Grotte de la Mer de Glace

Useful Information

Location: Mer de Glace glacier, Hotel de Montenvers, Mont Blanc, near Chamonix.
Open: MAY to 01-JUL daily 8:30-16.
02-JUL to 28-AUG daily 8:30-17.
29-AUG to 09-OCT daily 8:30-16.
Trains start every 20 or 30 minutes, according to demand.
Fee: Adults EUR 25, Children (4-15) EUR 20, Children (0-3) EUR 12.50, Family (2+2) EUR 75.
Classification: Explainglacier grotto
Light: electric
Guided tours: V=300,000/a[2008]
Address: Grotte de la Mer de Glace, 35, Place de la Mer de Glace, 74400 Chamonix, Tel: +33-, Fax: +33-.
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
Please check rates and details directly with the companies in question if you need more recent info.



The Grotte de la Mer de Glace was named after the famous glacier Mer de Glace (Sea of Ice) north of the Mont Blanc. The glacier is 7km long and 200m thick, which makes it the longest glacier in France. It begins at 2,400m asl, fed by three sources, the Glacier du Géant, the Glacier de Lechaud and the Cascade du Talèfre. Then it flows north-north-west and ends at a height of 1,400m asl. Its speed is very high, about 90m per year in the area of Montenvers.

The Grotte de la Mer de Glace is located inside the glacer, below the Hotel de Montenvers. From the Hotel a cable car was built to the glacier and the glacier grotto. But the lower station, which was once right above the glacier, is now far from the glacier. Since around 1990 the melting of the glacier increased and it is now far below the station. There is well maintained path leading down some 350 steps with a bridge at the end which connects the trail with the cave entrance. When the glacier with the cave inside moves during the year the bridge also moves with the glacier end. The trail leads down more than 100m, the loss of two decades, a rate of 5m per year in average.

However, the difficulties of creating a new cave every year increases. Continually extending the trail costs a lot of money. In 2009 the costes were 80,000 Euros and the opening of the cave had to be postponed for two weeks. The cave is rather close to the end of the glacier, which lost noth im length and thickness. It might be necessary in only a few years to move the cave several hundred meters upstream in only a few years. Accodring to the CNRS Laboratory of Glaciology in Grenoble the glacier is expected to lose between 600m and 900m over the next 20 years. So the existence of the cave is in danger. Probably the costs will be too big even for the amount of 300,000 visitors per year.

Other users of the glacier have similar problems. The local power provider EDF has a hydroelectric power station at Chamonix which is fed by the melting water of the glacier. The water is collected under the glacier, in a station located at 1,490m asl, placed in service in 1973 under 200m of ice. Today the ice has vanished and the station is in the open air. They are building a new collector station 1,000m further up, which will be covered by 100m of ice. Tunnels are built to connect it with the current station. And it is not clear how long this will be sufficient, in a few years the new station will probably again be useless. Actually the global warming produces melting water which is used for the production of electricity and causes the shrinking glacier.

The Hotel de Montenvers is easily reached using the Chemin de fer du Montenvers (Montenvers Railway), which starts in Chamonix. The 5.1km long line is a rack railway line with a 1,000mm gauge using the Strub rack design, invented by Emil Strub in 1896. The gradient is varying from 11% to 22% to overcome a height difference of 871m. The trains run at 14 to 20km/h and the ride takes about 25 minutes.