Remnants of the Srednii submarine volcano form a hazardous obstruction in the strait between Rasshua and Ushishur Islands. Flat-topped Khitraya Rock may be a young (Holocene) extrusion dome, and adjoining rocks may be the rim of an old caldera (Gorshkov, 1970). Sapper (1917), Neumann Van Padang (1938), and Gushchenko (1979) reported a submarine eruption between Rasshua and Ushishur Islands on 12 July, possibly in 1880 (the year is uncertain).