time for the collapse was considered to be 8,000 years ago. Later research indicated an age between 13,000 and 20,000 years ago, the most recent proposal is 8,800 ± 500 years before present. The postulated period coincides with a global clustering of volcano collapse events; perhaps global warming occurring during this time when the last glacial maximum approached its end predisposed volcanoes to collapse. On the other hand, the younger dates of around 8,000 years ago significantly post-date the end of glaciation, thus if the collapse occurred at that time it was probably unrelated to glacial fluctuations. This collapse and the collapse of Socompa farther south may have affected humans in the region. Young cone and Ajata After the collapse, the cone was relatively rapidly rebuilt during the Young Cone stage reaching a total volume of approximately . The units erupted during this time are also known as the "healing flows" or Parinacota 3. During this stage, volcanic activity was focused on the summit crater. This stage was relatively short and accompanied by an increase in the magma output of Parinacota to depending on how the duration of this stage is measured. The higher magma flux is comparable to peak output by other large stratovolcanoes. The maximum possible magma flux at Parinacota during this period is about . Apart from lava flows, sub-Plinian eruptions generated pumice and scoria flows, with some individual explosive eruptions dated to 4,800 ± 800, 4,300 ± 2,600 and 3,600 ± 1,100 years ago. Based on the patterns of tephra deposition in Lake Chungará, it is inferred that the rate of explosive activity increased after the early Holocene until recent times; in addition, tephra falls contributed calcium to the lake waters and impacted its biological productivity. It has been proposed that dust particles found in ice cores at Nevado Sajama may actually be tephra from Parinacota. Various Holocene dates have been obtained from rocks on the southern flank of the Young Cone; the youngest date for this stage was obtained by argon-argon dating: 500 ± 300 years ago. Further, an age of less than 200 BP has been determined by radiocarbon dating for a pyroclastic flow. Other recent activity, originally considered to be the youngest, formed the Ajata cones. These cones are constructed by basaltic andesite with a volume of about . The Ajata cones form four groups of different ages: The lower Ajata flows were