A tsunami (soo NAH mee) is a series of waves
most commonly caused by an earthquake
beneath the ocean floor. Tsunamis can kill and
injure people and cause great property damage
where they come ashore. Two kinds of tsunamis
could affect the North Coast.
Locally generated tsunamis occur when a
large earthquake displaces ocean floor near our
coast. The first waves may reach the coast within
minutes. There is no time for an official warning.
If you feel an earthquake on the beach or near
the coast, move immediately to higher ground.
Distance-source tsunamis may also be generated
by very large earthquakes in other areas of the
Pacific Ocean and may reach our coastline a few
hours after the earthquake occurred. Tsunami early
warning centers will alert local officials who may
order an evacuation.
volcanoes, or subterranean
earthslides may trigger
In deep water, a tsunami can
travel at speeds of 600 miles per
hour but only be a foot tall.
Near shore, waves slow down,
become shorter, then bunch up
and get much higher.
A series of successive waves
can inundate the shoreline and
move inland, often causing great
damage and death.
Why Tsunami Waves Get So Big
Tsunamis radiate from a point
of origin and can strike coastlines
thousands of miles away. Tsunamis
can race across the ocean at up to
In the deep ocean a tsunami wave
may be only a few feet or less, but
their length from wave crest
to wave crest may be a hundred
miles or more.
Reaching shallow water near shore,
the waves slow down and become
shorter, "bunch up", and get much
If you feel a strong earthquake when you are on the coast:
1. Move to higher ground (at least 100 feet above
sea level) or inland. A tsunami may be coming.
2. Stay away from the coast.
3. Wait for an official "all clear" on the radio.