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Transcript
Key Questions for
Understanding Section 16.1
Shoreline Features
1. How do large breakers erode solid
rock along shorelines?
• Breakers can hurl thousands of tons of
water, along with suspended rock
fragments, against a shore with such force
that they are capable of eroding solid
rock.
2. Explain how wave refraction causes
severe erosion along headlands.
• Along irregular coasts, waves bend toward
the headlands and most of the breakers’
energy is concentrated along the tips of
the headlands. Thus, headlands undergo
severe erosion.
3. What is a beach? What are beaches
composed of?
• A beach is a sloping band of sand,
pebbles, gravel, or mud at the edge of the
sea.
• Beaches are composed of loose sediments
deposited and moved about by waves
along the shoreline.
4. What determines the size of the
particles that make up a beach?
• The size of the sediment particles depends
on the energy of the waves striking the
coast and on the source of the sediment.
5. State 3 examples of the composition
of beaches and sources of sediment.
• Hawaiian beaches have black sand,
derived from volcanic rocks
• Bahamas and Florida have white and pink
sand, made from fragments of coral
• Beaches near the mouths of rivers are
composed of quartz and feldspar, washed
downstream by the rivers
6. What is an estuary?...
• An estuary is the area where the mouth of
a freshwater river enters an ocean. They
contain brackish water, a mix of fresh- and
saltwater. Estuaries are nurseries for
young ocean fishes.
7. What is a longshore bar?
• A longshore bar is a sandbar that forms in
front of most beaches, caused by the
deposition of sediment by waves breaking
in the surf zone.
8. How is the longshore current produced?
• As water from incoming breakers spills
over the longshore bar, a current flowing
parallel to the shore is produced.
9. How do longshore currents transport
sediment? What direction…
• Fine-grained material is suspended in the
turbulent water. Larger particles are
pushed along the bottom by the current.
• This transport is usually in a SOUTH
direction.
10. Describe each of the following
depositional landforms:
• Spit: a narrow bank of sand that projects
into the water from a bend in the
coastline. It forms where the shoreline
changes direction and is protected from
wave action.
10. Describe each of the following
depositional landforms:
• Barrier Island: a long ridge of sand or
sediment, deposited and shaped by the
longshore current, separated from the
mainland. They are formed as longshore
bars build up until they break the surface
of the water.
10. Describe each of the following
depositional landforms:
• Lagoon: shallow, protected bodies of
water behind barrier islands. They are
saltwater coastal lakes connected to the
ocean by shallow outlets.
11. Why are these depositional
landforms considered temporary?
• Changing wave conditions can slowly
erode beaches and rearrange shorelines.
• The longshore current causes barrier
islands to shift southward over time.
12. Describe the ways that erosion can
occur at a beach at both tides.
• At high tide, the longshore current can
deposit sediment on a beach so that it
extends in the direction of the current.
• Wherever sediments are exposed at low
tide, winds pick up dry sand and build
sand dunes.
13. Describe each of the following
protective structures…
• Sea walls: intended to protect beachfront
properties from powerful storm waves
• Actually, they reflect wave energy back
into the ocean
• They worsen beach erosion, eventually
undercutting the sea wall
13. Describe each of the following
protective structures…
• Jetties: intended to protect a harbor
entrance from drifting sand
• Actually, they trap sand upshore from a
harbor and prevent it from reaching
beaches downshore.
• They cause erosion downshore of the
harbor
13. Describe each of the following
protective structures…
• Breakwaters: intended to provide
anchorages for small boats
• Actually, they alter the longshore current
by slowing it down, causing sediment to
be deposited behind the breakwater,
which eventually fills in the anchorage.