Global Volcanism Program

Most Recent Weekly Report: 29 November-5 December 2023 Cite this Report

AVO reported that slow lava effusion continued at the summit crater of Great Sitkin during 29 November-5 December. Seismicity was low. Satellite radar data during 29-30 November showed radial cracks on the lava flow surface due to local uplift of lava above the vent and indicated that lava continued to flow E towards the intra-crater glacier. Weakly elevated surface temperatures and steam emissions were possibly observed in satellite data and webcam images, respectively, during 1-2 December. Weather clouds on other days often blocked views of the summit. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

Most Recent Bulletin Report: May 2023 (BGVN 48:05) Cite this Report

Continued slow lava effusion in the summit crater during November 2022-April 2023

Following minor explosive activity at Great Sitkin in June-August 2018 and June 2019, the first eruptions since 1974, an ash explosion on 25 May 2021 preceded the growth of a lava dome in the summit crater starting in mid-July. Continued lava effusion overtopped the summit crater wall and flowed down the N, S, and W flanks (BGVN 46:08, 47:05). This activity waned during January-April 2022, although slow lava effusion continued through October 2022. Since 23 July 2021, the Volcano Alert Level has remained at Watch (the second highest on a four-level scale) and the Aviation Color Code remained at Orange (the second highest on a four-color scale). This volcano in the central Aleutian Islands is monitored by the Alaska Volcano Observatory (AVO) using local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.

AVO reported that slow lava effusion within the summit crater, centered about 1.5 km E of the peak and 300 m lower, continued during November 2022-April 2023. Weather clouds usually obscured satellite and webcam observations. Elevated surface temperatures were sometimes identified in satellite images, and occasional steam plumes were observed rising from the lava flow. Seismicity was low with occasional detection of weak earthquakes.

By the end of the first week of November (figure 24), the flow field had extended more than 600 m E and about 430 m S from the vent into the remaining crater icefield. By the end of November, satellite images showed that the lobes had advanced an additional 25-30 m along the S edge of the flow field and about 15 m SE. The E lobe continued to advance slowly during December-April, while a smaller lobe to the S advanced towards the crater rim, burying an earlier lava flow. A satellite radar image on 2 April showed that the lava flow was primarily expanding E and more slowly S into the summit crater ice field, as seen in visual imagery on 5 April (figure 25).

Figure 24. Sentinel-2 satellite image of Great Sitkin on 4 November 2022 showing a hotspot and cooled lava flows from July 2021-June 2022 in the summit crater; the peak is to the right. Image uses “Geology” rendering (bands 12, 4, 2). Courtesy of Sentinel Hub Playground.

Figure 25. WorldView-3 near-IR satellite image of Great Sitkin on 5 April 2023. The lava flows from July 2021-June 2022 are partially snow-covered while the dark area is a more recent overtopping flow. Courtesy of Mathew Loewen, AVO.

Weekly Reports - Index

29 November-5 December 2023 Cite this Report

Source: US Geological Survey Alaska Volcano Observatory (AVO)

22 November-28 November 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 22-28 November characterized by a thick flow in the summit crater that mainly expanded E. Seismicity was low. Weakly elevated surface temperatures were identified in satellite imagery during 24-25 November. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

15 November-21 November 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 15-21 November, confirmed at least through 16 November by a radar image. The thick flow in the summit crater mainly expanded E. Seismicity was low. Steam emissions were visible in satellite and webcam images during 18-19 November. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

8 November-14 November 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 8-14 November. Views of the summit were obscured by weather clouds during most days; however, satellite radar observations on 8 November indicated continued surface growth concentrated on the E area of the summit lava flow. Seismicity was low with only a few local earthquakes recorded by the seismic network during the week. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

1 November-7 November 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 1-7 November, producing a thick flow in the summit crater that mainly expanded E. Seismicity was low with only a few earthquakes recorded by the seismic network during the week. Weakly elevated surface temperatures were identified in satellite data during 3-4 November. Weather clouds sometimes obscured views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

25 October-31 October 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 25-31 October, producing a thick flow in the summit crater that mainly expanded E. Seismicity was characterized as low with only a few daily earthquakes recorded by the seismic network. Weakly elevated surface temperatures were identified in satellite data during 24-27 October, indicative of the eruption of lava. Weather clouds sometimes obscured views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

18 October-24 October 2023 Cite this Report

AVO reported that slow lava effusion at Great Sitkin was confirmed in satellite radar data on 17 October and likely continued during 18-24 October. A thick lava flow in the summit crater mainly expanded E. Seismicity was low and only a couple of earthquakes were detected during 17-19 October. Weather clouds sometimes obscured satellite and webcam views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

11 October-17 October 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 10-17 October and was confirmed by radar data on 15 October. A thick flow in the summit crater mainly expanded E. Weakly elevated surface temperatures were identified in satellite data during 10-11 October. Seismicity was low and only a couple of earthquakes were detected during 15-16 October. Weather clouds often obscured satellite and webcam views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

4 October-10 October 2023 Cite this Report

AVO reported that slow lava effusion at Great Sitkin was confirmed by a radar image from 3 October and likely continued through 10 October. Seismicity was characterized as low, with only a few daily earthquakes recorded by the seismic network during 3-7 October. Weakly elevated surface temperatures were identified in satellite data during 8-10 October. Weather clouds sometimes obscured views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

27 September-3 October 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 27 September-3 October, producing a thick flow in the summit crater that mainly expanded E. Seismicity was characterized as low with only a few daily earthquakes recorded by the seismic network. Weakly elevated surface temperatures were identified in satellite data during 2-3 October. Weather clouds sometimes obscured views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

20 September-26 September 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 19-26 September, producing a thick flow in the summit crater that mainly expanded E. Seismicity was characterized as low with only a few daily earthquakes recorded by the seismic network during 24-25 September. Elevated surface temperatures and minor steaming were visible in webcam and satellite images on a few of the days; weather clouds sometimes obscured views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

13 September-19 September 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 13-19 September, producing a thick flow in the summit crater that mainly expanded E. A few daily earthquakes were recorded by the seismic network and seismicity was characterized as low. Weather clouds often prevented satellite and webcam observations, though no activity was observed on a few of the days with partly cloudy weather. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

6 September-12 September 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 6-12 September, producing a thick flow in the summit crater that mainly expanded E. Seismicity was low; earthquakes were detected daily and were numerous during 6-7 September. Web camera images showed diffuse gas emissions rising from the summit during 6-7 September and weakly elevated surface temperatures were identified in satellite data during 6-7 and 10-11 September. Weather clouds often prevented satellite and webcam observations. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

30 August-5 September 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 30 August-5 September, producing a thick flow in the summit crater that expanded E, based on a satellite image from 30 August and fieldwork. Seismicity was low; two earthquakes were detected during 2-4 September and five were recorded during 4-5 September. An AVO field geology team visited the volcano on 1 September and sampled the lava flow, did airborne photography and thermal imaging surveys, and measured gas emissions. During a visit on 3 September the team observed that the flows were warm and steaming, moving about 1 m every 3-4 days. Weakly elevated surface temperatures were identified in satellite data during 4-5 September. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

23 August-29 August 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 23-29 August, producing a thick flow in the summit crater. Seismicity remained slightly elevated throughout the week. Weather clouds often obscured satellite and webcam views, though slightly elevated surface temperatures and steaming from the lava flow were visible during 22-23 August. Steaming from the flow was again visible on 28 August. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

16 August-22 August 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 16-22 August, producing a thick flow in the summit crater. Seismicity remained slightly elevated throughout the week. Weather clouds often obscured satellite and webcam views, though strongly elevated surface temperatures were visible during 21-22 August. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

9 August-15 August 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 9-15 August, producing a thick flow in the summit crater. The eastern lobe continued to advance into glacial ice surrounding the crater, causing the ice to deform and crack, based on a 10 August satellite image. Seismicity remained slightly elevated throughout the week. Weather clouds often obscured satellite and webcam views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

2 August-8 August 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 1-8 August, producing a thick flow in the summit crater. The eastern lobe continued to advance into glacial ice surrounding the crater, causing the ice to deform and crack, based on a 1 August satellite image. Seismicity remained slightly elevated throughout the week. Weather clouds often obscured satellite and webcam views, though a clear image showed no unusual activity during 5-6 August and an image showed diffuse steaming from the lava surface during 6-7 August. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

26 July-1 August 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 26 July through 1 August, producing a thick lava flow in the summit crater. Seismicity remained slightly elevated throughout the week. Weather clouds often obscured satellite and webcam views, though a clear image from 29 July showed moderate steaming from the lava surface. During 27 and 29 July weakly elevated surface temperatures were observed in satellite data that was consistent with cooling lava. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

19 July-25 July 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 19-25 July, producing a thick lava flow in the summit crater. About 10-20 daily local earthquakes were recorded by the seismic network during 19-23 July, and about 20 low-frequency seismic events were detected during 21-22 July. Weather clouds often obscured satellite and webcam views, though a clear image from 19 July showed minor steaming from the lava surface and minimal change to the overall lava flow extent. Minor steaming was again visible in satellite images during 22-24 July. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

12 July-18 July 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 12-18 July; continuing effusion was last confirmed by satellite images on 8 July. Several daily local earthquakes were recorded by the seismic network. Weather clouds obscured satellite and webcam views. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

5 July-11 July 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 5-11 July. Several local earthquakes were recorded daily during 6-11 July. Minor degassing was observed in satellite data on 6 July and in webcam images during 10-11 July. Weather clouds obscured satellite and webcam views on other days. Elevated surface temperatures at the summit were identified in satellite images during 10-11 July. The Volcano Alert Level remained at Watch (the third level on a four-level scale) and the Aviation Color Code remained at Orange (the third color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

28 June-4 July 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 27 June-4 July. Periodic radar images confirmed that the flow field expanded to the east within the summit crater. Minor seismicity was ongoing, and a few daily small earthquakes were recorded. Elevated surface temperatures were identified in satellite images during 27-28 June and 1-2 July and minor steaming was visible in satellite and webcam views during 1-3 July; weather clouds sometimes obscured webcam and satellite views on the other days. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

21 June-27 June 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 20-26 June. Minor seismicity was ongoing, and a few small earthquakes were recorded during 25-26 June. Elevated surface temperatures were identified in satellite images during 20-21 June and minor steaming was visible in satellite and webcam views during 25-27 June; weather clouds sometimes obscured webcam and satellite views on the other days. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

14 June-20 June 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 14-20 June. The thick lava flow remained confined to the summit crater, and several small earthquakes were recorded daily. Elevated surface temperatures were observed during periods of clear satellite views during 16-17 June; weather clouds obscured webcam and satellite views on the other days. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

7 June-13 June 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 6-13 June, producing a thick lava flow confined to the summit crater. Seismicity remained low. Steam emissions were visible in satellite images during 7-8 June and slightly elevated surface temperatures were identified on 8 June; weather clouds prevented satellite and webcam observations on the other days. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

31 May-6 June 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 30 May-6 June producing a thick lava flow confined to the summit crater. Seismicity remained low; a few local earthquakes were recorded daily. Slightly elevated surface temperatures were identified in satellite images during 30-31 May and 3-4 June. Satellite data during 5-6 June confirmed that the flow was expanding E. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

24 May-30 May 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 23-30 May. A sequence of small low-frequency earthquakes was recorded for several hours on 23 May but did not result in any observed change in eruptive activity. Several small earthquakes were recorded daily during 24-27 May. No changes to the flow field were identified in satellite images acquired on 23, 27, or 28 May. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

17 May-23 May 2023 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 16-23 May. Satellite data acquired on 16 May showed that the thick lava continued to expand towards the E but remained confined to the summit crater. Elevated surface temperatures were identified in satellite images during 18 and 21-23 May. Seismicity was low with some variations; five small earthquakes occurred during 19-20 May and small low-frequency earthquakes that began at 1000 on 23 May were ongoing at least through 1206. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

10 May-16 May 2023 Cite this Report

AVO reported that lava likely continued to erupt at the summit of Great Sitkin during 9-16 May. Satellite data acquired on 11 May showed that the thick lava continued to expand towards the E but remained confined to the summit crater. Seismicity was low. Nothing significant was seen in satellite and webcam images during most of the week due to persistent weather clouds obscuring views. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

3 May-9 May 2023 Cite this Report

AVO reported that lava continued to erupt at the summit of Great Sitkin during 2-9 May. Satellite data acquired on 5 May showed that the thick lava continued to expand towards the E but remained confined to the summit crater. Seismicity was low, and during 7-8 May only a few small events were detected. Nothing significant was seen in satellite and webcam images during most of the week, though sometimes weather clouds obscured views. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

26 April-2 May 2023 Cite this Report

AVO reported that lava continued to slowly erupt at the summit of Great Sitkin during 26 April-2 May. Weather clouds obscured satellite and webcam views during most of the week. Seismicity was low, and during 27-28 April only a few small events were detected. Satellite data last acquired up to 24 April showed that the thick lava continued to expand toward the E and remained confined to the summit crater. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

19 April-25 April 2023 Cite this Report

AVO reported that lava continued to slowly erupt at the summit of Great Sitkin during 19-25 April. Weather clouds often obscured satellite and webcam views during most of the week. Seismicity was low, and during 21-22 April only a few small events were detected. Satellite data last acquired on 14 April showed that the thick lava continued to expand towards the E and remained confined to the summit crater. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

12 April-18 April 2023 Cite this Report

AVO reported that lava continued to slowly erupt at the summit of Great Sitkin during 11-17 April, producing a thick lava flow that expanded mostly to the E. Seismicity was low, and during 11-13 April only a few small events were detected. Elevated surface temperatures were identified in satellite images during 16-17 April, and steam emissions were visible in webcam views during 17-18 April. Weather clouds often obscured satellite and webcam views during most of the week. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

5 April-11 April 2023 Cite this Report

AVO reported that lava likely continued to slowly effuse at the summit of Great Sitkin during 5-11 April, producing a thick lava flow. Seismicity was low, and during 9-10 April only a few events were detected. A satellite radar image on 2 April showed that the lava flow was mostly expanding to the E and slowly to the S into the summit crater ice field. Elevated surface temperatures were identified in satellite images during 4-6 April. Weather clouds obscured views during 7-10 April. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

29 March-4 April 2023 Cite this Report

AVO reported that lava likely continued to slowly effuse at the summit of Great Sitkin during 29 March-4 April, producing a thick lava flow. Minor earthquakes and seismic events were noted during 1-2 April. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

22 March-28 March 2023 Cite this Report

AVO reported that a 23 March satellite image confirmed that lava continued to slowly erupt at the summit of Great Sitkin, producing a thick lava flow. The flow advanced to the E and likely continued to be fed through 28 March. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

15 March-21 March 2023 Cite this Report

AVO reported that eruptive activity at Great Sitkin continued during 15-21 March, characterized by the eruption of lava that was confined to the summit crater. Radar data from 20 March confirmed slow growth of the lava flow. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

8 March-14 March 2023 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 8-14 March. Satellite images and web camera views were mostly cloudy, though elevated surface temperatures were identified in satellite images during 8-9 March. Seismicity was low. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

1 March-7 March 2023 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 1-7 March. Satellite images and web camera views were cloudy. Seismicity was low. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

22 February-28 February 2023 Cite this Report

AVO reported that slow lava effusion at Great Sitkin was confirmed by recent satellite images. A radar image from 19 February showed advancement of the E lobe of the flow field. Additionally, a smaller lobe to the S was advancing towards the crater rim where lava previously spilled down the SW flank in 2021-2022. Lava effusion in the summit crater was visible in 24 and 26 February satellite images. Seismicity was very low 22-28 February with a few local earthquakes detected during 22-23 and 24-25 February. Weather cloud cover sometimes prevented webcam and satellite views. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

15 February-21 February 2023 Cite this Report

AVO reported that a 15 February satellite image confirmed continuing lava effusion at Great Sitkin and growth of the flow field to the E, though effusion likely continued through 20 February. Weather clouds often obscured satellite and webcam views; steam emissions were observed during 17-18 February and weakly elevated surface temperatures were identified in satellite images during 19-20 February. Seismicity was very low during 21-22 February with one small local earthquake detected. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

8 February-14 February 2023 Cite this Report

AVO reported that a 6 February satellite image confirmed continuing lava effusion at Great Sitkin and growth of the flow field to the E; effusion likely continued during 7-14 February. Weather clouds often obscured satellite and webcam views, though steam emissions were observed during 8 and 11-12 February. Seismicity was low most of the week; a network outage began at 2120 on 12 February and prevented transmission of seismic data. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

1 February-7 February 2023 Cite this Report

AVO reported that seismicity at Great Sitkin was low during 1-7 February. No activity was observed, though weather clouds obscured satellite and webcam views. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

25 January-31 January 2023 Cite this Report

AVO reported that slightly elevated surface temperatures at Great Sitkin were identified in satellite images during 25-26 January. Seismicity was low during 25-31 January and a few small earthquakes recorded during 27-28 January. Satellite and webcam views were mostly cloudy. A 26 January radar image confirmed growth of the flow field to the E. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

18 January-24 January 2023 Cite this Report

AVO reported that slightly elevated surface temperatures at Great Sitkin were identified in satellite images on 18 January, suggesting continuing lava effusion at a low rate primarily to the S and E. A few small earthquakes were detected on most days by the local seismic network. No activity was observed in mostly cloudy satellite and web camera images during 19-24 January. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

11 January-17 January 2023 Cite this Report

AVO reported that radar images acquired on 13 and 15 January confirmed ongoing slow lava effusion at Great Sitkin; effusion likely continued through 17 January. Slightly elevated surface temperatures were identified in satellite images during 10-11 January and a few small earthquakes were detected on most days during 10-17 January. Weather clouds sometimes obscured satellite and webcam views. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

4 January-10 January 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 4-10 January, though weather clouds often obscured satellite and webcam views. A few small daily earthquakes were detected during 6-10 January and slightly elevated surface temperatures were identified in satellite images during 7-10 January. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

28 December-3 January 2023 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 28 December 2022-3 January 2023, though weather clouds mostly obscured satellite and webcam views. In general, a few small daily local earthquakes were recorded, though there were many during 1-2 January. A large steam plume was seen rising from the lava flow on 29 December and slightly elevated surface temperatures were identified in satellite images during 2-3 January. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

21 December-27 December 2022 Cite this Report

AVO reported that satellite data acquired on 22 December confirmed that the lava flow field at Great Sitkin was advancing E. Slow lava effusion likely continued during 23-27 December, though nothing significant was visible in sometimes cloudy satellite images or detected in seismic data. Elevated surface temperatures were identified in satellite images during 21-23 and 25-27 December. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

14 December-20 December 2022 Cite this Report

AVO reported that slow lava effusion likely continued at Great Sitkin during 13-20 December, though satellite and webcam observations were mostly obscured by clouds. Nothing notable was observed in clear webcam and satellite views during 19-20 December. No significant seismic activity was detected. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

7 December-13 December 2022 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 27 November-11 December based on satellite images. Cloud cover mostly prevented satellite and webcam observations during 7-12 December. Seismicity remained at low levels. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

30 November-6 December 2022 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 30 Novmeber-6 December. Lobes of lava advanced an additional 25-30 m along the S edge of the flow field and about 15 m SE, based on 25 November satellite images. Cloud cover prevented satellite and webcam observations during 30 Novmeber-6 December. Seismicity remained at low levels. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

23 November-29 November 2022 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 23-29 November and the flow field continued to grow. Elevated surface temperatures were identified in satellite images during 27-29 November. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

16 November-22 November 2022 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 15-22 November and the flow field continued to grow. Flow lobes extended about 600 m E of the vent and about 430 m S. Seismicity was low, with the occasional detection of low-frequency earthquakes. Satellite and webcam images were often cloudy through the week. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

9 November-15 November 2022 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 9-15 November and seismicity was low. Satellite images were often cloudy, though elevated surface temperatures were identified on 9, 13, and 15 November. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

2 November-8 November 2022 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 2-8 November and seismicity was low. Satellite images were often cloudy, though elevated surface temperatures were identified almost daily. The flow field continued to grow, with lobes of lava extending more than 600 m E and around 430 m S. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

26 October-1 November 2022 Cite this Report

AVO reported that seismicity at Great Sitkin was very low during 25 October-1 November and nothing significant was seen in partly cloudy satellite or web camera views. Lava effusion likely continued. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

19 October-25 October 2022 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 19-25 October along with low levels of seismicity. Slightly elevated surface temperatures were identified in satellite images during 21-22 October. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

12 October-18 October 2022 Cite this Report

AVO reported that slow lava effusion continued at Great Sitkin during 11-18 October. Satellite images were mostly cloudy, though continued slow growth of the flow field and steaming from a new flow margin were identified in satellite images on 12 October. Seismicity remained at low levels. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

5 October-11 October 2022 Cite this Report

AVO reported that continuing slow lava effusion at Great Sitkin was confirmed by a 5 October satellite image and likely continued during 6-11 October. Seismicity remained at low levels, though it slightly increased during 5-6 October. Elevated surface temperatures were identified during 4-8 October; weather clouds prevented webcam and satellite views during 8-11 October. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

28 September-4 October 2022 Cite this Report

AVO reported that continuing slow lava effusion at Great Sitkin was confirmed by a 27 September satellite image and likely continued during 28 September-4 October. Elevated surface temperatures were identified during 28-29 September; weather clouds often prevented webcam and satellite views during the rest of the week. Seismicity remained at low levels. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)

21 September-27 September 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 20-27 September. Elevated surface temperatures were identified during 20-21 September; weather clouds often prevented webcam and satellite views during the rest of the week. A data outage that affected the local seismic network was resolved by 23 September. Seismicity was low during 24-25 September. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

14 September-20 September 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 13-20 September, an analysis confirmed by clear satellite images during 13-15 September. Lava flowed outward from the vent area but flows at the margins did not advance. Minor steam emissions were also visible during 13-14 September and elevated surface temperatures were identified during 13-15 and 17-18 September. Weather cloud cover occasionally prevented webcam and satellite views. A data outage affected the local seismic network during 16-20 September, though no significant activity was detected on regional geophysical networks. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

7 September-13 September 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 6-13 September, though weather cloud cover prevented visual confirmation with webcam and satellite images. Seismicity was very low. Weakly-elevated surface temperatures consistent with lava effusion in the summit crater were identified overnight during 12-13 September. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

31 August-6 September 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 30 August-6 September with lava thickening over the vent and expanding outward; the lava flows did not advance. Minor steaming from the summit was observed during 30-31 August, and elevated surface temperatures were identified in satellite images during 2-5 September. Seismicity was very low. Weather clouds sometimes prevented satellite and webcam views. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

24 August-30 August 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin probably continued during 24-30 August with lava around the vent likely thickening. Weather clouds often obscured satellite and webcam views during most of the week; elevated surface temperatures were occasionally visible. Seismicity was very low. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

17 August-23 August 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 16-23 August; no changes to the flow margins were visible but the lava had deepened around the vent. Weather clouds often obscured satellite and webcam views during most of the week. Seismicity was low and occasional local earthquakes were recorded. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

10 August-16 August 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 9-16 August; no changes to the flow margins were visible but the lava had deepened around the vent. Weather clouds often obscured satellite and webcam views during most of the week. Seismicity was low and occasional local earthquakes were recorded. Elevated surface temperatures were identified in satellite images on most days. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

3 August-9 August 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 2-9 August; no changes to the flow lengths were visible but the lava had deepened around the vent. Weather clouds often obscured satellite and webcam views during most of the week, though no activity was visible when views were clear. Seismicity was low and occasional local earthquakes were recorded. Elevated surface temperatures were identified in satellite images during 5-9 August. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

27 July-2 August 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 26 July-2 August. Weather clouds obscured satellite and webcam views during most of the week, though satellite radar data confirmed ongoing effusion; flows thickened but did not advance. Seismicity was low, and occasional local earthquakes were recorded. Steam emissions were visible in satellite and webcam images during 29-30 July. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

20 July-26 July 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 19-26 July. Elevated surface temperatures were identified in satellite images during 19-20 July; weather clouds obscured satellite and webcam views during most of the rest of the week. Seismicity was low, and occasional local earthquakes were recorded. Steam emissions were visible in satellite images during 25-26 July. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

13 July-19 July 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 12-19 July. Elevated surface temperatures were identified in satellite images on most days; weather clouds sometimes obscured satellite and webcam views. Seismicity was low, and occasional local earthquakes were recorded. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

6 July-12 July 2022 Cite this Report

AVO reported that the eruption at Great Sitkin continued during 6-12 July. Elevated surface temperatures were occasionally identified in satellite images; weather clouds sometimes obscured satellite and webcam views. Seismicity was low, and occasional local earthquakes were recorded. Sulfur dioxide emissions were possibly detected during 9-10 July. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

29 June-5 July 2022 Cite this Report

AVO reported that the eruption at Great Sitkin continued during 29 June-5 July. The lava-flow field grew slightly, expanding 15 m E. Elevated surface temperatures were occasionally identified in satellite images; weather clouds sometimes obscured satellite and webcam views. Seismicity was low. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

22 June-28 June 2022 Cite this Report

AVO reported that the eruption at Great Sitkin continued during 21-28 June. Elevated surface temperatures were identified in satellite images during 26-27 June; weather clouds obscured satellite and webcam views on the other days. Seismicity was low. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

15 June-21 June 2022 Cite this Report

AVO reported that the eruption at Great Sitkin continued during 8-14 June. Elevated surface temperatures were identified in satellite data almost daily, consistent with lava effusion; weather clouds sometimes obscured satellite and webcam views. Seismicity was low with several small local earthquakes detected by the seismic network. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

8 June-14 June 2022 Cite this Report

Source: US Geological Survey Alaska Volcano Observatory (AVO)

1 June-7 June 2022 Cite this Report

AVO reported that the eruption at Great Sitkin continued during 31 May-7 June, though weather clouds sometimes hindered observations. Surface temperatures were occasionally identified in satellite data, consistent with lava effusion. A few small earthquakes were detected on a few of the days. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

25 May-31 May 2022 Cite this Report

AVO reported that the eruption at Great Sitkin continued during 24-31 May, though weather clouds sometimes hindered observations. Almost daily elevated surface temperatures were identified in satellite data, consistent with lava effusion, and satellite images during 28-29 May showed that the lava field had expanded. Steam emissions were occasionally visible. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

18 May-24 May 2022 Cite this Report

AVO reported that the eruption at Great Sitkin continued during 17-24 May. Almost daily elevated surface temperatures were identified in satellite data, consistent with lava effusion. Steam emissions were visible during 23-24 May. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

11 May-17 May 2022 Cite this Report

AVO reported that minor advancement of the lava flows at Great Sitkin indicated continuing slow lava effusion during 10-17 May. Daily elevated surface temperatures were identified in satellite data. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

4 May-10 May 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 3-10 May; a 5 May satellite image showed that the S flank flow had advanced 15 m. Elevated surface temperatures were identified in satellite data during 6-10 May. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

27 April-3 May 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 27 April-3 May; no significant seismic activity was detected and weather clouds obscured webcam and satellite views. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

20 April-26 April 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 20-26 April, and very low seismicity persisted. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

13 April-19 April 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 13-19 April, based on high-resolution satellite data. Weather clouds prevented visual observations on most days. Very low seismicity persisted. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

6 April-12 April 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 5-12 April and very low seismicity persisted. The lava flows on the S, W, and N flanks had advanced up to 10 m during 2-8 April, and elevated surface temperatures identified in satellite images during 8-10 April indicated continuing effusion. Steaming from the vent and flow field was occasionally identified in satellite images. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

30 March-5 April 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 30 March through 5 April and low seismicity persisted. Cloud cover prevented views of the volcano most of the week, but slow lava effusion continued; minor flow fronts advanced from the W and S lobes, as well as the E margin. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

23 March-29 March 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 22-29 March and very low seismicity persisted. Cloud cover prevented views of the volcano most of the week; one satellite image acquired on 24 March showed slow expansion of the flow field. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

16 March-22 March 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 15-22 March and very low seismicity persisted. Cloud cover prevented views of the volcano most of the week; slightly elevated surface temperatures were identified in satellite images during 20-21 March. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

9 March-15 March 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 8-15 March and very low seismicity persisted. The rate of effusion slightly increased from 28 February to 11 March, based on radar data collected on those two dates; lava was extruded in all direction from the vent and the southern lobe advanced 20 m. Snow covered most of the flow except for the advancing fronts of the lava lobes and around the vent area. Elevated surface temperatures were periodically identified in satellite images. Minor steaming was visible in webcam images on 12 March. The steaming was dense and also visible in satellite images during 12-13 March. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

2 March-8 March 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 2-8 March and very low seismicity persisted. Elevated surface temperatures were periodically identified in satellite images. A possible steam plume rising above the weather clouds was visible during 4-5 March. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

23 February-1 March 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 23 February-1 March and very low seismicity persisted. Weakly elevated surface temperatures at the summit were detected during 25-28 February. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

16 February-22 February 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 16-22 February, though cloudy conditions often prevented satellite and webcam views. Lava flows had continued to advance down the S, W, and N flanks, and were 1,050 m, 930 m, and 220 m long, respectively. Lava flows were also active on the SSW flank. Seismicity remained slightly above background levels, and a few, daily, small local earthquakes were recorded during 19-21 February. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

9 February-15 February 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 9-15 February, though cloudy conditions often prevented satellite and webcam views. Seismicity remained slightly above background levels, and elevated surface temperatures were periodically identified in satellite images. A steam plume was occasionally visible in webcam images. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

2 February-8 February 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 2-8 February, though cloudy conditions often prevented satellite and webcam views. Seismicity remained slightly elevated. The flow field expanded with up to 100 m of advancement of the S, W, and N flank lava flows. Elevated surface temperatures were periodically identified in satellite images. A steam plume was visible in webcam images during 5-6 February. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

26 January-1 February 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 26 January-1 February, though cloudy conditions often prevented satellite and webcam views. Clearer satellite and webcam views during 30-31 January confirmed growth of the flow field, including the W and S lava flows. Elevated surface temperatures were identified in satellite images during 31 January-1 February. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

19 January-25 January 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 18-25 January, and seismicity remained at very low levels. Elevated surface temperatures were identified in satellite data during 19-22 January. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

12 January-18 January 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 12-18 January, though cloudy conditions prevented satellite and webcam confirmation. Seismicity was very low and small events were occasionally recorded. Steam emissions were observed in webcam views during 14-15 January. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

5 January-11 January 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin probably continued during 5-11 January, though cloudy conditions prevented satellite and webcam confirmation. Seismicity was very low; several small seismic events were recorded during 9-10 January. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

29 December-4 January 2022 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 29 December 2021 to 4 January 2022 along with very low and persistent seismicity. Satellite images acquired on 29 December 2021 and 1 January 2022 showed that the lava flows on the W flanks had advanced. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

22 December-28 December 2021 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 21-28 December with advancing lava flows on the N, W, and S flanks. Very low seismicity persisted. Elevated surface temperatures at the summit were detected overnight during 21-24 and 26-27 December; weather clouds prevented observations during 25-26 December. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

15 December-21 December 2021 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 15-19 December and very low seismicity persisted. A radar image acquired during 14-15 December showed a growing flow field with lava lobes advancing down the N, W, and S flanks. Elevated surface temperatures at the summit were detected overnight during 15-16 and 18-19 December. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

8 December-14 December 2021 Cite this Report

AVO reported that slow lava effusion at Great Sitkin continued during 8-14 December and very low seismicity persisted. Elevated surface temperatures at the summit, that were sometimes intense, were detected overnight during 10-11 and 13-14 December. A radar image acquired during 12-13 December showed a growing flow field. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

1 December-7 December 2021 Cite this Report

AVO reported that slow lava effusion at Great Sitkin likely continued during 1-7 December. Elevated surface temperatures at the summit were periodically detected through the week. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

24 November-30 November 2021 Cite this Report

According to AVO satellite images acquired on 23 November showed that lava effusion at Great Sitkin continued, though at a low rate. Lava continued to fill the summit crater and the flows on the flanks advanced short distances. During 24-30 November seismicity remained slightly above background levels. Elevated surface temperatures were periodically detected. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

17 November-23 November 2021 Cite this Report

AVO reported that lava effusion at Great Sitkin had slowed or paused based on a 17 November satellite image that showed no advancement of the lava flows since 10 November. Seismicity remained elevated during 17-23 November and elevated surface temperatures were visible in occasionally clear satellite images. Steam emissions were sometimes visible in webcam images. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

10 November-16 November 2021 Cite this Report

AVO reported that lava effusion at Great Sitkin continued during 10-16 November. Elevated surface temperatures were visible in clear satellite images during 11 and 15-16 November. Two days later effusion was confirmed in satellite images; the N lava flow had not progressed but the W and S flank flows had advanced to 680 and 650 m, respectively. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

3 November-9 November 2021 Cite this Report

AVO reported that lava flows at Great Sitkin were approximately 680 m long on the W flank, 560 m long on the S flank, and 90 m long on the N flank by 30 October based on satellite images. Lava effusion probably continued during 3-9 November, though weather clouds prevented visual confirmation. Elevated surface temperatures were occasionally detected in satellite images during 2-3 and 5-6 November. Seismicity was low overall, though slightly increased during 6-7 November. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

27 October-2 November 2021 Cite this Report

AVO reported that lava flows on Great Sitkin’s S and W flanks were 600 m long by 27 October based on satellite images, and lava effusion likely continued during 27 October-2 November. Seismicity remained elevated and was characterized by small earthquakes consistent with ongoing lava flows. Elevated surface temperatures were occasionally detected in satellite images. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

20 October-26 October 2021 Cite this Report

AVO reported that lava effusion continued at Great Sitkin during 20-26 October. Lava advanced down the S and W flanks and were 500 m long by 20 October based on satellite images. Geophysical and web camera data streams returned back online during 22-23 October; seismicity remained slightly elevated and no explosive activity was recorded in both seismic and infrasound data through 26 October. Elevated surface temperatures were visible in satellite images during 25-26 October. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

13 October-19 October 2021 Cite this Report

AVO reported that lava effusion continued at Great Sitkin during 13-19 October. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion, though an outage affected geophysical data streams during 16-18 October. Satellite images acquired on 11 October showed that lava filled more than half of the summit crater, flowing onto the S and W flanks, and had recently reached the N crater rim. Lava traveled 330 m down the S flank, 350 m down the W flank, descended small valleys, and in some areas, advanced over snow and ice. Blocks that had detached from the end of the W flow descended 450 m. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

29 September-5 October 2021 Cite this Report

AVO reported that lava effusion continued at Great Sitkin during 29 September-5 October. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion. Elevated surface temperatures were detected in satellite images. By 3 October the dome had grown to 1,200 m E-W and 1,000 m N-S. Lava flows that continued to advance down the S and SW flanks were about 300-350 m long. The SW lobe was descending two drainages and produced hot avalanches that traveled 450 m downslope on top of a snow field. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

22 September-28 September 2021 Cite this Report

AVO reported that lava effusion continued at Great Sitkin during 22-28 September, though weather clouds sometimes prevented webcam and satellite views. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion. By 24 September the dome had overtopped the S and W crater rims and flowed 305 m down the S flank and 195 m down the W flank. The dome was about 25 m thick and had grown to 1,170 m E to W and 925 m N to S in dimension. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

15 September-21 September 2021 Cite this Report

AVO reported that lava effusion continued at Great Sitkin during 15-21 September, though weather clouds often prevented webcam and satellite views. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion. A radar image from 16 September indicated that the lava dome had grown to 1,130 m E-W and 910 m N-S, and was about 30 m thick. The edges of the dome touched the S and W rims of the crater. Elevated surface temperatures were identified in satellite data during 20-21 September. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

8 September-14 September 2021 Cite this Report

AVO reported that lava effusion continued at Great Sitkin during 7-14 September, though weather clouds often prevented webcam and satellite views. Seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion. A radar image from 9 September indicated that the lava dome had grown to 1,100 m E to W and 860 m N to S, and was 25-30 m thick. Lava began to advance though a gap in the S rim of the summit crater. Elevated surface temperatures were visible in satellite data on 14 September. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

1 September-7 September 2021 Cite this Report

AVO reported that elevated surface temperatures at Great Sitkin and daily small earthquakes were detected during 31 August-7 September, consistent with the growing lava dome. Gas plumes were observed almost daily in satellite data. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

25 August-31 August 2021 Cite this Report

AVO reported that the lava dome at Great Sitkin continued to grow, reaching 880 m in diameter by 25 August and 1,090 m during 28-29 August. Elevated surface temperatures and small earthquakes were detected during 25-31 August, consistent with the growing dome. Daily steam-and-gas plumes were observed in satellite data and by local observers. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

18 August-24 August 2021 Cite this Report

AVO reported that the lava dome at Great Sitkin remained active during 17-24 August; satellite imagery showed changes from a diameter of 800 m on 17 August to 850-860 m throughout 18-21 August. Elevated surface temperatures and daily small earthquakes were consistent with an active dome. Gas-and-steam plumes were visible to local ground observers and in satellite imagery during 20-22 and 24 August. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

11 August-17 August 2021 Cite this Report

AVO reported that the lava dome at Great Sitkin continued to be active, growing in diameter from 250 m on 6 August, to 380 m three days later, and to 700 m by 16 August. Steam-and-gas plumes were periodically observed in webcam images, in satellite data, and by observers on the ground during 11-17 August. Elevated surface temperatures and small earthquakes detected daily were consistent with the growing dome. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

4 August-10 August 2021 Cite this Report

AVO reported that unrest continued at Great Sitkin during 4-10 August with elevated seismicity, elevated surface temperatures, and explosions associated with a growing lava dome. Numerous earthquakes and small explosions were recorded on local infrasound and seismic stations during 4-5 August. During the morning of 5 August observers reported possible low-level lava fountaining from the active vent; the activity was also visible from Adak Island. Throughout the same day a volcanic plume comprised mostly of gas and steam (and possibly ash) was visible in webcam images rising to 3 km (10,000 ft) a.s.l. By 6 August the lava dome had grown to 250 m in diameter and had an approximate volume of about 1 million cubic meters. AVO noted that most of the crater was full of lava erupted in 1974 and that the current lava covered only 4-5 percent of the total summit crater area. Elevated surface temperatures were identified in satellite images during 6-10 August, though weather clouds mostly prevented satellite and webcam views. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

28 July-3 August 2021 Cite this Report

AVO reported that unrest continued at Great Sitkin during 28 July-3 August. Seismicity remained elevated and a small swarm was recorded during 1-2 August. Elevated surface temperatures and a north-drifting steam plume were identified in satellite images during 27-28 July. Minor steam emissions were visible during 31 July-3 August. The circular lava dome in the crater had grown to 180 m in diameter based on measurements taken using a 3 August satellite image. The Aviation Color Code and the Volcano Alert Level remained at Orange and Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

21 July-27 July 2021 Cite this Report

AVO reported that a satellite image of Great Sitkin acquired at 0932 on 22 July showed a small area of uplift, about 50 m in diameter, and elevated surface temperatures associated with the feature. These observations suggested magma rising near the surface, prompting AVO to raise the Aviation Color Code and the Volcano Alert Level to Orange and Watch, respectively. Small earthquakes were recorded during 23-25 July. A 26 July satellite image confirmed that the feature was a lava dome, and that it had grown to 130 m in diameter. Seismic data suggested that the dome probably emerged sometime during 14-22 July.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

26 May-1 June 2021 Cite this Report

On 27 May AVO reported that seismicity at Great Sitkin was low following a 25 May explosion, and satellite images showed minor steaming and slightly elevated surface temperatures. The Aviation Color Code and the Volcano Alert Level were lowered to Yellow and Advisory, respectively. Seismicity remained low through 1 June; moderately elevated surface temperatures were detected during 29-30 May.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

19 May-25 May 2021 Cite this Report

An increase in local earthquake activity at Great Sitkin during 24-25 May prompted AVO to raise the Aviation Color Code to Orange and the Volcano Alert Level to Watch on 25 May. An explosive eruption began later that day at 2104; the Aviation Color Code and the Volcano Alert Level were raised to Red/Warning, respectively. The explosions lasted for 1-2 minutes and produced an ash plume rising to 4.6 km (15,000 ft) a.s.l. that was observed by local mariners. Witnesses 42 km away heard “a very loud explosion.” After the explosive period seismicity decreased and satellite image images showed a detached plume drifting E. Around mid-morning on 26 May AVO lowered the Aviation Color Code and the Volcano Alert Level to Orange/ Watch, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

12 May-18 May 2021 Cite this Report

AVO reported that elevated surface temperatures at Great Sitkin had been identified in satellite images since January and had been increasing in frequency during the previous two months. A minor increase in seismicity began to be recorded on 9 May and volcanic gas emissions increased on 10 May. AVO raised the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory on 12 May.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

21 October-27 October 2020 Cite this Report

AVO reported that seismicity at Great Sitkin had decreased during the previous several months and had returned to background levels by 21 October. Additionally, eruptive activity or unusual surface temperatures had not been observed in clear satellite images. The Aviation Color Code was lowered to Green and the Volcano Alert Level was lowered to Normal.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

26 February-3 March 2020 Cite this Report

AVO reported that seismicity at Great Sitkin had increased during the previous month and by 26 February was above background levels; the Aviation Color Code was raised to Yellow and the Volcano Alert Level was raised to Advisory. No eruptive activity was evident in geophysical or satellite data.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

10 July-16 July 2019 Cite this Report

On 15 July AVO reported that seismicity at Great Sitkin had decreased to background levels during the past few weeks with no evidence of eruptive activity in geophysical or satellite data. The Aviation Color Code was lowered to Green and the Volcano Alert Level was lowered to Normal.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

5 June-11 June 2019 Cite this Report

AVO reported that a small steam explosion at Great Sitkin was detected in seismic data at 1318 on 7 June. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

29 May-4 June 2019 Cite this Report

A small steam explosion at Great Sitkin was detected in seismic data at 2140 on 1 June, prompting AVO to raise the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory. Low-level seismic activity was elevated just before and after the event.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

20 February-26 February 2019 Cite this Report

On 25 February AVO reported that seismicity at Great Sitkin had decreased to background levels during the past month and there was no evidence of explosive activity. The Aviation Color Code was lowered to Green and the Volcano Alert Level was lowered to Normal.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

8 August-14 August 2018 Cite this Report

AVO reported that a small phreatic explosion at Great Sitkin was recorded by the seismic network at 1105 on 11 August. The event was preceded by small local earthquakes. Cloudy satellite images prevented views of the volcano during 12-14 August. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

27 June-3 July 2018 Cite this Report

AVO reported that after the brief explosion at Great Sitkin on 10 June seismicity gradually declined to background levels. On 27 June AVO lowered the Volcano Alert Level to Normal and the Aviation Color Code to Green.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

20 June-26 June 2018 Cite this Report

AVO reported continuing low-level unrest at Great Sitkin during 20-26 June; seismic activity remained at or near background levels. A recently analyzed satellite image acquired on 11 June, one day after short-duration explosive event was recorded, showed a minor ash deposit on the snow extending 2 km from a vent in the summit crater. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

13 June-19 June 2018 Cite this Report

AVO reported that satellite images captured after the short-lived steam explosion at Great Sitkin on 10 June indicated minor changes in the summit crater, characterized by possible new fumaroles in the N part of the main crater and slightly more vigorous steaming at pre-existing fumaroles. Seismicity declined to background levels during 15-16 June.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

6 June-12 June 2018 Cite this Report

Seismicity at Great Sitkin was elevated during the previous five days, though at 1139 on 10 June a seismic signal indicating a possible short-lived steam explosion prompted AVO to raise the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory. No infrasound signal associated with the event was detected, and no volcanic clouds rose about the meteorological cloud deck at 2.4 km (8,000 ft) a.s.l.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

17 January-23 January 2018 Cite this Report

On 18 January AVO reported that seismicity at Great Sitkin had declined over the past two months to near background levels. In addition, no significant activity was observed in satellite data during this time period and no steam plumes were noted. AVO lowered the Aviation Color Code and Volcano Alert Level to Green/Normal.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

29 November-5 December 2017 Cite this Report

AVO reported that during 28 November-5 December low-level unrest continued at Great Sitkin. Nothing noteworthy was identified in seismic data nor in partly cloudy to cloudy satellite images. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

22 November-28 November 2017 Cite this Report

Recent observations of a robust steam plume and a period of gradually increasing seismicity over several months at Great Sitkin prompted AVO to raise the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory on 22 November. On 19 November local observers photographed a light-colored vapor plume rising about 300 m above the vent and drifting 15-20 km S. A satellite image acquired on 21 November showed steam continuously jetting from a small fumarole on the W side of the 1974 lava flow within the summit crater, and at least one area where snow and ice had been melted.

Seismicity had fluctuated but increased overall since July 2016, most notably in June 2017. The seismic activity was characterized by earthquakes less than M 1, and occurred either just below the summit or just offshore the NW cost of the island, 30 km below sea level. Possible explosion signals were recorded in seismic data on 10 January and 21 July 2017, but there were no confirmed emissions.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

29 May-4 June 2002 Cite this Report

On 27 and 28 May, AVO recorded anomalous seismicity at Great Sitkin. The seismicity consisted of two periods of seismic tremor on 27 May (lasting for 20 and 55 minutes) and two earthquake swarms on 28 May (beginning at 0406 and 1328). The earthquake swarms each began with a relatively large event (ML (local magnitude) 2.2 and ML 4.3) followed by tens to hundreds of smaller aftershocks, most located 5-6 km SE of the crater at depths of 0-5 km. Both the tremor and the earthquake swarms represent significant changes from what is considered to be normal, "background" seismicity at Great Sitkin. However, aftershocks declined significantly overnight, and no tremor episodes were detected after the 27th. There were neither signs of surface volcanic activity on satellite imagery nor ground-level reports of anomalous activity. Great Sitkin remained at Concern Color Code Green.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

Bulletin Reports - Index

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

02/1974 (CSLP 27-74) Explosive activity and light-colored plume

09/1974 (CSLP 27-74) Lava dome still growing, overspilling crater rim

06/2002 (BGVN 27:06) Abnormal tremor and earthquake swarms in May 2002

09/2018 (BGVN 43:09) Small phreatic explosions in June and August 2018; ash deposit on snow near summit

07/2019 (BGVN 44:07) Small steam explosions in early June 2019

08/2021 (BGVN 46:08) Explosion on 25 May 2021 and new summit crater lava dome in July 2021

05/2022 (BGVN 47:05) Continuing dome growth and lava effusion through April 2022

11/2022 (BGVN 47:11) Slow lava effusion continued during May-October 2022

05/2023 (BGVN 48:05) Continued slow lava effusion in the summit crater during November 2022-April 2023

Information is preliminary and subject to change. All times are local (unless otherwise noted)

February 1974 (CSLP 27-74)

Explosive activity and light-colored plume

Card 1804 (22 February 1974) Explosive activity and light-colored plume

The following was cabled from the Geophysical Institute on 22 February 1974. "Explosive activity was observed at 1855 local time from Adak, 48 km WSW of Great Sitkin volcano. An earthquake originating at the volcano of Richter magnitude 2.6 occurred at the time of onset. An estimated 10,000-foot light-colored plume was reported over the summit at dusk. Since that time bad weather has obscured the island."

Information Contacts: J. Kienle and D.B. Stone, Geophysical Institute, University of Alaska, Fairbanks AK; Dale Glover, NOAA, Adak AK.

September 1974 (CSLP 27-74)

Lava dome still growing, overspilling crater rim

Card 1938 (30 September 1974) Lava dome still growing, overspilling crater rim

D. Glover reported that, on a helicopter inspection trip to the volcano on 22 February, he ". . . found that a large lava dome had been emplaced in the crater, with mostly steam and gas being emitted." Foul weather prevented observations on all but three occasions between then and 29 March. About one week after the eruption, he noted, through a high-power telescope, ". . . that the dome had been extruded a considerable extent, with some ash being emitted. Since then activity has decreased to steam and gas emissions."

In mid-September, her reported that he had ". . . only been able to observe Great Sitkin volcano by high-power telescope and a few times from aircraft. The lava dome appears to continue to extrude with minor lava flows spilling over the lip of the crater. The size of the dome is hard to estimate but it is probably close to 700 m in diameter and 200-300 m high. We have recently installed seismic instrumentation on the volcano but we have not noticed any unusual activity." In summary, it appears that, following the initial release of the pressure head of volatiles on 19 February a dome has been extruded in the caldera of Great Sitkin. The new dome appears to be about the size of that extruded in 1945. Further, the dome is still active, overspilling the lip of the caldera as it grows. The extrusion has been quiet, with little of no associated explosiveness.

Information Contacts: Dale Glover, NOAA Adak Observatory, FPO Seattle WA; Dan Shackleford, Villa Park CA.

June 2002 (BGVN 27:06) Cite this Report

Abnormal tremor and earthquake swarms in May 2002

On 27 and 28 May the Alaska Volcano Observatory (AVO) detected anomalous seismicity at Great Sitkin, a volcano located 1,895 km SW of Anchorage, Alaska. On 27 May two periods of seismic tremor lasted for 20 and 55 minutes and on 28 May earthquake swarms began at 0306 and 1228. The earthquake swarms each began with a relatively large event (ML 2.2 and ML 4.3) followed by tens to hundreds of smaller aftershocks, most located 5-6 km SE of the crater at depths of 0-5 km. Both the tremor and earthquake swarms represent significant changes from background seismicity at Great Sitkin. However, aftershocks declined significantly overnight, and seismicity returned to background levels with a lack of recorded tremor since 27 May. Satellite imagery showed no signs of surface volcanic activity, and no reports of anomalous activity were received by AVO.

Information Contacts: Tom Murray and John Eichelberger, Alaska Volcano Observatory (AVO) (URL: http://www.avo.alaska.edu/).

September 2018 (BGVN 43:09) Cite this Report

Small phreatic explosions in June and August 2018; ash deposit on snow near summit

Episodic recent and historic volcanic activity has been reported at Great Sitkin, located about 40 km NE of the community of Adak in the Aleutian Islands. Prior to the recent 2018 activity, the last confirmed eruption in 1974 produced at least one ash cloud that likely exceeded an altitude of 3 km (figures 1 and 2). This eruption extruded a lava dome that partially destroyed an existing dome from a 1945 eruption. Most recently, a small steam explosion was reported on 10 June 2018. In response, the Alaska Volcano Observatory (AVO) raised the Aviation Color Code (ACC) to Yellow (Advisory) from the previous Green (Normal).

Figure 1. Eruption of Great Sitkin volcano in 1974. Photo taken from Adak Island, Alaska, located 40 km SW of the volcano. Photographer/Creator: Paul W. Roberts; courtesy of AVO/USGS (color corrected).

Figure 2. Worldview-3 satellite image of Great Sitkin on 21 November 2017 showing the crater, areas of 1974 and 1945 lava flows, and steam (indicated by the red arrow) from the reported seismic swarm and steam event ending in 2017. Photographer/Creator: Chris Waytomas; image courtesy of AVO/USGS.

AVO had previously reported that a seismic swarm had been detected beginning in late July 2016 and continuing through December 2017. Steam from the crater was also observed during this time period, in late November 2017 (figure 2). The seismicity was characterized by earthquakes typically less than magnitude 1.0 and at depths from near the summit to 30 km below sea level. Most earthquakes were in one of two clusters, beneath the volcano's summit or just offshore the NW coast of the island. Possible explosion signals were observed in seismic data on 10 January and 21 July 2017, but no confirmed emissions were observed locally or detected in infrasound data or satellite imagery.

The most recent eruption at Great Sitkin produced a small steam explosion which was detected in seismic data at 1139 local time on 10 June 2018 (figure 3). The explosion was followed by seismic activity which began diminishing after 24 hours, and by 15-16 June had returned to background levels.

Figure 3. View of Great Sitkin steaming on 10 July 2018. Photographed from Adak Island, Alaska, approximately 40 km SW. Photo by Alain Beauparlant; image courtesy of AVO/USGS (color corrected).

Due to heavy cloud cover on 10 June 2018, satellite views were obscured. Subsequent satellite data collected on 11 June showed an ash deposit on the surface of the snow extending to about 2 km SW from a vent in the summit crater (figure 4). Minor changes in the vicinity of the summit crater were observed from satellite data, including possible fumaroles north of the main crater. On 17 June an aerial photograph showed minor steaming at the vent (figure 5).

Figure 4. Satellite view of the Great Sitkin crater at 2300 UTC on 11 June 2018 showing an ash deposit extending for about 2 km to the SW. Ash was likely deposited during the brief explosion on 10 June 2018. Minor steaming from a vent through the 1974 lava flow is also visible in this image. View is from the southwest. Photographer/Creator: David Schneider; image courtesy of AVO/USGS.

Figure 5. Aerial photo showing minor steaming at the summit of Great Sitkin, 17 June 2018. A small ash deposit extends SW from the vent. Photographer: Alaska Airlines Captain Dave Clum; image courtesy of AVO/USGS.

Another small phreatic explosion was observed in seismic data at 1105 local time on 11 August. Small local earthquakes preceded the event but were not recorded following the explosion. The event is similar to three other phreatic explosions that have occurred over the past 2 years.

July 2019 (BGVN 44:07) Cite this Report

Small steam explosions in early June 2019

The Great Sitkin volcano is located about 40 km NE of Adak Island in the Aleutian Islands and has had a few short-lived eruptions over the past 100 years. Prior to the latest activity in early June 2019 described below, small phreatic explosions occurred in June and August 2018 (BGVN 43:09). An eruption in 1974 produced a lava dome in the center of the crater. The Alaska Volcano Observatory (AVO) is the primary source of information for this September 2018-June 2019 reporting period.

Low-level unrest occurred from September 2018 through February 2019 with slightly elevated seismic activity (figure 6). Small explosions were seismically detected by AVO on 30 October, 5 and 16 November, and 11 December 2018, but they were not seen in regional infrasound data and satellite data did not show an ash cloud.

On 1, 7, and 9 June 2019, AVO reported small steam explosions as well as slightly elevated seismic activity. Steam plumes and surficial evidence of an explosion were not observed during these events. On 18 June 2019 weakly elevated surface temperatures were recorded, field crews working on Adak observed some steam emissions, and a gas flight was conducted. Elevated concentrations of carbon dioxide detected above the lava dome were likely associated with the steam explosions earlier in the month (figures 7 and 8). From 23 June through the end of the month seismicity began to decline back to background levels.

Figure 6. A steam plume was seen at the summit of Great Sitkin on 7 December 2018. Photo by Andy Lewis and Bob Boyd; courtesy of AVO/USGS.

Figure 7. Some degassing was observed on the southern flank of the Great Sitkin during an overflight on 18 June 2019. Photo by Laura Clor; image courtesy of AVO/USGS.

Figure 8. View of Great Sitkin with white plumes rising from the summit on 20 June 2019. Photo by Laura Clor, courtesy of AVO/USGS.

August 2021 (BGVN 46:08) Cite this Report

Explosion on 25 May 2021 and new summit crater lava dome in July 2021

No major eruption has occurred at Great Sitkin since 1974, but intermittent steam emissions and small steam explosions, accompanied by slightly elevated seismicity, were observed during July 2016-December 2017, and most recently during June-December 2018 and in June 2019 (BGVN 43:09, 44:07). The volcano, located in the Aleutian Islands (figure 9) is monitored by the Alaska Volcano Observatory (AVO) using local real-time seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks. Events from July 2019 through July 2021 are summarized in this report.

Figure 9. Location map showing Great Sitkin and other nearby volcanoes in the Aleutian Islands. Courtesy of AVO.

On 15 July 2019, AVO reported that the seismicity recorded in June 2019 had decreased to background levels over the previous few weeks, with no evidence of eruptive activity in geophysical or satellite data. The Aviation Color Code (ACC) was lowered to Green and the Volcano Alert Level (VAL) was lowered to Normal. On 26 February 2020 AVO noted that seismicity had increased during the previous month, but by 21 October it had returned to background levels and no eruptive activity or unusual surface temperatures had been observed in satellite images. A Volcano Observatory Notice for Aviation on 13 May 2021 noted that elevated surface temperatures identified by AVO in satellite images since January had increased in frequency during the previous two months. A minor increase in seismicity began on 9 May and volcanic gas emissions increased on 10 May.

An increase in local earthquakes during 24-25 May prompted AVO to raise the ACC to Orange and the VAL to Watch. An explosive eruption began on 25 May at 2104; the ACC and the VAL were raised to Red/Warning, respectively. The explosions lasted for 1-2 minutes and produced an ash plume that rose to an altitude of 4.6 km (figures 10 and 11). Witnesses 42 km away heard “a very loud explosion.” After the explosive period, seismicity decreased and satellite image images showed a detached plume drifting E. Around mid-morning on 26 May, AVO lowered the ACC and VAL to Orange/Watch, respectively.

Figure 10. Eruption plume of Great Sitkin on 25 May 2021 at 2106 (local time) as seen from the RV Tiglax. Courtesy of Lauren Flynn (U.S. Fish and Wildlife Service).

Seismicity was low on 27 May 2021 and satellite images showed only minor steaming along with slightly elevated surface temperatures. Seismicity remained low through 1 June; moderately elevated surface temperatures were detected during 29-30 May. Aerial images on 30 May and 6 June showed ash deposits from the 25 May explosion (figure 11).

Figure 11. Two aerial images of the summit crater of Great Sitkin from different angles, one taken on 30 May 2021 at 1745 (top) and the other taken on 6 June 2021 (bottom). According to AVO, the black deposit in the summit crater is likely fresh ash deposits from the 25 May explosion. The black linear feature trailing down the flank in the middle foreground is a lahar (mudflow) deposit. Minor ashfall can be observed on the right flank. Courtesy of Steve Rhodes (AVO) (top) and Max Zelenevich (bottom).

According to AVO, a satellite image acquired at 0932 on 22 July 2021 showed a small area of uplift, about 50 m in diameter, and elevated surface temperatures associated with this feature. A Sentinel-2 satellite image suggested that the elevated surface temperature had begun on 12 July or earlier (figure 12). A 26 July satellite image confirmed that the feature was a lava dome that it had grown to 130 m in diameter (figure 13). Seismic data suggested that the dome probably emerged sometime during 14-22 July. Unrest continued during 26-31 July, with small earthquakes but no explosive activity. Elevated surface temperatures were detected on 27 and 28 July, and on 28 July a steam plume was observed drifting N in satellite imagery.

Figure 12. Sentinel-2 satellite image of Great Sitkin in false color (bands 12, 11, 4) on 12 July 2021, showing a hot spot in the summit crater with a gas emission. Courtesy of Sentinel Hub Playground.

Figure 13. GeoEye-1 satellite image of Great Sitkin showing the new circular lava dome in the summit crater on 26 July 2021. Courtesy of AVO.

May 2022 (BGVN 47:05) Cite this Report

Continuing dome growth and lava effusion through April 2022

Great Sitkin, in the Aleutian island arc, has had only a single ash explosion since 1974, on 25 May 2021. During mid-July 2021, a lava dome began to grow in the summit crater, accompanied by elevated surface temperatures (BGVN 46:08). The volcano is monitored by the Alaska Volcano Observatory (AVO) using local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks. The current report summarizes activity during August 2021-April 2022, during which time the lava dome continued to grow and discharge lava.

AVO reported that unrest continued during the reporting period. During the first week of August 2021, the circular lava dome had grown to 180 m in diameter, based on measurements taken using a 3 August satellite image, and had an approximate volume of 1 million cubic meters. During the morning of 5 August observers on Adak Island, 30 km SW, reported possible low-level lava fountaining from the active vent (figure 14). Throughout August, the lava dome remained active, growing in diameter from 250 m on 6 August, to 380 m three days later, 700 m by 16 August, 850-860 m by 21 August, and 1,090 m by 29 August (figure 15). The growing dome fueled lava discharges, numerous small earthquakes, and weak explosions. In addition, steam-and-gas plumes and emissions were periodically observed (figure 3). Based on satellite images, the crater’s surface temperature remained elevated throughout the reporting period. Cloudy conditions often prevented webcam and satellite views.

Figure 14. Photo of an active lava fountain at Great Sitkin at 0714 on 5 August 2021 as seen looking N from Adak Island. Photo by Peggy Kruse (AVO image 175201).

Figure 15. Lava dome growing on Great Sitkin on 6 August 2021, in a short-wave infrared (SWIR) false-color WorldView-3 satellite image. A lava tube breakout ~100 m long is visible through steam on the SSW margin. Courtesy of AVO (AVO image 175371).

Figure 16. Photo showing a steam plume rising from the dome at Great Sitkin at 0720 on 10 August 2021. Photo by Peggy Kruse (AVO image 175491).

During September, seismicity remained elevated and was characterized by small earthquakes consistent with lava effusion. By mid-September, the edges of the dome touched the S and W rims of the crater, and lava began to advance though a gap in the S rim of the summit crater. By 24 September the dome had overtopped the S and W crater rims and lava flowed 305 m down the S flank and 195 m down the W flank. The dome was about 25 m thick and had grown to 1,170 m E to W and 925 m N to S in dimension.

By 3 October the dome had grown to 1,200 m E-W and 1,000 m N-S. Lava flows continued to advance down the S and SW flanks and were about 300-350 m long (figure 17). The SW lobe was descending two drainages and produced hot avalanches that traveled 450 m downslope on top of a snow field. Satellite images acquired on 11 October showed that lava filled more than half of the summit crater, flowing onto the S and W flanks, and had recently reached the N crater rim. Lava had traveled 330 m down the S flank, 350 m down the W flank, descended small valleys, and in some areas, advanced over snow and ice. Blocks that had detached from the end of the W flow descended 450 m. Analysis of satellite imagery on 25 October showed that the lava dome covered an area greater than 1 km² and had overflowed the crater rim to the N, W, and S (figure 18). Elevated surface temperatures identified in satellite images during 25-26 October clearly showed the vent location (figure 19). By 30 October the lava had advanced about 680 m down the W flank, 560 m down the S flank, and 90 m down the N flank. During the latter part of October, seismicity remained slightly elevated and no explosions were recorded.

Figure 17. A pansharpened near-infrared WorldView-3 satellite image of Great Sitkin on 2 October 2021, showing lava flows and a small steam plume. Courtesy of AVO (AVO image 178461).

Figure 18. A visible WorldView-2 satellite image of Great Sitkin on 25 October 2021 shows the growing lava dome in the summit crater. At this point the dome covered an area greater than 1 km² and had overflowed the crater rim to the N, W, and S. A steam plume can be seen extendings from the active vent region to the S. Courtesy of AVO (AVO image 178581).

Figure 19. A short-wave infrared WorldView-3 satellite image of Great Sitkin on 25 October 2021. Red-orange areas represent high-temperature lava, purple is snow, light blue is vegetation, and browns to blacks are rock. Courtesy of AVO (AVO image 178481).

By mid-November the lava flows on the N and W flanks had not progressed, but the S-flank flow had advanced to 650 m. According to AVO, satellite images acquired on 23 November showed that slow lava effusion continued. Lava continued to fill the summit crater and the flows on the flanks advanced short distances. During 24-30 November seismicity remained slightly above background levels. Elevated surface temperatures were periodically detected. Steam emissions were sometimes visible in webcam images. Slow lava effusion continued during December, and seismicity was very low, but persistent. A radar image acquired during 14-15 December showed a growing flow field with lava lobes advancing down the N, W, and S flanks. Crater surface temperatures remained elevated.

Based on AVO reports, activity continued to decrease during January-April 2022. Slow lava effusion continued during this period, along with very low but persistent seismicity (figure 20). Crater surface temperatures remained slightly elevated, and occasional steam emissions were observed. Lava flows continued to advance, and by mid-February lava flows had reached 1,050 m, 930 m, and 220 m down the S, W, and N flanks, respectively. Lava flows were also active on the SSW flank. An AVO report in March indicated that snow covered most of the flow except for the advancing fronts of the lava lobes and around the vent area. During the first week of April lava flows on the S, W, and N flanks advanced up to 10 m; elevated surface temperatures identified in satellite images during 8-10 April indicated continuing effusion. Steaming from the vent and flow field was occasionally seen in satellite images.

Figure 20. Photo of Great Sitkin taken from Adak Island on 14 January 2022 showing steam rising lava flows advancing through snow on the flanks. Photo by Steve Skeehan (AVO image 181451).

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

November 2022 (BGVN 47:11) Cite this Report

Slow lava effusion continued during May-October 2022

After an ash explosion in 1974, the only confirmed volcanic activity at Great Sitkin through 2019 included small phreatic eruptions in June and August 2018 and June 2019, and an ash explosion on 25 May 2019 (BGVN 43:09, 44:07, 46:08). During mid-July 2021 a lava dome began to grow in the summit crater and effuse lava, which soon overtopped the summit crater wall and flowed down the N, S, and W flanks (BGVN 46:08, 47:05). This activity waned during January-April 2022, although slow lava effusion continued. The current report updates activity during May-October 2022. Great Sitkin, located in Alaska’s Aleutian Island chain, is monitored by the Alaska Volcano Observatory (AVO) using local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.

AVO reported that the slow lava effusion from a vent in the summit crater likely continued during May-October 2022 (figure 21). Satellite images showed that the flank flow had advanced 15 m S by the first week of May, and 15 m E by 1 July. During July through the first part of September the lava flow thickened around the vent in the summit crater, but did not advance. At the beginning of September the lava flow continued to thicken but also began to expand slowly within the summit crater, but not on the flanks; this slow expansion continued through October to the S and E. Consistent with the lava effusion, satellite data indicated that surface temperatures were elevated. During the reporting period, steam emissions were occasionally visible.

Figure 21. GeoEye-1 satellite image showing the lava flow field in Great Sitkin’s summit crater and upper flanks on 6 July 2022. The image shows that the slow lava effusion has flowed to the NE into the summit glacier, which is collapsing (see concentric curved crevasses) from melting due to lava interaction. Courtesy of Hannah Dietterich, AVO.

Sentinel-2 infrared images confirmed that lava effusion continued through September 2022, with either one or two distinct hotspots (figure 22). Weather clouds obscured satellite observations on most viewing days. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system recorded seven brief discrete pulses of 4-7 hotspots each in the summit crater during May-October 2022 (figure 23).

Figure 22. Sentinel-2 image of Great Sitkin showing two hotspots within the summit crater on 21 August 2022. Images taken with “Atmospheric penetration” rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Figure 23. Thermal anomalies at Great Sitkin during the year ending 19 October 2022, seen on a MIROVA graph of log radiative power. A pattern of brief pulses of thermal anomalies are evident during May-October 2022. Courtesy of MIROVA.

Seismic activity remained at low levels throughout; occasional local earthquakes were recorded. The Volcano Alert Level remained at Watch (the second highest level on a four-level scale) and the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

May 2023 (BGVN 48:05) Cite this Report

Continued slow lava effusion in the summit crater during November 2022-April 2023

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Synonyms

Great Sitchin | Sitchin | Chetkin | Belaya | Bolshoi Sitkin

Basic Data

Volcano Number

Last Known Eruption

Elevation

Latitude
Longitude

311120

2023 CE

1740 m / 5709 ft

52.076°N
176.13°W

Volcano Types

Stratovolcano
Caldera
Lava dome

Rock Types

Major
Andesite / Basaltic Andesite
Basalt / Picro-Basalt

Minor
Trachyte / Trachydacite

Tectonic Setting

Subduction zone
Intermediate crust (15-25 km)

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km

0
0
0
0

Geological Summary

The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

This volcano is located within the Aleutian Islands, a UNESCO Biosphere Reserve property.

References

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography.

Coats R R, 1950. Volcanic activity in the Aleutian Arc. U S Geol Surv Bull, 974-B: 35-47.

Coombs M L, White S M, Scholl D W, 2007. Massive edifice failure at Aleutian arc volcanoes. Earth Planet Sci Lett, 256: 403-418.

Henning R A, Rosenthal C H, Olds B, Reading E (eds), 1976. Alaska's volcanoes, northern link in the ring of fire. Alaska Geog, 4: 1-88.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior.

Keller F, Meuschke J L, Alldredge L R, 1954. Aeromagnetic surveys in the Aleutian, Marshall, and Bermuda Islands. Eos, Trans Amer Geophys Union, 35: 558-572.

Miller T P, McGimsey R G, Richter D H, Riehle J R, Nye C J, Yount M E, Dumoulin J A, 1998. Catalogue of the historically active volcanoes of Alaska. U S Geol Surv Open-File Rpt, 98-582: 1-104.

Montanaro C, Beget J, 2011. Volcano collapse along the Aleutian Ridge (western Aleutian Arc). Nat Hazards Earth Syst Sci 11: 715-730. https://doi.org/10.5194/nhess-11-715-2011

Motyka R J, Liss S A, Nye C J, Moorman M A, 1993. Geothermal resources of the Aleutian arc. Alaska Div Geol Geophys Surv, Prof Rpt, no 114, 17 p and 4 map sheets.

Myers J D, 1994. The Geology, Geochemistry and Petrology of the recent Magmatic Phase of the Central and Western Aleutian Arc. Unpublished manuscript, unpaginated.

Romick J D, Kay S M, Kay R W, 1992. The influence of amphibole fractionation on the evolution of calc-alkaline andesite and dacite tephra from the central Aleutians, Alaska. Contr Mineral Petr 112: 101-118.

Simons F S, Mathewson D E, 1955. Geology of Great Sitkin Island, Alaska. U S Geol Surv Bull, 1028-B: 29-32.

Smith R L, Shaw H R, Luedke R G, Russell S L, 1978. Comprehensive tables giving physical data and thermal energy estimates for young igneous systems of the United States. U S Geol Surv Open-File Rpt, 78-925: 1-25.

Eruptive History

There is data available for 9 confirmed Holocene eruptive periods.

2021 May 25 - 2023 Oct 11 (continuing) Confirmed Eruption Max VEI: 2

Episode 1 | Eruption Episode

2021 May 25 - 2023 Oct 11 (continuing)

Evidence from Observations: Reported

An explosive eruption began at 2104 on 25 May that lasted for 1-2 minutes and produced an ash plume rising to 4.6 km that was observed by local mariners. Witnesses 42 km away heard “a very loud explosion.”

List of 6 Events for Episode 1

Start Date	End Date	Event Type	Event Remarks
2021 May 25	- - - -	Explosion
2021 May 25	- - - -	Ash Plume
2021 May 25	- - - -	Ashfall
2021 May 25	- - - -	VEI (Explosivity Index)	VEI 2
2021 May 30	- - - -	Lahar or Mudflow
2021 Jul 18 ± 4 days	- - - -	Lava dome

2019 Jun 1 - 2019 Jun 7 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode

2019 Jun 1 - 2019 Jun 7

Evidence from Observations: Reported

List of 1 Events for Episode 1

	Start Date	End Date	Event Type	Event Remarks
	- - - -	- - - -	VEI (Explosivity Index)

2018 Jun 10 - 2018 Aug 11 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode

2018 Jun 10 - 2018 Aug 11

Evidence from Observations: Reported

List of 3 Events for Episode 1

Start Date	End Date	Event Type
- - - -	- - - -	Explosion
- - - -	- - - -	Ash
- - - -	- - - -	VEI (Explosivity Index)

[ 1987 Mar 18 ] Uncertain Eruption

Episode 1 | Eruption Episode

1987 Mar 18 - Unknown

Evidence from Unknown

List of 1 Events for Episode 1

	Start Date	End Date	Event Type	Event Remarks
	- - - -	- - - -	Flames

1974 Feb 19 - 1974 Sep 16 ± 15 days Confirmed Eruption Max VEI: 2

Episode 1 | Eruption Episode

1974 Feb 19 - 1974 Sep 16 ± 15 days

Evidence from Observations: Reported

List of 6 Events for Episode 1

Start Date	End Date	Event Type	Event Remarks
- - - -	- - - -	Eruption cloud
- - - -	- - - -	Lava flow	weak or small
- - - -	- - - -	Lava dome
- - - -	- - - -	Ash	weak or small
- - - -	- - - -	Earthquakes (undefined)	Before.
1974 Feb 19	- - - -	VEI (Explosivity Index)

[ 1953 May 11 - 1953 May 14 ] Discredited Eruption

1950 Nov 5 - 1950 Nov 29 Confirmed Eruption

Episode 1 | Eruption Episode

1950 Nov 5 - 1950 Nov 29

Evidence from Observations: Reported

List of 3 Events for Episode 1

Start Date	End Date	Event Type
- - - -	- - - -	Explosion
- - - -	- - - -	Ash
- - - -	- - - -	Lightning

1949 Dec 30 - 1950 Jan 7 Confirmed Eruption Max VEI: 1

Episode 1 | Eruption Episode

1949 Dec 30 - 1950 Jan 7

Evidence from Observations: Reported

List of 3 Events for Episode 1

Start Date	End Date	Event Type	Event Remarks
- - - -	- - - -	Explosion	weak or small
- - - -	- - - -	Ash
1949 Dec 30	- - - -	VEI (Explosivity Index)

[ 1946 Aug 14 ] Uncertain Eruption

Episode 1 | Eruption Episode

1946 Aug 14 - Unknown

Evidence from Unknown

List of 1 Events for Episode 1

	Start Date	End Date	Event Type	Event Remarks
	- - - -	- - - -	Volcanic "smoke"

1945 Mar Confirmed Eruption Max VEI: 2

Episode 1 | Eruption Episode

1945 Mar - Unknown

Evidence from Observations: Reported

List of 5 Events for Episode 1

Start Date	End Date	Event Type
- - - -	- - - -	Explosion
- - - -	- - - -	Lava flow
- - - -	- - - -	Lava dome
- - - -	- - - -	Earthquakes (undefined)
1945 Mar	- - - -	VEI (Explosivity Index)

1933 Nov Confirmed Eruption Max VEI: 2

Episode 1 | Eruption Episode

1933 Nov - Unknown

Evidence from Observations: Reported

List of 2 Events for Episode 1

	Start Date	End Date	Event Type	Event Remarks
	- - - -	- - - -	Explosion	weak or small
	1933 Nov	- - - -	VEI (Explosivity Index)

[ 1904 ] Uncertain Eruption

Episode 1 | Eruption Episode

1904 - Unknown

Evidence from Unknown

List of 1 Events for Episode 1

	Start Date	End Date	Event Type	Event Remarks
	- - - -	- - - -	Volcanic "smoke"

[ 1829 ] Uncertain Eruption

Episode 1 | Eruption Episode

1829 - Unknown

Evidence from Unknown

List of 1 Events for Episode 1

	Start Date	End Date	Event Type	Event Remarks
	- - - -	- - - -	Volcanic "smoke"

[ 1828 ] Uncertain Eruption

Episode 1 | Eruption Episode

1828 - Unknown

Evidence from Unknown

List of 1 Events for Episode 1

	Start Date	End Date	Event Type	Event Remarks
	- - - -	- - - -	Volcanic "smoke"

1792 May 26 ± 5 days Confirmed Eruption

Episode 1 | Eruption Episode

1792 May 26 ± 5 days - Unknown

Evidence from Observations: Reported

List of 2 Events for Episode 1

	Start Date	End Date	Event Type	Event Remarks
	- - - -	- - - -	Explosion	weak or small
	- - - -	- - - -	Flames

[ 1784 ] Uncertain Eruption

Episode 1 | Eruption Episode

1784 - Unknown

Evidence from Unknown

List of 1 Events for Episode 1

	Start Date	End Date	Event Type	Event Remarks
	- - - -	- - - -	Volcanic "smoke"

[ 1760 ] Uncertain Eruption

Episode 1 \| Eruption Episode
1760 - Unknown				Evidence from Unknown

Deformation History

There is no Deformation History data available for Great Sitkin.

Emission History

There is no Emissions History data available for Great Sitkin.

Photo Gallery

Great Sitkin in the Andreanof Islands is seen here from Finger Bay on Adak Island. The edifice was constructed within a caldera, part of which forms the high snow-covered peak to the right. The post-caldera cone contains a 0.8 x 1.2 km ice-filled summit crater. The rim forms the irregular summit on the left horizon. A lava dome 400-600 m wide was emplaced through a glacier in 1945.

Photo by Fred Zeillemaker, 1982 (U.S. Fish and Wildlife Service, courtesy of Alaska Volcano Observatory).

This September 1946 photo of Great Sitkin from the E rim of the summit crater shows a plume rising above a lava dome emplaced in the crater in March 1945. The fissures in the ice were produced as the dome grew through the summit glacier.

Photo courtesy of U.S. Geological Survey (published in USGS Bulletin 1028-B).

GVP Map Holdings

The maps shown below have been scanned from the GVP map archives and include the volcano on this page. Clicking on the small images will load the full 300 dpi map. Very small-scale maps (such as world maps) are not included. The maps database originated over 30 years ago, but was only recently updated and connected to our main database. We welcome users to tell us if they see incorrect information or other problems with the maps; please use the Contact GVP link at the bottom of the page to send us email.

Smithsonian Sample Collections Database

There are no samples for Great Sitkin in the Smithsonian's NMNH Department of Mineral Sciences Rock and Ore collection.

External Sites

Alaska Volcano Observatory (Link to Great Sitkin)

The Alaska Volcano Observatory (AVO) is a joint program of the U.S. Geological Survey (USGS), the Geophysical Institute of the University of Alaska Fairbanks (UAFGI), and the State of Alaska Division of Geological and Geophysical Surveys (ADGGS). AVO was formed in 1988, and uses federal, state, and university resources to monitor and study Alaska's hazardous volcanoes, to predict and record eruptive activity, and to mitigate volcanic hazards to life and property.

Copernicus Browser

The Copernicus Browser replaced the Sentinel Hub Playground browser in 2023, to provide access to Earth observation archives from the Copernicus Data Space Ecosystem, the main distribution platform for data from the EU Copernicus missions.

MIROVA

Middle InfraRed Observation of Volcanic Activity (MIROVA) is a near real time volcanic hot-spot detection system based on the analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) data. In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity.

MODVOLC Thermal Alerts

Using infrared satellite Moderate Resolution Imaging Spectroradiometer (MODIS) data, scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, developed an automated system called MODVOLC to map thermal hot-spots in near real time. For each MODIS image, the algorithm automatically scans each 1 km pixel within it to check for high-temperature hot-spots. When one is found the date, time, location, and intensity are recorded. MODIS looks at every square km of the Earth every 48 hours, once during the day and once during the night, and the presence of two MODIS sensors in space allows at least four hot-spot observations every two days. Each day updated global maps are compiled to display the locations of all hot spots detected in the previous 24 hours. There is a drop-down list with volcano names which allow users to 'zoom-in' and examine the distribution of hot-spots at a variety of spatial scales.

WOVOdat
   Single Volcano View
   Temporal Evolution of Unrest
   Side by Side Volcanoes

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

GVMID Data on Volcano Monitoring Infrastructure The Global Volcano Monitoring Infrastructure Database GVMID, is aimed at documenting and improving capabilities of volcano monitoring from the ground and space. GVMID should provide a snapshot and baseline view of the techniques and instrumentation that are in place at various volcanoes, which can be use by volcano observatories as reference to setup new monitoring system or improving networks at a specific volcano. These data will allow identification of what monitoring gaps exist, which can be then targeted by remote sensing infrastructure and future instrument deployments.

Volcanic Hazard Maps

The IAVCEI Commission on Volcanic Hazards and Risk has a Volcanic Hazard Maps database designed to serve as a resource for hazard mappers (or other interested parties) to explore how common issues in hazard map development have been addressed at different volcanoes, in different countries, for different hazards, and for different intended audiences. In addition to the comprehensive, searchable Volcanic Hazard Maps Database, this website contains information about diversity of volcanic hazard maps, illustrated using examples from the database. This site is for educational purposes related to volcanic hazard maps. Hazard maps found on this website should not be used for emergency purposes. For the most recent, official hazard map for a particular volcano, please seek out the proper institutional authorities on the matter.

IRIS seismic stations/networks

Incorporated Research Institutions for Seismology (IRIS) Data Services map showing the location of seismic stations from all available networks (permanent or temporary) within a radius of 0.18° (about 20 km at mid-latitudes) from the given location of Great Sitkin. Users can customize a variety of filters and options in the left panel. Note that if there are no stations are known the map will default to show the entire world with a "No data matched request" error notice.

UNAVCO GPS/GNSS stations

Geodetic Data Services map from UNAVCO showing the location of GPS/GNSS stations from all available networks (permanent or temporary) within a radius of 20 km from the given location of Great Sitkin. Users can customize the data search based on station or network names, location, and time window. Requires Adobe Flash Player.

DECADE Data

The DECADE portal, still in the developmental stage, serves as an example of the proposed interoperability between The Smithsonian Institution's Global Volcanism Program, the Mapping Gas Emissions (MaGa) Database, and the EarthChem Geochemical Portal. The Deep Earth Carbon Degassing (DECADE) initiative seeks to use new and established technologies to determine accurate global fluxes of volcanic CO₂ to the atmosphere, but installing CO₂ monitoring networks on 20 of the world's 150 most actively degassing volcanoes. The group uses related laboratory-based studies (direct gas sampling and analysis, melt inclusions) to provide new data for direct degassing of deep earth carbon to the atmosphere.

Large Eruptions of Great Sitkin

Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).

EarthChem

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).