large océan waves as high as 100 feet. (See Figure 1-5.) Wind waves
cause most of the damage to the océan coasts. Another type of wave,
the tsunami, is created by earthquakes or other tectonic disturbances
on the océan bottom. Tsunamis hâve caused spectacular damage at times,
but fortunately, major tsunamis do not occur frequently.
Wind waves are of the type known as oscillatory waves, and are
usually defined by their height, length, and period. (See Figure 1-6.)
Wave height is the vertical distance from the top of the crest to the
bottom of the trough. Wavelength is the horizontal distance between
successive crests. Wave period is the time between successive crests
passing a given point.
As waves propagate in water, only the form and part of the energy
of the waves move forward; the water particles remain.
The height, length, and period of wind waves are determined by the
fetch (the distance the wind blows over the sea in generating the waves),
the wind speed, the length of time the wind blows, and the decay distance
(the distance the wave travels after leaving the generating area). Generally, the longer the fetch, the stronger the wind; and the longer the
time the wind blows, the larger the waves. The water depth, if shallow
enough, will also affect the size of wave generated. The wind simultaneously generates waves of many heights, lengths, and periods as it
blows over the sea.
If winds of a local storm blow toward the shore, the generated
waves will reach the beach in nearly the form in which they are generated. Under these conditions, the waves are steep; that is, the wavelength is 10 to 20 times the wave height. Such waves are called seas.
If waves are generated by a distant storm, they may travel through
hundreds or even thousands of miles of calm areas before reaching the
shore. Under these conditions, waves decay - short, steep waves are
eliminated, and only relatively long, low waves reach the shore. Such
waves hâve lengths from 30 to more than 500 times the wave height, and
are called swetl.
1.33 CURRENTS AND SURGES
Currents are created in océans and adjacent bays and lagoons when
water in one area becomes higher than water in another area. Water in
the higher area flows toward the lower area, creating a current. Some
causes of différences in the élévation of the water surface in the océans
are tides, wind, waves breaking on a beach, and streams. Changes in water
température or salinity cause changes in water density that may also produce currents.
Wind créâtes currents because, as it blows over the water surface,
it créâtes a stress on surface water particles, and starts these particles moving in the direction in which the wind is blowing. Thus, a surface current is created. When such a current reaches a barrier, such as
coastline, water tends to pile up against the land. In this way, wind
1-7
cause most of the damage to the océan coasts. Another type of wave,
the tsunami, is created by earthquakes or other tectonic disturbances
on the océan bottom. Tsunamis hâve caused spectacular damage at times,
but fortunately, major tsunamis do not occur frequently.
Wind waves are of the type known as oscillatory waves, and are
usually defined by their height, length, and period. (See Figure 1-6.)
Wave height is the vertical distance from the top of the crest to the
bottom of the trough. Wavelength is the horizontal distance between
successive crests. Wave period is the time between successive crests
passing a given point.
As waves propagate in water, only the form and part of the energy
of the waves move forward; the water particles remain.
The height, length, and period of wind waves are determined by the
fetch (the distance the wind blows over the sea in generating the waves),
the wind speed, the length of time the wind blows, and the decay distance
(the distance the wave travels after leaving the generating area). Generally, the longer the fetch, the stronger the wind; and the longer the
time the wind blows, the larger the waves. The water depth, if shallow
enough, will also affect the size of wave generated. The wind simultaneously generates waves of many heights, lengths, and periods as it
blows over the sea.
If winds of a local storm blow toward the shore, the generated
waves will reach the beach in nearly the form in which they are generated. Under these conditions, the waves are steep; that is, the wavelength is 10 to 20 times the wave height. Such waves are called seas.
If waves are generated by a distant storm, they may travel through
hundreds or even thousands of miles of calm areas before reaching the
shore. Under these conditions, waves decay - short, steep waves are
eliminated, and only relatively long, low waves reach the shore. Such
waves hâve lengths from 30 to more than 500 times the wave height, and
are called swetl.
1.33 CURRENTS AND SURGES
Currents are created in océans and adjacent bays and lagoons when
water in one area becomes higher than water in another area. Water in
the higher area flows toward the lower area, creating a current. Some
causes of différences in the élévation of the water surface in the océans
are tides, wind, waves breaking on a beach, and streams. Changes in water
température or salinity cause changes in water density that may also produce currents.
Wind créâtes currents because, as it blows over the water surface,
it créâtes a stress on surface water particles, and starts these particles moving in the direction in which the wind is blowing. Thus, a surface current is created. When such a current reaches a barrier, such as
coastline, water tends to pile up against the land. In this way, wind
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