Warmer temperatures may have caused the monster landslide which trimmed the top of Mt Cook in 1991, according to a Swiss study of slope failures on three continents.
On December 14 1991, 12 million cubic metres of Mt Cook/Aoraki - including 10m from its top - collapsed and roared down the ice fields of the east face. It lowered the mountain's height by 10m to 3754m.
A special issue of Philosophical Transactions of the Royal Society A today, investigating the thrust of climate change on geological hazards, reported that snowy and icy slopes have been failing more frequently over the past couple of decades.
An international team of researchers led by Christian Huggel from the University of Zurich analysed weather patterns in the days and weeks before slope failures on three continents, and found that all the avalanches followed unusually warm periods that ended with sudden temperature drops.
The rock and ice which detached from the eastern face of Mt Cook and scoured the surface as it travelled 7.5km followed such a pattern, the researchers said.
In the week immediately before the avalanche, temperatures warmed to 14.4degC at the base of the detachment zone, then rapidly cooled to subfreezing temperatures.
Rapid thaws from short-term, unusually warm temperatures enhanced melting and water production, which reduced the strength of the rock; and the sudden refreezing blocked the movement of meltwater in the bedrock, causing destabilising pressure changes.
Similar slope failures were 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 researchers said that large slope failures will increase in high-mountain areas as the number of warm extreme events increase.
In another study, Nature science journal reported British scientists Bill McGuire, Paul Harrop and Kim Deeming, looked closely at an ancient collapse on Mount Etna in Sicily, concluding that it was likely triggered by a warm and wet period around 10,000 years ago.
The most prominent feature on Mount Etna, Valle del Bove, a natural amphitheatre over 1000 times larger than the Colosseum and bounded by kilometre-high cliffs was excavated from the eastern flank of the volcano in a catastrophic collapse 7500 years ago, when the surface was exposed to extraterrestrial cosmic rays and warmer and wetter weather.
These researchers said rain and meltwater from snow and ice on top of a volcano can interact with fresh magma, causing pressures to build within the pores of rocks, which destabilises slopes.
They predicted that the warmer and wetter conditions to come under climate change may increase potential for more collapses of volcanic slopes.
NZPA
source: newshub archive
