Rasshua is a large volcano forming the 6 x 13 km elongated Island of Rasshua in the central Kuriles. Rasshua volcano is truncated by a large caldera whose eastern rim is below sea level. There are 2 young active central cones in the caldera, from where most activity in the recent past has taken place. Historic activity consisted in explosive ash eruptions from the eastern cone, but there are prehistoric lava flows from the western cone that flooded the caldera and reached the coast.
Fumarolic activity continues in the eastern crater and in the saddle between the 2 summit cones.