Connectivity and hydrological efficiency dynamics at active volcanoes, Mexico.

Connectivity is an emergent property that describes how complex topography favors or impedes sediment transfer processes. In active volcanic areas, high connectivity may lead to extremely efficient processes, such as lahars. The aim of the present study is to examine the behavior (activation-deactivation) of sub-basins affected by volcanic and anthropogenic processes by studying the changes in connectivity and hydrological efficiency. Two volcanic zones in Mexico were selected: Volcán de Colima and Popocatépetl volcano, the two most active and dangerous volcanoes in the country. The joint index of connectivity (IC) and lateral hydrological efficiency index (LHEI) were calculated for both volcanic areas in basins recently affected by eruptive activity (Volcán de Colima) and co-seismic landslides (Popocatépetl). The analyses enabled the identification of eleven recently activated sub-basins (3.82 km) at the Volcán de Colima and fifteen (3.77 km) at the Popocatepetl volcano, as a consequence of natural processes and economic activities. Critical thresholds indicating the percentage area of land cover/use at which a sub-basin reaches high or very high LHEI values and the percentage of land cover/use change required for a sub-basin to modify its behavior (activation-deactivation) were identified using classification trees. The holistic capacity of the concepts of connectivity and hydrological efficiency permits analyzing the spatiotemporal variations of sediment transport based on the interactions between the hydrogeomorphological dynamics of volcanic processes and the territorial impact of socio-economical activities. Through this approach, new active areas have been identified in both volcanoes; the knowledge of the processes that occurred in these areas represents a key factor for hazard and risk assessment for the population in the near future.