ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, July 27, 2018, 1:32 PM AKDT (Friday, July 27, 2018, 21:32 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 continues at Cleveland volcano. Weakly elevated surface temperatures consistent with cooling lava were observed in high resolution satellite data over the past week. No significant activity was detected in seismic and infrasound (pressure) sensor data throughout the week. Steaming at the summit was visible in both web camera and satellite images at times. During the week, a small deposit of ballistic blocks was observed in satellite data within the summit crater and just below the eastern crater rim. These blocks suggest very small explosive activity occurred recently at the summit that is below the detection threshold of the seismic and pressure sensors.
Future explosive activity is likely and is expected to occur without warning. Previous explosions have produced hazardous conditions primarily near the volcano, but occasionally they have been large enough to produce a drifting ash cloud.
Cleveland volcano is monitored by only two seismic stations, which restricts 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.
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.
GREAT SITKIN VOLCANO
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 continues at Great Sitkin Volcano. No activity was observed in cloudy to clear satellite data throughout the week. Seismicity levels throughout the week have been low but above background.
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.
Great Sitkin Volcano is a basaltic andesite volcano that occupies most of the northern half of Great Sitkin Island, a member of the Andreanof Islands group in the central Aleutian Islands. It is located 43 km (26 miles) east of the community of Adak. The volcano is a composite structure consisting of an older decapitated volcano and a younger parasitic cone with a 2-3 km diameter summit crater. A steep-sided lava dome, emplaced during an eruption in 1974, occupies the center of the crater. Great Sitkin erupted at least three times in the 20th century, most recently in 1974. That eruption produced a lava dome and at least one ash cloud that likely exceeded an altitude of 25,000 ft above sea level. A poorly documented eruption occurred in 1945, also producing a lava dome that was partially destroyed in the 1974 eruption. Within the past 280 years a large explosive eruption produced pyroclastic flows that partially filled the Glacier Creek valley on the southwest flank.
OTHER ALASKA VOLCANOES
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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John Paskievitch, Acting Scientist-in-Charge, USGS
firstname.lastname@example.org (907) 786-7497
David Fee, Acting 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.