dry in the past; around 28,000 years ago and between 13,000 and 8,200 years ago a wet period was accompanied by advances of glaciers. The middle Holocene was dry, after 4,000 years before present climate became wetter again. Because of the aridity, relatively little sediment is flushed into the Peru-Chile Trench from land, which has effects on the tectonics of the region and the chemistry of the magmas erupted in the volcanoes. Winds at Parinacota come generally from the west, except during the wet season when easterly winds are common. This wind pattern is controlled by the formation of a high-pressure area and a shift of the subtropical jet stream to the south. Flora and fauna The Andes are a long mountain chain with different climates at various latitudes and elevations. Thus, vegetation differs from one location to the other. In the region of Parinacota, between altitude the vegetation is formed by shrub steppe such as Baccharis incarum, Baccharis tola, Fabiana densa; the dominant species are Deyuexia breviaristata, Festuca orthophylla, Parastrephia lucida and Parastrphia quadrangularis. During the wet season, this vegetation is augmented by herbaceous plants. Above a grass vegetation dominates, which on rocky ground occasionally gives way to cushion vegetation such as Azorella compacta, whose yellow colour is characteristic and can be seen from large distances. This type of xeric vegetation is also known as "puna". Polylepis tarapacana is the only true tree found at these altitudes and forms small woods, up to elevations of . Close to water, the bofedal marsh-like vegetation prevails, with Oxychloe andina being the dominant species. Some genera and species are endemic to the puna; they include Chilotrichiops, Lampaya, Parastrephia and Oreocerus. Among the ecological factors that determine vegetation in the region are lack of water, saline soils, plentiful solar irradiation, herbivores, wind and cold nighttime temperatures. These plant species which release airborne pollen can often be identified in samples taken from Parinacota's icecap, where winds deposit the pollen grains.Animal species that live around Parinacota include flamingo, guanaco, huemul, rhea, vicuña and viscacha. Among predatory animals feature the Andean cat, the pampas cat and the puma. The most abundant animal species however are rodents, some of which can be found up to the highest treelines and which include the viscacha and the burrowing tuco-tuco. Also important are birds, such as the rhea, the tinamous, flamingos and various predatory and wetland birds, including the Andean