|Tyatya volcano is a regular strongly truncated large stratovolcano with a base diameter of 15-18 km and a height of up to 1485 m, on top of which there is a shallow slightly oval caldera 2.1 x 2.4 km in size, in which there is an inner cone with a base diameter of about 1.5 km. In the north and south, the slopes of the volcano descend to the shores of the Sea of Okhotsk and the Pacific Ocean. On the northeastern slope of the volcano at an altitude of 750 m, there are the remains of a secondary crater, from which a lava flow descends to the sea. The remains of three small side cones, two of them with lava flows, are at the western foot; several more small heavily destroyed cones are located in the southern sector of the foot. In the cliff of the caldera, a layered structure is visible with the prevalence of lavas over pyroclastics. The rocks of the lower and middle parts of the volcano are mainly olivine basalts. The upper part of the caldera cone is composed of basic andesites and andesibasalts.
The inner cone is located almost in the center of the caldera, at its top there are two explosive funnels separated by a jumper; the total crater is 400 x 250 m in size. Lava flows descend along the southwestern slopes of the cone, which cover the entire southwestern segment of the atrio. Two small branches of the flows descend about 3 - 3.5 km along the slope of the main cone, older lava flows descend to its foot and have a total length of up to 8 - 9 km. In the western part, the lava flows of the small cone along the outer slope of the stratovolcano descend to the foot. In addition, the lava flows of the small cone poured over the edge of the caldera and descended along the northern and northeastern slopes of the volcano to a height of 700 m. Most of the central cone and the bottom of the caldera are covered with slag. Lava and pyroclastic central cone belong to olivine basalt.
Two small lava flows of the basaltic composition of the eruption of 1812 reach the northwestern lowering of the somma ridge (Khrenov et al., 2015).
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