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 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

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

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

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