5B – Slide 1
Topic 5B:
Tsunami
Online Lecture:
Tsunami
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What are tsunami?
What cause tsunami?
Why are tsunami so destructive?
What can we do to protect ourselves from tsunami?
What should we know to protect ourselves?
What is a tsunami?
5B – Slide 2
http://www.asiantsunamivideos.com/
○ What does a tsunami
look like as it comes ashore?
Water surging up the shoreline,
like a fast-rising tide.
Does NOT resemble an
ordinary breaking wave.
○ What cause tsunami?
Earthquakes are the most common cause,
but also landslides, volcanoes, giant meteors, etc…
anything that causes a large amount of water to move.
Called “Seismic Sea Waves” by scientists.
Deep-Water Tsunami
○ How large are tsunami
out in the middle of the ocean?
○ How fast are tsunami
out in the middle
of the ocean?
400+
mph
As fast as jet
airplanes!
5B – Slide 3
100+ miles long
but no more than
a few feet high
few feet
2.5 miles
300 miles
Are tsunami
dangerous
in the middle
of the ocean?
Why or why not?
few feet
2.5 miles
300 miles
Tsunami Warnings
Earthquake “waves” are much
faster than tsunami. (DEMO)
5B – Slide 4
○ How do scientists detect tsunami?
– seismometers
Not all earthquakes cause tsunami:
(detect earthquakes) ● must make the earth move up or down
● close to the bottom of the ocean
– tide gauges
– pressure sensors on the bottom of the ocean
Assuming our systems and procedures work perfectly, will
there always be time to issue a warning? Why or why not?
Shallow-Water Tsunami
5B – Slide 5
○ Like an ordinary wave, the ocean bottom gets in the way
of tsunami orbitals, slowing down the tsunami.
The crest behind is going faster than the crest in front,
squeezing the water in the middle: the only place it can
go is up.
50+ feet high
is not unusual.
300+ ft possible.
The energy spread over miles is being concentrated in a small area (shallower water + slowing
down). The water in front has to keep going, no
matter what is in the way, as it is pushed by the
water behind for 10+ minutes.
Fastest Crest
Slowest
Crest
Middle
Crest
5B – Slide 6
Photographs
of Tsunami
Destruction I
Banda
Aceh,
Indonesia
Gleebruk Village,
Indonesia
Before
After
Photographs of Tsunami Destruction II
Patong Beach,
Thailand
5B – Slide 7
Velankani Beach,
India
Tsunami Safety
5B – Slide 8
○ Even if there is no official warning, under what circumstances might it be a good idea to get away from the coast
for fear of a tsunami?
– Strong Earthquake
– Unusually Low Tide
Before
After
Watch out
for the 2nd
or 3rd crest!
A tsunami like the one in Asia 2004 will most likely to strike the
United States along the coast of Alaska &/or the Pacific Northwest
(Northern California, Oregon, Washington) where there is a trench.