Alaska Volcano Observatory

Although intermittent thermal anomalies were sporadically observed in satellite images by AVO throughout 2007, on June 12, steam emissions caused a plume that extended 200 km from the volcano, and pilots reported the height as up to 12,000 feet (3650 m). Significant thermal anomalies were observed in satellite images on June 17 and 26, and AVO geoscientist interpret these as being suggestive of low-level eruptive activity. Weaker thermal anomalies were observed on July 3, 5, and 12.
On July 20, 2007, an intense thermal anomaly and associated steam/gas plume were observed at Cleveland in satellite images, prompting AVO to raise the aviation color code from YELLOW to ORANGE, and the volcano alert level to WATCH. AVO later received photographs of the event, showing small bursts of ash rising a few thousand feet above the summit. Persistent thermal anomalies were observed in satellite data for the following week. During the first week in August, they were intermittently visible, and then occasionally visible. Photographs taken on July 27 show fresh volcanic ejecta on Cleveland.
On Sunday, August 12, a pilot reported that Cleveland was not steaming and showed no signs of activity. During the following two weeks, occasional thermal anomalies were observed in satellite imagery, despite the mostly cloudy conditions
On Thursday, September 6, 2007, AVO lowered the aviation color code to YELLOW, and the volcano alert level to ADVISORY, due to the decreased intensity of the thermal anomalies.
On October 12, AVO reported that retrospective analysis of seismic data indicated an explosion at Cleveland on October 3, 2007. A thermal anomaly was detected on October 7.
On November 20, AVO observed a weak thermal anomaly near the summit of Cleveland.
On January 17, 2008, a minor ash emission was detected in satellite data. AVO estimates that the cloud height was likely less than 10,000 ft (3048 m). A weak thermal anomaly was observed at the summit in several satellite images following the ash event.
A weak thermal anomaly was again detected in satellite imagery on January 30. Although Cleveland was often obscured by clouds in early February, a break in clouds on the night of February 7 permitted a brief satellite view of a diffuse, low-level (5000 ft or less) ash plume that extended up to about 12 km southeast of the volcano. On February 8, aircraft pilots reported seeing a plume from Cleveland up to 20,000 ft. Satellite data from AVO showed a diffuse ash cloud extending northwest from the volcano.

On March 4, 2008, a pilor reported minor ash to 5,000 feet above sea level in the vicinity of Cleveland, and a weak thermal anomaly was observed the following day. Thermal anomalies continued throughout March and April, and a small, low-altitude (less than 15,000 feet) discrete ash cloud was observed in satellite images from May 7, 2008.

On Monday, July 21, 2008, fishing boats reported an eruption occurred at Cleveland at approximately 12:00 AKDT. AVO raised the color code/alert level to ORANGE and Watch. The eruption continued, with a persistent ash emission from 10,000 to 20,000 feet above sea level. Also on July 21, a strong thermal anomaly was observed in satellite images, perhaps indicative of a lava flow. By August 6, the thermal anomalies had decreased in intensity, indicating that hot flows erupted onto the upper west, south, and southeast flanks had slowed. At that time, the last ash plume observation (satellite imagery) was July 29, although visibility is often limited. AVO lowered the color code/alert level to YELLOW and Advisory on August 6.
Due to increasing thermal anomalies, AVO again raised the level of concern color code and alert level ot ORANGE and Watch on August 10, 2008. A small ash plume to 25,000 feet was observed on August 12. Eruptive activity declined, and the color code/alert level was lowered to YELLOW and Advisory on August 25.
A thermal anomaly was last noted on September 4, 2008, and AVO lowered the color code/alert level to Unassigned/Unassigned on October 9, 2008.

From McGimsey and others (2011): "Cleveland began 2007 in Aviation Color Code YELLOW and Volcano Alert Level ADVISORY following intermittent eruptive activity throughout 2006 (Neal and others, 2008b). Discussions in weekly AVO staff meetings, during January and early February 2007, on downgrading Cleveland to Aviation Color Code GREEN were interrupted by the detection of new thermal anomalies [see table 5 in original text]. Satellite data from February revealed evidence of recent activity involving ejection of bombs and debris on the upper flanks and generation of water-rich flows that travelled halfway to the coast. No ash emissions or ash fall deposits were observed. This level of activity -accompanied by persistent thermal anomalies - occurred throughout the spring and early summer. On July 20, an intense thermal anomaly (fig. 40) was accompanied by a steam and gas plume visible in satellite images [see fig. 41 in original text], and mariners in the area reported low-level ash emissions [see fig. 42 in original text]. Several small SO2 plumes were detected in Ozone Monitoring Instrument (OMI) satellite data (Dave Schneider, AVO/USGS, written commun., 2010). The ash and SO2 emissions signaled an increase in eruptive activity prompting AVO to raise the Aviation Color Code and Volcano Alert Level to ORANGE/WARNING.
"Over the next 3 weeks, thermal anomalies were observed when weather conditions allowed for clear views, but no steam or ash emissions were observed. A pilot got a close view of the summit crater on July 27 and reported evidence of recently emplaced debris including blocks rimming the crater and sulfur deposition [see fig. 43 in original text].
"A new Web camera aimed at Cleveland was installed in Nikolski, 75 km (45 mi) to the east, on August 6, but poor weather frequently precluded imaging the volcano. During the last 2 weeks of August, thermal anomalies decreased in size and intensity. The Aviation Color Code and Volcano Alert Levels were downgraded to YELLOW/WATCH on September 6 in response to the apparent waning of eruptive activity. Thermal anomalies continued to be observed, but with lower temperatures and intensities [see fig. 44 in original text].
"Retrospective analysis of seismic data from stations located on Umnak Island, and distant pressure sensors [see table 5 in original text], suggested that an explosion occurred at Cleveland on October 3, 2007. No other evidence of this activity was forthcoming. Thermal anomalies continued to be seen through mid-November, visible during the few non-cloudy satellite views. During late November and through December, no thermal anomalies or activity were reported, and Cleveland ended 2007 in Aviation Color Code/Volcano Alert Level YELLOW/ADVISORY.
"As in 2006, AVO tracked and responded to Cleveland activity in 2007 by relying heavily on remote sensing of the volcano and rapid response to reports received from pilots or other sources. Automatic PUFF runs of hypothetical ash trajectories appeared on the PUFF Website."
From Neal and others (2011): "Cleveland volcano on remote Chuginadak Island in the central Aleutians continued to produce infrequent but sudden explosions of ash in 2008 with a brief period of more vigorous activity in late July. Cleveland is unmonitored by ground-based seismic instrumentation. A web camera 73 km (45 mi) east in the community of Nikolski on Umnak Island is often obscured by weather. In an area of frequent thick cloud cover, satellite remote sensing is limited in application to reliably detect thermal anomalies and ash clouds resulting from volcanic explosions.
"Cleveland volcano began 2008 at Aviation Color Code YELLOW and Volcano Alert Level ADVISORY. Daily satellite monitoring detected an ash cloud drifting north from Cleveland in imagery on January 17; the cloud rose less than about 3 km (10,000 ft) ASL and it was visible in satellite imagery for 2 hours before dissipating. A weak thermal anomaly (TA) persisted in the summit area following this event, visible to analysts in rare, clear satellite images over the next few weeks. Another low-level (below about 1.5 km or 5,000 ft ASL) ash cloud was visible in a satellite image on February 8. Later that day, two pilot reports of volcanic ash from Cleveland reaching altitudes of 20,000 ft (6,100 m) ASL, confirmed on satellite imagery, prompted AVO to elevate the volcano to ORANGE/WATCH. With the exception of a weak, possible TA several days later, no further activity was detected and Cleveland was returned to YELLOW/ADVISORY status on February 12.
"Minor, short-lived ash explosions continued through the winter and were caught by the twice-daily routine satellite monitoring by AVO analysts or pilots on February 16, February 22, February 29, and March 4. Weak Tas seen in satellite imagery often followed these ash bursts; Tas continued to be spotted into the spring. ASTER satellite data in mid-April indicated intermittent low level activity producing ejecta and flowage deposits of very limited extent [fig. 28; imageid 14231].
"In late April and early May, the TA at Cleveland became more persistent. On May 7, an ash cloud was detected in satellite imagery and AVO received a report from the F/V Raven Bay of a dusting of ash north of the community of Nikolski. Satellite imagery detected impact craters in snow near the summit of the volcano, consistent with an explosive event. A weak TA was detected on June 8.
"No further reports of activity were received until July 21 when fishing vessels reported an explosive eruption of Cleveland about 12 p.m. Several mariners documented activity with photographs and video [figs. 29; imageid 15336, 30; imageid 15097 and 31; imageid 15373]. The ash cloud was described as moving generally northwest from the volcano but the cloud was not visible in satellite imagery, perhaps due to thick regional cloud cover. AVO declared ORANGE/WATCH based on these reports. Subsequently, pilots reported the Cleveland ash plume to be between 15,000 and 17,000 ft ASL and moving southeast from Cleveland. An AVO scientist aloft over Okmok in a USCG C-130 also observed the Cleveland ash cloud - distinctly darker than the regional meteorological clouds - approaching from the west.
"On July 22, satellite imagery showed a greater than 50 km (31 mi) long plume of gas and water vapor with some ash drifting east and southeast at an altitude of between 3 and 6 km (10,000 and 20,000 ft). A strong and persistent TA may have reflected the presence of a lava flow in the summit crater and along the upper steep portion of the volcano. A fairly continuous, weak ash plume continued at least through July 25. On July 27, satellite images showed a possible ash cloud drifting southeast with a cloud top of less than 6 km (20,000 ft). The strong TA near the summit of the volcano decreased in intensity during the first week of August and on August 6, AVO downgraded Cleveland to YELLOW/ADVISORY.
"On August 11, AVO reinstated ORANGE/WATCH because of the persistent TA interpreted to reflect effusion of lava from the summit crater. An August 12 satellite image showed a small ash cloud rising to about 25,000 ft (7,600 m) ASL and drifting southwest about 60 mi (100 km) before dissipating. Despite an intermittent thermal anomaly, AVO detected no further ash emissions and downgraded the volcano to YELLOW/ADVISORY on August 25 and to UNASSIGNED on October 9. (Note: in prior year reports, AVO has used the term 'Not Assigned' for this status).
"The volcano was relatively quiet until October 28 when an ash cloud rising to about 15,000 ft (4,600 m) ASL and drifting east was spotted in satellite imagery. On October 29, another cloud was 100 mi (160 km) long and drifting northeast at 10,000 ft (3,050 m) with little or no ash observed. A strong TA over the summit of the volcano was noted on October 30, but given the low-level nature of the recent activity, AVO did not elevate the Color Code or Alert Level.
"On December 24, after a persistent TA near the summit, AVO returned to YELLOW/ADVISORY based on the observation that ash emission events often follow a protracted and strong thermal signal. About 1 week later, on January 2, 2009, Cleveland produced a short-lived ash burst to an estimated 20,000 ft (6,000 m) ASL."
On December 23, 2008, AVO noted a persistent thermal anomaly at Cleveland and raised the volcanic alert level and the aviation color code to Advisory/Yellow on December 24. Clouds obscured satellite views of Cleveland until December 28, when a clear view showed that the December 23 anomaly persisted.
From McGimsey and others (2014): "On January 2, 2009, a brief but explosive ash emission was detected in satellite images. The plume was visible in satellite images for several hours, rose to about 20,000 ft (6 km), and drifted east-southeast up to 240 km (150 mi) downwind dispersing harmlessly over the North Pacific. Flowage deposits draped the flanks with the two largest flows (about 100 m wide; 328 ft) extending down the northeastern and northwestern flanks for at least 2 km (1.2 mi). The eruption produced airwaves that registered on seismometers on adjacent Umnak and Unalaska Islands, as well as on a pressure sensor at Shishaldin Volcano on Unimak Island. Similar airwaves were observed from the November 3, 2008 eruption of Cleveland (M. Haney, AVO/USGS, written commun., 2009, AVO internal log entry).
"No further activity was noted until the end of January when satellite images showed evidence of recent eruptive activity visible around the summit of Cleveland. Retrspective analysis on January 23 of prior satellite data indicated that a short-lived, low-level ash emission may have occurred early on the morning of January 21."