Mer de Glace

The Mer de Glace is the longest and largest glacier in France, a river of ice that flows down from the high Mont Blanc range toward the valley of Chamonix. It is about seven kilometres long and in places more than two hundred metres thick, and it is fed by several glaciers that merge higher up, including the Géant glacier. Its name, the sea of ice, comes from the rippled, wave-like surface that the first visitors noticed when they came to look at it in the eighteenth century. William Windham and Richard Pococke reached it in 1741, an event that helped to launch Alpine tourism.

The usual route to it is the Montenvers railway, a rack-and-pinion line that leaves from a station in Chamonix and climbs through forest in about twenty minutes to a viewpoint on the opposite side of the valley. The line opened in 1908 and the trains are a pleasure in themselves. At the top there is a terrace with the Montenvers refuge, an old mountain hotel and restaurant, and a panorama that includes the granite spires of the Aiguilles, the Grandes Jorasses and the glacier itself. The Glaciorium, an exhibition centre, explains how glaciers form and move and shows what is happening as the climate warms.

The glacier has been shrinking noticeably for decades and has lost many metres of thickness since the early twentieth century. A staircase of several hundred steps now leads down to the ice, because the surface has dropped so far below the old viewpoint, and the steps are extended every year. A cable car also takes visitors down to the ice cave, a tunnel dug into the glacier each season, which is rebuilt as the ice flows and melts. The cave is carved with small rooms and sculptures. Entry depends on seasonal conditions and the arrangements for tickets and timings change from year to year, so check the current schedule and the tickets on offer before you go.

Many visitors combine the glacier with the surrounding trails, walking along the high balcony paths to look down on it. The mountain air is cold even in summer, and the area can be slippery, so wear warm clothes and stout shoes. Part of the site is accessible for visitors with reduced mobility, but not every area. Dogs on a lead are welcome on the train and at the top.

The visit takes half a day, including the train journey. It fits well with the Aiguille du Midi cable car and the Musée Alpin in the town, and it can be done in winter or summer. The site suits families and walkers, and gives a clear picture of what climate change looks like in the Alps.