Study highlights volcanoes that erupt with little warning
Certain types of volcano may erupt with very little warning, making it extremely difficult to alert local people and give them time to evacuate, according to new EU-funded research. The study, published in the journal Nature, was supported in part by the DEMONS ('Deciphering eruptions by modelling outputs of natural systems') project, which received EUR 1.4 million from the European Research Council under the Ideas Programme of the Seventh Framework Programme (FP7). Normally, volcanic eruptions are preceded by weeks or even months of warning signs, such as earth tremors, gas emissions and changes in the shape of the volcano. However, the eruption of the Chaitén volcano in Chile in early 2008 broke that pattern. 'This eruption was particular noteworthy because the volcano had been quiescent for over 9,000 years,' explained Professor David Dingwell at Ludwig-Maximilians University in Munich, Germany. 'The best estimates suggest that the last eruption took place in the year 7240 BC.' The first signs that the volcano was about to awake from its long slumber came on the evening of 30 April 2008 when the nearby town of Chaitén was shaken by earthquakes powerful enough to knock objects off shelves. Barely 24 hours later, ash began to fall on the town, and on 2 May a massive explosion sent a column of ash and debris high into the sky. Chaitén is a rhyolite volcano (rhyolite being a particularly viscous kind of magma). The 2008 Chaitén eruption is the first ever explosive rhyolite eruption to be scientifically monitored. Volcanologists were particularly intrigued by the suddenness of the eruption. In this study, Professor Dingwell and Jonathan Castro of the University of Orléans in France sought to find out just how fast the magma rose to the surface at Chaitén. Previous studies have shown that the magma in other volcanoes rises relatively slowly, at a rate of a few centimetres per second. It is this slow movement of the magma towards the surface that triggers the earthquakes and other signs that often indicate an imminent eruption. The lack of warning signs at Chaitén suggested that the magma must have risen up through the Earth's crust extremely rapidly. The scientists studied pumice from the eruption, subjecting it to high temperatures and pressures in the laboratory. The results were both surprising and frightening, as they suggested that the magma had risen to the Earth's surface from depths of over five kilometres in less than four hours, travelling at speeds of around one metre per second. 'This figure is very disturbing because it implies that a Plinian eruption can develop with astonishing speed,' commented Professor Dingwell. 'In such a case, it would be well nigh impossible to give adequate warning of an impending eruption, in particular if the period of activity preceding it also happened to be very short. 'The problem with such short periods of heightened activity is that they may, but do not necessarily, forecast an eruption,' he added. Fortunately, the residents of Chaitén were able to escape unharmed. However, the scientists recommend that all rhyolite volcanoes that have shown signs of activity within the past 10,000 years be monitored more closely. They conclude: 'In more densely populated regions, this would be essential to avoid a major volcanic disaster.'
Countries
Germany, France