Plate Tectonics

The Earth's surface comprises a series of thin plates floating on a semi-liquid mantle. At plate boundaries, separation (indicated by large red arrows) allows new crustal material to emerge (as in the Mid-Atlantic Ridge). Where plates move together, typically the edge of one plate will slide under another (subduction zones, indicated by small red arrowheads), resulting in areas of volcanic (as in the "Ring of Fire" around the Pacific Plate) and earthquake activity (as in the Pacific Northwest). [Some scientists predict that the next major earthquake in California may cause everything east of the San Andreas Fault to fall into the Atlantic Ocean].