GLG110 Geologic Disasters and the Environment

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GLG110 Geologic Disasters and the Environment
Today Chapter 9Coastal processes
Instructor Professor Ramon Arrowsmith Email
ramon.arrowsmith_at_asu.edu Office PSF-640
480-965-3541
TA Tom Foltz Email Thomas.foltz_at_asu.edu Office
PSH-574
Course Website http//glg110.asu.edu
http//www.maui.net/mauibnb/hookipa_beach_photos.
htm
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Outline

• Tides
• Coastal Hazards
• Coastal processes
• Waves
• Beach form and beach processes
• Rip currents
• Coastal erosion
• Controlling factors
• Seacliff erosion
• Coastal Hazards and engineering structures
• Human activity and coastal erosion

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Tides

• Twice daily rise and fall of the sea caused
• by the gravitational attraction between
• earth and moon (lunar tides)
• earth and sun (solar tides)

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Lunar Tidal Bulges
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Interaction between lunar and solar tides during
the lunar month causes

• Neap tides when two tidal components are
  out-of-phase, hence lower than usual, and
• Spring tides when two tidal components are
  in-phase, hence higher than usual.

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Tides
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Mont-Saint-Michel France
Exposed tidal flats
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Tidal Flat - Wales
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Disaster of the day Beach erosion
Significant Losses From Coastal Erosion
Anticipated Along U.S. Coastlines Approximately
25 percent of homes and other structures within
500 feet of the U.S. coastline and the shorelines
of the Great Lakes will fall victim to the
effects of erosion within the next 60 years,
according to a study released today by the
Federal Emergency Management Agency (FEMA).

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http//www.fema.gov/pdf/hazards/hnz_erosn.pdf
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USGS 1997-98 El Niño Coastal Monitoring Program
Examples http//walrus.wr.usgs.gov/elnino/coastal/
coastal.html
Pacifica
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Esplanade Drive, Pacifica Nine homes have been
red-tagged in most critical area of coastal land
loss in Central California. The cliffs here have
been retreating at an average rate of about 2
feet/year since 1950, but retreated over 30 feet
during two weeks in February 1998. Attempts were
made in early January to emplace a seawall at the
base of the cliffs. Winter storms rolled in and
left the machinery stranded. Seven of these 9
homes have now been demolished.
http//walrus.wr.usgs.gov/elnino/coastal/pacifica.
html
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Coastal hazards and risk

• Coasts are dynamic environments
• Much population along coasts
• Most serious hazards
• Rip currents
• Coastal erosion
• Tsunamis
• Tropical cyclones (hurricanes and typhoons)

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WAVE EROSION
breaking waves silt, sand, gravel
erosion
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BEACHES

• Source of beach
• sediments
• rivers
• cliff erosion
• marine life
• Sand composition
• black? white? yellow?

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BEACHESSEASONAL CHANGES

• Summer
• gentle waves
• add beach sand
• Winter
• storm waves
• erode beach
• sand

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Sandy Beach, North Carolina Barrier Island
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Boulder Beach, Massachusetts
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WAVES

• Wave height depends on
• WIND!
• Wind velocity
• Wind duration
• Distance over which wind blows

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Deeper water wave forms and definitions (Keller,
2002)
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Waves and shallow water depth (lt0.25L)
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WAVE PARTICLE MOTION

• Circular
• Biggest at
• surface

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Changes in Waves as they Approach the Beach

• Wave height increases
• Wave length decreases
• Velocity decreases
• Period doesnt change

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Wave refraction and concentration of wave energy
on rocky points
Keller, 2002
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BEACHESMajor Parts of a Beach
Keller, 2002
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Beach and longshore drift
Aka Littoral drift
Keller, 2002
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Rip currentsreturn flow of water from incoming
waves
Keller, 2002
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Coastal erosionWashington coast (before)
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Coastal erosionWashington coast (after)
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Coastal erosion
Oblique Aerial Photography - Coastal Erosion from
El-Niño Winter Storms S. Washington/N. Oregon
http//coastal.er.usgs.gov/response/
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Coastal erosion Santa Barbara, CA
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Coastal erosion Before Hurricane

• U.S. Geological Survey

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Coastal erosion After Hurricane

• U.S. Geological Survey