Chapter9 - Chapter 9 Earthquakes and Volcanoes Tectonic...

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Chapter 9 Earthquakes and Volcanoes Tectonic Activity Has deformed, recycled, reshaped Earth’s crust repeatedly during past 4.6 billion years Sometimes occur as dramatic events, but more often slow and deliberate motions Principal tectonic and volcanic zones lie along plate boundaries Earth’s Surface Relief Features Relief: vertical elevation differences in the landscape Æ topography, the “lay of the land” Topography of the Earth grouped into three orders of relief Broadest category: continental platforms and ocean basins Very large topographic features: continental masses, mountain masses, plains, lowlands; in oceans, includes mid-oceanic ridges, subduction trenches Smaller-scale landforms, i.e. local relief (hills, valleys, cliffs, etc.) Hypsometry Hypsometry = measurement of surface elevations above certain plane (i.e. sea level) Compared to Earth’s diameter (ca. 8000 mi.), surface is of low relief Highest point is Mt. Everest (29,035 ft.) Average elevation of exposed land is 2870’ Oceans are much deeper than continents are high Louisville’s elevation? Earth’s Topographic Regions Six types of topographic regions Plains High tablelands Hills and low tablelands Mountains Widely-spaced mountains Depressions Crustal Formation Processes Tectonic activity produces continental crust Three categories: Residual mountains and continental cores (shields) Tectonic mountains and landforms produced by active folding and faulting Volcanic features Continental shields – nucleus of crystalline rock Æ other crust is added Nucleus is called craton Where craton is exposed on surface = continental shield
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Cold and stiff portions of the lithosphere with deep roots Most are over 2 billion years old (Precambrian) and have been eroded to low elevation Crustal Formation Sea-floor spreading Æ oceanic crust Æ subduction, remelting Æ rise of magma Magma may reach surface via volcano or be intrusive body of rock, such as batholith Crustal Deformation Processes Stress Tension (stretching) Compression (shortening) Shear (tearing and twisting) How rocks respond = strain Folding (bending) Faulting (breaking) Stress and Strain Folding Converging plate boundaries compress rocks, deforming them into “folds” Upfolded strata = anticline Downfolded strata = syncline Folds can be pushed over Æ overturned anticline Faulting Rock strata strained to a point where they break or fracture Faulting is the displacement of rock formations on either side of the fracture Fault zones are areas of crustal movement When rock fractures, fault line shifts and energy is released Æ earthquake Fault plane is the fracture surface – two sides of the fault move along this plane Normal Fault Rocks pull apart and move vertically along inclined fault plane One block drops Side that drops down is hanging wall Side that stays higher is
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This note was uploaded on 04/20/2008 for the course GEOS 200 taught by Professor Hanchette during the Spring '08 term at University of Louisville.

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Chapter9 - Chapter 9 Earthquakes and Volcanoes Tectonic...

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