A tsunami is a very long ocean wave generated by sudden displacement of the sea floor or ocean mass. Tsunamis can hit with little or no warning in areas prone to earthquakes and volcanoes. In deep water, tsunamis travel very quickly but slow down and pile up in shallow water, increasing their amplitude and hazards. Mitigation requires emergency planning, public education, and disseminating warning information so people can evacuate to higher ground quickly when alerts occur.

1. Tsunamis
By: Neha Jain
Aditya Sharma

2. What is a tsunami ?
A tsunami is a very long ocean wave
generated by sudden displacement of the
sea floor or of the oceanic mass
The displacement of an equivalent volume
of water generates the tsunami

3. Terminology
The term “tsunami” is a Japanese word
meaning “harbour wave”
It was so named because the wave is
harmless until it enters a harbour
It is frequently called a “tidal wave”, but it
has nothing to do with tides

4. Hazards and risks of tsunamis
Tsunamis can hit with little or no warning
The most prone areas are those
associated with earthquakes and
volcanoes .

5. Structure of a wave
Wavelength, λ, can exceed 200 km
normal ocean waves have wavelengths of about
100 m
trough; peak; wave height, h; amplitude
From Murck et al. (1996)

6. Velocities in deep water
Tsunamis travel very quickly relative to
normal ocean waves
This is particularly the case in open water,
where velocities increase with water depth
Velocities can reach 1,000 km/hr in
open ocean (normal ocean wave: ~90
km/hr)

7. Shallow water
In shallow water, the tsunami waves pile
up
As a result, velocities and wavelengths
decrease...
…but at the same time, amplitudes can
increase enormously...

8. Causes of tsunamis - all involve
displacement of water
Earthquakes
Volcanic activity
Landslides
Meteorite impacts

9. Tsunami hazards
Extensive flooding
Action of wave on coastal structures, both
natural and built
The incredible force of the waves can
remobilize huge objects
The event may create drawdown

10. Effects of tsunami drawdown
Release of dissolved gases (CH4, CO2, H2S)
previously contained in shallow sediments
Potential ignition of gases by their rapid
expulsion
As a result, a wave of noxious and burning
gases may engulf people BEFORE the wall of
water arrives

11. Mitigation efforts

12. Warning times
Every ~750 km of travel distance is equal
to about 1 hour of warning time
So, as discussed above, there is very little
warning time for tsunami generated by
local sources, compared to those from
distant sources

13. Response to tsunami
Requires good emergency planning and
preparation…
…an educated and trained public …
…which has access to information…
…so the dissemination of this info needs
to be efficient and reliable

14. Personal mitigation
Run (don’t walk) to higher ground
Tell your family and friends
Never go to the beach to watch tsunamis