Kīlauea summit eruption in Halemaʻumaʻu crater - September 30, 2021

On September 30, 2021, Hawaiian Volcano Observatory gas scientists used a FTIR spectrometer on the rim of Halema‘uma‘u crater to measure the composition of gases being emitted during Kīlauea's summit eruption, which began the afternoon of Septembe 29, 2021. The eruption is generating a plume consisting primarily of sulfur-dioxide (SO₂), but also containing water vapor (H₂O), carbon dioxide (CO₂), and halogen gases such as HCl and HF.  Sulfur dioxide (SO2) emission rates were estimated at around 20,000 tonnes per day the morning of September 30, 2021. This is significantly lower than the initial emission rates of 85,000 tonnes per day that were measured just after the eruption started on the afternoon of September 29, 2021. USGS photo by T. Elias.