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| Okmok Caldera | |
|---|---|
| Name | Okmok Caldera |
| Location | Unimak Island, Aleutian Islands, Alaska |
| Coordinates | 53°26′N 168°08′W |
| Elevation | 2,287 ft (698 m) |
| Type | Caldera |
| Volcanic belt | Aleutian Arc |
| Last eruption | 2008 |
Okmok Caldera is a large volcanic caldera located on Unimak Island in the Aleutian Islands chain of Alaska. The caldera sits within the Aleutian Arc and is one of the most active centers in the region, notable for its explosive eruptions that have influenced North Pacific Ocean air traffic, United States aviation policy, and regional ecology. Its activity has been studied by organizations including the United States Geological Survey, the National Oceanic and Atmospheric Administration, and academic institutions such as the University of Washington.
Okmok Caldera occupies much of northeastern Unimak Island near the entrance to the Bering Sea and lies within the jurisdiction of the Aleutians West Census Area. The caldera is part of the Aleutian Arc, which results from subduction of the Pacific Plate beneath the North American Plate along the Aleutian Trench. Regional geology links include nearby volcanic centers such as Mount Mageik, Mount Cleveland, Shishaldin Volcano, and Makushin Volcano, and tectonic interactions with the Komandorsky Islands and the Rat Islands. The caldera rim rises above coastal plains influenced by Bering Sea currents and proximity to the Gulf of Alaska, and its basaltic to andesitic products reflect magmatic processes comparable to those at Mount St. Helens and Kīlauea.
Okmok has produced multiple Holocene eruptions recorded in tephrochronology and historical accounts associated with Russian Empire exploration, Aleut (Unangan) oral histories, and modern observations by the USGS and NOAA. Notable eruptions occurred in 43 BCE (approximate), 431 CE (approximate), 1663, 1945, 1997, and 2008. The 1997 eruption generated a large ash cloud that affected Trans-Pacific aviation routes and prompted studies by International Civil Aviation Organization affiliates; the 2008 eruption produced a sustained ash plume that impacted Anchorage, disrupted flights referencing Ted Stevens Anchorage International Airport, and prompted alerts by the Volcanic Ash Advisory Center. Tephra from Okmok has been correlated with ice-core records from Greenland and Antarctica and with paleoenvironmental datasets used by researchers at Lamont–Doherty Earth Observatory and Scripps Institution of Oceanography.
The caldera is roughly 10 km across and hosts nested cones, lava flows, and multiple vents, including lava domes and cinder cones within the caldera floor. Morphological comparisons have been made to other calderas such as Crater Lake, Santorini, Rotorua, and Mammoth Mountain, while petrology links relate to studies at Cascade Range volcanoes like Mount Rainier and Mount Adams. Hydrothermal alteration around Okmok connects to geothermal investigations similar to those at Yellowstone National Park and Hawaii Volcanoes National Park. The caldera floor contains a central cone complex and crater lakes that interact with glacial and periglacial processes observed on Aleutian summits and on Mount Erebus in Antarctica.
Eruptions have deposited tephra across Unimak Island', influencing plant succession observed by ecologists from University of Alaska Fairbanks and affecting habitats used by seabirds such as Aleutian cackling goose, horned puffin, and short-tailed albatross. Ash fall has altered soil chemistry and impacted marine productivity in adjacent waters of the Bering Sea and North Pacific Ocean, with fisheries agencies like the Alaska Department of Fish and Game monitoring effects on species including Pacific cod, walleye pollock, and salmon. Climate scientists from institutions such as NASA and NOAA have examined Okmok's injections of sulfur dioxide in relation to transient radiative forcing episodes similar to those attributed to Mount Pinatubo and Krakatoa, and to paleoclimate signals studied by the National Center for Atmospheric Research.
Human interactions include indigenous Aleut (Unangan) occupation and oral traditions, early encounters during Russian America fur trade expeditions associated with entities like the Russian-American Company, and modern impacts on Aleutian communities and United States infrastructure. The 2008 eruption prompted evacuations and emergency responses coordinated by the State of Alaska and Federal Aviation Administration, and influenced aviation routing used by carriers linked to Alaska Airlines and international operators. Scientific expeditions from institutions such as the Smithsonian Institution and research collaborations with the USGS have documented archaeological and cultural responses to past eruptions in regional contexts akin to responses recorded after eruptions at Krakatoa and Montserrat.
Monitoring is performed by the Alaska Volcano Observatory (a partnership of the USGS, University of Alaska Fairbanks, and NOAA), which uses seismic networks, GPS, satellite remote sensing including instruments on Landsat, MODIS, and Sentinel platforms, and gas sensing by programs tied to NASA and NOAA. Research on Okmok spans volcanology, tephrochronology, petrology, and hazard assessment with contributions from universities such as University of Alaska Anchorage, University of Colorado Boulder, University of Cambridge, and Caltech. International collaborations include data sharing with the International Association of Volcanology and Chemistry of the Earth's Interior and modeling efforts that inform policy at ICAO and disaster planning by FEMA.
Category:Volcanoes of Alaska Category:Calderas of the United States