Regular monitoring of the temperature, gas chemistry, and gas emission at volcanoes with relatively low activity levels can help scientists determine whether and how magma is moving beneath the volcano. These types of measurements have been made sporadically at Mount Baker since the early 1970's.
In March 1975, gas emissions and temperatures increased dramatically at Mount Baker's Sherman Crater – almost half the glaciers within the crater melted and the measured amount of released heat increased more than 10 times. Fumarole temperatures reached "superheated" status and registered over 130 C° in some areas of Sherman Crater. Higher amounts of carbon dioxide and sulfur gases, assumed to be hydrogen sulfide, were detected very shortly after the signs of activity increased in 1975, but emissions of both have decreased through time. Additionally, since the 1970's, the amount of heat released has decreased and the distribution of hot zones within Sherman Crater has reorganized.
The gases at Mount Baker arrive at fumaroles area after having bubbled through and interacted with an extensive groundwater system that overlies the magma. Despite being "filtered" through the blanket of ground water, changes in the gas chemistry can point to periods when there is more magma within the volcanic plumbing system. In contrast to most other volcanoes in the Cascades, gas emissions at Mount Baker are typically high enough to be measured with airborne techniques, making such changes easier to detect. The existence of higher gas emissions, particularly the observation of high CO2 over time, provides strong evidence for ongoing magmatic activity at depth. Increases in the ratio of CO2 to other gases at Mount Baker suggested that the increase in activity in 1975 resulted from an emplacement of a small amount of fresh magma into the mid-crust beneath the volcano, or potentially from opening a network fractures to a deeper reservoir of (more primitive) magmatic gases. The prevalence of deep long-period seismicity at Mount Baker is also thought to be linked to movement of either magma or gases beneath the volcano.
The continued monitoring of gases, temperatures, and seismicity at Mount Baker is important for detecting changes in the deep system of magma and predicting volcanic unrest. Fumarole samples and gas emissions are measured every year or two, unless increases in seismicity or deformation are detected, which would cause much more frequent sampling to be carried out.
Fumarole chemistry data collected from Sherman Crater is available online via the Mount Baker Volcano Research Center.