THE POTENTIAL CANARY ISLAND MEGA TSUNAMI


The ocean calms as it drags cars, buildings and people out to sea. Only those farther than 5 miles inland from an Atlantic coast will be spared. This may one day be the reality humanity must endure, far worse than Hurricane Katrina, or the Indonesian Tsunami in 2004, which may be referred to as "ripples in a pond" compared to this catastrophic event.

In 2001, this scenario was proposed by Steven Ward, a researcher at the University of California, and Simon Day, a researcher of University College’s Benfield Greig Hazard Research Centre in London. According to their work, a massive landslide triggered by a catestrophic flank collapse from the eruption of volcano, Cumbre Vieja, on the island of La Palma in the Canary Island chain has the potential to create tsunami up to 100 meters high as the landmass slides violently into the Pacific Ocean. The landslide is estimated to be between 150 to 500 km of rock. Dr. Day has stated that the volcano on La Palma erupts every few decades to a century, and the next eruption may not be the one to trigger the massive landslide, so it is very difficult to estimate when this event is likely to occur.

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Figure 1: The Canary Islands

The island of La Palma is the youngest and western-most island of the Canary Islands, and is still volcanically active. The Canary Islands are located off the coast of Morocco in North-Western Africa. Refer to Figure 1 for a view of the Canary Island chain and its location. The largest of the island’s three volcanoes, Cumbre Vieja, is a very active stratovolcano and has erupted in the years 1470, 1585, 1646, 1677, 1712, and twice in recent history, once in 1949 and another in 1971. During the eruption in 1949, a large part of the western edge of Cumbre Vieja sank 4 meters. This movement formed a new normal fault through the western half of the volcano. This creates the potential for a 15-20 km (9-12 miles) wide by 15-25 km (9-15.5 miles) long section of the volcano to slide into the sea. Figure 2 displays that the Cumbre Vieja Volcano (shown in tan) makes up the entire southern half of La Palma.

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Figure 2: The Volcanoes of La Palma

According to Ward and Day’s computer modeling of the event (biased on the scenario of a 500km block that is 1400m thick, 25 km long, 15km wide ) water will be displaced close to 3,000 feet into the air, resulting in tsunami waves that will travel around 500 miles per hour and reach a height of about 330 feet as they crash into Morocco. Between eight and nine hours later, the waves will have traversed the Atlantic Ocean and would reach the eastern coast of the United States. These waves, although dissipated from the intense waves devastating Western Africa, will be around 150-170 feet high and devastate an area 4-5 miles inland. Brazil, France, and the Atlantic coast of the United Kingdom are also believed to be hit by large waves. Figure 3 demonstrates the speed and magnitude of the resulting tsunami as it propagates radially away from La Palma in all directions.


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Figure 3: Wave Propagation

Smaller tsunami events have been recorded in recent times such as the Chehalis Lake mudslide in British Colombia, Canada. On December 3rd, 2007, a steep slope gave way resulting from a larger rainstorm which sent a large amount of earth into the lake's waters at high speeds. According to debris, the waves created by this slide reached 30-40 feet high when they hit the shore. Figure 4 shows a picture of the aftermath of the landslide, and Figure 5 shows large pine trees that have been ripped out of the ground and are now floating in the lake. This tsunami in Chehalis Lake displays the destructive force of landslide generated tsunami, and can be viewed as a small scale model of what could happen pending a landslide on La Palma Island.


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Figure 4: Landslide in Chehalis Lake in British Colombia, Canada

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Figure 5: Uprooted trees due to the Chehalis Lake tsunami

Scientists against the Canary Island Mega Tsunami theory have argued that although this situation may be possible, it is clearly the worst case scenario. A huge piece of La Palma Island's left side would have to fall almost entirely intact in order to transfer enough energy to the ocean water which would cause a displacement large enough to create a "Mega Tsunami". Instead, scientists of the Southampton Oceanography Centre assure the public that this scenario is unlikely. According to their examination of submarine deposits due to previous landslides, on the Canary Islands, the earth would most likely fall in multiple pieces at separate times, reducing the amount of energy transferred at one time, and thus creating many smaller, less significant waves. According to geologists who have examined the island, La Palma is comprised of two major layers. The first, and lower layer is made up of 10-350 meters of pillow lava and basaltic dykes, and the upper layer is made up of pryoclasts and basalt lava. This structure will limit the amount of landmass that will fall at one time. Instead, the unstable region of Cumbre Vieja will most likely fall in steps. Another argument against the theory of a mega tsunami is there is no evidence to conclude that a mega tsunami of nearly the same magnitude has occurred in recorded history. In fact, the two closest events, the collapses of the islands of Krakatoa (Krakatau) in Indonesia and Santorin of the Cycladic Islands of Greece were found to have created extremely large waves in the immediate areas, but these waves did not travel large distances as do tsunami generated by earthquakes. Another opposing argument is that the computer model was done using inaccurate date, that is not supported by factual information. This includes that the model was baised on a 25km long block, when the fault is currenlty only 4km long and as such a triggered landslide would not extend 21km more than the acutal falut.. Also, argued is that the position of the faulit line was cahnged to a non exciting one that is 2-3km further away than the actual fault.

The threat of a "Mega Tsunami" due to a landslide of a Canary Island Stratovolcano is unlikely. The Cumbre Vieja volcano may not even erupt within our lifetime, and if were to erupt, its weaked slope may not even fall as a result. When this mass finally falls, there is a small chance that it will fall smoothly as one enormous mass but rather smaller, less-harmful masses. The hype surrounding this catastrophe is the result of over-eager computer modeling.

References:

http://www.noc.soton.ac.uk/gg/classroom%40sea/general_science/killer_waves.html
http://www.maine.gov/doc/nrimc/mgs/explore/hazards/tsunami/jan05.htm
http://archives.cnn.com/2001/TECH/science/08/29/tidal.wave/index.html
http://www.drgeorgepc.com/TsunamiMegaEvaluation.html
http://www.canada.com/globaltv/bc/story.html?id=9a23f00b-50d3-4e9e-b1b3-88251571e0ce&k=29814
http://www.intlvrc.org/18cgc.doc
http://www.es.ucsc.edu/~ward/papers/La_Palma_grl.pdf
http://www.lapalma-tsunami.com/tsunami.html
http://www.lapalma-tsunami.com/