Volcanoes reign when Iceland thaws.

Volcanoes reign when Iceland thaws

Benjamin Franklin is credited as the first to suggest how volcanoes could cool the Earth's climate, a theory he penned after a severely cold winter in Europe followed the summer eruption of the Icelandic volcano Laki. Ample evidence now supports the idea that eruptions can alter the climate, but what about the reverse process? Can climate shifts affect volcanoes?

Recently, scientists proposed that eruptions on Iceland might be more frequent during warm ages, or interglacials, when Iceland is largely free of ice. Now sediments from the bottom of the Norwegian Sea bolster this theory, report Hans P. Sejrup and colleagues from the University of Bergen in Norway.

Buried within the sediments are four layers of volcanic ash from Icelandic eruptions over the last 300,000 years. According to the researchers, the layers indicate times when intense eruptions wracked the island, spewing out tens of hundreds of times the amount of material emitted during the current era. All of these layers happen to fall within interglacial periods, which punctuate the longer ice ages.

Presumably, the ash layers might not reflect a change in eruptions. It could be that ash appears in the sediments only during interglacials because ice covered the oceans during colder times. Yet evidence from the fossilized bodies of surface plankton discredits this explanation, says Sejrup. The plankton show that during interglacial periods, the sea ice cover in this northern region did not melt during the summer seasons, yet an ash layer still formed in the sediments during that time.

Alternatively, the researchers propose that ice caps help quiet volcanoes by bearing down on Earth's crust, essentially putting a weight on the magma chambers that feed volcanoes. When the ice melts, the pressure on the chambers disappears, allowing the volcanoes to erupt. Some evidence suggests the volcanoes are most active immediately after an ice age.