Disasters: asteroids, tsunamis and Yellowstone

By Frederic Friedel

On Sunday, December 26, 2004 at 7:58:53 a.m. local time the fourth largest earthquake in the world since 1900 occurred off the west coast of northern Sumatra. The resulting tsunami caused more casualties than any other in recorded history, killing more than a quarter of a million people.

A village near the coast of Sumatra lays in ruin after the Tsunami that struck South East Asia [photo Wikimedia]

Some time after the disaster had struck I received a letter from John Nunn, mathematician, chess grandmaster, author and publisher, who is very knowledgeable on any subject connected with science. John wrote:

“I think this whole Indian Ocean Tsunami disaster demonstrates how badly people assess risks involving rare but catastrophic events. There is a consistent error in such assessments: risks involving human agencies are regularly over-estimated, while risks involving natural agencies are regularly under-estimated. Thus the following risks are over-estimated:
- Terrorism
- Nuclear power stations
- Genetically modified food
The following risks are under-estimated
- Volcanic eruptions
- Earthquakes
- Asteroid impacts
- Epidemics
It is depressing to consider the vast amounts spent on anti-terrorism measures, many of them quite pointless, while a few million dollars would have provided a tsunami warning system which would have saved a huge number of lives.”

For some years I myself have been posing the following question to friends and associates: Which of the following events should we be most afraid of?

  1. International terrorism and the personal threat to us or our community.
  2. A nuclear mega-accident, resulting from atomic weapons or catastrophic failure of a nuclear power station.
  3. An asteroid or comet striking the earth.
  4. Genetically modified life-forms escaping from laboratories and causing widespread death and debilitation.
  5. Catastrophic climate change brought about by excessive levels of CO2 emitted into the atmosphere.
  6. The Yellowstone National Park.

After a while I usually pass out a “hint”: one of the above disasters is infinitely more devastating and capable of killing orders of magnitude more people than the other five. It is also much more likely to occur. And finally there is, in the foreseeable future, absolutely nothing we can do about it.

Before I reveal the most dangerous of the above events, at the end of this article, let us look at a few hazards to humanity more closely.

2004 MN4

Hard to see: 2004 MN4 in a telescope image

Will the world as we know it end on April 13 2029? This question is not as flippant as it looks. In fact for a few days at the end of 2004 it looked like this was a distinct possibility. An asteroid was discovered and calculated to impact Earth in 2029. According to NASA it would strike with an energy of about 1400 megatons of TNT, 25 times more than the largest thermo-nuclear bomb ever tested and about 100 times more powerful than the Tunguska explosion over Siberia in 1908.

On December 24 NASA published an impact chance figure for 2004 MN4, the unimaginative name given to the large space rock, of “around 1 in 62” (or 1.6%), the highest probability for any asteroid ever observed. In the course of a week the agency corrected its estimate on the basis of more observations to 1 in 37 or 2.7%.

Subsequently the asteroid was precovered (discovered on older photographs). In addition, NASA finished conducting radar measurements with the Arecibo radio telescope in Puerto Rico. The result of the new calculations was a zero percent chance of Earth impact. 2004 MN4 will pass the earth at a distance of 36,350 km (or 22,600 miles), which is closer to the planet than geosynchronous satellites that relay TV and communication signals. The flyby will occur on April 13, 2029, which coincidentally is a Friday (paraskavedekatriaphobes can find relief here). On that day the rock will be easily visible to the naked eye, having a magnitude of 3.3. You will be able to see it at around 11 p.m. in Europe, moving past the constellation of Gemini at a rate of 42° per hour, which is less than half as fast as the International Space Station moves across the sky.

It should be noted that all impact estimates rely on complete knowledge of the inner solar system and all the interactions that 2004 MN4 will have from now until the year 2029. Unfortunately this knowledge is far from complete, and even a tiny change in the path of the rock, due for instance to an encounter with an unknown object, will produce a substantial variation in the final earth-crossing position.

Currently there are 671 known asteroids with earth-crossing orbits. These are being tracked by NASA’s Near Earth Object Program. None is considered potentially hazardous to earth in the near future.

Risk assessment

In the follow-up to the original fairly dire risk calculations published by NASA, John Nunn retracted “asteroid impacts” from his list of humanity-threatening natural disasters. “Thinking about it a bit more, I don’t believe there is much danger from an asteroid impact. I had thought about the 1908 Tunguska impact, equivalent to perhaps a 10-megaton hydrogen bomb. Assuming one impact a century, this sounds quite dangerous. But if you assume that the impact kills everyone in an area of a thousand square kilometres, then, with surface area of Earth = 500 million square kilometres, that would be about 12 people per square km. Thus the impact could be statistically expected to kill 12,000 people.”

That number, spread over the century, is the equivalent of 120 per year. More people are killed in hippopotamus attacks or by TV sets falling off shelves. A web page entitled “The Odds of Dying” (have a few hours free if you go there) gives precise figures: the lifetime odds for dying of heart disease is 1 in 5, of cancer 1:7, stroke 1:23, car accidents 1:100, firearms 1:325, air travel 1:20,000, lightning 1:83,000, earthquake 1:132,000, asteroid impact 1:200,000 and Tsunamis 1:500,000.
 
 The devastating Indian Ocean Tsunami of December 26, 2004, caused well over 250,000 deaths. But how does it compare to other natural disasters in recent history? Here are a few statistics:

2003: An earthquake in Bam, Iran, officially killed 26,271
1976: An earthquake in Tangshan, China, killed 242,000
1970: A cyclone in Bangladesh killed 500,000
1923: The Tokyo earthquake killed 140,000
1887: China’s Yellow River broke its banks in Huayan Kou killing 900,000
1826: A tsunami killed 27,000 in Japan
1815: A volcanic eruption of Mount Tambora on Indonesia killed 90,000
1556: An earthquake in China’s Shanxi and Henan provinces killed 830,000

Mega Tsunamis

Let us return to Tsunamis. Devastating as the December 26 2004 tidal wave was, it pales to insignificance compared to some of the geological time-bombs that are slumbering around the globe. These can produce mega-tsunamis that are more destructive than anything we have witnessed in mankind’s history. And the next episode is likely to emanate from a balmy island off the coast of North Africa. It will cause a wall of water to cross the Atlantic Ocean with the speed of a jet airliner and devastate the East Coast of the United States.

Mega-tsunamis are generally landslide-generated. The greatest danger comes from large volcanic islands which are prone to massive fault-driven events. For instance the sea floor around Hawaii is covered with the remains of truly colossal landslides that occurred millions of years ago. Fortunately, such events are very rare, but concern is growing that ideal conditions for such an event currently exist — on the island of La Palma in the Canaries. During a 1949 eruption of the southern volcano, Cumbre Vieja, a gigantic fissure appeared across the side of the volcano, and the western half slipped a few meters towards the Atlantic before stopping in its tracks.

Schematic by the Universidad de Barcelona

Scientists believe that the western flank of the volcano might give way completely during a future eruption, causing a mass of around 500 thousand million tonnes to slide into the Atlantic Ocean. This would generate an almost inconceivably destructive wave, which would surge across the entire Atlantic in a few hours. The worst case scenario envisages an initial bulge of water 900 meters high. This subsides to form waves in excess of 100 m in height that strike neighbouring islands. After an hour waves 50 to 100 m high hit the Northwest African coast. Spain and the UK experience waves 7 to 10 m high, two to five hours after the collapse. After nine hours, the Florida coastline can expect to face around a dozen waves between 20 and 25 m high. It would engulf the East Coast of the US, sweeping away everything up to a distance of 20 km inland.

This page will tell you more: Mega-tsunami, Wave of Destruction. And here’s a recent film that dramatizes such an event.

Yellowstone

Which brings us back to our little quiz at the top of this page: which disaster should we fear most? The correct answer, as many of you might have suspected, was Yellowstone National Park. It turns out that this famous tourist attraction, visited by millions of people each year, is a so-called “super-volcano”, one that’s eruption would be unlike anything we have ever witnessed — at least in the last 75,000 years.

Super-volcanoes are created when magma collects in a giant reservoir in the Earth’s crust. It can increase to an enormous size, building up pressure until it finally erupts on a “mega-colossal” scale (scientists classify volcanic explosions as gentle, explosive, severe, cataclysmic, paroxysmal, colossal, super-colossal and mega-colossal). The explosion of Yellowstone would cover the entire North American continent with many inches of ash and debris, bringing all life to a standstill. And it would send ash, dust, and sulfur dioxide into the atmosphere, which would circle the Earth, darkening the skies for a number of years, causing temperatures to plummet. Many species of animals and plants would face extinction. The last time a super-volcano blew, Toba, 74,000 years ago in Sumatra, it reduced the human population on Earth to just a few thousand individuals. Mankind was pushed to the edge of extinction.

The good news is that Yellowstone has a fairly stable eruption cycle of 600,000 years. The bad news: the last eruption was 640,000 years ago.

In case you are enjoying all of this, here are some links: