that had generated the new dacite produced movements within the volcano. Eruption history The ancestral composite volcano that holds Huaynaputina is part of the Pastillo volcanic complex, which developed in the form of thick andesitic rocks after the Miocene, and appears to be of Miocene to Pleistocene age. It underwent sector collapses and glacial erosion, which altered its appearance and its flanks. The amphitheatre which contains the Huaynaputina vents formed probably not as a caldera but either a glacial cirque, a sector collapse scar or another kind of structure that was altered by fluvial and glacial erosion. Other extinct volcanoes in the area have similar amphitheatre structures. It is likely that the development of the later Huaynaputina volcano within the composite volcano is coincidental, although a similar tectonic stress field controlled the younger vents. Recently emplaced, postglacial dacite bodies occur in the Huaynaputina area, some of which probably formed shortly before the 1600 eruption. Cerro Las Chilcas also predates the 1600 eruption and appears to be the earliest volcanic centre in the area. The Cerro El Volcán dome formed during the Quaternary and may be the remnant of a cluster of lava domes south of Huaynaputina. Holocene Tephra and block-and-ash flow deposits from Holocene eruptions can be found within the amphitheatre. Some tephra layers that are 7,000 to 1,000 years old and close to Ubinas volcano have been attributed to activity at Huaynaputina. Three eruptions of the volcano have been dated to 9,700 ± 190, less than 7,480 ± 40 years ago and 5,750 years Before Present, respectively. The first two eruptions produced pumice falls and pyroclastic flows. The first of these, a Plinian eruption, also deposited tephra in Laguna Salinas, north of Huaynaputina, and produced a block-and-ash flow to its south. A debris avalanche deposit crops out on the eastern side of the Río Tambo, opposite to the amphitheatre; it may have been formed not long before the 1600 eruption. The existence of a volcano at Huaynaputina was not recognized before the 1600 eruption, with no known previous eruptions other than fumarolic activity. As a result, the 1600 eruption has been referred to as an instance of monogenetic volcanism. The pre-1600 topography of the volcano was described as "a low ridge in the center of a Sierra", and it is possible that a cluster of lava domes existed at the summit before the 1600 eruption which was blown away