Maly Semyachik is a stratovolcano located in the eastern part of Kamchatka Peninsula, Russia. It is a compound stratovolcano located in a 10-km-wide caldera within the 15×20 km mid-Pleistocene Stena-Soboliny caldera. Three overlapping stratovolcanoes were constructed sequentially along a NE-SW line, with the youngest cone, Tseno-Semyachik, at the southwest end. A brilliant green-blue (mostly) crater lake fills the historically active Troitsky Crater, which formed during a large explosive eruption of Ceno-Semiachik about 400 years ago.
The lake periodically changes color. In 2006 it was bright turquoise. There’s also a photo from 2012, the lake was bright gray.
Minerals are believed to be responsible for the color of this hot, acidic lake. There are local hiking tours to this beautiful lake.