Earthquake Facts - Working Page

Plate Tectonics

There are six major plates, named for the continents embedded within them, such as the North American, African, and Antarctic plates and dozens of smaller, or minor, plates. The plates make up Earth's outer shell, called the lithosphere. Churning currents in the molten rocks below propel them along like a jumble of conveyor belts. The movement of the plates creates three types of tectonic boundaries: convergent, where plates move into one another; divergent, where plates move apart; and transform, where plates move sideways in relation to each other.

Convergent Boundaries
Where plates serving landmasses collide, the crust crumples and buckles into mountain ranges. India and Asia crashed about 55 million years ago, slowly giving rise to the Himalaya

Divergent Boundaries
In the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates. Mountains and volcanoes rise along the seam
On land, giant troughs such as the Great Rift Valley in Africa form where plates are tugged apart.

Transform Boundaries
The San Andreas Fault in California is an example of a transform boundary, where two plates grind past each other along what are called strike-slip faults

24/3/10 More coming later