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Dynamic Earth Class 9 7 February 2006 Any Questions? Note: Exam #1 Date shown on hardcopy syllabus at February 14th, but said February 15th. The correct date is February 14th (On-line version is correct) Elastic Rebound Theory Elastic Rebound Theory Seismograph Record and Pathway of Three Types of Seismic Waves World Seismicity, 1963–2000 Plate Margin Volcanism Hawaiian Volcanism Why do some volcanoes (e.g, Augustine Volcano) erupt violently whereas other volcanoes (e.g. Kilauea Volcano) erupt relatively quietly? Monday, February 06, 2006 (Associated Press) S C I E N C E: Augustine Volcano continues to erupt Augustine Volcano continued to erupt today, with the volcano producing a continuous crescent-shaped plume of steam, and ash and gas speeding down the flanks of the island mountain and into the sea. The Alaska Volcano Observatory made hourly updates on its Web site with each one beginning the same way — “Eruption is in progress.” The volcano on an uninhabited island has been erupting since Saturday, with explosions thrusting particles almost five miles into the skies around south-central Alaska. With winds shifting the ash away from major air routes, airlines cautiously resumed dozens of flights that had been canceled as a precaution. Ash particles can damage engines. Alaska Airlines on Tuesday resumed all flights to and from Kodiak Island and Anchorage, the state’s largest air hub, said spokeswoman Amanda Tobin. The airline had canceled all of its 36 Anchorage flights Monday night as a precaution. Flights to and from Kodiak had been canceled Sunday and Monday. Volcanic Hazard Augustine Earthquake Activity Extrusive Basalt Rhyolite Intrusive Gabbro Granite Classification of Igneous Rocks Determined by composition (both chemical and mineralogical): magnesium (Mg) + iron (Fe) = mafic feldspar + quartz (Si) = felsic Classification of Igneous rocks Bowen’s reaction series Series of chemical reactions that take place in silicate magmas as they cool First investigated in the 1920s and 1930s by N. L. Bowen Important experiments that help us understand the evolution of magmas Bowen’s Reaction Series Early Crystallization Fractional crystallization The modification of magma by crystallization and removal of mineral phases Because only certain elements will go into a given mineral, this will tend to change the composition of the remaining liquid Magma Differentiation Magma Chamber Beneath Midocean Spreading Ridge Where do magmas come from? Basalts: Broadly speaking, we know that mantle rocks (45% SiO2) partially melt (10 to 15%) to produce basalts (50% SiO2) Volcanism Due to Partial Melting in a Subduction Zone Where do magmas come from? With the addition of some water, basalts will partially melt to produce Andesite (60% SiO2) Factors Affecting Melting Temperatures Tectonic Settings of Igneous Activity Volcanic Island Arc, Indonesia Oceanic Hot Spot Hawaii Continental Volcanic Arc N. Cascades Tectonic Settings and Volcanic Activity Earthquake distribution defines plate boundaries December 26, 2004 Earthquake off Sumatra Earthquake Focus Subsidence in Banda Aceh Subsidence in Banda Aceh Tsunami Series of very long-wavelength waves on the ocean / “tidal wave” = Has nothing to do with tides Tsunami Generation of a Tsunami Tsunami waves Very small out in the open ocean Amplitude of only ~ 1 meter Very long wavelengths (up to 100 km) Travel very fast (as much as 500 mph) Tsunami waves When waves reach shallow water, they "feel" the shallow bottom, just like ordinary waves, and they slow down (to 20-30 mph) Because of the massive energy, this slowdown causes them to build up very high (up to 50-100 m) December 26, 2004 Tsunami in Indian Ocean Hilo: May 23, 1960 Maximum inundation in Hilo (along the Wailoa River) exceeded half a mile. Maximum wave height at Hilo was 11 m (36 ft) 61 people died. Japan: May 24, 1960, 22 hours after the earthquake (7 hours after the Hilo tragedy) The tsunami killed 200 people in Japan Hilo after 1946 tsunami Kaiaka Bay 1952 Tsunami wave passing under bridge at Haleiwa 1946 tsunami -- Hilo harbor: 159 fatalities Beach in Laie, O`ahu before tsunami generated by 1957 quake in Aleutians Runup Maximum height above sea level reached by a tsunami when it reaches shore Inundation Horizontal distance from the normal water's edge reached by a tsunami 2000 Tsunami can be generated by any process that displaces a large amount of water: Sub-sea earthquakes Giant landslides Volcanic eruptions Meteorite impacts Thursday Video: Continental Drift: Legacy of Fire