ch18 review questions

Pick out the true statement. Tidal reach means the farthest inland the water goes at high tide. A flood tide that arrives as a visible wall of water is called a tidal bore. The tide-generating force is a combination of only two forces, the gravitational attractions of the Sun and Moon. Since the Sun is much larger than the Moon, its gravity is the biggest contributing factor to the tide-generating force. Ebb tide causes the shoreline to migrate inland.

A flood tide that arrives as a visible wall of water is called a tidal bore. Tidal reach is the difference between high and low tides. Centrifugal force caused by Earth's rotation contributes to tides. The Sun is so distant it accounts for only 46% of the force. Flood tide causes the shoreline to migrate inland. (Section refs: 18.4, p. 620)

Pick out the false statement. Friction between ocean water and the ocean floor causes the movement of the tidal bulge to lag slightly behind the Moon's orbital motion. This lag causes the Moon to exert a slight pull on the tidal bulge. This pull acts as a brake to slow Earth's spin. This braking causes days to grow longer by a fraction of a second every century. All of these factors have caused the tidal reach of today to be larger than it was millions of years ago.

All of these factors have caused the tidal reach of today to be larger than it was millions of years ago. The tidal reach (the vertical difference between high and low tides) was larger in the geologic past than it is today because the Moon then was much closer to Earth than it is today. (Section refs: 18.4, p. 620)

Pick out the false statement. The thermocline is the level below which water temperature drops sharply. The thermocline occurs at a depth of 300 m in the tropics but only 100 m in the polar regions. Sea-surface temperature has greater seasonal variation in the temperate latitudes than in the tropics. Sea-surface temperature varies within a narrow range because of the high heat capacity of water. Sea-surface temperature varies much less than seasonal temperature changes on land.

The thermocline occurs at a depth of 300 m in the tropics but only 100 m in the polar regions. There is no pronounced thermocline in polar seas; the water there is all very cold. Note Fig. 18.8. (Section refs: 18.3, p. 616)

No ocean crust is older than 200 million years because by that time it has been destroyed by subduction.

True All ocean crust subducts and therefore is destroyed by the time it is 200 million years old. (Section refs: 18.2, p. 611)

At any particular location, high tide arrives 50 minutes later each day because it takes Earth 24 hours and 50 minutes to catch up with the Moon in its orbit and be back in high-tide position.

True Because the Moon progresses in its twenty-eight-day orbit around Earth in the same direction as the Earth rotates, it takes Earth 24 plus 50 minutes to "catch up" and reach high-tide position. (Section refs: 18.4, p. 620)

Saltwater is denser than freshwater, so objects (including you) float higher in it.

True Dissolved ions fit between water molecules without changing the volume, making salt water denser than fresh water. Any object floats higher in a denser fluid. (Section refs: 18.3, p. 614)

Spring tides are extra high tides that occur when the Sun, the Moon, and Earth are aligned; this happens at new- and full-moon times.

True Extra-high spring tides occur when the Sun, the Moon, and Earth are aligned. Note Fig. 18.15. (Section refs: 18.4, p. 620)

Pulses of sound reflected off subsurface layers create a seismic-reflection profile that shows ocean crust structure.

True Reflections of sound waves off subsurface layers do create profiles that show ocean crust structure. Note Fig. 18.2. (Section refs: 18.1, p. 610)

The continental slope descends at a steeper angle than either the continental shelf or the continental rise, but even so its slope is only a few degrees.

True The continental slope is steeper than the continental shelf and the continental rise, but its slope is still just a few degrees. (Section refs: 18.2, p. 612)

Alvin can dive to depths of more than 4 km (2+ mi)

True The deep-sea submersible Alvin can dive deeper than 4 km (2+ mi). See Fig. 18.1. (Section refs: 18.1, p. 609)

Estuaries are river valleys flooded by seawater.

True The definition applies to estuaries. (Section refs: 18.6, p. 633)

Cold, salty water sinks; warm, less salty water rises. This phenomenon is called thermohaline circulation.

True Thermohaline circulation is driven by differences in water density, caused by differences in temperature and salinity. Cold, salty water sinks because it's denser than warm freshwater. (Section refs: 18.3, p. 617)

A combination of surface currents and vertical thermohaline circulation acts like a conveyor belt and moves water and heat among ocean basins and from ocean surface to ocean floor.

True Water and heat move horizontally and vertically through the ocean because of surface currents and thermohaline circulation. (Section refs: 18.3, p. 617)

Beaches usually consist of sand grains because waves winnow out finer sediment and carry it to deeper water, and break larger pieces down to sand-grain size.

True Waves move fine sediment from beaches to deep water and break large pieces down, so beaches usually consist of only sand-sized particles. (Section refs: 18.6, p. 627)

Oil spread on rough seas has a calming effect because it decreases the shear between molecules of air in the wind and molecules of water on the sea's surface.

True Waves result from the shear described; oil decreases the amount of friction and therefore the magnitude of shear. (Section refs: 18.5, p. 624)

Pick out the appropriate pair of terms to match this statement: a surfer loves these; a swimmer hates these. swash, longshore currents rip currents, backwash breakers, rip currents embayments, tombolos eustatic changes, swash

breakers, rip currents Breakers are the waves that curve over the base which surfers ride; rip currents are strong, localized seaward flows that trap and drown swimmers. (Section refs: 18.5, p. 624)

Pick out the false statement. Continental crust: is more buoyant than ocean crust. sits higher than ocean crust. currently lies mainly in the northern hemisphere; because of plate tectonics that has not always been the case. consists of igneous, sedimentary, and metamorphic rocks. can be no older than 200 million years.

can be no older than 200 million years. It is ocean crust that can be no older than 200 million years because by then it has subducted. (Section refs: 18.2, p. 611)

Pick out the false statement. The Coriolis effect: is a phenomenon created by the rotation of Earth. is a deflection of wind or water flowing over Earth's surface. causes opposite directions of deflection in the northern and southern hemispheres. causes north-flowing currents in the northern hemisphere to curve to the west. must be taken into account when aiming artillery shells over long distances.

causes north-flowing currents in the northern hemisphere to curve to the west. They curve to the east. Read more in Box 18.1 The Coriolis Effect. (Section refs: 18.3, p. 616)

Pick out the false statement. Ocean crust: comprises broad continental shelves along active continental margins and much narrower shelves along passive margins. is thinner but denser than continental crust. is composed of gabbro and basalt overlain by sediment. gets older the farther you go from the ridge axis. can be no older than 200 million years.

comprises broad continental shelves along active continental margins and much narrower shelves along passive margins. Just the reverse is true; shelves are narrow along the active margins, broad along passive margins. Note Fig. 18.3. (Section refs: 18.2, p. 610)

Pick out the false statement. Turbidity currents: created the continental slopes by depositing turbidites. and river erosion create submarine canyons. travel at a maximum speed of 60 km/h. leave deposits of graded beds called turbidites. may deposit overlapping turbidites that form a submarine fan.

created the continental slopes by depositing turbidites. Turbidites are deposited by turbidity currents that have raced down the continental slopes; they do not form the slopes. (Section refs: 18.2, p. 613)

Pick out the false statement. Rogue waves: by definition are more than twice the size of most large waves. have been documented as high as 34 m (112 feet). can be caused by constructive wave interference and by interaction of waves with strong currents. can be caused by the focusing effect of some coastline or sea floor shapes. fortunately are rare; fewer than 50 have been documented in recorded history.

fortunately are rare; fewer than 50 have been documented in recorded history. They're not rare. Recent radar studies from satellites show that on the average there are ten rogue waves somewhere in the world at any given time. (Section refs: 18.5, p. 624)

Which of the following are not living organisms? mangroves sargassum algae polyps groins

groins Groins are concrete or stone walls that protrude perpendicularly to the shore and are built to prevent beach drift. The other choices, in order, are trees, seaweed, tiny invertebrates that form coral reefs, and the individual coral animal. Note Fig. 18.30. (Section refs: 18.7: Organic Coasts; 18.9, p. 640)

Pick out the false statement. Ocean water: has an average salinity of 3.5%. receives its salt from groundwater and river water. has increased in salinity by about 0.5% each century. contains positive ions like sodium, potassium, calcium, and magnesium derived from the chemical weathering of rocks. contains negative ions like chloride and sulfate derived from volcanic gases.

has increased in salinity by about 0.5% each century. Ocean-water salinity stays fairly constant because the amount of salt continuously added balances the amount of salt that precipitates out. Note Fig. 18.7. (Section refs: 18.3, p. 615)

Pick out the false statement. Hurricanes: are huge storms that develop over warm equatorial ocean water. can have winds exceeding 155 mph. can have waves higher than 15 meters. have high air pressure in their centers that pushes on the sea surface and creates high waves. have produced catastrophic flooding worldwide, from Bangladesh to New Orleans.

have high air pressure in their centers that pushes on the sea surface and creates high waves. Hurricanes have low pressure centers, which allow the sea surface to rise and cause coastal flooding. (Section refs: 18.9, p. 640)

All seas: have salinity ranging between 1 and 4.1%. have a surface temperature of 17°C, ± 2°C. have similar floors consisting of wide, gently sloping continental shelves, steeper continental slopes, gentle rises, and flat plains. have yearly temperature fluctuations of about 15°C. have calm bottom waters with no apparent circulation.

have salinity ranging between 1 and 4.1%. Average surface temperature is 17°C; surface temperatures range from near freezing near the poles to 35°C in restricted tropical seas. Sea-floor bathymetries vary greatly. Yearly temperature fluctuations vary between 2 and 8°C. There are bottom currents. (Section refs: 18.3, p. 615)

Which location is associated with high salinity of seawater? near the mouth of a river in restricted seas which do not mix freely with the main ocean areas of low evaporation, high rainfall near the equator None of the possible answers is an area of high salinity.

in restricted seas which do not mix freely with the main ocean Restricted seas would experience high evaporation rates and little influx of new waters. Evaporation leaves salt behind. (Section refs: 18.3, p. 615)

Choose the proper order to name the following types of coastal wetlands: those that are dominated by grasses, by moss and shrubs, and by trees. swamps, bogs, marshes marshes, bogs, swamps bogs, marshes, swamps swamps, marshes, bogs The classification is outdated; any name will do for any type of dominating vegetation.

marshes, bogs, swamps Only choice b presents the names in the proper order. The classification is not outdated. (Section refs: 18.7, p. 634)

Pick out the false statement. Estuaries: are valleys flooded by seawater. have brackish water in them. originated as glacial valleys. are recognized on maps by their jagged coastlines. are found in the Chesapeake Bay; Hudson River, New York; and Columbia River, Oregon.

originated as glacial valleys. Flooded glacial valleys are called fjords. (Section refs: 18.6, p. 633)

Pick out the false statement. Upwelling zones: are areas where water flows in a vertical direction. result when water deflected in toward the coast creates an oversupply there. bring nutrients up from depth. occur near the equator to replace water displaced by winds blowing steadily from east to west. can be driven by density differences caused by temperature and salinity differences.

result when water deflected in toward the coast creates an oversupply there. Upwelling zones result when water is deflected away from the coast, and deep water rises to fill the deficit created. Note Fig. 18.12. (Section refs: 18.3, p. 616)

What force causes the tidal bulge on the side of the Earth opposite the Moon (the secondary bulge)? the centrifugal force caused by the orbiting of the Earth-Moon system around its center of mass the centripetal force caused by the orbiting of the Earth-Moon system around its center of mass the Sun's gravitational attraction the Moon's gravitational attraction the Sun's and the Moon's gravitational attractions combined

the centrifugal force caused by the orbiting of the Earth-Moon system around its center of mass On the side of the Earth away from the Moon, the magnitude of the centrifugal force is greater than the magnitude of the Moon's gravitational force, so the tidal bulge is away from the moon. Note Fig. 18.12 and read more in Box 18.2 The Forces Causing Tides. (Section refs: 18.4, p. 620)

What term has nothing to do with protecting beaches from erosion? tombolos groins breakwaters seawalls jetties

tombolos Tombolos are narrow ridges of sand that link sea stacks to the mainland. See Figs. 18.29, 18.31, and 18.41. (Section refs: 18.6, p. 632; 18.9, p. 640 )

In the accompanying diagram, which letter(s) designate(s) the Moon's position(s) for neap tides? A only D only A and C B and C D and C

B and C At quarter-moon times, the gravitational forces of the Sun and Moon are acting on Earth at right angles, so each partially offsets the influence of the other. See Fig. 18.12: (Section refs: 18.4, p. 620)

Pick out the false statement. A particle of water in a wave is going in a circular motion as viewed in cross section. Submarines traveling deeper than about half the prevailing wavelength in an area (the wave base) would be experiencing smooth water. Constructive interference of comparable-sized swells tends to cancel them out and produce smooth water. Waves form because of shear between molecules of air in the wind and molecules of surface water. The character of waves in open seas depends on the strength and fetch of the wind.

Constructive interference of comparable-sized swells tends to cancel them out and produce smooth water. Constructive interference would create larger waves. (Section refs: 18.5, p. 624)

Pick out the false statement. Coral reefs are complex environments consisting of colonies of tiny invertebrates, algae, shell debris, and associated organisms. An individual coral animal is a polyp. Corals grow only in clear, well-lit, warm water with normal oceanic salinity. Coral animals are tiny invertebrates that secrete silicic shells. Coral reefs are classified on the basis of their shapes, fringing, barrier, or atoll.

Coral animals are tiny invertebrates that secrete silicic shells. Coral animals secrete calcite shells, so the coral mounds are limestone. Note Fig. 18.25. (Section refs: 18.7, p. 634; Figure 18.25)

Alvin and the H.M.S. Challenger are deep-sea submersibles used to explore the ocean bottom.

False Alvin is a submersible, but the H.M.S. Challenger was a British Navy ship that did ocean research as early as the 1870s. Note Fig. 18.1. (Section refs: 18.1, p. 609)

Property owners may try beach nourishment if their land is on an accretionary coast.

False Beach nourishment (trucking or shipping in huge amounts of sand) may be tried if the properties are on an erosional coast, where the sea washes sediment away faster than it can be naturally supplied. (Section refs: 18.9, p. 641)

Bioturbation is an oceanic worm that stirs up sediment on the abyssal plains.

False Bioturbation is the process in which organisms ("bio") like clams and worms stir up tidal flat sediments. (Section refs: 18.6, p. 628)

The Sargasso Sea, located at the center of the North Atlantic gyre, is an area of rapidly rotating surface water and tangled sargassum seaweed.

False The location is properly stated, but the waters are noncirculating and have therefore allowed the seaweed to accumulate. (Section refs: 18.3, p. 616)

Pick out the false statement. Deeper seawater is fairly homogenous worldwide. Saltier water generally floats above fresher water. Water from rivers or rain tends to stay in a layer above saltier water for quite a while before it mixes. The boundary between surface-water salinities and deep-water salinities is called the halocline. Warm water can hold more salt in solution than can cold water.

Saltier water generally floats above fresher water. Freshwater is less dense so it floats on saltwater. (Section refs: 18.3, p. 615)

Trenches: result from sea-floor spreading. are found at divergent plate boundaries. border continental and island volcanic arcs. may be over 100 km (62 mi) deep. All of the possible answers are correct.

border continental and island volcanic arcs. Trenches are found at convergent ocean-continent boundaries, and the deepest (the Mariana trench) is about 11 km (6+ mi) deep. (Section refs: 18.2, p. 613)

Pick out the false statement. Seamounts: develop as hot-spot volcanoes. that are capped with limestone coral reefs are called guyots. occur in chains that are progressively older farther from the place of origin. are covered by thick layers of pelagic sediment composed of coral reef fragments. are on plate material that sinks as it gets older and colder.

are covered by thick layers of pelagic sediment composed of coral reef fragments. Pelagic sediment is a blanket of microscopic plankton shells and fine clay on the ocean bottom. (Section refs: 18.2, p. 613)

Pick out the false statement. The abyssal plains: are underlain by cool oceanic lithosphere. of the western Atlantic Ocean stretch from the base of the continental rise to the base of the mid-ocean ridge. are covered by pelagic sediment. are covered by microscopic plankton shells and fine flakes of clay. are dissected by submarine canyons.

are dissected by submarine canyons. Submarine canyons dissect the continental shelves and slopes. (Section refs: 18.2, p. 613)

Surface currents: affect only the upper 30 feet of water. flow smoothly, with little or no turbulence. are caused by different salinities at different locations. are influenced by Earth's rotation. are found only in low- and mid-latitude areas.

are influenced by Earth's rotation. They affect the upper 100 m, commonly have eddies, are caused by the interaction of wind and surface water, and are found worldwide. Note Figs. 18.9 and 18.10. (Section refs: 18.3, p. 616)