Alaska Volcano Observatory

From Cameron and others, 2017: "In early 2014, Shishaldin Volcano began a low-level eruption that produced intermittent lava within the crater, low-level steam plumes, and occasional dustings of ash and ballistics on its upper flanks. This activity persisted from January 30 through the remainder of 2014. During the eruption, AVO monitored Shishaldin using the seismic array on Unimak Island, infrasound arrays at Akutan (135 km [84 mi] to the southwest) and Dillingham (582 km [362 mi] to the northeast), satellite imagery, a Web camera on adjacent Isanotski volcano looking northwest to Shishaldin, mariner observations, and pilot reports.
"Web and satellite imagery of Shishaldin Volcano showed persistent, low-level steam plumes beginning on January 17, although such activity is not unusual at Shishaldin. On January 30, satellite data showed increased surface temperatures in the summit crater, and AVO upgraded theAviation Color Code and Volcanic Alert Level to YELLOW/ADVISORY. Activity increased in early February, manifested by intermittent seismic tremor and airwave explosion signals recorded on distant infrasound instruments. On February 7, satellite data showed an ice-rich cloud at altitudes as high as 7,600 m (25,000 ft) ASL coming from Shishaldin, and AVO increased the daily watch schedule. Although this activity may have indicated a low-level eruption present in the summit crater, the eruption began no later than March 25, when satellite data indicated temperatures in the summit crater consistent with lava extrusion, and seismic and infrasound data recorded small explosions. On March 28, citing the inferred presence of lava in the summit crater, AVO upgraded the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH. On March 30, 2014, a passing mariner photographed a darkened area at the crater rim, likely from a minor ash emission.
"Throughout April, seismic and infrasound stations continued to record intermittent explosion signals, and steaming often was visible in clear Web camera views. On April 26, AVO received a PIREP of a steam plume at Shishaldin at an altitude as high as 3,800 m (12,500 ft) ASL. Probable ash darkened the upper flanks of the summit crater in Web camera images taken on May 5. On May 13, AVO again observed elevated surface temperatures at the crater consistent with lava extrusion in the crater. One month later on June 14, a NASA Earth Observing-1 Advanced Land Imager (EO-1 ALI) image showed a dusting of ash on the snow around the summit crater. A mariner report on June 28 also described a slight dusting of ash on the snow, and satellite data from July 1, 17, and 27 showed fresh deposits of ash on the flanks of the edifice, suggesting persistent, low-level eruptive activity within the summit crater, consistent with heightened seismicity and elevated surface temperatures.
"AVO personnel conducting fieldwork photographed incandescence within the summit crater on August 10, 2014. Activity at Shishaldin remained remarkably consistent throughout August and September-elevated surface temperatures observed in satellite imagery, evidence of explosions from infrasound and seismic data, intermittent tremor, and occasional steam plumes viewed by pilots or in the Web camera.
"On October 1, satellite data again indicated temperatures within the summit crater consistent with extrusion of new lava. However, these elevated temperatures decreased by mid-October. Temperatures increased again on October 25, consistent with the reappearance of lava within the summit crater. This was accompanied by an increase in seismic tremor and explosions detected by infrasound. In response, AVO issued a Volcanic Activity Notice (VAN) on October 28 but the Aviation Color Code and Volcanic Alert Level remained at ORANGE/WATCH. After an apparent lull in eruptive activity between November 3 and November 20, the number and size of earthquake events at Shishaldin increased sharply, and AVO increased the watch schedule. At 10:00 UTC (1 a.m.
AKST) on November 24, seismic activity again increased sharply, prompting AVO to issue another VAN at 10:49 UTC (1:49a.m. AKST) warning of a greater risk of ash emission outside the crater. For the next 2 days, surface temperatures increased and there was an increase in the number of seismic events and explosions detected by infrasound. A robust steam plume was observed in satellite imagery, but no significant ash deposition occurred outside the crater. This slightly elevated activity lasted 2 days, after which the usual low-level eruptive activity continued at Shishaldin into 2015."
In late January 2015, strongly elevated temperatures were observed in satellite images, consistent with active lava within the crater. A wispy, low-leve ash emission was observed in webcam images on February 2, 2015.
Throughout February and March, 2015, clear satellite views often show elevated surface temperatures at the crater, seismicity remained above background, and low-level steam emissions were frequently seen in webcam images. It is likely that low-level eruptive activity continued within the summit crater. On April 16, 2015, several pilot reports of an ash plume at Shishaldin resulted in the issuance of an Ash Advisory SIGMET. No ash was visible in satellite and web camera images. Throughout April, and until at least the time of this writing (May 15, 2015), Shishaldin continued to show evidence of low-level eruptive activity, including elevated seismicity, elevated surface temperatures within the summit crater, and a visible steam plume. On May 8, observers from a cruise ship in the area reported a steam/ash plume from Shishaldin, heading east. On the morning of May 15, a robust steam plume was detected in web camera views, possibly containing small amounts of ash.
Low-level eruption continued at Shishaldin throughout May, 2015. On June 18, 2015, pilot reports and satellite imagery indicated a weak ash plume rising a few hundred feet from the summit crater; weak ash emissions continued on June 19, 2015. Elevated seismicity, with intermittently observed elevated surface temperatures continued at Shishaldin throughout June, July, August, September, and October.
On November 20, 2015, AVO lowered the Aviation Color Code and Volcano Alert Level to YELLOW/ADVISORY, because no elevated surface temperatures had been observed since October 19, 2015. Slightly elevated seismicity continued at Shishaldin, and robust steam plumes were often observed.
On March 10, 2016, AVO lowered the Aviation Color Code and Volcano Alert Level to GREEN/NORMAL, stating "There has been an steady decrease in detected thermal activity at Shishaldin over the past several months. No anomalous activity has been observed in several clear satellite images of Shishaldin since moderately elevated surface temperatures were detected on January 13, 2016. Airwaves associated with low-level explosive degassing have not been detected in infrasound data since Feb. 7. Low-amplitude seismic tremor consistent with an open, degassing system system continues to be seen in seismic data and is considered to be within the bounds of background activity for Shishaldin."