Alaska Volcano Observatory

From Cameron and others, 2023: "The 2018 eruption of Mount Veniaminof took place from early September to late December, ending a roughly 5-year repose since the end of its previous eruption in October 2013 (Dixon and others, 2015). Eruptive activity took place from a ~300-meter-high cone within the summit-defining, ice-filled caldera of Mount Veniaminof. All known historical eruptions have taken place at this cone, although only 5 of the 18 documented historical events produced lava flows.
"Seismic unrest at Mount Veniaminof began late on September 2, 2018. AVO responded on September 3 by raising the Aviation Color Code and Volcano Alert Level from GREEN and NORMAL to YELLOW and ADVISORY, and on September 4 raised them again to ORANGE and WATCH. Lava fountaining, which likely began as early as September 6, was underway by September 7. By September 14, a lava flow extended about 800 m [2600 ft] down the south flank of the summit cone. This flow eventually covered about 600,000 square meters (m2) [6.5 million square feet (ft2) or 0.23 square miles (mi2)], and intermittent ash emissions reached an altitude of 20,000 ft (6,000 m) ASL. Trace ashfall dusted nearby Perryville, Alaska, 35 km [22 mi] south of the volcano.
"More details of the 2018 eruption are published in Loewen and others (2022) and Waythomas and others (2022). Information about the 2018 eruption is derived from geophysical instrumentation on or near the volcano, including an 8-station seismic network, regional infrasound sensors, frequent satellite images of the eruption, occasional aerial photographs taken by passing pilots, and webcam images of the volcano from Perryville. Overall, eruptive activity consisted of occasional explosive emissions of ash and steam, episodes of lava fountaining, and the effusion of lava flows. Nearly continuous seismic tremor began at Mount Veniaminof late on September 2, and in response, AVO raised the Aviation Color Code from GREEN to YELLOW and the Volcano Alert Level from NORMAL to ADVISORY the next day. By the early afternoon of September 4, minor ash emissions were apparent in webcam images and were seen by observers in Perryville. This prompted AVO to raise the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH.
"Satellite imagery showed a trace amount of ashfall over the southwest sector of the caldera icefield. Webcam images obtained throughout the days of September 4-5 showed distinct, pulsatory ash emissions consistent with small Strombolian explosions. Diffuse ash emissions that reached an altitude of about 10,000-15,000 ft (3,000-4,600 m) ASL were observed by passing pilots on September 5. On September 7, incandescence was observed in early morning webcam images from Perryville, and mid-infrared satellite images showed strongly elevated surface temperatures at the intracaldera cone. These observations indicated that lava fountaining was underway by September 7, though initial lava effusion may have begun as early as September 6. Seismicity at the time was characterized by long-period events and pulsatory tremor bursts, the latter of which lasted as long as a few minutes, though it also included intermittent harmonic tremor (primarily on September 3). The tremor became more continuous around September 7.
"On September 11, a passing pilot observed and photographed several thin, ribbon-like lava flows, fed by low fountaining or spattering, on the south flank of Mount Veniaminof’s intracaldera cone and coalescing at the cone’s base. A WorldView-3 satellite image acquired on the same day showed lava erupting from as many as four small vents in the same area and feeding a lava flow covering about 50,600 m2 [545,000 ft2]. On September 16 and 18, Sentinel-2 satellite images showed definitive steam emissions associated with lava-ice interaction at the terminus of the lava flow, and on September 25, robust, vertically rising steam emissions associated with lava-ice interaction were evident in Perryville webcam images. Aerial photographs taken on September 26 confirmed that the lava flow had begun melting into the ice and snow on the south side of the intracaldera cone. Conspicuous concentric subsidence cracks grew around the periphery of the lava flow as the glacier responded to this melt-induced loss of mass.
"Sulfur dioxide emissions were detected near Mount Veniaminof on September 20, 24, and 25 by multiple satellite sensors. The volcano emitted about 500 metric tons (t) [~550 U.S. tons] of SO2 on September 25, whereas emissions detected on September 20 and 24 were barely above background levels. Regional seismic networks detected ground-coupled airwaves on September 25–27, indicating Strombolian explosions were taking place. On September 27, an infrasound array in Dillingham, Alaska (322 km [200 mi] north of the volcano), also recorded explosive signals from the volcano.
"Lava effusion characterized activity in early October and was associated with continuous tremor, nighttime incandescence, and persistent, strong thermal signals at the intracaldera cone. Measurements from the Ozone Monitoring Instruments (OMI) and the Infrared Atmospheric Sounding Interferometer (OMPS) detected sulfur dioxide emissions on October 4 and 10, but at amounts just above background levels (fig. 5). The total surface area of new lava flows by October 3, as determined from satellite data, was 184,000 m2 [about 2 million ft2].
"Visibility improved considerably on October 18 compared to the previous several weeks, allowing a webcam in Perryville to record a billowy, low-altitude ash cloud extending southeast from the intracaldera cone. Several satellites detected SO2 on October 17 and 18, with OMI measuring about 270 t [300 U.S. tons] of SO2 emitted near Mount Veniaminof on October 18. Ash emissions reached an altitude of about 20,000 ft (6,000 m) ASL on October 19, and on October 23, satellite imagery showed minor ash deposits in the summit crater. Trace ashfall was reported in Perryville on October 25. Satellite observations that day indicated that lava had covered a total area of about 385,000 m2 [about 0.15 sqaure miles (mi2)]. The volcano remained restless through the end of October, with continued lava effusion and intermittent minor ash emissions. Sulfur dioxide was again detected in satellite data on October 30 and 31, but in amounts just slightly above background levels.
"By about November 3, activity at Mount Veniaminof began transitioning to episodic emissions of more robust steam and ash clouds, which appeared in satellite and webcam data. Satellite imagery from the early morning of November 5 showed an eastdrifting ash cloud, confirmed by a pilot’s observation, extending at least 60 km [37 mi] beyond the vent and reaching a maximum altitude of about 14,000 ft (4,300 m) ASL. From November 6 to 19, satellite data and occasional webcam images showed a persistent volcanic cloud of steam and ash extending as far as about 64 km [40 mi] from the intracaldera cone at an altitude that varied from 8,000 to 12,000 ft (2,400 to 3,700 m) ASL. Satellite instruments also detected SO2 near the volcano throughout early to mid-November, though the seasonal decline in ultraviolet light made the detection and accurate estimation of atmospheric SO2 loading less certain.
"On November 19, volcanic tremor increased in amplitude to reach the highest levels that had been measured up to that point in the eruption. This increase in seismicity was accompanied by infrasound detections on an array in Dillingham, which continued for the next few days. Satellite data from November 19 indicated that lava and tephra from the eruption now covered 540,000 m2 [0.2 mi2].
"Conditions at the volcano escalated again on November 21, with increasing ash emissions and tremor amplitudes. An ash cloud detected in satellite imagery now extended more than 240 km [150 mi] southeast from the vent, reaching an altitude of at least 15,000 ft (4,600 m) ASL. This cloud was also observed from Perryville, where residents reported distinct "booming" sounds - likely explosions - coming from the direction of the volcano. The level of seismicity and the extent of the ash cloud prompted AVO to raise the Aviation Color Code and Volcano Alert Level to RED and WARNING.
"Mount Veniaminof emitted ash nearly continuously for much of November 21 as the ash cloud continued lengthening to the southeast, eventually reaching a distance of at least 400 km [250 mi] from the vent. Trace ashfall was again reported at Perryville on November 21 and 22. Activity began to decline by the late afternoon of November 21 (AKST), and on November 22, AVO lowered the Aviation Color Code and Volcano Alert Level to ORANGE and WATCH. Clear webcam views from Perryville on November 22 showed nearly continuous ash emissions extending as far as 100 km [62 mi] beyond the vent and reaching an altitude of about 10,000 ft (3,000 m) ASL. Unobstructed nighttime views showed incandescence at the summit.
"Coincident with a gradual decline in tremor amplitude, by November 25, ash emissions were no longer evident from the intracaldera cone. On November 27, however, the RSAM of volcanic tremor increased slightly, and AVO detected occasional infrasound pulses on arrays in the Alaskan cities of Dillingham, Sand Point, and Akutan. This slight increase in activity was associated with the appearance of minor ash emissions in satellite data. From November 30 to December 3, data transmission from the Mount Veniaminof remote seismic stations was interrupted, so AVO relied primarily on satellite observations and regional infrasound data to maintain surveillance. During this period, satellite data continued to show elevated surface temperatures, and small volcanic clouds were visible in some images.
"By December 6, the continuous tremor signal that had been characteristic of the eruption transitioned into frequent long-period (LP) earthquakes. This change likely indicated that lava effusion had paused or ended. Over the next several days, LP earthquakes and tremor bursts lasting as long as tens of seconds took place frequently, along with occasional harmonic tremor. A partly cloudy Sentinel-2 satellite image from December 10 showed that a light snow dusting covered parts of the intracaldera lava flows, and that only minor steam emissions continued. The weakening of seismic activity, absence of continuous tremor, and apparent cooling of the lava flows further indicated that eruptive activity had ceased.
"AVO detected many ground-coupled airwaves associated with LP earthquakes on December 11, but no other outward signs of unrest were observed in satellite or webcam imagery. This quiescence quickly changed as ash emissions from the intracaldera cone were again observed in Perryville webcam images on December 13 and 16. As cloud cover decreased over the volcano, satellite imagery again showed elevated surface temperatures, indicating a resumption in lava effusion, and also showed small volcanic clouds again extending from the intracaldera cone. This resumption of activity was accompanied by the return of the low-level, nearly continuous seismic tremor, which persisted until December 16, at which point the tremor signal ended and was replaced by many discrete, low-frequency events. Webcam images from Perryville showed minor ash emissions through December 17, after which the volcano was obscured by clouds. Satellite data confirmed that Mount Veniaminof emitted SO2 during the brief unrest in early to mid-December; additional SO2 emissions, possibly from the volcano, were also detected over the Seward Peninsula during this interval, about 966 km [600 mi] to the north.
"A Sentinel-2 satellite image acquired on December 20, 2018, showed no active lava effusion or additional advancement of the active lava flows. Slight fluctuations in seismic tremor amplitude took place from December 21 to 28, and on December 23, strong thermal signals again appeared in satellite data. From December 23 to 24, AVO observed lava-fountain-associated incandescence in webcam images. This activity was brief, however, and by December 27, all satellite, seismic, and webcam data indicated that active lava effusion had slowed, or perhaps stopped completely. From December 27, 2018, through the end of the year, the level of unrest at Mount Veniaminof gradually declined.
"By the end of the eruption, new lava flows covered 600,000 m2 [0.23 mi2] of land. This material came from a cluster of small vents on the upper south flank of a cinder cone within the ice-filled caldera. The flows melted into ice and snow, slowly creating melt depressions around their peripheries. However, no unusual water outflows were observed exiting the caldera through its main drainage, located northwest of the cone. The amount of lava and ash erupted from September 7 to December 27, 2018, resulted in the generation of about 1,200,000 cubic meters (m3 ) [42.4 million cubic feet (ft3)] of lava and 20,000-30,000 m3 [706,000-1,06,000 ft3] of ash, though no aircraft reported encountering ash throughout the eruptive period."
From Orr and others, 2023: "The activity at Mount Veniaminof during 2019 was mostly associated with a prior eruptive period that took place from early September to late December 2018 (Cameron and others, [2023]). Unrest at the volcano declined gradually after this period until it seemed likely that the eruption had paused or ended. On January 4, 2019, AVO lowered the Aviation Color Code and Volcano Alert Level from ORANGE and WATCH to YELLOW and ADVISORY.
"Satellite imagery showed slightly elevated surface temperatures on Mount Veniaminof throughout 2019, although cloud cover frequently impeded observations. The elevated surface temperatures were probably associated with the cooling of lava flows emplaced on the intracaldera cone in 2018 (Cameron and others, 2023). Minor steam emissions were occasionally visible in webcam views from nearby Perryville. Seismicity indicative of minor unrest - primarily low-amplitude tremor and discrete events - continued into April 2019 before finally declining to background levels. AVO lowered the Aviation Color Code and Volcano Alert Level to GREEN and NORMAL on April 30, 2019, after about four months with no significant unrest."