ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE U.S. Geological Survey Friday, September 12, 2014, 3:44 PM AKDT (Friday, September 12, 2014, 23:44 UTC)
54°45'19" N 163°58'16" W,
Summit Elevation 9373 ft (2857 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE
This past week, AVO continued to see elevated temperatures within the summit crater and possible air-waves indicative of low-level eruption at Shishaldin. Overall, however, seismicity remains low. Web camera and most satellite images have been mostly obscured by clouds.
Shishaldin volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a spectacular symmetric cone with a base diameter of approximately 16 km (10 mi). A small summit crater typically emits a noticeable steam plume with occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, with at least 54 episodes of unrest including over 24 confirmed eruptions since 1775. Most of Shishaldin's eruptions have produced small ash and steam plumes, although a recent eruption in April-May 1999 generated an ash column that reached a height of 45,000 ft above sea level.
52°49'20" N 169°56'42" W,
Summit Elevation 5676 ft (1730 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW
AVO detected no sign of significant volcanic unrest at Cleveland over the past week. Cloudy conditions obscured most satellite and web camera views of the volcano. Several rockfall signals detected by the new local seismic network indicate continued instability of volcanic debris on the steep upper flanks of the volcano. During fieldwork in late July and August, AVO scientists witnessed several small rockfall events high on Cleveland.
Cleveland volcano forms the western half 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 within its summit crater. These extrusive episodes are typically followed by explosions that destroy the lava flow, generate small ash clouds generally below 20,000 ft ASL, and launch debris onto the upper slopes of the volcanic cone.
61°17'56" N 152°15'14" W,
Summit Elevation 11070 ft (3374 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN
A possible outburst of water from beneath a glacier on the lower south flank of Mount Spurr was detected beginning about 11:20 AKST on September 11. The flow appears to have been a single event lasting about 20 minutes. Similar and larger duration events have been recorded at Mount Spurr on several occasions since seismic monitoring of the volcano began in the early 1990s. The most recent one was in June 2012. AVO has no visual confirmation of an outburst or high-flow event, but based on the similarity of yesterday's seismicity to previously confirmed events, it is likely one occurred.
Since yesterday's event, no further signals have been recorded. Additional outbursts may occur with no warning, however. Visitors to the area should use caution in drainages on the south flank of Mount Spurr, especially those downstream of the Kidazgeni Glacier.
Mount Spurr volcano is an ice- and snow-covered stratovolcano located on the west side of Cook Inlet approximately 120 km (75 mi) west of Anchorage. The only known historical eruptions occurred in 1953 and 1992 from the Crater Peak flank vent located 3.5 km (2 mi) south of the summit of Mount Spurr. These eruptions were brief, explosive, and produced columns of ash that rose up to 20 km (65,000 ft) above sea level and deposited several mm of ash in south-central Alaska, including approximately 6 mm of ash on Anchorage in 1953. The last known eruption from the summit of Mount Spurr was more than 5,000 years ago. Primary hazards during future eruptions include far-traveled ash clouds, ash fall, pyroclastic flows, and lahars or mudflows that could inundate drainages all sides of the volcano, but primarily on the south and east flanks.
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.
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.