Fig. 1

a Isopach map showing the hazard zones that are most prone to be affected by volcanic ash fallout (mm) in case of a Cotopaxi-1877 eruptive scenario, based on its hazard map (Mothes et al., 2016a, 2016b) and in case of a Tungurahua-2006 eruption scenario, based on its hazard map (Samaniego et al. 2008 and Eychenne and Le Pennec, 2012). Red lines show the high-voltage electric transmission lines, green stars indicate the sampling location of the ash used in this study and black polygons are the main urban zones. Inset shows the location of Ecuador in South America, b Ash venting from Cotopaxi in September 2015. c Ash emission from Tungurahua in March 2016