Tsunamis are large ocean waves caused by underwater earthquakes, landslides, volcanic eruptions or meteor impacts. While hardly noticeable at sea, tsunami waves grow enormously in size as they reach shorelines, causing devastating damage. Tsunami inundation refers to how far inland tsunami waves penetrate, which varies in each location and is determined by bathymetry, topography, and other geological factors. Common signs of approaching tsunamis include earthquakes, receding or suddenly surging water, and unnatural ocean sounds. Immediate evacuation to high ground can save lives when these signs are noticed.

1. T
S
U
N
A
M
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2. Tsunami, are dangerous
natural disasters caused
by large movements of
rock in the ocean or by
extra-terrestrial bodies.
While these giant waves
may hardly be
noticeable out at sea
where the water is
deep, they quickly start
to rise much higher than
normal waves when
they come in to
shore. Waves tens of
meters tall have
incredible energy and
can demolish entire
cities causing terrible
devastation. Here are
the main causes of these
destructive waves.

3. Tsunami Inundation
Tsunami inundation is the final and most destructive phase of tsunami evolution. The first two
phases, generation and propagation, were explored in previous units. Tsunami inundation refers
to the distance inland that a tsunami wave penetrates and varies for each different coast or
harbor affected by a tsunami. Simulating this process is very difficult because of the complex
variables associated with varying bathymetry, topography and elevation along coastlines. How
tsunami waves affect coastlines is determined by the bathymetry of the ocean floor, the
elevation and topography of the shoreline, the resonant period of a particular bay, basin, or
coastal shelf and the direction, or flow, of the tsunami.
Wave behavior at the shore depends on the relationship between wavelength and water depth
and wavelength and height. Some of the greatest inundation and runup from tsunami waves have
been produced as a result of seiche, when the period of oscillation of a coastal feature creates
constructive interference with subsequent tsunami waves.
As tsunamis reach the coast, they most often look like a rapidly rising tide or a flash flood.
Because large tsunamis are rare, people were generally unfamiliar with the way a tsunami
looked until widespread, easily viewable footage of the 2004 Indian Ocean tsunami and the 2011
Japanese tsunami were made available. The image of the massive shore-breaking waves,
reinforced by depictions of tsunamis in popular culture, has added to dangerous misconceptions
and misinformation about tsunamis.

4. Tsunami waves are very unique and fundamentally different from wind waves or swells. Not only do tsunami
waves have a much longer wavelength than wind-generated waves, but they also have a much longer period, or
length of time between wave crests. Tsunamis have periods up to an hour between waves, which means it could
take thirty minutes for a crest to pass. In contrast, a typical swell that would draw surfers would have a period
from 17-20 seconds. Wind chop would have a much shorter period of only a few seconds. The “peeling”
behavior seen in surfing waves is a result of a short period, where a crest takes a relatively short amount of
time to pass. This is why some tsunamis start with a massive receding of the water level followed by a surging
flood. In that case, the trough of the wave arrived first, and it can take more than thirty minutes for the water
to surge and inundate the coastline.

5. There are six major forces involved in damage
caused by tsunami inundation: surge force,
debris impact, hydrostatic force, hydrodynamic
(drag) force and buoyant force. Of those forces,
only two occur during initial impact, debris
impact and surge forces. These may be the most
destructive forces during tsunami inundation.
The remaining three forces, hydrostatic,
hydrodynamic and buoyant forces, occur
following initial impact.

7. Causes of Tsunami
Undersea Earthquakes – Over 85% tsunamis that
have occurred over the years can be attributed to
deep sea earthquakes. But the real cause lies in the
origin of the earthquake.
The surface of whole world is covered with tectonic
plates which are constantly moving, some more than
others. Powerful earthquakes can happen at the
boundaries of oceanic and continental
plates. Oceanic plates are heavier and slowly get
forced down under lighter continental plates when
they meet, but the downward movement, called
“subduction” isn’t smooth. Instead, the ocean plate
may get stuck for a period of time while energy
builds up, and then suddenly the plate slips down
and that energy is released as an earthquake. If this
happens underwater, the earthquake can create a
massive wave that could come to shore as a tsunami.

8. Undersea Landslides – The ocean floor is not flat, but
instead has peaks and valleys just like the surface
above. And just like on land, unstable piles of rock and
dirt can suddenly fall, creating a landslide. Underwater
landslides release a lot of energy and can also produce
giant waves.
Undersea Volcanoes – Hot molten rock, or magma,
under the ocean can suddenly explode up into the
water. The explosive force can push up a great wave that
may become a tsunami.
Meteoroid Impacts – As if there weren’t enough dangers
on earth, large rocks from space (meteoroids or even
huge asteroids) can strike the earth and cause incredible
damage. If one lands in the ocean, it may create a big
wave that expands outwards in every direction, millions
of times bigger than just dropping a pebble into a
puddle.

10. Examples of Tsunami Warning Signs
•An earthquake: swaying buildings and trees or
trembling ground
•Water suddenly surging inland
•An unusually low or receding waterline
•Eerie silence along a coast instead of the usual sound
of surf
•Sucking, hissing, bubbling and boiling may be heard
as rocks, pebbles and water are drawn out to sea
•Unusual bubbles in the water
•Exposed seafloor for hundreds of feet
•Warning broadcast from a low flying aircraft
•Warnings from Emergency Broadcast Systems
•Sirens
•Telephone calls
•Text messages
•Radio alerts
•Television alerts

11. THE EVACUATION
•When you hear a tsunami sign or warning grab your emergency kit and drive inland as fast as you can. Your
family should be with you obviously. To ensure the evacuation runs smoothly especially if you have children, take
the following steps.
•Whenever you hear the tsunami warning, be prepared to live and make sure your family members are all
prepared to leave with you.
•Give clear and simple instructions to your family members that will be easy to remember. This is particularly if
you have children who may not understand what is going on.
•Select a common area for you and your family members to reunite should you be separated in the evacuation.
•Teach all your family members especially children how to listen and detect tsunami warning signs
If you truly believe that a tsunami is coming before the alerts are sent evacuate immediately, it is better to be
wrong than to be dead
•Listen to instructions and advice from local authorities on how to survive a tsunami. Your local authorities will
send out instructions on radio and other media platform, so keep a look out for such instructions.
•If the person live in a coastal area, make sure that he and his family members are good swimmers. The two main
causes of death are drowning and being crushed by falling debris. To avoid drowning ensure that you know how
to swim.
•Sometimes it may be impossible to avoid a tsunami. Should this happen and you find yourself trapped in the
water, look for something that can float and hold on to it. Floating objects such as doors, tree trucks, fishing
equipment’s among others can save your life. When the rescue time comes he will be easier to spot.

12. HOW TO CREATE A POST TSUNAMI REHABILITATION PLAN
A rehabilitation plan is one that will help you and your family adjust to life after the tsunami has hit. Survival
does not end with the tsunami. Most probably essentials such as water, food and even electricity will be
tough to come by. Therefore it is important to prepare a rehabilitation plan in advance.
For the plan to be effective it needs to have the following.
•Have a stash of fresh water, it may be bottled or filtered water. As a family or as a community it is important
you have water reserves stored away for tsunami emergency purposes
•Using undamaged shelters and structures. As a community the key to surviving a tsunami aftermath is
working together.
•Having a generator or any other secondary source of electricity/energy is welcome. This may be difficult
especially since generators are cumbersome. However, there are portable models out there and even
models that work on solar power.
•As a community your plan should have a shelter and food distribution mechanism for all those affected.
•The plan should also factor in gas raptures and fires caused by broken gas pipes.