The island Yankicha (Russian: o.Янкича ) consists of the summit caldera and has a maximum width of 2.5 kilometers. The caldera has a diameter of 1.6 kilometers, and is breached on the south, forming a sea-water crater bay. The bay has an estimated depth of 30 meters, and there is strong evidence of ongoing underwater volcanic activity, as evidenced by frequent bubbles, altered water chemistry and the presence of bacteria mats. Two small lava domes for small islands in the central lagoon, and numerous fumaroles and hot springs are along the southeast caldera shoreline.