[UWNews.org] Seismic activity at Mount St. Helens has changed significantly during the past 24 hours and the changes make us believe that there is an increased likelihood of a hazardous event, which warrants release of this Notice of Volcanic Unrest. The swarm of very small, shallow earthquakes (less than Magnitude 1) that began on the morning of 23 September peaked about mid-day on 24 September and slowly declined through yesterday morning.

However, since then the character of the swarm has changed to include more than ten larger earthquakes (Magnitude 2-2.8), the most in a 24-hr period since the eruption of October 1986. In addition, some of the earthquakes are of a type that suggests the involvement of pressurized fluids (water and steam) or perhaps magma. The events are still occurring at shallow depths (less than one mile) below the lava dome that formed in the crater between 1980 and 1986.

The cause and outcome of the earthquake swarm are uncertain at this time. Several causes are possible, but most point toward an increased probability of explosions from the lava dome if the level of current unrest continues or escalates….

Wow. This is very disconcerting, especially since I’ve been on top several times over the last few years. The next few weeks will be really interesting to see what happens.

More information can be found on the USGS Website, the Pacific Northwest Seismograph Network, KOMO News, and the Seattle Times.