Volcanic activity between 21.5 and 16.5 million years ago endowed Lesvos with important hot springs, natural resources that have been exploited by humans over the years. The warming of the waters is linked to the intense volcanic activity that occurred in the northeastern Aegean region due to subduction of the African lithospheric plate under the Eurasian one. As the subducting African plate reaches a depth of tens of kilometers, its ocean floor rocks melt. The liquid magma that is created is lighter than the neighboring materials of the asthenosphere, as a result of which it moves upwards and reaches the surface of the earth where it forms the large volcanoes found today in Lesvos, Vatoussa, Lepetymnos, Agra, Anemotia and Mesotopos.

Today this submergence is taking place south of Crete and the major volcanoes of Lesvos have now fallen silent. However, large concentrations of hot magma remain at shallow depths beneath Lesvos. These act like giant heaters, heating the water that seeps into the crust. When it approaches the magma chamber, the meteoric water heats up. It then finds passages through existing cracks and fissures and exits to the surface of the earth through the hot springs. During their journey inside the earth, the waters acquire their mineral components, which are also responsible for their therapeutic effect. When this water cools, then it cannot keep the minerals in solution and so redeploys them. In this way, deposits of silver and lead were created in the area of Mithymna (Molyvos), which man exploited by opening mines.

In Lesbos, the most important hot springs are in Polichnitos, the hottest in Europe, Lisvori, Thermi, Geras Gulf, Eftalou, which is the most radioactive healing spring in Lesvos, Argeno and Kryfti in Plomari.