Page 539 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 16 Oceans, Coastal Systems, and Wind Processes 503
(b) Headland
(c) Cove
Bay
Diverging
Converging
Refracted wave fronts
(d) Lighthouse on headland bluff on Farne Island, England.
Wave energy diffused
Wave energy concentrated
(a) Wave energy is concentrated as it converges on headlands and is diffused as it diverges in coves and bays.
Cove
Diverging Converging
Headlands
Headlands
▲Figure 16.10 Wave refraction and coastal straightening. [(b, c, d) Bobbé Christopherson.]
as the lighthouse at Peggy’s Cove, Nova Scotia, can also be deadly. People lose their footing and are washed off the rocks near the lighthouse by waves, particularly while storm-watching. Slippery conditions and heavy seas ham- per recovery efforts, and deaths occur too frequently.
In contrast, out-of-phase wave trains will dampen wave energy at the shore. When you observe the break- ers along a beach, the changing beat of the surf actually is produced by the patterns of wave interference that oc- curred in far-distant areas of the ocean.
Wave Refraction In general, wave action tends to straighten a coastline. Where waves approach an irregu- lar coast, the submarine topography refracts, or bends, approaching waves around headlands, which are pro- truding landforms generally composed of resistant rocks (Figure 16.10). The refracted energy becomes focused around the headlands and dissipates in coves, bays, and
the submerged coastal valleys between headlands. Thus, headlands receive the brunt of wave attack along a coast- line. The result of wave refraction is a redistribution of wave energy, so that different sections of the coastline vary in erosion potential, with the long-term effect of straightening the coast.
Waves usually approach the coast at a slight angle (Figure 16.11). In consequence, as the shoreline end of the wave enters shallow water and slows down, the portion of the wave in deeper water continues to move at a faster speed. The velocity difference refracts the wave, produc- ing a current that flows parallel to the coast, zigzagging in the prevalent direction of the incoming waves. This longshore current, or littoral current, depends on wind direction and the resultant wave direction. A longshore current is generated only in the surf zone and works in combination with wave action to transport large amounts of sand, gravel, sediment, and debris along the shore.
Georeport 16.3 Surprise Waves Flood a Cruise Ship
On March 3, 2010, a large cruise ship in the western Mediterranean Sea, off the coast of Marseilles, France, was struck by three surprise waves about 7.9 m in height. Two passengers were killed and many injured as windows shat-
tered and water flooded parts of the ship’s interior. rescue personnel took the injured to hospitals in Barcelona, Spain. Scientists are studying what causes such abnormal waves, which tend to happen in open ocean; elements include strong winds and wave interference.