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 causes a tsunami?
A
tsunami can be generated by any disturbance that displaces a large water
mass from its equilibrium
position.
In the case of earthquake-generated tsunamis, the water column is disturbed
by the uplift or
subsidence
of the sea floor. Submarine landslides, which often accompany large earthquakes,
as well as
collapses
of volcanic edifices, can also disturb the overlying water column as sediment
and rock slump
downslope
and are redistributed across the sea floor. Similarly, a violent submarine
volcanic eruption can
create
an impulsive force that uplifts the water column and generates a tsunami.
Conversely, supermarine
landslides
and cosmic-body impacts disturb the water from above, as momentum from
falling debris is
transferred
to the water into which the debris falls. Generally speaking, tsunamis
generated from these
mechanisms,
unlike the Pacific-wide tsunamis caused by some earthquakes, dissipate
quickly and rarely
affect
coastlines distant from the source area.
Important Facts to Know about Tsunamis
Tsunamis that strike coastal locations in the Pacific Ocean
Basin are most always caused by
earthquakes. These earthquakes might occur far away or near where you live.
Some tsunamis can be very large. In coastal areas their height can be as
great as 30 feet or more
(100 feet in extreme cases), and they can move inland several hundred feet.
All low-lying coastal areas can be struck by tsunamis.
A tsunami consists of a series of waves. Often the first wave may not be
the largest. The danger
from a tsunami can last for several hours after the arrival of the first
wave.
Tsunamis can move faster than a person can run.
Sometimes a tsunami causes the water near the shore to recede, exposing the ocean floor.
The force of some tsunamis is enormous. Large rocks weighing several tons
along with boats and
other debris can be moved inland hundreds of feet by tsunami wave activity.
Homes and other
buildings are destroyed. All this material and water move with great force
and can kill or injure
people.
Tsunamis can occur at any time, day or night.
Tsunamis can travel up rivers and streams that lead to the ocean.
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.