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Geological Processes
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The crust and mantle
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Convection cells/currents Internal heat pushes soft rock in the asthenosphere upward. As the rock cools it then moves downward
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Types of boundaries between the Earth’s plates Divergent Plate Boundary Plates move in opposite directions Magma rises, filling the crack creating new crust Block between the fault cracks and drops into athenosphere. Video animation
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Types of boundaries between the Earth’s plates Divergent plate boundaries create rift valleys and oceanic ridges Ex) the Great Rift Valley Most volcanic activity happens along mid- ocean ridges
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Types of boundaries between the Earth’s plates Convergent Plate Boundary Plates crash together Subduction: Continental plate rides over the oceanic plate. Over time the subducted plate will melt and rise as molten rock or magma Trench forms at the boundary Video animation
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Types of boundaries between the Earth’s plates Convergent collisions: 1.Ocean and ocean: ocean shrinks and islands are created 2.Continent and continent: creates mountains Ex) Himalayas Video animation
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Types of boundaries between the Earth’s plates Transform Fault Boundary Plate slide and grind past one another along a fault (fracture) in the lithosphere Mostly under- water
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Types of boundaries between the Earth’s plates Transform plate boundaries create faults Ex) San Andreas Fault in California Lots of earthquakes
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Plate Tectonics
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Subduction and earthquakes
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Volcanic Eruption of Mount St. Helens
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Mount St. Helens Before and After the May 18, 1980, Eruption
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Composition by Volume of Good-Quality Soil
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Soil Profile Soil varies in composition, texture, structure, and color at different depths. Soil horizons are zones or layers of soil. A soil profile is a vertical section through all the soil horizons.
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Soil Profile
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A Soil Profile Showing Different Horizons
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Soil Texture
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Soil Erosion
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Protecting soil against degradation Reduced tillage—low disturbance to topsoil when planting seeds Uses special machinery Nearly ½ of US acreage is farmed this way
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Protecting soil against degradation Crop rotation—the practice of alternating the kind of crop grown in a particular field from one season or year to the next
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Protecting soil against degradation Contour Farming—plowing furrows sideways across a hillside to help prevent formation of rills and gullies
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Protecting soil against degradation Terracing—transforms slopes into series of steps like a staircase, enabling farmers to cultivate hilly land
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Protecting soil against degradation Shelterbelts—windbreaks; rows of trees that are planted along the edges of fields to slow the wind
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