A small steam plume is visible within from the North Crater of Cerberus at Semisopochnoi Volcano in this Planet image, June 2, 2020. No tephra deposits are visible.

A small steam plume is visible within from the North Crater of Cerberus at Semisopochnoi Volcano in this Planet image, June 2, 2020. No tephra deposits are visible.

Date: Jun 2nd, 2020
Volcano(es): Semisopochnoi
Photographer: Dietterich, Hannah
URL: avo.alaska.edu/image/view/159341

Semisopochnoi 2019/7

From Orr and others, 2023: "Activity at the north cone of Mount Young, which began in September 2018, continued in 2019 with sporadic eruptive activity. Seismic tremor and explosion signals captured most of this activity, along with infrequent infrasound detections and occasional satellite observations of steam and small ash deposits. Although the eruptive style and geophysical characteristics of the 2019 unrest were similar to those of 2018, AVO’s ability to observe them in real time was limited for the first half of the year owing to a prolonged data outage. This outage, caused by a communication failure at the regional data network telemetry hub in Amchitka, lasted from November 2018 to June 2019, at which point communications were restored and the missing data were recovered.
"Owing to the data outage, the first activity observed at the volcano in 2019 comprised satellite observations of steam in January and a small ash deposit on June 2. Although the north crater of Mount Young has persistently steamed since 2018, the ash deposits observed on June 2 appear to be a more recent change, having followed tremor bursts in mid-May that probably correspond to when they erupted. AVO began receiving seismic data again on June 11 but kept the Aviation Color Code and Volcano Alert Level at UNASSIGNED until early July, when increased tremor prompted a change to YELLOW and ADVISORY. On July 18, the detection of SO2 emissions in TROPOMI satellite data and the recording of ground-coupled airwaves triggered AVO to raise the Aviation Color Code and Volcano Alert Level to ORANGE and WATCH. SO2, steam plumes, ground-coupled airwaves, and infrasound were detected throughout the summer, but no ash deposits were observed. After a period of quiescence, AVO lowered the Aviation Color Code and Volcano Alert Level to YELLOW and ADVISORY on September 18.
"Beginning on December 7, the detection of many explosions by regional infrasound sensors indicated a renewal of activity at Semisopochnoi Island, triggering AVO to raise the Aviation Color Code and Volcano Alert Level to ORANGE and WATCH. In addition to producing infrasound, the explosions were accompanied by ash emissions visible in satellite imagery, ground-coupled airwaves, and one SO2 detection (on December 12). No ash plumes reaching altitudes greater than 10,000 ft (3,000 m) ASL and no large ash deposits were observed during this eruptive period. The last activity recorded at the volcano in 2019 was an infrasound detection on December 18. On January 9, 2020, AVO lowered the Aviation Color Code and Volcano Alert Level back to YELLOW and ADVISORY."
On February 15, 2020, AVO again detected a series of small explosion bursts from seismic data, and raised the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH. Although seismic activity remained above background, clear satellite views of Semisopochnoi on February 25, 2020, showed no signs of eruptive activity and AVO lowered the Aviation Color Code and Volcano Alert Level to YELLOW/ADVISORY on February 26, 2020. Seismic unrest continued, and by March 15 was characterized by nearly continuous tremor and frequent small explosion signals. AVO raised the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH. Small explosions continued for several days, and clear satellite images showed a robust steam plume and minor ash deposits around North Cerebus' crater rim. Activity has since subsided. No explosions have been recorded since March 17, 2020, and no surface activity has been seen in satellite data, though the volcano was mostly obscured by clouds. On April 1, 2020, citing no further signs of eruptive activity at Semisopochnoi in the past two weeks, AVO lowered the Aviation Color Code and Volcano Alert Level to YELLOW/ADVISORY. Seismicity was at low levels, characterized by occasional small earthquakes. In early April, a robust steam and gas plume containing detectable sulfur dioxide was seen in satellite data.
Unrest continued at Semisopochnoi throughout the summer of 2020. In June, there were periods of moderate seismic tremor, at times accompanied by ground-coupled airwaves. In mid-June, high-resolution satellite images showed steaming from the North Cerebus crater, along with a light ash deposit near the crater. Periods of seismic tremor and observed sulfur-dioxide plumes continued to be observed in June and July. Seismicity declined in August, 2020, and remained low through the fall. On November 20, 2020, citing no eruptive activity since mid-June, AVO lowered the Aviation Color Code and Volcano Alert Level to UNASSIGNED, because AVO's satellite link for transmitting data failed on November 11,

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