Mer de Glace

Mer de Glace is a valley glacier in the Mont Blanc massif above Chamonix, extending roughly 7 km in length with a thickness of around 200 m. The ice moves slowly downhill and forms crevasses and serac towers that shift constantly.

English traveler William Windham visited the site in 1741 and made it known across Europe through his accounts. The rack railway to Montenvers opened in 1909 and provided easy access for tourists for the first time.

The name translates to Sea of Ice and dates back to the 18th century, when travelers compared the wavy surfaces to a frozen ocean. The Grotte de Glace is carved afresh each year and features sculptures and furniture shaped from clear blue ice.

The terrain requires sturdy footwear and warm clothing, as temperatures remain cool even in summer. Access to the ice cave involves a long metal staircase that can become slippery when wet.

Markers along the rock walls show former ice levels and illustrate the retreat of the ice over decades. The flow rate reaches around 90 m per year as the mass moves downhill.