CO₂ degassing in the Oregon Cascades

The carbon isotope content of dissolved inorganic carbon was measured for large cold springs in the central Oregon Cascades. Low ¹⁴C activities in some of the springs are interpreted to result from the dissolution of diffuse emissions of magmatic CO₂, even though volcanic activity has not occurred in this area for more than 1300 yr. On the basis of dissolved magmatic carbon concentrations in the springs, we infer a diffuse magmatic CO₂ degassing rate of 3.4 × 10⁵ kg/yr per kilometer of arc for the central Oregon Cascades. The CO₂ flux calculated from estimates of the mean magmatic intrusion rate and experimentally determined values of CO₂ content in melts is consistent with that determined from our measurements of the dissolved CO₂ flux at springs.