Nisyros, also spelled Nisiros (; ), is a volcanic Greek island and municipality located in the Aegean Sea. It is part of the Dodecanese group of islands, situated between the islands of Kos and Tilos.
Its shape is approximately round, with a diameter of about , and an area of . Several other islets are in the direct vicinity of Nisyros, the largest of which is Gyali, with a population of 22 citizens. The Municipality of Nisyros includes Gyalí, as well as uninhabited Pacheiá, Pergoússa, Kandelioussa, Ágios Antónios, and Strongýli. It has a total land area of and a total population of 1,048 inhabitants (2021).
Geology
thumb|right|Stefanos, the largest crater of the volcano.
thumb|Landscape
The island has a caldera, and was formed within the past 150,000 years, with three separate eruptive stages, ranging from explosive and effusive andesitic eruptions to explosive and effusive dacitic and rhyolitic activity. Its coasts are generally rocky or pebbled, but there are also a few sandy beaches (mainly in the northeastern part). The volcano is currently active but not erupting, and fumaroles are found at the craters. The latest eruptive activity was a steam explosion in 1888,
Geothermal energy
Nisyros has one of the most important, high-enthalpy geothermal fields in Greece, with a fluid temperature of over 350°C and a high pressure of 18bar; based on feasibility studies, the geothermal potential of the island is at least 50MW.
Over time, efforts have been made by the operator, PPC Renewables, to exploit geothermal energy in the area for energy production.
The most recent plan was to gradually create and operate a geothermal plant with a capacity of 20 to 25MW in cooperation with international specialized institutions. Given the estimated energy needs of Nisyros (1–2MW), it was considered possible to supply electricity to the neighbouring islands of Kos, Tilos, Kalymnos, and Leros. However, long-lasting protests by the local community of Nisyros have blocked any plans to exploit the geothermal field for years. Indeed, in 1997 the Municipality of Nisyros held a referendum on the issue, with the result being 87% against the plans of the PPC.
Entities of Nisyros, such as the Nisyros Studies Company, some municipal authorities, and many scientists of the sector, have expressed their objections to the plans of PPC Renewables, raising safety issues due to the particular danger of the volcano of Nisyros, the seismic activity that often follows similar drilling, and the management of toxic waste. A point of friction was that the local community felt that it had been ignored in the decision-making process and in the planning of the project.
Settlements
thumb|left|Street of Mandraki
The island is reachable by ship from Piraeus, Rhodes, and Kos, and in summer, there are many daily trips from the village of Kardamena on Kos. There is also a heliport. The main town and port of the island is Mandraki (pop. 660). Other villages are Paloi (239), Nikia (61), and Emporeios (27). According to the 2011 census, the municipality's resident population is 1,008 (including 21 on Gyali), although in summer it is augmented by many tourists as well as expatriate Nisyrians who visit the island for their vacations. Tourism is not so heavily developed as on other Greek islands. Deposits of perlite and pumice on Gyali provide much of the wealth of the island. The island used to be self-sufficient, and many crops were grown on its terraced slopes. Today, though, they are cultivated on a smaller scale.