Temporal Variations in Scrubbing of Magmatic Gases at the Summit of Kilauea Volcano, Hawai'i

Measurements of gas compositions and emission rates play a major role in monitoring restless volcanoes. However, thermodynamic calculations imply that scrubbing by groundwater will prevent most HCl and significant SO2 emissions until dry pathways are established, thus leading to underestimates of gas released from magma and magma volumes. Despite the significance, direct evidence for scrubbing is mostly lacking. Based on 50 water samples collected between 2003 and 2011 from the deep NSF Well at the summit of Kilauea Volcano, we show that the chemical and stable isotope compositions of groundwater were modified by magmatic gas condensation. Temporal variations of dissolved SO42- and Cl- in the water coincided with changes in magmatic and volcanic activities. The temporal variations in water level and chemical and isotopic compositions support prior inferences of magmatic SO2 and HCl scrubbing by groundwater at Kilauea Volcano.