HOW DANGEROUS ARE TSUNAMIS?

Twenty years ago today, the deadliest tsunami in recorded history inundated Asian countries and killed about 230,000 people.  The Sumatra-Andaman Earthquake, also called the Boxing Day Earthquake (Boxing Day is a holiday celebrated after Christmas Day, mostly in Europe and Commonwealth nations):

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  Was caused by a subsea earthquake possibly as high as 9.3 magnitude (this was #2 to the largest, which was the 1960 Chile earthquake at 9.5) off the coast of Sumatra, Indonesia.

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  Waves were as high as 167 feet in Aceh province, and two hours later, Sri Lanka saw 20 feet (with run-ups as high as 41 feet--there is a difference in these two terms), and  Thailand had run-ups of up to 64 feet.  
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  At Phuket, Thailand, the second wave was the largest at 20 feet.  Also two hours after the earthquake, India saw heights as much as 33 feet.   3100 miles away in Somalia, there was a run-up of 30 feet.

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  The maximum height above sea level a tsunami reaches on shore is called the run-up.
• In this tsunami, the second wave was the most damaging, and there were smaller first and third waves.
• The time between the waves is usually unpredictable and varied, typically ranging from 5 minutes to 2 hours.  Dangerous tsunami currents  can last for days.
• 
  Costas Synolakis writes that the U.S. is not ready for a giant tsunami.  He founded the University of Southern California Tsunami Center in 1996 and this year was named manager of the year.

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  Indonesia is building a Giant Sea Wall to protect Jakarta.
• More for flood control and land reclamation than to protect from a tsunami, for Jakarta is sinking.
• Cost of $40 billion for a 20-mile wall.  Or maybe $80 billion.
• Should be in place by 2027.
• A Stanford report argues against walls.
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  Japan's Great Wall.
• The 2011 Great Tohoku Earthquake, Tsunami and Nuclear Disaster killed 20,000.
• Nearly 250 miles of tall concrete walls are are now standing along their northeast coast to soften future tsunami damage at a cost of $12 billion.
• Previous walls were only 26 feet tall, but that tsunami reached 50 feet.
• They now stand 45 feet tall, with portions up to 82 feet, and wider bases.

Historically, there have been truly monumental tsunamis, caused by asteroids, landslides, volcanoes and earthquakes.

• The more serious tsunamis come from asteroids, volcanoes and landslides.
• That Chicxulub asteroid event over the Yucatan Peninsula 66 million years ago created tsunamis of 330 feet high waves.  
• Also killed off the dinosaurs.
• But a major asteroid the size of a football field hits Earth only every 2000 years, while one large enough to threaten civilization comes only once every few million years.
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  Between 1 and 1.5 million years ago, the Nuuanu Slide occurred, when the eastern half of the Koolau Volcano on Oahu collapsed, causing a mega-tsunami that ravaged the West Coast of North America. 
• Watch this video.
• That event sent nearly half of Oahu into the Pacific Ocean, leaving behind part of the volcano, where I now live on Nuuanu Avenue.
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  My Chapter 6 of SIMPLE SOLUTIONS for Planet Earth projects that a more serious landslide can occur on the Big Island, which would jeopardize the West Coast.
• 1.4 million years ago, one-third of the East Molokai Volcano collapsed, generating a tsunami in the near field of 2000 feet.

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  Around 200,000 years ago, a volcano caused a collapse of Tenerife, Canary Islands, causing a mega-tsunami.  Another such  event has been predicted here again, which could in 9 hours reach Florida with 82 feet high tsunami waves.
• Hawaii is especially vulnerable for landslides, as around 105,000 years ago, a submarine landslide deposited  sediments on Lanai at an elevation of up to 1394 feet.  This same event reached as high as 262 feet on Oahu.
• I can go on and on, but if you're interested in these details, go to Wikipedia.

As natural disasters go, tsunamis are considered to be relatively rare.

• Especially in the Atlantic Ocean.  There have been a few, and more might be possible in the future.  The Great Lisbon Earthquake and Tsunami in 1755 might have killed up to 50,000.  This event changed history.

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  In the past 100 years, there have been 58, claiming 260,000 lives.
• That Boxing Day Tsunami itself accounted for 230,000 lives.  #2 was the 2011 Japan Tohoku disaster with 20,000 lives.

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  78% of tsunamis from 1900 to 2015 occurred in the Pacific Ocean.  Only 5% originated in the Indian Ocean, where that #1 killer originated.
• Thus, much of the alert warning technology is in the Pacific Ocean, although, after that disaster of 20 years ago, other areas are beginning to take precautions.

Some countries have never seen a tsunami, especially if landlocked.  

• The five countries with the lowest risk of all natural disasters from TEMPO.com are:  Qatar, Saudi Arabia, Malta, Singapore and Uruguay.
• Wikipedia has  quite a different list:
• Safest, #1 Andorra and Monaco
• #3  San Marino
• #4  Luxembourg
• #6  Singapore
• #8  Malta
• #13  Switzerland
• #16  Qatar
• #105  Uruguay
• #129  Saudi Arabia
• #158  Japan
• #168  USA
• #175  Russia
• #178  China
• #184  India
• #185  Philippines
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  Why such a difference?  Don't know.  Singapore could someday suffer from a tsunami, but have never had that problem.  
• The Indian Ocean monster occurred on the other side of Indonesia, so Singapore was not seriously affected, for the maximum tsunami height was less than a meter or yard.
• With all those typhoons flying around the Philippines, down to Vietnam, and up to Japan, why has Singapore never faced one?  It is too close to the equator, and cyclonic storms don't go there.
  
• Singapore is outside the earthquake zone, and has only felt minor tremors, never one which caused structural damage.
• Want a safe place with high tech and good living?  Visit Singapore, one of my favorite places.  Singapore was this year named as the safest destination in the world for travelers by Forbes Advisor.

Since 1788, the U.S. has been struck 21 times by tsunamis.

• Lituya Bay, Alaska has seen a handful.
• On 27October1936, a landslide caused a 490 foot wave that travelled about 2000 feet inland.

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  On 10July1958, a magnitude 7.7 earthquake occurred, causing a rockfall which generated a gargantuan 1720 feet wave (nearly as tall as the new World Trade Center and largest ever recorded).  Five deaths.
• Another landslide on 1January1853 created a wave of 394 feet.

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  An 8.1 earthquake hit near Alaska's Aleutian Islands on 1April1946, killing 165, 159 in Hawaii.
• The Great Alaska Earthquake on 27March1964 at 9.2 magnitude, created a 220 feet high tsunami, killing 120.
• Afraid of tsunamis?  Avoid Hawaii.  Want to read the right column?  Click on that link.

These Are the 10 U.S. Counties Facing the Greatest Risk From a Tsunami:

COUNTY	RISK SCORE	RELATIVE RISK
1. Honolulu County, Hawaii	100	Very High
2. Maui County, Hawaii	98.6	Relatively High
3. Hawaii County, Hawaii	97.3	Relatively High
4. Aleutians West Census Area, Alaska	95.9	Relatively High
5. Del Norte County, California	94.6	Relatively High
6. Kauai County, Hawaii	93.2	Relatively High
7. Kenai Peninsula Borough, Alaska	91.9	Relatively High
8. Clatsop County, Oregon	90.5	Relatively Moderate
9. Humboldt County, California	89.2	Relatively Moderate
10. Santa Cruz County, California	87.8	Relatively Moderate

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