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Science & Nature • Geography

Umnak Island

Umnak Island is a volcanic island in Alaska’s Aleutian Islands, part of the Fox Islands group.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

Umnak Island is a volcanic island in Alaska’s Aleutian Islands, part of the Fox Islands group. It is the third-largest island in the Aleutian archipelago and is known for Mount Okmok, geothermal features, and the only documented geyser site in Alaska.

Geography

Umnak is a long, narrow island in the eastern Aleutians, separated from Unalaska Island by Umnak Pass. Sources describe it as about 70 miles long, with a mountainous volcanic landscape and low vegetation. The island is bounded by the Bering Sea to the north and the Pacific Ocean to the south.

Geology and volcanoes

The island is dominated by volcanic activity, especially Mount Okmok, which contains a large caldera. Geological sources also identify active geothermal areas and the Geyser Bight field, which is the only documented geyser site in Alaska.

Human settlement

Umnak is mostly unpopulated today. The main settlement identified in the results is Nikolski, a small village near the southwest tip of the island, with roughly 40 people.

Natural environment

Umnak lies within the Alaska Maritime National Wildlife Refuge and supports tundra-like vegetation, wildlife, and coastal habitats. The island’s remote setting and volcanic terrain make it ecologically distinctive.

Key facts

  • Umnak Island is part of the Aleutian Arc and lies southwest of Unalaska Island.
  • It has a land area of 686.01 square miles (1,776.76 km²) and is the third-largest island in the Aleutians.
  • The island is volcanic and includes Mount Okmok, a large caldera volcano.
  • Geyser Bight on Umnak is the only documented geyser site in Alaska.
  • The island is sparsely populated, with the village of Nikolski near its southwest end.

Frequently asked questions

Where is Umnak Island located?
Umnak Island is in the Aleutian Islands of Alaska, United States, in the Fox Islands group.
How large is Umnak Island?
Its land area is 686.01 square miles (1,776.76 km²), making it the third-largest island in the Aleutians.
What is Umnak Island known for?
It is known for its volcanic landscape, Mount Okmok, geothermal activity, and Alaska’s only documented geyser site.
Is Umnak Island inhabited?
Yes, but only sparsely; the results mention roughly 40 people living in Nikolski near the southwest tip.
What ocean bodies border Umnak Island?
The island is bordered by the Bering Sea to the north and the Pacific Ocean to the south.

References

  1. Wikipedia — https://en.wikipedia.org/wiki/Umnak
    Supports: Island group, area, rank in the Aleutians, Mount Okmok, and Umnak Pass.
  2. Alaska Volcano Observatory — https://avo.alaska.edu/pdfs/B1028L.pdf
    Supports: Geographic setting, island dimensions, and volcanic/geologic context.
  3. NASA Earth Observatory — https://science.nasa.gov/earth/earth-observatory/umnak-island-91099/
    Supports: Population estimate, Alaska Maritime National Wildlife Refuge, and geothermal features including geysers.
  4. Alaska Division of Geological & Geophysical Surveys — https://dggs.alaska.gov/webpubs/dggs/ri/text/ri1992_001.pdf
    Supports: Geyser Bight as the only documented geyser site in Alaska.
  5. Encyclopaedia Britannica — https://www.britannica.com/place/Umnak-Island
    Supports: General identification of Umnak Island as an island in the Aleutians.