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46 Cards in this Set
- Front
- Back
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What are gas hydrates?
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-methane gas (CH4) trapped in an ice latticework
-occur in cold temperatures and fairly high pressures and may represent a future source of natural gas |
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Why are offshore petroleum deposits so important?
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-they are very large and produce many millions of barrels (42 gallons) each year
-worth several billion dollars annually -politically speaking: make us not so dependent on other countries for oil, etc. |
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What are calcareous shells composed of?
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-calcium carbonate
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What are siliceous shells composed of?
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-silica
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What kind of shell deposits is not dissolved at great depths?
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-siliceous shells
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What is terrigenous sediments?
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-sediment that is near land and continental shelf deposits
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What is neritic sediments?
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-sediments on the outer shelf, slop, and rise of continental shelfs
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What is pelagic sediments?
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-sediments associated with the deep ocean
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What is a sediment corer?
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-a very effective, but slow device that allows sediment to be removed and processed from the sea floor
-weights are dropped off the device once the core sample has been taken -the coring tube has a plastic liner that allows the sediment to be removed |
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What are atolls made of?
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-coral reef that is in a ring around a sunken seamount that is below the water's surface.
-many different creatures create a coral reef including snails, worms, sea urchins, etc |
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How are atolls formed?
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-first a fringing reef is formed around an island mass
-then sinking sea mount causes water to rise and reef to grow upwards at the same rate to create a barrier reef (lagoon between reef and the island is formed) -process continues until the seamount eventually is completely below the surface and the atoll forms a ring around the seamount |
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What are abyssal hills?
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-volcanic features less than 1000 m high on the sea floor
-earth's most common topographic feature |
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What are guyots?
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-submerged flat-topped seamounts
-also known as tablemounts -most often in the Pacific Ocean -between 1000 m and 1700 m below the surface -their weight has helped depress the oceanic crust and the plate moving away from the hot spot or ridge allows them to sink below the surface |
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What is a continental shelf?
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-a nearly flat region of varying width that slopes very gently toward the ocean basins
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What it is continental slope?
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-the steeper slope extending to the ocean basin floor
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What is continental rise?
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-a gentle slope formed by the accumulation of sediment on the seafloor
-it is a region of sediment deposition by turbidity currents, underwater landslides, and any other processes that carry sand, mud, and silt down the continental slope |
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What are deep sea fans?
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-also known as abyssal fans
-formed due to turbidites -underwater structures made of sediments that look the deltas found at the end of rivers -fan of sediment form towards the top of the sedimental rise |
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What are the four main regions of the seafloor?
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-abyssal plains, continental shelves, deep ocean trench, mid ocean ridge
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Describe deep ocean trenches.
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-long narrow topographic depressions in the seafloor
-deepest parts of the earth's floor -occur at convergent plate boundaries -ex. mariana trench |
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Describe mid-ocean ridges.
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-steep mountain ranges underwater
-new crust is formed here ("spreading centers") -rift valley is in the center and the plates move away |
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Describe continental shelf.
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-self is narrow along the mountainous coasts of active continental margins and wide along low-lying land at passive continental margins
-they have been covered and uncovered by fluctuations in sea level |
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Describe abyssal plain.
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-flat plain on the ocean floor
-form as sediment deposits cover the irregular topography of the sea floor |
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What valuable commodities do manganese nodules contain?
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--manganese, iron, copper, covalt, and nickel
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Where are manganese nodules located?
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-mapped in all oceans except the arctic
-most abundant in the central Pacific north and south of the biogenous oozes of the equator |
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Describe continental drift.
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-hypothesis proposed that all existing land areas were once joined to from one giant continent called Pangea
-the continent then broke up and drifted into their present positions |
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What is the evidence for continental drift?
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-obvious 'jigsaw puzzle fit' of existing continents
-aligned mountain ranges (appalachians into Europe) -rock type and geologic structure (mineral deposits) -fossils of the same species on different continents |
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Who was the promoter of continental drift?
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-alfred wegner 1915
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Why was continental drift not accepted by scientists?
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-no known mechanisms to drive the continents
-the amount of energy needed would be tremendous -no experimental evidence to support it |
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what new developments transformed continental drift into plate tectonics?
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-new technology to explore the seafloor
-rock and water sampling -sediment coring -accidental discovery of the driving mechanisms -seafloor was not featureless -40,000 mile chain of mid-ocean ridges -bedrock is nearly all YOUNG basalt |
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Why is plate tectonic important to geology?
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-changed from a primarily descriptive discipline to offering logical explanations for volcanoes, earthquakes, mechanism of mountain building, creation of mineral ore deposits, locations of earth's continents
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What are the three type of plate boundaries?
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-divergent, convergent, transform faults
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Describe divergent boundaries and give examples.
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-plates moving apart
-mid-ocean ridges-plates separate and are filled with magma -on land: continental rifting such as in Eastern Africa |
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Describe convergent boundaries and give examples.
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-3 types
-subduction: oceanic lithosphere subducts under continental -subduction zone volcanoes form (andes and cascade mtns.) -subduction: oceanic under oceanic -forms volcanic island arc from magma (Japan and Philippines) -collision: continental collides with continental -neither one wants to subduct, so they crumple to form mountains (India) |
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Describe transform faults and give examples.
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-two plates slide past one another
-no subduction, but large amounts of pressure (san andreas fault) |
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What is palemagnetism and what does it have to do with seafloor spreading?
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-the study of the earth's magnetization throughout history
-shows evidence of the spreading at the mid ocean ridge -megnetite found in magma -either positively or negatively polarized -equal strips of polarization on each side of the ridge |
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What are hot spots and where do they occur?
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-specific fixed areas of isolated volcanic activity
-found under continents and oceans, in the center of plates, and at the mid-ocean ridge |
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What is intraplate volcanism?
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-the volcanoes that are above hot spots
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What drives the movement of lithospheric plates? (3 processes)
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-convection cells: in the earth's mantle creating bouyant mantle plumes
-pull slabs: attributed to the sinking of dense lithosphere into the asthenosphere -ridge push: caused by the position of oceanic lithosphere off the flanks of mid-ocean ridges |
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Describe deep ocean trench.
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-where oceanic crust is being subducted by another
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Define submergent coastlines.
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-coasts that sink relative to sea level
-occurs if sea level rises or weight on crust increase |
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Define emergent coastlines.
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-coasts rising relative to sea level
-occurs if sea level falls, decrease in weight on crust, or coast is uplifted by tectonic processes |
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What kind of shells are not dissolved at great depths?
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-siliceous shells
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What are some economic offshore mineral deposits that are being mined?
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-Gold/Platinum: Alaska, southwest African coasts
-Diamonds: Southwest Africa Coast -Titanium: Australia |
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What are some potential offshore minerals that could be mined in the future?
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-phosphorites: many locations a long Australia, Africa, and Southern California
-Polymetallic Nodules: deep ocean locations |
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Give a brief summary of plate tectonics.
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-Earth's rigid lithosphere is composed of 12 major plates that are in constant motion
-the plates move atop a plastic and partially melted portion of the upper mantle called the asthenosphere -the plates are created at mid-ocean ridges called spreading centers and are "driven" by convection currents within the mantle -most major interactions take place at plate boundaries -most important non-boundary actions are due to plates passing over "hot spots" in the upper mantle |
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Why has there been so much attention paid to nodules for many years?
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-they are a potential source of valuable minerals such as cobalt, nickel,and nickel
-numerous in the Pacific Ocean |
