The Bolshoi Semiachik volcanic complex was constructed within a 10-km-wide caldera whose rim is exposed only on the west. The caldera occupies a large 20 x 30 km late-Pleistocene volcano-tectonic depression near the Pacific Coast of eastern Kamchatka. Post-caldera volcanism includes resurgent doming and the construction of numerous stratovolcanoes and lava domes, several of which have been active during the Holocene. Zubchatka (Bolshoi Semiachik), Zapadny Barany, Vostochny Barany, Zentralny Semiachik, Popkov, Plosky, and Burlyashchy volcanoes are the largest of the volcanic complex. The youngest volcanism and intense modern hydrothermal activity, which is among the most vigorous of Kamchatka, is located outside the caldera to the SE.