Exam covers Oceans The Sea oor Beaches Coasts Plate Tectonics Volcanoes Earthquakes The History of how the theory of plate tectonics came to be Early Theory Pre continental drift Alfred Wegener continents stationary ocean oor is all very old All continents seem to t together like a jigsaw Plate Tectonic theory resulted from post WW2 Era Two important Data Sets As a result of WW2 1 Global Mapping most EQ s occur in distinct zones and many occur on the sea oor Ocean 2 Record of Earth Magnetic Field Paleomagnetism The Three types of plate boundaries 1 Divergent Ocean Ocean Divergence MORs or Continent Continent divergence rift zone oor EQ s occur in areas with distinct features rift zones many volcanoes in the area Basaltic Mild Eruptions Area of Killer Lakes 2 Convergent Continent Ocean Collision Ocean crust subducts underneath continental crust because friction causes partial melting rising magma creates volcanoes as part of the magmatic arc Trenches and volcanic belts Continent Continent Collision The end result of an entire ocean plate being subducted Continental crust will not follow into the subduction zone the two pieces of continental crust will become welded together in a suture zone old site of subduction Mountain Building Ex The Himalayas Ocean Ocean Collision One oceanic plate moves underneath another Partial melting at depth causes magma to rise and creates island arcs a string of islands that runs parallel to the trench Angle of subjecting plate determines distance from islands to trench Trenches and Volcanic Island Arc Ex The Aleutian Islands Alaska 3 Transform Plates move past each other aren t moving towards or away from each other Conservative crust isn t created or destroyed Commonly connect large divergent convergent features create a zig zag pattern Geologic Features you would nd at each plate boundary and why those features exist Divergent Boundaries MORs plates created shallow EQs rifting new oceans form volcanoes sea oor spreading Convergent Boundaries trenches plate destroyed via subduction volcanic belts arcs subduction zone deep EQ s accretionary prism volcanoes mt building Transform Boundaries MORs EQs conservative not gaining or loosing Where do you nd deep EQ s Shallow EQ s Mid ocean Ridge MOR EQ s occur at shallow depths 10km caused by rocks pulling apart Trench EQ s occur at shallow deep depths deepest depths at farther distances from trench caused by rocks coming together EQ s in linear features cutting across MOR s occur at shallow depths caused by rocks moving past each other Difference between hot spot Volcanoes and volcanoes formed at plate boundaries Hot Spots a mantle plume that causes volcanism in a stationary location regardless of plate movement Hotspot leaves a line of volcanoes on the crust as the plate moves above the hotspot Volcanoes created by the hotspots can be dated and rate and direction of plate movement determined Oceanic Hotspots Ex emperor seamount Hawaiian island chain Continental Hotspot Ex yellowstone Volcanoes created at Ocean Ocean Convergent Boundaries Partial melting at depth causes magma to rise and creates island arc Volcanoes created at Continent Ocean Convergent Boundaries Friction caused partial melting and the arising magma creates volcanoes as part of the magmatic arc Sea Floor Spreading occurs at MORs as the plates diverge hot molten rock comes up to the surface to make new crust Sea oor is expanding but the size of the crust is not because of the subduction zone crust get sucked back down towards the mantle Viscosity how it effects lava composition and how explosive of an eruption you get Viscosity resistance to ow Higher viscosity slow peanut butter Lower Viscosity faster water Low Viscosity Lava easily releases gases and rarely pyroclastic higher lava temperature basaltic quiet eruptions High Viscosity Lava clogs gas and forms vesicles usually pyroclastic and explosive higher silica content more so felsic rocks higher amount of gas dissolved in magma andesitic explosive eruptions What determines different properties of Lava how much quartz is in it temperature gases and viscosity Different Volcanic Products Lava molten rock outside of Earth primarily of basaltic composition Gases water vapor most common gas released expanding gases propel pyroclastic material high into atmosphere column rising from volcano more gas more pyroclastic material Pyroclastic Flows mixture of gas and pyroclastic debris violently expelled from a volcano during an eruption common in andesitic type eruptions Lahars a mud or debris ow slurry of pyroclastic material water and rock Plateau Basalts very large stretches of land or ocean oor of basaltic lava resulting from quiet eruptions least violent eruptions crack in the earth Columnar Jointing series of polygonal columns usually 5 or 6 sided and forms due to the contraction of lava during cooling Also commonly due to water quenching Pillow Basalts extruded basalt on the sea oor that cools into semi spherical pillows As hot lava contacts cool water it quenches and then extends further again and again This is common as oceanic hotspots and MORs Characteristics of different types of volcanoes 1 Composite Volcano Stratovolcano alternating layers of pyroclastic and lava ows andesitic in composition steepness increased by pyroclast attened by lava ows Lava ows protect loose pyroclast less erosion Short eruptions 2 Cinder Cone Volcano Constructed of pyroclastic material ejected from central vent no lava ows typically ma c or intermediate pyroclasts much smaller than shield volcanoes short life span because the gases burn out and because it has loose pyroclasts rapid erosion 3 Shield Volcano broad gently sloping at dome shield low viscosity lava frequent daily eruptions ex Hawaiian Islands Activity is predictable low risk commonly have spatter cones small steep cones surrounding a vent caused by belching small amounts of gas High quartz violent eruption volcanoes andesitic volcanoes Volcanic Eruptions Mt Tambora caused the year without a summer Krakatoa blew apart an Island lowered global temperatures Mt St Helens composite volcano explosive history more quartz Mt Vesuvius buried cities of Pompeii and Herculaneum two day eruption happened long time ago Icelandic Volcano put a ton of ash in the air and stopped air travel in Europe for ve days Tsunami Boxing day Indian Ocean 1500X more powerful than a nuclear bomb did not have tsunami warning systems Japanese walls were not high enough and