GEOG 1001 9.26.16
GEOG 1001 9.26.16 Geog 1001
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This 2 page Class Notes was uploaded by Melanie Basinger on Monday September 26, 2016. The Class Notes belongs to Geog 1001 at University of Cincinnati taught by Nicholas Dunning in Summer 2016. Since its upload, it has received 9 views. For similar materials see Introduction to Physical Geography in Geography at University of Cincinnati.
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Date Created: 09/26/16
Introduction to Physical Geography 9.26.16 Earth Structure and Tectonics – Part 2 Hot spot: an isolated convection cell in the Asthenosphere over which magma is brought to the surface. Hot spots remain stationary, but Lithospheric plates move across these “bubbles” in the Asthenosphere o The Hawaiian Islands are an example of volcanoes created as the Pacific Plate has traveled across a hot spot in the underlying Asthenosphere over the past 60+ million years o Shield volcano: relatively gently erupting, dome shaped volcano built up by successive lava flows (associated with hot spots and spreading centers). Shield volcanoes have gentle slopes down which floods of lava flow at relatively slow rates. Since eruptions are typically not explosive, they pose relatively little danger to humans, though property loss can be high QUIZ QUESTION #4: The island of Hawaii is an example of Gently erupting shield volcanoes located over a hot spot in the asthenosphere Divergent Plate Boundaries o Spreading center: area where lithospheric plates are diverging because of underlying convection currents in the Asthenosphere Most spreading centers are found along the ocean floor where the lithosphere is thinnest o Mid-ocean ridge/rift: linear range of fault-block mountains and volcanoes on the ocean floor along a spreading center o In a few places mid-ocean ridges have risen above the ocean’s surface such as in Iceland (which is part of the Mid-Atlantic Ridge) o When/where continental bodies occur over convection cells continents can be pulled apart (e.g., the Red Sea and Great Rift Valley of Africa) o Tectonic movement at spreading centers is often both divergent and transform (where sections of the boundary become offset) because different parts of the diverging plates are moving at different speeds Transform Plate Boundaries o Transform plate boundary: where two lithospheric plates, or portions of a fractured plate, slide laterally past one another (e.g., the San Andreas Fault system) o The 7.0 magnitude earthquake that struck Haiti on Jan. 12, 2010 occurred along a transform boundary between the Caribbean and North American plates Convergent Plate Boundaries o Convergent plate boundary: area where lithospheric plates are being pushed together resulting in crustal subduction or suturing o Subduction zone: area where a crustal plate descends into the Earth’s interior, breaks apart, and melts Deep ocean trench: a deep scar (trench) on the ocean floor along a subduction zone QUIZ QUESTION #5: Which type of plate boundaries causes deep trenches? Convergent plate boundaries/subduction zone Lithospheric plate material of greater density (e.g., mafic or ultramafic seabed lavas) are most likely to be subducted As plates are subducted they break apart (generating progressively deeper earthquakes) and partially melt (generating volcanoes). When the descending plate reaches a sufficient depth, it softens into a fluid state and is reincorporated into the Asthenosphere o Tsunami: ocean wave generated by earth movement o Composite volcano: violently explosive volcano composed of layered ash and lava (associated with subduction zones) o Some composite volcano eruptions include dangerous pyroclastic flows Pyroclastic flow: stream of super-heated volcanic gas and rock fragments that moves rapidly down-hill Ex: Pompeii About 70% of the world’s active volcanoes are associated with a series of subduction zones defining the Pacific “Ring of Fire.” o The Cascade Mountain Range (and Cascadian Subduction Zone) of the Pacific Northwest includes numerous composite volcanoes, some of which pose considerable risk to major population centers like Seattle- Tacoma and Portland QUIZ QUESTION #6: What are among the most naturally dangerous places on Earth to live? Along subduction zones (because of both major earthquakes and explosive volcanoes)
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