zone from , with cushion plants and tussock grass; a Puna zone from , and a pre-Puna zone from with thorny shrubs. In oases and river valleys of the depression between the pre-Cordillera and the Andes, shrubs such as Atriplex grow; however, the surrounding Atacama Desert is mostly devoid of plant life. At higher altitudes, meltwater from snow supports more life on Licancabur than on similar mountains. Chinchillas (in 1955), grasses, tola bushes, butterflies, flies and lizards are found at elevations reaching above sea level. Life further down the mountain could be supported by the fertilizing effect of dust from volcanic rocks. Polylepis incana might have been more prevalent at Licancabur during wetter times, and is now more common in Bolivia. The upper parts of the mountain had been avoided by hunters, and after some attempts at high elevations during the 1920s chinchilla hunting disappeared from the area. Eruptive history Licancabur formed as three units, all of which feature lava flows; the last one also includes pyroclastic deposits. The bulk of the cone was formed by the second unit. The emplacement of the second unit was preceded by the injection of basic magma into the magma chamber. The oldest flows crop out on the western and northern sides of the volcano and are partially covered by more-recent flows from Licancabur and flows from Sairecabur. The neighbouring Juriques dates to the Pleistocene. Flows from both volcanoes appear to be pre-glacial. The older lavas have compositions similar to shoshonite and to old Sairecabur lavas, and tend to be more basic than recent lavas. Weak explosive activity left pyroclastic deposits on the volcano. Licancabur formed primarily after the late glacial period, between 12,000 and 10,000 years ago. Flank lava flows are its youngest feature: They were not affected by glaciation, and some have levees and ridges. Lava flows reaching Laguna Verde have been radiocarbon dated to 13,240 ± 100 BP, and 13,270 ± 100 years old lacustrine sediments have been buried by flows. The volcano has not erupted during recorded history, and the state of Inca ruins indicates that eruptions during the last millennium are improbable, Bubbling and water temperatures of have been observed in the crater lake of Licancabur, which may remain liquid due to geothermal heating. Renewed activity would most likely consist of the emission of lava and pyroclastic flows either from the crater or the flanks. Human settlement Despite being