Ice keeps mount Rainer stable (Image: Kevin P. Casey/Getty)

EARTH is starting to crumble under the strain of climate change.

Over the last decade, rock avalanches and landslides have become more common in high mountain ranges, apparently coinciding with the increase in exceptionally warm periods (see “Early signs”). The collapses are triggered by melting glaciers and permafrost, which remove the glue that holds steep mountain slopes together.

Worse may be to come. Thinning glaciers on volcanoes could destabilise vast chunks of their summit cones, triggering mega-landslides capable of flattening cities such as Seattle and devastating local infrastructure.


For Earth this phenomenon is nothing new, but the last time it happened, few humans were around to witness it. Several studies have shown that around 10,000 years ago, as the planet came out of the last ice age, vast portions of volcanic summit cones collapsed, leading to enormous landslides.

To assess the risk of this happening again, Daniel Tormey of ENTRIX, an environmental consultancy based in Los Angeles, studied a huge landslide that occurred 11,000 years ago on Planchón-Peteroa. He focused on this glaciated volcano in Chile because its altitude and latitude make it likely to feel the effects of climate change before others.

“Around one-third of the volcanic cone collapsed,” Tormey says. Ten billion cubic metres of rock crashed down the mountain and smothered 370 square kilometres of land, travelling 95 kilometres in total (Global and Planetary Change, DOI: 10.1016/j.gloplacha.2010.08.003). Studies have suggested that intense rain cannot provide the lubrication needed for this to happen, so Tormey concludes that glacier melt must have been to blame.

With global temperatures on a steady rise, Tormey is concerned that history will repeat itself on volcanoes all over the world. He thinks that many volcanoes in temperate zones could be at risk, including in the Ring of Fire – the horseshoe of volcanoes that surrounds the Pacific Ocean (see map). “There are far more human settlements and activities near the slopes of glaciated active volcanoes today than there were 10,000 years ago, so the effects could be catastrophic,” he says.

The first volcanoes to go will most likely be in the Andes, where temperatures are rising fastest as a result of global warming. Any movement here could be an early sign of trouble to come elsewhere. David Pyle, a volcanologist at the University of Oxford, agrees. “This is a real risk and a particularly serious hazard along the Andes,” he says.

Meanwhile, ongoing studies by Bill McGuire of University College London and Rachel Lowe at the University of Exeter, UK, are showing that non-glaciated volcanoes could also be at greater risk of catastrophic collapse if climate change increases rainfall.

“We have found that 39 cities with populations greater than 100,000 are situated within 100 kilometres of a volcano that has collapsed in the past and which may, therefore, be capable of collapsing in the future,” says McGuire.

Early signs Mount Cook (Aoraki), New Zealand Just after midnight on 14 December 1991, 12 million cubic metres of rock and ice peeled away from the summit of New Zealand’s highest mountain. The landslide travelled 7.5 kilometres and narrowly missed slumbering hikers in an alpine hut. It occurred after an exceptionally warm week, when temperatures were 8.5 °C above average, and reduced the height of the mountain by around 10 metres. Mount Dzhimarai-Khokh, Russia More than 100 people were killed on 20 September 2002 when their villages were swept away after part of the peak, in the north Caucasus mountains, collapsed. Over 100 million cubic metres of debris travelled 20 kilometres. Warming permafrost is thought to have been partly to blame. Mount Rosa, Italy Following an unusual spring heatwave across Europe in 2007, the Alpine mountain suffered a spectacular rock avalanche, in which 300,000 cubic metres of rock fell, landing in a dry seasonal lake. Had the lake contained water, the avalanche would have generated a massive outpouring, with catastrophic consequences for the village of Macugnaga downstream.