Tsunamis are series of large waves created by the displacement of water in seas or oceans. They are most commonly caused by earthquakes under the sea floor or volcanic eruptions. Tsunamis have a small amplitude offshore but grow significantly larger as they reach shallower coastal waters. Areas near coastlines are devastated by the fast moving wall of water which can reach heights of 30 meters, destroying homes and structures. The 2004 Indian Ocean tsunami caused widespread damage in the Andaman and Nicobar Islands due to the lack of a warning system.

1. TSUNAMI
BY
DILRAJ KAUR MALHOTRA

2. CONTENTS
• WHAT IS TSUNAMI ?
• CAUSES ?
• EFFECTS OF TSUNAMI ?
• AREAS AFFECTED
• TSUNAMI IN ANDAMAN AND NICOBAR ISLANDS IN 2004

3. WHAT IS A TSUNAMI ?
A tsunami is a series of
waves created when water is
moved very quickly.
Underwater earthquakes are
the most common causes of
tsunamis, but underwater
volcanic activity can also
trigger a displacement in the
water, and create a mega-
wave.

4. CAUSES
TSUNAMIS HAVE A SMALL AMPLITUDE
(WAVE HEIGHT) OFFSHORE, AND A
VERY LONG WAVELENGTH (OFTEN
HUNDREDS OF KILOMETERS LONG),
WHICH IS WHY THEY GENERALLY
PASS UNNOTICED AT SEA, FORMING
ONLY A SLIGHT SWELL USUALLY
ABOUT 300 MILLIMETRES (12 IN)
ABOVE THE NORMAL SEA SURFACE.
THEY GROW IN HEIGHT WHEN THEY
REACH SHALLOWER WATER, IN A
WAVE SHOALING PROCESS. A
TSUNAMI CAN OCCUR IN ANY TIDAL
STATE AND EVEN AT LOW TIDE CAN
STILL INUNDATE COASTAL AREAS.

5. CAUSES
• MOST TSUNAMIS ARE CAUSED
BY SUBMARINE EARTHQUAKES
WHICH DISLOCATE THE
OCEANIC CRUST, PUSHING
WATER UPWARDS.
• TSUNAMI CAN ALSO BE
GENERATED BY ERUPTING
SUBMARINE VOLCANOES
EJECTING MAGMA INTO THE
OCEAN.
• A GAS BUBBLE ERUPTING IN A
DEEP PART OF THE OCEAN CAN
ALSO TRIGGER A TSUNAMI.

6. EFFECTS OF TSUNAMI ?
• TSUNAMIS MAY REACH A MAXIMUM
VERTICAL HEIGHT ONSHORE ABOVE SEA
LEVEL, OFTEN CALLED A RUN UP HEIGHT,
OF 10, 20, AND EVEN 30 METERS.
• FOR A TYPICAL OCEAN DEPTH OF 4000M,
A TSUNAMI MOVES WITH A SPEED ABOUT
700KM/HR.
• THE FAST-MOVING WATER ASSOCIATED
WITH THE INUNDATING TSUNAMI CAN
CRUSH HOMES AND OTHER COASTAL
STRUCTURES.
• DRAWBACK BEGINS BEFORE THE WAVE
ARRIVES AT AN INTERVAL EQUAL TO
HALF OF THE WAVE'S PERIOD. IF THE
SLOPE OF THE COASTAL SEABED IS
SMALL, DRAWBACK CAN EXCEED
HUNDREDS OF METERS. PEOPLE
UNAWARE OF THE DANGER SOMETIMES
REMAIN NEAR THE SHORE TO SATISFY
THEIR CURIOSITY OR TO COLLECT FISH
FROM THE EXPOSED SEABED. DURING
THE INDIAN OCEAN TSUNAMI, THE SEA
WITHDREW AND MANY PEOPLE WENT
ONTO THE EXPOSED SEA BED TO

7. AREAS AFFECTED
• TSUNAMIS OCCUR MOST FREQUENTLY IN THE
PACIFIC OCEAN, BUT ARE A GLOBAL
PHENOMENON; THEY ARE POSSIBLE
WHEREVER LARGE BODIES OF WATER ARE
FOUND, INCLUDING INLAND LAKES, WHERE
THEY CAN BE CAUSED BY LANDSLIDES.
• JAPAN IS A NATION WITH THE MOST RECORDED
TSUNAMIS IN THE WORLD. THE EARLIEST
RECORDED DISASTER BEING THAT OF THE 684
A.D.
• THERE WERE NO TSUNAMI WARNING SYSTEMS
IN THE INDIAN OCEAN ON THE 26TH DECEMBER
2004. HAD THERE HAD BEEN, MANY LIVES
COULD HAVE BEEN SAVED.
• A 10 YEAR OLD TOURIST NAMED TILLY SMITH,
WHO HAD STUDIED TSUNAMIS AT SCHOOL,
NOTICED THE RECEDING TIDE AND FROTHING
BUBBLES, AND TOLD HER PARENTS THERE WAS
GOING TO BE A TSUNAMI. HER PARENTS TOLD
THE REST OF THE BEACH AND EVERYONE WAS
EVACUATED SAFELY.

8. TSUNAMI IN ANDAMAN AND
NICOBAR ISLANDS IN 2004

9. THANK YOU