Instead of attempting to regurgitate some facts I learned today, here is an excerpt from my buddy, wikipedia.com:
¨ The 250 km˛ ice formation, of 30 km in length, is one of 48 glaciers fed by the Southern Patagonian Ice Field located in the Andes system shared with Chile
. This icefield is the world's third largest reserve of fresh water. The Perito Moreno Glacier is one of only three Patagonian glaciers that are not retreating. Periodically the glacier advances over the L-shaped "Lago Argentino" ("Argentine Lake") forming a natural dam which separates the two halves of the lake when it reaches the opposite shore. With no escape route, the water-level on the Brazo Rico side of the lake can rise by up to 30 meters above the level of the main lake. The enormous pressure produced by this mass of waters finally breaks the ice barrier holding it back, in a spectacular rupture event. This dam/rupture cycle is not regular and it naturally recurs at any frequency between once a year to less than once a decade. The glacier was named after the explorer Francisco Moreno, a pioneer who studied the region in the 19th century and played a major role in defending the territory of Argentina in the conflict surrounding the international border dispute with Chile.
The sounds of thunder were heard on numerous occasions during our visit to Perito Moreno National Park today. Our visit took place for the major part of the morning and early afternoon. At first, the weather appeared to be working against us with signs of rain and a gray gloomy spaning across the sky. I was dissapointed but remembered that anything goes in Patagonia. And, within fifteen minutes, the sun began to peer its way...thank you! We saw caught FASCINATING sights in our boat ride but, the most impressive views came from our mini-hike up some hills surrounding the glacier. Afterwards, we walked along another trail and were able to see the glacier from up close. Throughout our entire stay, we could hear the sounds of thunder as parts of the glacier fell off avalanche style. It was quite a sight!