Magmatic carbon and helium discharge from shrub mud volcano, Copper River basin, southeastern Alaska, USA

Shrub mud volcano, in the Copper River basin of southeastern Alaska, has been erupting warm (50 degreesC) mud and water and CO2-rich gas since 1996. This recent discharge, most of which occurs from vents at the summit, contrasts with historical activity at this and nearby mud volcanoes in having significantly higher temperatures and flow rates. The current rate Of CO2 emission from high-bicarbonate thermal waters at Shrub is similar to 10 t/d, and the estimated rate of CO2 upflow from depth is 20-40 t/d. The chemical and isotopic compositions of the gas and water from both Shrub and adjacent mud volcanoes indicate derivation from similar combination of mantle (magmatic) and crustal (marine sedimentary rock) sources. The recent increases in flow rate and vent temperatures at Shrub have most likely resulted from increases in the permeability in the upflow conduits, rather than increases in magmatic heat and volatile inputs.