1. Assuming that the average speed of sound waves in water is 1500 meters per second, the water depth if the signal sent out by an echo sounder requires 6 seconds to strike bottom and return to the recorder is 9000 meters.
2. The three major features that comprise the continental margin are the continental shelf, continental slope, and continental rise. The continental shelf is considered a flooded extension of the continent. The continental slope has the steepest slope.
3. The continental margin along the west coast of South America differs from the continental margin along the east coast of North America by along the west coast of South America there is stress between the converging plates resulting in the deformation of the continental margin and deep-ocean trenches. The continental margin here is narrow. Along the east coast of North America material is accumulating on the passive margins resulting in an increase in the size of the continents. Also, it is wide and consists of thick accumulations of shallow-water sediments.
4. "Most of the submarine canyons found on the continental slope and rise were formed during the Ice Age when rivers extended their valleys seaward." This is not true because these submarine canyons extend to depths far below the maximum lowering of sea level during the Ice Age making it so that the formation cannot be attributed to stream erosion. The erosional work repeatedly carried on by the turbidity currents is thought to be the major force in the excavation of most submarine canyons.
5. Turbidites are turbidity current deposits characterized by graded bedding. Graded bedding means sedimentary layers where the sediment grain size from bottom to top decreases. When turbidity currents lose momentum and come to rest along the ocean basin floor the coarser sediments drop out and decrease in size. These sediments are called turbidites.
6. The evidence that helped confirm the existence of turbidity currents in oceans was core samples that displayed graded bedding. These deep-sea sediment samples related turbidity currents to submarine erosion and transportation of sediment.
7. Abyssal plains are more extensive on the floor of the Atlantic than on the floor of the Pacific because the Atlantic Ocean has fewer trenches to act as traps for the sediments carried down the continental slope, it has more extensive abyssal plains than the Pacific. Abyssal plains are more widespread where there are no deep-ocean trenches adjacent to the continents.
8. An atoll is a continuous or broken ring of coral reef surrounding a central lagoon. Darwin’s theory on the origin of atolls was that coral reefs form on the flanks of sinking volcanic islands. As an island slowly sinks, the coral continues to build the reef complex up warp. The theory was confirmed.
9. The three basic types of sea floor sediments are lithogenous sediment, biogenous sediment, and hydrogenous sediment. Lithogenous sediment is derived from rocks, biogenous sediment is derived from organisms, and hydrogenous sediment is derived from water.
10. If you were to examine recently deposited biogenous sediment taken from a depth in excess of 4,500 meters (15,000 feet), it would be more likely rich in siliceous. Calcareous ooze does not accumulate where depths are greater because the cold sea water contains more carbon dioxide which is more acidic than warm water thus at greater depths of about 4,500 meters calcareous shells dissolve before they reach bottom.
11. Mid-ocean ridges and deep-ocean trenches are related to sea floor spreading by deep-ocean trenches are long, relatively narrow features that represent the deepest parts of the ocean and mid-ocean ridges are the sites of sea floor spreading. Deep-ocean trenches are the sites where moving crustal plates are destroyed as they plunge back into the mantle and leads to igneous activity. At mid-ocean ridges new sea floor is created.
12. The primary reason for the elevated position of the oceanic ridge system is the fact that newly created oceanic crust is hot, and therefore occupies more volume than cooler rocks of the deep-ocean basin.
13. J. Tuzo Wilson’s proposal for continental rifting is when a thick segment of continent lithosphere remains stationary over a hot spot for a extended period, the conditions are right for continental rifting. It affects previous notions about convection currents is that hot spots are causing the rifting than the convection currents are not the only method of plate tectonics.
14. The continental collisions that created the Appalachian and Ural Mountains were continental-continental convergence. Two plates collide and neither plate subducts because they both have the same density. The result is the collision of two continental blocks forming mountains such as the Appalachian and Urals.
15. Presently Los Angeles is south of San Francisco. Millions of years from now, their positions may be reverse where Los Angeles may be north of San Francisco. This could occur due to the San Andreas fault which is a transform fault. The Pacific plate is moving toward the northwest past the North American plate. San Francisco is on the North American plate while Los Angeles is on the Pacific plate.
Chapter 20: Mountain Building and the Evolution of Continents(Next)
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