intro to coasts / tectonic classification / hydrographic regime / waves /tides / beaches / barrier islands / inlets / deltas Introduction to Coasts

Importance of the coastal zone

With global warming leading to the prospect of increasing rates of sea level rise, studying the coastal zone has never been more important on a global basis. In Bangladesh one-meter relative sea level rise will inundated a predicted 17.5 percent of the country, displacing 13 million people. Along China's coastline the same rise in sea level would cover 125,000 square kilometers, home to 73 million people.(from Climate Alert Volume 8, No. 2 March-April 1995) In the Pacific small island nations are literally going under. Closer to home, the United States erosion rates average .6 to .9 m/yr (2-3 ft/yr) along the Atlantic Coast and are as high as 2 m/yr (6 ft/ yr) along the Gulf Coast. (Evaluation of Erosion Hazards. 2000, Heinz Center) Large coastal cities are spending billions of dollars a year protecting their infrastructure from erosion or rebuilding following severe storms. However, the engineering structures that protect the coast will ultimately lead to the destruction of the coastal wetland so vital to marine fisheries and the entire coastal ecosystem.

Suggested Reading

The Coastal Zone: A resource at Risk, June 2002, Haines, Geotimes

Coastal Systems, 2002, Intergovernmental Panel on Climate Change (UNEP)

To man:

  • Population density: A large percentage of the world's population live on or near the coast. 53% of US population lives within 50 miles of the Coast (Coastal Coalition map of population density)
  • Ports: Focus of shipping and commerce
  • Resource
    • Placer deposits
    • oil and gas
    • Aggregate: sand and gravel
    • Water: coastal aquifers
    • Fishing industry
  • Esthetics: Tourism

To other life forms:

Processes

Waves and tides

    The shore is where energy transferred through the oceans is expended on land and where sediment eroded from land is transferred into the oceans. Waves and tides move sediment both parallel and perpendicular to the shore. Solar energy, responsible for winds, and gravity provide the energy that drives nearly all coastal processes.

Fluvial and sediment discharge from stream

  • More than 90% of the sediment reaching the oceans is transported by rivers. Without this sediment most beaches would not exists. Fluvial and sediment discharges from streams interact with waves and tides to produce a variety of coastal landforms such as deltas, barrier islands and related coastal estuaries.

Eustatic and isostatic sea level changes

  • Sea level changes continually alter the region of the coast affected by shoreline processes. The present increase in sea level is causing widespread erosion that is affecting most coastal communities.

Man

Anthropogenic activities are affecting the coast far more than we could have anticipation. Deforestation in some countries has increased flooding and sediment discharge, whereas the building of dams has trapped sediment and controlled discharge to the point where erosion now dominates regions that were once depositional. Coastal estuaries are vanishing from over population and coastal flooding has been exacerbated by the over-pumping of coastal aquifers. Pollution is destroying coral reefs and coastal ecosystems that once buffered the coast, and increased carbon dioxide and other atmospheric emissions by man are fueling climate change and sea level rise.

Sources of energy driving coastal processes

solar energy:

    • Solar energy produces wind that transfers energy to waves.

    Ultimately man gets energy from the sun. After all, we eat plants (and plant eating animals) which convert solar energy to food energy through the process of photosynthesis.

Geothermal heat and gravity drive tectonic activity:

      • Tectonic activity produces most large seismic sea waves either through earthquakes or volcanic eruptions.

gravity: waves and tides

      • Gravity is the restoring force important to the motion of waves
      • The gravitational energy producing tides comes from the sun and moon as well as the Earth.

Coastal environments

Coastal types vary tremendously according to geologic history, climate, sediment supply, wave and tidal regime, and other local influences. Some of the more common coastal types are listed below. A more comprehension discussion of coastal features will be covered my lecture on the classification of coasts.

Dominantly clastic coasts (may also contain substantial wetlands)

Wetland - Dominated Coasts

Rocky Coasts

      • Tectonically active rocky Coasts
      • Glaciated Coasts (rocky coasts with pocket beaches)
      • Plateau/sea cliff

Reef coasts: atolls and barrier reefs

Read and explore

Artificially armored, urban coast

Much of Salem, Boston, New York, Atlantic City, etc.

Factor influencing coastal Morphology

Variations in coasts reflect the following influences, influences, many of which are interdependent.

  • Climate
  • Tectonic environment
    • Coasts along active margin (collision coasts)
    • Coasts along passive margin (trailing edge coasts)
  • Hydrographic regime (waves and tides)
  • Fluvial sediment discharge
  • Composition
  • History: Glaciation, changes in sea level, tectonics
  • Man

Sites to explore


Some conflicts and future problems