France’s largest glacier once looked so mighty sliding down the granite slopes of the Mont Blanc, Western Europe’s tallest peak, that early explorers struggled to find the words to capture it. “You must imagine your lake put in agitation by a strong wind, all frozen at once,” wrote British adventurer William Windham, one of the first tourists to explore the glacier in 1741. “Perhaps even that would not produce the same appearance.” That description gave the place its current name—la Mer de Glace, the Sea of Ice. At that time and until the late 1980s, thousands of years of ice covered the steep valley. Visitors walked from the nearby town of Chamonix to Montenvers, where the glacier was so close they only had to hike down a few meters to touch […]