Deformation monitoring at Mount Baker
The USGS first established a deformation-monitoring network on Mount Baker in 1981. Using helicopter support, 14 benchmarks were installed, and 16 line lengths and slope angles were measured with an Electronic Distance Meter (EDM) and theodolite between benchmark pairs in 1981. These measurements were repeated in 1983, and 3 additional lines were measured. No significant differences from the initial 1981 measurements were noted.
The network sat idle until 2004, when a research team from Western Washington University began conducting campaign GPS surveys on Mount Baker. In 2004, 2006, 2007, and 2009 additional measurements were made and a few new benchmarks were installed. Based upon these surveys, the distances between stations had generally decreased by several centimeters in the ~25 years between the surveys, suggesting deflation of the volcano.
Mount Baker is also monitored by several gravity stations, which were initially installed by the University of Washington in response to volcanic unrest in 1975. In the months following the 1975 increase in fumarolic activity, a gravity decrease was measured on the volcano, perhaps because of mass lost due to the fumarolic discharge. The gravity network was reoccupied and expanded in 2005 and 2006 by scientists and students from Western Washington University. At Sherman Crater, they found that a major gravity increase had occurred in the ~30 years since the last time gravity measurements had been made. The new data indicated that a magma body that was emplaced in 1975 (or earlier) had become more solidified and denser since the initial measurement. This is consistent with the measured deflation, as well as gas emissions, which collectively argue that the 1975 unrest was driven by a magmatic intrusion.
At the present time, there are no continuous GPS monitoring stations near Mount Baker. The campaign GPS network will be episodically (~every 10 years) reoccupied by CVO to track the rates and styles of deformation. Of course, if Mount Baker experiences another episode of unrest, like that in 1975, additional measurements of the campaign GPS network and gravity stations will provide data on what is happening within the volcano.