Characteristics of Tsunamis
Characteristics of Tsunamis : Tsunamis travel outward in all directions from the source area. Their speed depends on the depth of water, and the waves undergo accelerations or decelerations while passing over the ocean bottom's varying depths. In the deep and open ocean they can reach speeds of more than 800 kilometres per hour with the distance between waves being as great as 650 kilometres. The height of the waves may range from 30 to 60 centimetres, producing only a gentle rise and fall of the sea surface. These waves will not be noticed by ships or aircraft. As waves enter the shoaling (shallow) waters along a coastline, their speed diminishes, their height increases and the waves become closer together. The shape of the coastline and the ocean floor are important factors in the destruction caused. A wave may be very small at one point on a coast and much larger at other points. Sounds and inlets have a funnelling effect that increases the height of tsunami waves. There are many indications that a tsunami has been generated. One may be a recession of water caused by the trough coming before the wave. Conversely, a rise in water level may be the first event. Finally, under certain conditions the crest of an on-coming wave may overtake the preceding trough while some distance offshore, which will cause the wave to proceed shoreward as a bore-a wave with a churning front. The forces and destructive effects of tsunamis should not be underestimated. At some locations, the advancing turbulent front will be the most destructive part of the wave. In other locations, the greatest damage will be caused by the outflow of water back to the sea between waves. In this situation the wave will gather all debris in its path and can undermine roads, buildings and other infrastructure. Ships, unless moved away from shore, may be pushed against breakwaters, wharves and other craft, or washed ashore and left grounded after the withdrawal of seawater
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