Oceanography (2+1)

Waves-terms and classification

a. Catastrophic waves : Sudden violent and temporary waves caused by earthquackes, volcanic activity etc are  called catastrophic waves. Catastrophic waves are produced with the sporadic occurrence of volcanoes, earthquakes or landslides in the ocean. These waves are generated less frequently, but they have more damaging effect. Three common types of catastrophic waves are tsunamis, landslide surges and storm surges.

b.Tsunamis: These are seismic waves formed when a severe shock such as earthquake affects the ocean. They have wave length of 200Km and can travel as fast as 700 km/h.

c.Landslide surges: Rise or pilling up of water against  shore produced by land slide.

d.Storm surges: Storm surge is associated with weather  and is very dangerous. The air pressure over a section of the ocean of the ocean affects the sea level. Sea level under a strong high pressure system is pushed downward to a level several contimeter below normal sea level. Conversly under an extreme low pressure, such as hurricane or tropical storm, a mound of water develops and is pushed along by the strom front. As the storm system approaches land the mound of sea water becomes a mass of wind driven, elevated water, usually associated with large storm waves.  Storm surges are more dangerous when they coincide with high tides they are responsible for the majority of flooding and destruction associated with hurrieanes, 90% of people killed by hurricanes are killed by storm surges.

e. Shallow water waves : Waves in the water shallower than L/2.

f. Shearwave : waves that causes particles in a medium to vibrate back and forth at right angles to the direction of waves propagation.

g. Surface wave : Waves on the ocean surface formed at the boundary between two fluids of very different density. Surface wave have the property of reflection refraction and interference.

Wind produced waves

             Three types of wind generated waves are sea, swell and surf. Most waves are formed by wind usually by stormm systems. Unlike the storm systems over the land, ocean storm systems can be quite large, some exceeding 805Km is diameter. These systems breakup as they approach land but over the ocean there is little to affect them. The wind transfers its energy to the water through wave building directly under the storm system is an area of mixed wave types termed as sea. Factors that affect the amount of energy transfered to the wave depend on wind speed, the duration of time that the wind blows in one direction and the "Fetch" the distance over which the wind blows in one direction. Fully developed sea is defined as the maximum size to which waves can grow under given conditions of wind speed, duration and fetch. At this point the waves of a fully developed sea will gain as much energy from the wind as they lost to gravity as breaking white caps.

• Sea:The wind transfers its energy to the water through wave building directly under the storm system is an area of mixed wave types termed as sea.
• Swells: As waves move away from the events that ruffle them, they assume a uniform pattern and begin to move in trains of equivalent period and height. These trains are called swells. Swells can travel thousands of miles.
• Surf: As swells approach shore their pattern is modified by shallow water and consequently they are shortened and as the crest increases, they move more swiftly. This modified form of swell is called surf. Surf is  different from sea and swell i.e. It does not have the circular motion of wave particles.