Explore Patagonia The RN-3 coastal route Parque Nacional Los Glaciares The RN-40 and the Cordillera Share The immense pack ice of the GLACIAR PERITO MORENO (also called Ventisquero Perito Moreno) is one of Argentina’s greatest natural wonders. It’s not the longest of Argentina’s glaciers – nearby Glaciar Upsala is twice as long (60km) – and whereas the ice cliffs at its snout tower up to 60m high, the face of Glaciar Spegazzini can reach heights double that. However, such comparisons prove irrelevant when you stand on the boardwalks that face this monster. Perito Moreno has a star quality that none of the others rivals. The glacier zooms down off the icecap in a great motorway-like sweep, a jagged mass of crevasses and towering, knife-edged séracs almost unsullied by the streaks of dirty moraine that discolour many of its counterparts. When it collides with the southern arm of Lago Argentino, the Canal de los Témpanos (Iceberg Channel), the show really begins: vast blocks of ice, some weighing hundreds of tonnes, detonate off the face of the glacier with the report of a small cannon and come crashing down into the waters below. These frozen depth-charges then surge back to the surface as icebergs, sending out a fairy ring of smaller lumps that form a protecting reef around the berg, which is left to float in a mirror-smooth pool of its own. That said, it’s more likely you’ll have to content yourself with the thuds, cracks, creaks and grinding crunches the glacier habitually makes, as well as the wonderful variety of colours of the ice: marbled in places with streaks of muddy grey and copper-sulphate blue, while at the bottom the pressurized, de-oxygenated ice has a deep blue, waxy sheen. The glacier tends to be more active in sunny weather and in the afternoon, but early morning can also be beautiful, as the sun strikes the ice cliffs. With the wind coming off the ice, the temperature at the glacier can be a lot colder than in El Calafate, so take extra clothes. Do not stray from the boardwalks: many deaths have been caused by ricocheting ice or wave surges. Brief history Perito Moreno is considered to be a “stable” glacier in the sense that it is neither advancing nor retreating. It is famous for the way it periodically pushes right across the channel, forming a massive dyke of ice that cut off the Brazo Rico and Brazo Sur from the main body of Lago Argentino. Isolated from their natural outlet, the water in the brazos (arms) would build up against the flank of the glacier, flooding the surrounding area, until eventually the pressure forced open a passage into the canal once again. Occurring over the course of several hours, such a rupture is, for those lucky enough to witness it, one of nature’s most awesome spectacles. The glacier first reached the peninsula in 1917, having advanced some 750m in fifteen years, but the channel did not remain blocked for long and the phenomenon remained little known. This changed in 1939, when a vast area was flooded and planes made a futile attempt to break the glacier by bombing it. In 1950, water levels rose by 30m and the channel was closed for two years; in 1966, levels reached an astonishing 32m above their normal level. The glacier then settled into a fairly regular cycle, completely blocking the channel approximately every four years or so up to 1988; after that there was a sixteen-year gap until another rupture in 2004. Since then there have been major ruptures in March 2006, 2008 and, most recently, in March 2012.