In 2005 an event stunned the mountaineering community way beyond the French Alps: the Bonatti pillar on the Drus was totally washed away by a series of huge rock falls between June and September. Succeeding to 2003, one of the driest and warmest summer of the century, with constant rock falls all over the Alps ranges, an ‘annus horribilis’ for all climbers, with many routes totally impracticable as far too dangerous, including the ‘classic’ approach to Mont Blanc by the Gouter couloir, banned for most of the summer, this exceptional event put to light the damaging impact of the Global warming on the Alps and consequently on all mountaineers. Hence this question: and what about the future?
Up to then, the typical layman believed such events as quite normal and part of the fact that the Alps were "young" mountains still growing etc... when the most recent explanations given by the scientists - their leading reseachers being Ludovic Ravanel and Philip Deline - aside when caused by earthquakes (which on The Drus seems only to have caused the 1905 rock fall), were the result of a more complex dual movement:
But scientists now start to have some ideas (although still with uncertainties) of what is really at stake underground at high altitude.
For Philip Deline (CNRS 26th January 2011, Domancy - Haute-Savoie) the study of the rock falls in high altitude and the degradation of permafrost encounters 3 specific problems :
The work done by the young Chamonix scientist (geomorphologist) and mountain guide, Ludovic Ravanel with Philip Deline (who wrote in 2003 a superb thesis on the same subject covering the Italian side of the Mont Blanc), both from the Laboratoire EDYTEM, université de Savoie, CNRS, 73376 Le Bourget-du-Lac, on the evolution of the Drus has allowed a much better understanding of those rock falls and how in the future it will increase with the Global warming.
Thanks to the unique mass of photos and testimonials existing on the Drus which he gathered, Ludovic has managed to describe the evolution of the Drus over the last 150 years (being from one of the oldest Chamonix family with many generations of mountain guides - today they are 9 Ravanel at the Chamonix guides company - was certainly of great help to his work). One thing he states for certain is that “the ice acts as cement in the flaws of the rock. But when temperatures increase near to 0°C, it does not play anymore its cementing role”. And since 1936, the overall temperature in the Mont Blanc range has increased by 2° C. So the phenomenon considered for very long as a natural process and hazard is drastically increasing.
From Ludovic Ravanel, we learn that from 1860, date of the first valid photo of the Drus until the beginning of the 20th century nothing much happened. From 1905 untill 2011, 11 major rock falls occurred. The first one - 20 000 m3 - in 1950 modified the West face of the Drus over a 100 m between the heights of 3 220 m and 3 330 m.
The second significant rock fall - 27 000 m3 - occurred in September 1977. Two alpinists were bivouacking on the face. They were be taken off by helicopter.
To visualize the volume represented note that 1 000 m3 of rock fall is equivalent to at least a block of 10x10x10 m.
The Drus is of course not the only mountain to suffer. In 1997, 2 millions m3 disappeared from the Brenva on the Italian side of Mont Blanc. However, it is the best observed and best researched of all, so greatly helping the understanding of the causes. Pillars and crests are the most exposed parts of the mountains.
In 2003, the summer was so warm, that rock avalanches occurred everywhere. The danger was such that even the classic route of the Mont Blanc by the Gouter couloir had to be banned. A rock fall of 6 500 m3 occurred on the Drus but went unnoticed as the mountain range was deserted due to the very high rock fall threats. On the summit of the Matterhorn, 1 000 m3 of rock fell down requiring the rescue of 90 alpinists by helicopter (see more about this event on the link supplied by Hansw in the 'links' section).
Two years later, on the 29th and 30th of June 2005 a series of huge rock falls destroyed completely the Bonatti pillar - Between June and October 2005 in all 265 000 m3 of rocks fell down. The damage covered over 600 m in height and 100 m wide and two more followed in September.
Left: ca1900 (Jullien brothers) from la Pierre à Bayer, 2090 m a.s.l, view angle, N115°;
Right: 1908 (unknown author) from le Montenvers, 1913 m a.s.l, view angle, N100°;
Centre: the 1905 rockfall scar, seen during the 1905-1906 winter (unknown author);
Dotted line: scar of a rockfall that occurred before the end of the LIA (Little Ice Age).
The 1905 event was due to an earthquake which distroyed the Argentière church tower. Of a magnitude estimated at 5-6 and an intensity in Chamonix of VII, it also caused the top of the Sans Nom Peak to be shortened of 9 m (15 m in 1860). No more rock fall did occur until the middle of the 1930s.
DETAILS OF THE 1997 ROCK FALL
Upper half of the rockfall scar of September 1997 (ph. J.-C. Marmier, 1998).
White arrows: fractures plans N 30°E – 75°N.
Black arrows: fractures plans N 120°E – 80° NW.
Dotted line: scar of the 1992 rock fall.
In June 2005, rock falls increase until those of the 29th and 30th of June. They took away the South-West pillar climbed solo by Walter Bonatti over 6 days in 1955 and known to everyone as The Bonatti pillar.
3 rock falls occur on the 29th: at 11h03, the 2003 formed overhang goes up 120m; then at 13h53, the West half of the pillar falls down; at 14h22, the first part transformed in an overhang falls down, 150 m higher than in 2003.
The largest fall occurs on the 30th at around 03h00 washing away the rest of the pillar.
Up until the end of July 2005, blocks will continue to fall, followed by several ones at the beginning and end of September resulting in a total of 265 000 m3.
On the pictures to the right one can see the rock dumps which extended itself over 90 000-95 000 m2 on the Drus glacier and its moraine system. Distances covered were of 1 200 m vertically and 1 330 m in length.
The largest blocks - 30-35 m3, up to 100 m3 - are in the center: those megablocks cover smaller ones. The thickness, over 5 m on average goes up to 10 m locally.
During 6 years, nothing much happened.
Then, on the 10th and 11th of September 2011, 43 000 m3 of rock fell down. Ice appeared from the crack: the PERMAFROST!
I took this photo on the 11/09/2011 at 13h26 from Les Mottets facing the West face of the Drus, after having climbed the 'Caline' route.
Suddenly we heard a huge and continuous rumbling noise and grey clouds covered the West face of the Dru. (They lasted the hour we stopped at the place and much longer after we departed).
We then saw several huge blocks as big as houses coming off from where the top of the Bonatti pillar used to be!
Conclusion by the specialist Ludovic Ravanel:
From 1855 until 1950, the situation stayed stable. Then in the second half of the XXth century the rock falls continually increased. During the two decades of 1990 and 2000, the warmest, "they exploded in frequency and volume".
To end on a humourous tone, Pierre Alain had a story running that two climbers from Marseille, Georges Livanos and Robert Gabriel who were trying to make the first ascent of the West face of the Petit Dru had put so many pegs that it made the whole wall unstable hence one of the next big rock falls. "The Greek" never denied that story.
For those who want to know much more, read the work of Ludovic Ravanel, Philip Deline and their colleagues made accessible in two cases in English as well as in French
A. Philip Deline Thesis summary: (French only) Étude géomorphologique des interactions entre écroulements rocheux et glaciers dans la haute montagne alpine. Le versant sud-est du massif du Mont Blanc, Vallée d'Aoste, Italie
B. Published in 2008 in French and English by Ludovic Ravanel and Philip Deline The West Face of Les Drus (Mont-Blanc massif): slope instability in a high-Alpine steep rock wall since the end of the Little Ice Age
c. Also published in 2009 by 8 scientists of whom Ravanel and Deline (French and English) giving a more general view of rock landslides with examples in the Himalayas (Daulaghiri) and in the Alps (Brenva glacier and The Drus): Geomorphic impacts of large and rapid mass movements: a review
A huge rock fall estimated at 2 million m3 on the Brenva spur triggered a snow avalanche and land slide on the 18th January 1997 killing 2 skiers and damaging a hotel.
Characteristics of the last rock avalanches on the Brenva Glacier (Mont Blanc massif).
A: scars (thick lines) and tracks (thin lines) of the rock avalanches of the 19 November 1920 (white lines) and 18 January 1997 (black lines).
B: 1997 scar on the Eperon de la Brenva (G. Mortara, February 1997); C: 25-m-high ridges of the 1997 mixed deposit in the distal area (E. Dal Molin, 18 January 1997).
White line: 2005 rockfalls scar;
white square: location of the laser scanner;
white point: temperature sensor implanted in the NW face of les Flammes de Pierre;
white arrows: fractures plans N30°E-75°NW; black arrows: fractures plans N120°E-80° NW; A, B and C: see text below.
As with other parts of the Mont Blanc range, the Aiguille Verte - the Drus has very steep slopes - their average steepness is 75° with for The Drus (3 754 m high) of more than 1 000 m of height.
The Petit Dru is a monolith well separated on the West-South-West horn of the Aiguille Verte (4 122 m). Its West face is made of compact rock, while the adjacent faces are more fractured. The North face is quite broken with an ice-nival niche resulting from a flow. The West face is currently marked on two-third of its height by a large light grey surface 70 m wide, testimony of the 2005 Bonatti pillar disparition.
This galling scar, high of 600 m can be divided in 3 parts.
The lower quarter (section C) corresponds to a N30°E–75°NW vast fracturing plan revealed by several rock falls.
In the central (section B) the galling scar is constituted by 2 parallel dihedrals, the largest results from the section C fracture plan. The other goes up into the superior quarter of the scar (section A) and delimits the upper part of the 2005 rock falls. So 3/4 of the galling scar are orientated West-North-West and the upper quarter South-South-West.