ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, July 29, 2016, 1:40 PM AKDT (Friday, July 29, 2016, 21:40 UTC)
55°25'2" N 161°53'37" W,
Summit Elevation 8261 ft (2518 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE
Clear weather on Thursday, July 28 allowed for visual confirmation of low-intensity eruptive activity at Pavlof, and the Aviation Color Code and Volcano Alert Level were increased to ORANGE/WATCH. Vigorous degassing produced a steam-rich plume that was observed in web camera images and by local observers. At times, minor volcanic ash emissions were observed by pilots, local observers and in satellite images. The drifting steam and ash cloud was below 15,000 ft above sea level and dissipated rapidly. Seismicity has steadily increased over the past week both in occurrence rate and amplitude. Signals are now seen more clearly across the entire seismic network at Pavlof, with activity alternating between periods of continuous tremor and periods of discrete, low-frequency earthquakes. It is possible that steam and minor ash emissions were occurring during these periods of tremor earlier in the week but were obscured by low clouds.
At present, the volcano remains in a state of low-level unrest. Continued steam emissions, with or without minor amounts of volcanic ash, are likely. Geophysical monitoring data and satellite images can likely detect increased activity associated with significant ash emissions but may be unable to provide timely short-term forecasts. Pavlof last erupted in mid-May 2016, and prior to that in late March 2016. Pauses in activity of days to weeks are common during eruptive episodes of Pavlof Volcano. A return to increased eruptive activity remains possible and could occur with little or no warning. AVO will continue to monitor the volcano closely and will issue additional information as necessary.
Pavlof Volcano is a snow- and ice-covered stratovolcano located on the southwestern end of the Alaska Peninsula about 953 km (592 mi) southwest of Anchorage. The volcano is about 7 km (4.4 mi) in diameter and has active vents on the north and east sides close to the summit. With over 40 historic eruptions, it is one of the most consistently active volcanoes in the Aleutian arc. Eruptive activity is generally characterized by sporadic Strombolian lava fountaining continuing for a several-month period. Ash plumes as high as 49,000 ft ASL have been generated by past eruptions of Pavlof, and during the March 2016 eruption, ash plumes as high as 40,000 feet above sea level were generated and the ash was tracked in satellite data as distant as eastern Canada. The nearest community, Cold Bay, is located 60 km (37 miles) to the southwest of Pavlof.
52°49'20" N 169°56'42" W,
Summit Elevation 5676 ft (1730 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW
Low-level unrest continues at Cleveland. Elevated surface temperatures in the summit crater were observed in satellite images during periods of clear weather over the past week. AVO field crews conducted an overflight of the volcano this week, and observed incandescence from a vent in the summit crater, indicating continued unrest. No significant activity detected in seismic, or infrasound (pressure sensor) data over the past week.
Cleveland volcano forms the western portion of Chuginadak Island, a remote and uninhabited island in the east central Aleutians. The volcano is located about 75 km (45 mi) west of the community of Nikolski, and 1500 km (940 mi) southwest of Anchorage. The most recent significant period of eruption began in February, 2001 and produced 3 explosive events that generated ash clouds as high as 39,000 ft above sea level. The 2001 eruption also produced a lava flow and hot avalanche that reached the sea. Since then, Cleveland has been intermittently active producing small lava flows, often followed by explosions that generate small ash clouds generally below 20,000 ft above sea level. These explosions also launch debris onto the slopes of the cone producing hot pyroclastic avalanches and lahars that sometimes reach the coastline.
OTHER ALASKA VOLCANOES
Other Alaska volcanoes show no signs of significant unrest: http://www.avo.alaska.edu/activity/
AVO scientists conduct daily checks of earthquake activity at all seismically-monitored volcanoes, examine web camera and satellite images for evidence of airborne ash and elevated surface temperatures, and consult other monitoring data as needed.
For definitions of Aviation Color Codes and Volcano Alert Levels, see: http://www.avo.alaska.edu/color_codes.php
FOR MORE INFORMATION ON ALASKA VOLCANOES: http://www.avo.alaska.edu
SUBSCRIBE TO VOLCANO ALERT MESSAGES by email: http://volcanoes.usgs.gov/vns/
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John Paskievitch, Acting Scientist-in-Charge, USGS
firstname.lastname@example.org (907) 786-7497
Jeff Freymueller, Coordinating Scientist, UAFGI
email@example.com (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.