Clues to Etna's future eruptions

By Dr David Whitehouse
BBC News Online science editor

A British geologist says he has discovered a way to predict how much lava will pour out of Mount Etna in the future.

Etna's plume seen from space

The technique is based on monitoring earthquakes in the region, as they are statistically related to Etna's output 25 years later.

The method does not allow specific eruptions to be predicted, but it does provide a way to predict the total lava output over a several-year future period.

The information could prove invaluable to farmers on the flanks of the volcano as well as to civil planners and the emergency services.

Until now, techniques for predicting the behaviour of volcanoes have met with limited success. The best that can be done are predictions over a few hours or days for a volcano that is obviously preparing to erupt.

Time lag

Dr John Murray, of the Department of Earth Sciences at Britain's Open University, has been visiting and measuring Mt Etna for many years.

Dr John Murray has monitored Etna for 34 years

He told BBC News Online: "I have gone to Etna every year since 1969 to survey its eruptions, and I have calculated the volume of lava it is producing. It's a very active volcano. There is a lot of stuff coming out."

In a paper published in the journal Geology, Dr Murray has compared Etna's lava output with a record of local earthquakes.

"Etna has been monitored very well since 1870 and was one of the first volcanoes to have a long seismological record," he says.

He found that there is a relationship between quakes and lava output.

However, that relationship is delayed. There is a 25-year time lag between increased number of earthquakes and increased lava outflow.

Busy time

"The statistical evidence is overwhelming that the relationship is real, most fascinating are the possible reasons for it, which at this stage must remain speculative," he told BBC News Online.

"The 25-year time lag is intriguing and may represent the time required for events at depth to have an effect on surface output."

Dr Murray estimates that between 2007 and 2015, Etna's output will be about half of what it was between 1987 and 1995.

However, Etna's largest eruption since 1669 occurred in 1993. This means that although the predicted lava output for the near future is lower than the recent past, in absolute terms, the volcano will still be very active.