Strongyli islet is a volcanic cone, located at the north of Nisyros. It is built from approximately 675m of depth up to 128m of altitude with an overall volcanic relief of 803m.
Strongyli cone is the most geometric volcanic structure of the area with very steep slopes up to 60o. At its top there is a small crater of 200m diameter and 30m of depth with remnants of older manmade terraces for cultivation. This ideal cone-shaped volcanic edifice consists of gray andesites and minor pyroclastics. Oceanographic missions using the THETIS submersible and the ROV Hercules revealed that in the submarine area of the islet, along the NW flank, an underwater crater of several meters in diameter exists along with fractures in different directions, between NE-SW to E-W. New underwater craters trending ENE-WSW were also discovered, but without any sign of hydrothermal activity (Nomikou and Papanikolaou 2010; Nomikou et al. 2013; 2021).
