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- 1. 1 Coastal Processes and Hazards 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: Golden Gate Bridge data set Tropical cyclones - high winds (100+ km/hr) - flooding from intense precipitation - storm surges Tidal floods – storm surges coinciding with tidal peaks Tsunami’s – seismic sea waves
- 2. 2 Margins Structure of the ocean margins Passive margin There are two general ocean margins – passive and active margins – both are related to plate tectonics The geologic hazards vary according to the continental margins
- 3. 3 Coastal Geology Structure of the ocean margins Active Margins Components of the active margin
- 4. 4 Coastal Geology All coasts are divided into natural compartments called littoral cells. Each cell contains a complete cycle of sedimentation including sources, transport paths, and sinks. Active margin The Littoral Cell www.surfrider.org/structures/images/canyons.jpg
- 5. 5 Coastal Geology 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. Active margin The Littoral Cell
- 6. 6 Coastal Geology Structure of the ocean margins Summer versus winter beaches Active margin Beaches
- 7. 7 Coastal Processes and Hazards Coastal hazards that arise along the different margins include: Golden Gate Bridge data set • Erosion – due to wave action and fluctuating sea levels • Deposition – from littoral transport
- 8. 8 Perceptions and adjustment to hazards Golden Gate Bridge data set 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. 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.
- 9. 9 Perceptions and adjustments to hazards From a philosophical perspective: Golden Gate Bridge data set 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 eventually destroy it.
- 10. 10 Coastal Processes and Hazards From a philosophical perspective: Golden Gate Bridge data set 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.
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- 12. 12 Erosion Golden Gate Bridge data set • Sea level has risen 15 – 20 cm during the last century. www.wildwildweather.com/forecastblog/wp-conte
- 13. 13 Emerging shorelines Changing sea levels over time produce emerging shorelines. Tectonic uplift also causes land to slowly emerging from the sea.
- 14. 14 Submerging shorelines Changing sea levels over time produce submergent shorelines.
- 15. 15 Erosion Effects of waves Waves are a powerful force. The net effect is to straighten out shorelines and transport large volumes of sediment.
- 16. 16 Erosion 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.
- 17. 17 Erosion Effects of waves Waves are a powerful force. Can cause severe erosion problems along coastal areas.
- 18. 18 Erosional Landforms – winter, 1989
- 19. 19 Erosional Landforms – February, 1990
- 20. 20 Erosional Landforms – February, 1991
- 21. 21 Erosional Landforms – February, 1993
- 22. 22 Erosional Landforms – March, 1999
- 23. 23 Erosion El Nino conditions produce more extreme wave conditions Warmer than normal waters produce warm air masses that hold lots of rain and produce severe storms and waves.
- 24. 24 Erosion El Nino conditions produce more extreme wave conditions Normal wind and water motion
- 25. 25 Erosion El Nino conditions produce more extreme wave conditions El Nino wind and water motion
- 26. 26 Deposition 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.
- 27. 27 Deposition Sand transportation – is a natural process but has also been affected by humans. Groins – encourage deposition in desired locale.
- 28. 28 Deposition 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.
- 29. 29 Deposition Sand transportation – is a natural process but has also been affected by humans. breakwaters – designed to protect and encourage harbor development.
- 30. 30 Deposition Sand transportation – is a natural process but has also been affected by humans. Man-made structures in action.
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