Volcano Big Semyachik, located in the Central part of the Eastern volcanic belt of Kamchatka, about 25 km South-East from the Uzon Caldera, is a complex volcanic massif. The volcano is a complex structure located in the Caldera, the diameter of which is 10 km away. the Absolute height of the main volcanic formations around 1739 m, and the diameter of the base of the array is 15 km away.

The side of the Caldera is very well expressed in the West and southwest of the array. As for the rest of the Caldera, the Caldera block it and postcaldera education. Around it you can see a series arc faults. The formation of the Caldera was the release of large masses of pyroclastic layers with the formation of caked tuffs and ignimbrites.

The Large array Semyachik consists of postcaldera volcanic formations that fill the entire Central and overlying the Eastern part of the Caldera. Postcaldera volcanic formation consists of seven cone-shaped volcanoes, base diameter is 3 to 8 km, and The largest is Big Semyachik (Gear), occupying the Eastern part of the Caldera. Its absolute height is 1720 m. the Central part of the Large array Semyachik took four of the volcano, representing a conical hill with a base diameter of up to 3 km and a relative height of 500 m.

In ancient times the height of the volcano reached 3 km, but under the influence of erosion for many years, the volcano has become much lower. Climbing up the peaks give the volcano a stern and majestic. The top of the volcano has a jagged shape, so it got another local name is Gear.

Volcano Big Semyachik widely developed fumarole-connection with sulfatar and hydrothermal activity. Volcanic rocks in large areas, after changing to alunite, palitaw and Khalitov have a colorful bright color and loose addition. The most active modern connection with sulfatar activity is manifested on the destroyed Bubbling volcanoes and Central Semyachik, and over a large area between them.