rising into the sky from Huaynaputina before they were enveloped by raining pumice and ash. Caldera collapse It was initially assumed that caldera collapse took place during the 1600 event, as accounts of the eruption stated that the volcano was obliterated to its foundation; later investigation suggested otherwise. Normally very large volcanic eruptions are accompanied by the formation of a caldera, but exceptions do exist. This might reflect either the regional tectonics or the absence of a shallow magma chamber, which prevented the collapse of the chamber from reaching the surface; most of the magma erupted in 1600 originated at a depth of . Some collapse structures did nevertheless develop at Huaynaputina, in the form of two not readily recognizable circular areas within the amphitheatre and around the three vents, probably when the magmatic system depressurized during the eruption. Also, part of the northern flank of the amphitheatre collapsed during the eruption, and some of the debris fell into the Río Tambo canyon. Volume and products The 1600 eruption had a Volcanic Explosivity Index of 6 and is considered to be the only major explosive eruption of the Andes in historical time. It is the largest volcanic eruption throughout South America in historical time, as well as one of the largest in the last millennium and the largest historical eruption in the Western Hemisphere. It was larger than the 1883 eruption of Krakatoa in Indonesia and the 1991 eruption of Pinatubo in the Philippines. Huaynaputina's eruption column was high enough to penetrate the tropopause and influence the climate of Earth. The total volume of volcanic rocks erupted by Huaynaputina was about , in the form of dacitic tephra, pyroclastic flows and pyroclastic surges, although smaller estimates have been proposed. It appears that the bulk of the fallout originated during the first stage of the eruption, the second and third stage contributing a relatively small portion. For comparison, another large Holocene eruption in the Central Andes—the eruption of Cerro Blanco in Argentina about 2,300 ± 60 BCE—produced a bulk volume of of rock, equivalent to a Volcanic Explosivity Index of 7. Estimates have been made for the dense-rock equivalent of the Huaynaputina eruption, ranging between , with a 2019 estimate, that accounts for far-flung tephra, of . Tephra fallout Ash fall from Huaynaputina reached a thickness of within a area of southern Peru, Bolivia and Chile, and of over closer to