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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
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