TSUNAMIBY

DILRAJ KAUR MALHOTRA

CONTENTS

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

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.

CAUSESTSUNAMIS 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.

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.

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 INVESTIGATE.

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.

TSUNAMI IN ANDAMAN AND NICOBAR ISLANDS IN 2004

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