waves are very different from other ocean waves. Ordinary
waves, which are in fact caused by the wind blowing
over the water, affect only the surface of the ocean.
Water movement due to these wind-generated waves rarely
extends below a depth of 500 feet even in large storms.
Ordinary wind-generated waves never travel at more than
60 miles per hour and are usually much slower. Tsunami
waves, on the other hand, could easily keep pace with
a Boeing 747 with speeds that can exceed 700 kilometers
per hour (500 miles per hour or more) in the deep ocean.
Yet the incredibly fast waves may be only a foot or
two high in deep water.
waves also have much greater wavelengths. Wind waves
are rarely longer than 1,000 feet from crest to crest,
but tsunami waves are often an incredibly long 100 miles
between crests. With a height of 2 or 3 feet spread
out over 1,000 feet miles, the slope of even the most
powerful tsunami would be impossible to see from a ship
or airplane, passing unnoticed in deep water.
popular misconception is that there is only one giant
wave in a tsunami. On the contrary, a tsunami may consist
of 10 or more waves forming what is called a “tsunami
wave train”. The individual waves follow one behind
the other, anywhere from 5 to 90 minutes apart.
Tsunamis evolve through three overlapping but quite distinct
physical processes: generation
by any force that disturbs the water column, propagation
from deeper water near the source to shallow coastal
areas and, finally, inundation of
is the process by which a sea floor disturbance, such
as movement along the fault reshapes the sea surface
into a tsunami.
of the tsunami transports seismic energy away from the
earthquake site through undulations of the water. At
this point, the wave is so small compared with both
the wavelength and the water depth that researchers
apply linear wave theory, which assumes that the height
itself does not affect the wave’s behavior. The
theory predicts that the deeper the water and the longer
the wave, the faster the tsunami.
a tsunami approaches shore, it begins to slow and grow
in height. Just like other water waves, tsunamis begin
to lose energy as they rush onshore, but despite these
losses, tsunamis still reach the coast with tremendous
amount of energy. Tsunamis have great erosion potential.
Capable of inundating, or flooding,
hundreds of meters inland, the fast-moving water associated
with the inundating tsunami can crush homes and other
coastal structures. Tsunamis may reach a maximum vertical
height onshore above sea level, often called run-up
height, of 10, 20, and even 30 meters.