Earth and Science G12

1. Tropical cyclones - high winds (100+ km/hr)
- flooding from intense precipitation
- storm surges
Golden Gate Bridge data set
Tidal floods – storm surges coinciding with tidal peaks
Tsunami’s – seismic sea waves
About 75% of the US population lives in coastal areas. Impacts from
coastal hazards can be substantial. The source of the hazards
includes several “non-geologic” processes such as:
Coastal Processes and Hazards
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2. Passive margin
Margins
Th ge goic haz a ry cc ing to the continental margins
There are two general ocean margins – passive and active margins – both
are related to plate tectonics
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3. Components of the acltive margin
Structure of the ocean margins
Active Margins
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4. www.surfrider.org/structures/images/canyons.jpg
All coasts are divided into natural compartments called littoral cells. Each
cell contains a complete cycle of sedimentation including sources,
transport paths, and sinks.
CThe Littoral Cell
y
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5. Active margin
CThe Littoral Cell y
The presence of sand on any particular beach depends on the transport of
sand within the cell. When structures such as dams or harbors
interfere with sand transport, downcoast beaches will erode.
Therefore,the littoral cell and its budget of sediment are essential
planning tools for regional and coastal management.
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6. Active margin
CoasBelaches logy
Structure of the ocean margins
Summer versus winter beaches
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7. Coastal Processes and Hazards
Coastal hazards that arise along the different margins include:
• Erosion – due to wave action and fluctuating sea levels
• Deposition – from littoral transport
Golden Gate Bridge data set
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8. Perceptions and adjustment to hazards
More and more the question is becoming:
do we continue to subsidize development in risky coastal areas?
From 1978 to 1982, $43 million dollars in federal flood insurance was paid
in damage claims to barrier-island residents, which far exceeded the
premiums they paid.
Golden Gate Bridge data set
It is becoming increasingly obvious that the most sensible thing to do with
many such structures is to abandon the costly and ultimately doomed
efforts to protect or maintain them, and simply leave these areas in
their dynamic, natural, rapidly changing state, most often as
underdeveloped recreation areas.
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9. Perceptions and adjustments to hazards
From a philosophical perspective:
1. Coastal erosion is a natural process rather than a natural
hazard; erosion problems occur when people build structures in
the coastal zone.
2. Any shoreline construction causes change.
3. Engineering structures designed to protect a beach may
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10. Coastal Processes and Hazards
From a philosophical perspective:
4. Stabilization of the coastal zone through engineering structures
protects the property of relatively few people at a larger general
expense to the public.
5. Once constructed, shoreline engineering structures produce a
trend in coastal development that is difficult if not impossible to
reverse.
Golden Gate Bridge data set
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11. End
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12. Golden Gate Bridge data set
Erosion
• Sea level has risen 15 – 20 cm during the last century.
www.wildwildweather.com/forecastblog/wp-conte
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13. Emerging
shorelines
Changing sea levels over time produce emerging shorelines. Tectonic
uplift also causes land to slowly emerging from the sea.
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14. Submerging
shorelines
Changing sea levels over time
produce submergent
shorelines.
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15. Effects of waves
Waves are a powerful force. The net effect is to straighten out shorelines
and transport large volumes of sediment.
Erosion
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16. Effects of waves
Waves are a powerful force. The net effect is to straighten out shorelines
and transport large volumes of sediment.
Wave erosion – force
is concentrated on
headlands,
resulting in
excessive erosion.
Called wave
refraction and
results from wave
“drag” on ocean
floor.
Erosion
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17. Erosion
Effects of waves
Waves are a powerful force. Can cause severe erosion problems along
coastal areas.
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18. Erosional Landforms – winter, 1989
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19. Erosional Landforms – February, 1990
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20. Erosional Landforms – February, 1991
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21. Erosional Landforms – February, 1993
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22. Erosional Landforms – March, 1999
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23. Warmer than normal
waters produce warm
air masses that hold
lots of rain and
produce severe storms
and waves.
El Nino conditions produce more extreme wave conditions
Erosion
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24. El Nino conditions produce more extreme wave conditions
Normal wind and water
motion
Erosion
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25. El Nino conditions produce more extreme wave conditions
El Nino wind and water
motion
Erosion
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26. Effects of waves
Waves are a powerful force. The net effect is to straighten out shorelines
and transport large volumes of sediment.
Wave deposition –
waves spread out
here, have less
energy.
Longshore drift
moves sand as a
sheet along the
coastline.
Deposition
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27. Sand transportation – is a natural process but has also been affected by
humans.
Groins – encourage deposition in
desired locale.
Deposition
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28. Sand transportation – is a natural process but has also been affected by
humans.
Jetties – designed
to keep river
channels from
filling in and
relocating due
to sand
deposition.
Deposition
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29. Sand transportation – is a natural process but has also been affected by
humans.
breakwaters –
designed to
protect and
encourage
harbor
development.
Deposition
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30. Sand transportation – is a natural process but has also been affected by
humans.
Man-made
structures in
action.
Deposition
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31. Links
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