The Bolshoy Semyachik Volcano is a complex volcanic range with a diameter of about 15 km and numerous volcanic formations rising 1,500–1,700 m above sea level, the bases of which have merged together. There are seven cone-shaped stratovolcanoes, the largest of which is Zubchatka Volcano. The next largest is Zapadny Barany (Western Ram) Volcano (1,426 m), then Vostochny Barany (Eastern Ram) Volcano (1,320 m), and Problematichny (Problematic) Volcano (1,317 m). The age of the caldera is over 100,000 years.
Hydrothermal activity here includes vapor jets, boiling mud volcanoes, hot lakes, and thermal fields. The most powerful thermal fields emitting sulfurous gases cover an area of 0.03–0.07 km2 and are situated on the slopes of the Burlyashchiy (Seething) and the Central Semyachik volcanoes. It is very rare to see such huge areas of colored clays and yellowish rock formations.
The most famous thermal field is the Paryashchaya Dolina (Steaming Valley), which is 250 meter in diameter. The temperature of steam and surface soil reaches 96–970 °С. Everything here fizzles, squelches, gurgles and bubbles. There are numerous small pools with fountains of turbid water, as well as small mud volcanoes in a variety of colors and shapes.
Nearby, on the slopes and in gullies, another thermal field, Verkhneye (Upper), stretches for over 500 meters. The most powerful vapor jets are located here, with temperatures up to 1,370 °С and a discharge of 120 meters per second. The din they create can sometimes be heard for several kilometers, such as the loud Past Drakona (Mouth of the Dragon) cauldron.
The distinctive Chernoye (Black) Lake, 60 × 20 meters in size and situated on the Central Semyachik Volcano, releases 3,000 kcal of heat each second. Strong steam jets from the lake bottom shoot water up and create the impression of boiling water. Iron sulfide (pyrite) causes the water to be black. The thermal fields which emit sulfurous gases on Bolshoy Semyachik Volcano are located in the high mountains, where the dominate vegetation type is mountain tundra. Wildlife found in Kamchatka high-mountain ecosystems are typical here, including reindeer, bighorn sheep, pikas, ground squirrels, marmots, water pipits, rock ptarmigans, lesser sand plovers, Asian rosy finches, and snow buntings.
S.P. Krasheninnikov was the first researcher to explore this area in early April 1739. The expedition organized by V.I. Vlodaets in 1947 was the first to study the Semyachik Volcano system.