcium 5.1
Calcium 1.8
Magnesium 2.8
Aluminum 1.5
Sodium 2.3
Sodium 0.2
Potassium 1.7
Features of the Crust
Asthenosphere = mantle
Oceanic crust
(lithosphere)
Abyssal Oceanic
floor
ridge
Folded mountain belt
Abyssal Trench
floor
Volcanoes
Abyssal plain
Abyssal
hills
Continental
shelf
Craton
Continental
slope
Continental
rise
Abyssal plain
Continental crust
(lithosphere)
Mantle (lithosphere)
Mantle
(lithosphere)
Mantle (asthenosphere)
Lithosphere = oceanic + continental crust
Internal Earth Processes
• Geological changes originating from the
earth’s interior
– Residual heat from the earth’s core
– Radioactive decay in the earth’s crust
• Convection cells
• Mantle plumes
Spreading
center Oceanic tectonic
Oceanic tectonic
plate
plate
Ocean trench
Collision between
two continents
Plate movement Plate movement
Tectonic plate
Oceanic
Subduction
crust
zone
Oceanic
crust
Continental
crust
Continental
crust
Material cools
as it reaches
the outer
mantle
Mantle
convection
cell
Two plates move
towards each other.
One is subducted
back into the mantle
on falling convection
current.
Cold dense
material falls
back through
mantle
Hot material
rising
through
the mantle
Mantle
Hot outer
core
Inner
core
Plate Tectonics
p. 208
• Theory explaining the movement of
tectonic plates and the processes that
occur at their boundaries.
– more commonly referred to as
“continental drift” theory
– Plates slide across surface of Earth and
can break or collide
– Plate Boundary = area where two plates
meet
Reykjanes
Ridge
EURASIAN PLATE
JUAN DE
FUCA PLATE
CHINA
SUBPLATE
PHILIPPINE
PLATE
Transform
fault
NORTH
AMERICAN
PLATE
PACIFIC
COCOS
PLATE
PLATE
Transform
fault
East Pacific
Rise
INDIAN-AUSTRLIAN PLATE
MidIndian
Ocean
Ridge
Southeast Indian
Ocean Ridge
MidAtlantic
Ocean
Ridge
EURASIAN
PLATE
ANATOLIAN
PLATE
CARIBBEAN
PLATE
ARABIAN
PLATE
AFRICAN
PLATE
SOUTH
AMERICAN
PLATE
Carlsberg
Ridge
SOMALIAN
SUBPLATE
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
Tectonic Plate Boundaries
Divergent boundary
Convergent boundary
•Subduction zone
Transform fault
Divergent Boundary
Lithosphere
Asthenosphere
Plates move apart, forms as mantle magma forms oceanic crust,
occurs along ocean basins
EX: Mid Atlantic Ridge, East Pacific Rise
Convergent Boundary
Trench
Volcanic island arc
Rising
magma
Subduction
zone
Lithosphere
Asthenosphere
Plates collide, resulting in subduction OR mtn building, occurs at
plate boundaries
EX: Indian Plate, Western South America
Transform Faults
Transform
fault
Lithosphere
Asthenosphere
Plates slide past each other in opposite but parallel directions, occurs
along Fault Lines
EX: San Andreas Fault
Ring of Fire
Volcanoes
Earthquakes
Natural Hazards: Earthquakes
• Features
– Shock waves
– Focus and epicenter
• Magnitude
– Richter Scale
– 1 (insignificant) to
9 (great) 10X
• Aftershocks
• Primary Effects
– shaking
• Secondary Effects
– Rockslides, fires, and flooding
– tsunamis
Expected Earthquake Damage
No damage expected
Minimal damage
Canada
Moderate damage
Severe damage
Fig. 10-10 p. 211
United States
Natural Hazards: Volcanic Locations
• Volcanic Eruptions occurs at three geographic
locations p. 207
1. Subduction Zones = Pacific Basin Ring of Fire
2. Spreading Centers (Ocean Ridges) = Iceland
3. Hot Spots = rising plume of magma that
flowed from crack in crust, Hawaiian Islands
Natural Hazards: Volcanic Eruptions
extinct
volcanoes
• Ejecta
(rock and ash)
• Molten lava
• Gases
central
vent
magma
conduit
magma
reservoir
Solid
lithosphere
Upwelling
magma
Partially molten
asthenosphere
ROCK CYCLE REVIEW
Rock Cycle
• Cycle of creation, destruction, and
metamorphosis.
– Three major rock classifications:
• Igneous
• Sedimentary
• Metamorphic
Minerals and Rocks
• Minerals
–
–
–
–
Naturally occurring
Crystalline structure
Inorganic
Solid
• Rocks – solid, cohesive, aggregate of one
or more crystalline minerals
– Igneous (granite, lava)
– Sedimentary (limestone, sandstone)
– Metamorphic (marble, slate)
Lithification Sedimentary Rock
Deposition
Transport
Erosion
Shale, Sandstone,
Limestone
External Processes
Heat,
Pressure
Weathering
Internal Processes
Igneous Rock
Granite, Pumice,
Basalt
Heat,
Metamorphic Rock
Pressure
Slate, Quartzite,
Marble
Magma
(Molten Rock)
External Earth Processes
• Weathering – breakdown of solid rock
– Mechanical (physical) weathering
• Frost wedging, freeze thaw cycle
– Chemical weathering
• Oxidation (losing or gaining of electrons)
• Hydrolysis (splitting of water)
• Erosion – process by which earth
particles are moved from one place and
deposited in another
–
–
–
–
Wind
Water
Ice
Gravity
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
Landforms resulting from external processes
Soil
• Complex mixture of …
–
–
–
–
–
–
eroded rock
mineral nutrients
decaying organic matter
water
air
micro-organisms
• Renewable resource
– Weathering of rocks
– Sedimentation
– Decomposition of organic matter
What is soil?
• Mixture of :
– Minerals – weathered rock, essential nutrients
– Water – trapped in pore spaces, responsible for leaching
or illuviation
– Gases – located in pore spaces
– Humus – dead “stuff”, decaying organic materials
thanks to fungi and decomposers, Leaf Litter
Humus
NOT HUMMUS
Soil Composition
Soils: Formation
• Soils form as parent rock material is weathered
(broken down) into smaller pieces via chemical or
mechanical weathering
– Chemical : lichens excreting acids that break apart rock
– Physical: physical forces, freeze/thaw cycles, critters,
biological activity
Soils: Formation
p. 212, 215
 Soil horizons  Distinctive layers
Immature soil
O horizon
Leaf litter, organic
A horizon
Topsoil
B horizon
Humus
Subsoil, clay/cations
leached from above
accumulate here
Regolith
Bedrock
Young soil
C horizon
Weathered Parent
Material
Mature soil
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)
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)
Soil Organisms
Provide ecosystem services:
- Maintain soil fertility
- Cycle organic matter (nutrients)
- Break down toxins (bioremediation)
- Clean water as it percolates down
Soil Properties
 Infiltration
Water
Water
 Leaching
 Porosity
High permeability
Permeability
Low permeability
Porosity vs. Permeability
 Porosity : amount of pore space, # of pores
Water
Water
CLAYS:
High porosity
Impermeable
SANDS:
High permeability
Low permeability
Low porosity
Permeable
 Permeability : ability to transmit fluids
Soil Properties
1. Texture : the way the soil feels
 Depends on amount of each sized
particles termed soil fraction
 Sand-largest-feel gritty
 Silt-medium-feel soft, silky, floury
 Clay-small-feel sticky, hard to
squeeze, greatest surface area
Soil Properties
100%clay
 1. Texture
0
80
20
Increasing
percentage clay
Increasing
percentage silt
60
40
40
60
20
80
0
100%sand
80
60
40
20
100%silt
Increasing percentage sand
 Structure: % clay, % sand, % silt
100%clay
Soil
Texture
Triangle
0
80
clay
20
60
Increasing
percentage clay
40
clay
loam
20
100%sand
loam
Silt
0.002-0.05
mm
Clay
less than
0.002 mm
Increasing
percentage silt
80
silty
loam
loamy
sand
80
0.05-2 mm
silty clay
loam
sandy
loam
0
Sand
60
sandy clay
loam
sand
2-64 mm
silty
clay
sandy
clay
40
Gravel
silt
60
40
Increasing percentage sand
20
100%silt
Properties of Soils with Different Textures
Why care about soil texture?
predicts fertility and use
Texture
Nutrient
Capacity
Infiltration
Water-Holding Aeration
Capacity
Clay
Good
Poor
Good
Poor
Poor
Silt
Medium
Medium
Medium
Medium
Medium
Sand
Poor
Good
Poor
Good
Good
Loam
Medium
Medium
Medium
Medium
Medium
Refer to Fig. 10-15 p. 215
Tilth
Why care about soil texture?
predicts fertility and use
Chemical Properties of Soil
• pH
• Fertility
– 20 minerals needed for plant growth
– Major Nutrients (N-P-K)
• Nitrogen
• Phosphorus
• Potassium
– Minor Nutrients
• Soil Tests
Soil Erosion
The movement of soil components from one place
to another by wind and water.
• Sheet erosion – water moves down a slope or
across a field in a wide flow
• Rill erosion – surface water forms fast-flowing
rivulets that cut channels in the soil
• Gully erosion – rivulets join together and cut
channels wider and deeper until they become
ditches and gullies.
Global Soil Erosion
• loss of soil organic matter
• flooding
• reduced ability to store
water
• sedimentation
• increased use of fertilizer
Areas of serious concern
Areas of some concern
Stable or nonvegetative areas
Desertification
Conversion of rangeland, rain-fed cropland, or
irrigated cropland to desert-like land, with a
drop in agricultural productivity of 10% or more.
•
•
•
•
•
•
Causes
Overgrazing
Deforestation
Surface mining
Erosion
Salinization
Soil compaction
•
•
•
•
•
Consequences
Worsening drought
Famine
Economic losses
Lower living
standards
Environmental
refugees
Soil Degradation
 Salinization -
the accumulation
of salt
Evaporation
Evaporation
Transpiration
 Waterlogging –
saturation of soil with
irrigation water or
excess precipitation so
the water table rises
close to the surface.
Waterlogging
Less permeable
clay layer
Solutions: Soil Conservation
Conventional-tillage
Conservation tillage
Cropping methods
Windbreaks
Conventional tillage
• Crop cultivation
method in which a
planting surface is
made by plowing
land, breaking up
the exposed soil,
and then
smoothing the
surface.
Conservation tillage
• Crop cultivation in
which soil is
disturbed little
(mini-mum tillage
farming) or not at
all (no-till farming)
to reduce soil
erosion, lower
labor costs, and
save energy.
Terracing
Contour planting and strip cropping
Alley cropping
Windbreaks
Soil Restoration
Crop Rotation
– planting a field with different crops
from year to year to reduce soil nutrient
depletion.
Soil Restoration
Organic Fertilizers
• Animal manure
– Improves soil structure
– Adds organic nitrogen
– Stimulates beneficial soil bacteria and fungi
• Green manure
– Fresh and growing green vegetation
• Compost
– Microorganisms break down organic matter in
the presence of oxygen
Soil Restoration
Commercial Inorganic Fertilizers
Nitrogen, Phosphorus and Potassium
– N, P, K
• Advantages
– Easily transported, stored, and applied
• Disadvantages
–
–
–
–
Not adding humus
Reducing organic matter content
Lowering oxygen content
Supply only 2 or 3 of the more than 20
nutrients needed
– Require large amounts
– Release nitrous oxides