earth’s internal properties
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Earth’s Internal Properties. Continental Drift & Plate Tectonics Science 2201 Chapter 17. October 17, 1989. May 18, 1980. Earthquakes and volcanoes: evidence that our planet is not at rest. global distribution of earthquakes and volcanic centers…above crustal plate boundaries - PowerPoint PPT PresentationTRANSCRIPT
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Earth’s Internal Properties
Continental Drift & Plate Tectonics
Science 2201
Chapter 17
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October 17, 1989
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May 18, 1980
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Earthquakes and volcanoes: evidence that our planet is not at rest.
• global distribution of earthquakes and volcanic centers…above crustal plate boundaries
• The surface of the earth is constantly changing and no feature on earth is permanent.
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Why is the Earth so restless?
• “Convection Conveyer-belt”
• The heat that drives the motion of the mantle comes from two sources:
---Radioactive decay of materials in the mantle
---Heat left over from the formation of the earth
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James Hutton 1726-1797
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• "catastrophism," earthly changes were sudden & caused by a series of catastrophes
• This belief prevailed until the 1700s
• "uniformitarianism • 1785 James Hutton• The present is the key
to the past
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Uniformitarian Principle
• the geologic forces and processes -- gradual as well as catastrophic -- acting on the Earth today are the same as those that have acted in the geologic past.
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Alfred Wegener 1880-1930
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Theory of Continental Drift
• (Wegener, 1915)
• continents plowed through crust of ocean basins, which would explain why the outlines of many coastlines(like South America and Africa) look like they fit together like a puzzle
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Continental Drift: a theory ahead of its time
• impossible for a large mass of solid rock to plow through the ocean floor without breaking up
• mid 20th Century, new evidence from ocean floor exploration rekindled interest in Wegener's theory, ultimately leading to theory of plate tectonics.
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Plate Tectonics: A modern version of
Wegener’s old idea • the outer rigid lithosphere consists of about
20 rigid segments called plates
• Most plates contain both continental and oceanic crust—a major departure from the continental drift theory
• The word tectonics comes from the Greek root "to build."
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Folding and Faulting
• Compressive forces from moving plates can cause rock to bend & wrinkle into wavelike folds
• The crack or break in the rock is called a fault and the movement of the rock is “faulting”
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Earthquakes
• Great forces of stress occurs as plates of rock pushed in opposite directions
• sudden movement as the blocks slide and then come to rest in a new position that eases the pressure
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The entire San Andreas fault system is more than 800 miles long and extends to depths of at least 10miles within the Earth. In detail, the fault is a complex zone of crushed and broken rock from a few hundred feet to a mile wide.
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Seismograph
• Richter Scale based on the amount of seismographic movement
• An earthquake with a number of 2 is just strong enough to be felt, 5 can cause much damage, 7 or more is classified as a major earthquake
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Plate Boundaries
• 3 Main Types–Divergent
–Convergent
–Transform
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Divergent Plate Boundaries
• plates are being pulled apart
• sea floor spreading at Mid-Atlantic Ridge
• Eurasia and North America are separating at a rate of about 5 cm per year
• East African Rift Valley
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Convergent Plate Boundaries
• two plates are coming together
• 3 associated surface feature– deep ocean trench and chain of volcanic
islands – folded mountains – ocean plate subduction beneath continent
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Transform Plate Boundaries
• one plate scrapes past the other
• San Andreas fault in California
• No mountain building or volcanism is associated with transform boundaries.
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Mountains
• great masses of rock pushed high into the air by forces inside the earth
• may be folded, tilted, shaped into domes, or built up from volcanic material
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Forming Mountains
• Folded mountains are formed when layers of rock are pushed into a series of wavelike folds by tremendous sideward forces
• Appalachian Mountains & Rocky Mountains
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Forming Mountains
• Fault-block mountains formed when folded layers of rock crack, producing a fault
• Sierra Nevadas
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Forming Mountains
• Domed mountains formed when magma flows up between two layers of rock
• Black Hills of shown rising from the Great Plains of South Dakota
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Forming Mountains
• Volcanic mountains formed by the build up of lava and other materials thrown up when a volcano erupts
• Hawaiian Islands
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Volcanoes
• A mountain formed around a crack in the earth’s crust
• Cracks in crust allow magma to rise up
• Some erupt quietly, others violently
• Magma lava
• Obsidian
• Pumice
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3 main types of volcanoes
• Shield volcanoes link –Kilauea in Hawaii
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3 main types of volcanoes
• Cinder cone link—Paricutin in Mexico
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3 main types of volcanoes
• Composite or Stratovolcano link
– Ranier in U.S.
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Hot Springs
• Formed when underground water is heated by rock, and then flows to surface before cooling
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Geysers
• A hot spring that throws its water into the air from time to time
• Almost all geysers are on 3 places: Yellowstone National Park, Iceland, and New Zealand
• How geysers work: – (understanding boiling)