The Summer of Tsunami by S. Campbell Williams

The continental shelf waters begin to oscillate after the rise in sea level.

Coastal waters may rise as high as 30 metres (about 100 feet) above normal sea level in 10 to 15 minutes. As the velocity lessens, the wavelengths become shortened and the wave amplitudes (heights) increase. A ship on the high seas experiences the passage of a tsunami as an insignificant rise and fall of only half a metre (1.6 feet), lasting from five minutes to an hour or more.Īs the waves approach the coast of a continent, however, friction with the rising sea bottom reduces the velocity of the waves.

These long periods, coupled with the extremely low steepness and height of the waves, enables them to be completely obscured in deep water by normal wind waves and swell. The waves’ periods (the lengths of time for successive crests or troughs to pass a single point) are very long, varying from five minutes to more than an hour. The wavelengths are enormous, sometimes exceeding 500 km (about 310 miles), but the wave amplitudes (heights) are very small, only about 30 to 60 cm (1 to 2 feet). In deep water a tsunami can travel as fast as 800 km (500 miles) per hour.

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The Summer of Tsunami by S. Campbell Williams