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Transcript
Chapter 4 Continental Margins and Basins Continental Margins • These are the areas of the edges of the continents that are under water – Passive margins face edges of diverging plates and have little earthquake/volcanic activity. Ex: East Coast of USA – Active margins face edges of converging plates and have lots of activity. Ex: West Coast of USA • 2 subdivisions: Continental Shelf and Slope Continental Shelf • Shallow extension of the continent – Can be narrow, quickly becoming steep – Or can be broad, gently sloping downward • They look much like the continent from which they extend: hills and depressions • The sediment on the shelf is eroded dirt and debris from the dry land above it – Sediment is rich in minerals, oil and gas Continental Slope • The transition between the shelf and the deep-ocean floor – The shelf break marks the transition – Very steep • Continental rise is past the slope – It is oceanic crust covered with sediment from the land Activity • Draw, label, and color figure 4.8 on pg 93 •Draw, label, and color figure 4.10 on pg 94 Submarine Canyons • These canyons cut into the continental shelf and slope, ending in a deep-sea fan • Sometimes they extend from the mouth of a river that drains sediment and fast flowing water out to sea – Created by erosion like canyons on land • Sometimes they are created by earthquakes that cause an “avalanche” of sediments Deep-Ocean Basins • The seafloor is a blanket of sediment covering the basalt rock • Consists of oceanic ridge systems and plains • The plains are scattered with islands, hills, trenches, active and extinct volcanoes, and seafloor spreading Oceanic Ridges • A chain of mountains formed during seafloor spreading – Composed of “new” basaltic rock with no sediment – If they extend above the water, they are called islands • Seamounts and Guyots • Seamounts are volcanoes that are below ocean surface – From hot spots or spreading centers – Found alone or in groups • Guyots are flat-topped seamounts that once went above the ocean surface – flattened by waves and erosion Distance from North America (Km) 5,700 4,600 4,800 5,000 5,200 5,400 5,600 5,800 6000 0 150 300 450 600 750 900 1,050 1,200 1,350 Atlantic Ocean Depth (m) 0 39o N Trenches and Island Arcs • Trenches are deep pits in the ocean where the converging plate is subducted – Recall the cold ocean crust is sinking into the upper mantle of the continental plate – V-shaped due to spherical shape of Earth • Parallel to the side of the trench, the molten rock from the subducted plate is coming back up through volcanoes called an island arc. – Example is Caribbean islands Mapping the Oceans • Cartography – the science of making maps – Dry land forms are mapped using topography. – Underwater landforms are maps using bathymetry. Alvin explored the Titanic (HOV) The Trieste explored the Mariana’s Trench in 1960 (HOV) Hercules ROV SONAR • Sound Navigation and Ranging provided a rapid method of looking through water to identify features in the water beneath a vessel and on the sea floor.