How does the geology of ocean basins differ from that of continents? The dominant geologic processes in ocean basins are volcanism and sedimentation. Deformation, weathering, and erosion are much less important in ocean basins than they are on land. Oceanic crust forms at mid-ocean ridges where plates separate, accumulates sediments, and is destroyed by subduction over a few tens of millions of years. Deep-sea sediments, however, provide a nearly continuous record of their relatively brief geologic history.
What coastal processes act on shorelines? Winds blowing over the ocean generate swell; as those waves approach the shore, they are transformed into breakers in the surf zone. Wave refraction results in longshore drift and longshore currents, which transport sand along beaches. Tides, generated by the gravitational pull of the Moon and the Sun on ocean water, can also generate currents that transport sediments.
How do hurricanes affect coastal areas? Hurricanes are intense tropical storms with extremely high winds and very low atmospheric pressures. The low pressure results in the formation of a dome of seawater, known as a storm surge. As the hurricane moves ashore, the storm surge floods low-lying areas, often causing more extensive damage than the storm’s high winds.
What processes shape shorelines? Waves and tides, interacting with plate tectonic processes, shape the topography of coastlines, which vary from beaches and tidal flats to uplifted rocky coasts.
What are the major components of a continental margin? A continental margin is made up of a shallow continental shelf; a steeply descending continental slope; and a continental rise, a gently sloping apron of sediment deposited at the lower edges of the continental slope. Active continental margins result from subduction near a continent. Passive continental margins form when seafloor spreading carries a continent far from a plate boundary. Waves and tides affect the continental shelf, but the continental slope is shaped primarily by turbidity currents, which carry large loads of sediment down the slope. Turbidity currents also produce submarine fans and submarine canyons.
What are the main features of the deep seafloor? The deep seafloor is constructed as basalt is extruded in rift valleys along mid-ocean ridges. Abyssal hills are formed by normal faulting as the newly formed oceanic crust moves away from the rift valley. The newly formed crust is soon covered with fine-grained sediments precipitated from surface waters. Near the continental margins, terrigenous sediments add to this sediment cover to create the flat abyssal plains. Volcanic islands, submerged seamounts and guyots, and basalt plateaus are produced on the seafloor by igneous processes.
What kinds of sedimentation occur in and near ocean basins? The two main types of marine sediments are terrigenous sediments and biologically precipitated sediments. Terrigenous sediments are primarily muds and sands eroded from continents and deposited by wave action and tidal currents along the continental shelf. Biological sedimentation on the shelf results from the buildup of calcium carbonate from the shells and skeletons of organisms. Pelagic sediments consist of clay particles and foraminiferal and siliceous oozes composed of the biologically precipitated calcium carbonate and silica shells of planktonic organisms living in the surface waters.