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Lecture 6

EESA06 Lecture 6 Notes.docx

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Environmental Science
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Lisa Tutty

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Feb 11, 2013 EESA06 Lecture 6 Notes Lecture 5  A volcano erupting is not a hazard; only when it threatens human interest is when it is a hazard  Risk is how severe an event is and the impact it will have on humans  Poor communities will be more socially vulnerable than rich communities  Disaster is within a specific geographic area (regional, national)  Catastrophe affects far beyond the area that is directly effected  The heat within the earth causes a lot of hazards at the boundaries of these plates  Magnitude 10 earthquake is very uncommon, while smaller disasters don’t happen very often  The larger the disaster, the less likely it is to happen  Different magmas have different viscosities  You get basaltic/mafic magma at a hot spot; nothing to do with the boundaries  Only reason Hawaiian islands exist is because there is a mantle plume there and it burns through the plate  The magma at the plumes is mafic (rich in iron and magnesium)  Volcanoes are also found at convergent zones when an oceanic plate is subducted, MOR, or at divergent boundaries  Big volcanoes come from subduction zones  When volcanoes explode, especially at subduction zones, they blow a lot of ash into the atmosphere  The ash goes up into the atmosphere and comes down hot and meters thick  Ash from volcano in Yellowstone National Park covered most of the United States; can go into the atmosphere and block the sunlight  Volcano eruptions send greenhouse gases and aerosols into the atmosphere  Volcanos have gases that are deadly; cling to the ground and can kill small children  Can result in earthquakes and landslides  Difference between lahar and pyroclastic flow o lahars can happen at anytime during an eruption or later, can be cold or not, and are super concentrated mudflows o pyroclastic flows can happen only during an eruption and are composed of very hot gas mixed with volcano sediments  Avalanche of St. Helens caused by pressure blowing off the side of the mountain  Types of volcanoes: o Composite volcano is built of layers of ash and lava; looks like a cone o Shield volcanoes are very large and are built of layers of lava o Cindercones are smaller and built of ash Feb 11, 2013  Most earthquakes happen at plate boundaries because that is where the friction is  Red represents shallow earthquakes  Deep earthquakes are caused by subduction  Richter scale is one of the few ways in which we measure how strong an earthquake is  Earthquake is when you get a break in the rocks and there is movement along that break; break happens along a plane  Reverse fault have forces of compressing, and hanging wall moves up instead of down  Strike-slip fault is the same as a transform fault; means two blocks are sliding past one another  Right block is coming towards you so it is a right lateral fault  Rocks are breaking because stress is built up; forces have been acting on them for a while and you get movement along that break forming an earthquake  Earthquakes have certain hazards, such as ground shaking which can liquefy the sediment; can cause landslides, result in fires and tsunamis 
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