CPO Earth Sciencespringvillescience.weebly.com/uploads/1/2/5/2/12526844/... · 2019. 11. 15. ·...
Transcript of CPO Earth Sciencespringvillescience.weebly.com/uploads/1/2/5/2/12526844/... · 2019. 11. 15. ·...
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
Chapter 12 Connection
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