WAVE BASE - the depth to which wave energy penetrates below the surface. Wave base is related to the size of waves; "wave base equals about one half of the wave length." Wave energy is dissapated by grinding action against the sea bottom. The interaction of wave against the sea bottom results in THREE KINDS OF WAVES depending on water depth...
BACKSWASH - return runnoff from swash.
WAVE REFRACTION - wavelength shortening causes wave diffraction (the "bending" of waves as they move toward shore). The result is that a LONGSHORE CURRENT develops along shore flowing in the same direction as the incoming waves. This results in:
LONGSHORE TRANSPORT: longshore current carries sediment along the beach, contantly moving sand on the beach.
BEACH DRIFT - the path of sand particles up and down the beach - the net movement of sand grains are down current.
DIFFERENT KINDS OF COASTS
ESTUARY - a "drowned" river valley caused by changes in sea level. Examples include the Hudson River, the Chesapeake, and the lower Delaware River and Bay.
BARRIER ISLANDS - sand-built islands that parallel a gentle slope shoreline.
Features associated with inlets and river mouths:
Hurricanes and winter storms (with great windspeed, fetch, and duration) cause sand erosion.
STORM SURGE: the "piling" of water in advance of a storm.
The removal of dunes removes sand reserves and the "natural shore defenses" against storm wave and current erosion.
GROINS - walls built perpendicular to the beach designed to "stabilize the beach"; they trap sand on the up-current side, but shut off the sand supply to the down-current side (resulting in erosion, i.e. the destruction at Westhampton Beach, NY after winter storms.)
JETTY - very large"groins" built on either side of an inlet to prevent sand from filling an inlet.
BREAKWATERS - large walls built parallel to shore several hundred yards offshore. These structures make calm waters for boat harbors, but calm waters result in siltation in harbors.
SEAWALLS - Large rock or concrete walls built along the back beach to protect property. Seawalls "increase" wave energy during storms and cause beach sand loss, resulting sometimes in the complete loss of the beach (and sometimes the seawall!). E.G. Seabright, NJ.
"sand tax" - a small tax added to housing and motels along developed beaches used to "replenish" sand to beaches prone to erosion; it is cheaper than rebuilding after storms, keeps insurance costs down.
SPRING TIDES - the highest tides occur when the moon and sun "pull together" during new and full moon cycle.
NEAP TIDES - moon and sun at right angles
Tidal Currents - the bulge of the tide flows as a current landward and seaward as sea level rises and falls.
TIDAL DELTAS - tidal waters moving in and out of an inlet on a barrier creates a tidal delta.
Tsunamis are giant waves caused by earthquakes at sea or along sea coasts; typically only a "Pacific Ocean" problem, but could occur anywhere. The size of a tsunami depends on earthquake intensity and location; earthquakes and volcanic eruptions primary cause.
The islands of Hawaii are prone to tsunamis (partly because they are in the middle of the Pacific Ocean. The shores facing the Alaska side of the islands are particularly prone to giant tsunamis (because Alaska frequently has great quakes). The islands of Hawaii also are prone to massive underwater landslides that trigger tsunamis. One such landslide on the side of the "Big Island" (Hawaii) may be responsible for a deposit of coral 2000 feet up on the side of Lanai (another Hawaiian Island). Thie implications of such deposits is quite foreboding for the future of modern island resorts!
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