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Why the Earth quakes and moves THE UNIMAGINABLE forces be hind earthquakes and volcanoes are no secret Yet the notion that these forces cause whole continents to move is barely as old as the Beatles. In the 19605, the process known as plate tectonics became clear when re searchers were mapping the deep sea in detail. They realized the ocean floors were spreading apart along mid-ocean ridges, where upwelling magma con stantly created new material; in other places the continents were slowly col liding. In essence, the map was moving. Seven major plates and many smaller ones make up the lithosphere, the outer surface of the Earth that’s up to 155 miles thick in some parts. Those enor mous plates slide over a layer of molten rock, the asthenosphere, at the blistering rate of 0.5 to 4 inches per year. The San Andreas fault, where the Pa cific and North American plates scrape crossways, BIG MELT: Cascades of lava create a variety of new landforms. is a lively example of a “transform bound ary.” Eviction can cause stress to build up until it releases all at once in an earth quake, like the one that hit the San FVan cisco Bay area in 1989, causing 62 deaths and an estimated $6 billion in damage. The Himalayas are the most dramatic illustration of a “convergent boundary,” a slow-motion pileup of continental and oceanic plates. Incredible forces have lifted the world’s tallest mountain range as the Indian plate grinds under the Eur asian plate like a shoe under a rug. Con vergence often creates volcanoes such as those in the Andes. The result is our puzzle-piece map of the world, left ova* from the splitting up of the supercontinent of Pangea about 200 million years ago. ca Julian Smith USA WEEKEND-Sept. 14-16,2007 Gfada' FRANCESCO RUGGER! GETTY IMAGES Smells like the real thing . Now made with essential oils extracted fresh from nature. 9 —\ \ IS m ) ; *• SCENTEDOIL^I ««j. ~ m / e#sential ’ M Jjl 4 rose (^Johnson 2007 S.C Jofwson & Sop Inc. AT icshts re