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F Comm. No. 2019-12 <br />•, Cycles of explbsive and effusive eruptions at Kilauea Volcano,, Hawaii <br />Donald A. Swanson', Timothy R. Rose2, Adonara E. Mucek3, Michael O. Garcia3, Richard S. Fiske2, and Larry G. Mastin4 <br />'U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, Hawaii 96718, USA <br />'Department of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013, USA <br />3Department of Geology and Geophysics, SOEST (School of Ocean and Earth Science and Technology), University of Hawai'i, <br />Honolulu, Hawai'i 96822, USA <br />'U.S. Geological Suivey, Cascades Volcano Observatory, Vancouver, Washington 98683, USA <br />ABSTRACT <br />The subaerial eruptive activity at Kilauea Volcano (Haivai`i) for <br />the past 2500 yr cAm be divided into 3 dominantly effusive and 2 domi- <br />nantly explosive periods, each lasting several centuries. The prevail- <br />ing; style of eruption for 60%, of this time was explosive, manifested <br />by repeated phreatic and phreatomagmatic activity in a deep summit <br />caldera. During dominantly explosive periods, the magma supply rate <br />to the shallow storage volume beneath the summit dropped to only a <br />few percent of that during mainly effusive periods. The frequency and <br />duration of cTplosive activity are contrary to the popular impression <br />that Kilauea is almost unceasingly effusive. Explosive activity appar- <br />ently correlates Kith the presence of a caldera intersecting the water <br />table. The'decrease in magma supply rate may result in caldera col- <br />lapse, because erupted or intruded magma is not replaced. Glasses <br />-with unusually high MgO, TiOs, and KBO compositions occur only in <br />explosive tephra (and one related lava flow) and are consistent with <br />disruption of the shallow reservoir complex during caldera formation. <br />Kilauea is a complex, modulated system in which melting rate, supply <br />rate, conduit stability (in both mande and crust), reservoir geometry, <br />water table, and many other factors interact with one another. The <br />hdaards associated with explosive activity at Klauea's summit would <br />have major impact on local society if a future dominantly explosive <br />period were to Iast several cenhn-ics. The association of lowered <br />magma supply, caldera formation, and explosive activity might char- <br />acterize other basaltic volcanoes, but has not been recognized. <br />INTRODUCTION <br />Kilauea (Hawai'i) is an iconic effusive volcano, known for its lava <br />flows and high fountains. Approximately 17% (250 km') of the volca- <br />no's subaerial narks has been resurfaced by lava flows in the past ?QO yr <br />(Fig. 1). and the ongoing Pu'u '0'6 eruption on the east rift zone, nearly <br />continuous since 1983, covered >125 km= with >4 km' of lava by 2014. <br />Our analysis of Klauea's past 2500 yr shows, however, that explo- <br />sive eruptions were dominant for periods lasting several centuries, not just <br />brief diversions at an otherwise effusive volcano. We find that Kilauea has <br />been in a dominantly explosive mode –60% of the past 2500 yr. The ef- <br />fusive style of the p ;tit 200 yr is, from that perspective, misleading. <br />For this paper we distinguish lava fountains, which at Kilauea in- <br />variably feed lava flows and contain only juvenile components, from ex- <br />plosive eruptions, which do not feed. lava flows and have at least some <br />lithic components. In this usage. most of Kilauea'S explosive eruptions are <br />phreatomagmatic or phreatic, though some may be products of overpres- <br />surized may=ntatic gats. <br />Kilauea had many explosive eruptions older than chose discussed <br />here (Easton, 1987), but details are lacking. We deal with only the past <br />2500 yr. for which many ages and stratigraphic. controls are available, <br />and examine only periods lasting centuries, not short-term events of sev- <br />eral years or less. <br />TWO DONIINANTLY EXPLOSIVE, PERIODS <br />Recent studies indicate two long periods of time during which ex- <br />plosive activity dominated ,the summit region and adjacent south slope <br />of Kilauea (Fig. 2A). More than 140'calendar-calibrated "C ages (Ta- <br />Sites of dated flows 155.25•W <br />1 <br />0 1500-180Q CE <br />PACIFIC <br />• 1000-1500 CE <br />o P, <br />OCEAN <br />• 200 BCE -1000 <br />CE V <br />• >200 BCE <br />P <br />J <br />P <br />9.5"N <br />of <br />oe <br />P 1P <br />tcilometers <br />KN <br />Ages of map units <br />19x5' <br />W Post -1800 CE <br />10 15th century <br />cE <br />PACIFIC OCEAN <br />= pOre-01000('% <br />Mad rnd from .r to arrcr <br />155.25° W <br />W". 2�J6 , <br />Figure 1. Locations of all 14C -dated lava flow samples on Kuauea <br />Volcano (Hawai'f), color coded by time periods discussed in text. <br />Data are available in Table DRi (see footnote 1). Two sample loca- <br />tions north of Kilauea Caldera (KC) with ages older than 200 BCE are <br />shown beyond the limit of Kilauea, because the dated flows are in <br />the subsurface overlain by tephra. Map colors indicate gene.. A ..ges <br />of lava flows compiled from map units of Wolfe and V ris (1996), <br />assuming that their unit poo is entirely younger than iJO0 CE. All <br />flows younger than 1800 CE were recorded during or shortly after <br />the eruption. The 151h century'Aili'au flow field is shown separately <br />to emphasize its large size; samples along Its margin date the flow <br />field (Clague et al., 1999). Other flow fields: PO—Pu'u 'O'6 flow field <br />(1983–presentL which has enlarged somewhat from depiction of <br />Wolfe and Morris (1996) used here; MU—Wuna Ulu flow field (1969- <br />74); KN—Kipuka Nene flow field (200-300 BCE). <br />bles DR2 and DR3 in the GSA Data Repository'; Stuiver and Reimer. <br />1993; Reimer et al., 2004) define the length -of each explosive period, as . <br />interpreted in Fiske et al. (2009) and Swanson et al. (2012a). <br />The Uwekahuna Ash contains deposits of explosive eruptions be- <br />tween ca. 200 BCE and 1000 CE (Fiske et al., 2009). Only three lava <br />flows have been, found interbedded with the Uwekahuna Ash. Two are <br />south of Kilauea Caldera; a third is interleaved with tephra low on the <br />caldera wall and may correlate paleomagneticadly with one of the other <br />flows (Fiske et al.; 2009). The Keanakako'i Tephra Member was produced <br />between ca. 1500 and 1800 CE (Swanson et al.. 201.2a). Only one lava <br />flow was erupted at Kilauea's summit during that time, from the outermost <br />ring. fault bounding the south caldera. Thus, for 2 periods of time lasting <br />1200 yr and 300 yr, 10auea's summit, normally the site of frequent lava <br />. flows (Holcomb, 1987; Neal and Lockwood. 2003), had little effusive ac - <br />'GSAIData Repository item 2014233, Tables DRI-DR3 and Figure DRi, <br />showing all "C ages of lava flows and tephra and their calendar -calibrated ages, <br />and Tables DR4 and DR5, presenting chemical data, is available online at www <br />.geosociety.org/pubs/ft'-)014.htm, or off request from editing@geosociety.org or <br />Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA. <br />rGEOLOGY, July 2014: v. 42; no. 7: p. 631-634; Data Repository item 2014233 I doi:10.1130/G35701 1 1 Published online 22 May 2014 <br />(V2014 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org. 631 <br />