Volcanic hazards could become fiercer and more frequent
Apr 23, 2010 15 comments
The erupting Icelandic volcano that wrought havoc on European air traffic may have calmed for now, but geologists are warning that volcanic hazards such as this could become more commonplace due to climate change. They believe there is evidence that melting ice is placing an increasing strain on volcanic regions across the globe, which could trigger a range of different geological hazards. These findings appear in a special issue of Philosophical Transactions of the Royal Society A.
Perhaps the most topical paper is research led by Freysteinn Sigmundsson at the University of Iceland, which looks specifically at volcanic activity in Iceland. The researchers point out that volcanic activity was 10 times more frequent following the last deglaciation period in Iceland 10–12 thousand years ago. Iceland's icecaps have been thinning continuously since 1890 so the researchers argue that we could be heading towards another period of fierce volcanic eruptions. They note, however, that there is no direct evidence to link the recent activity of the Eyjafjallajökull volcano with ice-melt.
A fiery land
Sigmundsson's team has developed a model of how Icelandic volcanism might respond to the removal of ice mass. This model is tailored to Iceland's volcanic situation, which is unique because the country is located along the Mid-Atlantic Ridge and is above a "hotspot" – an upwelling of hot rock that emerges from deep within the Earth's interior. As the North American plate and the Eurasian plate diverge from each other, at the Mid-Atlantic ridge, pressure is reduced in the molten rock deep beneath Iceland. This can induce melting in this region known as the mantle, which can lead to volcanic activity at the surface.
Sigmundsson and his team suspect that a sudden removal of pressure, due to melting glaciers, could lead to additional upwelling in the Earth's mantle. Their visco-elastic model is applied to the Vatnajökull ice cap, the largest glacier in Iceland covering 8% of the country, which is thinning at a rate of approximately 50 cm each year. They find that this extent of thinning should correspond to a pressure release of the order 0.5–1.5 kPa each year.
This figure is comparable with the 3.2 kPa per year released due to the regular plate tectonics beneath Iceland so it could significantly increase volcanism at the surface, say the researchers. They emphasize, however, that it may take decades or even centuries for this molten material to reach the surface if it makes it at all. This uncertainty is due to the complicated nature of flow in the mantle, which is dependent on a range of factors including magma chemistry and the availability of underground fissures.
The plume may reappear
Michael Sheridan, a volcanologist at the University of Buffalo in the US, believes that it is this poor understanding of the sub-surface geology that means we cannot assume that this latest eruption of Eyjafjallajökull is over just yet. "Icelandic volcanoes that erupted from fissures have, in the past, produced a profound climatic effect that can last several decades," he warns. "This volcano has a much more enigmatic record than others that have more frequent eruptions. It's not like we know the size of its magma chamber, the volume of its products or its history."
Eyjafjallajökull, which lies in the south of Iceland, has been so problematic because of the plumes of volcanic ash that have been carried on the wind across western Europe. Plumes of ash, however, are not the only volcanic hazards that can emerge when volcanic material interacts with ice. A more local threat is meltwater floods that result from the sudden release of water from glacial and subglacial lakes, known locally as jökulhlaups.
But these geological hazards are not confined to just Iceland. In a separate paper in the series, Hugh Tuffen, a researcher at Lancaster University in the UK, argues that rising global temperatures could also increase the number of global hazards caused by the melting of ice on glaciated volcanoes. Tuffen says that there is compelling statistical evidence that melting ice during the last deglaciation period triggered a dramatic acceleration in volcanic activity.
Unprepared for the hazard
Tuffen believes that we could be stumbling towards a similar situation with little understanding of the physical interactions between ice and volcanic activity. "We think the melting of ice can destabilize volcanoes, but in ways that we still don't fully understand," he says.
Tuffen is particularly concerned about the threat of mudflows and landslides that can result from both volcano collapse and glacial melt. "The communities living beneath the volcanoes of the Andes in South America may be particularly vulnerable," he says. The sort of threat he is referring to was realized in 1985 when the Nevado del Ruiz volcano erupted in Columbia, triggering mudflows that killed more than 23,000 people in one event.
Jenny Collier, a geologist at Imperial College in the UK agrees that there is more work to be done on the influence of ice melt on volcanism. "Volcanoes are inherently unstable structures – being steep sided and formed of layers of loose and variable material," she says.
About the author
James Dacey is a reporter for physicsworld.com