page_title: Umnak
section_title: Eruptions
hierarchical_section_title: Umnak / Eruptions
caption_attribution_description: English: Satellite view of Umnak, Alaska, showing the Okmok volcano
context_page_description: Umnak is one of the Fox Islands of the Aleutian Islands. With 686.01 square miles of land area, it is the third largest island in the Aleutian archipelago and the 19th largest island in the United States. The island is home to a large volcanic caldera on Mount Okmok and the only field of geysers in Alaska. It is separated from Unalaska Island by Umnak Pass. In 2000, Umnak was permanently inhabited by only 39 people.
context_section_description: On Saturday July 12, 2008, Okmok Volcano on Mount Okmok, located on Umnak, erupted for several days, through a fresh vent sending wet, ash and gas-rich plume that reached an altitude of 50,000 feet (15,000 m) in the air and forcing the evacuation of Fort Glenn, a private cattle ranch located on the island. Ash fell not only on the eastern part of the island but also on a fishing village 65 miles (105 km)  on the northeast. However, the Aleut village, Nikolski, on the opposite side of Umnak Island with a population of about 40 people to the west of Okmok Volcano escaped from the southeasterly path of the ash clouds. The ash plume also disrupted operation of flights to the Dutch Harbor airport as it spread across many miles of the North Pacific.
  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 6 miles (9.7 km) across the volcano's caldera floor.
caption: Okmok Volcano
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