The hydrothermal explosion craters in the caldera

In the heart of the volcanic island Nisyros are several impressive craters formed by hydrothermal explosions. In these events, rising magma heated underground water suddenly, creating extreme pressure and causing powerful steam blasts. The last such eruptions occurred in 1886, and new activity is still possible, as the volcano and its magma chambers remain active.

The best known are the large Stefanos Crater and the Polyvotis Crater, where you can see boiling mud pools and numerous fumaroles reaching temperatures of over 100 °C. However, these craters are dangerous in calm weather, as heavy carbon dioxide gas can accumulate at the bottom. The mud pools themselves are also hazardous — keep a safe distance.

Further southeast lie the Kaminakia Craters, less risky but equally fascinating geologically, with black volcanic scoria and thick sulfur crusts.

Since 2015, Nisyros has been part of the UNESCO Global Geopark Network, which aims to protect the island’s unique volcanic heritage, promote education and research, and encourage sustainable geotourism.