Download
beaches n.
Skip this Video
Loading SlideShow in 5 Seconds..
Beaches PowerPoint Presentation

Beaches

228 Views Download Presentation
Download Presentation

Beaches

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Beaches

  2. What is a beach? • Area along coast where sediment accumulates • Coastal zones begin when waves interact with seafloor

  3. BeachesShoreline Divisions • Littoral zone • Part of coast that stretches from land plants to where waves start to break • Shoreface • Permanently covered by water • Foreshore • Exposed at low tide and covered at high tide • Backshore • above mean high tide – only affected by storms

  4. BeachesShoreline Divisions Divided by wave action: • Breaker zone • Where waves become unstable and break • Surf zone • Shallower waves move up beach face • Swash zone • alternately covered by “swash” and uncovered by “backwash”

  5. BeachesSediment Profile • Berm • Flat-top ridge of backshore • Berm crest • High point on a beach • Beach face • Sloping portion of the beach • Longshore bars • In winter, sediment from berm is transported below breaker zone

  6. Quartz wide Cobble Pink sand narrow sand Black sand Shell BeachesTypes • Shape and structure • Composition • Size • Color

  7. winter summer BeachesSummer and Winter • Summer • Winter • Gentle waves • Erosive storm waves • Carry sand to shore but too weak to carry back to sea • Sand carried seaward to offshore sandbars • Wide, sandy beach • Narrow, rocky beach

  8. Beach ProcessesRefraction • Wave crests approach shore at an angle • Slows over shallow water • Wave bends • Wave rays travel perpendicular to wave crest • Energy focused on headlands  erosion

  9. Beach ProcessesRip Currents • Incoming waves create underwater sandbar close to shore • Waves cause sandbar to collapse • Excess water is pushed through gap • Creates a strong, narrow current away from shore

  10. Beach ProcessesLongshore Current and Transport • Longshore current moves parallel to shore • Longshore transport moves sediment along shore by LS current • Zig-zag motion has an overall net transport • Swash moves sediment onto beach at an angle • Backwash moves sediment down perpendicular to shore

  11. Sandy shore Rocky shore Beach DynamicsDeposition and Erosion • Deposition • Accumulation of sediment • Coasts build out by waves and currents • Erosion • Little incoming sand, usually no major river • Sediment is removed • Reshaping of coastline by wave action

  12. BeachesDepositional Features • Longshore current deposits sand in a line downcurrent • Sand spits • Bay mouth bars • When a sand spit closes off a bay • Barrier island • Long sand island enclosing a bay or lagoon

  13. BeachesErosional Features • Arches • Weaker rocks erode Stack Arch • Stacks • Offshore column formed from collapsed arch • Tombolo • Sand bar connecting to a rock or offshore outcrop Tombolo

  14. Cliff Wave cut bench BeachesErosional Features • Wave cut bench • Cliff • Cliff bottom attacked by waves • Waves undercut cliff to form wave cut notch • Overhanging rock collapse • As cliff retreats, area of flat rock exposed

  15. BeachesErosional Features • Marine terrace • If sea level lowers or land uplifted, wave cut bench becomes marine terrace

  16. BeachesHuman Impacts • Parallel concrete structures • Absorbs wave energy • Sea walls • Actually promotes erosion • Groins • Wall perpendicular to shore • Stops erosion • Erodes downcurrent side • Jetties • Designed to maintain navigation routes • Erosion and deposition • Breakwaters • Wall parallel to shore • Reduce wave energy • Interrupts beach drift

  17. Miami Beach after before BeachesHuman intervention • Beach nourishment • Import sand into coastal areas • Dredging • Underwater excavation to clear waterways