Physics Of The Tsunami

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Physics Of The Tsunami

- and Understanding Why It Causes Devastation -

 

By

 

Mobolaji Aluko

alukome@comcast.net

 

 

January 5, 2004

 

Introduction

 

On Boxing Day December 26, 2004, the world awoke to a horrific news: a tsunami had “boxed” out whole towns and villages in and around islands in the Indian Ocean/Pacific Ocean of South-East Asia (from Indonesia to India to Thailand), and extended its grievous reach to the Horn of Africa (Somalia).  The death toll is still rising – and at last count as many as 150,000 human beings – not to talk of fauna and flora – are missing and/or presumed dead.

 

 

 

 

How could this devastation have occurred?

 

Well, let us look at some back-of-the-envelope arithmetics of the physics of the Tsunami.

 

 Tsu-nami (Japanese for “harbor-wave”)

 

Some speeds to consider

 

In normal stride, an adult walks roughly at the speed of 5 kilometers per hour (km/h) or 3.1 miles per hour (mph). A person who runs 100 meters in 9 seconds runs at 40 km/h - or roughly 25 mph [1 mph = 1.60934 km/h;  1 km/h =0.621371 mph.].   Above 55 mph (or 88 km/h), you will get a speeding ticket driving in most highways in the US.  Commercial jet airplanes typically fly at 540 mph (870 km/h) - roughly  ten times the typical car speeding limit. The speed of sound at sea level is roughly 760 mph or 1,223 km/h [= Mach 1]  and the speed of light is just about less than 1,000 times the speed of sound - 1,079,252.849 km/h to be exact.

 

The Tsunami and Channel Flow

 

Think of a long rectangular container filled with water, tilted such that water can flow out  from one end.   For a tsunami here, the water is ocean water; the bottom of the container is the ocean floor  - and the sudden tilt of the container is caused by an earthquake. In the case in question, it was a megathrust earthquake of moment magnitude 9.0 on the Richter scale.

 

 

 

 

And that water flows onto coastal land and beyond (as far as 1 km or 0.6 miles inland)  – into where human beings live.

 

 

The Speed of the Tsunami

 

So what was the speed of the Tsunami that hit parts of South-East Asia on December 26, 2004 ?

 

It depends on where in the ocean the quake which started the channel flow of water began, causing a shallow-water wave.  Multiply the ocean depth (in meters) by roughly 10 (actually 9.8 meter per second squared), square root the product, multiply it by 3.6 – and you get roughly its speed in km/h [ see Table 1 below.] 

 

We are told that the SE-Asia tsunami moved up at speeds up to 800 km/h – which means that it must have come from depths of about

5,000 m (5 km). [Average depth of the Pacific Ocean is about 4,188 m, and its deepest Mariana Trench is about 11,000 m.]

 

 

Of Tornadoes and Hurricanes

 

The speed of the water when it got to land is much slower – but you get the idea that it could be sufficiently fast to sweep objects in its path away.  Even equally devastating is the HEIGHT of the water when it hits land, drowning life.

 

I have also given in Table 2 the equivalent wind speeds and categories for  the more familiar depressions, storms,  tornadoes and hurricanes.  In August/September 2004, the mid-Atlantic/Southeast states (particularly the state of Florida) witnessed five major land-falling hurricanes:  Hurricane Charley ( around August 13) was 145 mph [233 km/h;  Level 4] and Gaston (at 75 mph, a Level 1 Hurricane in August; reclassified as a hurricane after the season),   and the rest in September were  Frances (around September 5; 105 mph; 169 km/h;  Level 2), Ivan (around September 16; at 200 km/h, a Level 3 Hurricane) while Hurricane Jeanne was about 75 mph (120 km/h a Level 1 Hurricane; around September 26).  Only Gaston missed Florida.

 

Noting that the density of sea water is about 1,030 kg / cubic meter while that of dry air is 1.2 kg per cubic meter at room temperature – and with kinetic energy directly proportional to mass and to the square of the moving medium’s speed - one can see that water of the same speed as air packs about 1000 times more energy ! [Doubling the speed (for example) quadruples the kinetic energy.]

 

Lord have mercy !

 

So Please Donate

 

Now that you have a rough idea of how devastating a tsunami is – and why it wrought what it did in South-East Asia and the Horn of Africa, please donate to your favorite charity.  Don’t forget Somalia in the Horn of Africa, thank you.

 

May God rest the soul of those who died, and may God bless the lives of those who donate. [Amen.]

 

 

Mr. Wilson Iguade

[Nigeria/Naijapolitics Tsunami Donation Contact Person]

P.O Box 794601

Dallas, Texas 75379, USA

Cell: 469/569-3595

 

American Red Cross International Response Fund

P. O. Box 37243

Washington, DC 20013

800 HELP-NOW

http://www.redcross.org

 

See also: International Red Cross and Red Crescent Societies (www.ifrc.org)

 

Action Against Hunger

247 W. 37th St.

Suite 1201

New York, NY 10018

212 967 7800

 

Doctors Without Borders/Medecins Sans Frontiers

P. O. Box 1856

Merrifield

VA 22116-8056

888 392 0392

http://www.doctorswithout-borders.org

 

World Vision

P. O. Box 9716

Dept W

Federal War, WA 98063-9716

888 511 6592

http://www.worldvision.org

 

The U.S. Fund for UNICEF (800-FOR-KIDS),

 

Catholic Relief Services (800-736-3467)

 

 

 

Bibliography

 

http://news.bbc.co.uk/1/hi/world/asia-pacific/4136289.stm

Taken from “Animated Guide: The Tsunami disaster”

 

http://en.wikipedia.org/wiki/Density_of_air

Density of Air

 

http://hypertextbook.com/facts/2002/EdwardLaValley.shtml

Density of Sea Water

 

http://www.geophys.washington.edu/tsunami/general/physics/meaning.html

What Does “Tsunami” mean ?

 

http://www.news-journalonline.com/NewsJournalOnline/News/Neighbors/DailyJournal/03AreaDJ02123004.htm

Hurricanes top news story

 

 

 

Table 1:  Relationship of Tsunami Water Speeds to Ocean Depth

 

Ocean

Depth

meters

Tsunami

Speeds

Km/h

Tsunami

Speeds

mph

Comment on Ocean Depth

10

36

22

 

100

 114

71

 

150

139

86

 

200

  161

100

Nigeria’s offshore resource derivation isobath

Off the Atlantic Coast

300

197

122

 

400

228

142

 

500

 255

158

 

1,000

 360

224

 

1,038

367

228

Average depth of Arctic Ocean

2,000

 509

316

 

3,000

 624

388

 

3,872

708

440

Average depth of Atlantic and Indian Oceans

4,000

 720

447

 average overall depth of oceans

4,188

737

458

Average depth of Pacific Ocean

5,000

 805

500

 

5,450

 840

522

 Eurasia Basin – deepest in Arctic Ocean

7,000

 952 

591

 

7,725

 1,000

621

 Java Trench – deepest in Indian Ocean

8,000

1,018

632

 

8,648

 1,059 

658

 Puerto Rico Trench – deepest in Atlantic Ocean

10,000

 1,140

708

 

11,000

 1,194

741

 

11,033

 1,196

743

 Mariana Trench – deepest in Pacific Ocean

12,000

 1,247

774

Just above the speed of sound (~ 1200 km/h)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Source: http://mbgnet.mobot.org/salt/oceans/data.htm

 


 

       Table 2:  Classifying Depressions, Storms, Hurricanes and Tornadoes

 

Category

Damage

Wind

Speeds

mph

Wind

Speeds

Km/h

Tropical Depressions

 

23-39 mph

37-63 km/h

Tropical Storms

 

40-73 mph

64-117 km/h

Hurricanes (or Typhoons)*

Saffir/Simpson Scale

Category

Damage

Wind

Speeds

mph

Wind

Speeds

Km/h

Level 1

Minimal

74-95 mph

119-153 km/h

Level 2

Moderate

96-110 mph

154-177 km/h

Level 3

Extensive

111-130 mph

178-209 km/h

Level 4

Extreme

131-155 mph

210-250 km/h

Level 5

Catastrophic

>155 mph

>250 km/h

 

 

 

 

Tornadoes

Fujita Intensity Scale

Category

Damage

Wind
speeds

mph

Wind
speeds

Km/h

F0

Light

40–72 mph

64-116 km/h

F1

Moderate

73–112 mph

117-180 km/h

F2

Significant

113–157 mph

181-253 km/h

F3

Severe

158–206 mph

254-331 km/h

F4

Devastating

207–260 mph

333-418 km/h

F5

Incredible

261–318 mph

420-512 km/h

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

*The term hurricane is used for Northern Hemisphere tropical cyclones east of the International

Dateline to the Greenwich Meridian. The term typhoon is used for Pacific tropical cyclones north

of the Equator west of the International Dateline.

 

Sources:

http://hypertextbook.com/facts/StephanieStern.shtml

http://www.infoplease.com/ipa/A0193170.html

http://www.ucar.edu/educ_outreach/webweather/hurricane2.html

http://www.hawaii.navy.mil/hurricane/hurr_info.htm

http://www.aoml.noaa.gov/general/lib/laescae.html

http://www.nhc.noaa.gov/aboutgloss.shtml

 

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