On the night of 13 December 1991, a group of climbers had gathered in a hut on New Zealand's highest peak, Mount Cook, in preparation for an attempt on the summit. The ascent would mean risking their lives, but that threat was nothing compared with what was about to come. Shortly after midnight, 12 million cubic metres of rock and ice crumbled from the peak and roared down the east face of the mountain, travelling at over 200 km per hour for more than seven kilometres before plunging to the valley floor. The cataclysmic rock avalanche narrowly missed the hut, leaving the stunned climbers safe, but awed. "Essentially, the top of Mount cook fell off - which is incredible," a mountaineer told TVNZ at the time. The group had a very lucky escape from what on the face of it was an act of God - a purely natural disaster.

But was it? A few analysis suggests that climate change may have helped to trigger this avalanche, as well as others in different parts of the world. given current projections of even warmer temperatures into the future, some scientists are now warning that we should expect more potentially deadly avalanches to come, and also more frequent, and fiercer, volcanic eruptions and earthquakes.

Until recently, the idea that current and future climate change could ramp up these sorts of geological hazards wasn't well appreciated. Climate scientists have until now been focussing on the atmosphere and the hydrosphere, most probably because those are the primary areas of interest for most of them. Now Earth scientists are starting to become involved in the study of future climate impacts - and they are bringing with them a knowledge of how past climate change has triggered a response from the Earth's crust. Scientists led the new work on the 1991 Mount Cook avalanche, and on four others that happened recently in Alaska and the European Alps. The scientists painstakingly analysed the meteorological conditions in the weeks leading up to the disasters and found that all had one thing in common: each of the avalanches was preceded by an unusually warm period.

For Mount Cook, between 1960 and 1990, the average year-round air temperature at the summit was -7.87 deg C. In 1991, the winter was particularly cold, then, in November and December, the summit temperature regularly rose above zero. Next came a cooling, which brought temperatures to below seasonal averages. But in the week immediately before the avalanche, the summit warmed again, with temperatures on December 11 soaring to 9.7 deg  - about 8.5 deg C above the long-term average for that date. The ice on the summit began to melt in earnest. Then 24 hours before the avalanche, the temperature plummeted below freezing. The unusually warm conditions melted more snow and ice than normal, causing relatively large amounts of water to leak through clefts and joints into the rock.

Then the plunge in temperature suddenly froze this water, making it swell and forcing some of the rock to break away. The team also analysed avalanches and landslides on Mount Steller in Alaska in 2005 and 2008, and on Mount Miller, also in Alaska, in 2008, and on Mount Miller, also in Alaska, in 2008, as well as on Monte Rosa in the Swiss Alps, in 2005 and 2007. They found that while the precise temperature patterns before each event varied, the weeks or days before were unusually warm.

Several studies have found that during the 20th century, there have been more unusually warm periods, such as summer heat waves. In the past two to three decades, there has also been an increase in the number of large avalanches and landslides in some high-altitude regions, such as the peaks of the European Alps. They can never say that a particular event would not have happened even without global warming but the rising incidence of large rock and ice avalanches in Alaska and the Caucasus, together with an increase in rock-falls in the alps and elsewhere, is just what would be expected to be seen as the world warms. Since climate models suggest that warmer periods will become up to four times more common in the next several decades, this means we are likely to experience more avalanches. The main concern is very large events - like those in Alaska - will occur in more populated regions, like the Swiss Alps and it is rather likely that the probability for this will increase - but we cannot quantify it. Mountain regions are particularly sensitive to climate change because melting snow means less heat is reflected back towards space and more is absorbed. In fact, temperatures in the European Alps have been rising at double the rate of the global average since the late 19th century. Recent studies show that the permafrost in the European Alps has warmed by between o.5 and 0.8 deg C in the upper tens of metres during the 20th century.