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 Glacier, part of Los Glaciares National Park, is one of South America’s most popular tourist attractions.

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.