USGS Volcano Notice - DOI-USGS-AVO-2023-10-20T11:24:33-08:00

Summary 

• The current eruption of Shishaldin Volcano started on July 10, 2023, and has included twelve explosive events that have generated volcanic ash clouds that rose to altitudes as high as 45,000 ft above sea level. The last explosive event occurred on October 3.
• Intervals between the explosive events have typically been characterized by low levels of seismic activity and gas emissions. Following the last explosive event, however, both seismic activity and gas output have remained somewhat elevated.
• Satellite and web camera data show that degassing is occurring from the summit and a linear, hot feature that extends a few hundred meters down the northeast flank.  
• Current levels of seismicity and gas output suggest that magma remains at shallow levels within the volcano.
• This new phase of activity may mean that the vent is “open” and that the likelihood of explosive activity has decreased.
• We expect increased seismic activity will provide warning before additional explosive activity if it were to occur. However, collapse events at the volcano’s summit could create ash clouds as high as 25,000 ft asl and could occur with little warning.

Current Observations

Volcanic gases

Since the last explosive event on October 3, satellite data have shown that sulfur dioxide (SO₂) emissions from the volcano have remained elevated with greater than 1000 tons of SO₂ detected per day. This is different than the periods in between previous explosive events, when SO₂ was either not detected or was at low levels.

Seismic activity

Over the past two weeks, seismic activity has remained elevated at the volcano. It consists of nearly constant seismic tremor and frequent, small, long-period, or low-frequency, earthquakes. These signals are consistent with the movement of volcanic fluids and gases within the volcano.

Satellite and web camera observations

Recent clear views in webcam and high-resolution satellite images show that the summit region has been emitting abundant steam. This rises from the summit itself as well as a linear, hot feature that extends about 1300 feet (400 meters) from the summit down the northeast flank.

Collapse events

The eruption has resulted in some physical changes to the upper part of the volcano, including formation of steep collapses that intersect the summit crater and extend as linear gullies over 1000 ft northeast and southwest from the summit crater. The walls of the summit crater and these gullies are steep and have collapsed repeatedly. The collapses occur without warning and can form fast-moving rock and debris flows that generate ash clouds. These ash clouds have risen to 15,000 to 20,000 feet above sea level and drifted tens of miles beyond the volcano with the wind. 

Prognosis 

The presence of elevated levels of volcanic gases and seismicity suggest that magma is located at shallow levels beneath the summit of Shishaldin; however, there is no evidence for lava at the surface.

Eruptive sequences at Shishaldin and at other volcanoes show that eruptions can transition from mostly explosive to mostly lava-producing (or effusive). The degassing we see now at Shishaldin may tell us we have entered a new phase of activity where explosions are less likely.

The duration of previous Shishaldin eruptions has been variable, ranging from days to up to a year. It is unclear whether this eruption is reaching its end, or if it has paused.

Potential hazards

Future explosive eruptions from Shishaldin will likely have the same impacts and hazards as those of the eruption sequence so far – ashfall and airborne ash. Since July, trace to minor amounts of ashfall have been reported on the communities of False Pass, Cold Bay, King Cove and Sand Point, and on vessels in nearby marine waters. Airborne ash clouds have resulted in flight cancellations to nearby communities as well as rerouting of transpacific flights.

Modest collapse events involving newly erupted material or over-steepened ground at the volcano’s summit region may continue even once the current eruption is over. They can occur without warning and form fast-moving rock and debris flows on the slopes of the volcano that generate ash clouds. These ash clouds could rise as high as 25,000 feet above sea level and drift downwind.

Shishaldin experienced a large flank collapse during the late Pleistocene (roughly 9500 years ago), essentially removing the preexisting edifice. Even though there have been modifications to surficial features of the summit crater during the current eruption, we consider the possibility of a Shishaldin flank collapse unlikely.

For a full description of volcanic hazards associated with Shishaldin Volcano, please see the following report: https://avo.alaska.edu/pdfs/RI_2002_4.pdf

Current monitoring

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 lightning data, and satellite data to detect eruptions.

To view information about Shishaldin Volcano: https://www.avo.alaska.edu/activity/Shishaldin.php