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Geology and Soils

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Geology and Soils Overgrazing Deforestation Erosion Salinization Soil compaction Causes of Desertification (a) Terracing (b) Contour planting and strip cropping (c ... – PowerPoint PPT presentation

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Title: Geology and Soils


1
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
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