Geol. 105 Notes 5

Geol. 105 Notes 5 - -tsunami: used to be called tidal...

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-tsunami: used to be called tidal waves, but they have nothing to do w / tides -biggest tsunamis occur b /c of subduction zone activity, where the subducting plate buckles, and energy is released upward into water, as wave hits coast all of the energy is compressed, leading to tsunami -as wave hits shallow water, its height rises dramatically to compensate (all of energy is still present at this point), resulting in floods -velocity of wave: -C=velocity, g=gravity, D=depth -C=square root (gD) -tsunami deposits are left after the event, they allow scientists to measure when and where tsunamis occurred in the past -most tsunami occur in the Pacific Ocean (Ring of Fire) -Hilo-tsunamis in 1946, 1960 (after 9.5 Chile earthquake) -tsunami typically associated w / earthquakes, but also occur do to landslides, collapsing of volcanoes (Krakatau) -Northern Sumatra (Sunday, Dec. 26, 2004)-magnitude 9.0 earthquake in northern part of Sumatra, 283100 people killed, 1126900 displaced by earthquake and tsunami; IX Mercalli in Banda Aceh -can a tsunami occur in the Atlantic Ocean?: yes, Canary Islands due to volcanic collapse -volcanic eruptions: plate tectonics and magmas -where we have volcanoes: spreading centers (basaltic), subduction zones (explosive eruptions-Ring of Fire), hot spots -subduction zone volcanoes: -subducting plates absorb water, when they subduct the water goes into the mantel and lowers the melting temp. of the mantel, this melted rock rises, leads to eruptions -potentially active volcanoes of western US-located along the Cascade Mountains in northwest -hot spots-heat source located in the mantel?, burns hole in plates (oceanic or continental); hot spot is a fixed location, while the plates move over the hot spots -common elements in earth’s crust: oxygen (45.20%), silicon (27.20 %), aluminum, iron, calcium, magnesium, sodium, potassium, titanium, hydrogen, phosphorus, manganese -much more silicon in continental crust than in oceanic crust (continental has 30-70 km thickness, oceanic crust is less) -igneous rock types: -extrusive-lava, extruded at the surface -intrusive-granite, intruded in crust or lithosphere
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-types volcanic rock- SiO2 less than 55% (basalt), SiO2 55 /65% (adesite), SiO2 greater than 65% (rhyolite); another type, dacite, is located between andesite and rhyolite -types plutonic rock-gabbro (less than 55%), diorite (between 55 /65%), granite (greater than 65%) -types of magma: felsic=high silicon (rhyolite, granite), intermediate=middle amounts
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Geol. 105 Notes 5 - -tsunami: used to be called tidal...

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