1. GSC 1530: Chapter 20 Shorelines

2. Shorelines, both ocean and lake, can be very beautiful settings However, shorelines are some of the most geologically dynamic settings on Earth Processes like shoreline erosion, sea level increases and deadly coastal storms (e.g., hurricanes) threaten the lives and property of billions of people worldwide As of 2008 about 165 million people in the U.S. live within 50 miles of a marine coast

3. Shorelines Terminology Oceanic shoreline – land line marking contact between land and sea Oceanic shore – area between lowest high tide and highest land point affected by storm waves Coast – area extending from the landward backshore boundary to the limit of ocean-related features like dunes Coastline – coast’s seaward edge All locations can vary

4. Coastal Processes Terminology Current ( ) - unidirectional flow of water and energy caused by wind, water density differences and water temperature differences Oceanic currents redistribute heat through the ocean and therefore play a critical role in climate (see figures)

5. Warm, less salty surface current Cold, salty deep current Gulf Stream Gulf Stream: 50-90 miles wide; maximum discharge: 540 billion tons/hour

7. Coastal Process Terminology Tides ( ) - periodic, rhythmic rise and fall of water along coastlines due to the gravitational tug of the Sun and Moon on the Earth Most oceanic coastlines experience two high tides and two low tides each day Spring tide Neap tide

9. Tidal Cycle

11. Coastal Process Terminology Tsunami ( ) – omni directional flow of water away from a central point caused by any event (e.g., seafloor earthquake, submarine landslide) that vertically displaces water from its equilibrium position Don’t call tsunamis “tidal waves” earthquake triggered tsunami

12. Japan Tsunami 2011 Japanese Tsunami Photograph

13. Wave Terminology Wave – undulation of the water surface Currents, tides and tsunamis generate waves Wavelength – the horizontal distance between two adjacent wave crests or two adjacent wave troughs (see figure) Wave frequency – the number of waveforms that pass a fixed point per unit of time The higher the wave frequency the greater the wave’s impact or penetration energy

14. Wave frequency – the number of crests, or troughs, of a waveform that pass a fixed point per unit of time Common units – cps (cycles per second); Hertz (Hz); 1 Hz = 1cps Wave base – the maximum depth to which energy from a surface wave is transmitted; equal to the wave’s wavelength/2

15. As a wave approaches a shoreline, waves of oscillation transform to waves of translation – the predominant water flow is horizontal

17. Note “breaking” waves; they can perform substantial shoreline erosion

18. Major Factors Controlling Shoreline Erosion Topography (e.g., steep or shallow) of shoreline Resistance of shoreline rocks or sediments to erosion Erosive force of daily currents, tides Frequency and intensity of high-energy storm events (e.g., hurricanes) or abnormal events like tsunamis Frequency of tectonic events (e.g., earthquakes)

19. Sea arch

20. Wave undercutting

21. Sea arch Sea stack

22. Importance of recognizing the rates of shoreline erosion?

25. Evidence for long- term fluctuations in sea-level is found in wave-cut platforms in rocky coastlines (see figures)

26. What long-term cyclic process could cause significant fluctuations in sea level? wave-cut platforms

27. Source: Geology of Michigan and the Great Lakes, 2008

28. Emergent and Submergent Coasts Emergent coast – coastline rises relative to sea level as a consequence of sea level decline or land uplift Submergent coast – coastline is lowered (covered by water) relative to sea level as a consequence of sea level increase or land subsidence Global warming and cooling and plate tectonic motion can obviously affect long-term sea levels; what rapid, high energy process could quickly create emergent or submergent coasts? (see slide)

30. Coastal Processes Shoreline erosion and sediment movement are also influenced by wave refraction Wave refraction – change in shape of a waveform as it approaches shore; occurs when portions of the wave pass into waters of unequal depth (see figure)

33. Coastal straightening due to long-term wave erosion

34. Wave Refraction Wave refraction is also responsible for establishing the longshore current and initiating littoral drift (beach drift) (see slides)

35. = littoral drift or beach drift

36. Dynamic Coastal Settings Mainland beaches, barrier islands, spits and estuaries are some of the most dynamic settings on Earth Let’s examine the geological characteristics of these settings and the hazards associated with their development

37. Barrier Islands Mainland Beach Spit

38. Beach – an accumulation of unconsolidated sediment along the landward margin of an ocean or lake

39. Dynamic Coastal Environments

40. An elongate, narrow, low-elevation island, composed of unconsolidated sediment, that parallels the mainland

42. Aerial view of the NC “Outer Banks” barrier islands

43. Spit – an elongate ridge on unconsolidated fine-grained sediment that extends from the mainland into the mouth of an adjacent bay

45. Estuary – a coastal embayment formed by the flooding of a river’s mouth; often result from the rise in sea level that accompanies the melting of Ice Age ice sheets – an example of a submergent coast

46. Earth DIGIT CD

47. Estuary

48. Human Impacts Let’s examine some of the impacts and consequences of human interaction with these dynamic coastal environments Question to ponder: why do we develop land in these dynamic coastal environments? What ongoing controversy surrounds this development?

49. Long Island, New York

50. eye

54. 1969 Hurricane Camille Storm Surge Effects, MS Coast Storm Surge – one or more domes (walls) of water that sweeps across the coast near where the eye of the hurricane makes landfall; can be 40-50 mi wide and have heights of 10-30 ft above the mean high tide! Before storm surge After storm surge

55. Superstorm Sandy Damages, 10/2012

56. Shoreline development controversy?

57. An elongate, narrow, low-elevation island, composed of unconsolidated sediment, that parallels the mainland

58. Sand Galveston Island Gulf of Mexico Distance (meters) 0 4 8

59. 1900 Galveston Island Hurricane Damage An estimated 8000 - 12000 people on the island lost their lives from storm surge waves of 15 – 20 feet height Status of Galveston Island today?

61. Human Intervention Humans have tried multiple methods to minimize coastal erosion and storm impact; none of these approaches are failsafe or permanent and none can protect the coast from massive storms Many of these approaches benefit some coastal properties while concurrently harming others Let’s examine some of the common approaches

62. Soft Stabilization

63. Hard Stabilization

64. Possible negative consequences?

65. Beach Groin Longshore current and littoral drift deposited sediment Waves accelerated erosion

67. Fig. 7.17 Breakwaters may also increase coastal erosion rates at specific sites

68. Effects of beach nourishment along Miami Beach, FA Typical costs: $2-10 million per mile; 3-9 year average renourishment frequency!

69. Beach Nourishment

71. Great Lakes Shores Always investigate shoreline processes before purchasing property in the Great Lakes basin. Lake Michigan Lake Erie Lake Michigan