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Home , Dacite, Ignimbrite, Keanakakoi eruption, Trachyte

Bull Volcanol (2016)78:34 DOI 10.1007/s00445-016-1027-2

SHORT SCIENTIFIC COMMUNICATION

Discovery of a sequence at ,

Thomas Shea1 & Jacqueline Owen2

Received: 2 December 2015 /Accepted: 29 March 2016 # Springer-Verlag Berlin Heidelberg 2016

Abstract are common in many intraplate Keywords Pyroclastic density currents . Ignimbrites . ocean islands but have been missing from the known geo- Hawaii . Hualālai . Trachyte logical record in Hawaii. During a recent field campaign, the remnants of a trachytic ignimbrite sequence have been discovered at Hualālai volcano, fortuitously preserved Introduction from subsequent basaltic flow cover. We provide a preliminary description of these deposits, as well as bulk Ignimbrites (here defined loosely as pyroclastic density cur- and glass chemical analyses to determine their potential rent BPDC^ deposits consisting dominantly of a poorly sorted relationship with other nearby from Pu’u mixture dominated by juvenile and ash, e.g., Branney Wa’awa’a(PWW)andPu’u Anahulu (PA). The results and Kokelaar 2002) are widespread along arc, back-arc, and suggest that these ignimbrites are from neither PWW nor continental intraplate regions that erupt evolved (e.g., PA, but instead may relate to trachytes that are found as , trachytes, ). Large ignimbrites have also wallrock blocks some 20 km distant. Therefore, de- been identified at several oceanic intraplate settings, including spite being rare overall in Hawaii, the ignimbrites—and at the Canary Islands (Freundt and Schmincke 1995), the more generally trachytes—were probably widespread (e.g., Duncan et al. 1999), and Cape Verde (Eisele around Hualālai. Compared to other intraplate ocean et al. 2015). Along the Canary Islands, this type of volcanic islands, the combination of a fast-moving plate, high mag- activity has produced many hundreds of cubic kilometer of ma supply, and eruption rates underneath Hawaiian volca- deposits. Evolved magmas typically erupt in intraplate ocean- noes may explain the scarcity of ignimbrites preserved at ic islands during post-shield volcanism. Their origin is often the surface. Their presence at Hualālai could reflect unusu- attributed to fractional crystallization (±replenishment) of al conditions of edifice stress during the transition from alkalic that produces phonolites or trachytes, and/or shield to post-shield volcanism. mixing of basalts with assimilated sediments or crustal intru- sions, which typically yields rhyolites (Freundt and Schmincke Editorial responsibility: K.V. Cashman 1995; Freundt-Malecha et al. 2001;HansteenandTroll2003; Edgar et al. 2007;Sigmarssonetal.2013). Electronic supplementary material The online version of this article In Hawaii, exposed volcanic sequences involving evolved (doi:10.1007/s00445-016-1027-2) contains supplementary material, which is available to authorized users. magmas are comparatively rare at the surface. Exceptions in- clude the voluminous Pu’u Anahulu-Pu’uWa’awa’atrachyte * Thomas Shea flow and cone association at Hualālai, Hawaii (Stearns and [email protected] Macdonald 1946), trachyte domes and flows on West (e.g., Pu’u Koae, Mt Eke, Pu’u Launiupoko, Stearns and Macdonald 1942;Velde1978), and the rhyodacitic Mt. 1 Department of Geology and Geophysics, SOEST, University of Kuwale flow on (Van der Zander et al. 2010). To date, Hawaii, 96822 Honolulu, HI, USA however, no ignimbrites have been identified, in contrast with 2 Lancaster Environment Centre, Lancaster University, Lancaster, UK other intraplate sites such as the Canary Islands. Pyroclastic 34 Page 2 of 8 Bull Volcanol 78:34 (2016) density current deposits recognized at Kilauea are distinct in During recent field work, we identified a previously being basaltic and lithic-rich/juvenile-poor, with an inferred undescribed sequence on top of the Pu’u Anahulu flow. phreatomagmatic origin (McPhie et al. 1990; Swanson et al. This sequence was preserved from erosion and weathering at 2012). In this brief communication, we describe the first dis- only a few sites (nine locations are described here, cf. Fig. 1), covery of ignimbrite deposits in Hawaii, at Hualālai volcano. although the base of the deposit still blankets the flatter por- We briefly speculate on the potential for other similar deposits tions of some of the Pu’u Anahulu flow lobes. The thickest to be buried underneath the recent lava flow cover and the section (preserving the most comprehensive record of the ig- hazard implications of such eruptions for Hawaii. nimbrite deposits) was trenched about 1.5 km from the nearby Pu’uWa’awa’a trachyte cone (location 1) (Fig. 2a). The ignimbrite deposits were subdivided into four major eruptive units (EU1-EU4) based on abrupt changes in Description of deposits lithofacies relationships that could be recognized between dif- ferent outcrops. The grouping into different eruptive units re- The Pu’u Anahulu (PA) trachyte flow on the north flank of flects each inferred flow cycle. The Pu’u Anahulu flow under- Hualālai is a topographically prominent feature (≤260 m from neath the tephra sequence usually consists of holocrystalline base to top) that has been linked to the nearby trachyte pyroclastic (microlites and microphenocrysts) trachyte blocks 10–50 cm cone of Pu’uWa’awa’a (PWW; Fig. 1; Stearns and Macdonald in size, enclosed within either (1) a weathered mixture of ash 1946; Cousens et al. 2003; Shamberger and Hammer 2006). The to coarse ash-sized trachyte grains and soil, or (2) a basal Pu’u Anahulu and Pu’uWa’awa’a trachytes are >100 ka (Clague pumice-bearing ignimbrite (massive lithofacies, 1987; Cousens et al. 2003), and by far the oldest subaerial mLT) containing disrupted lenses of soil, which are interpreted Hualālai rocks exposed (Hualālai’s next youngest exposed flows have been remobilized by the ignimbrite (Figs. 2a and 3c). This are ∼13 ka, Moore et al. 1987). ignimbrite (eruptive unit EU1) has a fine ash and a low

KO MK ML >11ka ML 3-5ka HL

ML KIL

HL 5-11ka

Huehue 8 group Rift zone 9 6 7 5 Pu’u Anahulu flow Hualālai Waha group 4

5 km 3 ML 1.5-3ka 2 Legend HL >11ka

Mauna Loa Hualālai (ML) (HL) basalts alkali basalts

Pu’u Wa’awa’a cone 1 ML 1859 Hualālai vents <13 ka

Pu’u Wa’awa’a-Pu’u Anahulu HL 3-5ka Trachytes

HL 1.5-3ka Other Hualālai wells cones trachyte locations N Minimum inferred extent of Pu’u Anahulu flow Hualālai summit Ignimbrite outcrops 2 km

Fig. 1 Geological setting of Hualālai ignimbrites. (Left) Digital elevation wells in which trachyte was recovered (BHuehue group^) (cf. Cousens model of Hualālai volcano with prominent trachyte exposures (Pu’u et al. 2003). (Right) Geological map of the Pu’uWa’awa’a-Pu’u Anahulu Wa’awa’a cone and Pu’u Anahulu flow) on northern flank. Yellow stars area (modified from Sherrod et al. 2007). Only certain areas of the Pu’u show the location of other trachyte blocks found as lithics in more recent Anahulu trachyte remain uncovered by <13 ka post-shield activity. basaltic products (BWaha Pele group^), red stars mark the location of Numbers refer to main stratigraphic locations described in the text Bull Volcanol (2016)78:34 Page 3 of 8 34 cm a LITHOFACIES DESCRIPTION b massive pumice lapilli tuff pumice lapilli unit

soil coarse ash/fine lapilli unit dark-clast-rich unit

Post-ignimbrite deposits unit w/ color gradient trachyte blocks/flows basaltic tephra SSS soil/weathered material

Basal bed comprises coarse iii strongly indurated mLT/paleosoil pumice ash with variable Location 1 150 EU4 reddish coloration both at SSS diffuse stratification mpLT bottom and top. Grades into weathered ignimbrite/paleosoil. EU4 Legend diffuse cross stratification marked cross stratification Unit consists of tripartite basal erosive surface mLT-mLTpip lithofacies with grainsize 2 variations (slight normal then SSS gradual transition inverse grading), with top bed iii EU3 indurated, surrounded by dark tuff that propagates into top ignimbrite via pipe structures. EU3 Top third of massive lapilli tuff iii facies is indurated. 100 dsLT iii 5 iii Base of unit is a coarse pumice SSS 7 3 iii SSS 8 ash-rich series of beds iii displaying diffuse stratification iii SSS SSS mLT and bedding, with iii iii EU2b pinching-swelling. Like units EU5? below, grades into ignimbrite EU2b iii dspLT with increasing induration 9 iii towards the top. SSS iii iii Unit marked by pinch and swell mLT cross-stratified beds with highly iii variable grainsize and a few 4 pumice-rich beds. High SSS 50 EU2a iii 6 iii abundance of dark/dense iii xsLT material overall. Grades into EU2a ignimbrite towards the middle. SSS

iii Ignimbrite unit with slight iii iii reverse grading of pumice iii iii iii grains and frequent ash/tuff iii iii lenses with different lithologies iii mLT-lensT EU1 in lower half (pumice ash, +pumice ash, soil pods). Change in color from EU1 brown at base to light grey/yellowish, and to tan at top. 0 Indurated towards the top.

SSS SSS SSS SSS SSSSSS SSS SSS SSS Pu’u Anahulu trachyte flow PA

Location 1 Fig. 2 a Stratigraphic column of pyroclastic density current deposits at explanation). b Variations in PDC stratigraphy across the different location 1. Lithofacies nomenclature used follows Branney and Kokelaar locations, ordered arbitrarily by distance from the Hualālai summit. (2002), m = massive, LT = lapilli-tuff or lapilli-ash, p = pumice, Stratigraphy and lithofacies are here represented as simplified patterns, ds = diffuse-stratified, xs = cross-stratified, lensL = pumice lapilli lens. along with information pertaining to lithofacies contact, state of Lithofacies were grouped into eruptive units EU1-EU4 (see text for induration, and stratification abundance of pumice lapilli that reach ∼3–4 cm in size at location distinctive from other units due to slight changes in color 1. In addition to soil pods, lenses of fine light gray ash or coarser (darker toward the top, Figs. 2a and 3d, e). At location 1, the dark gray ash are abundant near the contact with the blocky top of this unit is dark, highly indurated, and displays small surface of the Pu’u Anahulu flow. The presence of remobilized pipe structures that progress into the overlying ignimbrite. soil at the contact with Pu’u Anahulu blocks suggests that the Finally, EU4 has a thin basal subunit composed of coarse PDC sequence and Pu’u Anahulu were not produced by the pumice ash (normally then reversely graded Bmassive coarse same eruption. pumice ash^ mpT) that again transitions into a massive lapilli The EU1 ignimbrite is overlain by a cross-stratified unit tuff (mLT) facies. Units EU1, EU2a, and EU4 are found in all rich in obsidian and cryptocrystalline trachyte, interbedded locations on the PA flows (Fig. 2b). Some locations show low with indurated fine ash layers and coarser pumice lapilli beds angle imbrication or bed-parallel fabric marked by pumice (Bcross-stratified lapilli-ash^ xsLT lithofacies, Figs. 2a and 3b, clasts, typically within the coarser-grained portions of the c, e). This subunit grades into another ignimbrite and together dsLT and xsLT lithofacies. comprise EU2a. EU2b is found at a few locations and consists Each repeated sequence of a fines-poor, diffuse to cross- of a series of fines-poor diffuse stratified, coarse pumice lapilli stratified unit grading fairly abruptly (usually over <15 cm) into beds (Bdiffuse stratified pumice lapilli-ash^ dspLT) that grade an ignimbrite is interpreted here as a distinct flow unit. into a thinner massive lapilli tuff (mLT) unit (Fig. 3a). Individual flow units aggrade progressively, starting as either EU3 has a faintly stratified fines-poor coarse ash-rich base granular fluid-based (diffuse-bedded units) or traction- (diffuse-stratified lapilli tuff lithofacies dsLT) that is fairly dominated (cross-stratified units) currents that transition into 34 Page 4 of 8 Bull Volcanol 78:34 (2016)

a mLT b

EU2a dspLT xsLT EU2b

pLT

EU1 mLT

c pipes mLT d mLT EU3

xsLT EU3 EU2 dsLT

mLT xsLT

mLT mLT EU1 mLT EU2b PA paleosoil pLT

10 cm 10 cm PA block

e

EU3

EU2a

Blocky ‘mound’ EU1 on PA flow

Fig. 3 Field photographs of the Hualālai ignimbrite sequence. a EU1 normally then inverse-graded EU3 base with dark-colored indurated ignimbrite and EU2a eruptive unit with a stratified to cross-stratified layer and two pipe structures. The dsLT lithofacies grades progressively fine lapilli base interbedded with fine ash beds that transitions into the into a mLT. d A slightly more distal location with somewhat diffuse, overlying ignbimrite. The color transition is fairly abrupt but clasts from discontinuous Pu’u Anahulu paleosoil pods within EU1 ignimbrite. e EU2 base clearly continue into the massive lapilli tuff. b Unit EU2b with Contact of the PDCs with substrate and pinching-swelling behavior. coarse lapilli-rich and diffuse-stratified basal lithofacies displaying a clear Interaction of the current with small-scale topography (the trachyte pinch-and-swelling character. Note the abrupt color and grain size blocks from underlying Pu’u Anahulu flow) results in much thinner transition between the fines-poor pLT base and the underlying EU2a EU1 and EU2 deposits (marked by two arrows) ignimbrite. c Faulted/deformed sequence with diffuse-stratified, fluid-escape dominated, more dilute current (massive lapilli cementation of the moist tuff as ignimbrites were overridden by tuff) (e.g., Branney and Kokelaar 2002; Brown and Branney the subsequent hot, granular-fluid based PDC currents, or, al- 2004). The contact between inferred eruptive units is dominant- ternatively, by migration of residual gasses after emplacement. ly erosive. Upward increases in induration and pinkish colora- Numerous small pieces of silicified (i.e., composed of pure tion within each main ignimbrite unit could result from partial SiO2 as verified by energy-dispersive spectrometry) vegetation Bull Volcanol (2016)78:34 Page 5 of 8 34 were found within the EU2 ignimbrite lithofacies. The pieces are We also note a subtle compositional change from EU1 to EU5. generally discontinuous and oriented parallel to PDC stratifica- The early PDCs have lower MgO and TiO2 and higher alkali tion and have an irregular tubular internal structure that suggests contents compared to the later PDC phases. The later phases are they were branches of small trees and brush entrained during also most similar to the Waha Pele compositions. The PDC emplacement. This interpretation indicates a minimum of feeding the Hualālai ignimbrites may have therefore been a few years between EU1 and EU2. Alternatively, they may be slightly chemically zoned. In this scenario, effusion of Waha rhizoliths (silicified roots), in which case no inferences about the Pele trachytes would have followed the eruption of Hualālai duration/timing of breaks in activity can be made. A more thor- ignimbrites. ough inspection of the distribution, orientation and state (e.g., fragmented or continuous in the tuff) of this silicified material is required to constrain the time gap between the first two erup- Eruption style tive units. With so few outcrops, our record of stratigraphic variations within this ignimbrite sequence is naturally incomplete. Nature and origin of pyroclasts Therefore, making inferences about deposit area, thickness, and volume, which may help characterize the intensity of the Pyroclasts collected from the different units are almost exclu- eruption(s) that produced the Hualālai ignimbrites, is not war- sively trachytic microvesicular pumice, obsidian, and poorly ranted at this point. vesicular cryptocrystalline grains (Plate A1 in the Supplementary Nevertheless, a few observations can be made based on the Material). Crystalline clasts are strongly dominated by flow- nature of the deposits and the pyroclast characteristics. The aligned alkali and are mostly -free. A few trachyte composition of all analyzed PDC grains and the gen- ash particles of submillimeter non-vesicular microcrystalline ba- eral lack of basaltic wallrock within the eruptive units suggest salts were found in thin sections of EU1 and EU2 material, but that the Hualālai ignimbrite eruptions were dominantly mag- not in the overlying units. matic, with little involvement of external water. These PDCs Glasses within pumice, obsidian, and cryptocrystalline are therefore different in nature from the other instances of clasts were analyzed using the electron microprobe (see density current deposits found in Hawaii, which are typically Supplementary Material for analytical conditions and corre- generated during phreatomagmatic activity (Swanson et al. sponding data table) to (1) verify their composition and (2) 2012). The presence of substantial amounts of non- or assess their origin. Only domains that displayed less than poorly-vesicular obsidian and cryptocrystalline material along about 10 % microlites were analyzed to avoid glasses overly with the erupted pumice at the base of each PDC unit may be modified by syn-eruptive crystallization. The glass analyses linked with the disruption of a cryptodome or dense conduit were compared to four Hualālai trachyte groups previously plug (i.e., vulcanian activity). A broad range of relative vesic- analyzed for bulk composition using XRF (Cousens et al. ularities and crystallinities is consistent with a mixture of plug 2003; Shamberger and Hammer 2006): the Pu’uWa’awa’a material that was accompanied by subsequent emission of pyroclastic cone, the Pu’u Anahulu flow, and the trachytes highly vesicular pumice during a more intense eruption phase of Waha Pele (found as lithic blocks co-erupted with recent (e.g., Hoblitt and Harmon 1993; Giachetti et al. 2010). ) and Huehue (extracted from a water well). Hualālai Thorough pyroclast componentry, grain-size, and density ignimbrite glass analyses were also compared to glass analy- analyses are required to verify this hypothesis. ses from Pu’uWa’awa’a pyroclasts (obsidian and pumice with <10 % microlites). Despite their generally similar major element compositions Implications for trachyte volcanism at Hualālai within the array of eruptives at Hualālai (Fig. 4a), the four and on the island of Hawaii main trachyte groups show subtle differences in bulk chemis- try (Fig. 4b, c, d). Somewhat surprisingly, the PDC glass com- Widespread trachytes under Hualālai positions are distinct from nearby Pu’uWa’awa’aorPu’u Anahulu trachytes and much more similar to the Waha Pele The possible cogenetic relationship between the Waha Pele tra- blocks, found nearly 20 km to the south. At 103 ka, the Waha chyte and the ignimbrites described herein would imply that Pele trachyte is substantially younger than the Pu’uAnahulu trachytic PDCs may have covered a large area of Hualālai vol- flow (114 ka) and probably derives from an effusive eruption cano. Gravity studies by Moore et al. (1987) and Kauahikaua as well (Cousens et al. 2003). Therefore, although the Hualālai et al. (2000) also support the idea of voluminous trachyte de- ignimbrites and the Waha Pele blocks may have originated posits underneath the <13 ka basalt cover. These studies showed from the same subsurface magma reservoir, they likely repre- that Hualālai differs from other nearby volcanoes in lacking clear sent different eruptions or, at least, different eruptive phases. high gravity anomalies that are typically associated with rift zone 34 Page 6 of 8 Bull Volcanol 78:34 (2016)

Bulk compositions 16 15 Hualālai a b Hualālai trachytes 2σ glass +10%An 14 +0.5%Ol+0.5%Ox 2σ bulk +0.5%Bt 12 14 b 10

Trachyte O (wt.%) 2 O (wt.%) 2 8 K 13 Basanite Mugearite HH bulk O + O+K 2 2 6 Hawaiite PWW bulk Na Na PWW glass WP bulk 4 12 Alkalic EU5 Basaltic PA Tholeiitic EU4 PDC bulk 2 Andesite EU2 glass Basalt EU1 0 11 45 50 55 60 65 61 62 63 64 65 SiO (wt.%) SiO2 (wt.%) 2 0.8 0.8 c d +10%An +0.5%Ox

WP bulk HH bulk +0.5%Ol +0.5%Bt 0.6 0.6 PA bulk WP bulk

HH bulk (wt.%) 2 PA bulk PWW bulk TiO MgO (wt.%) 0.4 PWW bulk 0.4

+10%An +0.5%Ol σ 2 glass 2σ glass +0.5%Bt +0.5%Ox 2σ bulk 2σ bulk 0.2 0.2 3.23.6 4 4.4 3.23.6 4 4.4

FeOtot (wt.%) FeOtot (wt.%) Fig. 4 Geochemical characteristics of Hualālai trachytes. a Bulk crystallization of different mineral phases typical of the Hualālai compositions of all Hualālai products (blue symbols and orange field) trachytes (An anorthoclase, Ox oxide, Bt , Ol ). Note that showing the clear gap in composition between erupted lavas. b, c,andd SiO2 and MgO are usually lower and the alkalis higher in glasses from Major-element plots of Pu’uWa’awa’a and Hualālai ignimbrites glasses, PWW pyroclasts (green triangles) when compared with their bulk compared with bulk analyses of Pu’uWa’awa’a (PWW), Pu’u Anahulu compositions (blue field). This is because most samples analyzed are (PA), Waha Pele (WP), and Huehue (HH) samples (PWW and PA not 100 % glassy (at least a few microlites are always present). Similar compositions are from an upcoming study, WP and HH from Cousens differences are observed between Hualālai ignimbrite glasses (yellow, et al. 2003). Error bars show average standard deviations for both glass orange, and red circles) and Waha Pele bulk compositions (purple field) and bulk analyses. Gray arrows are differentiation paths for fractional intrusives and cumulate bodies. Instead, most of the western because the chemical differences between the different tra- and northern regions of Hualālai display low gravity anomalies chytes are not easily accommodated by either simple fraction- (cf. Fig. 8 in Denlinger and Morgan 2014). Given that Hualālai ation models involving a single differentiating magma (e.g., possesses rift zones and cumulate bodies similar to those of Cousens et al. 2003) or magma mixing models involving two neighboring volcanoes (e.g., Shamberger and Hammer 2006), magma end-members (i.e., the four Pu’uAnahulu,Pu’u the low gravity anomalies must represent significant volumes of Wa’awa’a, Huehue, Waha Pele bulk compositions do not line low density material under the recent basalt. As proposed by up on a unique fractional crystallization or mixing trend, Fig. 4). Moore et al. (1987), this low-density material may be trachyte. Why then, did Hualālai erupt uncharacteristically large vol- Our finding that trachyte PDCs may have mantled a large area umes of trachytes compared to other Hawaiian volcanoes? of Hualālai agrees well with gravity observations and lends The unusual timing of trachyte production and eruption, both further support to the idea of widespread 90–120-ka trachyte occurring prior to the post shield stage of Hualālai, may indi- under the cap. cate unusual conditions of crustal stress, volcanic load and/or The compositional variability of the different Hualālai tra- rift-zone organization. Such special conditions may be chytes could be attributed to (1) chemical zoning in a large brought about by accelerated edifice slumping or large-scale magma reservoir, (2) at least four different small trachyte res- collapses (e.g., Denlinger and Morgan 2014). The timing of ervoirs scattered underneath Hualālai, or (3) delays between the North Kona slump on the western submarine side of eruptions that would allow trachyte magma to differentiate. Hualālai (≥130 ka, Moore and Clague 1992) and the Alika The second hypothesis appears the most realistic simply landslides—produced by collapse(s) of (∼112– Bull Volcanol (2016)78:34 Page 7 of 8 34

128 ka, McMurtry et al. 1999)—roughly coincide with the Acknowledgments The field work was greatly facilitated by Elliott onset of trachyte volcanism at Hualālai. Whether these events Parsons and the Hawaii Experimental Tropical Forest (HETF), the Hawaii Division of Forestry and Wildlife, and the Department of Land may have influenced the structure and/or stress conditions of and Natural Resources. We thank Stephen Worley and The Big Island subaerial Hualālai directly remains to be demonstrated. Further Country Club for providing access and vehicles to examine some of the higher spatial resolution gravity surveys of the area may help deposits. John Sinton is also acknowledged for the numerous fruitful dis- determine whether the subsurface distribution of trachytes is co- cussions on Hawaii trachytes. This paper benefited from the helpful reviews of David Clague and Valentin Troll, as well as the insightful editorial com- herent with eruptions controlled by regional volcano tectonics. ments of Kathy Cashman. This project is supported by a National Science Foundation grant EAR 1250366 to Thomas Shea and an AXA Postdoctoral Fellowship to Jacqueline Owen. Occurrence of ignimbrites in Hawaii

The relative scarcity of ignimbrites in the geological record of References Hawaii compared to other locations such as Atlantic ocean islands is probably due to a combination of several factors. Branney MJ, Kokelaar BP (2002) Pyroclastic density currents and the Hawaii is the Earth’s most active , with a high magma sedimentation of ignimbrites. Geol Soc Lond Mem 27 supply rate, underlying a fast-moving plate. Potentially, the Brown RJ, Branney MJ (2004) Event-stratigraphy of a -forming high magma supply, even after a volcano enters its post- ignimbrite eruption on : the 273 ka Poris Formation. Bull Volcanol 66:392–416 shield stage, prevents large volumes of magmas from differ- Clague DA (1987) Hawaiian population, magma supply rates, entiating and reaching trachyte compositions (e.g., Shaw 1985; and development of magma chambers. Bull Volcanol 49:577–587 Clague 1987), favoring instead the formation of large volumes Cousens BL, Clague DA, Sharp WD (2003) Chronology, chemistry, and of alkali basalts with subordinate hawaiites, mugearites, and origin of trachytes from Hualalai Volcano, Hawaii. Geochem (Spengler and Garcia 1988; Frey et al. 1990; Geophys Geosyst 4(9) Denlinger RP, Morgan JK (2014) Instability of Hawaiian volcanoes. In Sherrod et al. 2007). In contrast, lower supply rates and Poland MP, Takahashi TJ, Landowski CM, eds, Characteristics of slower-moving plates at Atlantic hotspots may allow large bod- Hawaiian volcanoes: U.S. Geological Survey Professional Paper ies of magmas to differentiate and erupt as large ignimbrite 1801, 429 p. sheets. Duncan AM, Gaspar JL, Guest JE, Wilson L (1999) Volcano, São – Another consequence of the high magma supply and erup- Miguel, Azores. J Volcanol Geotherm Res 92:1 209 ā Edgar CJ, Wolff JA, Olin PH, Nichols HJ, Pittari A, Cas RAF, Reiners tion rates in Hawaii is that volcanoes such as Hual lai can be PW, Spell TL, Martí J (2007) The late quaternary Diego Hernandez completely resurfaced by lava flows in a matter of <15 thou- formation, Tenerife: volcanology of a complex cycle of voluminous sand years (Moore et al. 1987). Therefore, exposure of ignim- explosive phonolitic eruptions. J Volcanol Geotherm Res 160:59–85 brites at the surface is also less likely in Hawaii than at other Eisele S, Freundt A, Kutterolf S, Ramalho RS, Kwasnitschka T, Wang K- locations where resurfacing rates are substantially slower. As a L, Hemming SR (2015) Stratigraphy of the Pleistocene, phonolitic Cão Grande Formation on Santo Antão, Cape Verde. J Volcanol result, the smaller-volume, thinner Hawaiian ignimbrites may Geotherm Res 301:204–220 simply be hard to detect. Freundt A, Schmincke H-U (1995) Petrogenesis of rhyolitetrachyte- basalt composite ignimbrite P1, , Canary Islands. J Geophys Res 100:455–474 Freundt-Malecha B, Schmincke H-U, Freundt A (2001) Plutonic rocks of Hazard implications on Gran Canaria: the missing link of the bimodal volcanic suite. Contrib Mineral Petrol 141:430–445 The ignimbrites described here are probably of much smaller FreyFA,WiseWS,GarciaMO,WestH,KwonS-T,KennedyA volume than those that erupted at other ocean islands such as (1990) Evolution of volcano, Hawaii: petrologic those in the Canaries, which often reach several tens of meters and geochemical constraints on postshield volcanism. J Geophys Res 95:1271–1300 in thickness (e.g., Freundt and Schmincke 1995; Troll and Giachetti T, Druitt TH, Burgisser A, Arbaret A, Galven C (2010) Bubble Schmincke 2002; Brown and Branney 2004;Sigmarsson nucleation, growth, and coalescence during the 1997 Vulcanian ex- et al. 2013). Nonetheless, the Hualālai ignimbrites were prob- plosions of Soufriere Hills Volcano, Montserrat. J Volcanol ably voluminous and widespread enough to cause significant Geotherm Res 193:215–231 regional destruction. This type of event is not likely to occur in Hansteen TH, Troll VR (2003) Oxygen isotope composition of ā from the oceanic crust and volcanic edifice beneath Gran Canaria the future around Hual lai, because trachyte volcanism ap- (Canary Islands): consequences for crustal contamination of ascend- pears to have stopped at about ∼92 ka. Such eruptions are still ing magmas. Chem Geol 193:181–193 nevertheless possible at other Hawaiian volcanoes (e.g., Hoblitt RP, Harmon RS (1993) Bimodal density distribution of Mauna Loa, Mauna Kea), since trachytes seem to erupt both cryptodome dacite from the 1980 eruption of Mt. St. Helens, Washington. Bull Volcanol 55:421–437 in between the shield and post-shield volcanic stages ā Kauahikaua J, Hildenbrand T, Webring M (2000) Deep magmatic struc- (Hual lai) and during the late post-shield stages (, tures of Hawaiian volcanoes, imaged by three dimensional gravity Island of Hawaii, and West Maui, Island of Maui). models. Geology 28:883–886 34 Page 8 of 8 Bull Volcanol 78:34 (2016)

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