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Geology: Processes, Hazards, and
Soils
G. Tyler Miller’s
Living in the Environment
13th Edition
Chapter 10
Dr. Richard Clements
Chattanooga State Technical Community College
Modified by Charlotte Kirkpatrick
Key Concepts
Internal geologic processes
External geologic processes
Minerals, rocks, and the rock cycle
Earthquakes and volcanoes
Soil structure and formation
Soil conservation
How do we know?
• Most of the evidence for the structure of the
earth’s interior come from indirect evidence:
1. density measurements
2. seismic wave studies
3. measurements of heat flow from the interior
4. lava analyses
5. research on metorites
Geologic Processes
 Structure of the Earth
Core: innermost zone, very hot. Has an
inner core that is solid and an outer core
that is molten
Mantle: thick, solid zone for the most
part. Rigid outermost part called
Lithosphere has beneath it the very hot
melted rock of the Asthenosphere.
Crust: outer part of the earth composed
of Continental Crust (Granite) and
Oceanic Crust (Basalt)
Geologic Processes
Fig. 10-2 p. 204
Features of the Crust
Fig. 10-3 p. 205
Internal and External Earth
Processes
• Internal Geologic Processes: generally build
up the planet’s surface. Heat from the interior
provides the energy plus gravity plays a role as
well.
• Two types of movement in the mantle’s
asthenosphere:
– Convection Cells: movement of mantle rock in a
convection current
– Mantle Plumes: movement of mantle rock in an
upward column
Convection Cells and Plate Movement
Internal Earth Processes
 Plate tectonics: theory explaining the
movement of the plates that occur at their
boundaries
 Divergent boundary: spreading plates, such
as at the oceanic ridges
Internal Earth Processes
 Convergent boundary: where the plates come
together
 Subduction zone: due to the density difference
between oceanic and continental crust the oceanic
crust will be carried downward and a trench is
formed here. Earthquakes are common as well as
volcanoes.
Internal Earth Processes
 Transform fault: fault line that develops when
plate movement is in opposite direction and
therefore the plates slide past one another along a
fracture.
Incidence of Earthquakes and
Volcanoes
Ring of Fire
Volcanoes
Earthquakes
Figure 10-5a
Page 207
Slide 6
Tectonic Plates
Reykjanes
Ridge
EURASIAN PLATE
JUAN DE
FUCA PLATE
NORTH
AMERICAN
PLATE
CHINA
SUBPLATE
Transform
PHILIPPINE
fault
PLATE
PACIFIC
COCOS
PLATE
MidPLATE
Indian
Transform
Ocean
fault
Ridge
East Pacific
Rise
INDIAN-AUSTRLIAN PLATE
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
Figure
10-5b
Page 207
Slide 7
External Earth Processes: Erosion
and Weathering Refer to Fig. 10-7 p. 209
 Erosion: process by which material is dissolved,
loosened or worn away from one part of the
earth’s surface and deposited in other places.
 Mechanical weathering: Large rock mass is
broken into smaller fragments of the original
material. Ex. Frost wedging
 Chemical weathering: one or more chemical
reactions decompose a mass of rock usually
reaction with O2, CO2, and water.
Minerals and Rocks
 Mineral (diamond, bauxite): element or
inorganic compound that occurs naturally and is
solid.
Rock Types: Rocks are any material that make up
a large, natural, continuous part of the earth’s
crust. May contain one or more minerals.
Igneous (granite, lava)
Sedimentary (limestone,
sandstone)
Metamorphic (marble, slate)
Transport
Deposition
Sedimentary Rock
Shale, Sandstone,
Limestone
Erosion
Heat,
Pressure
Weathering
External Processes
Internal Processes
Igneous Rock
Granite, Pumice,
Basalt
Heat,
Metamorphic Rock
Pressure
Slate, Quartzite,
Marble
Magma
(Molten Rock)
Refer to
Fig. 10-8 p. 210
Natural Hazards: Earthquakes
 Features: Energy released as shock waves when
the stressed parts of the earth shift.
 Focus: point of initial movement.
 Epicenter: the point on the surface directly
above the focus
 Magnitude: severity of the earthquake as
measured on a Richter scale. It is measured by a
seismograph. The amplitude of the vibrations
caused by the energy released by the earth
movement is what is measured. Each increase in
the scale is 10 times greater in magnitude.
Natural Hazards: Earthquakes
Fig. 10-9 p. 210
Natural Hazards: Earthquakes
 Aftershocks and foreshocks may show
up before or after a main shock from
minutes to days.
 Primary effects: shaking and vertical or
horizontal displacement
 Secondary effects: rock slides, urban fires,
flooding caused by subsidence, and
tsunamis.
How to reduce earthquake risk
•
•
•
•
Locating active faults
Making maps of high risk areas
Establishing buildings codes that regulate risk
trying to predict when and where earthquakes
will occur.
Expected Earthquake Damage
No damage expected
Minimal damage
Canada
Moderate damage
Severe damage
Fig. 10-10 p. 211
United States
Volcanoes
• Occur in same areas as earthquakes.
• Occurs where magma reaches the earth’s surface through a
central vent or a long crack
• Can release ejecta (chunks of lava rock to ash), liquid lava,
or gases (water, carbon dioxide, sulfur dioxide)
• Much of the sulfur dioxide will remain in the air and
become acid rain
• Some are very explosive eruptions like Mt. St. Helens and
Mt. Pinatubo; others are much quieter like the Hawaiian
Island volcanoes
• Benefit: produces very fertile soil
Natural Hazards: Volcanic Eruptions
extinct
volcanoes
central
vent
magma
conduit
Fig. 10-11 p. 211
magma
reservoir
Solid
lithosphere
Upwelling
magma
See Introductory Essay p. 203
Partially molten
asthenosphere
How to Reduce Volcano Risk
•
•
•
•
Land use planning
Better prediction of volcanic eruptions
Effective evacuation plans
Studying phenomenon that precedes the
eruption
– Tilting or swelling of the cone,
– Changes in magnetic and thermal properties of the
volcano
– Changes in gas composition
– Increased seismic activity
Soils: Formation
Soil: a complex mixture of eroded rock mineral
nutrients, decaying organic matter, water, air and
billions of living organisms, mostly of the
microscopic decomposers.
Soil horizons: mature soil is arranged in a
series of zones called soil horizons. Each has a
very distinct texture and composition that varies
with different types of soils.
Soil profile: cross sectional view of the horizons
in a soil. Most mature soils have at least 3 horizons
of the possible horizons.
Soils: Formation
Soil Horizon O: Surface litter layer, consists
mostly of freshly fallen and partially decomposed
leaves, twigs, animal waste, fungi and other
organic materials.
Soil horizon A: Topsoil layer, a porous mixture
of partially decomposed organic matter called
humus, some inorganic mineral particles. Usually
darker and looser than deeper layers. A fertile soil
will have a thick topsoil with lots of humus.
B and C horizons: inorganic matter and
broken-down rock
Immature soil
O horizon
Leaf litter
A horizon
Topsoil
Regolith
B horizon
Subsoil
Bedrock
C horizon
Young soil
Parent
material
Fig. 10-12 p. 212
Mature soil
Food Web of Soil
Rove beetle
Pseudoscorpion
Flatworm
Centipede
Ant
Ground
beetle
Mite
Adult
fly
Roundworms
Fly
larvae
Beetle
Protozoa
Mite
Springtail
Millipede
Bacteria
Sowbug
Slug
Fungi
Actinomycetes
Snail
Mite
Earthworm
Organic debris
Figure 10-13
Page 213
Slide 17
Importance of Nitrogen Cycle
Nitrogen fixing
by lightning
Commercial
inorganic
fertilizer
Organic fertilizers,
animal manure,
green manure, compost
Crop
plant
10-6-4
N-P-K
Dead
organic matter
Application
to land
Nitrogen fixing
Decomposition
Supply of
available plant
nutrients in soil
Weathering
of rock
Nutrient removal
with harvest
Absorption of nutrients
by roots
Nutrient loss
by bacterial
processes
such as
conversion
of nitrates to
nitrogen gas
Figure 10-14
Page 214
Nitrogen fixing
by bacteria
Nutrient loss
from soil erosion
Slide 18
Soil Profiles for Different Biomes
Soil Profiles for Different Biomes
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)
Figure 10-15 (2)
Page 215
Slide 20
Soil Properties
 Infiltration: When water percolates downward
through the soil through the pores.
 Leaching: During the percolation the water
dissolves various soil components in the upper
layers and carries them to the lower layers.
Soil Properties
 Texture: the relative amounts and types of mineral
particles. (clay, silt, sand, and gravel)
 Loams: are a roughly equal mixture of all the
above.
 Structure: ways soil particles are organized and
clumped together.
Fig. 10-16
p. 216
100%clay
0
80
20
Increasing
percentage clay
Increasing
percentage silt
60
40
40
60
20
80
0
100%sand
80
60
40
20
Increasing percentage sand
100%silt
Soil Properties
 Porosity: determined by soil texture, it measures
the volume of pores or spaces per volume of soil
and the average distances between those spaces.
 Permeability: the rate at which water an d air
move from upper to lower soil layers. Influenced by
the average size of the pores and the soil structure.
 pH: Measures alkalinity or acidity of soil and
influences the uptake of nutrients by plants. To
correct soil that is too acidic, add lime. When too
alkaline add sulfur.
Fig. 10-17 p. 217
Water
High permeability
Water
Low permeability
Table 10-1 p. 216
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
Soils: Erosion
Sheet erosion: occurs when water moves
down a slope or across a field in a wide flow and
peels off fairly uniform sheets or layers of soil.
Rill erosion: occurs when surface water forms
fast-flowing rivulets that cut small channels in the
soil.
Gully erosion: when rivulets of fast-flowing
water join together and with each succeeding rain
cut the channels wider.
See Fig. 10-18 p. 217
Harmful effects of Soil Erosion
• Loss of soil fertility and its ability to hold
water
• Runoff of sediment that pollutes water, kills
fish and shellfish, clogs irrigation ditches,
boat channels, reservoirs, and lakes.
• Soil is a renewable resource because natural
processes regenerate it; however, we use it
or degrade it faster than it naturally
regenerates (in tropical soil it may take 2001,000 years) therefore making it a
nonrenewable resource.
How Serious Is the Problem of Soil
Erosion?
• Causes loss of soil organic matter and vital plant
nutrients
• Reduced ability to store water for use by crops
• Increased use of costly fertilizer to maintain soil
fertility
• Increased water runoff on eroded mountain slopes
that can flood agricultural land and dwellings in the
valleys below
• Increased buildup of soil sediment in waterways and
coastal areas that reduce fish production and harms
other aquatic life
• Increased input of sediment into reservoirs
Global Soil Erosion
Areas of serious concern
Fig. 10-19 p. 218
Areas of some concern
Stable or nonvegetative areas
Dust Bowl
Kansas
Colorado
Dust
Bowl
Oklahoma
New Mexico
Texas
MEXICO
In-text figure
Page 219
Slide 25
Soil Erosion in the U.S.
• Erosion in the U.S. has been a major concern for
years as the farmers plowed over the fields every
year at harvest and left it bare for a long period of
time allowing it to be eroded mainly by wind.
• Since the great Dust Bowl of the 1930’s, caused by
a severe drought and over-plowing for years, the
development of the Soil Conservation Service ahs
made the prevention of soil erosion their top
priority. (now known as the National Resources
Conservation Service) See page 219.
Desertification: the productive potential of arid
and semiarid land falls below 10% or more due to a
combination of factors.
 Salinization: Excess buildup of salts from over
irrigation. Causes stunted plant growth, lower crop
yields, and eventually kill the plant and ruins the
land.
 Waterlogging: Large amounts of irrigation water
are used to leach salts deeper into the soil.
However many times the soil doesn’t have good
drainage and there is an accumulation of water as
the water table rises. The roots get enveloped in
water and lower their productivity and killing them
after prolonged exposure.
Evaporation
Evaporation
Transpiration
Waterlogging
Fig. 10-22 p. 221
Less permeable
clay layer
Solutions: Soil Conservation
 Soil Conservation: reducing soil erosion and
restoring soil fertility. Most often done by
keeping the soil covered.
 Conventional-tillage: Soil is plowed in the fall
and left bare through winter and early spring and
vulnerable to erosion
 Conservation tillage: disturb soil as little as
possible while planting crops.
Minimum tillage and no-till farming allow for the
land to remain with crops residues and cover
vegetation without disturbing the topsoil.
Solutions: Soil Conservation
Cropping methods: various cropping
methods are used to reduce erosion, largely by
working with the land and protecting the removal
of topsoil. Include: terracing, contour planting,
strip cropping, alley cropping, windbreaks, and
gully reclamation.
 Land Classification: classify the land to identify
whether it is suitable for cultivation.
Advantages and Disadvantages
of Conservation Tillage
Figure 10-26a
Page 224
Terracing
Contour planting and strip cropping
Slide 32
Figure 10-26b
Page 224
Slide 33
Additional Soil Conservation Cropping Methods
Windbreaks
Alley cropping
Figure 10-26c
Page 224
Figure 10-26d
Page 224
Slide 34
Slide 35
Soil Restoration
 Organic fertilizer: plant and animal waste
 Animal manure: from cow, goat ,chicken,
horses, etc.
 Green manure: from plant wastes
 Compost: sweet dark brown humus like
material rich in organic matter.
 Spores: spores that attach to roots to help
absorb nutrients
 Crop rotation: rotate crops that deplete soil with
those that conserve and add nutrients to the soil
Commercial inorganic fertilizer :
contain nitrogen, phosphorous and potassium.
They may contain trace amounts of other
required nutrients.
Easily transported, stored and applied. Used
extensively worldwide.
Problems:
•They don’t add humus to the soil
•Reduce soil organic matter and ability to hold water
•Lowers oxygen content and ability to take up nutrients
•Not all nutrients needed are included
•Lots of energy needed for production, transport and applica
•Increase global warming by release of N2O