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