Over the past few weeks we've been seeing regular small explosions in the seismic record coming from Shishaldin's crater. Each explosion shows up as a low frequency seismic wave that travels through the ground, followed by a high frequency airwave pulse. The airwaves arrive later because energy from the explosion travels more slowly through the air than it does through the ground. While small explosions are often part of the background activity at Shishaldin, we haven't seen them showing up this clearly in the past 2 years. Elevated surface temperatures suggest there is fresh lava in the crater. Since the explosions were observed around the time that the lava was erupted into the crater, the two are probably closely related. We can't say whether the explosions are directly caused by the erupting lava, though, or whether they are just small puffs of gas coming from the crater floor.

The Alaska Volcano Observatory (AVO) has experienced numerous seismic station failures and our ability to monitor activity at some volcanoes has failed or is heavily impaired. For volcanoes with failed ground instrumentation networks, AVO is unable to (1) assess whether this volcano may be building towards an eruption and/or (2) quickly confirm or dismiss reports of activity. Because these volcanoes are no longer seismically monitored, they will move from volcano alert level Normal and Aviation Color Code Green to "unassigned". As at other volcanoes without real-time seismic networks, AVO will continue to use satellite and infrasound data, and reports from pilots and ground observers to detect signs of eruptive activity. We will update this news item with links to announcements of monitoring status changes as they occur.

Monitoring instruments at Aniakchak Volcano can no longer seismically monitor unrest at the volcano. The final Aniakchak station failure was confirmed on January 23. The Information Statement for Aniakchak is
here.

Monitoring instruments at Fourpeaked volcano can no longer seismically monitor unrest at the volcano. The Information Statement from February 7 that moved Fourpeaked to Unassigned is here.


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