Salts of the Andes

摘要

Tony Waltham writes Among the varied geological treats in South America's great Andes mountain chain, salt appears in two spectacular forms. The salt flats of the Bolivian altiplano are widely known, but the salt springs in Peru are rather less so. The finest and most visited, and by far the largest of the Bolivian salt flats is the Salar de Uyuni, in the southwestern part of the country. This unbroken salar (salt flat) extends across 10 500 km~2, a horizontal landscape of pure white only surpassed by the polar ice caps (Fig. 8). In the summer rainy season of January to March, drainage from a large mountain basin normally floods the salar to a depth of a few centimetres. Though the winters are cold, at its altitude of 3653 m. solar radiation powers massive evaporation, and the lake is soon gone - to leave behind another sliver of precipitated salt. Drilling has proved salt to at least 120 m thick; this forms 11 major cycles of sedimentation that reach back through the Pleistocene. In early Devensian times the lake rose to 100 m deep, and covered a much larger area, but Uyuni has been an evaporating basin throughout the Holocene.