report from the city. The scale of the eruption and its impact on climate have been determined from historical records, tree ring data, the position of glaciers, the thickness of speleothems and ice, plant flowering times, wine harvests and coral growth. Stratigraphically, the eruption deposits have been subdivided into five formations. Prelude and sequence of events The eruption may have been triggered when new, "Dacite 1" magma entered into a magmatic system containing "Dacite 2" magma and pressurized the system, causing magma to begin ascending to the surface. In the prelude to the eruption, magma moving upwards to the future vents caused earthquakes beginning at a shallow reservoir at a depth of ; according to the accounts of priests, people in Arequipa fled their houses out of fear that they would collapse. The rising magma appears to have intercepted an older hydrothermal system that existed as much as below the vents; parts of the system were expelled during the eruption. Once the magma reached the surface, the eruption quickly became intense. A first Plinian stage took place on 19 and 20February, accompanied by an increase of earthquake activity. The first Plinian event lasted for about 20 hours and formed pumice deposits close to the vent that were thick. The pumice was buried by the ash erupted during this stage, which has been recorded as far as Antarctica. This stage of the eruption produced at least of rocks, comprising the bulk of the output from the 1600 eruption. A sustained eruption column about high likely created a mushroom cloud that darkened the sky, obscuring the sun and the stars. Afterwards, collapses in the amphitheatre and within the vent enlarged both features; they also decreased the intensity of the eruption. A first pyroclastic flow was deposited already during this time when the column became unstable. The Plinian stage was channelled by a fracture and had the characteristics of a fissure-fed eruption. Possibly, the second vent formed during this stage, but another interpretation is that the second vent is actually a collapse structure that formed late during the eruption. Much of the excavation of the conduit took place during this stage. After a hiatus the volcano began erupting pyroclastic flows; these were mostly constrained by the topography and were erupted in stages, intercalated by ash fall that extended to larger distances. Most of these pyroclastic flows accumulated in valleys radiating away from Huaynaputina,