The last volcanic action in Nisyros occurred several thousand years ago, and of course it has not recorded in historical sources. Nevertheless, Nisyros is characterized as a dormant active volcano, and this view is based on three elements:
The first is the relatively recent age of the last volcanic eruptions. The last magical action in the area of ??Nisyros is manifested about 20,000 years ago, and there is some evidence that the latest eruption of glass is probably less than 10,000 years old.
The second is that the processes that give rise to the volcanic action, the sinking of the African lithosphere under the Aegean Sea and the big fissures continue to be active in the area.
The third element is the thermal status of the area, mainly the information from the deep boreholes carried out in Nisyros, with the aim of identifying a geothermal reservoir capable of generating electricity. At the bottom of the first deep drilling, 1,700 meters below sea level, temperatures near 500 degrees Celsius were met, which makes it necessary to have melted rock at low depths of between 3 and 5 km.
In the figure, the results of the geological, volcanic and geothermal surveys in Nisyros are illustrated schematically, representing a section of the island's earth's crust. Here we can see the older non-volcanic rocks, the volcanic building with the caldera draft and the adventures of older and new magmatic chambers.
The upper of the two hot horizons of geothermal fluid, identified by deep drilling, is the source of all hot surface events in Nisyros. This is where hot springs and hot gas escapes, the flames of the island.
The most intense and most spectacular hot event in Nisyros is the steam activity in the area of ??Ramos, especially in the Stefanos crater and the Lofos region. Gases released from hundreds of points in the region have a maximum temperature of 100.1 degrees Celsius. At the same temperature the soil is in the fume area. Gases mainly consist of water vapor (94% by volume) and carbon dioxide (5%). Less than 0.5% hydrogen sulfide, nitrogen and methane are released. At the mouth of the holes where the gases emerge, beautiful sulfur crystals are deposited, while the liquefied water vapor strengthens the surrounding soil with dilute sulfuric acid due to the dissolution of the hydrogen sulphide in the vapor. So the fabrics that come in contact with the ground are destroyed in a very short time. The characteristic smell of the "egg clown" in the region is also due to the presence of hydrogen sulphide, which even at infinitesimal concentrations is felt by the sense of smell.
Outside the area of ??Ramos, the release of hot gases (water vapor) occurs at several points, mainly along the island's large active fissures. The most well-known on the southern side are the confluence of the caldera and the area of ??Fira.
In the northern part, they are located at the base of the caldera cliff, at the top of the dome Nifios and at the entrance of the village Emporios. The temperature of the water vapor at all these points varies between 36 and 40 degrees.