These Ice pinnacles start as a solid glacier or snow field.
At this location the slowly moving ice compound eats a part of the international road between Argentina and Chile every winter. Therefore a caterpillar has to cut through the glacier every spring to free this short stretch of road from its solid winter ice cover.
The lower ice pack cut off from the glacier is usually between 1.5 and 3 meters (5 to 10 ft) thick. At this altitude - more than 4000 meters high - and below freezing temperatures the sun starts to sublimate (not melt) the ice during the day. Some spots loose a bit more ice and start to form shallow pits. The bottom of the hollow receives more radiation than the walls each day leaving the walls mostly intact but making the dells grow deeper and deeper until they reach the plain earth at the bottom. Several pits may merge until some free standing blades remain oriented towards the general direction of the sun.
At this place the penitentes are about man's size, but can reach up to 6 meters (18ft) when grown out of larger ice or snow fields.
The first one to describe the penitentes was Charles Darwin when making an excursion into the Andes on his historic journey where he developed the idea of the evolution of species. He must be in good humour when naming the ice blades penitentes (those who perform the Catholic Sacrament of Penance and Reconciliation/Confession).
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