Esan is a small volcanic complex of seven overlapping andesitic-to-dacitic lava domes on the eastern tip of the Oshima Peninsula across the Tsugaru Strait from Honshu. The complex consists of five late Pleistocene and two early Holocene lava domes, Esan and Misaki. A minor phreatic eruption in 1846 produced a mudflow that caused many fatalities. The latest activity was a small eruption in 1874. Active fumaroles occur at a thermal area on the upper NW flank.