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Geological Processes
The crust and mantle
Convection cells/currents
Internal heat pushes soft rock in the asthenosphere upward. As the rock cools it then moves downward
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
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
Types of boundaries between the Earth’s platesConvergent 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
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 mountainsEx) Himalayas
Video animation
Video animation
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
Types of boundaries between the Earth’s plates
Transform plate boundaries create faults Ex) San Andreas Fault in California
Lots of earthquakes
Plate Tectonics
Subduction and earthquakes
Volcanic Eruption of Mount St. Helens
Mount St. Helens Before and After the May 18, 1980, Eruption
Composition by Volume of Good-Quality Soil
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.
Soil Profile
A Soil Profile Showing Different Horizons
Soil Texture
Soil Erosion
Soil Erosion
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
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
Protecting soil against degradation
Contour Farming—plowing furrows sideways across a hillside to help prevent formation of rills and gullies
Protecting soil against degradation
Terracing—transforms slopes into series of steps like a staircase, enabling farmers to cultivate hilly land
Protecting soil against degradation
Shelterbelts—windbreaks; rows of trees that are planted along the edges of fields to slow the wind