Argentina's Perito Moreno glacier is one of only a few ice fields worldwide that have withstood rising global temperatures.
Nourished by Andean snowmelt, the glacier constantly grows even as it spawns icebergs the size of apartment buildings into a frigid lake, maintaining a nearly perfect equilibrium since measurements began more than a century ago.
"We're not sure why this happens," said Andres Rivera, a glacialist with the Center for Scientific Studies in Valdivia, Chile. "But not all glaciers respond equally to climate change."
Viewed at a safe distance on cruise boats or the wooden observation deck just beyond the glacier's leading edge, Perito Moreno's jagged surface radiates a brilliant white in the strong Patagonian sun. Submerged sections glow deep blue.
And when the wind blows in a cloud cover, the 5-kilometer-wide glacier seems to glow from within as the surrounding mountains and water turn a meditative gray.
Every few years, Perito Moreno expands enough to touch a point of land across Lake Argentina, cutting the nation's largest freshwater lake in half and forming an ice dam as it presses against the shore.