Dynamics of the December 2020 Ash‐Poor Plume Formed by Lava‐Water Interaction at the Summit of Kīlauea Volcano, Hawaiʻi. (16th March 2023) - Cahalan, Ryan C.
Abstract: On 20 December 2020, after more than 2 years of quiescence at Kīlauea Volcano, Hawaiʻi, renewed volcanic activity in the summit crater caused boiling of the water lake over a period of ∼90 min. The resulting water‐rich, electrified plume rose to 11–13 km above sea level, which is among the highest plumes on record for Kīlauea. Although conventional models would infer a high mass flux from explosive magma‐water interaction, the plume was not associated with an infrasound signal indicative of "explosive" activity, nor did it produce a measurable ash‐fall deposit. We use multisensor data to characterize lava‐water interaction and plume generation during this opening phase of the 2020–21 eruption. Satellite, weather radar, and eyewitness observations revealed that the plume was rich in water vapor and hydrometeors but transported less ash than expected from its maximum height. Volcanic lightning flashes detected by ground‐based cameras were confined to freezing altitudes of the upper cloud, suggesting that the ice formation drove the electrification of this plume. The low acoustic energy from lava‐water interaction points to a weakly explosive style of hydrovolcanism. Heat transfer calculations show that the lava to water heat flux was sufficient to boil the lake within 90 min. Limited mixing of lava and water inhibited major steam explosions and fine fragmentation. Results from one‐dimensional plume modeling suggest that the models may underpredict plume height due to overestimation of crosswind air‐entrainment. Our findings shed light on an unusual style of volcanism in which weakly explosive lava‐water interaction generated an outsized plume. Plain Language Summary: On 20 December 2020, after more than 2 years without an eruption at Kīlauea Volcano, lava erupted through the debris along the summit crater wall and flowed downslope into a hot, acidic water lake. The lava quickly heated and boiled the water, generating a volcanic cloud or plume that reached 11–13 km above sea level, among the highest plumes on record for Kīlauea. After 90 min, the lake had boiled away, leaving behind a new, growing lava lake. In this study, we investigated the processes that occurred during the interaction between the lava and the water lake and the tall plume that developed. Based on observations from weather radar, eyewitnesses, camera footage, acoustic measurements, and numerical modeling, we show the following: (a) interaction between the lava and water did not cause explosions, (b) the plume contained very little ash but carried abundant water vapor that formed ice at higher altitudes, which created lightning, and (c) heat transfer from lava to the water caused the plume to rise much higher than expected for an ash‐poor eruption. Key Points: Weakly explosive water‐lava interaction boiled Kīlauea's summit crater lake in 90 min and created an 11–13 km high, ash‐poor plume The water‐rich plume produced multiple lightning flashes generated by hydrometeor charging microphysics Lava supplied heat to the plume via boiling without contributing mass, which led to a taller plume than expected