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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.