Ch 17 (Part II) SHORELINES

1. Ch 17 (Part II) SHORELINES • Waves • Longshore transport • Erosional shores • Depositional shores • Emergent and submergent shores • Sealevel rise

2. Shorelines a) Waves Ocean WAVES = orbital wave (waves of oscillation) Energy advances But: Water does not! Water moves in circular orbits = erosion

3. Shorelines a) Waves Breaking WAVES • Waves ‘feel’ bottom when it comes to within half of the wavelength • Wave length decreases, wave height increases • At critical point the wave becomes too steep and breaks • Surf sloshes onshore Fig. 17.13

4. a) Waves Summertime and wintertime beach conditions Summertime beach Wintertime beach

5. a) Waves Wave refractionstrongly influences erosion and sediment transport Waves refract around headlands, increasing wave impact on headlands, decreasing it on beaches. Waves travel more slowly in shallow water so they refract towards the beach. Fig. 17.13

6. Shorelines b) Longshore transport Longshore transport • Swash is oblique, backwash straight, causing beach drift of sediment along the shore • Oblique waves also cause longshore currents parallel to beach Beaches = Rivers of sand!

7. Longshore currents and rip currents

8. Shorelines c) Erosional Shores Wave refraction along an irregular shoreline • Wave energy is concentrated at headlands and dispersed in bays • Causes erosion of headlands and creation of erosional features Figure 10-14b Fig. Story 17.13

9. Shorelines c) Erosional Shores • Headland • Wave-cut cliff • Wave-cut terrace (bench) • Sea cave • Sea arch • Sea stack

10. Shorelines d) Depositional Shores BEACHES • Source of beach • sediments • rivers • cliff erosion • marine life • Sand composition Beaches See Fig. 17.18

11. Shorelines d) Depositional Shores BEACHES • Source of beach • sediments • rivers • cliff erosion • marine life • Sand composition See Fig. 17.18

12. Shorelines d) Depositional Shores • Spit • Bay barrier (baymouth bar) • Tombolo • Barrier island • Delta

13. e) Emergent and submergent coasts Emergent coasts • Develop because of uplift of an area or a drop in sea level • Features of an emergent coast • Wave-cut cliffs • Wave-cut platforms

14. e) Emergent and submergent coasts Uplifted, ancient wave-cut benches exposed in southern California

15. e) Emergent and submergent coasts Submergent coast • Caused by subsidence of land adjacent to the sea or a rise in sea level • Features of a submergent coast • Highly irregular shoreline • Estuaries – drown river mouths

16. e) Emergent and submergent coasts Chesapeake Bay is a good example of a submergent coastline

17. f) Sea-level rise Fossil fuel burning has added greenhouse gases to atmosphere Global warming follows (up to 0.6 C in past century) Sea-level rise: thermal expansion of seawater and ice-sheet melting, 4mm/yr, 20-90 cm during this century

18. Chapter 17: Earth beneath the ocean Y W X Z The area labeled “W” is the __________. A. abyssal plain B. continental rise C. continental shelf D. continental slope

19. Chapter 17: Earth beneath the ocean Y W X Z The area labeled “X” is the __________. A. abyssal plain B. continental rise C. continental shelf D. continental slope

20. Chapter 17: Earth beneath the ocean Y W X Z The area labeled “Y” is the __________. A. abyssal plain B. continental rise C. continental shelf D. continental slope

21. Chapter 17: Earth beneath the ocean Which of the following statements is false? A. Deep-sea sedimentation leaves a more continuous geologic record than continental sedimentation. B. The oceans lack folded and faulted mountains like those on continents. C. The oldest oceanic crust is much younger than the oldest continental crust. D. Weathering and erosion are more important in the oceans than on continents.

22. Chapter 17: Earth beneath the ocean In which of the following locations would you most likely find outcrops of basalt on the ocean floor? A. on the abyssal plain B. on the continental rise C. on the continental shelf D. on the flank of a rift valley

23. Chapter 17: Earth beneath the ocean A traverse from North America across the Atlantic Ocean to continental Europe would reveal that the ocean floor ____________. A. has high undersea mountains near both continents and is flat in the middle B. has deep trenches near both continents C. has a number of active volcanoes along most of the width of the traverse D. is approximately symmetric about the Mid-Atlantic Ridge

24. Chapter 17: Earth beneath the ocean Graded beds of sand, silt, and mud deposited on submarine fans are called ______. A. alluvial fans B. dunes C. tills D. turbidites

25. Chapter 17: Earth beneath the ocean Which of the following materials would one expect to find on a continental shelf at a passive margin? A. basalt B. pelagic sediments C. terrigenous sediments D. volcanic ash

26. Chapter 17: Earth beneath the ocean What are foraminifera shells, the most abundant biochemically precipitated pelagic sediment, made of? A. calcium carbonate B. silicon dioxide C. sodium chloride D. iron sulfide

27. Chapter 17: Earth beneath the ocean Which of the following forms a barricade between the open ocean and the main shoreline? A. abyssal hills B. barrier islands C. guyots D. wave-cut terraces

28. Chapter 17: Earth beneath the ocean The zigzag motion that carries sand grains along a beach is known as ________. A. longshore drift B. meandering C. refraction D. turbidity