Mount Okmok

Mount Okmok is a shield volcano on Umnak Island in the central Aleutian Islands of Alaska noted for its large caldera. The volcano forms a prominent volcanic complex on the island and is part of the Aleutian volcanic arc.

The caldera floor and surrounding slopes host numerous cones and lava deposits; the caldera is roughly 9 to 10 kilometres in diameter. The volcano is monitored for activity because eruptions produce ash that can affect air traffic and local communities.

Okmok produced a significant eruption in 2008 that generated ash plumes and local disruption; it has a history of Holocene eruptions. The volcanic complex has been studied by volcanologists for its caldera-forming events and post-caldera cone activity.

Located on Umnak Island in the Aleutian chain, the volcano lies far from Alaska’s mainland and is surrounded by harsh maritime conditions and sparse settlement. Access is by boat or aircraft to the island, and conditions are remote and weather-dependent.

• Large caldera and monitoring: Contains a broad caldera roughly 9 to 10 kilometres across and is one of the Aleutian volcanic centers monitored for activity by the Alaska Volcano Observatory.
• Recent eruption (2008): Produced a significant eruption in 2008 that generated ash emissions and disrupted local operations on Umnak Island.