Alaska Volcano Observatory

From Dixon and others, 2020: "Mount Cleveland began the seventh straight year at an elevated Aviation Color Code and Volcano Alert Level in 2017. Activity consisted of intermittent elevated surface temperatures, degassing from the summit cone, and the extrusion of small lava domes punctuated by explosions. Mount Cleveland began 2017 with fewer but similarly sized explosions to those in previous years that transitioned into more frequent but smaller explosions towards the end of the year...
"Mount Cleveland began 2017 at Aviation Color Code YELLOW and Volcano Alert Level ADVISORY. The last explosion on October 24, 2016, left a deep crater at the start of 2017. Activity in January consisted of intermittent gas plumes and elevated surface temperatures. By January 21, satellite imagery confirmed that a new lava dome partially occupied the summit crater. The dome measured 30 m (100 ft) in diameter on January 24, and by February 3 it was 70 m (230 ft) in diameter. The extrusion of this lava dome and potential for explosive activity prompted AVO to increase the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH on February 3. The dome ceased growing at 75 m (250 ft) in diameter around February 11 and remained unchanged into March, and weakly elevated surface temperatures and minor gas emissions were detected in satellite imagery and web-cameras during this time, consistent with cooling lava. After several weeks of inactivity, the Aviation Color Code and Volcano Alert Level was downgraded from ORANGE and WATCH to YELLOW and ADVISORY, respectively, on March 8.
"The first explosion of 2017, which occurred on March 24 at 16:15 UTC (08:15 AKDT), removed the lava dome. The short-duration explosion showed characteristics similar to previous dome-related explosions with a very sharp onset followed by about 10 seconds of additional signal in infrasound data. Cloud cover prevented the observation of ash cloud from this event. This explosion prompted the Aviation Color Code and Volcano Alert Level to be upgraded from YELLOW and ADVISORY to ORANGE and WATCH, respectively.
"On April 5, the Aviation Color Code and Volcano Alert Level was downgraded from ORANGE and WATCH to YELLOW and ADVISORY, respectively, because of inactivity since the explosion on March 24. Satellite imagery showed a new lava dome was extruded into the summit crater sometime before April 15 and by April 23 grew into a smooth 45-m- (150-ft-) diameter dome. The presence of a growing lava dome in the summit crater of Mount Cleveland prompted an Aviation Color Code and Volcano Alert Level upgrade to ORANGE and WATCH, respectively, on April 24. Extrusion of lava continued, and by April 28 three stacked domes had formed. The lowermost dome was 60 × 50 m (200 × 160 ft), the second dome 40 × 30 m (130 × 100 ft), and the newest and topmost dome was 15 m (50 ft) in diameter. The topmost circular dome continued to grow, and by May 2, it was greater than 20 m (65 ft) in diameter. Satellite imagery from May 8 showed no change in the size of the top dome, signifying that lava effusion had ceased at Mount Cleveland.
"On May 17, 03:17 UTC (May 16, 19:17 AKDT), an automated infrasound alarm indicated an explosion. A continuous broadband signal was recorded clearly in seismograph data and was also seen in infrasound data at stations CLES and CLCO for 10 minutes after the initial explosion. The extended infrasound signals were likely caused by jetting (continuous, vigorous gas emissions) after the destruction of the lava dome in the vent. The resulting ash plume drifted approximately 140 km (87 mi) to the southwest at an altitude of 4.6 km (15,000 ft) and was observed in visible Geostationary Operational Environmental Satellite imagery until nightfall. Satellite imagery just after the explosion showed that the dome was completely removed, and impact craters from ballistic dome fragments were formed on the upper flanks of the volcano. The Mount Cleveland summit crater was dome free through May 26.
"On June 6, a series of repeating small low-frequency seismic events were recorded on seismograph station CLES, 3.5 km (2.1 mi) from the summit, but these events were not seen on nearby seismograph station CLCO, 15 km (9 mi) from the summit. The seismicity was consistent with lava dome growth, but poor viewing conditions prevented the confirmation of dome growth. On June 26, the Aviation Color Code and Volcano Alert Level was reduced from ORANGE and WATCH to YELLOW and ADVISORY, respectively, owing to the decline in activity.
"On July 4, 11:19 UTC (03:19 AKDT), a moderate 10-minute eruption was detected by both seismograph and infrasound sensors, prompting the Aviation Color Code and Volcano Alert Level to be upgraded from YELLOW and ADVISORY to ORANGE and WATCH, respectively. This explosion differed from the previous explosion by being preceded by at least five low-frequency seismic events. Additionally, a burst of tremor was recorded 15 seconds prior to the onset of the main explosion.
Satellite data from July 17 show that a new 25-m- (80-ft-) diameter lava dome was emplaced in the summit crater. It grew to more than 50 m (160 ft) in diameter with increased vertical inflation by August 1. Satellite imagery on August 7 showed no change in the lava dome from the previous satellite images, signifying that lava effusion had ceased. This small lava dome was observed by an AVO field crew during an overflight of Mount Cleveland on August 17.
"The fourth explosion in 2017 occurred on August 22 at 18:43 UTC (10:43 AKDT). The one-minute explosion had no precursory activity and was detected by both seismograph and infrasound sensors. Satellite imagery suggested that this explosion, like the previous three eruptions, removed the existing lava dome. The crater remained empty for more than a month until another explosion occurred on September 26, 01:47 UTC (September 25, 17:47 AKDT). The initial blast lasted 3 seconds, but after a brief 15-second pause, a roughly 2-minute-long broadband signal was detected in both seismic and infrasound data suggesting an initial vulcanian blast that was followed by continuous emissions. An ash cloud was visible in a NOAA-19 satellite image south of Mount Cleveland for 30 minutes after the explosion.
"The explosions later in 2017 were smaller and more frequent than those at the beginning of the year. Two small explosions occurred on September 28 at 13:19 and 13:58 UTC (05:19 and 05:58 AKDT, respectively) with amplitudes approximately 100 times smaller than the explosion 2 days prior. Another small explosion occurred on October 1, at 13:05 UTC (05:05 AKDT).
Satellite observations on October 1 showed a new lava dome greater than 70 m (230 ft) in diameter, and by October 15, the dome had doubled in area to cover 12,500 square meters (m2;134,500 square feet [ft2]) at a height of 15-20 m (50-65 ft). The dome continued to increase in both area and height through October 23. On October 28, a small, short-duration (30 sec) explosion occurred at 18:45 UTC (10:45 AKDT). A smaller explosion occurred on October 30 at 11:20 UTC (03:20 AKDT). Satellite imagery suggests that the October explosions removed a portion of the central vent from the dome. A small explosion occurred on November 12 at 09:56 UTC (00:56 AKST) followed by a similar-sized explosion on November 14 at 12:15 UTC (03:15 AKST). The latter event was preceded by two local earthquakes 1 hour prior to the explosion. Another small explosion occurred on November 16 at 22:44 UTC (13:44 AKST) that was similar to the previous events. Between November 17, 22:00 UTC (13:00 AKST) and November 18, 08:20 UTC (November 17, 23:20 AKST), a small volcanic-tectonic earthquake swarm occurred in the vicinity of Mount Cleveland, but its significance to the Mount Cleveland eruption sequence has yet to be determined. A small explosion occurred on December 4, 07:21 UTC (December 3, 22:21 AKST) that was seen just at the closest seismograph station to the summit (CLES).
"Decreased activity following the December 4, 2017, explosion was interpreted as cessation of lava effusion at Mount Cleveland, which prompted AVO to change the Aviation Color Code and Volcano Alert Level from ORANGE and WATCH to YELLOW and ADVISORY, respectively, on December 12. However, less than a day later, another explosion occurred on December 13 at 13:20 UTC (04:20 AKST) necessitating that the Aviation Color Code and Volcano Alert Level to be returned to ORANGE and WATCH, respectively. The ash cloud from this eruptive event was visible in satellite imagery and drifted east at an altitude of 6.1 km (20,000 ft). The final explosion of 2017 occurred on December 18 at 03:17 UTC (December 17, 18:17 AKST), and like recent explosions was smaller than the explosions in early 2017. The Aviation Color Code and Volcano Alert Level remained at ORANGE and WATCH, respectively, for the remainder of the year."
From Cameron and others, 2023: "In addition to the preexisting volcanic activity alarms at Mount Cleveland, AVO implemented two new alarms in 2018 to help detect sudden explosions. One alarm uses the co-located seismic and infrasound sensors at station CLES to quickly detect smaller explosions, and the other uses seismic data in the very-long-period band from station CLCO. This second alarm became especially useful after CLES had an extended data outage starting in September 2018; for the latter part of the year, AVO had only CLCO to supplement the usual remote sensing techniques used to monitor Mount Cleveland.
"Mount Cleveland began 2018 at Aviation Color Code ORANGE and Volcano Alert Level WATCH, a response to its previous explosion on December 18, 2017, at 03:17 UTC (December 17 at 17:17 HAST). After several months without explosive activity, on February 9, 2018, AVO downgraded the Aviation Color Code and Volcano Alert Level to YELLOW and ADVISORY. The first explosion of 2018 took place on March 2 at 14:57 UTC (04:57 HAST) and was detected by AVO’s automated infrasound alarms. The acoustic amplitude of the explosion was similar to that of the previous explosion, and ground-coupled airwaves were detected as far as the Pavlof Volcano and Korovin Volcano seismic networks (747 km [464 mi] and 1,025 km [637 mi] away, respectively). A small volcanic cloud was observed in satellite data moving east-northeast shortly after the explosion. The event prompted AVO to raise the Aviation Color Code and Volcano Alert Level again to ORANGE and WATCH. After a few days with no substantial eruptive activity, on March 5, AVO downgraded the Aviation Color Code and Volcano Alert Level to YELLOW and ADVISORY.
"The next explosion took place on March 15 at 06:19 UTC (March 14 at 21:19 HADT) and was detected by the Mount Okmok infrasound array. The ground-coupled airwaves from this event were also detected by the Mount Okmok seismic network. Mount Cleveland produced another short-lived explosion on April 4 at 11:55 UTC (02:55 HADT), and possible jetting took place about 40 minutes later. In contrast to other explosions on Mount Cleveland, which typically have no notable precursory activity, a low-frequency seismic event preceded the April 4 explosion by about 19 hours. Satellite imagery taken after the explosion indicated the presence of hot material on the west flank from the summit down to the coast and a small volcanic cloud drifting at an altitude of about 19,000 ft (5,800 m) ASL. AVO upgraded the Aviation Color Code and Volcano Alert Level to ORANGE and WATCH in response to this explosion. Activity on the volcano declined after April 4, and on April 6, AVO downgraded the Aviation Color Code and Volcano Alert Level back to YELLOW and ADVISORY. Another small explosion took place on April 13 at 15:59 UTC (06:59 HADT).
"The next explosion at Mount Cleveland took place on May 5 at 06:08 UTC (May 4 at 21:08 HADT) and was detected by both the newly implemented seismic and acoustic alarms at CLES and by the previously running alarms on the CLCO infrasound array. A small volcanic cloud from the explosion, visible in satellite imagery, drifted southeast at an altitude of about 22,000 ft (6,700 m) ASL. In response to the event, AVO raised the Aviation Color Code and Volcano Alert Level to ORANGE and WATCH. After no new explosive activity, on May 6, AVO downgraded the Aviation Color Code and Volcano Alert Level back to YELLOW and ADVISORY. The event on May 5 was the last in Mount Cleveland’s first cluster of explosions in 2018.
"On June 3 and 9, two small swarms of local earthquakes took place near Mount Cleveland but did not appear to be associated with any explosive activity... Satellite imagery indicated that between June 19 and 25, a new lava dome measuring 80 m [260 ft] in diameter grew within the crater. The appearance of the dome prompted AVO to upgrade the Aviation Color Code and Volcano Alert Level to ORANGE and WATCH because the presence of lava over the active vent increased the possibility of a vent-clearing explosion. After a few months without explosive activity, on August 22, AVO downgraded the Aviation Color Code and Volcano Alert Level to YELLOW and ADVISORY.
"A data outage took place at the local monitoring station (CLES) on September 23 and persisted for the rest of the year, leaving the seismometer at the distal station (CLCO) as the only local instrumentation to supplement AVO’s remote sensing techniques.
"The second cluster of explosions to affect Mount Cleveland in 2018 began on December 10 at 08:55 UTC (December 9 at 22:55 HAST). The seismic amplitude of this first explosion, which was similar to that of previous explosions in 2018, triggered the seismic alarm at station CLCO. The seismic stations in the town of Nikolski, Alaska, and at Mount Okmok recorded ground-coupled airwaves. Satellite imagery taken after the explosion indicated that most of the summit lava dome was removed and that new debris flow deposits extended 2.6 km [1.6 mi] east-northeast of the summit. Another explosion took place on December 12 at 20:52 UTC (10:52 HAST), with an amplitude about 1.5 times larger than the previous explosion. The same day, AVO upgraded the Aviation Color Code and Volcano Alert Level to ORANGE and WATCH.
"The next explosion in the cluster took place on December 16 at 16:37 UTC (06:37 HAST). It triggered the seismic alarm and was also detected by the Mount Okmok seismic network in the form of weak, ground-coupled airwaves. This explosion was slightly larger than the previous one, producing a small ash cloud that reached an altitude of about 25,000-30,000 ft (7,600-9,100 m) ASL, possible SO2 gas emissions, and a single stroke of lightning (detected by the World Wide Lightning Location Network). Mount Cleveland produces volcanic lighting infrequently; its only other known occurrences took place in 2009 and 2014. The final explosion of Mount Cleveland in 2018 took place on December 29 at 03:17 UTC (December 28 at 17:17 HAST). A pilot weather report from after the explosion described an ash cloud reaching an altitude as high as 17,000 ft (5,200 m) ASL. Mount Cleveland remained at Aviation Color Code and Volcano Alert Level ORANGE and WATCH for the remainder of 2018."
From Orr and others, 2023: "Mount Cleveland was relatively quiet during 2019, producing only one small explosive eruption in early January. Despite the paucity of eruptions, its behavior otherwise was similar to that of previous years, with elevated surface temperatures and nearly continuous degassing from the summit that produced weak steam emissions.
"The volcano began 2019 at an Aviation Color Code and Volcano Alert Level of ORANGE and WATCH, having erupted a few days earlier on December 29, 2018. On January 7, 2019, after several days of quiescence, AVO downgraded the Aviation Color Code and Volcano Alert Level to YELLOW and ADVISORY. The volcano answered with a small explosion on January 9, recorded in local seismic and infrasound data. No associated plume was observed above the meteorological clouds, which reached an altitude of about 10,000 ft (3,000 m) ASL at the time. Later satellite imagery showed a thin tephra deposit extending southeast from the summit. AVO did not change the Aviation Color Code and Volcano Alert Level in reaction to this event.
"Satellite imagery taken on January 12 revealed the presence of a new dome 75 m [250 ft] in diameter, and by January 17, it had grown to 90 m [300 ft]. In response, AVO raised the Aviation Color Code and Volcano Alert Level to ORANGE and WATCH. The dome stopped growing soon after, and when no explosion took place, the Aviation Color Code and Volcano Alert Level were lowered back to YELLOW and ADVISORY on February 25."