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“Our” Earth Plate Tectonics • Tectonic plates – large pieces of the crust and part of the mantle called the lithosphere • seven very large ones and lots of small ones • constantly moving/floating (116cm/year) on the plastic part of the mantle because of convection currents in the soft rock underneath them –this is called continental drift Plate Boundaries • Divergent boundaries – plates move apart – Mid-ocean ridges are mountains created by the rising lava • Divergent Boundary Mid-ocean ridges • Convergent boundaries – plates come together – can develop chains of volcanoes, mountains, and earthquakes • Continental Drift - Tetrionic Plates – subduction is where the denser plate dives under another • Juan de Fuca plate is diving under the North American plate (this is not good) • Animation of Earthquake and Tsunami in Sumatra • Stuck in tsunami For most recent EQ -- http://www.pnsn.org/recenteqs/latest.htm Earthquakes • energy is released as plates slip along a fault line • the focus is where the slippage occurs • the epicenter is the point on the surface above the focus • measured using the Richter Scale • each number increased on the scale is about 10 times the amount of ground shaking and 30 times more energy - the building can withstand winds and typhoons of up to 200km/h (with the top swaying by a maximum of 75cm/0.3inches) and earthquakes of up to 7 on the Richter scale; Built to withstand 200 mph winds and an earthquake of up to 9.5 magnitude. Earthquake Waves • Primary / Longitudinal / P waves – fastest waves – travel out in all directions from the epicenter – compress the earth’s crust • Secondary / Transverse / S waves – slower than P waves – travel up and down – travel out in all directions from the epicenter • Surface waves: – move only across the earth’s surface – causes the most damage because of a circular motion caused by up and down AND back and forth motion Weathering and Erosion - breaking rocks apart • Physical (mechanical) weathering – glaciers moving, water (ice) expanding, wind, and plant roots – erosion: wind and water can loosen and move sediment – deposition: the sediment then builds up somewhere else • Chemical weathering – O, H2O, and CO2 chemically react with many minerals forming new compounds