Okmok Caldera itself had been formed and reshaped in two major eruptions which occurred 12,000 and 2,000 years ago. Direct observations of later volcanic activity are known since 1805, with 16 eruptions recorded every 10 to 20 years. The 1817 eruption deposited several feet of ash and scoria rock debris on the northeastern caldera rim, with ash falling on Unalaska Island. Floods that occurred during this destroyed an Aleut village at Cape Tanak on the northeast Bering Sea Coast of the island. In the recent 1997 eruption, the ash clouds traveled across the volcano's caldera floor.