Exploring the hidden tunnels beneath the Mer de Glace reveals a network created in the 1960s, accessible via a cable car from Chamonix. Visitors navigate a challenging ascent to witness the glacier’s core and understand the hydroelectric power station’s role in supplying energy to thousands. As climate change threatens the glacier’s existence, plans are in place to adapt water capture methods, ensuring continued electricity production while preserving this unique underground marvel for future generations.
Discovering the Hidden Tunnels Beneath the Mer de Glace
For both tourists capturing the beauty of the Mer de Glace and experienced skiers navigating its expansive 11-kilometer stretch, the existence of a hidden underground gallery created five decades ago remains a mystery. The impacts of climate change are hastening the glacier’s melt, potentially making this the final year to capture its majestic views.
Accessing the Underground Marvels
To explore these fascinating tunnels, one must embark on a private cable car ride from Chamonix in Haute-Savoie. “We ascend to the catchment area, situated just above 1400 meters in elevation, before entering the mountain’s galleries,” shares Jean-David Allier, the hydroelectric power station manager at Les Bois for the EDF group.
This journey marks the beginning of a sprawling labyrinth of 10 kilometers of tunnels, excavated using dynamite in the late 1960s. After a scenic two-kilometer trek—either by walking or biking—visitors can access the glacier. “Our facility includes pedestrian and hydraulic galleries, allowing us to reach operational levels for maintenance, directly beneath the catchment area,” Allier explains.
Venturing to the water flowing beneath the glacier presents a challenge, requiring visitors to be in good physical shape, especially with 300 meters of mountain towering above them. “There are 314 steps, which means a 70-meter elevation gain,” Allier elaborates. Upon reaching the summit, an additional 800 meters must be traversed to finally arrive at the glacier’s core, positioned at 1560 meters altitude. “Currently, we have between 45 and 50 meters of ice above us. This is where we can observe the torrent emerging from the Mer de Glace. At present, the water flow is quite low, but during summer, it significantly increases, enabling us to generate electricity,” Allier reveals.
The hydroelectric station supplies power to around 50,000 households from March to December, utilizing a partial diversion of glacier water through the galleries. The 300-meter drop provides the necessary energy to drive the turbines, but concerns linger about the glacier’s future. “The glacier’s terminus is merely a few meters away, and its terminal tongue is receding. One day, we may find ourselves exposed to the open air,” Allier warns. But how long until that day arrives? It could be just a matter of months to a year.
In preparation for these changes, EDF plans to utilize an alternative opening located slightly lower to capture surface water, much like a river, as the glacier continues to vanish. “With this water capture strategy, we aim to maintain our current electricity production levels until 2100,” highlights Guillaume Marchal, the project manager for the reconfiguration of the Mer de Glace water catchment within the EDF group.
This electricity fuels various operations, including the renowned Montenvers train, which transports tourists to the Mer de Glace, many of whom remain unaware of this hidden power station. “Those who initiated this project in the 1970s were truly visionary,” praises one interviewee. Another adds, “We must harness this water while it’s available.”
If you have a passion for the mountains and aren’t claustrophobic, consider that EDF is actively seeking new talent to ensure these tunnels endure for another half-century.