Download Tsunamis

Tsunamis
What is a tsunami?
• A tsunami is a series of waves created
when a body of water is displaced.
• Tsunamis can be caused by earthquakes,
volcanic eruptions, landslides or asteroids
at sea.
• Sometimes weather events such as
hurricanes or cyclones (with high winds)
can cause storm surges which look similar
to a tsunami but are not true tsunamis.
• Most tsunamis are caused by the
movement of tectonic plates at convergent
plate boundaries.
• Tsunamis are unlikely to occur at
divergent or transform plate boundaries
because water is not vertically displaced
there.
• Everyday waves in the ocean have a wavelength
of about 100m.
• Tsunamis have a wavelength of about 200km.
• This means that after the tsunami wave passes
a certain point, the next wave won’t arrive for 2030 minutes.
• At sea the tsunami may only be 1m high, and
they go unnoticed in the open ocean.
• It is only when the waves go ashore that they
become dangerous and devastating.
• In the deep ocean tsunamis move at the
speed of a jet aircraft (800km/h).
• As they approach the shore they slow
down to about 70 km/h and increase in
height.
• Tsunamis can knock down buildings,
uproot trees and smash boats to pieces.
http://videos.howstuffworks.com/howstuffw
orks/230-how-tsunamis-work-video.htm
Warning signs of a tsunami
• There are often no warning signs.
• If there has been an earthquake near a body of
water, a tsunami may form.
• Just before the tsunami comes ashore, the
shoreline goes way out exposing areas that are
usually underwater.
• There is sometimes a sucking sound as the
water rushes away.
• At this point the only thing to do is run away,
when the wave comes ashore it will travel faster
than you can run.
• Water receding prior to a tsunami coming
ashore.
The Boxing Day Tsunami 2004
• The Indian Ocean tsunami was caused by an
earthquake at a convergent plate subduction
zone.
• The earthquake measured between 9.1 and 9.3
on the Richter scale which is the strongest
earthquake ever recorded on a seismograph.
• More than 225 000 people died in this tsunami in
11 countries
• Some of the waves were more than 30 m high!
• Photo from the boxing day tsunami
Copy and Answer These Questions in Your Notes:
TSUNAMIS
1. What is a tsunami?
2. How are tsunamis formed?
3. What is the wavelength and speed of a
typical tsunami?
4. Why are tsunamis dangerous?
5. What are some indications that a tsunami
may be on its way?