Tsunamis

1
Tsunamis
2
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.

3
(No Transcript)
4

• 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.

5

• 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 wont arrive for
  20-30 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.

6
(No Transcript)
7

• 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/howstuffworks/230-
how-tsunamis-work-video.htm
8
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.

9

• Water receding prior to a tsunami coming ashore.

10
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!

11

• Photo from the boxing day tsunami

12
(No Transcript)
13
Copy and Answer These Questions in Your
NotesTSUNAMIS

• What is a tsunami?
• How are tsunamis formed?
• What is the wavelength and speed of a typical
  tsunami?
• Why are tsunamis dangerous?
• What are some indications that a tsunami may be
  on its way?