Semisopochnoi volcano covered by clouds from satellite (image: Sentinel 2)
AVO reported that ash plumes below 1.5 km (5,000 ft) a.s.l. from Semisopochnoi were identified in satellite images on 14 and 17 December; ash plumes on 17 December drifted about 15 km SE. During 17-20 December seismicity was characterized by tremor bursts and small explosions, though cloudy weather conditions prevented visual confirmation.
Wed, 11 Dec 2019, 06:00
AVO reported that during 10-17 December activity at Semisopochnoi remained elevated, with bursts of tremor and small explosions detected in both seismic and infrasound data. An 80-km-long gas-and-steam plume possibly containing ash was visible in satellite images during 11-12 December. The Aviation Color Code remained at Orange and the Volcano Alert Level remained at Watch.
Read allSat, 7 Dec 2019, 15:46
Seismic signal from Semisopochnoi volcano as recorded on Adak Island (image: AVO)
An eruption is probably occurring at the volcano. The Alaska Volcano Observatory (AVO) detected seismic signals of strong volcanic tremor, probably corresponding to the arrival of magma in the summit vent, but the nature of the eruption itself is unclear:
Read allWed, 4 Dec 2019, 06:00
Strong tremor at Semisopochnoi was recorded by local seismic and regional infrasound networks beginning at 0026 on 7 December, heralding the start of an eruption and prompting AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch. The meteorological cloud deck over the volcano was at around 3 km (10,000 ft) a.s.l.; no ash signals were detected above this altitude. A period of intermittent explosions was detected, and afterwards seismicity remained elevated at least through 9 December.
Read allThu, 21 Nov 2019, 22:42
The U.S. Geological Survey Alaska Volcano Observatory (AVO) noted that weak seismicity levels continue. No eruptive activity has been detected by regional infrasound data, and no anomalous activity was observed in cloudy satellite data over the past day.
Mon, 23 Sep 2019, 05:55
Seismicity at the volcano has decreased over the past few weeks with no observations of seismic tremor since September 15.
Read allWed, 18 Sep 2019, 06:00
AVO lowered the Volcano Alert Level for Semisopochnoi to Advisory and the Aviation Color Code to Yellow on 18 September noting a decrease in seismic activity over the past few weeks and an absence of tremor since 15 September. Low-levels sulfur dioxide emissions persisted, and the crater lake continued to fill with water.
Read allWed, 4 Sep 2019, 06:00
AVO reported that low-level eruptive activity at Semisopochnoi possibly continued during 4-10 September. Seismic activity was relatively minor and characterized by intermittent low-frequency earthquakes. Satellite images were mostly cloudy, though a low-altitude steam plume drifting 50 km S was visible on 8 September.
Read allWed, 28 Aug 2019, 06:00
AVO reported that low-level eruptive activity at Semisopochnoi possibly continued during 28 August-3 September. Seismic activity was relatively minor and characterized by intermittent low-frequency earthquakes. Minor tremor was detected until 30 August.
Read allWed, 21 Aug 2019, 06:00
AVO reported that during 17-23 August seismicity at Semisopochnoi remained elevated and was characterized by periods of continuous tremor and discrete low-frequency earthquakes; seismic data went offline starting sometime on 17 August, though was available by around 22 August. Ground-coupled airwaves, indicative of explosive activity, were sometimes recorded in seismic data; an infrasound signal was recorded during 23-24 August. Cloudy weather often prevented satellite views of the volcano, though a steam plume was visible on 18 August and sulfur dioxide emissions were detected during 21-22 August.
Read allWed, 14 Aug 2019, 06:00
AVO reported that during 14-17 August seismicity at Semisopochnoi remained elevated and was characterized by periods of continuous tremor and discrete low-frequency earthquakes; seismic data became unavailable starting sometime on 17 August. Cloudy weather often prevented satellite views of the volcano, however some recent clear views indicated that the N cone crater had a smooth featureless area, indicating water or tephra at an elevation several meters below the previous floor. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.
Read allWed, 7 Aug 2019, 12:05
AVO reported that during 31 July-6 August seismicity at the volcano remained elevated and was characterized by periods of weak, continuous tremor and discrete low-frequency earthquakes. Satellite images were mostly cloudy, though a possible steam plume was visible during 5-6 August.
Read allWed, 7 Aug 2019, 06:00
AVO reported that during 7-13 August seismicity at Semisopochnoi remained elevated and was characterized by periods of continuous tremor and discrete low-frequency earthquakes. No unusual activity was observed in satellite images, though views were often cloudy. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.
Read allWed, 31 Jul 2019, 06:00
AVO reported that during 31 July-6 August seismicity at Semisopochnoi remained elevated and was characterized by periods of weak, continuous tremor and discrete low-frequency earthquakes. Satellite images were mostly cloudy, though a possible steam plume was visible during 5-6 August. The Volcano Alert Level remained at Watch and the Aviation Color Code remained at Orange.
Read allWed, 24 Jul 2019, 06:00
On 24 July AVO reported that satellite data from the previous week indicated that the 100-m-wide crater lake in the N cone of Semisopochnoi's Cerberus three-cone cluster was gone, and a new shallow inner crater about 80 m in diameter had formed on the crater floor. The lake had persisted since January 2019. Seismicity during 25-30 July was characterized by periods of continuous tremor, low-frequency earthquakes, and small explosion signals.
Read allWed, 17 Jul 2019, 06:00
AVO reported that data from local seismic and infrasound sensors likely detected a small explosion at Semisopochnoi on 16 July. No ash was visible in cloudy satellite images although none was expected from an explosion of its size. A small plume drifted 18 km from the vent but had no indication of ash.
Read allSat, 6 Jul 2019, 08:26
Yesterday, the Alaska Volcano Observatory raised the alert level of the volcano due to an increase in seismicity above background levels.
Read allWed, 3 Jul 2019, 06:00
An increase in seismicity above background levels on 4 July at Semisopochnoi prompted AVO to raise the Aviation Color Code to Orange (the second highest level on a four-color scale) and the Volcano Alert Level to Watch (the second highest level on a four-level scale). Elevated seismicity continued through at least 9 July. No eruptive activity was detected in regional infrasound data, and cloudy conditions obscured satellite views of the volcano. [Correction: the Aviation Color Code was raised to Yellow and the Volcano Alert Level was raised to Advisory.].
Read all