About 50 people set out on foot from the Swiss village of Fiesch at dawn on July 31. As the sun rose over 13,000-foot (4,000-meter) Alpine peaks, the procession moved slowly up a mountainside and into the cool of a pine forest, stopping at a tiny church.

By 7:30 the group had swollen to around a hundred—too many to fit inside the chapel of Maria Heimsuchung, or Mary of the Visitation, so a makeshift altar was erected outside.

"Glacier is ice, ice is water, water is life," intoned priest Toni Wenger, before beseeching God to stop the glaciers high above them from melting.

By changing a few, crucial words in the liturgy, Father Wenger reversed a Catholic ritual that for 350