Minerals & volcanism of Nisyros island

The nearly circular island of Nisyros, located at the eastern end of the Aegean volcanic arc, is one of Greece’s four officially “active” volcanoes alongside Methana, Milos, and Santorini. Each of these volcanic systems is geologically unique, making Greece an extraordinary natural laboratory for volcanology.

Since 2015, Nisyros has been part of the UNESCO Global Geoparks Network, which aims to protect its outstanding volcanic heritage, promote education and sustainable geotourism, and preserve local culture. Well-marked hiking trails, interpretive panels, and the excellent Volcanological Museum of Nisyros in Nikia make the island an open-air classroom for understanding how volcanoes work and what hazards they pose.

Geodynamics & volcanic origin
South of Crete, the African tectonic plate is subducting beneath the Eurasian plate. At about 100 km depth, rocks melt and produce magma enriched in gases, which rises northward, creating the Aegean volcanic arc — a sweeping chain of both dormant and active volcanoes.

Volcanic activity on Nisyros
Nisyros was built in several stages: first submarine lava flows, later massive explosive eruptions forming the current caldera. In its center lie multiple craters — especially the famous Stefanos Crater, shaped by hydrothermal explosions, the last of which occurred in 1886. Bubbling mud pools, sulfur vents, and fumaroles prove that the volcano is dormant but not extinct. Today, geologists continuously monitor seismicity, ground deformation, and gases.

Hiking & geotourism
Nisyros is a paradise for nature lovers and hikers:

From Mandraki to the ancient Paliokastro and down to the caldera rim.

Trails from the Evangelistria Chapel into the Stefanos and Polyvotis craters.

Ascent to Profitis Ilias, the island’s highest peak, with breathtaking views.

Minerals & collecting
The island is rich in volcanic minerals: sulfur crystals, pyroxene, garnet in skarns, and quartz. Responsible small-scale collecting is tolerated, but large-scale removal and antiquities are prohibited.

Safety
Visiting the craters is impressive but dangerous:

CO₂ accumulates near the ground and can cause suffocation.

Boiling mud and acidic fumaroles can cause severe burns.

Stay no longer than 15–30 minutes in the Stefanos crater.

Avoid the Polyvotis craters due to toxic gases and potential reactivation.