"Eyjafjallajökull is not divulging its longer- term intentions either. According to geophysicist Páll Einarsson of the University of Iceland, the magma feeding the current eruption seems to be coming from down deep rather than a shallow chamber. So it is impossible to gauge just how much magma could emerge during this episode of activity. The best clues may come from the historical record. That isn't encouraging, according to volcanologist Lee Siebert, director of the Global Volcanism Program at the Smithsonian Institution in Washington, D.C. "

It certainly isn't. Eyjafjallajökull has a history of prolonged eruptions. Its last eruption went from 1821 to 1823. The time before that, in 1612, the eruption continued, on and off, for over a year. Even the minimum estimate by scientists is that it will continue exploding for a month and most estimate six more months or more. This means that issues of ash clouds and airplanes can arise again.

Even more ominously, Mt. Katla, a giant volcano that historically has had eruptions that have changed the climate, lies nearby. Each time Eyjafjallajokull has erupted in the past 2,000 years - in 920, in 1612 and between 1821 and 1823 - Katla has exploded within six months. The last eruption of Katla, in 1918, killed crops across war-torn Europe, causing massive food shortages. The precipitation triggered by the ash turned the trenches of World War I into quagmires. The volcano also has a history of melting the nearby glacier, causing serious floods. At the peak of its 1755 eruption, the flood discharge has been estimated to have been the equivalent of the combined discharge of the Amazon, Mississippi, Nile and Yangtze rivers.

Historically, Katla goes off every 90 years, so it is about time for it to erupt again. Iceland's President, Olafur Grimsson, has been quoted by the BBC saying that his nation has been "waiting for that eruption" for some years, and has made preparations for rescue and emergency services." He also added "So I think it is high time for European governments and airline authorities across the globe to start planning for the eventual Katla eruption."

Currently, Katla shows no immediate signs of erupting, although some scientists say that it has shown more signs of restlessness since the late 1990s.

David Fuller's view If Mt Katla erupts anytime soon, we should not be surprised by more bad news for the airlines industry, some upward pressure on prices for agricultural commodities and quite possibly another cold winter for much of the globe. Meanwhile, it is seasonally cold in the UK and most of Europe, following a balmy April, although this may be unrelated to volcanoes.