Description: On August 25, 2025, AVO raised the Aviation Color Code and Volcano Alert Level to YELLOW/ADVISORY, stating:
"Over the past month, signs of volcanic unrest at Shishaldin Volcano have been gradually increasing. Sulfur dioxide emissions have increased, a more vigorous vapor plume from the summit crater has been observed, and seismic and infrasound data have shown moderate increases in both the number of events and their amplitude. 
"These observations represent a departure from background behavior and the Aviation Color Code and Volcano Alert Level are thus being increased to YELLOW/ADVISORY.
"An eruption is not certain, and this unrest could eventually decline over time. In the lead up to prior eruptions of Shishaldin, heat emissions were observed in satellite data as magma approached the floor of the summit crater. We have not detected elevated surface temperatures in the summit crater or observed anything else of significance, including during helicopter overflights by an AVO field crew on August 17 and 22, to indicate that magma is rising in the conduit.  
"Eruptions at Shishaldin are sometimes preceeded by days to weeks of seismic tremor (continuous shaking of the ground) that would provide warning of a possible explosive eruption. 
"Gas emissions from the summit crater have at times been mistaken by observers for ash emissions under certain viewing conditions (location of the sun relative to the observer), but there is no evidence for ash deposits on the snow around the summit crater in high resolution satellite data.  The absense of ash deposits was confirmed by the close overflight observations of the summit crater made last week by an AVO field crew."
Over the following weeks, Shishaldin continued to experience relatively high rates of volcanic earthquakes. Infrasound signals and steaming were observed when weather conditions permitted. Sulfur dioxide emissions were seen regularly in satellite data.
Over November and December, frequency of definitive satellite SO2 detections decreased (these detections are dependent on sufficient UV illumination). Other signs of unrest continued approximately the same as in previous months. There was a particularly impressive steam plume on November 27, prompting several passing pilots to submit pilot reports.