The instruments in place at the start of volcanic unrest at
Mount St. Helens in 2004 were inadequate to record the large
earthquakes and monitor the explosions that occurred as the
eruption developed. To remedy this, new instruments were
deployed and the short-period seismic network was modified.
A new method of establishing near-field seismic monitoring
was developed, using remote deployment by helicopter. The
remotely deployed seismic sensor was a piezoelectric accelerometer mounted on a surface-coupled platform. Remote
deployment enabled placement of stations within 250 m of
the active vent.