A study was conducted about the Mont Blanc infamous Grand Couloir on the Aiguille du Goûter, and they have provided the optimal time window to pass through the Death Couloir.
The Grand Couloir is a short passage on the Goûter Route at 3340 meters (10960 ft) altitude, and it continues with the Ridge Route that goes to the Goûter Refuge (3835 meters, 12582 ft) shown in the picture above.
Grand Couloir deaths
The route is on the north side of the mountain, in France, and it is extremely popular with mountaineers. But this Grand Couloir du Goûter and the Goûter ridge route sees more accidents than any other in the Alps. The average is 3.7 fatalities and 8.5 injuries per summer season since 1990. I suggest that you continue by seeing this short video:
Grand Couloir destabilization events study
There was a study conducted several years ago about best ways of crossing the Couloir. This is a multi-disciplinary 32-pages long study of the normal route up to Mont Blanc, completed in June 2020. But if you have no time, here are the most important facts to know.
The study was initiated by the EDYTEM laboratory and it includes numerous researchers from EDYTEM, ISTerre, LISTIC and PACTE institutes. It was conducted within the framework of ALCOTRA AdaPT Mont-Blanc (Adaptation of Territorial Planning to Climate Change in the Mont Blanc Area) project, and Prevrisk Haute Montagne (Emerging Natural Hazards on High Mountains) project. The study was finalized thanks to the financial support of the Petzl Foundation.
They used the following:
- Seismic sensors to detect destabilization events and estimate their size.
- An automatic digital camera to monitor changes in snow cover in the couloir.
- Three subsurface temperature sensors placed 10 cm deep in the rock to analyse the presence and thermal regime of the permafrost on the western face of the Aiguille du Goûter.
- Apyroelectric sensor to record the number of climbers crossing the Grand Couloir.
- High-resolution topographical measurements using terrestrial laser scanning to closely define the topography of the couloir, locate the start points of destabilisation events and measure the volumes of material destabilised.
- Two weather stations measuring air temperature in the vicinity of the Tête Rousse glacier (IRSTEA station) and the Goûter refuge (REQUEA station).
- A rain gauge positioned at the foot of the couloir (3270 m) to measure liquid precipitation.
The rock destabilization is governed primarily by the gradual melting of the snow. During the study destabilization events number was three times greater when the snowpack was melting than when the couloir was free of snow.
When the couloir was completely free of snow, the frequency of rock destabilization events was much lower and appeared to be related mainly to the number and amplitude of freeze-thaw cycles and occasional liquid precipitation.
The most important results regarding passing through the Death Couloir are as follows:
- There are rockfalls on average every 24 minutes in critical hours.
- Rockfalls are most frequent after rainfall and when the snow melts.
- The number of rock destabilization events was twice as high in July than in August.
- According to the observations, it is just as dangerous to cross the couloir at 1 PM as it is at 10 PM.
- Climbers arriving from Nid d’Aigle need to cross the couloir as early as they can. If possible do this before noon when the western face of the Aiguille du Goûter is still in the shade, rather than waiting until late afternoon or early evening, the part of the day when the risk is highest.
- The maximum rockfalls frequency is in the interval 18-20 PM.
- The best time to cross is between 9 and 10 AM.
These are very clear findings based on a thorough research and observations. There is no guarantee that you will be safe in any interval, but it would be very wise to follow what they suggest. The complete study you can read here.