Shoreline Features and Processes

1. Shoreline Features and Processes Chapter 16, Section 3

2. Forces Acting on the Shoreline • Waves along the shoreline are constantly eroding, transporting, and depositing sediment. Many types of shoreline features can result from this activity • The impact of large, high-energy waves against the shore can be very violent • Cracks and crevices quickly open in the cliffs, and water is forced through • Abrasion is the sawing and grinding action of rock fragments in the water • Waves are also very effective at breaking down rock material and supplying sand to beaches

3. Impact and Abrasion

4. Wave Refraction • Wave Refraction – the bending of waves • Most waves move towards the shore at an angle • When the waves get closer, they are refracted, bent, so that they come into the shore parallel • Because of refraction, wave energy is concentrated against the sides and ends of headlands that project into the water, whereas wave action is weakened in bays

5. Wave Refraction

6. Longshore Transport • Longshore Current – flow parallel to shore and move large quantities of sediment along the shore • Turbulence allows long shore currents to easily move fine suspended sand and to roll larger sand and gravel particles along the bottom • Longshore currents can change directions because the direction that waves approach the beach changes with the seasons • Longshore currents generally flow southwards along the Western coast of North America

7. Longshore Currents

8. Erosional Features • Shoreline features that originate primarily from the work of erosion are called erosional features • Wave erosion is steadily wearing away the California coast • The cliffs along our coast are created when tectonic processes push the land up at the same time the ocean waves crash against them, eroding them away • Wave-cut cliffs result from the cutting action of the surf against the base of coastal land • As erosion continues, it will reduce the cliffs into a bench-like feature, called a platform • The surf can erode headlands, creating sea caves, when two sea caves meet, a sea arch will form • Arches all eventually collapse into sea stacks

9. Wave-Cut Cliffs

10. Sea Arches

11. Depositional Features • Sediment that is transported along the shore and deposited in areas where energy is low produce depositional features • Where longshore currents and other surf zone currents are active, several features related to the movement of sediment along the shore may develop • A spit is an elongated ridge of sand that projects from the land into the mouth of an adjacent bay

12. The term baymouth bar is used when a sandbar completely crosses a bay, cutting it off from the ocean A tombolo is a ridge of sand that connects an island to the mainland or another island Barrier Islands – narrow sandbars parallel to, but separated from the coast

13. Spit, Bars, and Tombolos

14. Barrier Islands

15. Evolution of Shoreline Features

16. Stabilizing the Shore • Shorelines are among Earth’s most dynamic places and are changing constantly • Erosion along the coast causes significant property damage every year • Groins, breakwaters, and seawalls are some structures built to protect a coast from erosion or to prevent the movement of sand along a beach • A groin is a barrier on the beach to trap sand that is moving parallel to the shore

17. A breakwater protects ships from the force of large breaking waves as they pull out of harbor A seawall is built parallel to shore and protects the shore from waves Beach nourishment is the addition of large quantities of sand to the beach system

18. Protective Structures

19. Assignment • Read Chapter 16, Section 3 (pg. 461-467) • Do Section 16.3 Assessment #1-12 (pg. 467)