Alaska Volcano Observatory

After three months of no detected activity, an explosion occurred at Cleveland volcano at about 06:08 UTC, June 5, 2014, as detected on the Dillingham acoustic infrasound array and at seismic stations at Korovin Volcano. The event appears to have been of short duration and with similar amplitude to previous explosions at Cleveland. The Aviation Color Code and Alert Level remained at YELLOW/ADVISORY. No further activity was observed until weakly elevated surface temperatures seen in satellite data on July 7, 2014, and a vigorous steam and gas plume on July 8 and 9. In late July, 2014, clear satellite views showed persistently elevated surface temperatures in the summit crater, and typical gas and steam emissions. AVO field crews at Cleveland in August noticed typical steam and gas emissions from the summit. Elevated surface temperatures were again visible in satellite data in late August and early September. On September 11, AVO announced new monitoring capabilities at Cleveland: broadband and short-period seismometers, infrasound, and a webcam. Elevated surface temperatures and minor steaming continued at Cleveland throughout 2014. Satellite views in late November showed a small mound of lava in the summit crater, likely extruded around November 24, 2014. Seismicity remained at low levels.
From Dixon and others, 2017: "Cleveland began [2015] at Aviation Color Code YELLOW and Volcano Alert Level ADVISORY and remained so for nearly 5 months. During this period, elevated temperatures were observed, as well as minor intermittent seismicity and steaming. At the volcano’s summit, the dome emplaced after the November 6, 2014, explosion remained the same size through February 2015. Elevated surface temperatures were observed in clear satellite images (fig. 22 [original text]). The diameter of the dome was about 45 m (150 ft) with an approximately 20 m (65 ft) depression that formed a shallow crater in the center. Incandescent fumaroles were detected on February 27 in cracks on the summit dome resulting from inflation of the dome. By March 27, satellite imagery confirmed growth of the dome to about 50 m (164 ft) in diameter (surface area 1,800 m2 or 19,000 ft2).
"After a sustained decline in eruptive activity over the span of a few weeks, Mount Cleveland was downgraded from Aviation Color Code/Volcano Alert Level YELLOW/ADVISORY to UNASSIGNED on May 28. Three weeks later, elevated surface temperatures returned, and a light dusting of ash visible on the upper flanks of Cleveland signified renewed activity. AVO increased the Aviation Color Code/Volcano Alert Level to YELLOW/ADVISORY on June 17 in response to this activity. Satellite imagery showed accelerated lava dome growth in the few days prior to raising the color code. The dome had increased to 55 × 85 m (180 × 280 ft) (outline area almost 3,900 m2 or 42,000 ft2). On July 21, the Aviation Color Code/Volcano Alert Level was elevated from YELLOW/ADVISORY to ORANGE/WATCH when an explosion at 16:17 UTC (08:17 AKDT) of similar amplitude as the explosion on November 6, 2014, at Cleveland was detected by the Cleveland infrasound array and ground-coupled airwaves on the Okmok seismograph network (fig. 23 [original text]). The explosion data, with no clear compression or rarefaction has been interpreted as a swelling and disruption of the conduit plug, followed by a more energetic 'uncorking' of the system (David Fee, UAFGI/AVO, written commun., 2015). This interpretation is similar to that for the previous explosion in November 2014. Satellite imagery showed that the lava dome was completely removed during this explosion and replaced by a small 40 m (130 ft) diameter crater. The hot summit vent surrounded by slightly cooler deposits likely from the July 21 explosion is shown in figure 24 [original text].
"On July 27 at 06:49 UTC (July 26 at 08:49 AKDT), a typical shallow subduction thrust earthquake of M=6.9 occurred about 80 km (50 mi) southeast from Cleveland. This earthquake was strictly tectonic and not related to the explosion at Cleveland, although many aftershocks were recorded on the Cleveland and neighboring seismograph networks.
"On July 30, strongly elevated surface temperatures were noted, consistent with dome growth after the explosion of the prior week. Two days later, on August 1 at 11:28 UTC (03:28 AKDT), a small airwave signal (40 times smaller than the July 21 explosion) in the region of Cleveland was detected, but was not considered a major explosion. Elevated surface temperatures were consistently observed in satellite imagery and a small steam plume was visible in the web camera following this small explosion. On August 4, AVO personnel overflew the summit of the volcano and observed a fresh lava dome forming that had a hot core (about 550-600 °C). Only
minor degassing was detected during the flight. Images from this overflight are shown in figures 25A and B [original text].
"A second explosion occurred on August 7 at 06:03 UTC (August 6, 22:03 AKDT) that was approximately one-half the amplitude of the July 21 explosion and much shorter in duration (1-2 seconds; fig. 26 [original text]). As viewed from satellite imagery, the lava dome that had been growing steadily since July 21 was only partially removed along its southern margin. On August 15, another overflight of the summit by AVO personnel showed more robust degassing and a dome with extrusions of partially new lava (
fig. 25 [original text]; Werner and others, 2017). Satellite data from August 14 show that the 80m (262 ft) diameter lava dome deflated in the center and a 25-30 m (82-98 ft) diameter area of incandescent fractures across the dome surface was observed.
"August 29 marked the first notable earthquake swarm since the installation of a seismograph network on Cleveland in the summer of 2014 (fig. 27 [original text]). The swarm began around 19:03 UTC (11:03 AKDT) and continued for several hours before diminishing. This earthquake swarm was concurrent with elevated surface temperatures; however, nothing of note was recorded in the infrasound data.
"Elevated temperatures and minor steaming persisted for a few weeks following the two explosions. Strongly elevated temperatures decreased after July 30 and moderately elevated temperatures decreased regularly after that. This led to a lowering of the Aviation Color Code/Volcano Alert Level from ORANGE/WATCH to YELLOW/ADVISORY on October 14, and Cleveland remained at this level for the remainder of the year. Intermittent weakly elevated surface temperatures and minor steaming characterized the activity
for the latter months of the year. A summary of the eruption between 2011 and 2015 is shown in figure 28 [original text]."