Eruptions in sync: Improved constraints on Kīlauea Volcano's hydraulic connection
Introduction
The relationship between summit and flank activity at volcanoes offers unique insight into the extent and interconnection of magmatic systems. Volcanoes such as Etna (Acocella and Neri, 2003) and Kīlauea (Eaton and Murata, 1960) commonly exhibit eruptions with associated summit and flank activity, and notable eruptions at Tolbachik (1975–1976; Fedotov et al., 1980), Nyiragongo (1977; Tazieff, 1977), Stromboli (2002 and 2007; Calvari et al., 2005, Calvari et al., 2010) and Bárdarbunga (2014; Gudmundsson et al., 2016) involved flank eruptions associated with withdrawal of magma from their summits. At Nyiragongo in 1977, the drainage of perched summit magma through flank vents was a major factor in the unusually rapid lava flows that devastated downslope communities (Tazieff, 1977).
Kīlauea is an archetype volcano for summit–flank interaction. Native Hawaiians were well aware of the basic relationship between the summit and rift zones (i.e. flanks) prior to the arrival of the first Westerners, and “supposed [the volcano deity] Pele went by a road under ground from her house in the crater [Kīlauea caldera] to the shore” (Ellis, 1825; Appendix). Modern studies have affirmed the close tie between summit and rift zone activity at Kīlauea based on the timing of activity at these sites, as well as geophysical and geochemical data (Swanson et al., 1976, Cervelli and Miklius, 2003, Anderson et al., 2015, Rowe et al., 2015). Rift zone eruptions are often preceded by summit inflation and accompanied by summit deflation, confirming the basic conceptual model in which magma, rising from the mantle, accumulates in the summit magma reservoir complex and then flows laterally at shallow depths to erupt along the rift zones (Fig. 1) (Eaton and Murata, 1960).
The recent eruptions at Pu‘u ‘Ō‘ō and Halema‘uma‘u (Fig. 2) mark the first time in the historic record that long-term (>1 yr) eruptions have been concurrent at the summit and a rift zone, offering new insights into the relationship between these two segments of the magmatic system. In our study, we jointly analyze measurements of lava lake level (surface height) and ground deformation (GPS and tilt) with rift zone eruption data to understand how rift zone eruptive events influence summit activity. We show that rift zone eruptions regulate summit activity in several important ways, demonstrating the importance of the hydraulic linkage between Kīlauea's summit and rift zones, and offering further evidence that volcanic systems can maintain magmatic connections over tens of kilometers which can persist for decades.
The main focus of this paper is the phase of concurrent summit and ERZ activity (2008–2018), which was abruptly interrupted in May 2018 while this manuscript was being revised. Although the new 2018 activity on the Lower East Rift Zone is not addressed in detail here, it is relevant to the insights gained from this study (see Note in Revision, Section 9).
Section snippets
Background
Early indications of a connection between Kīlauea's summit and rift zones originated from observations that the lava level and/or caldera floor at the summit would drop following rift zone eruptions (Ellis, 1825, Bishop, 1827, Dana, 1849; Appendix). More recent ground deformation measurements confirm that the summit magma reservoir complex deflates in association with rift zone eruptions, such as in 1955 and 1960 (Eaton and Murata, 1960, Macdonald and Eaton, 1964). An absence of earthquakes
Vent elevation and lava level
ERZ vent elevations were compared to summit lava lake level during periods when eruptions were concurrent and monitoring data were available. These periods include the 1922 and 1923 ERZ eruptions, in which ERZ vent elevation data comes from Macdonald et al. (1983), and the past ten years of the recent summit eruption, in which ERZ vent elevations are taken primarily from a 2005 5 m resolution DEM and a 2013 TanDEM X DEM (Poland, 2014) or from kinematic GPS measurements (Appendix). We also
Short-term ERZ changes
We analyze the short-term response of the summit lava lake to the formation of new ERZ vents for both the early 1900s summit lava lake period and the recent summit eruption (2008–2018). The former involved two brief ERZ eruptions in the 1920s (May 1922 and August 1923), and the latter five ERZ vents which opened as new episodes of the Pu‘u ‘Ō‘ō eruption (March 5, 2011; August 3, 2011; September 21, 2011; June 27, 2014; May 24, 2016). We disregarded the vents for Kahauale'a 1 and 2 flows
East Rift Zone vent elevation influences summit pressure
Our data demonstrate that ERZ vent elevation plays a controlling influence on summit pressure, as recorded by deformation and lava lake surface height. Despite variable initial values, dropped to a level just slightly above during most of the ERZ eruptive events examined here, with similar to for the March 2011 event (Fig. 4A). These data suggest that the summit reservoir drains to, or nearly to, a state of pressure that depends upon the ERZ vent elevation during rift zone eruptive
Modeling
Is it plausible for minor changes in the ERZ to significantly impact eruption rate and summit pressure? Patrick et al. (2015a) demonstrated that eruptive fluxes observed in April–June 2012 were driven by very modest overpressures; 12 m of overpressure at the summit (roughly 0.3 MPa) above magmastatic yielded an eruption rate of 1 m3 s−1. The ∼25 m of elevated summit lava level (Fig. 8) equates to excess pressures of only 0.2–0.6 MPa driving the ERZ eruption, assuming bulk magma column densities
Discussion
The coupled fluctuations in lava level and deformation at the summit and Pu‘u ‘Ō‘ō (Fig. 6) add further quantitative constraints on the efficient hydraulic connection along the ERZ (Tilling, 1987, Cervelli and Miklius, 2003). This connection implies that changes at any point along this span can have an effect on the overall magmatic system. In our study period, changes were driven by four processes originating from either a) the summit or b) the ERZ (Fig. 9), and are enumerated below.
Conclusions
Our study analyzed lava lake level, vent elevation data and deformation to examine the interaction between Kīlauea's summit lava lake in Halema‘uma‘u Crater and its ERZ eruption at Pu‘u ‘Ō‘ō. The specific conclusions are:
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The summit lava lake maintained a dynamic equilibrium with Pu‘u ‘Ō‘ō and the ERZ vent, demonstrating that an efficient hydraulic (magmatic) connection exists. The summit lava lake maintained a level that was 50–150 m higher than the lava level in Pu‘u ‘Ō‘ō. This minor height
Note during revision
While this manuscript was being revised, inflation at the summit and Pu‘u ‘Ō‘ō began in March 2018 and continued through April. This inflation culminated in an intrusion east of Pu‘u ‘Ō‘ō on April 30, which then fed a new eruption on the Lower East Rift Zone that began on May 3. This Lower East Rift Zone eruption drained magma from the summit reservoir, leading to the summit lava lake disappearing, and the collapse of Halema‘uma‘u Crater and much of the surrounding floor of Kīlauea Caldera.
Acknowledgments
HVO staff maintained the deformation and seismic network used in this study. The authors wish to thank the National Park Service for facilitation. Funding for the thermal cameras was provided by the American Reinvestment and Recovery Act (ARRA). We thank D. Trippanera, M. Poland, an anonymous reviewer, and the editor for reviewing the manuscript. This work was supported by the U.S. Geological Survey's Volcano Science Center.
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