Imaging Magma Under St. Helens

Active Source Experiment gets underway

Over most of the past month small teams of scientists (students doing the hard work, as usual) have been criss-crossing the extended Mount St. Helens region checking out roads and trails to be used to access sites for the installation of many hundreds of small seismic sensors. This process started in the Visualization Lab at Rice University using a variety of spatial information databases to plan the best locations for shot-points and receiver lines.

 

Once a "theoretical" plan was generated it was time for the real world.  With map, compass and hand-held GPS receivers crews spent many days bumping along rough roads, dealing with all sorts of different obstacles to determine the exact locations for the sensors in lines extending radially away from the volcano.  Of course roads and trails in this region are not straight so the lines of instruments also will not be straight, but in some cases cross-country hiking will be done to try to make sure that they are at least approximately straight.  As important as the laptop computer is for note taking, junk food is also important to sustain the crews over very long days; nutella and chips are good for hours of bumpy driving.

 

Early in the season downed trees across minor roads requires some sweat.

 

While surveying was being done for receiver lines the drilling for the shot holes was also underway.  A truck mounted drill produces a hole up to 30 meters deep to be loaded with explosives to generate artificial "earthquakes"  (seismic sources).

 

The location of all the shot points are in a radial pattern centered on Mount St. Helens and located along roads.

 

Some people may wonder if explosive sources might "wake up" the volcano or do other damage to the area.  Actually, such events are not at all unusual and of course none of these have any chance what so ever of effecting volcanic activity of any type. The amount of explosives used in our case is small, smaller than typical explosions in the region for other purposes that take place many days of the year.

 Here is a map of artificial seismic sources (explosions) located by the Pacific Northwest Seismic Network (PNSN) over a few summers.  Such explosions often involve far more explosives than those for our experimental shots and can generate lots of sound.  They are mostly used for quarrying rock for construction projects or for blasting out rock for road building.  Our shots are under ground and probably will not be heard unless one is very close.  The seismic recording instruments are so sensitive that they can "feel" the small thumps our shots make at great distances.

 

In the mean time, to make sure that the many crews to be used for deploying the seismic sensors know how to do it, a comprehensive training session was held at the PASSCAL Instrument Center in New Mexico for the team leaders.

 

Check back in a week or so for more reports on how things are going.