Alaska Volcano Observatory

From McGimsey and others (2014): "On July 20, AVO upgraded the Aviation Color Code/Volcano Alert Level from UNASSIGNED to YELLOW/ADVISORY after thermal anomalies were observed in satellite imagery during routine satellite monitoring on July 16-17. On August 2, the Aviation Color Code/Volcano Alert Level was upgraded to ORANGE/WATCH based on persistent thermal anomalies detected at the volcano's summit as well as satellite evidence of new lava in the summit crater on July 31.
"In 2011, Cleveland's summit crater was about 200-225 m (660-740 ft) wide at the rim; its depth varies through time with the impacts of eruptive activity, but can be as much as 80-100 m (260-330 ft). Extrusion of lava in the summit crater presumably began around the time of the onset of persistent thermal anomalies, during July 16-17; a new dome in late July 2011 was approximately 40 m (130 ft) across. Satellite images of the summit on August 3 showed the dome to be approximately 50 m (160 ft) across and no more than 20 m (65 ft) above the summit crater floor. The dome may have grown to 60 m (200 ft) across by August 6 implying an approximate lava volume of 115,000 cubic meters (150,420 cubic yards) or 7 percent of the crater's total volume of approximately 1,6 million cubic meters (2,1 million cubic yards). Satellite imagery showed no significant new tephra deposits indicating that activity from mid-July into early August was primarily extrusive. This was consistent with an August 9 WorldView-1 satellite image of Cleveland's summit showing steaming, light-colored alteration deep inside the summit crater around the new lava dome, and with oblique aerial photographs taken on August 8 by NOAA scientists.
"On August 10, AVO received a mariners report from the National Weather Service (NWS) Ocean Prediction Center of possible ash floating on the sea surface approximately 25 km (13,5 nmi) north-northwest of Cleveland. The same source reported the absence of any floating ash earlier in the day at about 30 km (16 nmi) north of the volcano. No ash clouds were detected in satellite data during the times of the these reports. Analysis of satellite data indicated that during August 6-13, the lava dome grew only slightly larger than detected in the previous image acquired August 6. Although it is possible that these accounts of drifting ash are valid, AVO was unable to confirm them.
"On August 30, AVO downgraded Cleveland's Aviation Color Code/Volcano Alert Level from ORANGE/WATCH to YELLOW/ADVISORY, based on the absence of distinct thermal signals at the summit. Satellite observations on September 6 indicated that the lava dome had grown to about 120 m (390 ft) in diameter and consistently elevated surface temperatures were again observed. As a result of these observations, AVO upgraded Cleveland to Aviation Color Code/Volcano Alert Level ORANGE/WATCH. By this time, the lava dome essentially filled the summit crater.
"TerraSAR-X satellite radar images from the German Remote Sensing Data Center (DFD) and the German Aerospace Center (DLR), acquired over Cleveland volcano from August to November 2011, provided an image time series showing the partial growth of the 2011 lava dome in the summit crater.
"The lava dome continued to grow through late September, expanding in diameter from approximately 120 m (390 ft) on September 6 to approximately 168 m (550 ft) by September 20, and reaching a height approximately 15-20 m (50-60 ft) below the crater rim by September 26. Additional growth of the lava dome past October 20 was minor.
"Extrusion of lava either slowed or ceased between October 1 and October 5. Satellite data from October 9 indicated that the central portion of the lava dome became slightly depressed, indicating minor deflation of th edome. Subsidence of the dome continued into late October.
"AVO downgraded Cleveland's Aviation Color Code/Volcano Alert Level from ORANGE/WATCH to YELLOW/ADVISORY on November 3 based on the absence of consistent thermal anomalies in satellite images and apparent cessation of lava effusion after October 9.
"On November 10, satellite images showed that a small secondary dome had emerged atop the center of the semi-deflated lava dome. The diameter of this new dome was approximately 15-20 m (50-65 ft) and it likely began to grown on or before November 2. The original dome remained unchanged in size.
"Lava within the summit crater remained mostly unchanged from November 10 to November 24. A satellite image from November 25 showed that the small secondary dome had subsided into a broad blocky, hummocky depression approximately 70 m (230 ft) in diameter and the overall dome had subsided approximately 30 - 35 m (100-115 ft) from its maximum elevation in early October. The dome continued to subside into early December, and by December 7, nearly the entire extrusive feature had collapsed into the conduit and its surface was approaching the pre-August crater-floor elevation.
"On December 29 at approximately 04:12:07 AKST (13:12:07 UTC), an explosion from Cleveland produced a small ash cloud that rose to approximately 3.5 km(11,500 ft) ASL. The ash cloud drifted to the east and over the southwestern tip of Umnak Island. The eruption triggered two operational ash alarms used by AVO. The first alarm was triggered at approximately 05:33 AKST (14:33 UTC) indicating likely ash signatures in NOAA's AVHRR satellite image n19.11363.1402. A NOAA-NESDIS ash cloud alarm was triggered at approximately 05:34 AKST (14:34 UTC) from the same AVHRR satellite image. Calculations based on the satellite data and local meterologic conditions indicated a maximum ash cloud height of 3.5 km (11,500 ft) ASL, with a mean effective ash particle radius of 5.06 microns (1,99 x 10^-4 in.), a total mass of 0.84 kt (925 tons), and a total area of 173 square km (66.8 square miles) (M. Pavolonis, written commun., December 29, 2011).
"In response to the ash cloud, AVO upgraded the Aviation Color Code/Volcano Alert Level from YELLOW/ADVISORY to ORANGE/WATCH at 07:55 ASKT (16:55 UTC) on December 29, 2011.
"Infrasound signals from the December 29 explosion were first detected on seismic stations and infrasound arrays deployed at Okmok volcano, located approximately 139 km (90 mi) northeast of Cleveland on Umnak Island. Infrasonic waves are sound waves that span a frequency range from below 20 Hz (the lower limit of human hearing) to 0.001 Hz. Infrasound signals are recorded at seismic stations by the infrasound airwaves coupling with the ground at seismic station(s) and mechanically vibrating the ground in which the seismometer sits. The recorded seismic signal is known as a ground-coupled airwave produced by a volcanic explosion or eruption. Based on the speed of sound in Earth's atmosphere and the distance between seismic station OKWE and the summit of Cleveland the origin time of the explosion was calculated at approximately 04:12:04 AKDT (13:12:07 UTC) (Matt Haney, David Fee, and Silvio de Angelis, UAFGI, written commun., December 29, 2011).
"AVO downgraded the Aviation Color Code/Volcano Alert Level for Cleveland volcano from ORANGE/WATCH to YELLOW/ADVISORY at 13:57 AKST (22:57 UTC) on December 29 following no additional reports of eruptive activity occurring at the volcano. Cleveland remained at Aviation Color Code/Volcano Alert Level YELLOW/ADVISORY throughout the remainder of 2011.
"A review of the infrasound data prior to the December 29 explosion revealed several small explosive eruptions from Cleveland volcano on December 25. The first occurred at approximately 03:13 AKST (12:13 UTC) and had an infrasound amplitude of approximately one-half the December 29 event. The second eruption occurred on December 25 at approximately 06:32 AKST (15:32 UTC).
"A small ash cloud was retrospectively detected in satellite imagery for the December 25 event. The eruption cloud was very minor, did not have a large ash signal at the image's collection time of 06:32 AKST (15:32 UTC), and was only weakly visible in a thermal infrared image. The cloud had dissipated by the time the next image was acquired at 06:46 AKST (15:46 UTC).
"Satellite data from December 26 displayed evidence of ejected blocks that had rolled down the upper northern and western flanks of the volcano, some as far as about 1.5 km (5,000 ft) from the crater's rim. There was no indication of fresh ash deposits on the volcano's upper northern and western flanks."
From Herrick and others (2014): "On January 30, a new lobe of lava about 40 m (130 ft) across was detected at the bottom of the summit crater. On January 31, the Aviation Color Code and Volcano Alert Level was upgraded to ORANGE/WATCH due to the presence of this small lava flow and the increased potential for explosive dome destruction.
"On February 3, satellite data showed no significant change within the summit crater. By February 7, the dome had grown to about 50 m (160 ft) across and 1 week later, 60 m (200 ft). On February 22, additional new lava had broken the surface of the dome producing a 20-m-diameter (66-ft) lobe atop the existing lava pad. Evidence of continued effusion was reported through the end of February and slightly elevated temperatures were reported during clear conditions.
"Three explosions occurred from the Cleveland summit crater in the first 2 weeks of March; the March 8 explosion produced a small ash cloud that dissipated quickly. Details of how much of the new lava dome was destroyed in each explosion are unknown, but by March 11, it was entirely removed. Cloudy conditions prevailed and ash emissions that may have been produced after March 8 went unnoticed. On March 23, the Aviation Color Code and Volcano Alert Level was downgraded to YELLOW/ADVISORY based on the lack of evidence of renewed lava effusion.
"On March 26, a new lava flow about 70 m (230 ft) across was detected within the crater. On March 28, the Aviation Color Code and Volcano Alert Level was upgraded to ORANGE/WATCH. By April 4, the dome was gone, likely removed in an explosion at about 09:12 UTC on April 4. Subsequent satellite images showed that large blocks, 15-20 m (50-65 ft) across, littered the crater floor. Four additional explosions occurred between April 7 and April 19 during a period of frequently elevated temperatures detected in satellite images. No unequivocal ash clouds were detected following each event; however, weather and satellite overpass timing could have played a role. The AVO Web camera was not functioning during this time.
"Elevated surface temperatures persisted through April and into May. By April 25, a new dome had appeared in the crater, only to be destroyed sometime before April 29. An ambiguous seismic event had been recorded by the Makushin network at 16:14 UTC on April 29. It may have been related to the dome’s demise, but this remains inconclusive (M. Haney, USGS/AVO, written commun., November 2013). On May 3, the third detected lava flow of 2012 was observed in the crater forming a dome about 25 m (82 ft) in diameter.
"Explosions occurred on May 4 and 5, but no ash cloud or strong thermal signal was noted for either event. Satellite observations on May 6 showed that the May 3 lava dome was gone, presumably destroyed during the May 4-5 explosions. After 3 weeks with no further explosions and only rare instances of elevated surface temperature, the Aviation Color Code and Volcano Alert Level was downgraded to YELLOW/ADVISORY on May 30. An AVO staff member flying near Cleveland noted white steam rising from the crater.
"Cleveland remained at YELLOW/ADVISORY despite the detection of another explosion by infrasound on June 4. Only minor tephra and possibly flowage deposits were noted on a June 9 satellite image. On June 19, an explosion produced an ash cloud seen by a pilot, and the cloud also was captured on the AVO Web camera and detected by infrasound. The pilot estimated the cloud height to be 35,000 ft (11 km) ASL. Following detection of the explosion and confirmation of a high ash cloud, AVO upgraded the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH.
"Several more explosions occurred in late June, July, August, and November; all were detected either on infrasound networks or distant seismic stations. Three of these produced small ash clouds detected by satellite images and one by the AVO Web camera. Satellite observations of the volcano documented minor changes in the summit crater but no additional, intact lava flows were noted through the end of 2012."
From Dixon and others (2015): "Early in 2013, a faint white steam cloud emanating from the summit crater was occasionally seen in satellite images. On January 30, 2013, after more than a week of consistently elevated temperatures in AVHRR images, satellite observations indicated a new lava flow inside the summit crater (table 8 in original text). Extrusion began sometime after January 7, when clear satellite images showed no lava in the crater, and before the January 30 satellite image showing a new lava flow. The round dome-like feature was about 100 m across. Significantly elevated temperatures continued in satellite images, visible even in fairly cloudy conditions. By February 9, a second lava extrusion 25 m (82 ft) across was perched across the late January dome. After learning of the existence of new lava in the summit crater, AVO upgraded the Aviation Color Code and Volcano Alert Level on February 6 to ORANGE/WATCH. AVO downgraded to YELLOW/ADVISORY on March 8 after no further escalation of activity."