(5)The mechanism of tidal waves and warning of tidal waves

An earthquake generated on the shallow sea bottom causes a warping movement, which transmits the movement to the surface of the sea. This wave runs in a centrifugal way, sometimes with a speed of more than 700km/h. The wave runs slower near the seashore, but here the tidal wave could become much taller.

Figure 8:How a Tsunami is formed

1 When an earthquake occurs beneath the sea floor, the surface of the sea is lifted up by the movement of the earth's crust.

2 The motion creates a long wave, which spreads in every direction. (Where the sea is deep, it spreads sometimes at a speed of 100 kilometres an hour.)

3 The wave becomes higher and higher as the sea becomes shallower.

4 The wave becomes even higher because of the geographical features of the sea floor. (It becomes especially high in the inner part of a harbour or bay.)

5 When the wave is high, it crawls up from the sea onto the land.

BACK　　　CONTENTS　　　NEXT