A New Inclusive Volcanic Risk Ranking, Part 1: Methodology

The ever-increasing population living near active volcanoes highlights the need for the implementation of effective risk reduction measures to save lives and reduce the impact of volcanic unrest and eruptions. To help identify volcanic systems associated with potential high risk and prioritize risk reduction strategies, we introduce a new Volcanic Risk Ranking (VRR) methodology that integrates hazard, exposure, and vulnerability as factors that increase risk, and resilience as a factor that reduces risk. Here we present a description of the methodology using Mexican volcanoes as a case study, while a regional application to Latin American volcanoes is presented in a companion paper (Guimarães et al., submitted). With respect to existing strategies, the proposed VRR methodology expands the parameters associated with hazard and exposure and includes the analysis of 4 dimensions of vulnerability (physical, systemic, social, economic) and of resilience. In particular, we propose 41 parameters to be analyzed, including 9 hazard parameters, 9 exposure parameters, 10 vulnerability parameters and 13 resilience parameters. Since the number of parameters evaluated for each risk factor is different, they are normalized to have the same weight based on dedicated sensitivity analyses. In order to best illustrate the methodology, the proposed VRR is here applied to 13 Mexican volcanoes and compared with other approaches. We found that the volcanoes associated with the highest combination of hazard, exposure and vulnerability (3-factor VRR) for this geographic area are Tacaná and El Chichón regardless of the analyzed time window of eruption occurrence (i.e., <1 and <10 ka). Nonetheless, the volcanoes with eruption <1 ka that require the most urgent actions as associated with no or few resilience measures in place are Michoacán-Guanajuato Volcanic Field and San Martín Tuxtla (4-factor VRR); the top volcanoes in the 4-factor VRR with eruption <10 ka are Michoacán-Guanajuato Volcanic Field and Las Cumbres.

Ground Deformations Controlled by Hidden Faults: Multi-Frequency and Multitemporal InSAR Techniques for Urban Hazard Monitoring

This work focuses on the study of land subsidence processes by means of multi-temporal and multi-frequency InSAR techniques. Specifically, we retrieve the long-term evolution (2003–2018) of the creeping phenomenon producing ground fissuring in the Ciudad Guzmán (Jalisco state, Mexico) urban area. The city is located on the northern side of the Volcan de Colima area, one of the most active Mexican volcanoes. On September 21 2012, Ciudad Guzmán was struck by ground fissures of about 1.5 km of length, causing the deformation of the roads and the propagation of fissures in adjacent buildings. The field surveys showed that fissures follow the escarpments produced during the central Mexico September 19 1985 Mw 8.1 earthquake. We extended the SAR (Synthetic Aperture Radar) interferometric monitoring starting with the multi-temporal analysis of ENVISAT and COSMO-SkyMed datasets, allowing the monitoring of the observed subsidence phenomena affecting the Mexican city. We processed a new stack of Sentinel-1 TOPSAR acquisition mode images along both descending and ascending paths and spanning the 2016–2018 temporal period. The resulting long-term trend observed by satellites, together with data from volcanic bulletin and in situ surveys, seems to suggest that the subsidence is due to the exploitation of the aquifers and that the spatial arrangement of ground deformation is controlled by the position of buried faults.