tsunami's

What is a tsunami?

A tsunami (pronounced tsoo-nah-mee) is a wave train, or series of waves, generated in a body of water by an impulsive
disturbance that vertically displaces the water column. Earthquakes, landslides, volcanic eruptions, explosions, and even the
impact of cosmic bodies, such as meteorites, can generate tsunamis. Tsunamis can savagely attack coastlines, causing
devastating property damage and loss of life.

What does "tsunami" mean?

Tsunami is a Japanese word with the English translation, "harbor wave." Represented by two
characters, the top character, "tsu," means harbor, while the bottom character, "nami," means "wave."
In the past, tsunamis were sometimes referred to as "tidal waves" by the general public, and as "seismic
sea waves" by the scientific community. The term "tidal wave" is a misnomer; although a tsunami's
impact upon a coastline is dependent upon the tidal level at the time a tsunami strikes, tsunamis are
unrelated to the tides. Tides result from the imbalanced, extraterrestrial, gravitational influences of the
moon, sun, and planets. The term "seismic sea wave" is also misleading. "Seismic" implies an
earthquake-related generation mechanism, but a tsunami can also be caused by a nonseismic event,
such as a landslide or meteorite impact.

How do tsunamis differ from other water waves?

Tsunamis are unlike wind-generated waves, which many of us may have observed on a local lake or at a coastal beach, in that
they are characterized as shallow-water waves, with long periods and wave lengths. The wind-generated swell one sees at a
California beach, for example, spawned by a storm out in the Pacific and rhythmically rolling in, one wave after another, might
have a period of about 10 seconds and a wave length of 150 m. A tsunami, on the other hand, can have a wavelength in excess
of 100 km and period on the order of one hour.

As a result of their long wave lengths, tsunamis behave as shallow-water waves. A wave becomes a shallow-water wave when
the ratio between the water depth and its wave length gets very small. Shallow-water waves move at a speed that is equal to
the square root of the product of the acceleration of gravity (9.8 m/s/s) and the water depth - let's see what this implies: In the
Pacific Ocean, where the typical water depth is about 4000 m, a tsunami travels at about 200 m/s, or over 700 km/hr. Because
the rate at which a wave loses its energy is inversely related to its wave length, tsunamis not only propagate at high speeds, they
can also travel great, transoceanic distances with limited energy losses.