GIS-based volcanic hazards, vulnerability and risks assessment of the Guallatiri Volcano, Arica y Parinacota Region, Chile

Abstract

This paper introduces the first GIS-based volcanic hazard, vulnerability and risk assessment of Guallatiri volcano. Volcanic hazard assessment is based on the study of five key volcanic phenomena observed during Holocene eruptions of Guallatiri volcano: i) tephra transport, dispersal and deposition; ii) flooding by lahars; iii) lava flows; iv) pyroclastic density currents; and v) ballistic projectiles. A qualitative approach is considered, assuming a relative probability of occurrence for each scenario. Hazard maps are constructed via computer modelling based on field data and some volcanic analogues and relative probability values are assigned to each scenario (the lowest magnitude/intensity scenario has the highest probability value and vice versa). After summing them up through the raster calculator tool, the result corresponds to an integrated volcanic hazard map, that shows the areas likely to be adversely affected by different volcanic processes. Vulnerability was assessed through its social, physical and territorial components considered by dividing the study area into basic administrative units (rural entities), according to the 2017 Chilean Census. Social vulnerability is evaluated through density of people, education qualification, and dependence index. Physical vulnerability is evaluated through the number of houses, and territorial vulnerability, through a critical infrastructure cadaster. A vulnerability level is assigned according to the vulnerability indicator intervals using the quantile method. In order to evaluate the overall risk, the integrated hazard map and vulnerability assessments are aggregated through the arithmetic multiplication of the layers. Consequently, three thematic risk maps are obtained: social, physical and territorial. This analysis depicts that ash transport, dispersal and fallout, indeed has the greatest impact because it is more widely distributed. If a high magnitude eruption occurred during autumn, winter or spring/summer, ash cloud movements would be to the NW, E or SE, respectively reaching Chile, Peru, Bolivia, Argentina, Brazil, and Paraguay. For volcanic processes closest to the volcanic edifice, the higher risk areas would be located towards the N, NW, and SW of the volcano affecting areas up 13 km to the localities of Chungará Viejo, Ancuta, and Guallatiri. In the case of explosive events, areas prone to be affected by tephra deposition could be blanketed with layers up to 50 cm thick, while flooding by bulky lahars could extend for up to ~19 km, and pyroclastic density currents up to ~10 km, whereas for effusive events, lava flows would extend for up to ~7 km. Consequently, the places identified here as those being at highest social risk are Nigramalla, Ancuta, and Guallatire. Due to its remoteness, this volcano and their hazards/vulnerability/risks have been underestimated so far. A future eruption will threaten these areas and the local economy mainly related to the tertiary (e.g., tourism), and primary (e.g., livestock) sectors.