IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_2I-O4Room A5

Date/Time: July 24 9:40-9:55

Estimating the location and volume of shallow magma storage at Kīlauea Volcano fromobservations of episodic ground deformation
Kyle Anderson1 , Jessica Johnson2 , Michael Poland1 , Asta Miklius1 , Matthew Patrick11

USGS Hawaiian Volcano Observatory, USA, 2 Center for the Study of Active Volcanoes, University ofHawaii at Hilo, USA
E-mail: kranderson@usgs.gov

A variety of geophysical observations suggest the presence of at least two long-lived magma reservoirs beneaththe summit of Kīlauea Volcano. Although the locations of the reservoirs are known generally, their volumes arepoorly constrained. Episodic pressure perturbations in the shallow magmatic system, however, generate cycles
of ground deformation that provide valuable constraint on the location and volume of the more shallow of thetwo reservoirs. These cycles of ground deformation, divided into three different classes based on their temporal
histories, have been labeled deflation-inflation (DI) events. Recorded by tilt, GPS, InSAR, and strain data, a typical
DI cycle consists of deflation of the summit region over a period of roughly 8 hours to 3 days, in many cases at
a quasi-exponentially decaying rate, followed by a recovery over hours to a few days to roughly the original level.
Since the opening of Kīlauea’s summit vent in 2008, the rate of DI event occurrence has increased, and DI-related
ground deformation has also closely tracked the level of the summit lava lake. Cyclic deformation at the summit isalso often reflected, after a pause of roughly one-half to three hours, at the Pu‘u ‘Ō‘ō eruptive vent 20 km from thesummit, suggesting that DI events reflect perturbations of magma flow and pressure conditions throughout muchof Kilauea’s interconnected shallow plumbing system.

We invert deformation data recorded during more than 400 individual DI events to estimate the location ofKīlauea’s shallow magma reservoir (the Halema‘uma‘u reservoir) and look for changes associated with eruptiveactivity. We find that the three classes of DI events share a common source region, located near the east marginof Halema‘uma‘u Crater, which has moved little if at all in more than ten years (the time span of the most accuratedeformation records). The depth of this source is shallow but poorly resolved from the tilt data alone; however,GPS, InSAR, and strain data can provide additional constraint. The volume change associated with individual DI
events is probably less than one million cubic meters, although the estimate is correlated with source depth. Whilethe deformation data cannot constrain the total volume of the Halema‘uma‘u reservoir, we are able to estimate
volume by assuming that the summit lava lake is in magmastatic equilibrium with the reservoir such that its surface
height may be used as a manometer. Using probabilistic estimates of host rock rigidity and magma density
together with volume change obtained from inversion of the deformation data, we estimate that the Halema‘uma‘ureservoir has a volume of several cubic kilometers.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

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