Coastal Geology in our National Parks
Coastal Hazards
Natural hazards such as storms, rip currents, and tsunami are driving forces in coastal processes and landforms. When combined with increasing sea levels, these events may have tremendous impacts on our coastal environments and beaches. Coastal communities must be aware of natural hazards and take steps to prevent the loss of life and property caused by these events. Pre- and post-storm management plans should be developed and used to ensure the safety and protection of coastal populations and natural resources.
Humans often attempt to alter and control the coastal zone for increased public safety and property preservation (see Human Impacts). However, these modifications may actually increase storm impacts in some locations. In addition, storm events are necessary to sustain many coastal environments. Storms provide much of the sediment to fragile, shallow marine and estuarine ecosystems. Many wetland environments depend on storm activities for sediment build-up and survival when faced with rising sea levels. As an alternative to “out-engineering” natural hazards, coastal laws, policies, and buffer zones may be implemented to dissuade population expansion into high-risk coastal areas (Adapted from Carter 1988).
Coastal Storms
During the passage of major storms, coastal parks are frequently impacted by strong winds; heavy rains; larger - than - usual waves in the surf along the coast; and “storm surges,” which are really wind and low atmospheric pressure -induced temporary increases in the elevation of the ocean in the immediate area of the storm. When these large cyclonic storms originate near the equator, they are called tropical cyclones, and when their winds reach speeds in excess of about 74 miles per hour, they are called hurricanes. When these large cyclonic storms originate over North America or over the near-continent portions of the Atlantic Ocean, they are called extra-tropical cyclones or nor’easters.
Hurricanes usually pass over the eastern coast of North America in one or two days, most often during the period from June to November. Nor’easters, on the other hand, sometimes produce sustained gale force winds in excess of about 39 miles per hour for two to four days. Nor’easters occur most frequently from October through April.
Cape Hatteras is subjected to an unusually high frequency of both tropical cyclones and extra-tropical cyclones. Many ships have been sunk in the treacherous waters that develop during these large cyclonic storms.
For further information please visit the following links:
This is a great educational page which provides information on hurricane basics.
A United States Geological Survey page which details hurricane impacts on the coastal environment.
Rip Currents
Rip currents are strong and swift, moving 1 to 2 meters per second, which is faster than an average person can swim! These currents are created due to set-up near the shoreline. Set-up is a slight (~ cm) increase in water levels compared to those found seaward of the surf zone. Set-up creates unstable conditions that are eventually relieved through the formation of rip currents. These dangerous currents generally form at a low point or saddle in a sandbar. Because rip currents tend to be narrow, swimmers caught in a rip current should swim parallel to the shore to escape being taken out to sea. Swimmers should be especially cautious during storm events, which may increase the frequency and strength of rip currents.
Tsunami
Tsunami are very large ocean waves that are radially generated from volcanic eruptions, earthquakes or sub aqueous slumping. In the open ocean, these waves may travel at speeds in excess of 493 mph! Oddly enough, deep ocean vessels would not notice the passing of these waves due to their flat, low wave propagation in the deep parts of the ocean. In contrast, when tsunami reach shallow water, they slow down considerably and may reach great heights (up to 33 feet). Tsunami have caused great destruction and loss of life due to an abrupt change in water levels many meters above the normal high water mark. Numerous cities and areas in the United States have experienced tsunami including Hilo, HI, the Pacific Northwest (Washington, Oregon, California), and Alaska. A new system, the International Tsunami Warning System, is now used to alert the public to impending tsunami.
http://walrus.wr.usgs.gov/tsunami/cascadia.html – USGS site that describes local tsunami of the Pacific Northwest.
http://www.ess.washington.edu/tsunami/ - An interactive, on-line, tsunami-information resource created and maintained by the Geophysics Department at the University of Washington.
http://walrus.wr.usgs.gov/tsunami/links.html – USGS tsunami links page.
http://www.fema.gov/hazards/tsunamis/tsunami.shtm – FEMA site containing pubic information and interesting tsunami facts.
http://www.nws.noaa.gov./om/brochures/tsunami.htm – Interesting NOAA brochure with general tsunami information.