Global Volcanism Program | Image GVP-02369
The currently active Troitsky crater of Maly Semiachik formed during an explosive eruption about 400 years ago. The eastern crater wall shows light-colored hydrothermally altered rocks of the vent complex that are overlain by darker lava flows and fall deposits from eruptions that followed formation of the crater. A hot, acidic lake now fills the crater, which has been the source of historical eruptions.
Photo by Oleg Volynets (Institute of Volcanology, Petropavlovsk).