Abstract Chemical denudation rates during the 2014–15 Barðarbunga eruption, calculated using river chemical fluxes, increased substantially confirming that volcanic activity and its products such as fresh lava, and acidic volatiles accelerates these rates. Although the long-term net effect of the combined input of volcanic gases and basalt from the eruption appears to be the overall net drawdown of CO 2 , it is found that the rapid release of acid gases to surface waters once the basaltic lava comes in contact with surface waters will lead to a short-term release of CO 2 from these waters.