The waves radiate outward in all directions from the disturbance and can propagate across entire ocean basins. For example, in 1960 an earthquake in Chile caused a tsunami that swept across the Pacific to Japan.
Tsunami waves are distinguished from ordinary ocean waves by their great length between peaks, often exceeding 100 miles in the deep ocean, and by the long amount of time between these peaks, ranging from five minutes to an hour.
The speed at which tsunamis travel depends on the ocean depth. A tsunami can exceed 500 mph in the deep ocean but slows to 20 or 30 mph in the shallow water near land. In less than 24 hours, a tsunami can cross the entire Pacific Ocean.
In the deep ocean, a tsunami is barely noticeable and will only cause a small and slow rising and falling of the sea surface as it passes. Only as it approaches land does a tsunami become a hazard.
As the tsunami approaches land and shallow water, the waves slow down and become compressed, causing them to grow in height. In the best of cases, the tsunami comes onshore like a quickly rising tide and causes a gentle flooding of low-lying coastal areas.
In the worst of cases, a bore will form. A bore is a wall of turbulent water that can be several meters high and can rush onshore with great destructive power.
Behind the bore is a deep and fast-moving flood that can pick up and sweep away almost anything in its path, such as what happened in Papua New Guinea in 1998 when more than 2,000 people were killed and villages destroyed.
Minutes later, the water will drain away as the trough of the tsunami wave arrives, sometimes exposing great patches of the sea floor. But then the water will rush in again as before, causing additional damage.
This destructive cycle may repeat many times before the hazard finally passes. Persons caught in the path of a tsunami have little chance to survive. They can be easily crushed by debris or they may simply drown. Children and the elderly are particularly at risk, as they have less mobility, strength and endurance.
Tsunamis typically cause the most severe damage and casualties very near their source. There the waves are highest because they have not yet lost much energy to friction or spreading.
In addition, the nearby coastal population, often disoriented from the violent earthquake shaking, has little time to react before the tsunami arrives.
The largest tsunamis, however, can cause destruction and casualties over a wide area, sometimes as wide as the entire Pacific Basin. These types of Pacific-wide tsunamis may happen only a few times each century.
108: Great post. Thanks.
The waves radiate outward in all directions from the disturbance and can propagate across entire ocean basins.
Would it be possible to generate a tsunami of this size by detonating a nuclear device on the sea floor?