Wednesday March 28, 2012

1. WednesdayMarch 28, 2012 (Beach and Shoreline Processes and Features)

2. The Launch Pad Wednesday, 3/28/12 Explain the process of “beach drift.” When waves wash up onto shore, they don’t always hit at 90o to the beach. They will wash up at the angle of the wind. However, when the water recedes back from the beach, it is usually at 90o. Therefore, the angle of swash doesn’t equal the angle of backwash, and a zigzag pattern is set up. This will steadily move the material on the beach down the coastline.

4. Announcements • I will be available after school today until 4:45.

5. Latest News How Cosmic Collisions May Have Altered Earth's Evolution Click below for article: http://www.space.com/15072-earth-composition-cosmic-collisions-chondrites.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+spaceheadlines+%28SPACE.com+Headline+Feed%29&utm_content=Google+Feedfetcher

6. Continue Worksheet The Coastal Zone and Waves

7. Wave Erosion Wave erosion is caused by wave impact and pressure. Wave erosion breaks down rock material and supplies sand to beaches. The sawing and grinding action of water armed with rock fragments is called abrasion.

8. Sand Movement on the Beach Beaches are composed of whatever material is available.

9. Sand Movement on the Beach Some beaches have a significant biological component.

10. Sand Movement on the Beach Beach material does not stay in one place. Wave energy moves large quantities of sand parallel and perpendicular to the shoreline.

11. Beach and Shoreline Processes Wave refraction is the bending of a wave so that the wave arrives parallel to the shore The result of wave refraction is that wave energy is concentrated against the sides and ends of headland. Wave erosion straightens an irregular shoreline

12. Beach and Shoreline Processes Longshore transport consists of the movement of sediments (generally sand, but may also consist of coarser sediments such as gravels) along a coast at an angle to the shoreline, which is dependent on prevailing wind direction.

13. Beach and Shoreline Processes • Beach drift is one of the most important transport mechanisms results from wave refraction. • Since waves rarely break onto a shore at right angles, the upward movement of water onto the beach (swash) occurs at an oblique angle. • However, the return of water (backwash) is at right angles to the beach, resulting in the net movement of beach material laterally. • This movement is known as beach drift. • The endless cycle of swash and backwash and resulting beach drift can be observed on all beaches. – sediment moves in a zigzag pattern along the beach face.

14. Beach and Shoreline Processes • Longshore current is current that flows in the surf zone. • Longshore current flows parallel to the shore, and moves substantially more sediment than beach drift.

15. Beach Drift and Longshore Currents Figure 15.18

17. Shoreline Features Shoreline features created by erosional effects include: Wave-cut cliffs Wave-cut platforms Marine terraces Sea arches Sea stacks

18. Figure 15.24 A

19. A Sea Stack and a Sea Arch Figure 15.21

20. Shoreline Features Depositional Features A spit is a ridge of sand extending from the land into the mouth of an adjacent bay with an end that often hooks landward.

21. Figure 15.24 C

22. Shoreline Features Depositional Features A baymouth bar is a sand bar that completely crosses a bay.

23. Aerial View of a Spit and Baymouth Bar Along the Massachusetts Coastline Figure 15.22 A

24. Shoreline Features Depositional Features A tombolo is a ridge of sand that connects an island to the mainland.

25. Figure 15.24 B

26. Shoreline Features Depositional Features Barrier islands occur mainly along the Atlantic and Gulf Coastal Plains. They run parallel the coast and can originate in several ways.

27. Stabilizing the Shore Shoreline erosion is influenced by several local factors • the proximity to sediment-laden rivers • the degree of tectonic activity • the topography and composition of the land • the prevailing wind and weather patterns • the configuration of the coastline

28. Stabilizing the Shore Responses to Erosion Problems “Hard stabilization” refers to building structures to lessen the effects of shoreline erosion. Types of structures Groins are barriers built at a right angles to the beach that are designed to trap sand. Breakwaters are barriers built offshore and parallel to the coast to protect boats from breaking waves. Seawalls armors the coast against the force of breaking waves. Often these structures are not effective.

29. Stabilizing the Shore Responses to Erosion Problems Alternatives to hard stabilization: In beach nourishment, sand is added to the beach system. Relocating buildings away from a beach

30. Miami Beach Before and After Beach Nourishment Figure 15.28 A

31. Stabilizing the Shore Responses to Erosion Problems Shoreline erosion problems are different along the different U.S. coasts. Along the Atlantic and Gulf Coasts, development occurs mainly on barrier islands that face the open ocean. These islands receive the full force of storms. Development has taken place more rapidly than our understanding of barrier island dynamics.

32. Stabilizing the Shore Responses to Erosion Problems Shoreline erosion problems are different along the different U.S. coasts. The Pacific Coast is characterized by relatively narrow beaches backed by steep cliffs and mountain ranges. The major problem here is the narrowing of the beaches. Sediment for beaches is interrupted by dams and reservoirs; therefore, rapid erosion occurs along the beaches.