Goûter Couloir: rockfall by hour, accidents and how to cross it

The Goûter Couloir, also called the Grand Couloir, cuts into the west face of the Aiguille du Goûter (3,863 m) in the Mont Blanc massif. The normal route crosses its lower part at 3,270 m, over about 70 m horizontally, then follows its left flank for almost 500 m of elevation gain up to its top at 3,817 m. The crossing and this climb along the left flank form the most exposed sector. The face is made of highly fractured gneiss and mica schist, with a slope of 45 to 60° over 700 m of height, in an area where permafrost is degrading. About 20,000 climbers use it each summer.

Rockfalls are most frequent during the snowmelt period, on a permafrost-affected rock face. In 2019 their frequency followed air temperature with a 2-hour delay: they increased about 3 hours after air temperatures turned positive at the top of the couloir, and when the couloir came into the sun (between 12 and 1 pm early in the season, between 1 and 2 pm late in the season). They only decreased after 8 pm, when the air at the top fell back below 0 °C. The few days of heavy rain produced more rockfall than the day before, and a small share of rockfalls is triggered by the climbers themselves, in the upper left part of the couloir.

From 29 June to 4 September 2019, five seismic sensors recorded 2,648 rockfalls in the couloir, or 39 a day. Activity is lowest in the morning, with a minimum between 9 and 10 am, then rises through the afternoon to peak late in the day. The most energetic rockfalls occur between 3 and 10 pm. The first half of the summer is the most active: 72% of events took place in July, against 28% in August.

Rockfall frequency in the couloir, summer 2019

Source: Mourey et al., 2022, Natural Hazards and Earth System Sciences 22, 445-460 (continuous seismic monitoring, day and night). An earlier Alpes Ingé study, limited to daytime visual observation over 42 days in 2011, had found one rockfall every 28 minutes on average.

Crossing very early in the morning is the traditional practice, and the 2019 measurements point the same way: morning is the quietest period, and the Petzl Foundation names the 9-10 am slot as the best one to cross. But the study shows that climbers' actual timing depends on the hut they chose and their ascent schedule, not on the hazard. Those starting from the tramway reached the couloir around 10 am at the earliest in 2019 (first train at Nid d'Aigle at 8:30 am, against 8:05 am in 2026), and the traffic peak, from 10 am to 3 pm, landed when rockfall was rising. On the way down, many cross again in the afternoon, sometimes until 6 pm, the hour when rockfall is most frequent. The choice of hut therefore sets the exposure, as the table below sums up.

These figures come from all the PGHM Chamonix rescue reports, analysed by the EDYTEM laboratory and the Petzl Foundation. The victims are of 37 nationalities. Few climbers accompanied by a professional are among the casualties. The number of accidents tends to fall in the couloir crossing, while it rises sharply on the Goûter ridge. In France, the summer season averages 35 fatal mountaineering accidents, 3.7 of them each summer in the Grand Couloir since 1990.

The rules below, relayed by the French hiking federation FFRandonnée in March 2018 from mountain video-maker Julien Moreau, complement without replacing the advice of a guide or hut warden. Cables are fitted in the couloir and on the last part of the Goûter ridge.

On 7 July 2022 the Petzl Foundation had the Payot ridge, which avoids the crossing, climbed by guides John Taylor and Vincent Oliva (also a geologist) and by Olivier Moret. It is graded AD, harder than the normal route, with rotten rock and delicate climbing in the upper part, which borders the right bank of the couloir: a rockfall there ends up in the crossing, and more traffic would raise the hazard in the crossing. The Foundation concluded that it is not a safe and credible alternative. To avoid the Goûter, the Trois Monts traverse from the Aiguille du Midi remains.

During heat waves the route can become too dangerous. In 2015 the Goûter hut was closed by prefectural decree from 15 to 31 July and from 6 to 19 August, 23% of its opening period, and overnight stays fell by 17% at the Goûter and 39% at Tête Rousse against the average of the three previous years. In 2026 the Tête Rousse and Goûter huts closed from 11 to 26 August because of rockfall risk (FFCAM alert). Before any departure, ask the hut warden, a guide or the PGHM in Chamonix.