Chapter 10: Geology Processes, Hazards, and Soil

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Chapter 10 GeologyProcesses, Hazards, and Soil
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Three Major Zones of the Earths Structure

• Core innermost layer has a solid inner part
  surrounded by a liquid core of molten material.
• Mantle middle layer, a thick solid zone that
  surrounds the earths core. Most of the mantle is
  solid, but under the outermost part is a zone of
  hot, melted rock that flows like soft plastic
  asthenosphere
• Crust
• Continental Crust underlies the continents
• Oceanic Crust which underlies the ocean basins

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Internal Processes

• The inside of the earth is constantly changing by
  geologic processes most take thousands to
  millions of years.
• Internal Processes- geologic changes originating
  from the earths interior they build on the
  planets surface
• Heat provides energy gravity also plays a role.
• Residual heat from earths formation is still
  being given off as the interior core cools and
  the outer core cools and solidifies.
• Decay of radioactive elements in the crust adds
  to the heat flow from within.
• The internal heat within the earths core causes
  the mantle to deform and flow slowly.
• Convection Cells where large volumes of heated
  rock move (resembles convection in the
  atmosphere)
• Mantle Plumes where mantle rock flows slowly
  upward in a column and then moves out in a radial
  pattern in all directions.

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Tectonics Plates

• Convection currents and mantle plumes move upward
  as the headed material is displaced by cooler,
  denser material sinking under the influence of
  gravity
• The energy and heated material cause the movement
  of the tectonic plates.
• Tectonic Plates rigid plates about 100 km
  thick composed of the continental and oceanic
  crust and the outermost part of the mantle ? All
  parts called the lithosphere
• Plates move constantly
• Some plates move faster than others

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Theory of Plate Tectonics

• Plate Tectonics the theory explaining the
  movement of the plates and the processes that
  occur at their boundaries
• Developed from the theory of continental drift -
  throughout earths history, continents have split
  and joined as plates have drifted thousands of km
  back and forth across the planets surface
• Creates mountains, the oceanic ridge system,
  trenches, and other features
• Causes volcanoes and earthquakes
• Concentrate many minerals we extract and use
• Also explains certain patterns of biological
  evolution we can trace life-forms that migrated
  from one area to another

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Plate Boundaries

• Divergent Plate Boundaries plates move in
  opposite directions (divide)
• Convergent Plate Boundaries plates are pushed
  together (collide)
• Subduction carries the oceanic lithosphere
  downward into the subduction zone. A trench forms
  at the boundary between the two converging plates
  
• Stresses in the plate undergoing subduction
  causes earthquakes
• Transform Plate Boundaries occur where plates
  slide past one another along a fracture (fault)
  in the lithosphere most transform faults are on
  the ocean floor.

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External Processes

• External Processes geological changes based
  directly or indirectly on energy from the sun and
  on gravity
• Erosion - the process by which material is 1)
  dissolved, loosened, or worn away from part of
  the earths surface and 2) deposited in other
  places.
• Streams are the most important agent of erosion
  produce valley, canyons, and deltas
• Weathering caused by mechanical or chemical
  processes usually produces loosened material that
  can be eroded.
• Mechanical weathering in which a large rock
  mass is broken into smaller fragments frost
  wedging is when water collects in pores and
  cracks of rock, expands upon freezing, and splits
  off pieces of the rock.
• Chemical weathering in which one or more
  chemical reactions decompose a mass or rock
  usually a reaction of rock material with oxygen,
  carbon dioxide, and moisture in the atmosphere
  and the ground.

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Minerals, Rocks, and the Rock Cycle

• Mineral an element or inorganic compound that
  occurs naturally and is solid. Most minerals
  occur as inorganic compounds composed of various
  combinations of elements.
• Rock any material that makes up a large,
  natural, continuous part of the earths crust
  some contain only one mineral, but most consist
  or two or more minerals.
• Rocks are constantly exposed to various physical
  and chemical conditions that change them over
  time.
• Rock Cycle the interaction of processes that
  change rocks from one type to another

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Three Major Rock Types

• Igneous
• Sedimentary
• Metamorphic

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Igneous Rock

• Igneous Rock formed below or on the earths
  surface when molten rock material (magma) wells
  up from the earths upper mantle or deep crust,
  cools, and hardens into rock.
• Granite formed underground, Lava rock
• Forms the bulk of earths crust
• Source of many nonfuel mineral resources

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Sedimentary Rock

• Sedimentary Rock formed from sediment when
  preexisting rocks are weathered and eroded into
  small pieces, transported from their sources, and
  deposited in a body of water
• Sandstone and Shale from deposited layers of
  sediment
• Dolomite and Limestone formed from the compacted
  shells, skeletons, and other remains of dead
  organisms
• Lignite and Bituminous coal formed from plant
  remains.

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Metamorphic Rock

• Metamorphic rock produced when a preexisting
  rock is subjected to high temperatures (which may
  cause it to melt partially), high pressures,
  chemically active fluids, or a combination of
  agents
• Anthracite form of coal
• Slate
• Marble

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Earthquakes

• Fault fracture in the earths crust
• Earthquakes are caused by the faulting or the
  abrupt movement on a fault.
• Energy is released as shock waves, which move
  outward form the earthquakes focus the point
  of initial movement
• Epicenter is the point on the surface directly
  above the focus
• Magnitude used to measure the severity of an
  earthquake
• Measures the amount of energy released in an
  earthquake as indicated by the size of vibrations
  when they reach the seismograph.
• Each unit represents an amplitude that is 10
  times greater than the next smaller unit.

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More About Earthquakes

• Aftershocks gradually decrease in frequency
  over a period of up to several months
• Foreshocks can happen from seconds to weeks
  before the main shock
• Earthquakes cause
• Shaking
• Permanent displacement of the ground
• Rock slides
• Urban fires
• Flooding
• Tsunamis

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Reducing Earthquake Hazards

• Examine historical records and make geological
  measurements to locate active fault zones
• Make maps showing high-risk areas
• Establish building codes that regulate the
  placement and design of buildings
• Predicting when and where earthquakes will occur

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Volcanoes

• Volcano occurs where magma, molten rock,
  reaches the earths surface through a central
  vent or a long crack
• Can release debris ranging from large chucks of
  lava rock to ash
• Liquid lava
• Gases into the environment Sulfur dioxide can
  remain in the atmosphere for up to three years.
• Volcanic activity is concentrated in the same
  areas as earthquakes
• Creates highly fertile soil produced by the
  weathering of lava

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Reducing Volcano Hazards

• Land use planning
• Better predictions of volcanic eruptions
• Effective evacuation plans
• Studying phenomena that precede an eruption
• Tilting or swelling of the cone
• Changes in magnetic and thermal properties of the
  volcano
• Changes in gas composition
• Increased seismic activity

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Soil Basics

• Soil a complex mixture of eroded rock, mineral
  nutrients, decaying organic matter, water, air,
  and billions of living organisms, most of them
  microscopic decomposers
• Renewable resource produced very slowly by
• Weathering rock
• Deposit of sediments by erosion
• Decomposition of organic matter in dead organisms
  
• Soil Horizons a series of zones each with a
  distinct texture and composition
• Most mature soils have at least three of the
  possible horizons

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Soil Basics - Continued

• Soil Profile a cross-sectional view of the
  horizons in a soil
• Thick topsoil layer with lots of humus a
  fertile soil that produces high crop yields
• The roots of most plants and most of a soils
  organic matter are concentrated in these two
  upper layers
• As long as vegetation anchors theses layers, soil
  stores water and releases it in a nourishing
  trickle or a devastating flood
• Infiltration the downward movement of water
  through soil
• Water seeps down and dissolves various soil
  components in the upper layers and carries them
  to lower layers in a process called leaching

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Soil Horizons

• Surface Litter Layer O Horizon
• Freshly fallen and partially decomposed leaves,
  twigs, animal waste, fungi, organic materials
• Topsoil Layer - A Horizon
• Porous mixture usually darker and looser than
  deeper layers
• Partially decomposed organic matter called
  hummus
• Some inorganic mineral particles
• Recycled by bacteria and other microorganisms
  break down some complex organic compounds into
  simpler inorganic compounds soluble in water.
• Soil moisture carries these nutrients into the
  roots of plants and transported through stems and
  into leaves
• Dark brown or black topsoil nitrogen-rich and
  high in organic matter
• Gray, bright yellow, or red topsoils - low in
  organic matter and need nitrogen enrichment to
  support most crops

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Soil Horizons (continued)

• Subsoil - B Horizon contains most of the soils
  inorganic matter, mostly broken-down rock
  consisting of varying mixtures of sand, silt,
  clay, and gravel
• Parent Material C Horizon lies on a base of
  unweathered parent rock called bedrock
• Two top layers of most well-developed soils teem
  with bacteria, fungi, earthworks, and small
  insects

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Differences Between Soils

• Soils can vary in their content of
• Clay (very fine particles)
• Silt (fine particles)
• Sand (medium-size particles)
• Gravel (coarse to very-coarse particles)
• The amounts of the different sizes and types of
  mineral particles determine the soil texture
• Loams soils with roughly equal mixtures of
  clay, sand, silt, and humus
• The best soils for growing most crops because
  they hold lots of water, but not too tightly for
  plant roots to absorb

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Soil Measurements

• Soil Porosity a measure of the volume of pores
  of spaces per volume of soil and of the average
  distances between those spaces
• Porous soil has many pores and can hold more
  water and air
• Soil Permeability the average size of the
  spaces or pores in a soil determines
  permeability the rate at which water and air
  move from upper to lower soil layers
• Soil Structure the ways in which soil particles
  are organized and clumped together.
• Soil Acidity or Alkalinity pH influences the
  uptake of soil nutrients by plants

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Soil Erosion

• Soil Erosion the movement of soil components,
  especially surface litter and topsoil, from one
  place to another.
• Causes the buildup of sediments and sedimentary
  rock on land and in bodies of water
• Two main agents Flowing water and wind
• Some is natural and some is caused by human
  activities
• Roots of plants help anchor the soil
• Farming, logging, construction, overgrazing by
  livestock, off road vehicles, burning vegetation,
  and other activities can destroy plant cover and
  leave soil vulnerable to erosion.

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Types of Water Erosion

• Three types of water erosion
• Sheet erosion occurs when surface water moves
  down a slope or across a filed in a wide flow and
  peels off 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 occurs when rivulets of
  fast-flowing water join together with each
  succeeding rain cut the channels wider and deeper
  until they become ditches or gullies
• Two harmful effects of soil erosion
• Loss of soil fertility and its ability to hold
  water
• Runoff of sediment that pollutes water, kills
  fish, and clogs irrigation ditches, boat
  channels, reservoirs, and lakes

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How Serious is Global Erosion?

• Top soil is eroding faster than it forms on about
  38 of the worlds croplands
• 17 of the worlds land was degraded by soil
  erosion
• NW China a combination of overplowing and
  overgrazing is causing massive wind erosion of
  topsoil
• Creates dust plumes of eroded soil which block
  out the sun and reduce visibility in Chinas
  northeastern cities and reduce visibility and
  increase air pollution
• Nearly 40 of the land used for agriculture is
  seriously degraded by erosion, salt buildup, and
  waterlogging
• Soil degradation has reduced food production on
  about 16 of the worlds cropland

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Economic and Ecological Effects of Soil Erosion

• 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
  fertility
• Increased water runoff on eroded mountain slopes
• Increased soil sediment in navigable waterways
  decreases fish production and harms other forms
  of wildlife
• Increased input of sediment into reservoirs

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Soil Erosion in the U.S.

• 1/3 of the nations original prime topsoil has
  been washed or blown into streams, lakes, and
  oceans as a result of overcultivation,
  overgrazing, and deforestation.
• Soil is eroding 16x faster than it can form.
• Great Plains has lost 1/3 of its topsoil in 150
  years
• Soil erosion decreased by 40 between 1985 and
  1997 soil erosion costs 3.4 million per hour

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Desertification

• Desertification the productive potential of
  arid or semiarid land falls by 10 of more
  because of
• Natural climate change than causes prolonged
  drought
• Human wasting or degrading of topsoil
• About 40 of the worlds land and 70 of all dry
  lands is suffering from desertification
• Threatens the livelihoods of at least 135 million
  people in 100 countries and causes economic
  losses of 42 billion per year
• Ways to slow desertification
• Reduce overgrazing
• Reduce deforestation
• Reduce destructive forms of planting, irrigation,
  and mining
• Plant trees and grasses that will anchor the
  soil, hold water, and reduce global warming

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Salinization and Waterlogging

• 17 of the worlds cropland that is irrigated
  produces 40 of the worlds food
• Irrigated land can produce crop yields two to
  three times greater than those from rain
  watering.
• Irrigation water is a dilute solution of various
  salts, and too much salt can be toxic
• Irrigation water not absorbed into the soil
  evaporates leaves behind a thin crust of
  dissolved salts in the topsoil salinization
  the accumulation of salts
• Can stunt crop growth
• Lower crop yields
• Eventually kills plants and ruin the lands
• Waterlogging supplying large amounts of
  irrigation water to leach salts deeper into the
  soil
• Water accumulates underground
• Gradually raises the water table

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Soil Conservation

• Soil Conservation involves reducing soil
  erosion and restoring soil fertility
• Conventional-tillage Farming farmers plow the
  land and then break up and smooth the soil to
  make a planting surface
• Conservation-tillage Farming minimum-tillage or
  no-till farming
• Goal is to disturb the soil as little as possible
  while planting crops.
• Minimum break up and loosen the subsurface soil
  without turning over the topsoil, previous crop
  residues, and any cover vegetation.
• No-Till Farming special machines inject seeds,
  fertilizers, and weed kills into slits make in
  the unplowed soil.

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Methods to Reduce Soil Erosion

• Terracing can reduce soil erosion on steep
  slopes by converting the land is a series of
  broad, nearly level terraces that run across that
  land contour
• Retains water for crops at each level
• Reduces soil erosion by controlling runoff
• Contour Farming involves plowing and planting
  crops in rows across the contour of gently sloped
  land
• Each row acts as a small dam to help hold soil
  and slow water runoff
• Strip Cropping involves planting alternating
  strips of a row crop and another crop that
  completely covers the soil - the cover strip
  traps soil that erodes from the row crop, catches
  and reduces water runoff, and helps prevent the
  spread of pests and plant diseases

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Methods to Reduce Soil Erosion

• Alley Croping Agroforestry in which several
  crops are planted together in strips or alleys
  between trees and shrubs
• Windbreaks or Shelterbelts of trees
• Can reduce wind erosion
• Help retain soil moisture
• Supply some wood for fuel
• Provide habitats for birds, pest-eating and
  pollinating insects, and other animals.
• Gully Reclamation involves restoring severely
  eroded bare land by planting fast-growing shrubs,
  vines, and trees to stabilize the soil, building
  small dams at the bottoms of gullies to collect
  silt and gradually fill the channels, and
  building channels to divert water from the gully
• Land Classification can be used to identify
  easily erodible land that should be neither
  planted in crops nor cleared of vegetation

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Maintaining and Restoring Soil Fertility

• Organic Fertilizers from plant and animal
  materials
• Animal manure
• Green manure
• Compost
• Spores of mushrooms, puffballs, and truffles
• Commercial Inorganic Fertilizers produced from
  various minerals
• Crop Rotation planting areas or strips with
  nutrient depleting crops on year the next year
  with legumes
• Reduces erosion by keeping the soil covered with
  vegetations
• Helps reduce crop losses to insects by presenting
  them with a changing target.

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Inorganic Fertilizers

• Commercial Inorganic Fertilizers Contain
• Nitrogen, phosphorus, potassium
• Other plant nutrients in trace amounts
• Easily transported, stored, and applied
• Disadvantages
• Doesnt add humus to the soil
• Reduce the soils content of organic mater, so it
  reduces its ability to hold water
• Lowers the oxygen content of the soil
• Supplies only 2 3 of the 20 or so nutrients
  needed by plants
• Requires large amounts of energy to produce,
  transport, and apply
• Releases Nitrous oxide, a greenhouse gas that can
  enhance global warming from the soil
• Can cause water pollution cause cultural
  eutrophication causing algae blooms that use up
  oxygen dissolved in the water
• Rain water seeping through the soil can leach
  nitrates in commercial fertilizers into
  groundwater