Mer de Glace

Where it sits. The Mer de Glace is the largest glacier in France, a valley glacier flowing north-west out of the Mont Blanc massif above Chamonix. Its ice is fed by the Glacier du Géant and the Glacier de Leschaux, which merge in the Vallée Blanche and turn down a steep rock trough between the Aiguilles de Chamonix on one side and the Grandes Jorasses and the Drus on the other. The trunk is about seven kilometres long today, some two kilometres wide at the confluence and up to 200 metres thick, and it moves roughly ninety metres a year at the centreline — close to a centimetre an hour, fast enough that the crevasse pattern visible from the viewpoint changes noticeably from one season to the next. The surface is not white but grey and brown, striped with medial moraines of rock carried down from the ridges above.

Discovery, literature and a railway. William Windham and Richard Pococke reached the ice in 1741 and reported it to a European audience, comparing the frozen surface to a lake caught mid-ripple and frozen in an instant; the name that stuck is a translation of the impression. In July 1816 Percy and Mary Shelley crossed from Chamonix to the balcony at Montanvert, and Mary Shelley placed the central confrontation of Frankenstein here: Victor climbs to the glacier and meets his creature on the ice, in one of the earliest passages in English fiction to use a real Alpine landscape as a moral setting rather than as decoration. Film adaptations have restaged that meeting repeatedly, though nearly always on sound stages and studio ice rather than on the glacier, which is why the Mer de Glace is more famous in print than on screen. What made the ice genuinely accessible was engineering: the Montenvers rack railway opened in 1908, climbing 5.1 kilometres and 870 metres from Chamonix to a station at 1,913 metres in about twenty minutes, its red carriages hauled up a gradient that reaches 22 per cent.

A glacier you can measure with your feet. The Mer de Glace is the most legible record of Alpine warming available to a casual visitor, because the route down to the ice has had to be extended repeatedly. In the 1980s the ice cave carved fresh each spring stood close to the level of the station buildings. Today reaching it involves a small gondola followed by several hundred metal steps down the flank of the trough, and painted markers on the rock record where the surface lay in 1990, 2000, 2010 and 2015, each one visibly higher than the last. The trunk has lost well over a hundred metres of thickness at Montenvers since the mid-twentieth century and continues to thin. The Glaciorium, an interpretation centre opened at Montenvers in 2012, sets out the measurements; the staircase makes the same point without words.

What you actually see today. From the Montenvers terrace the glacier lies below you in a long curve, with the Aiguille du Dru — a 3,754-metre granite obelisk whose west face shed a large section in a 2005 rockfall — standing directly opposite. Beside the station are the Grand Hôtel du Montenvers, built in 1880 and still operating, a small crystal and fauna museum, and the Temple de la Nature, a stone rotunda from 1795 built for early tourists. The ice cave is cut anew each year into the flank of the glacier and lit inside, a tunnel of blue-grey ice with rooms and sculpted furniture. Serious walkers use Montenvers as a trailhead: the Grand Balcon Nord traverses back to Plan de l'Aiguille in about two hours, and ladders on the true right bank give access to the Refuge du Couvercle and the high routes.

Getting there and timing. The Montenvers train leaves from its own station beside the main SNCF station in Chamonix; services run from roughly May to early October and on a reduced winter timetable. Walking up instead takes two to two and a half hours from Chamonix on a well-graded path through forest. Reservations are worth having in July and August, when the queue for the last descent can be long. In late winter the glacier serves an entirely different purpose: the Vallée Blanche ski route, begun from the Aiguille du Midi, ends either on the ice below Montenvers with a climb up the ladders to the train, or continues to Chamonix when snow cover in the lower gorge allows, which it does less often every decade.