Description: From Neal and others (2005): "In mid-May 2002, AVO detected an increase in the number of shallow, low-frequency seismic events at Shishaldin. In addition, a number of 2-3 minute-long tremor-like signals were recorded. No correlative thermal anomalies or other observations of unusual activity were reported to AVO. AVO mentioned the activity in its weekly update of May 17. On May 24, AVO reported in its weekly update that the numbers of locatable low-frequency seismic events had decreased to background levels. Based upon this observation and the lack of correlative satellite-detected thermal anomalies or ground observer reports of anomalous activity, AVO concluded that the seismicity was probably typical of ongoing phreatic activity in the central crater and did not reflected significant restlessness. AVO made no further mention of Shishaldin in May or June weekly updates.
"On August 16, AVO received notification of a pilot report of possible volcanic activity at Shishaldin via the NWS Alaska Aviation Weather Unit (AAWU). The pilot report indicated: 'Shishaldin Volcano appears to be erupting. Steam and dark clouds rising to 10,500 [feet] moving NW-SE'. During a follow up phone call to the area, AVO learned that a NWS weather observer in Cold Bay, about 100 km (60 miles) east of the volcano, reported a steam plume above Shishaldin. According to operational protocols, the AAWU issued an eruption SIGMET advising the aviation community of the possibility of airborne volcanic ash.
"Upon receiving the pilot report, AVO examined seismic and satellite data and determined that Shishaldin was at a normal background state and had not erupted. Further discussions with the NWS weather observer in Cold Bay indicated that the observed steam plume was not unlike those commmonly seen at Shishaldin."