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Jersy Marińo, Instituto Geológico Minero y Metalúrgico (Peru)
Marco Rivera, Instituto Geológico Minero y Metalúrgico (Peru)
Lourdes Cacya, Instituto Geológico Minero y Metalúrgico (Peru)
Jean Claude Thouret, Université Blais Pascal (France)
Luisa Macedo, Instituto Geológico Minero y Metalúrgico (Peru)
Claus Siebe, Universidad Nacional Autónoma de México (Mexico)
Robert Tilling, PMA GCA (United States)
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The city centre of Arequipa -second largest city in Peru (about one million people)- is located 17 km away from Misti Volcano (5822 a.s.l.) and about 3.5 km vertically below it. During the last 50,000 years, vulcanian and sub-plinian eruptions at Misti have produced about ten sizeable piroclastic flows and twenty tephra falls (Thouret et al., 2001). However, numerous ash falls, pyroclastic flows, and lahars from prehistoric subplinian eruptions, as recent as 2,000 years ago, have affected the region of Arequipa around the volcano. Misti's only well-recorded historical activity consisted of small eruptions during the mid-15th century (Chávez, 1992). The Chili River and the main ravines (Pastores, San Lázaro, Huarangal, Huarangueros, Agua Salada) drain the W, S, and SE flanks of the volcanic edifice and cut through Arequipa city. Channeled through them, numerous pyroclastic flows and lahars have reached 12 to 25 km distance from source.
In this map the susceptible areas to be affected with more frequency by the different volcanic phenomenons as ash and pumice fall, piroclastic flows, lahars, debris avalanche and lava flows they are represented with different colors. The areas of high hazard are distinguished in red color, the areas considered as moderate hazard are identified in orange and the low hazard areas are differentiated in yellow. To delimite the danger areas or zones the geologic studies, model for computer for lahars, energy lines calculations to determine distances up to where they can reach future piroclastic flows and debris avalanches besides examples of other eruptions happened in the world they were realized.
High hazard area, it can be severely affected by piroclastic flows, piroclastic surge, lahars, ash and pumice fall, debris avalanches and/or lava flows which are generated during an eruption of the Misti. Due to their proximity to the volcano, it is the most hazard area. Any eruption type can affect it even those of low magnitude, as the one happened in the XV Century that had IEV 1 at 2, and they are estimated to happen each 500 to 1500 years. Moderate hazard area, it can be practically affected by all the dangers that would reach the previous area, to exception of lava flows. This area is lower danger than the red zone and it can be only affected during eruptions of big magnitude (IEV 3 - 5), as the eruptions had taken place for 2000 and 11000 years. Eruptions of this magnitude happen each 2000 to 10000 years. Low hazard area, it is the furthest area from the volcano and therefore it is the lowest hazard. It can be affected by piroclastic flows, piroclastic surge, ash and pumice fall, but only in eruptions of very big magnitude (IEV> 5), as those had happened for 13600 and 33000 years they summoned voluminous piroclastic flows (ignimbrite). The frequency of this type of events is low it is estimated in one each 10000 to 20000 years.
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