Principles of Geology

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Principles of Geology

• Chapter 20
• Shorelines

Mian Liu 2007 Fall
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Outline

• Introduction the shoreline
• Waves
• Shoreline features
• Erosional problems
• Tide, Tsunami, and Hurricane

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The shoreline A dynamic interface

• The shoreline is a dynamic interface (common
  boundary) between air, land, and the ocean
• The shoreline is constantly being modified by
  waves
• Today the coastal zone is experiencing intense
  human activity

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Figure 20.2
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Major Geological Agents working at shorelines

• Waves
• Tides
• Tsunami

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Outline

• Introduction the shoreline
• Waves
• Shoreline features
• Erosional problems
• Tide, Tsunami, and Hurricane

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• What caused waves?
• Wind
• Properties of winds important for wind
  generation
• Wind speed
• The length of time the wind has blown
• The fetch, or distance of open water over which
  the wind has blown

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Characteristics of waves

• Wave height
• Wave length
• Wave period

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Wave motions
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Waves

• Types of waves
• Wave of oscillation
• Wave energy moves forward, not the water itself
• Occur in the open sea in deep water
• Wave of translation
• Begins to form in shallower water when the
  water-depth is about one-half the wavelength and
  the wave begins to feel bottom

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Outline

• Introduction the shoreline
• Waves
• Shoreline features
• Erosional problems
• Tide, Tsunami, and Hurricane

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Nearshore circulation

• Wave refraction
• Longshore current
• Rip current
• Swash and backwash

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Wave refraction
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Wave refraction

• Bending of a wave
• Causes waves to arrive nearly parallel to the
  shore
• Consequences of wave refraction
• Wave energy is concentrated against the sides and
  ends of headlands

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Rip current
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Wave erosion

• Wave impact
• Plucking
• Dissolution
• Abrasion

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Erosional Coastal features

• Sea cliffs
• Wave-cut platform
• Stacks
• Arches

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Depositional Coastal features

• Spits
• Baymouth bars
• Tombolo
• Barrier islands

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backwash
swash
Beach rift
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• Barrier islands
• Mainly along the Atlantic and Gulf coasts
• Low ridges of sand that parallel the coast 3 to
  30 kilometers offshore
• Probably form in several ways

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Barrier islands along the Texas coast
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Tides currents

• Flood currents - advance into the coastal zone
• Ebb current - seaward-moving water as the tide
  falls
• Tidal flats - areas affected by the alternating
  flood currents and ebb currents
• Tidal deltas - deposited from tidal currents

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Tides

• Tides and Earths rotation
• Tidal friction against the ocean floor acts as a
  weak brake that is steadily slowing Earths
  rotation
• The day is increasing by 0.002 seconds per
  century
• This small effect becomes very large over
  millions of years
• Length of each day must have been shorter in the
  geologic past

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Tropical Storms

• tropical cyclone the maximum sustained surface
  wind is 64 kt (74 mph or 119 km/hr) or more.
• Hurricane used for Northern Hemisphere tropical
  cyclones east of the International Dateline to
  the Greenwich Meridian.
• Typhoon used for Pacific tropical cyclones
  north of the Equator west of the International
  Dateline.

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Major damages by hurricanes

• Storm surge
• Wind
• Inland flooding

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Table 20.A
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Tsunami
A tsunami (pronounced tsoo-nah-mee) is a wave
train, or series of waves, generated in a body of
water by an impulsive disturbance that vertically
displaces the water column. Earthquakes,
landslides, volcanic eruptions, explosions, and
even the impact of cosmic bodies, such as
meteorites, can generate tsunamis. Tsunamis can
savagely attack coastlines, causing devastating
property damage and loss of life.
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Shoreline erosion problems
New Jersey
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Coasts shaped by Tectonics and sea level change

• Emergent coasts - uplift or sea level drop (e.g.,
  Californian coast)
• Submergent coasts - subsidence or sea level rise
  (e.g., NE coasts)

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End of Chapter 20