The Perito Moreno Glacier is a glacier located in the Los Glaciares National Park in southwest Santa Cruz province, Argentina. It is one of the most important tourist attractions in the Argentine Patagonia. The 250 km2 (97 sq mi) ice formation, and 30 km (19 mi) 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, located 78 kilometres (48 mi) from El Calafate, 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 Perito Moreno Glacier is one of only three Patagonian glaciers that is growing. The reason remains debated by glaciologists. The terminus of the Perito Moreno Glacier is 5 kilometres (3 mi) wide, with an average height of 74 m (240 ft) above the surface of the water of Lake Argentino, in Argentina. It has a total ice depth of 170 metres (558 ft). Pressures from the weight of the ice slowly pushes the glacier over the southern arm ("Brazo Rico") of "Lago Argentino" ("Lake Argentina") damming the section and separating it from the rest of the lake. With no outlet, the water-level on the "Brazo Rico" side of the lake can rise by as much as 30 meters above the level of the main body of Lake Argentina. Periodically, the pressure produced by the height of the dammed water breaks through the ice barrier causing a spectacular rupture, sending a massive outpouring of water from the Brazo Rico section to the main body of Lake Argentina. As the water exits Brazo Rico, the scored shoreline is exposed, showing evidence of the height of the water build-up. This dam ice bridge rupture cycle recurs naturally between once a year to less than once a decade. The last rupture occurred on January 19th 2013, and previously, March 4th 2012, 2008, 2006, 2004, 1988, 1986, 1980, 1977, 1975, 1972, 1970, 1966, 1963, 1960, 1956, 1953, 1952, 1947, 1940, 1934 and 1917. It ruptures, on average, about every four to five years. As of February 2012, before the March 2 rupture, the glacier dammed the Brazo Rico. The water level there had risen 5.6 meters. 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. 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. Tour companies generally provide crampons to customers.
