If the eruption resumes, what kinds of precursors are likely to provide warning?
If dome growth were to resume, we would expect it to be preceded by several days or more of seismicity, ground deformation, and perhaps increased volcanic gas emissions as magma again rises up the conduit toward the surface. However, small explosions of steam or volcanic gas, capable of ejecting rocks inside the crater and minor amounts of ash above the crater rim, could occur without warning. Six such explosions occurred between 1989-1991 at St. Helens, a period when the volcano was not erupting. Other types of non-eruptive activity that may occur include rockfalls from the dome or crater walls and small mudflows triggered by rapid snow melt or heavy rainfall.
