How does tsunami energy travel across
the ocean and how far can tsunamis waves reach?
Once a tsunami has been generated, its energy is distributed
throughout the water column, regardless of the ocean's depth. A tsunami is
made up of a series of very long waves. The waves will travel outward on
the surface of the ocean in all directions away from the source area, much like
the ripples caused by throwing a rock into a pond. The wavelength of
the tsunami waves and their period will depend on the generating mechanism and
the dimensions of the source event. If the tsunami is generated from
a large earthquake over a large area, its initial wavelength and period will be
greater. If the tsunami is caused by a local landslide, both its
initial wavelength and period will be shorter. The period of the tsunami
waves may range from 5 to 90 minutes. The wave crests of a tsunami can be
a thousand km (1500 miles) long, and from a few to a hundred kilometers (150
miles) or more apart as they travel across the ocean. On the open
ocean, the wavelength of a tsunami may be as much as two hundred kilometers (316
miles), many times greater than the ocean depth, which is on the order of a
few kilometers (3+-miles). In the deep ocean, the height of
the tsunami from trough to crest may be only a few centimeters to a meter or
more - again depending on the generating source. Tsunami waves in the deep
ocean can travel at high speeds for long periods of time for distances of
thousands of kilometers and lose very little energy in the process. The
deeper the water, the greater the speed of tsunami waves will be.
For example, at the deepest ocean depths the tsunami wave speed will be as much
as 800 km/hr (571mph), about the same as that of a jet
aircraft. Since the average depth of the Pacific ocean is 4000 m (14,000
feet) , tsunami wave speed will average about 200 m/s or over 700 km/hr (500
mph). At such high speeds, a tsunami generated in Aleutian
Islands may reach Hawaii in less than four and a half hours. In 1960,
great tsunami waves generated in Chile reached Japan, more than 16,800 km (26,544
miles) away in less than 24 hours, killing hundreds of people.