the atacama desert is the driest place on earth, and is virtually sterile because it is blocked from moisture on both sides by the andes mountains and by the chilean coast range. the cold humboldt current and the pacific anticyclone are essential to keep the dry climate of atacama desert. the average rainfall in the chilean region of antofagasta is just 1 mm per year. some weather stations in the atacama have never received rain. evidence suggests that the atacama may not have had any significant rainfall from 1570 to 1971. it is so arid that mountains that reach as high as 6,885 metres (22,590 feet) are completely free of glaciers and, in the southern part from 25°s to 27°s, may have been glacier-free throughout the quaternary — though permafrost extends down to an altitude of 4,400 metres and is continuous above 5,600 metres. studies by a group of british scientists have suggested that some river beds have been dry for 120,000 years.