Warmer temperatures might have caused a prehistoric Sicilian volcanic landslide as well as several recent avalanches on the white slopes of Alaska, New Zealand, and the Alps. These two studies are published today in a special issue of Philosophical Transactions of the Royal Society A investigating the thrust of climate change on geological hazards.
UK scientists Kim Deeming, Bill McGuire, and Paul Harrop looked closely at an ancient collapse on Mount Etna in Sicily, concluding that it was likely triggered by a warm and wet period in the early Holocene around 10,000 years ago.
The most prominent feature on Mount Etna is Valle del Bove, a natural amphitheatre over 1,000 times larger than the Colosseum and bounded by kilometre-high cliffs — excavated from the eastern flank of the volcano in a catastrophic collapse. The researchers calculated the amount of time the surface was exposed to extraterrestrial cosmic rays and found that the collapse happened 7,500 years ago, around the time when the weather was warmer and wetter.
Rain and meltwater from snow and ice that cap the volcano can interact with fresh magma, causing pressures to build within the pores of rocks, which destabilizes slopes, they propose. The warmer and wetter conditions to come, the authors suggest, may increase potential for volcano collapses.
Within the past couple decades, snowy and icy slopes have been failing more. An international team of researchers led by Christian Huggel from the University of Zurich in Switzerland analyzed weather patterns in the days and weeks before slope failures on three continents. They found that all the avalanches followed unusually warm periods that ended with sudden temperature drops.
In 1991, rock and ice detached from the eastern face of New Zealand’s Aoraki/Mount Cook (pictured) and scoured the surface as it travelled 7.5 km. In the week immediately before the avalanche, temperatures warmed to 14.4 degrees Celsius at the base of the detachment zone, then rapidly cooled to subfreezing temperatures. Rapid thaws from short-term, unusually warm temperatures enhance water production, which reduce the shear strength of the rock; and the sudden refreezing blocks the movement of meltwater in the bedrock, causing destabilizing pressure changes.
This was also observed on Mounts Steller and Miller in Alaska in 2008, as well as in two epic avalanches in the last five years on Monte Rosa in the Alps. The authors think that large slope failures will increase in high-mountain areas as the number of warm extreme events increase.
In the keynote review, McGuire writes, “Periods of exceptional climate change in Earth history are associated with a dynamic response from the geosphere.” Responses include volcanic activity, earthquakes, landslides, tsunamis, glacial outbursts, rock-dam failure floods, debris flows, and destabilizations of gas-hydrates, which are crystalline solids consisting of gas molecules encaged by water molecules. According to McGuire, anthropogenic climate change doesn’t just affect oceans and the atmosphere.
This set of 14 papers came out of the Third Johnston–Lavis Colloquium addressing the issue of climate forcing of geological and geomorphological hazards held at University College London in September 2009.
Image: Mount Cook by I. Owens