These marble caves are found in Patagonia, Chile in the second largest freshwater lake in South America. The lake has an area of 1850 km²; 970 km² are in the Chilean Aisén Region, and 880 km² in the Argentine Santa Cruz Province, making it the biggest lake in Chile, and the fourth largest in Argentina. The lake has a maximum depth of 586 metres, and is fed by rivers coming from several glaciers of the Patagonian Andes. Marble Cave is located approximately in the middle of the lake, on the Chilean side.
The blue colour of General Carrera Lake is due to small particles carried by the ice in the glaciers, which remain suspended in the water once the ice melts. The glacial meltwater is slightly turbid and refracts the blue part of sunlight.
The caves are made entirely of marble: marble forms when limestone or dolomite is metamorphosed. The whole block of marble has been calculated as weighing 5 billion tons; the stone is light grey in colour with some darker striations. The marble was exposed by the movements of glaciers during the Pleistocene. The caves were formed from wave action over 6,200 years, as water penetrated the huge blocks of rock and carved them in such a way that they formed beautiful caves and tunnels.
Marble, being made of calcium carbonate, is slightly soluble in water. When the lake reached its present level, the process of solution started. The marble began to dissolve, and it dissolved faster at the water surface. Small cracks within the marble were gradually worn into wider fractures; waves washed away the dissolved material. It took only a few thousand years to create these caves and tunnels.
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