VOLCANIC HAZARD ASSESSMENT OF GUAGUA PICHINCHA (ECUADOR) BASED ON PAST BEHAVIOR AND NUMERICAL-MODELS

The active crater of Guagua Pichincha volcano is located only about 10 km west of Quito, the capital city of Ecuador. Archeological and historical records confirm that, in the last few millennia, human communities were repeatedly affected by volcanic eruptions in this region. Tephrostratigraphic studies and C-14 datings indicate that the eruptive history of Pichincha in the last 40,000 years has been characterized mostly be explosive eruptions with an average frequency of one event every few centuries. These eruptions produced relatively small volumes of dacitic pumice fallout and pyroclastic surge and flow. Eruptions of the last 10,000 years has also included lava dome growth and lateral blasts by dome explosions. Based upon the history of the volcano, the explosive eruptions of 970 and 1660 A.D. were selected as those representing, in the case of reactivation, the maximum phenomena to be expected. The eruption behaviour (ash fallout and pyroclastic surge) has been simulated by physical-numerical models on digitized topographic map, and the results have been used to evaluate the harzardous areas.