Insight into the May 2015 summit inflation event at Kīlauea Volcano, Hawai‘i

Evolving magma temperature and volatile contents over the 2008–2018 summit eruption of Kīlauea Volcano

“…However, because the low-viscosity mafic melt and open-vent structure of Halema‘uma‘u facilitates gas escape, reservoir pressurization has been inferred to reflect accumulation of melt due to changes in either influx (e.g., recharge from the South Caldera reservoir or deeper storage regions) or outflux (e.g., to the East Rift Zone) ( 4 , 44 ). For example, the inferred causes of the May 2015 summit intrusion, the 2018 eruption, and the prevalent hours- to days-long deflation-inflation summit deformation events are months of increased magma influx ( 4 , 6 , 27 ), months of reduced magma outflux ( 45 ), and transient restrictions of magma influx or outflux ( 6 , 8 , 38 ). However, the general controls on magma mass balance over days to years are unknown.…”

“…The May 2014 and May 2015 intrusions were also preceded by a month of Halema‘uma‘u reservoir pressurization without other clearly associated changes in the summit magma system. The lack of clear changes in magma properties would seem to suggest they were induced by decreased magma outflux, although at least in 2015, changes in East Rift Zone lava effusion were not apparent ( 4 , 6 , 27 ). The June 2014 and May 2016 Pu‘u‘Ō‘ō vent openings were not preceded by notable pressurization of the shallow summit magma system, suggesting they were not primarily caused by increased melt flux from the summit but rather by processes along the rift zone.…”

“…We assume a temporally fixed geometry for the three magma reservoirs ( Fig. 1 and Supplementary Text) but constrain the 2015 intrusion to be an active deformation source only over May 13 to 17 ( 27 ). We adopt the 2-km-deep 4-km 3 ellipsoidal Halema‘uma‘u reservoir geometry and 3-GPa rock shear modulus from ( 11 ), consistent with other studies ( 7 , 9 , 10 , 58 , 59 ).…”

“…To obtain time series of pressure change in the Halema'uma'u reservoir, we must consider other known sources of ground deformation at the Kīlauea summit: the South Caldera reservoir (7,8), 2015 intrusion (27), and steady slip along the south flank décollement (fig. S3) (57).…”

“… ( A ) Simplified flowchart of methods and data input/output. Additional constraints on GNSS inversions are from previous geodetic studies ( 11 , 27 , 57 , 60 ). Additional constraints on VLP magma resonance inversions are from previous modeling ( 9 ), gravity data ( 37 ), and geochemical (gas and ejecta) data ( 13 , 16 , 24 , 36 ).…”