Active fumaroles occur in two fields below the summit, with a number of tiny vents located between the two summit peaks; vapour emissions are visible from close distance. The summit fumaroles have temperatures of less than and their gases contain large quantities of carbon dioxide, water and larger amounts of hydrogen sulfide than sulfur dioxide perhaps due to the latter being filtered out by a hydrothermal system. The fumaroles have emplaced abundant sulfur and silification has been observed. Satellite images have observed relatively invariant temperature anomalies (hot spots) on Uturuncu between its two summit peaks; these temperature anomalies of about are among the largest fumarole fields visible to satellites. The existence of intense fumarolic activity on the northwestern slope at was already reported in 1956.