GEOL 106 March 1 Lecture.docx

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Queen's University
Geological Sciences and Geological Engineering
GEOL 106
John Hanes

GEOL 106 – March 1, 2013 Transform fault margins under water, in the Mid-Atlantic Ridge  Right angle cracks o Like ripping news paper  Two plates are sliding against each other an rubbing o In between the two plates = transform margin o Ex. San Andreas fault Plate tectonics will not stop anytime soon Where do earthquakes occur?  99% occur at plate margins  1% of earthquakes occur not at plate margins: intraplate earthquakes, most are along former plate margins o Rivers are often faults ex. St. Lawrence, Ottawa, and Mississippi River  Epicentres of earthquakes are down the river  The rivers used to be plate margins because during Pangea, a bunch of cracks opened up in 3s, forming rivers  Failed arm: one of the 3 cracks that failed to open up  Still potentially prone to earthquakes o 20,000 years ago there were ice sheets covering continents, ex. Canada, which caused stress o 12,000 years ago, the ice sheets were lifted up, causing readjustment and potential cracks o Knowing plate boundaries is important for Seismic risk  90% at depths less than 100 km o Constructive margin o Collision of plates in the Subduction zone o On transform faults  10% at depths between 100 and 700 km o Subduction zones from the destructive margins  Destructive margins are most dangerous because they cause reverse dip slip faults  Earthquakes cannot occur in the asthenosphere because it is plastic  Lithosphere can continue until 700 km in the cracks created by the destructive margins -EndofSeismicRisk- Volcanic Risk Igneous o Rocks formed when liquid (magma) cools and “crystallizes”, forming mineralized grains, turning into ropy lava Volcano: a place where magma comes to surface Magma (liquid “rock) o Where does it originate? o Mainly in the upper mantle (down to approx. 200 km)  Liquid is formed in the mantle where there is extra heat where the silly putty comes up, creating upwelling  Magma comes up from the destructive and constructive margins o Sometimes in the crust when other magma comes up and melts new magma o Most magma sources are closely related to plate margins
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