Volcano Update from Archive
AVO is increasing the Aviation Color Code to YELLOW and the Volcanic Alert Level to ADVISORY for Okmok volcano. Over the past 24 hours there have been short bursts of volcanic tremor at Okmok volcano. These bursts are occurring at a rate of one per hour on average. This is the first sign significant seismic activity at the volcano since the cessation of eruption in August 2008 and represents an increase above typical background activity.
This increase in seismic activity does not necessarily indicate that an eruption will occur, or that an eruption is likely. Clouds currently obscure satellite views of the volcano. However there is no evidence that an eruption has occurred. The AVO Operations Room is currently being staffed 24/7 due to unrest at Redoubt Volcano.Okmok volcano was in vigorous eruption from July 12 through mid-August, 2008. Energetic, intermittent ash emission from several vents within the caldera blanketed much of the northeast portion of Umnak Island with ash and dusted Unalaska/Dutch Harbor with fine ash on several occasions. Rain-induced remobilization of debris from high on the volcano's flanks produced lahars down many drainages, forming new deltas at the coastline. A new, 200-300 m-high (660-980 ft) tephra cone developed inside the caldera at the primary eruption site. Since late August 2008, seismicity at Okmok has generally declined. The last confirmed ash emission at Okmok occurred on August 19, 2008.
Okmok volcano is a 6-mile-wide caldera that occupies most of the eastern end of Umnak Island, located 75 miles southwest of Unalaska/Dutch Harbor in the eastern Aleutian Islands. Okmok has had several eruptions in historic time typically consisting of ash emissions occasionally to over 30,000 feet ASL but generally much lower; lava flows crossed the caldera floor in 1945 and 1958. Prior to 2008, the volcano last erupted in February 1997 producing lava flows and intermittent ash emissions over the course of several months.
The nearest settlement is Nikolski, population about 35, roughly 45 miles west of the volcano. A ranch caretaker family lives at Fort Glenn on the flank of the volcano about 6 miles east of the caldera rim. Unstable, muddy surfaces and slopes of new volcanic debris within the caldera are prone to liquefaction and collapse. In addition, new lakes, ponds, and deep craters with steep, collapsing banks present hazards to anyone visiting the caldera. The interior of the new tephra cone was hot when imaged with an infrared camera in mid-September. Volcanic gas was not measured; however, noxious gases could be present around this new tephra cone. All drainages leading downslope from the rim of the caldera should be considered hazardous as ash and other loose debris may be remobilized suddenly by heavy rains. The Crater Creek drainage on the north-northeast flank of Okmok should be avoided as it may experience sudden flooding events if water impounded within the caldera breaches new tephra dams. None observed.None observed.Unstable, muddy surfaces and slopes of new volcanic debris within the caldera are prone to liquefaction and collapse. In addition, new lakes, ponds, and deep craters with steep, collapsing banks present hazards to anyone visiting the caldera. The interior of the new tephra cone was hot when imaged with an infrared camera in mid-September. Volcanic gas was not measured; however, noxious gases could be present around this new tephra cone. All drainages leading downslope from the rim of the caldera should be considered hazardous as ash and other loose debris may be remobilized suddenly by heavy rains. The Crater Creek drainage on the north-northeast flank of Okmok should be avoided as it may experience sudden flooding events if water impounded within the caldera breaches new tephra dams. None observed.None observed.
This increase in seismic activity does not necessarily indicate that an eruption will occur, or that an eruption is likely. Clouds currently obscure satellite views of the volcano. However there is no evidence that an eruption has occurred. The AVO Operations Room is currently being staffed 24/7 due to unrest at Redoubt Volcano.Okmok volcano was in vigorous eruption from July 12 through mid-August, 2008. Energetic, intermittent ash emission from several vents within the caldera blanketed much of the northeast portion of Umnak Island with ash and dusted Unalaska/Dutch Harbor with fine ash on several occasions. Rain-induced remobilization of debris from high on the volcano's flanks produced lahars down many drainages, forming new deltas at the coastline. A new, 200-300 m-high (660-980 ft) tephra cone developed inside the caldera at the primary eruption site. Since late August 2008, seismicity at Okmok has generally declined. The last confirmed ash emission at Okmok occurred on August 19, 2008.
Okmok volcano is a 6-mile-wide caldera that occupies most of the eastern end of Umnak Island, located 75 miles southwest of Unalaska/Dutch Harbor in the eastern Aleutian Islands. Okmok has had several eruptions in historic time typically consisting of ash emissions occasionally to over 30,000 feet ASL but generally much lower; lava flows crossed the caldera floor in 1945 and 1958. Prior to 2008, the volcano last erupted in February 1997 producing lava flows and intermittent ash emissions over the course of several months.
The nearest settlement is Nikolski, population about 35, roughly 45 miles west of the volcano. A ranch caretaker family lives at Fort Glenn on the flank of the volcano about 6 miles east of the caldera rim. Unstable, muddy surfaces and slopes of new volcanic debris within the caldera are prone to liquefaction and collapse. In addition, new lakes, ponds, and deep craters with steep, collapsing banks present hazards to anyone visiting the caldera. The interior of the new tephra cone was hot when imaged with an infrared camera in mid-September. Volcanic gas was not measured; however, noxious gases could be present around this new tephra cone. All drainages leading downslope from the rim of the caldera should be considered hazardous as ash and other loose debris may be remobilized suddenly by heavy rains. The Crater Creek drainage on the north-northeast flank of Okmok should be avoided as it may experience sudden flooding events if water impounded within the caldera breaches new tephra dams. None observed.None observed.Unstable, muddy surfaces and slopes of new volcanic debris within the caldera are prone to liquefaction and collapse. In addition, new lakes, ponds, and deep craters with steep, collapsing banks present hazards to anyone visiting the caldera. The interior of the new tephra cone was hot when imaged with an infrared camera in mid-September. Volcanic gas was not measured; however, noxious gases could be present around this new tephra cone. All drainages leading downslope from the rim of the caldera should be considered hazardous as ash and other loose debris may be remobilized suddenly by heavy rains. The Crater Creek drainage on the north-northeast flank of Okmok should be avoided as it may experience sudden flooding events if water impounded within the caldera breaches new tephra dams. None observed.None observed.
