DisastersGeologists warn of warming-induced landslides flattening cities

Published 18 October 2010

There are 39 cities around the world with populations greater than 100,000 — and an untold number of smaller towns and villages — which are situated within 100 kilometers of a volcano that has collapsed in the past and which may, therefore, be capable of collapsing in the future; thinning glaciers on volcanoes could destabilize vast chunks of summit cones, triggering mega-landslides capable of flattening cities such as Seattle and devastating local infrastructure

It would be going too far to say that Earth is starting to crumble under the strain of climate change, but what is undeniable is that 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. The collapses are triggered by melting glaciers and permafrost, which remove the glue that holds steep mountain slopes together.

Kate Ravilious writes in New Scientist that worse may be to come. Thinning glaciers on volcanoes could destabilize 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 meters of rock crashed down the mountain and smothered 370 square kilometers of land, traveling 95 kilometers in total. 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 the 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.

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.

Ravilious writes that 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, United Kingdom, 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 kilometers 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 meters of rock and ice peeled away from the summit of New Zealand’s highest mountain. The landslide traveled 7.5 kilometers 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 meters.

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. More than 100 million cubic metres of debris traveled 20 kilometers. Warming permafrost is thought to have been partly to blame.

Mount Rosa, Italy

Following an unusual spring heat wave across Europe in 2007, the Alpine mountain suffered a spectacular rock avalanche, in which 300,000 cubic meters 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.

—Read more in Daniel Tormey, “Managing the effects of accelerated glacial melting on volcanic collapse and debris flows: Planchon–Peteroa Volcano, Southern Andes,” Global and Planetary Change (16 September 2010) (doi:10.1016/j.gloplacha.2010.08.003) (sub. req.)