by Betsy Herbert, Earth Matters

posted in the Santa Cruz Sentinel March 17, 2016

It was Feb. 13 — month 10 of my yearlong trip around the world — and I stood bedazzled in front of the spectacular Perito Moreno Glacier in Patagonia, Argentina. It’s hard to comprehend the size of this aquamarine-tinted mass of ice. It’s 19 miles long, 3 miles wide, and 200 feet tall where its front edge meets Lake Argentina.

Perito Moreno Glacier, part of Los Glaciares National Park, is one of South America’s most popular tourist attractions, and with good reason. Chances are, if you wait for five or 10 minutes on the park’s viewing deck, you’ll witness the glacier as it drops or calves huge chunks of ice into the lake. This is part of a natural process that occurs as the glacier slowly expands and moves forward down the valley toward the lake.

Perito Moreno is one of 48 glaciers within the Southern Patagonian Ice Field, the world’s third largest reserve of fresh water. A few thousand years ago, glaciers here in the southern Andes covered much larger areas than they do today. They advanced like gargantuan caterpillars, fed by voluminous year-round snowfall characteristic of this part of the world. As they grew and moved slowly downhill, the glaciers eroded the rocky landscape, carving out expansive valleys edged by steep cliffs.

Our group took a small cruise boat onto Lake Argentina — getting as close as we dared — to watch Perito Moreno Glacier as it was calving. Park guides explained that this was a critical time; every three or four years, as the glacier expands forward, it connects to a point of land that juts out from the shore of Lake Argentina.

When the glacier meets this point of land, it forms an ice dam dividing the lake in half. The level of the top half of the lake begins to rise as water collects behind the dam. Eventually, the ice dam gives way, and an enormous surge of water smashes through, roaring down to the bottom half of the lake and thrilling expectant spectators.

Park guides told us that they have a 24-hour web-camera aimed at Perito Moreno’s ice dam and they expected it to break at any time. That day, we were lucky to see the glacier calving chunks as big as houses. Like most of the other observers with their cameras ready, we were hoping to actually witness the collapse of the ice dam ... but it wasn’t to be that day.

Park guides explained that Perito Moreno Glacier is exceptional in yet another way; it is still expanding, despite global warming. Most other glaciers in the world, as well as in the Southern Patagonian Ice Field, are shrinking in response to increasing average global temperatures.

Why Perito Moreno Glacier is still expanding while most others are shrinking is still somewhat of a mystery. Every glacier has its own unique line of equilibrium. Above that line, the glacier takes on ice; below the line, it loses ice. Our parks guides explained that, to date, the enormous snow accumulation in the Andes has been enough to keep Perito Moreno growing, even as it loses a tremendous amount of ice at its front.

On March 10, just three weeks after my visit to Perito Moreno Glacier, I was watching the news in Quito, Ecuador, when I learned that the glacier’s great ice dam had just burst, creating an awe-inspiring show of collapsing ice and surging water. You can view the collapse of Perito Moreno’s ice dam on YouTube: https://youtu.be/JBpZvkNuUwU