Fears of a huge new eruption in Iceland

On the second anniversary of the ash cloud that grounded Europe's flights, Iceland is facing further volcanic havoc, warns Andy Hooper.

This month marks the second anniversary of the eruption of Eyjafjallajokull that left millions stranded across Europe, and cost airlines an estimated euros 150 million a day for six days. But alarmingly, there are signs of high activity beneath the much larger, neighbouring Katla caldera in Iceland - a possible sign of an impending eruption. This should prompt extensive high-level contingency planning across Europe, as Katla has the potential to be much more damaging than Eyjafjallajokull.

Since Iceland was settled in the ninth century, Katla has erupted on average every 60 years, but has not had a significant eruption since 1918. Ominously, eruptions of Eyjafjallajokull in 1821-23 and 1612 were followed within months by eruptions of Katla. Judged by the historical calendar, an eruption is overdue.

Last July, a flood of water burst from beneath the ice cap on top of Katla, washing away a bridge. This indicates that an extra pulse of heat reached the base of the ice. Since then, there have been erratic movements of the surface of the volcano, measured by precise GPS instruments, and bursts of high earthquake activity beneath Katla's caldera. These observations imply that magma has risen to shallower depths.

Katla's eruption in 1918 produced five times as much ash as the 2010 Eyjafjallajokull one. A major eruption could result in large parts of Iceland being flooded as snow and ice melted; significant poisoning of Icelandic agriculture; destruction of property; and, of course, the grounding of aircraft across Europe.

If enough material is ejected it could even have a cooling effect on the global climate for a few years. A precedent for that would be the 1783-84 eruption from the fissure of Laki, which is part of the same volcanic system, Grimsvotn, that erupted last year. This was a very large eruption of 15 cubic kilometres (3.6 cubic miles), compared to the fraction of a cubic kilometre ejected in 2010, and had a huge impact on the northern hemisphere, reducing temperatures by up to 3?C. This had catastrophic effects far beyond the shores of Iceland (where at least a fifth of the population died), with thousands of recorded deaths in Britain due to poisoning and extreme cold, and record low rainfall in North Africa.

Large eruptions such as this occur only every few hundred years on Iceland, but the potential for danger is significant. Even if deaths from famine are less likely today, a recent study of the potential effects of the air pollution caused by such an eruption estimates that it could lead to between 52,000 and 228,000 fatalities throughout Europe.

Meanwhile, nearby Hekla has erupted about once every 10 years in recent times, with the last being in 2000. Similarly, volcanoes beneath the largest ice cap, Vatnajokull, are entering a period of increased volcanic activity - the peak of a 140?year cycle.

This trend is being exacerbated by climate change. Vatnajokull has lost an estimated 400? billion tonnes of ice since the end of the 19th century. This has reduced the pressure on the hot mantle material beneath the crust, leading to increased magma generation. At the end of the last ice age, this same effect led to eruption rates some 30 times higher than at present. The current rate of ice loss is much lower than then, but we can still expect the formation of extra magma equivalent to that which erupted from Eyjafjallajokull in 2010 every 10 years or so.

There is a question mark over whether and when all this extra magma will erupt, however. Studies indicate that the timelag between generation and eruption could be as much as a few hundred years. In the meantime, the shrinking of the ice cap also causes stress changes in the crust that can encourage, or discourage, capture of the magma on its way up, depending on the path it takes.

The scale of the chaos that an eruption could cause is difficult to estimate. Partly it would depend on which way the winds are blowing but also on the style, size and duration of the eruption. Perhaps surprisingly, the magnitude is less important than the type of eruption.

While the Eyjafjallajokull eruption was relatively small, it caused such havoc because the materials ejected had the perfect make-up to ground flights: fine ash was deposited high enough to remain airborne for days, affecting the airspace of continental Europe. An eruption of Katla is likely to have a similar explosive style, due to the interaction of the magma and the overlying ice cap - the heat of the magma causes the transformation of ice to steam, which expands and fragments the magma.

A key goal for scientists and aviation authorities must be to develop predictive capability as to the nature of forthcoming eruptions. We would then be able to construct better plans for dealing with the impact, including the threat to agriculture and air travel.

To this end, my group at Delft University of Technology is working with the University of Iceland and others to develop more accurate models of volcanic plumbing systems. Using GPS receivers, satellite-borne radar, and advanced algorithms, we have been able to track the movement of magma and create maps of magma storage.

Just as importantly, the risks associated with the largest Icelandic eruptions, such as that which occurred in 1783-84, need to be thoroughly assessed. Even though these events occur only every few hundred years, the potential for widespread loss of life means we need to be properly prepared.

As we face continuing volcanic activity in Iceland and across the world, it is vital we improve the science of eruption prediction and so guard against the worst consequences.

Dr Andy Hooper is an assistant professor at Delft University of Technology