The crater was formed as a result of the largest Holocene eruption KHG about 6900 years BP. It is 2.1 x 2.8 km large and is filled with the lake 150 m deep; the upper part of an inter-crater dacite extrusive dome(s) forms three small closely spaced islands.
Mt. Nepriyatnaya (“Unpleasant”) forms the summit of the volcanic massif. Two lava bodies, formed during the most recent eruption (1600 14C yrs BP), descend from Mt. Nepriyatnaya to the south and to the north. While the south lava body (at the right) is a normal thick lava flow with well-expressed marginal levees, the specific topography of the northern body (at the left) likely indicates that it originated due to a sector collapse of the main dome. Lava flows, which come from Mt. Nepriyatnaya towards the Vitaminnoe Lake, formed about 4500 yrs BP. Lava domes of different ages are seen at the right. Kurile Lake caldera, Iliinsky and Zheltovsky volcanoes are seen at the background.
Bakening volcano from the east across the Verkhne (Upper) -Avachinskoe Lake. A large horseshoe-shaped crater, breached to the southeast, exposes the inner structure of the volcanic cone. The crater is believed to result from a sector collapse, likely of late Pleistocene age. Late Pleistocene extrusive dome is at the right.
The volcano is sitting on a dissected old volcanic massif. The massif is ice- and snow-clad, so little is known about the structure of its younger part. The summit resembles a lava dome. A number of tephra layers at the volcano's foot likely originated from Alney or from some smaller center(s) in its area, which now are covered with snow.