Perito Moreno is one of only three Patagonian glaciers that is actually growing. Pressure from the weight of the ice slowly pushes the glacier over the southern arm of Argentino Lake, damming the section and separating it from the rest of the lake. This causes the water level to rise nearly one hundred feet higher than the main body of the lake. All this excess water puts pressure on the ice barrier which eventually causes a spectacular rupture. A massive outpouring of water comes rushing into the main body of Arentino Lake. This dam-ice bridge-rupture cycle recurs naturally anywhere from once a year to once in a decade. On average it ruptures every four to five years.
Due to its size and accessibility, Perito Moreno is one of the major tourist attractions in southern Patagonia. It is less than two hours by bus from El Calafate, and many tour companies run daily visits. A large visitor centre at the site features a walking circuit which allows visitors to view the southern flank and the east facing edge of the glacier. If you are very lucky you may witness towers of ice breaking free from the glacier and crashing into the lake below.
In recent years, trekking tours on the ice have gained popularity. The two standard tours are a "mini-trekking" option, consisting of a short walk of about an hour and a half, and a "big ice" version, which is usually about five hours.