296

Tsunami

Hum

an1.6 m

30 m

Indian Ocean Earthquake and Tsunam

i Tilly Sm

ith probably never im

agined that w

hat she learned in geography class w

ould help save lives. W

hen the Indian O

cean tsunam

i hit on D

ecember 26, 2004,

Tilly and her family

were vacationing at

Miakho Beach in

Phuket, Thailand. Tilly, 10 years old, noticed som

ething strange happening on the beach. The w

ater at the beach suddenly w

ent away. In

the distance, she could see boats bouncing w

ildly and the water

bubbling. The ocean w

ater returned quickly and kept com

ing onto shore. Tilly scream

ed for her family to leave the beach right

away. H

er parents warned others. D

ue to her knowledge of

the early warning signs of tsunam

is, the girl from England

saved other tourists on the beach that day.

What is a tsunam

i?Tilly had just learned that underw

ater earthquakes could cause tsunam

is. Tsunami is a Japanese w

ord meaning

“harbor wave.” U

nderwater earthquakes, landslides, and

volcanoes may cause tsunam

is. Not every earthquake leads

to a tsunami. Yet, large ocean earthquakes that m

ove the sea floor up and dow

n cause many tsunam

is.

The size of a tsunami depends on

many factors. H

ow large is the

earthquake? Where does the

earthquake occur? How

much of

the sea floor moves up and dow

n? H

ow deep is the ocean w

ater w

here the earthquake occurs? In the deep ocean, tsunam

is may be

only several feet high. Often ships

at sea never feel a tsunami. This

is not the case as the tsunami

travels toward shore and

shallower w

ater. The amount of w

ater begins to build. Wave

height increases as they approach land. Some w

aves may

travel 500-1,000 kilometers per hour and be as high as

35m

eters.

The Indian Ocean tsunam

iThe Indian O

cean tsunami m

ay be one of the deadliest natural disasters in m

odern history. Officials believe m

ore than 275,000 people died. The final num

ber of deaths may

never be known. The U

.S. Geological Survey originally

reported the earthquake at a 9.0 magnitude. This is the

strongest in the world since 1964 and the fourth largest since

1900. Scientists used data from around the w

orld to revise the earthquake to a 9.3 m

agnitude. This would m

ake it the second largest earthquake since the 9.5 m

agnitude earthquake in Chile in 1960. Earth’s surface is m

ade up of plates that are constantly in m

otion. Plates meet one another along plate boundaries.

Pressure along these boundaries builds over time and

sometim

es releases abruptly creating earthquakes.D

uring the Indian Ocean earthquake, 1,200 kilom

eters (750

miles) of the plate boundary slipped w

hen the Indian

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297U

NIT 4 T

HE C

HA

NG

ING E

AR

TH

Plate (part of the Indo-Australian Plate) slid under the Burm

a Plate (part of the Eurasian Plate). That is about 400

kilometers (250

miles) m

ore than the distance between

San Diego and San Francisco! The seabed rose m

ore than tw

o meters causing huge tsunam

i waves.

Imagine a plastic squeeze bottle filled to the top w

ith water.

As you squeeze the container the water spills out over the

top. The upward m

otion of the earthquake displaced an enorm

ous amount of w

ater similar to the squeeze bottle.

This displacement of w

ater created the tsunami that flooded

the coastlines. The Indian O

cean earthquake occurred off the west coast of

Sumatra, an Indonesian island. W

aves reached 20 to 30 m

eters (65 to 100 feet) high. The tsunami destroyed the

shores of Indonesia, Sri Lanka, and Thailand. The tsunami

even traveled as far as Africa, nearly 8,000 kilometers

(5000m

iles) from the center of the earthquake.

The tsunami w

aves did not start from one central location,

but occurred along the entire 1,207 kilometers of fault line.

That is why the w

aves affected so many areas of the w

orld.

Indian Ocean tsunam

i warning system

Why did so m

any people die from the tsunam

i? Tsunamis are

rare in the Indian Ocean and a w

arning system w

as not in place. The last m

ajor tsunami in the region w

as caused by the 1883 volcanic eruption of K

rakatoa in Indonesia.

People were not aw

are of the signs of a tsunam

i—a strong

earthquake in the area and a quick rise or fall in w

ater levels by the coast. H

istorically, tsunamis usually

happen in the Pacific Ocean

where m

any earthquakes occur. In the Pacific, there are tw

o w

arning centers monitoring the

area: the Alaska and the Pacific Tsunam

i Warning Centers. The

Alaska Tsunami W

arning Center includes the w

est coast of the U

nited States and Canada. The Pacific Tsunam

i W

arning Center covers Haw

aii and all other Pacific areas. The centers m

onitor the size and location of earthquakes in the ocean. If a tsunam

i is possible, the center sends out a w

arning estimating w

hen the tsunami w

ill reach land. This allow

s coastal areas to have time to evacuate.

One m

onth after the Indian Ocean tsunam

i, the United

Nations recom

mended a w

arning system for the Indian

Ocean. Plans are in place to have as m

any as 27 centers created, one for each Indian O

cean country. In May of 2005,

Thailand opened a center linked to the Pacific Tsunami

Warning Center. There has been discussion about creating a

global warning system

that would include the Atlantic

Ocean and the Caribbean.

Questions:

1.W

hat causes a tsunami?

2.W

hat are signs that a tsunami m

ight be coming?

3.W

hy was there no tsunam

i warning system

in the Indian O

cean?

Chapter 12 Connection