Deck 14: Waves,Beaches,And Coastal Erosion

Question 1

What factors do NOT influence the size of most waves?

A) atmospheric pressure
B) wind velocity
C) fetch
D) time of wind across water
E) constant direction of wind across water

Answer 1

A

Question 2

What happens to wave energy and erosion when riprap or seawalls are installed?

A) Wave height rises against the wall, and erosion concentrates at the base of the wall.
B) Waves that strike the riprap are reflected back against the incoming waves to cancel them.
C) Waves move up and down against steep surfaces in deep water, so they don't do anything.
D) Waves lose their energy against riprap or seawalls, so they permanently protect the coast.
E) Waves pulverize the riprap and seawalls, creating sand that helps maintain the beach.

Answer 2

A

Question 3

Why does sea level rise during a near-shore storm?

A) Low atmospheric pressure of the storm permits sea level to rise.
B) The winds stir the water in circles, so it rises in the center.
C) High pressure in the storm forces the water up.
D) Waves cluster together, so the average sea level is higher.
E) The gravitational pull of the moon is stronger at such times.

Answer 3

A

Question 4

What is NOT among the solutions to reducing beach erosion?

A) Learn to live with actively eroding beaches, not fighting natural processes.
B) Move buildings and roads back from the beach after storms.
C) Remove old dams on rivers feeding sand to the beach.
D) Stabilize sea cliffs, so they don't collapse onto beaches.
E) Move cliff-top houses back from the cliffs to let cliffs erode.

Question 5

Where does beach sand NOT originate?

A) streams and rivers
B) erosion of sea cliffs
C) continental shelf as much as 50 km offshore
D) longshore drift
E) blown by the wind

Question 6

What is the main reason that once sandy beaches on the West Coast are now disappearing?

A) Sea level is rising with global warming, so waves are reaching farther onshore.
B) More frequent El Niño storms are eroding them.
C) More vigorous longshore drift is removing the sand.
D) Dams on rivers no longer supply sand and gravel to feed longshore drift.
E) People have placed riprap and cliff-protection structures, so less sea cliff material is eroding to make sand.

Question 7

Why are ocean waves generally larger than those on lakes?

A) Wind directions are much less constant over lakes.
B) Winds are always stronger over the ocean.
C) Fetch length is much longer in the ocean.
D) Ships generating the waves are bigger in the ocean than on lakes.
E) Tsunamis are generated in oceans but not in lakes.

Question 8

How can there often be big waves at the coast when there is little or no wind?

A) The storm generating the waves is far offshore.
B) There must be a point of land that is sheltering your location from the wind.
C) These are small tsunami waves generated by an earthquake.
D) A big ship must have gone by.
E) A playful elephant jumped into the water across the bay.

Question 9

How do sand dunes help maintain sand on a beach?

A) Sand dunes stop the landward advance of the waves.
B) People build their houses on top of them, thereby keeping the highest part of the barrier island intact.
C) Eroding dune sand spreads over the beach and takes up wave energy.
D) Sand dunes don't have much effect; they merely look picturesque.
E) They don't help maintain sand on a beach.

Question 10

To what depth of water do waves commonly move sand?

A) about 1 meter
B) about 5 meters
C) about 10 meters
D) about 30 meters
E) about 100 meters

Question 11

What factors most affect the energy of a wave impacting the shore?

A) incoming wave velocity and water density
B) water depth and wave velocity
C) wave height and water depth
D) wind strength and wave height
E) height of the wave and wave length

Question 12

Why are inlets through barrier bars or barrier islands not closed by longshore drift of sand?

A) Such inlets are always the outlets for onshore rivers to reach the sea, so they flush the sand out.
B) Rapid flow of water back and forth through the inlet as tides rise and fall keeps it clear.
C) Longshore sand drifted into such inlets drops into deeper water, so it drifts out to sea.
D) Sand drifted into such inlets encounters brackish water from the inlet and dissolves.
E) Sand drifted into such inlets is carried into the lagoon by incoming waves.

Question 13

What happens to a barrier island as sea level rises?

A) It gradually moves landward, rising with the sea level.
B) It completely erodes away.
C) It is gradually submerged beneath the sea.
D) Its sand is swept farther inland, disappearing in the former lagoon behind the island.
E) Companies try to scoop it up for use in road building before it completely submerges.

Question 14

What is the motion of a stick (or a water molecule)in a deep-water wave?

A) It moves straight up and down with the water surface.
B) It doesn't move. The wave merely moves over anything in deep water.
C) It shifts back and forth in a horizontal plane.
D) It moves in a circular motion in a vertical plane, with the top of the wave moving in the direction of wave travel.
E) It moves in a circular motion in a horizontal plane.

Question 15

What factors promote a steeper slope on the active underwater part of the beach?

A) deeper water
B) shallower water
C) larger waves
D) finer grains
E) higher average winds

Question 16

Why do waves not break in the open ocean?

A) Onshore winds drawn by rising warm air over land pull the tops of the waves to break.
B) Water in deep-water waves does not move forward with the wave; it moves in a circular motion.
C) Waves speed up in shallow water, so they lurch forward and break.
D) Water in deep-water waves moves only up and down; it switches to forward and back in shallow water.
E) Waves only break in the deep ocean during tropical storms.

Question 17

Which of the following evidence does NOT indicate that a barrier island migrated landward?

A) A lighthouse that was built onshore is now well offshore.
B) Oyster shells that grew in the sheltered lagoon behind the barrier island are now found on the front beach.
C) Stumps of trees that grew along the lagoon are now found on the front beach.
D) Barrier island beaches are now more easily eroded than they were one hundred years ago.
E) Fine-grained lagoon sediments are layered beneath the sands of the barrier island.

Question 18

Why does removal of logs and rocks from a beach endanger the sea cliffs behind them?

A) Waves can't get over the logs to get to the sea cliffs.
B) Waves have to be higher to reach over the logs and rocks to reach the sea cliffs.
C) Wave energy is taken up in moving the logs and rocks.
D) Logs bouncing up and down on the beach pound the grains together, making them more difficult to erode.
E) Logs and rocks break up the direct forward thrust of the waves, making them more erratic.

Question 19

Why does the beach slope under water become steeper near shore?

A) The sand grains are finer near shore.
B) The bottom has to rise rapidly to merge with the sand of the barrier island.
C) Sand from the onshore part of the beach has to drop abruptly because offshore the sand is under water.
D) Waves in shallow water drag on the bottom, so they lose energy and need a steeper slope to move the sand.
E) The waves are bigger near shore.

Question 20

Why can dune sand,which can easily spread on a beach,be easily eroded during a storm?

A) Dune sand is finer grained and thus more easily moved by waves.
B) Dunes are at the upper limit of the waves where the waves can easily drag them back downslope.
C) Dune sand stands at a steeper slope than the beach, so it can easily move down to the beach.
D) Dune sand is rounder grain than beach sand, so it easily rolls down the beach.
E) Dune sand is more angular than beach sand, so the grains do not fit together well.

Question 21

What factors promote a steeper slope on the active underwater part of the beach?

Question 22

What is a better solution to erosion than the variety of prevention efforts used on most coasts?

Question 23

In addition to sand moving along shore,how is beach sand permanently lost to the beach system?

Question 24

What is the relationship between wave height and energy of the wave?

Question 25

Where does beach sand originate? (Two quite different places)

Question 26

What is a shore profile? How is it created? Explain the concept of an equilibrium profile in regard to a shore profile.

Question 27

What is beach hardening? What are three examples of techniques used in beach hardening? Why are these not a good solution to preventing erosion of sand on beaches?

Question 28

About how far offshore does the active beach extend? Why is that the common limit?

Question 29

What do people who live at the top of coastal terraces in the west do to accelerate cliff erosion?

Question 30

When is hurricane season in the southeastern United States? Why is it then?

Question 31

On some beaches,why is gravel at the back part of the beach and sand is near shore?

Question 32

Why are once sandy beaches on the West Coast now disappearing?

Question 33

Explain the processes of wave refraction and longshore drift.What happens to sand as a result of these processes?

Question 34

What is a rip current? Describe the shoreline's shape as a result of rip currents,and the cause of the distinct shape.

Question 35

Why do barrier islands gradually migrate landward with time?