Fig. 4

a San Cayetano thermal spring discharging into a blue-colored pool from a cave-like structure (in April 2007). Mind the person in the circle for scale. b Ojo de Agua thermal springs discharging well-known milky-white waters (in December 2009). c Santa Teresita thermal springs discharging red-brown waters into a flat meadowland near the”lechería” site (in December 2009). d View of the Río Sucio river with its peculiar brown-orange waters converging with the clear waters of Río Hondura river ~ 18 km north of Irazú volcano (in December 2009). Pictures by D. Rouwet