Objectives:
The transition zone between the ocean (or large lake) and land is a dynamic environment. Landforms of the coastal zone are largely the products of ocean waves and currents acting on the shore. Depending on many factors induding the geology of the coastline, the haracter of the waves arriving at the shore, tidal effects, and long-term changes in sea level, either erosion or deposition can dominate along a particular coastal segment.
Variations in coastline configuration and bottom topography cause wave refraction (bending of waves) that favors erosion in some areas and deposition of sediment in other areas.
In addition to wind.driven waves, ocean coastlines are vulnerable to the effects of tides and, in some areas, tsunamis. Tidal effects are especially significant where the coastline has narrow openings. including estuaries• bays, and straits. Tsunamis are relatively rare-but potentially devastating-sea waves triggered by earthquakes, volcanic eruptions, or submarine landslides. Primarily occurring in the Pacific and Indian Ocean basins, they are capable of producing run-up heights of tens of meters of seawater as the tsunami arrives. considerably modifying the coastal sone. Tsunamis have struck with little or no warning causing great widespread death and destruction, as demonstrated by the occurrences of the 26 December 2004 Indian Ocean and the 11 March 2011 Japanese Great Tehoku tsunamis.
After completing this investigation, you should be able to:
• Describe ways in which wind-driven, tidal, and tsunami waves impart energy in shaping shoreline features.
• Demonstrate how wave refraction can concentrate or disperse wave energy.
• Describe the physical mechanism responsible for longshore currents and littoral drift.
Wave Refraction
As waves approach the coastline, they encounter increasingly shallow water. When waves enter water shallower than their wavelength, they begin to Interact with the ocean door. The period of these shallow-water waves remains unchanged so that as the wave slows, its wavelength shortens.