Volcanoes, with their vast outpourings of greenhouse gases and sun-screening ash clouds, can affect climate. But what about the other way around?

A special issue of the Philosophical Transactions of the Royal Society A, dated May 28, rounds up research on the ways that climate change can drive volcanic eruptions as well as other geologic hazards such as earthquakes and landslides. Among the litany of problems that studies in the issue link to a warming world: mountain slopes collapsing as snow and ice melt, seismic activity increasing as thinning ice deposits relieve pressure on some parts of the world and apply it elsewhere, and magma production being boosted by pressure changes in subglacial volcanoes such as those in Iceland.

It is that last implication that is timeliest, given the worldwide attention paid to the ash cloud from the Eyjafjallajökull volcano that has crippled air traffic across Europe for the past several days. Reduced ice loads atop volcanoes relieve pressure on magma chambers below and allow for more decompression melting of rock, a group of researchers wrote in one of the special issue's studies, based on observations and models of Iceland. But lead study author Freysteinn Sigmundsson of the University of Iceland told Reuters last week that the latest eruption did not appear to be driven by climate. "We believe the reduction of ice has not been important in triggering this latest eruption," he said. Any additional magma produced as a result of reduced ice loads may take decades or even centuries to reach the surface, the authors wrote.

Melt-driven pressure changes could also bring on more earthquakes. As deposits of Arctic ice grow thinner, those landmasses experience less pressure, whereas rising sea levels increase pressure on coastal regions worldwide. That tipping of the scales, wrote Bill McGuire of University College London, "may be sufficient to trigger a geospheric response." In past postglacial periods, McGuire noted, melting of ice sheets appears to have set off major seismic activity, as sections of the crust previously burdened by ice rise in a process known as isostatic rebound.

In another report in the special issue, Christian Huggel of the University of Zurich and his colleagues looked to recent slope failures in Alaska, the European Alps and New Zealand, finding that "all the failures were preceded by unusually warm periods." Over the coming decades, they noted, models predict that warm periods in the Swiss Alps will increase in frequency by 1.5 to 4 times, possibly more, which could result in an increase in avalanches there.

All told, McGuire wrote, the evidence "supports a robust link between changing climatic conditions and a broad portfolio of potentially hazardous geological and geomorphological processes." Although some have speculated that such processes are already under way, McGuire cautions that "no increase in the global incidence of either volcanic activity or seismic activity has been identified to date" and that the time scale on which any geologic responses to climate change would take shape is unclear.

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