Crossing The Grand Couloir

Posted by Jeremy Windsor on Jun 04, 2021

If you're planning on climbing the Voie Normale on Mt Blanc (4809m) sometime soon then it's worth knowing how to safely cross the Grand Couloir du Gouter ("Death Couloir"). Stretching up for more than 600m, this narrow chute cuts across the path to the Gouter Refuge and contains vast quantities of highly fractured gneiss perched precariously on a 45 to 50 degree slope. Unfortunately, rockfall is common and in the last 30 years this has contributed to more than a 100 deaths on the mountain. In 2018 and 2019 researchers supported by the Petzl Foundation set about studying the Grand Couloir in order to find ways of improving safety on the mountain. Here's what they found out... 

-Don't Wait Until Late

Not surprisingly, researchers reported an impressive amount of rockfall. On average, a lump of gneiss weighing 135kg or more was falling down the couloir every 37 (2019) to 50 (2018) minutes. This varied dramatically throughout the day. The quietest time was between 0900 and 1000. After then, the rate steadily increased and peaked in the evening between 1800 and 2000. Without doubt the results show that crossing early is best. If you arrive late in the day it's worth thinking about leaving it until the next morning to cross.

The Grand Couloir cuts across the path (broken red) leading from the Tete Rousse refuge (3167m) to the Gouter Refuge (3817m) on Mt Blanc's Voie Normale (Image: Petzl Foundation)

-Warm and Wet Conditions Are Worst

During the study period it became clear that there was tremendous day to day variation in the amount of rockfall. This wasn't random. When analysed alongside meteorological data it became clear that a pattern started to emerge - the greatest number of rockfalls occurred after periods of warm and wet weather. In the summer of 2017 a total of 11 mountaineers died as a result of rockfall in the Grand Couloir and led to the route being closed for several weeks. From their experience in 2018 and 2019, the researchers believed that the huge amounts of rockfall in the preceding year had been due to a combination of an early summer heat wave and a subsequent series of rain storms above 3000m. These factors combined to loosen the rock and expose many thousands of mountaineers to significant risk. The Voie Normale is not the place to be in warm conditions, especially in a heatwave or in the days following heavy rains high on the mountain.

Annually, more than 20,000 people pass through the Grand Couloir. The first passengers on the Mt Blanc Tramway arrive at Nid d'Aigle at 0830 and start arriving at the couloir at approximately 1000. Although traffic through the couloir peaks shortly before 1200, many still continue to make the crossing in the afternoon

-The White Stuff Won't Save You

Snow and ice normally act as a glue that holds rocks together. However this is not the case during warm summer months in the Grand Couloir. During 2018 and 2019, more than twice as many rockfall episodes occurred during July (68%) compared to August (32%). The presence of melting snow and ice were believed to be responsible. Water, the researchers believed, was loosening the rocks in two ways. First, and perhaps sometimes overlooked, the direct effect of running water pressing against weaknesses between the rocks. Second, and perhaps better known, there's the impact of "freeze and thaw" - the process of expansion and contraction that occurs when water moves between solid and liquid states. Together, these processes have an enormous impact on triggering rockfall. Once snow and ice disappears in the Grand Couloir the rate of rockfall reduces dramatically and only increases again following further precipitation.

Whichever way you look at it, these findings are another real example of the impact climate change has upon the mountain environment. If the Grand Couloir was covered in permafrost then rocks would not be hurtling down the mountainside at such an alarming rate. Sadly, the western face of the Aiguille du Gouter is getting warmer. Over the last decade upper parts of the couloir have seen a 2 degrees C increase in mean temperature and large areas of permafrost have been lost. Light coverings of snow and ice are not enough and simply make matters worse. Many of the most famous climbs in the Alps have changed, the Voie Normale on Mt Blanc looks set to join them.

Here's the final word from Jon Morgan, doctor and UIAGM guide,

The Grand Couloir has always been a dangerous place and the Petzl article gives some clues on how you might reduce your risk. Rockfall is a problem everywhere in the Alps and I do think it is getting worse with climate change, as is crevasse danger in high summer. Crowding of a honeypot mountain undoubtedly exacerbates the risk as, unless you are amongst the least fit people on the hill that day, you will be slowed down by other people, who themselves may knock down rocks too. I personally wouldn't go up the Grand Couloir again, but that is easy to say, having been up Mont Blanc many times. Is it more dangerous than other common routes on 4000m peaks? Yes, probably. As long as people know the risk and do the route in possession of the information, then I think that is OK. You can never make mountaineering safe and not even the suggested building of a tunnel under the couloir can do that, as half the accidents occur on the Gouter Ridge itself. Equally you could be unlucky by crossing at the safest time and still be hit. If you want to climb a huge snowy mountain in the Alps with far less people, no dangerous couloir and amazing views of lots of other stunning peaks, try the Dom (4545m). It is every bit as much of a challenge as Mont Blanc, as there is no lift assistance, so you really do climb it, from the valley, with a night in the hut. Also the hut is much lower than the huts on Mont Blanc, so what little sleep you do get will be better quality for your summit day!"

Thanks Jon for contributing to this post.

Terrifying footage of rockfall in the "Death Couloir" can be seen here.

Interviews with environmental activists Jim Duff and Robin Barraclough can be found in earlier posts. The impact of climate change upon other climbs in the Mt Blanc Massif can be found here.

Find out how to climb Everest in a fortnight here! Looking for an adventure? Chee Tor GirdleSkeleton RidgeWelsh 3000's Challenge?

If you would like to find out more about mountain medicine why not join the British Mountain Medicine Society? See this link for details.

Have something to say? Comment on this post