Hazard Notification System (HANS) for Volcanoes


U.S. Geological Survey
Monday, September 25, 2023, 4:15 PM AKDT (Tuesday, September 26, 2023, 00:15 UTC)

54°45'19" N 163°58'16" W, Summit Elevation 9373 ft (2857 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

A significant eruption of Shishaldin Volcano occurred this morning. Yesterday continued a pattern of increasing eruptive activity that started on the morning of September 23. Around 5:00 pm AKDT on September 24 (01:00 UTC, September 25) highly elevated surface temperatures detected from the summit in satellite data suggested more vigorous lava fountaining had started. This activity was accompanied by low-level ash emissions less than 15,000 ft (4.5 km) above sea level starting at around 6:00 pm AKDT (02:00 UTC September 25), but these dissipated quickly. Beginning at midnight AKDT (08:00 UTC, September 25), a series of seismic signals consistent with volcanic flows were recorded on the north side of the volcano. Early this morning starting around 5:40 am AKDT (13:40 UTC) a significant ash cloud formed and quickly reached 45,000 ft (14 km) above sea level and drifted east along the Alaska Peninsula. In response, AVO raised the Aviation Color Code to RED and the Alert Level to WARNING. This ash cloud detached from the volcano around 7:00 am AKDT (15:00 UTC) and drifted east-southeast at an altitude of 38,000 ft above sea level. Coincident with the eruption of the ash cloud, seismicity declined rapidly to near background levels around 06:00 am AKDT (14:00 UTC). Ash emissions continued at a lower altitude of about 20,000–25,000 ft above sea level until about 08:20 am AKDT (16:20 UTC) and no significant ash emissions from the volcano have been observed since. Small explosions continue to be detected in infrasound data and likely represent low-level eruptive activity near the vent area. In response to this significant decrease in seismicity and ash emissions, AVO lowered the Aviation Color Code to ORANGE and the Alert Level to WATCH around noon today.

Trace to minor amounts of ashfall were reported by the communities of False Pass, King Cove, Cold Bay, and Sand Point. No ashfall is expected from the current small explosions that are being detected in infrasound, but some may still be falling from the drifting ash cloud from this morning’s activity. 

This was the 11th period of elevated eruptive activity that resulted in significant ash emissions and mass flows of volcanic debris on the volcano's flanks since the onset of the current eruption. These periods of elevated eruptive activity have been preceded by increases in seismicity in the hours to days before they occur. Additional collapse of accumulated lava near the summit crater can occur without warning and generates hot mass flows on the upper flanks and small volcanic ash clouds. The ongoing eruption started on July 12, and it is unknown how long this episode will last. However, previous eruptions of Shishaldin Volcano have lasted weeks to months with repeated cycles of activity like those seen since July.

Local seismic and infrasound sensors, web cameras, and a geodetic network monitor Shishaldin Volcano. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lighting data, and satellite images to detect eruptions.

52°4'35" N 176°6'39" W, Summit Elevation 5709 ft (1740 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Slow eruption of lava in the summit crater likely continues. Seismicity remains low with a few earthquakes detected over the past day. Clouds obscured views of the volcano by satellite and web camera today.

The current lava flow at Great Sitkin Volcano began erupting in July 2021. No explosive events have occurred since a single event in May 2021.

Local seismic and infrasound sensors, web cameras, regional infrasound and lightning networks, and satellite data are used to monitor the volcano.

58°14'3" N 155°6'9" W, Summit Elevation 3599 ft (1097 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Seismic activity near Trident Volcano remained elevated over the past day with some earthquakes detected. No signifcant activity was observed in clear satellite and web camera views of the volcano over the past day.

The current period of seismic unrest began on August 24, 2022. Increases in seismic activity have been detected previously at Trident Volcano and other similar volcanoes and did not result in eruptions. We expect additional shallow seismicity and other signs of unrest, such as gas emissions, elevated surface temperatures, and ground movement, to precede any future eruption if one were to occur.   AVO issued an Information Statement on July 25 providing a more detailed update on the volcanic unrest at Trident Volcano and the broader Katmai volcanic cluster (https://www.avo.alaska.edu/news.php?id=1595).

Trident Volcano is monitored by local seismic sensors, web cameras, regional infrasound and lightning networks, and satellite data.


Matt Haney, Scientist-in-Charge, USGS mhaney@usgs.gov (907) 786-7497

David Fee, Coordinating Scientist, UAFGI dfee1@alaska.edu (907) 378-5460

The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.