in the Andes incorporates this large area of low relief at high altitude (high plateau) within the orogen: Existence of weaknesses in the Earth's crust prior to tectonic shortening. Such weaknesses would cause the partition of tectonic deformation and uplift into the eastern and western cordillera, leaving the necessary space for the formation of the altiplano basin. Magmatic processes rooted in the asthenosphere might have contributed to uplift of the plateau. Climate has controlled the spatial distribution of erosion and sediment deposition, controlling the lubrication along the subducting Nazca Plate and hence influencing the transmission of tectonic forces into South America. Climate also determined the formation of internal drainage (endorheism) and sediment trapping within the Andes, potentially blocking tectonic deformation in the central area between the two cordilleras, and expelling deformation towards the flanks of the orogen Convective removal of the dense lower lithosphere beneath the Altiplano caused that region to isostatically 'float' higher At various times during the Pleistocene epoch, both the southern and northern Altiplano were covered by vast pluvial lakes. Remnants are Lake Titicaca, straddling the Peru–Bolivia border, and Poopó, a salt lake that extends south of Oruro, Bolivia. Salar de Uyuni, locally known as Salar de Tunupa, and Salar de Coipasa are two large dry salt flats formed after the Altiplano paleolakes dried out. Climate The term Altiplano is sometimes used to identify the altitude zone and the type of climate that prevails within it: it is colder than that of the tierra fría but not as cold as that of the tierra helada. Scientists classify the latter as commencing at an elevation of approximately 4,500 meters (or about 15,000 feet). Alternate names used in place of altiplano in this context include puna and páramos. In general the climate is cool and humid to semi-arid and even arid, with mean annual temperatures that vary from near the western mountain range to near Lake Titicaca; and total annual rainfall that ranges between less than to the south west to more than near and over Lake Titicaca. The diurnal cycle of temperature is very wide, with maximum temperatures in the order of and the minimum in the order of . The coldest temperatures occur in the southwestern portion of the Altiplano during the winter months of June and July. The seasonal cycle of rainfall is marked, with the rainy season concentrated between December and March. The rest of