Implications of deflation-inflation event models on Kīlauea Volcano, Hawaiʻi

Abstract

Surface deformation of volcanic areas can reveal information about subsurface magma reservoirs and how magma is transported between them, which is an important part of volcano monitoring for hazard mitigation. One prominent style of deformation observed at Kīlauea volcano, Hawaiʻi, is episodic deflation-inflation (DI) events, which are recorded in surface deformation data and characterized by deflation of the summit region over hours to days followed by rapid re-inflation. The exact cause of DI events is unknown, however, a commonly proposed explanation is that a temporary blockage occurs in the conduit connecting the south caldera magma reservoir to the shallower Halemaʻumaʻu reservoir, thus interrupting the influx of magma. This model is investigated by testing the hypothesis that during the deflationary phase of a DI event, the volume of magma blocked from reaching the Halemaʻumaʻu reservoir is added to the south caldera reservoir. Using a mass balance approach and deformation modeling, the expected deformation (tilt) pattern was predicted for the reservoirs and compared to tilt observations from 16 large (>4 μrad magnitude) DI events between 2010 and 2012. While the predicted tilts due to inflation from the south caldera reservoir are strong enough to be detected, this signal is not seen in the tilt observations. We also explore the possibility that the blockage occurs below the south caldera reservoir, as well as alternative configurations that include a direct connection between the south caldera reservoir and the eruption site. None of the simple two-reservoir models we test are able to adequately satisfy the observations. Selected DI events show that tilt vectors change in both magnitude and azimuthal direction over the course of deflation. We conclude that the portion of the summit storage and plumbing system active during these DI events is more complicated than two connected chambers, and that it is more likely that these summit reservoirs have their own source conduits connecting in some complex way to the deep magma source.