Sulfur dioxide emissions associated with the May 2018 fissure eruption in Kilauea's Lower East Rift Zone

On 30 April 2018, the Pu`u`O`o cone in Kilauea's East Rift Zone collapsed suddenly and magma drained into a dike system that progressed rapidly downrift. On 3 May 2018, the first of a series of more than 20 vents opened in the Leilani Estates subdivision in the Lower East Rift Zone (LERZ) and began emitting lava and volcanic gases. At the time of this writing (July 2018), the eruptive episode continues and sulfur dioxide (SO₂) emissions from active fissures in the LERZ are higher than any that have been measured at Kilauea in decades.

Prior to the 2018 fissure eruption, convective processes in the lava lake at Kilauea's summit continuously brought volatile-rich magma close to the lake surface resulting in 5,000 metric tons of SO₂ being emitted from the summit every day. As lava at the summit receded throughout May 2018, frequent rockfalls into the lava reservoir occurred, which agitated its surface and led to ash-rich emissions with up to 12,000 metric tons per day (t/d) of SO₂. Around the beginning of June, a plug of debris began to collapse in on the lava reservoir and seal it off from the surface. Both ash and gas emissions dropped. By the end of June 2018, SO₂ emissions had decreased to less than a few hundred t/d, where they currently remain.

As the volcano's summit was collapsing, the eruption of lava and gas from fissures in the LERZ became increasingly vigorous. By the end of May 2018, lava effusion had shifted from multiple active fissures to Fissure 8, where lava fountains as high as 80 meters began to occur and feed flows of low-viscosity lava into the ocean. Currently the center of activity, Fissure 8 degasses more than 50,000 t/d of SO₂ and significantly impacts air quality on a regional scale. In fact, satellite instruments are detecting significant atmospheric SO₂ loads at locations more than 1,000 km downwind. But dense gas and water clouds created by the lava ocean-entry and degassing at Fissure 8 create conditions that make accurate determination of SO₂ emission rates difficult, and sophisticated methods for measuring plume height, plume speed and SO₂ column density must be applied. Here, we describe our strategies for quantifying gas emissions and how our measurements have informed the conceptual model of volcanic activity during Kilauea's ongoing fissure eruption, as well as providing valuable information for air quality assessments and forecasts.