TsunamiPredictionQuestioned

CUMBRE VIEJA, Canary Islands, Aug. 31 (UPI) -- An unlikely series of events involving a huge volcanic explosion that sends a gigantic block of rock into the Atlantic in the Canary Islands could cause a large wave called a tsunami to inundate many coastal regions of the ocean, according to two researchers. The scenario, developed with computer models by Simon Day and Steven Ward, is described in the September edition of Geophysical Research Letters.

The researchers hypothesize that a huge piece of rock, 150 to 500 cubic kilometers (about 38 to 125 cubic miles) would slide into the ocean at a speed of 100 meters (328 feet) per second as a result of a volcanic eruption at Cubre Vieja Volcano. The massive sliding block of rock would generate a dome of water 900 meters (984 yards) high. After 50 km (31 miles) of ocean travel, the wave would still be 500 meters (547 yards) high, the researchers say. Waves of 50 to 100 meters (54 to 109 yards) would hit some of the African shoreline. Newfoundland might experience a 10 meter (11 yard) wave and Florida might see 20 to 25 meter (22 to 27 yard) waves.

The researchers say that over the past million years there have been dozens of such landslides of a similar size. They suggest that geological research be done to detect deposits that washed ashore from the tsunamis generated from these events. The authors note that during human history there has not been a event of the magnitude they predict.

Part of their interest in Cumbre Vieja relates to changes in the structure of Cumbre Vieja that have been noted by Day. He believes that there are evolving stress patterns within the volcano's western flank. In 1949, Cumbre Viejo erupted and a huge portion shifted 4 meters. This may hint of a future failure leading to the detachment of the 150 to 500 cubic kilometer block.

According to one of the researchers, Simon Day, "What is new about this paper is that we've now got a much more precise model of the tsunami waves that are produced in the event of a giant landslide after a volcanic eruption in the Canary Islands."

But Day said there is not cause for immediate worry. "It's something we're concerned about, not because we're saying it's immanent. The landslides are triggered by eruptions and are fairly infrequent. And the next eruption isn't necessarily the one that's going to cause the collapse. There may be many more eruptions before the volcano eventually collapses. It's something that we think is going to be geologically inevitable, because this part of the volcano has collapsed very frequently in the past."

Day is vulcanologist and structural geologist at the Benfield Greig Hazard Research Centre at University College in London. Ward is at the Institute of Geophysics and Planetary physics at the University of California at Santa Cruz.

Gerard Fryer, a tsunami expert, told UPI, "The work is predominantly okay, but added, "I have some problems with it." Fryer said that, "There are no questions that these are maximum wave heights." Fryer said that the computation used "approximates the slide by adding all of them (composite landslides) together and ignores the horizontal water motion above the piece of the slide that's moving. One consequence of that is the outward radiating wave is too large and the backwards radiating wave is too small."

In spite of this, the work has "wonderful merit," Fryer said, because it allows an easy way to approximate a complicated landslide. Fryer Gerard Fryer is an associate geophysicist in the Hawaii Institute of Geophysics and Planetology, at the University of Hawaii at Manoa.

Harry Yeh, an assistant professor of civil engineering at the University of Washington and a tsunami expert, told UPI that the assumptions used in the paper for the initial conditions represented a source of great uncertainty.

(Reported by Joe Grossman in Santa Cruz, California)