An enormous ice tunnel that forms and collapses every four to five years on a famed Argentine glacier has experienced a rare winter rupture.

The spectacular crash of ice into Lake Argentino usually occurs during the Southern Hemisphere's summer, September through May.

The tunnel collapsed Wednesday morning before a scattering of people visiting the Perito Moreno glacier during the off-season.

The glacier cuts the lake in two. Water flows beneath the ice when the level on one side of the lake rises higher than the other. The rushing water erodes the ice and sometimes causes it to collapse.

Scientists debate whether global warming is responsible. Some say the winter melting phenomenon also happened in 1917 and 1951.