Potential Caribbean Area Mega-Tsunami Risk Assessment

By

R. B. TROMBLEY, Ph.D.

International Volcano Research Centre

3405 S. Tomahawk Rd., Suite # 31

Apache Junction, Arizona USA 85219-9169

(480) 671-1601

e-mail:

website: http://www.intlvrc.org

Abstract

The following presents the potential for a disaster on the east coast of the United States and the Caribbean areas grows as the geological evidence suggests that during a future eruption of Cumbre Vieja, on the island of La Palma in the Canary Islands, could cause a catastrophic failure of its west flank. This failure, if it occurs, could cause a landslide of 150 to 500km3 of rock into the ocean causing a mega-tsunami. Waves generated by the landslide of a 500km3 (150 km3) slide block at 100 m/s could transit the Atlantic ocean and arrive on the coasts of the United States and in the Caribbean with a 10-25 m (3-8m) height.

Introduction

The current geological evidence (Moss, McGuire, Page, 1999) suggests that during a future eruption of Cumbre Vieja volcano on the island of La Palma, in the Canary Islands, may experience a catastrophic flank collapse. For a 500 km3 slide block running westward 60 km down the offshore slope at 100 m/s, computer models predict that tsunami waves 10 to 25 m high will be felt at transoceanic distances spanning azimuths that target most of the Atlantic basin.

During most of the last 125 thousand years, Cumbre Vieja has been the most active volcano in the Canary Islands (Carracedo, et al, 1999). Subaerial Cumbre Vieja forms the southern third of the island of La Palma (see Figure 1), rising 2 km above sea level with average slopes of 15o to

20o. The early Holocene has seen major changes in Cumbre Vieja. Day, et al, 1999, observed that over the last several thousand years, the distribution and orientation of vents and feeder dykes within the volcano have shifted. It shifted from a triple rift system, which is typical of most oceanic island volcanoes, to one consisting of a single N-S rift with westward extending vent arrays.

Figure 1. The Island of La Palma in the Canary Islands.

History of Cumbre Vieja Volcano

Stretching 2,426 m (7,957 ft.) above the ocean floor, Cumbre Vieja is the largest volcano of the western Canary Islands. It is located on the island of La Palma and inhabited by about 85,000 people. La Palma island was created by lava flows from Cumbre Vieja about three million years ago. There are seven known historic eruptions on La Palma, starting in 1470 and up until 1971. During the 1949 eruption, the western half of Cumbre Vieja slid approximately 4 m towards the Atlantic Ocean. Another eruption could cause the 500 billion tonnes of land to slide completely into the ocean, causing a mega-tsunami predicted to hit the Caribbean and the east coast of the United States. When this mega-tsunami hits the east coast, it will cause widespread damage and destroy anything on or near the coast, including major cities like Boston, New York and Miami. Cumbre Vieja will erupt in the future; it is just a question of which eruption will cause the landslide that will create the most destructive mega-tsunami ever. Of the seven historic eruptions, all have had a value of two on the Volcano Explosive Index (VEI) on a scale of zero to eight. Volcano Frequency of Eruption Analysis (VFEA) shows that the average interval between eruptions is 89.33 years. For positively dated eruptions the average length is 57 days for an eruption.

How Volcanoes Cause Tsunamis

When there is a large impact or a large landslide, a rare wave called a mega-tsunami can occur. Many times greater than a normal tsunami, a mega-tsunami can reach heights from 40 metres to well over 100 metres tall. An earthquake moves a very large area only a few metres, compared to a landslide, (caused from a volcanic eruption) which moves a large area a great distance. The bigger the landslide, the more water displaced therefore the bigger wave. When a volcano erupts, the massive amounts of force cause the slopes of the volcano to shift, and in some instances fall. In the case of La Palma, the already loose and very steep slope could slide into the ocean, displacing large amounts of water and causing a mega-tsunami.

The most famous occurrence where a landslide has caused a mega-tsunami was in Lituya Bay, Alaska on July 9, 1958. After a magnitude 7.5 earthquake, land on one side of the bay fell into the water causing a massive and extremely localized wave. The wave was quoted from 50-150 metres tall and caused damage to plant life 525 metres above sea level on the opposite side of the bay.

Eruption Pro 10.7 Assessment

Eruption Pro 10.7 performs analysis on current available volcano eruption data from both historical and current available eruption data, near real-time measurement data including, seismic, deformation, thermal, frequency of eruption analysis, crater lake temperature (if applicable), COSPEC, & statistical procedures (Trombley, Toutain, 2000). It produces three forecasts; a statistically projected next eruption year, the next forecasted beginning eruption year with an 50% probability of eruption occurrence, and finally, the next forecasted beginning

eruption year with an 95% probability of eruption occurrence.

The following is the current assessment of Eruption Pro 10.7 relative to volcano Cumbre Vieja:

With the current data loaded, Eruption Pro 10.7 yields the following analysis for volcano Cumbre Vieja:

Statistical Forecasted Eruption Year = 1978

Year of Forecasted Eruption @ 50% = 2027

Year of Forecasted Eruption @ 95% = 2216

Probability for year 2008 = 11.23%

Forecast according to Repose Analysis = 2122 (Upper Limit)

(Since year 0 C. E. @95% Confidence Level)

Average Repose = 80.714 years

Confidence Level Interval = 70.169 years

Projected years maximum until next eruption = 114 Years
Warning and Prevention

There are a couple ways to forecast an incoming tsunami and very few ways to slow it down. As a large wave comes inland, the tide will recede greatly. By this time though, it is too late, the wave travels with great speed. While impossible to stop a tsunami, areas of high risk have tsunami warning systems to warn the population of an incoming tsunami. In the event of a mega-tsunami, water can go far enough inland so people cannot run far enough away. This is due to the wavelengths of a mega-tsunami being measured in kilometres whereas a normal wave is measured in metres. Japan does have tsunami walls, a concrete structure up to 13.5 feet high to redirect water from a tsunami. But these walls are not enough, as waves can be bigger and pass right over. Still, the only way to prevent damage from tsunamis is to not build in the areas susceptible to the destructive wave.

A mega-tsunami will eventually occur due to the collapse of the land area at the Cumbre Vieja. It may occur at the next eruption, the fifth eruption or the twentieth eruption. We just do not know. It is doubtful that the areas that may be effected by the catastrophic mega-tsunami that will eventually occur have adequately prepared for such a catastrophe. It can only be hoped that officials have at least examined and considered this eventual event.

Conclusions

The current geological evidence suggests that during a future eruption, Cumbre Vieja volcano on the Island of La Palma may experience a catastrophic failure of its west flank, dropping 150 to 500 km3 of rock into the sea. This event would produce a mega-tsunami which would cover the whole Atlantic Ocean including the east coast of the United States. The collapse of Cumbre Vieja's western flank would generate a destructive mega-tsunami which would strike both sides of the North and South Atlantic. Waves of up to 50 m in height are estimated for Florida and for the Caribbean islands and more than 40 m for the northern coast of Brazil. Although not as high, destructive waves have been forecast for the western coast of the Iberian Peninsula, France and Britain's Atlantic coastline. Presumably, in certain areas, the tsunami waves would travel as much as six to seven km inland, destroying everything in their path.

REFERENCES

1.  Carracedo, J. C., S.J. Day, H. Guillou and P. Gravestock, 1999, “The later stages of volcanic and structural evolution of La Palma, Canary Islands”. Geol. Soc. Am. Bull. 111, 755-768.

2.  Day, S. J., J. C. Carracedo, H. Guillou and P. Gravestock, 1999, “Recent structural evolution of the Cumbre Vieja volcano, La Palma, Canary Islands”, J. Volcan. Geotherm. Res. 94, 191-218.

3.  Donovan, S. K., Jackson, T. A., “Caribbean Geology, An Introduction”,

Jamaica, University of the West Indies Publishing, Chapter 1, Pg. 8

4.  Moss, J. L., W. J. McGuire, and D. Page, 1999, “Ground deformation monitoring of a potential landslide at La Palma, Canary Islands.”, J. Volcan. Geotherm. Res. 94, 251-265.

5. Simkin,T., Siebert, L., McClelland, L., Bridge, D., Newhall. C., Latter, J.H.,

"Volcanoes of the World", Washington, D.C. : Smithsonian Institution, 1981.

6.  Simkin, T., Siebert, L., McCleland, L., May, "Volcanoes of the World", 1984

Supplement, Washington, D.C.: Smithsonian Institution, 1984.

7.  Trombley, R. B., 2000, Transactions of the Fifteenth Caribbean Geological Conference, T. A. Jackson (Ed), Caribbean Geology – Into The Third Millenium, Chapter 23

8.  Trombley, R. B. and J. P. Toutain, 2000, “Eruption Pro 10.5 – The New & Improved Long-range Eruption Forecasting Software”, Proceedings of the 16th Caribbean Geological Conference, 16 June - 21 June 2002, Barbados, West Indies.

5