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Waves. Waves are motion of a water surface. Parts of a wave are wave crest , wave trough, wave height (H), wave amplitude, wave length (L),and wave period (T ). What Causes Waves?. Submarine disturbance Gravitational attraction of sun and moon Wind Wind velocity Wind duration
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Waves are motion of a water surface. • Parts of a wave are wave crest, wave trough, wave height (H), wave amplitude, wave length (L),and wave period (T).
What Causes Waves? • Submarine disturbance • Gravitational attraction of sun and moon • Wind • Wind velocity • Wind duration • Fetch (distance over which wind blows) • Simply put, wave size increases as all these factors increase.
A fully developed sea is a sea state where the waves generated by the wind are as large as they can be under current conditions of wind velocity and fetch. • Significant wave height is the average of the highest 1/3 of the waves present and is a good indicator of potential for wave damage to ships and for erosion of shorelines.
Progressive waves are waves that move across a surface. • As waves pass, wave form and wave energy move rapidly forward, but not the water. • Water moves in an orbital motion as the wave passes. • Diameter of orbit increases with increasing wave size and decreases with depth below the water surface.
Deep- and Shallow-Water Motion • Wave base is the depth to which a surface wave can move water. • If the water is deeper than wave base, orbits are circular and there is no interaction between the bottom and the wave. If the water is shallower than wave base, orbits are elliptical and become increasingly flattened towards the bottom.
There are three types of waves defined by water depth: • Deep-water wave • Waves do NOT interact with the seafloor. • Orbits of the water molecules are circular. • Intermediate-water wave • Shallow-water wave. • In shallow water, the sea bottom transforms the wave’s properties. This leads to wave refraction and waves collapse forming surf (breakers).
The shallower the water, the greater the interaction between the wave and the bottom alters the wave properties, eventually causing the wave to collapse. 7-3 • Wave speed decreases as depth decreases. • Wavelength decreases as depth decreases. • Wave height increases as depth decreases. • Troughs become flattened and the wave profile becomes extremely asymmetrical. • Period remains unchanged. Period is a fundamental property of a wave. • Refraction is the bending of a wave crest into an area where it travels more slowly.
Storm surge is the rise in sea level resulting from low atmospheric pressure and the accumulation of water driven shoreward by storm winds. 7-3 • Water is deeper at the shore area, allowing waves to progress farther inland. • Storm surge is especially severe when superimposed upon a spring high tide.
Tsunamis were previously called tidal waves, but are unrelated to tides. • Tsunamis consist of a series of long-period waves characterized by very long wavelength (up to 100 km) and high speed (up to 760 km/hr) in the deep ocean. • Because of their large wavelength, tsunamis are shallow-water to intermediate-water waves as they travel across the ocean basin. • They only become a danger when reaching coastal areas where wave height can reach 10 m. • Tsunamis originate from earthquakes, volcanic explosions, or undersea landslides.
Readings: • Science & Technology 8 p. 236-237 • Answer the questions: • Would it take a long or a short time for a note in a bottle to travel to land if thrown from a ship at sea? • Why are the rocks and stones found on pebble beaches usually rounded and smooth? • If you floated on a wave in the ocean, you would merely bob up and down. How then are surfers carried along by the waves they ride?
