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U.S. Geological Survey
Wednesday, December 6, 2017, 1:37 PM AKST (Wednesday, December 6, 2017, 22:37 UTC)

52°49'20" N 169°56'42" W, Summit Elevation 5676 ft (1730 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Unrest at Cleveland volcano is continuing at a low level. Nothing significant was observed in satellite images during periods of clear weather over the past day. No activity was detected by seismic or infrasound sensors during the past day.

Lava effusion is typically confined to the summit crater at Cleveland, with the last significant lava flow (that extended to the ocean) occurring in 2001. The lava domes that have been erupted since 2001 have all been destroyed by explosive activity within weeks to months after lava effusion. These explosions typically produce relatively small volcanic ash clouds that dissipate within hours; however, more significant ash emissions have occurred.

Cleveland volcano is monitored with a limited real-time seismic network, which inhibits AVO's ability to detect precursory unrest that may lead to an explosive eruption. Rapid detection of an ash-producing eruption may be possible using a combination of seismic, infrasound, lightning, and satellite data.

54°45'19" N 163°58'16" W, Summit Elevation 9373 ft (2857 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

The Alaska Volcano Observatory raised the Aviation Color Code to YELLOW and the Alert Level to ADVISORY at Shishaldin Volcano earlier today based on increased seismic and infrasound activity over the past few weeks. Seismic activity remains elevated and continuous infrasound (air pressure) waves were detected for more than 10 hours on instruments located in Sand Point (~230 km or 140 miles to the east). Satellite and web camera views of the volcano were obscured by clouds this morning but vigorous steam emission were observed yesterday afternoon during periods of clear weather. These observations represent increased unrest at Shishaldin, but do not necessarily indicate that an eruption will occur. Shishaldin is monitored by local seismic and infrasound sensors, satellite data, a web camera, a telemetered geodetic network, and distant infrasound networks.

52°4'35" N 176°6'39" W, Summit Elevation 5709 ft (1740 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Low-level unrest is occurring at Great Sitkin volcano. Nothing of note was observed in seismic data and in partially cloudy satellite data over the past day.

Great Sitkin volcano is monitored with a local real-time seismic network, which will typically allow AVO to detect changes in unrest that may lead to an explosive eruption. Rapid detection of an ash-producing eruption would be accomplished using a combination of seismic, infrasound, lightning, and satellite data. The last explosive eruption of Great Sitkin volcano occurred in February, 1974 and resulted in at least one ash cloud that reached about 7.6 km (25,000 feet) above sea level. The 1974 eruptive period also resulted in a lava flow of about 600,000 square meters that was emplaced on the floor of the snow-and-ice filled summit crater.

53°55'38" N 168°2'4" W, Summit Elevation 492 ft (150 m)
Current Volcano Alert Level: UNASSIGNED
Current Aviation Color Code: UNASSIGNED

The Alaska Volcano Observatory decreased the Aviation Color Code and the Volcano Alert Level to UNASSIGNED at Bogoslof earlier today due to decreased activity over the previous months. The last detected explosive activity at Bogoslof occurred on August 30, 2017. Over the past three months there has been no significant activity observed in seismic, infrasound, satellite or lightning data.

AVO only assigns Aviation Color Codes and Alert Levels to volcanoes that have a local seismic monitoring network. Activity at Bogoslof has been detected using instruments from distant sites, thus we can not say authoritatively that the volcano has returned to its normal background state. However, we are no longer detecting any activity that would be considered to be indicative of unrest. A resumption of eruptive activity is possible. It is likely that we would be able to detect significant explosive activity if it where to occur.


Information on all Alaska volcanoes is available at : http://www.avo.alaska.edu.

For definitions of Aviation Color Codes and Volcano Alert Levels, see: http://www.avo.alaska.edu/color_codes.php

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Michelle Coombs, Scientist-in-Charge, USGS
mcoombs@usgs.gov (907) 786-7497

Jeff Freymueller, Coordinating Scientist, UAFGI
jfreymueller@alaska.edu (907) 322-4085

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.
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