Geology and Soils

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Geology and Soils

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Geologic Processes Structure of the Earth

• Three major zones of the earth are the core,
  mantle, and crust.
• The crust is soil and rock that floats on a
  mantle of partly melted and solid rock.
• The core is intensely hot. It has a solid inner
  part surrounded by a liquid core of molten or
  semisolid material.
• The mantle is mostly solid rock, but an area
  called the asthenosphere is partly melted rock
  about the consistency of soft plastic.
• The crust is thin and is divided into the
  continental crust and the oceanic crust.

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Features of the Crust and Upper Mantle

• Two kinds of movement seem to occur in the mantle
• Convection currents move large volumes of rock
  and heat in loops within the mantle.
• Mantle plumes flow slowly upward, and when it
  reaches the top of the plume, it radiates out
  like the top of an open umbrella.

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Spreading center
Oceanic tectonic plate
Oceanic tectonic plate
Ocean trench
Collision between two continents
Plate movement
Plate movement
Tectonic plate
Oceanic crust
Oceanic crust
Subduction zone
Continental crust
Continental crust
Material cools as it reaches the outer mantle
Cold dense material falls back through mantle
Hot material rising through the mantle
Mantle convection cell
Mantle
Two plates move towards each other. One is
subducted back into the mantle on falling
convection current.
Hot outer core
Inner core
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Plate Tectonics

• About 15 rigid tectonic plates move across the
  surface of the mantle very slowly. The plates are
  about 60 miles thick and compose the lithosphere.
• The plates move at different rates. Some move
  about 1 centimeter per year, and others at the
  sea floor move as much as 18 centimeters (7
  inches) per year.
• The theory of plate tectonics became widely
  accepted in the 1960s and was developed from the
  idea of continental drift.
• The movement of these plates produces mountains
  on land and trenches on the ocean floor.
• Volcanoes and earthquakes are likely to be found
  at the plate boundaries.
• The plate tectonic theory also helps to explain
  how certain patterns of biological evolution
  occurred.

http//geology.com/plate-tectonics.shtml
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Plate Tectonics

• There are three types of boundaries for
  lithospheric plates
• Divergent boundary
• where plates move apart in opposite directions
• Convergent boundary
• where plates are pushed together by internal
  forces and one plate rides up over the other.
• Subduction zone
• A trench generally occurs at the subduction zone.
  
• Transform fault
• occurs where plates slide/grind past one another.
• The San Andreas Fault between the Pacific Plate
  and the North American Plate in California is an
  example

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San Andreas Fault
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Earths Major Tectonic Plates
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Reykjanes Ridge
EURASIAN PLATE
EURASIAN PLATE
Mid- Atlantic Ocean Ridge
ANATOLIAN PLATE
JUAN DE FUCA PLATE
NORTH AMERICAN PLATE
CARIBBEAN PLATE
CHINA SUBPLATE
Transform fault
ARABIAN PLATE
PHILIPPINE PLATE
PACIFIC PLATE
AFRICAN PLATE
COCOS PLATE
Mid- Indian Ocean Ridge
SOUTH AMERICAN PLATE
Transform fault
Carlsberg Ridge
East Pacific Rise
SOMALIAN SUBPLATE
INDIAN-AUSTRLIAN PLATE
Southeast Indian Ocean Ridge
Transform fault
Southwest Indian Ocean Ridge
ANTARCTIC PLATE
Plate motion at convergent plate boundaries
Plate motion at divergent plate boundaries
Convergent plate boundaries
http//www.nytimes.com/interactive/2011/03/11/worl
d/asia/maps-of-earthquake-and-tsunami-damage-in-ja
pan.html
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External Earth Processes

• Weathering is physical, chemical, and biological
  processes that break down rocks and minerals into
  smaller pieces.
• Mechanical weathering large rock mass is broken
  into smaller fragments.
• Frost wedging
• Chemical weathering reaction of rock material
  with oxygen, carbon dioxide and moisture in the
  atmosphere and on the ground.
• Biological weathering the conversion of rock or
  minerals into smaller particles through the
  action of living things.
• Erosion is a major external process by which
  material is dissolved, loosened, or worn away
  from one part of the earths surface and
  deposited else where.

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Natural Hazards Earthquakes

• Earthquakes occur when a part of the earths
  crust suddenly fractures, shifts to relieve
  stress, and releases energy as shock waves.
• Foreshocks may occur prior to the main shock and
  aftershocks occur up to several months after the
  main shock.
• Magnitude The energy released in the
  earthquake. Insignificant is less than 4.0 on
  the Richter scale, minor is 4.04.9, damaging is
  5.05.9, destructive is 6.06.9, major is
  7.07.9, and great is over 8.0.
• Primary effects include shaking and temporary to
  permanent displacement of the ground.
• Secondary effects include rockslides, fires, and
  flooding due to subsidence of the land.

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Natural Hazards Volcanic Eruptions

• An active volcano releases magma onto the earths
  surface. This release may be violent or quiet.
• Volcanic activity is generally concentrated in
  the same areas as seismic activity.
• Ejecta - Ash and gases may be ejected along with
  magma.
• Gases such as sulfur dioxide may remain in the
  atmosphere and cause acid rain.
• Particulate matter may remain in the atmosphere
  for up to 3 years and cause cooling of the
  atmosphere.
• Fertile soils are produced from the weathering of
  lava flows.
• Scientists are studying phenomena that precede an
  eruption to better predict their occurrence.

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Minerals and Rocks

• Mineral (diamond, quartz) - element or inorganic
  compound that is solid with a regular internal
  crystalline structure.
• Rock a solid combination of one or more
  minerals.

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ROCK TYPES

• Igneous (granite, basalt)
• formed below or on the earths surface when
  molten rock wells up and hardens.
• They form the bulk of the earths crust.
• Sedimentary (limestone, sandstone)
• formed from small, eroded pieces of rock that are
  carried to downhill sites.
• Layers accumulate over time and an increase of
  weight and pressure plus dissolved minerals bind
  the sediment particles together to form
  sedimentary rock.
• Metamorphic (marble, slate)
• produced from preexisting rock that is subjected
  to high temperatures, high pressures, chemically
  active fluids, or some combination of these.

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The rock cycle is the interaction of physical and
chemical processes that change rock from one type
to another. It is the slowest of the earths
cyclic processes.
Heat, Pressure
Heat, Pressure
Igneous Rock Granite, Pumice, Basalt
Magma (Molten Rock)
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Soils

• Origins
• Eroded rock, minerals, decaying organic matter,
  water, air, and billions of living organisms.
• Importance
• Soil provides nutrients for plant growth and is
  the earths primary filter for cleansing water
  and for decomposing and recycling biodegradable
  wastes.
• Maturity and Horizons 
• Layers of soil, called soil horizons, vary in
  number, composition, and thickness.
• Mature soils have developed over a long time, are
  arranged in soil horizons (series of horizontal
  layers), and have distinct textures and
  compositions in these layers that vary among
  different types of soils.
• Cross-sectional views of these layers are soil
  profiles.

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Soil Profiles in Different Biomes
Mosaic of closely packed pebbles, boulders
Alkaline, dark, and rich in humus
Weak humus- mineral mixture
Dry, brown to reddish-brown, with variable
accumulations of clay, calcium carbonate,
and soluble salts
Clay, calcium compounds
Desert Soil (hot, dry climate)
Grassland Soil (semiarid climate)
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Forest litter leaf mold
Acid litter and humus
Acidic light- colored humus
Humus-mineral mixture
Light-colored and acidic
Light, grayish- brown, silt loam
Iron and aluminum compounds mixed with clay
Dark brown firm clay
Humus and iron and aluminum compounds
Tropical Rain Forest Soil (humid, tropical
climate)
Deciduous Forest Soil (humid, mild climate)
Coniferous Forest Soil (humid, cold climate)
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Soils (cont.)

• The layers/horizons of mature soils have at least
  three parts.
• The top part/layer is the surface litter layer or
  O horizon. This layer is brown/black and composed
  of leaves, twigs, crop wastes, animal waste,
  fungi, and other organic material.
• The topsoil layer or A horizon is composed of
  decomposed organic matter called humus, as well
  as some inorganic mineral particles. Thick
  topsoil layers help hold water and nutrients.
• The B horizon (subsoil) and the C-horizon (parent
  material) have most of the soils inorganic
  mattersand, silt, clay, and gravel. The
  C-horizon rests on bedrock.
• Air and water fill spaces between soil particles.
  Plant roots need oxygen for aerobic respiration
• Downward movement of water through the spaces in
  the soil is infiltration. Water moving downward
  dissolves minerals and organic matter and carries
  them to lower levels this process is called
  leaching.

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Soils (cont.)

• Variations with Climate and Biomes
• Variations in Texture and Porosity
• Soil differences in texture are affected by the
  size of particles and the space between
  particles.
• Soil porosity is affected by soil texture. The
  average size of spaces or pores in soil
  determines soil permeability.

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Causes of Desertification

• Overgrazing
• Deforestation
• Erosion
• Salinization
• Soil compaction

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(a) Terracing
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(b) Contour planting and strip cropping
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(c) Alley cropping
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(d) Windbreaks
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Soil Degradation on Irrigated Land

• Salinization - Salts left behind when irrigation
  water is not absorbed into the soil can be left
  in the topsoil
• Waterlogging - occurs when saline water (from
  irrigation) envelops the deep roots of plants.
  This saline water accumulates underground and
  raises the water table.

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Reducing and Cleaning Up Salinization

• Reduce irrigation
• Switch to salt-tolerant crops
• Flush soils
• Not growing crops for 2-5 years
• Install underground drainage