If the volcano becomes active, the gaseous and liquid phases contained in the magma will reach the surface earlier, often causing dramatic changes to the chemical composition of hot gases (fumaroles) and springs.

One of the gases presenting significant quantitative variation in such cases is carbon dioxide (CO2), with hydrogen sulphide being another important indicator (H2S). In a selected site at the newest Nisyros crater (Polyvotis Minor), where egress of gases is most intense, a special station is installed, being capable of automatically monitoring the natural flow of CO2 and H2S.

The percentage of Radon in ground gases, as well as in the gases and hot fluids of Nisyros is periodically monitored; this is a good measure of active tectonic procedures.

For the comprehensive chemical monitoring of the volcano, regular sampling and full chemical analysis is also conducted (main elements, trace elements and isotopes) for gases in fumaroles and hot waters of the island.