Modeling Volcano Growth on the Island of Hawaii: Deep-Water Perspectives

Home , Kohala (mountain), Magma supply rate

Modeling volcano growth on the Island of Hawaii: Deep-water perspectives

Peter W. Lipman and Andrew T. Calvert U.S. Geological Survey, Menlo Park, California 94025, USA

ABSTRACT reasonably consistent with ages and volcano 1974; Robinson and Eakins, 2006), recognition spacing, but younger Loa volcanoes are off- of an early-alkalic (“preshield”) stage at Loihi Recent ocean-bottom geophysical surveys, set from the Kea trend in age-distance plots. Seamount (Moore et al., 1982; Garcia et al., dredging, and dives, which complement sur- Variable magma fl ux at the Island of Hawaii, 1995a), insights into volcano growth based on face data and scientifi c drilling at the Island and longer-term growth of the Hawaiian ages of submerged slope breaks and coral reefs of Hawaii, document that evolutionary stages chain as discrete islands rather than a con- (Moore and Campbell, 1987; Ludwig et al., during volcano growth are more diverse than tinuous ridge, may record pulsed magma 1991), and geodynamic models for growth rates previously described. Based on combining fl ow in the hotspot/plume source. and compositional evolution in response to plate available composition, isotopic age, and geo- motion over a hotspot (Moore and Clague, 1992; logically constrained volume data for each of INTRODUCTION DePaolo and Stolper, 1996; Ribe and Chris- the component volcanoes, this overview pro- tensen, 1999; DePaolo et al., 2001). vides the fi rst integrated models for overall This overview, inspired by the 100th anni- Until recently, compositions and ages bearing growth of any Hawaiian island. In contrast versary of the U.S. Geological Survey (USGS) on growth of Hawaiian volcanoes have largely to prior morphologic models for volcano Hawaii Volcano Observatory (HVO) in 2012, come from subaerial sampling of late eruptive evolution (preshield, shield, postshield), focuses on results of underwater studies of stages, and estimates of inception and early evo- growth increasingly can be tracked by age Hawaiian volcanoes that provide new perspec- lution have been heavily model dependent, using and volume (magma supply), defi ning wax- tives on the growth of intraplate volcanoes. volcano spacing and plate motion to infer propa- ing alkalic, sustained tholeiitic, and waning Recent studies have been especially productive gation rates and duration of edifi ce growth. The alkalic stages. Data and estimates for indi- for the Island of Hawaii (Fig. 1), where sonar present interpretive synthesis, by combining vidual volcanoes are used to model changing surveys, dives, and dredging by the University recent chemical and 40Ar/39Ar isotopic-age data magma supply during successive composi- of Hawaii, Monterey Bay Aquarium Research (mainly from underwater and drill-hole sam- tional stages, to place limits on volcano life Institute, National Oceanic and Atmospheric ples), revised edifi ce volumes, limitations from spans, and to interpret composite assembly Administration (NOAA), and USGS, and col- volcano structures and eruptive processes, and of the island. Volcano volumes vary by an laborations with the Japan Agency for Marine- geodynamic constraints, attempts to interpret order of magnitude; peak magma supply Earth Science and Technology (JAMSTEC) the growth histories of individual volcanoes and also varies sizably among edifi ces but is chal- have complemented on-land scientifi c drilling the composite growth of the entire island. While lenging to quantify because of uncertainty and abundant data from HVO. focused on construction of Hawaii Island, some about volcano life spans. Three alternative These results, in combination with a vast body data from older islands are referenced briefl y models are compared: (1) near-constant of older data, provide new insights about vol- where helpful to constrain volcano-growth volcano propagation, (2) near-equal volcano cano growth on Hawaii. More prior studies than models. In part, this analysis is a sequel to the durations, (3) high peak-tholeiite magma can be acknowledged have evaluated growth of impressive synthesis by Moore and Clague supply. These models defi ne inconsisten- Hawaii in relation to longer-term evolution of the (1992), while benefi ting from compilations for cies with prior geodynamic models, indicate Hawaiian Ridge. Notable were early recognition the geologic map of Hawaii Island (Wolfe and that composite growth at Hawaii peaked ca. of the southeastward younging of volcanoes Morris, 1996a, 1996b) and the state map of 800–400 ka, and demonstrate a lower cur- and distinction of the parallel Kea and Loa vol- Hawaii (Sherrod et al., 2007). Particularly use- rent rate. Recent age determinations for canic trends (Dana, 1849; Jackson et al., 1972), ful samples, compositional data, and imaging Kilauea and Kohala defi ne a volcano propa- and of course the insights about ocean-island of deep structure have come from the Hawaii gation rate of 8.6 cm/yr that yields plausible volcanism that emerged in the 1960s from the Scientifi c Drilling Project (HSDP; Stolper et al., inception ages for other volcanoes of the Kea plate-tectonic paradigm. Among recent critical 1996, 2009) and ~100 submersible dives and trend. In contrast, a similar propagation rate observations and interpretations are: quantifying bathymetric surveys during JAMSTEC cruises for the less-constrained Loa trend would propagation rates along the Hawaiian-Emperor in 1998–2002 (Takahashi et al., 2002; Robinson require inception of Loihi Seamount in the Ridge by isotopic dating (McDougall and et al., 2003; Coombs et al., 2006a). future and ages that become implausibly Swanson, 1972; Jackson et al., 1972; Clague Reliable age determinations for old Hawaiian large for the older volcanoes. An alternative and Dalrymple, 1987), volume estimates from lavas remain sparse, but recent application of rate of 10.6 cm/yr for Loa-trend volcanoes is submarine bathymetry (Bargar and Jackson, 40Ar/39Ar methods to young basalts, especially

Geosphere; October 2013; v. 9; no. 5; p. 1348–1383; doi:10.1130/GES00935.1; 15 ﬁ gures; 11 tables. Received 2 April 2013 ♦ Revision received 6 July 2013 ♦ Accepted 29 July 2013 ♦ Published online 14 August 2013

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21° HA Hana Ridge K A

B′ Laupahoehoe Slump M-G KP KO M-C Kiholo R Hilo Ridge MK A′ N Kona Slump B H Figure 7 HU Puna Ridge ML KL

MSB N LO 19°

100100 kkmm Ka Lae R 156° 154°

Figure 1. Map of the Island of Hawaii and adjacent sea ﬂ oor, showing locations of volcanoes (Kea trend in black; Loa trend in blue): HA—Haleakala; HU—Hualalai; K—Kahoolawe; KL—Kilauea; KO—Kohala; LO—Loihi; M-G—Mahukona (summit location of Garcia et al. [1990]); M-C—Mahukona (summit location of Clague and Moore [1991]); MK—Mauna Kea; ML—Mauna Loa. Historical eruptions are in red. Dashed line is the inferred buried east rift of Kohala that continues into Hilo Ridge. H—Hilo (site of HSDP hole); KP—Kohala platform; MSB—mid-slope bench offshore of Kilauea. Modiﬁ ed from Robinson et al. (2006). Cross sections A–A′ and B–B′ (short dotted lines) are depicted in Figure 6. Arrow at the base of Hilo Ridge is the site of dive K215 (Fig. 7).

underwater and subsurface samples, has TABLE 1. RECENT 40Ar/39Ar GEOCHRONOLOGIC RESULTS, ISLAND OF HAWAII improved controls on volcano growth (Table 1). Rock type Alkalic lavas have yielded stratigraphically Volcano (number of ages) References coherent results for Mauna Kea and Kilauea Kilauea Alkalic and transitional basalt (13) Calvert and Lanphere (2006) Transitional basalt (2) Hanyu et al. (2010) (Sharp and Renne, 2005; Calvert and Lanphere, 2006), but dating of low-K tholeiites continues Mauna Loa Tholeiite (1) Sharp et al. (1996) Tholeiite (1) Sharp and Renne (2005) to be problematic because of low radiogenic- Tholeiite (14) Jicha et al. (2012) argon yields. In such tholeiites, K resides Mauna Kea Alkalic and tholeiitic basalt (9) Sharp et al. (1996) mainly in glassy selvages next to groundmass Alkalic and tholeiitic basalt (9) Sharp and Renne (2005) minerals, leaving samples vulnerable to argon Kohala Transitional-alkalic basalt (2) Lipman and Calvert (2011) loss and/or argon-recoil problems in the reactor. Mahukona Transitional and tholeiitic basalt (2) Clague and Calvert (2009) Some tholeiite samples fail to yield meaningful Transitional and tholeiitic basalt (3) Garcia et al. (2012) ages without apparent petrographic or chemi- Note: Ages and analytical data are listed in Appendix A. cal reasons. In the most detailed 40Ar/39Ar study

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to date of Hawaiian tholeiites, on the 1.5 km 100 scarp along the submarine southwest rift zone Robinson & Eakins (2006) of Mauna Loa, only 14 of 45 analyzed samples 3 80 km

yielded “successful ages” (Jicha et al., 2012). 3 This review Less precise K-Ar determinations remain the main data for subaerial lavas on Kohala and 60 Mauna Kea, and attempts to improve resolution by unspiked K-Ar methods for Kilauea and Loihi basalts (Guillou et al., 1997a, 1997b) 40 yielded some results that are internally con-

tradictory or inconsistent with 40Ar/39Ar dates Total volcano volume, 10 (Calvert and Lanphere, 2006). Appendix A lists 20 the published 40Ar/39Ar and some recent K-Ar age determinations used for estimating volcano growth rates for the Island of Hawaii and under- 0 Mahukona Kohala Hualalai Mauna Mauna Kilauea Loihi water slopes. Kea Loa Volumes of individual volcanoes are also diffi cult to estimate, with probable uncertain- Figure 2. Interpreted volumes of volcanoes, Island of Hawaii: pub- ties of 10%–20%, but constrained by the com- lished (Robinson and Eakins, 2006) and proposed revised values posite island construct (213,000 km3; Robinson (assumption of small Mahukona; Garcia et al., 2012). and Eakins, 2006). Deep subsidence along the Hawaiian Ridge, defi ned by seismic profi ling (Hill and Zucca, 1987), requires volumes nearly sions and olivine cumulates. Details of volume terms have been used, somewhat ambiguously, twice early estimates that assumed growth on calculations are tabulated in Appendix B. concurrently to reference both morphology and fl at ocean fl oor (Bargar and Jackson, 1974). The The age, composition, structural, and vol- composition. As chemical and age data become prior estimates used vertical contacts between ume data for individual volcanoes can then be more abundant, especially for underwater volcanoes; here, edifi ce volumes are adjusted for used to model changing magma supply during samples that record early growth, tracking vol- sloping and interfi ngering boundaries (Table 2; sequential compositional stages, to place lim- canic evolution primarily by composition and Fig. 2; and discussion below). Effects of old its on the duration of volcano growth, and to time seems increasingly desirable. Much more seamounts and other irregularities of the ocean evaluate the composite assembly of the island is known about later stages than earlier ones, fl oor are neglected, as in prior estimates, but (Table 3). These data show that the growth although reliable age and eruption-rate data are unlikely to increase signifi cantly uncertain- stages of Hawaiian volcanoes are more diverse remain sparse. Modeling of growth commonly ties about total volume of the island construct. than previously documented, defi ne inconsisten- has assumed uniformly changing compositions Positive gravity anomalies at volcano summits cies at various scales with geodynamic models, and magma supply as the Pacifi c plate moves and proximal rift zones (Kinoshita et al., 1963; and indicate that composite volcanic growth at across a hotspot source, but recent data docu- Kauahikaua et al., 2000), interpreted as record- Hawaii peaked ca. 800–400 ka. ment considerable variation in stage durations, ing dense intrusions and olivine cumulates, also transitions between stages, periods of quies- help locate volcano boundaries where concealed MORPHOLOGIC AND cence, and interactions between concurrently by younger deposits. Each edifi ce is divided into COMPOSITIONAL GROWTH STAGES active edifi ces. subsections for which volumes can be calculated This paper distinguishes three main compo- from simplifi ed models, as done previously for Building on pioneering insights by Stearns sitional stages: waxing early alkalic, sustained Kilauea (Lipman et al., 2006). Further con- (1946), Hawaiian volcanoes have commonly main tholeiite, and waning late alkalic, versus straints come from eruption and lava-accumula- been discussed in terms of preshield, shield, morphologic evolution of the edifi ce (sub- tion rates, especially for younger volcanoes. For postshield, and rejuvenated stages (e.g., Clague marine, subaerial shield, late submergence). No volcanoes that onlap older edifi ces, an additional and Dalrymple, 1987; Peterson and Moore, volcano on Hawaii Island contains highly alkalic adjustment is made for the volume of deep intru- 1987; Clague and Sherrod, in press). These late volcanism considered characteristic of the rejuvenated stage, and the age signifi cance of this stage at older Hawaiian volcanoes currently TABLE 2. ESTIMATED VOLCANO VOLUMES, ISLAND OF HAWAII seems uncertain. Rocks assigned to this stage at Total volume (103 km3) Basis for changed volume volcanoes like East Maui (Haleakala) form an † Volcano Published* Revised Alternate (see text for details) age continuum with prior waning-alkalic erup- Loihi 1.7 1.0 1.0 Built on Punaluu slump Kilauea 31.6 11 11 Overlies south fl ank of Mauna Loa tions, while similar late-erupted rocks are sepa- Mauna Loa 74.0 83 83 Includes sub-Kilauea fl ank; underlain by south Hualalai rated from waning-alkalic lavas by long intervals Mauna Kea 41.9 22 22 Above large east rift (Hilo Ridge) of Kohala at West Maui or are absent at volcanoes such as Hualalai 14.2 26 24 Projected south, beneath Mauna Loa Kohala 36.4 64 54 Includes Hilo Ridge; underlies Mauna Kea Lanai (Sherrod et al., 2007; Clague and Sherrod, Mahukona 13.5 6 18 Unlikely to extend NE, beneath Kohala (Garcia et al., 2012) in press). Total 213.3 213 213 Island volume held constant All Hawaiian volcanoes are broadly shield Note: Blue italics—Loa-trend volcanoes; others are Kea-trend volcanoes. *Robinson and Eakins (2006). shaped in morphology regardless of composi- †Using larger Mahukona (Clague and Moore, 1991; Clague and Calvert, 2009) and decreased Kohala and tion, with sustained slopes rarely >15° both Hualalai. underwater and on land, except along fault and

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landslide scarps. Slopes are steeper underwater positional and morphologic changes have been (Mark and Moore, 1987), in part because much widely referenced as the shield-postshield tran- shoreline-generated hyaloclastite breccia accu- sition. However, capacity of a volcano to sustain mulates at angle of repose, in part because of subaerial growth is a function of volcano size steep slope-failure scarps at heads of submarine in relation to magma supply. At a large volcano landslides. such as Mauna Loa, subsidence can outpace The most pronounced change in topographic coastal lava accumulation late during the tholei- WTH profi le, from steeper submarine slopes to more itic stage (Lipman, 1995; Lipman and Moore, Notes gentle subaerial deposition as a seamount 1996). In contrast, Mauna Kea continued sub- becomes an island (Mark and Moore, 1987), aerial growth well after the change to late alkalic typically occurs during eruption of relatively volcanism (ca. 330 ka; Sharp and Renne, 2005), uniform tholeiite that constitutes >90% of vol- with submergence beginning to outpace growth cano volume. Although subaerial slopes are gen- only at ca. 130 ka (Moore and Clague, 1992). Early-alkalic stage similar to Kilauea? Only dated duration of early-alkalic stage Loa-trend propagation rate late-alkalic stage 330 k.y. End of main-tholeiite stage, ~120 ka Only dated duration of tholeiite-stage End of main-tholeiite stage, ~450 ka? End of main-tholeiite stage, ~1000 ka End of main-tholeiite stage, ~1200 ka erally low during the tholeiitic stage (commonly As a result of such competing processes, the <5°), much variation is present as a function dueling balance between growth and sub sidence of eruptive style. Sustained tube-fed pahoehoe at the shoreline can terminate at different stages sheet fl ows that grow by infl ation have dips of of compositional evolution. Accordingly, the only a few degrees (Hon et al., 1994), while record of slope-break (shoreline) submer- slopes reach 10° or steeper where built by small gence (Moore and Campbell, 1987; Moore and 100+ (k.y.) tholeiite eruptions as on upper slopes of Mauna Clague, 1992) provides critical evidence for Loa (above ~3000 m; Mark and Moore, 1987, declining eruption rates, but does not neces- their fi gure 3.2). sarily coincide with the shift from main-tholeiite Tholeiite-stage duration s are Kea-trend volcanoes. Bold indicates best-constrained ages. Independently of morphology and whether to late-alkalic stage. Additional factors modulat- on land or underwater, edifi ce growth can be ing volcano growth include changes in eruption

Variable life (high-tholeiite) Variable tracked by composition and magma supply. sites and duration: distal segments of rift zones (ka) 1300 800 100 — 275 750 850 300 580 550 450 90020002100 350 Tholeiitic 850 750 lavas typically deﬁ ne coherent major- can shut down as volcano size increases (e.g., Inception element arrays varying mainly in olivine con- Mauna Loa southwest rift zone [Moore et al., tent, as well documented for Kilauea and Mauna 1990b], Hilo Ridge of Kohala [Lipman and Cal- Loa (Wright, 1971; Clague et al., 1995; Sisson vert, 2011]), eruptions become focused higher et al., 2002). Early- and late-alkalic lavas are on the ediﬁ ce, and shorter-lived eruptions with more varia ble. Compositions that plot between high proportions of a’a to pahoehoe tend to gen- the dominant tholeiite array and the alkali-basalt erate steeper slopes higher on volcanoes. — 800 100+

(k.y.) boundary of MacDonald and Katsura (1964) Sparse age-volume results suggest modest have commonly been designated transitional asymmetry in volcano growth, with rapid early basalt (Wolfe and Morris, 1996a, 1996b; Sisson increase in magma supply, followed by a more

Tholeiite-stage duration et al., 2002; Coombs et al., 2006b), a usage con- protracted waning stage. As detailed later, the tinued here (see Fig. 4). Such transitional basalts, only documented duration for early-alkalic stage Near-constant lifespan which are abundant during shifts between com- volcanism (Kilauea) is fairly brief (~150 k.y.), 150 275 950 850+ (ka) 11001100 650 830 1300 125021002200 700 positional 950 850 stages at some vol canoes, have also but volume and average magma supply are

Inception been described as low-silica tholeiite, especially relatively large at Kilauea (~2500 km3, 0.017 in HSDP studies (e.g., Stolper et al., 2004; km3/yr) and Loihi (~1000 km3 in ~125 k.y., Rhodes et al., 2012). Even more subtle com- 0.008 km3/yr), in comparison to late-stage positional variations among tholeiites at indi- alkalic volcanism at Mauna Kea (~800 km3 in vidual volcanoes, over varied time scales, are 330 k.y., 0.0025 km3/yr), Kohala (~300 km3 in documented by trace-element and isotopic stud- ~230 k.y., 0.0013 km3/yr), Haleakala (300 km3 3 —

100+ ies (Frey and Rhodes, 1993; Kurz et al., 1995; in 950 k.y.: 0.0003 km /yr), and none at Lanai (k.y.) Pietruszka and Garcia, 1999; Marske et al., (Sherrod et al., 2007). 2007; Weis et al., 2011). Shifts between compositional stages are

Tholeiite-stage duration The change from sustained-tholeiite (“shield”) probably all gradational to varying degree to waning-alkalic eruptions (“postshield”) typi- (Clague and Sherrod, in press). The shift from

Near-constant propagation cally coincides with declining eruption rates, waxing-alkalic to tholeiitic stage is in progress

(ka) accompanied by submergence of the shoreline at Loihi Seamount, where compositional types 1100 830 2250 900 125 8001600 700+ 1050 275

Inception as volcano loading outpaces lava accumula- inter ﬁ nger on upper slopes (Moore et al., 1982; tion (Moore and Clague, 1992). Late-alkalic Garcia et al., 1995a). Thick lava sequences TABLE 3. SUMMARY OF ESTIMATED INCEPTION AGES AND DURATIONS OF MAIN-THOLEIITE STAGE, BASED ON ALTERNATIVE MODELS FOR VOLCANO GRO ALTERNATIVE BASED ON OF MAIN-THOLEIITE STAGE, AND DURATIONS AGES INCEPTION OF ESTIMATED 3. SUMMARY TABLE lavas also form steeper slopes than during the also inter ﬁ nger during prolonged transitions sustained tholeiite stage (up to 20°; Mark and from sustained-tholeiite to waning-alkalic stage Moore, 1987), a change probably resulting from (described as “late-shield”; Sherrod et al., 2007)

Complete age-volume models are presented in text sections for individual volcanoes. Italics indicate Loa-trend volcanoes; other smaller and briefer eruptions of alkalic basalt at Mauna Kea (Wolfe et al., 1997; Rhodes and and more silicic lavas (hawaiite, mugearite) that Vollinger, 2004) and Kohala (Lanphere and Note: Loihi Mauna Loa Hualalai Mahukona Kilauea Mauna KeaKohala 850 1300 500 800 Kahoolawe Haleakala 2200 1050 Volcano Maui Nui Island of Hawaii form thicker and more viscous ﬂ ows. Both com- Frey, 1987).

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Where stage transitions involve prolonged the young end of the Hawaiian Ridge varies framework to infer overall growth histories and interfi ngering, dating of the change is inher- by at least a factor of two (40–80 km), major make comparisons with geodynamic models. ently approximate. Perhaps the shift from early- fl uctuations in magma-generation and eruptive The time-volume distributions can be adjusted alkalic to main-tholeiite stage should be defi ned processes are recorded by the gaps between to varying degrees without violating available by the initial appearance of abundant tholeiite islands and seamounts, volcano volumes vary data, but application of consistent assumptions (as currently at Loihi)—a time of increasing by an order of magnitude (Table 2), propagation to the entire suite of volcanoes potentially pro- magma supply, when the continued eruption rates are inconsistent for some adjacent volca- vides insights about their diverse histories and of alkalic basalt becomes volumetrically over- noes, historical magma-supply and eruption the composite assembly of Hawaii. whelmed by tholeiitic lavas. For the change rates have varied at individual volcanoes, and Existing data are inadequate to evaluate from main-tholeiite to late-alkalic stage, the life spans of volcanoes also may vary substan- whether the main-tholeiite stage is characterized transition could similarly be defi ned at the initial tially as discussed later. Simple time-volume by sustained near-constant magma supply (Fig. appearance of abundant transitional and alkalic models, such as depicted in Figs. 3A and 3B, 3A; Wise, 1982), by a bell-curve peak (Fig. 3B; lava. For the growth models in this overview, likely are generalizations of magma-supply Holcomb et al., 2000), or by major variability however, uncertainties about transition ages are fl uctuations with fractal geometry on time from volcano to volcano. For the historical time rarely signifi cant at the precision of available scales from decades or less to that for growth frame at Kilauea and Mauna Loa, eruption and age control. of individual volcanoes, entire islands, and the magma-supply rates have fl uctuated on inter- ocean-channel gaps that separate them. vals of decades to centuries, perhaps antitheti- GROWTH AND MAGMA-SUPPLY Determining long-term magma supply is cally, with periods of intense eruptions alternat- MODELS especially challenging (Wright and Klein, 2013; ing with sustained intervals of reduced activity Poland et al., in press). Short-term shallow (Stearns and Macdonald, 1946; Lipman, 1980a; Modeling growth of Hawaiian volcanoes is magma supply at volcanoes like Kilauea has Klein, 1982; Swanson et al., 2011; Wright and complicated by many interacting processes. been estimated by combining historical obser- Klein, 2013; Gonnermann et al., 2012; Poland Factors favoring augmented growth in edifi ce vations, rates measured during eruptions, and et al., in press). Similar or longer-wavelength size and height include increasing lava-accu- intrusion volumes determined from geodetic fl uctuations are likely to have characterized mulation and magma-supply rates during the data (Swanson, 1972; Dzurisin et al., 1984; earlier activity, but data to evaluate long-term progression from early-alkalic to main-tholeiite Dvorak and Dzurisin, 1993; Cayol et al., 2000; trends are sparse. stage, along with intrusion-driven infl ation and Wright and Klein, 2013). Changes in magma Because the volcanoes of Hawaii differ expansion. At large tholeiite-stage edifi ces, vol- supply also have been inferred from lava-accu- substantially in volume (by an order of mag- cano height can be negatively impacted by load- mulation rates at dated stratigraphic sections nitude or more; Table 2), either the duration of driven subsidence, summit defl ation, caldera (e.g., Lipman, 1995; Sharp et al., 1996; Quane volcano growth or peak magma supply must collapse, fl ank spreading, and catastrophic slope et al., 2000), but accumulation rates inevitably vary greatly. Several alternatives are explored failures. All Hawaiian volcanoes likely increase vary greatly with distance from vents and rela- for growth of less-constrained volcanoes: in height rapidly during early submarine growth tion to local topography. (1) near-steady-state progression of volcano because of initially small size. Subaerial vol- Late growth histories of the older Hawai- inception, in accord with plate-motion mod- canoes rise more slowly, even when eruption ian volcanoes that are extinct or nearly so are els; (2) semi-equal durations (~1100 k.y.) but rates are higher, as the volcano area becomes constrained by data from subaerial lavas, but varied peak-eruption rates; and (3) shorter large and subsidence modulates growth by lava reconstructions of early evolution depend heav- durations at smaller volcanoes that maximize accumulation. ily on deep-water sampling. Even with recent peak-eruption rate during the tholeiite stage Most previous volcano-growth models for drill-hole and submarine sampling, no Hawaiian (Table 3). In addition, recent ages suggest that Hawaii have portrayed age-volume relations volcano exposes a complete record of all growth volcano progression has been asynchronous as variants of a fl attened bell curve, in which stages. Accordingly, to evaluate magma supply between the Kea and Loa trends (~N35°W on magma-supply and lava-accumulation rates during assembly of Hawaii, eruption rates that Hawaii). Measured and modeled propagation increase during early growth, peak during the have been determined for a stage at one volcano rates and growth stages, discussed in later sec- tholeiitic stage, and diminish during late alkalic are used to approximate volume-age evolution tions, suggest that volcanoes grew earlier along volcanism. A perceptive early model for Mauna at others. For each volcano, one or more growth the Loa trend than for similar positions along Kea (Wise, 1982; Fig. 3A) has been proposed models are developed for 100 k.y. intervals the Kea trend, at least for the more recent vol- with only modest differences for other vol- (25 k.y. for Kilauea and Loihi), constrained by canoes. Accordingly, growth along each trend canoes (Clague, 1987; Garcia et al., 1995a; available composition, age, and volume data, is summarized separately, in general order Lipman , 1995). and also by analogies with growth stages at other from younger volcanoes to less-documented Duration of eruptive stages has also been volcanoes, to permit inter-volcano compari- older ones. evaluated by geodynamic models involving sons and to interpret overall growth of Hawaii These discussions of available age, composi- steady-state plate motion over a fi xed hotspot, (Table 3). As these growth models are variably tion, and volume data, which are the framework as recorded by volcano spacing (Fig. 3C–3D; subjective and dependent on data availability, for proposed growth models of individual edi- Moore and Clague, 1992; DePaolo and Stol- uncertainties are accordingly large. One major fi ces, provide the basis for evaluating overall per, 1996; DePaolo et al., 2001), but eruptive uncertainty involves volcanoes of differing size island growth and resulting implications for behavior in Hawaii appears to be non–steady and volume: do smaller volcanoes have briefer geodynamic models of the Hawaiian hotspot/ state over a wide range of scales. Magma supply life spans than large ones, or are they character- plume. Readers mainly interested in general has increased markedly during the last few mil- ized by lower eruption rates, especially during interpretations and conclusions may prefer to go lion years (Bargar and Jackson, 1974; Clague the main-tholeiite stage? Nevertheless, available directly to the sections “Assembly of the Island and Dalrymple, 1987), volcano spacing along age, compositional, and volume data provide a of Hawaii” and “Discussion.”

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D C

Figure 3. Some prior age-volume and volcano-propagation models for growth of Hawaiian volcanoes. (A) Volume-time framework for the evolution of Mauna Kea volcano (Wise, 1982); the inferred rapid inception, sustained tholeiite stage, and prolonged late-alkalic stage are consistent with much of the more recent data summarized in this review. (B) Diagrammatic growth models for Hawaiian volcanoes (Holcomb et al., 2000, their fi gure 5B), inferring constant volcano volumes and propagation rates. (C) Estimated ages for stages in the life histories of volcanoes on or adjacent to the Island of Hawaii (Moore and Clague, 1992, their fi gure 8), inferring growth at constant propagation rates based largely on the end of shield building as determined from submerged slope breaks and the compositional change from tholeiite (shield) to late-alkalic (postshield) stage. (D) Map of Hawaii showing volcano locations as a function of time (DePaolo et al., 2001, their fi gure 1B), assuming a Pacifi c plate velocity of 9 cm/yr (numbered circles indicate volcano positions for which isotopic data are available), superimposed on the melt-supply model of DePaolo and Stolper (1996). HSDP—Hawaii Scientifi c Drilling Project. Abbreviations: H—Hualalai; HA— Haleakala; KI—Kilauea; KO—Kohala; L—Loihi; MK—Mauna Kea; ML—Mauna Loa. See cited papers for details about construction and interpretation of these published fi gures.

KEA-TREND VOLCANOES obtained during the Japan-USA research sup- Neal and Lockwood, 2003). Interlayered thin ported by JAMSTEC during 1998–2005 (Taka- tephra deposits record prolonged intervals of Because age and volume data are more hashi et al., 2002; Coombs et al., 2006a). volumetrically minor explosive activity, during robust for the Kea trend, these volcanoes are which lava eruptions were sparse (Fiske et al., discussed ﬁ rst, starting with Kilauea where Kilauea 2009; Swanson et al., 2012). Drill holes along composition, age, and eruptive evolution are Kilauea’s subaerial east rift zone have pene- constrained by study of its young subaerial Subaerial and underwater slopes of Kilauea trated similarly uniform tholeiites to depths as deposits, abundant seismic and other geo- display strikingly different records of growth. great as 1700 m below present sea level (Quane physical data on three-dimensional structure, The on-land surface is mantled by tholeiite et al., 2000). several multi-kilometer-deep drill holes, and lava varying mainly in olivine content (Wright, Offshore of Kilauea, all sampled pillow lavas especially the submersible dives and samples 1971), mostly erupted <1.5 ka (Holcomb, 1987; along Puna Ridge, the submarine continuation

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of the east rift zone, are similar tholeiite (Clague 500,000 Thol- Transit- Weakly alkalic Strongly alkalic et al., 1995; Johnson et al., 2002). In contrast, no eiitic ional outcrops of Kilauea tholeiite have been found 250,000 Clasts below bench along the submarine south ﬂ ank downslope Pillow rib from the summit. Below a prominent mid-slope - west bench at ~3000 mbsl (meters below sea level) Above 100,000 ? ? bench (MSB, Fig. 1), bedded volcaniclastic rocks Lower - east interpreted as debris-ﬂ ow deposits from ances- Hilina 50,000 ? tral Kilauea (Lipman et al., 2002) contain clasts of diverse submarine-erupted (high sulfur) alkali Two lower flows, Hilina Pali (Chen et al., 1996) basalt, including nephelinite and tephriphonolite 25,000 Upper Hilina (Sisson et al., 2002), that are more compositionally diverse than known elsewhere on Hawaiian volcanoes except during the late “rejuvenated” 10,000 stage. These have been interpreted as recording initial growth of Kilauea, broadly comparable to 5000 the current Loihi Seamount but including less- Lower evolved alkalic compositions. Breccia-matrix Puna 2500 and turbidite sands interbedded with the debris- Kulanaokuaiki

fl ow breccias contain glass grains of subma- (log scale) present before years Age, Tephra rine-erupted alkali basalt, mixed with degassed (Fiske et al., 2009) tholeiitic grains generated by shoreline entry 1000 of subaerially erupted lavas. This submarine Upper volcaniclastic sequence thins westward against 500 Puna breccias of Loa-type tholeiite interpreted as the Three flows of( 437 analyses) underlying fl ank of Mauna Loa. Above the mid- 250 (Wolfe & Morris, 1996b) slope bench, to the shallowest exposures at 1800 mbsl, scattered bedrock ribs expose only weakly Histor- ical alkalic to transitional pillow basalts (Fig. 4). 100 The change to subaerial-type tholeiitic lavas –2 0 +2 +4 +6 must lie concealed in shallower water, beneath Alkalinity the angle-of-repose mantle of shoreline-derived hyaloclastite. Figure 4. Summary of alkalinity versus ages of Kilauea lavas, illustrating intermittent eruption of volumetrically minor transitional Age and Volume basalt during the sustained-tholeiite stage since >50 ka. Calcu- lated alkalinity [(Na O + K O) – 0.37*(SiO – 39)] is defi ned as the Prior geometric analysis of Kilauea’s vol- 2 2 2 weight percent difference in Na O + K O between the sample and ume, including contrasts between subaerial and 2 2 submarine lava compositions, suggested a vol- the alkali/tholeiitic basalt line of MacDonald and Katsura (1964). ume of ~10,000 km3 for the edifi ce, with about Left column is the subaerial stratigraphic sequence of Kilauea one-quarter emplaced during the waxing-alkalic (Wolfe and Morris , 1996a); more alkalic lavas in the upper right stage (Lipman et al., 2006). This volume for the of the diagram are from the submarine south fl ank (italic labels). alkalic part of the edifi ce, substantially larger The strongly alkalic samples are clasts in debris-fl ow deposits from than that of Loihi Seamount at present, may below the mid-slope bench (MSB, Fig. 1); weakly alkalic basalts are have been modestly overestimated, because from prominent rib outcrops above the western side of the bench; subaerially erupted shoreline-derived tholei- and submarine transitional basalts form continuous exposures itic sand forms matrix between alkalic clasts above the eastern mid-slope bench. in some deep debris-fl ow deposits. The prior estimate of total Kilauea volume also neglected deep parts of associated summit and rift-zone (Calvert and Lanphere, 2006). Inception of even later (Fig. 4). These young ages for initial intrusions emplaced within the underlying Kilauea no earlier than ca. 250–275 ka is inferred eruptions and shift to the tholeiite stage contrast Mauna Loa fl ank, here roughly approximated from high-precision plateau ages of 234 ± 9 and with prior inference of earlier volcano inception as an additional 750–1000 km3 (Appendix A, 238 ± 10 ka on phlogopite from nephelinites that (600–700 ka) based on plate-motion models Table A1); further interpretation assumes a total record low magma supply generated by small (DePaolo and Stolper, 1996). Kilauea volume of ~11,000 km3. degrees of source melting at initial stages of Geothermal drill holes along Kilauea’s east Multiple 40Ar/39Ar incremental-heating ages volcano growth. Ages on weakly alkalic pillow rift have penetrated tholeiite sections 1700 m on early-alkalic and transitional basalts from basalt above the mid-slope bench range down to or more thick (Quane et al., 2000), document- Kilauea’s submarine south fl ank provide espe- 135 ka. Two ages from a thick breccia section ing proximal emplacement of this basalt type cially tight constraints on ancestral growth of of transitional lava are as young as 65 ± 28 ka at depths nearly to that of the shallowest alkalic this volcano, as well as a possible template for (Hanyu et al., 2010), suggesting that main-stage pillows on the offshore slope, helping to bracket early evolution of other Hawaiian volcanoes tholeiites only became dominant at ca. 100 ka or the shift between compositional stages and

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suggesting that the change may have been fairly dominated by explosive eruptions of only mod- ume of ~11,000 km3, requires rapidly increas- abrupt. Drill-hole samples have ages as old est volume (Swanson et al., 2011, 2012). ing average magma supply since 100 ka, with a as 351 ± 12 ka by the unspiked K-Ar method Age-volume relations for the overall growth of convex-upward slope that projects toward higher (Guillou et al., 1997b), but their reliability has Kilauea, as modeled here (Table 4; Fig. 5), show future rates (Fig. 5B). Such a supply rate also been questioned because of inconsistency with that magma-supply rates as high as 0.2 km3/yr seems improbably high to be applicable for the 40Ar/39Ar dates from submarine alkalic rocks must be recent, intermittent, or both. Such a rate, sustained-tholeiite stages at older volcanoes. As and potential for excess Ar and K loss to dis- if representative during the ~100 k.y. duration presently modeled, a volcano as large as Mauna turb ages in low-K samples (Calvert and Lan- of main-stage tholeiite eruptions, would have Loa could maintain a rate of 0.2 km3/yr for at phere, 2006). yielded a volcano volume almost twice that esti- most 100 k.y., even if its sustained-tholeiite stage Rare transitional ﬂ ows and tephra with atypi- mated from geometric modeling. Early growth were relatively brief (~700 k.y.; see section on

cally high TiO2 and alkalis at low SiO2 (3 analy- during the waxing-alkalic stage at Kilauea is Mauna Loa, especially Fig. 12). Even a lower ses of 437 tabulated for Kilauea; Wolfe and Mor- modeled to fi t the estimated volume for this present magma supply, reaching 0.1 km3/yr at ris, 1996b), erupted in the last few thousand years interval (~2.5 × 103 km3, during 275–100 ka; Kilauea after 100 k.y. in the sustained-tholeiite at Kilauea, support inference that the change Lipman et al., 2006), so even a present-day rate stage, produces a growth rate as high or higher to main-tholeiite stage is complex (Fig. 4) and of 0.2 km3/yr, constrained by a total Kilauea vol- than modeled for a modestly asymmetrical may still be incomplete, consistent with the relatively modest current volume estimated for the growing volcano. Examples include the A.D. TABLE 4. ALTERNATIVE KILAUEA GROWTH MODELS, AT 25 K.Y. INTERVALS 3 3 600–1000 Kulanaokuaiki tephra (Dzurisin et al., A. 0.10 km /yr current rate B. 0.20 km /yr current rate Age Magma supply Volume Magma supply Volume 1995; Fiske et al., 2009), an associated lava fl ow (ka) Event (km3/yr) (103 km3) (km3/yr) (103 km3) (Lipman et al., 2006, their table 5), older fl ows 275 Inception 0.001 0.001 of transitional basalt in Hilina fault scarps (Chen 250 Waxing alkalic 0.002 0.04 0.002 0.04 225 Waxing alkalic 0.004 0.08 0.004 0.08 et al., 1996), and a young alkalic fl ow at the base 200 Waxing alkalic 0.007 0.14 0.007 0.14 of the distal Puna Ridge (Clague et al., 1995; 175 Alkalic-transitional 0.012 0.24 0.012 0.24 Johnson et al., 2002). 150 Transitional 0.024 0.45 0.018 0.38 125 Transitional 0.040 0.80 0.025 0.54 100 Transitional-tholeiite 0.055 1.19 0.034 0.74 Magma-Supply and Growth Models 75 Sustained tholeiite 0.070 1.56 0.048 1.03 A prior effort to model growth of Kilauea 50 Sustained tholeiite 0.082 1.90 0.070 1.48 25 Sustained tholeiite 0.094 2.20 0.120 2.38 (Lipman et al., 2006), based on compositions 0 Sustained tholeiite 0.100 2.43 0.200 4.00 and ages of submarine samples collected during Total: 11.0 Total: 11.0 Note: Italics indicate the interval of compositional transition; colors indicate times of sustained compositional JAMSTEC research, a revised edifi ce volume, uniformity. and published estimates of late-20th-century magma supply (~0.1 km3/yr; Swanson, 1972; Dvorak and Dzurisin, 1993), became the starting point for this summary that refi nes the 0.25 Kilauea result and applies similar methods to the older volcanoes. 0.20 0.20 km3/yr Diverse observations now suggest that current rate /yr (linear) magma supply at Kilauea has varied sizably in 3 0.15 0.10 km3/yr geologically recent time. Data from the continu- current rate ing east rift eruption (since 1983) have docu- 0.10 mented varied eruptions rates, up to 0.2 km3/yr (Wolfe, 1988; Wright and Klein, 2013; Poland Figure 5. Age and magma-sup- 0.05

et al., 2012). Interpretation of geodetic data sug- ply growth models for Kilauea, Magma supply, km gests that the total magma supply has been close at 25 k.y. intervals. (A) Lin- 0.00 300 250 200 150 100 50 0 to 0.18 km3/yr since 1961, including intermit- ear scale for magma supply. tent dike intrusions along rift zones during this (B) Semi-log scale that better interval (Cayol et al., 2000). Evaluation of the illustrates variations during low 1 longer-term historical record of Kilauea erup- magma supply. Data are from 0.20 km3/yr tions, in conjunction with analysis of seismic Table 4, which also lists interval current rate data on magma-accumulation sites, also sug- volumes. /yr (semi-log) 0.1 0.10 km3/yr 3 gests supply rates to ~0.18 km3/yr since ca. 1960, current rate increasing from 19th- and earlier 20th-century rates of only 0.01–0.08 km3/yr (Pietruszka and Garcia, 1999; Wright and Klein, 2013). Exami- 0.01 nation of prehistorical eruptive deposits has

begun to document even more complex vari- Magma supply, km ability in eruptive rates at Kilauea, with multi- 0.001 hundred-year periods of lava eruption at high 300 250 200 150 100 50 0 rates alternating with similarly long intervals Age, ka

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magma-time plot for other volcanoes (see sec- man et al., 1990). Potassium-argon ages that of early-alkalic volcanism at Kohala is estimated tions on Kohala, Mauna Kea, and Hualalai, espe- have sizable uncertainties suggest that exposed at 1300 ka (Table 5). These ages require the cially Figs. 9, 10, and 13; also Wise, 1982; Frey Pololu rocks range from greater than 450 to ca. growth of Hilo Ridge before plausible inception et al., 1990; Garcia et al., 1995a; Lipman, 1995). 300 ka, and that the overlying waning-alkalic of Mauna Kea related to semi-steady propaga- More rapid onset of tholeiitic magma supply lavas were erupted from ca. 280 to 120 ka, tion along the Kea trend. For Hilo Ridge to be to rates as high as 0.2 km3/yr would require a possibly as recently as 60 ka (McDougall and part of Mauna Kea would require rapid propa- strongly asymmetrical growth-time curve, rela- Swanson, 1972; Sherrod et al., 2007). Largely gation from Kohala to Mauna Kea (at least 20 tively brief period of peak magma supply, and or entirely tholeiitic lower parts of the Pololu cm/yr, even if Kohala began as early as 1.5 Ma), prolonged decline in supply rates. Volcanics become more compositionally diverse then slowing greatly from Mauna Kea to Kilauea As an additional factor, the high supply rates upward (Lanphere and Frey, 1987), recording a (~5 cm/yr). estimated from geodetic and seismic data for broad “late-shield” transition, here estimated at The reinterpreted Kohala east rift zone, as rift extension during the past 50 years (Cayol ca. 350 ka (280 ka in Moore and Clague [1992]). inferred from the summit to the distal toe of et al., 2000; Wright and Klein, 2013) omit any A prominent slope break at 1000–1100 mbsl, Hilo Ridge, is the longest among volcanoes component of passive fl ank motion and slump- continuously traceable for at least 60 km around on Hawaii Island (135 km). In comparison, ing driven by gravitational spreading (Fiske the north submarine fl ank of the volcano, records Kilauea’s east rift zone, including its submarine and Jackson, 1972; Borgia et al., 2000; Morgan submergence associated with waning of the extension along Puna Ridge, is 115 km long. et al., 2003; Byrne et al., 2013). The model of sustained-tholeiitic stage at ca. 400 ka (Moore The only longer Hawaiian rift zone would be Cayol et al. (2000) infers average dike-induced and Clague, 1992; Smith et al., 2002) and shows the east rift zone of Haleakala and its submarine rift opening of 40 cm/yr, which seems unsus- that Kohala was once much higher than its pres- continuation along Hana Ridge, with an overall tainable for the prolonged duration of the tholei- ent summit elevation of 1678 m. Two large sub- length of 150 km. itic stage at Kilauea. Such a dike-intrusion rate, marine slope failures of Kohala’s north fl ank, Hana Ridge offers an instructive geometric if active since inception of tholeiite eruptions at the Laupahoehoe and Pololu slumps, occurred analog for evaluating size and geometry of the ca. 100 ka, would have produced a zone 40 km late during the sustained-tholeiite eruptions, inferred rift-zone connection from subaerial wide of 100% dikes along Kilauea’s proximal then were onlapped by younger lavas from Kohala to Hilo Ridge. This comparison can be east rift. In contrast, the intense dike swarm Mauna Kea (Smith et al., 2002). Only a few tho- illustrated (Fig. 8) by transposing major mor- forming >40% (to 70%) of rock along the north- leiite lavas have been sampled from underwater phologic features of eastern Haleakala onto west rift at the deeply eroded Koolau volcano on slopes, but abundant turbidite sandstones from Kohala (present-day shoreline, submerged Oahu, which appears geometrically analogous the submarine north fl ank (37 samples from 3 slope break at ~2000 mbsl that marks decline to Kilauea, is ~10 km wide adjacent to its cal- dives) have uniform tholeiitic glass composi- in tholeiitic-stage eruptions, and approximate dera and decreases to ~5 km width 15 km down tions without intermixed transitional or alkalic base of Hana Ridge adjusted on its north side rift (Walker, 1986, 1987). compositions, providing an indirect record of for large-scale slumping). The distance from the Because of these complexities and uncertain- a long-lived tholeiite stage at Kohala (Lipman present-day summits of the two volcanoes to ties, the preferred model for long-term magma and Calvert, 2011; M.L. Coombs, 2010, written submerged slope breaks along their ridge crests supply at Kilauea is that in Fig. 5A, gradually commun.). is similar (80–90 km), even though Hana Ridge reaching a multi-thousand-year average of 0.1 The southeast-trending subaerial rift zone continues 15 km farther underwater than the km3/yr since inception of its main-tholeiite stage of Kohala is interpreted as continuing beneath distal Hilo Ridge. The north-fl ank slope break at ca. 100 ka or younger. Mauna Kea to reappear as the submarine Hilo is convex northward for both volcanoes, despite Ridge (Figs. 1 and 6), as initially proposed by the presence of large submarine fl ank failures Kohala Holcomb et al. (2000) based on correlation of (Laupahoehoe slump for Kohala, Hana slump submarine slope breaks. This interpretation, in for Haleakala). The northward convexity along Kohala is discussed before Mauna Kea contrast to the more common depiction of Hilo the northeast coast and submerged slope break because its overall growth history is better con- Ridge as a rift zone of Mauna Kea (Fiske and of Hawaii results from younger infi lling of lavas strained by dating, providing a possible template Jackson, 1972; Moore and Clague, 1992; Wolfe from Mauna Kea and also probably from late for modeling early evolution of other Hawaiian et al., 1997), is supported by a residual-gravity tholeiitic-stage Kohala (Smith et al., 2002, their volcanoes. Recent underwater studies provide anomaly along the Hilo Ridge that projects fi gure 4). The geometrically similar convex- unique information on early edifi ce growth at more directly toward Kohala than toward Mauna ity on the north fl ank of Hana Ridge probably Kohala, long recognized as the oldest subaerial Kea (Kauahikaua et al., 2000) and by evidence records continued lava accumulation along this volcano on Hawaii, and show that this volcano for early inception of the ridge. Transitional to originally subaerial segment after slope failure is larger than previously thought (Table 2). weakly alkalic pillow lavas that are overlain by generated the Hana slump (Eakins and Robin- Prior to the JAMSTEC-supported dives dur- tholeiitic picrite at the toe of Hilo Ridge (Fig. 7), son, 2006). In contrast, the embayed south-fl ank ing 1998–2002, virtually all published composi- interpreted to mark the change from waxing- slope break on Hana Ridge, which is asym- tional and age data for Kohala had been obtained alkalic to tholeiitic volcanism, have yielded metrically close to the ridge crest, suggests that on land, where mixed tholeiitic to weakly alkalic 40Ar/39Ar plateau ages of ca. 1150 ± 35 ka (Lip- this side of the ridge was modifi ed by late slope basalts (Pololu Volcanics) are capped by wan- man and Calvert, 2011). The ridge also has an failures, and the resulting deposits are now con- ing alkalic-stage lavas of the Hawi Vol canics overall reverse magnetic direction, requiring the cealed beneath younger rocks from the Island of (Stearns and Macdonald, 1946; Lanphere and bulk of rift growth before 760 ka (Naka et al., Hawaii. Curvature of Hana Ridge appears some- Frey, 1987). However, many of the analyzed 2002, p. 46), much earlier than any dated tholei- what less than that projected for the Kohala rift subaerial samples, especially tholeiites of the itic lavas on subaerial Kohala (ca. 400 ka). By zone, but even so, the south fl ank of the trans- Pololu Volcanics, have been affected by varia ble analogy with the 150–175 k.y. span interpreted posed Hana Ridge would pass beneath Hilo and to extreme alkali leaching and exchange (Lip- for the waxing-alkalic stage at Kilauea, inception project beneath the summit of Mauna Kea.

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KOHALA-

Section A-A A-A Section Section ′ ′ L L KOHALA- MK summit H Shield tholeiite B 5 5 –5 Km –5 –10 Sea level –10 Sea level 0 B Kohala (submarine) Kohala

, along Mauna Kea, N slope Mauna Kea, ′ Section B-B’ Section , along crest of Kohala and its rift zones of Kohala , along crest le A–A le ′ Summit Kohala (subaerial) Kohala NW rift zone Mahukona? Curved longitudinal profile A-A longitudinal profile Curved Oceanic crust Oceanic Paleo S.L. (–1,100 m) Paleo , from the summit of Mauna Kea to the northeast base of the island; compare Wolfe Wolfe the summit of Mauna Kea to northeast base island; compare , from ′ gure 3). H—Hamakua Volcanics; L—Laupahoehoe Volcanics; MK—Mauna Kea; SA— Volcanics; L—Laupahoehoe Volcanics; 3). H—Hamakua gure No V.E. Water V.E. = 2.8 × V.E. le B–B NW A 4 4 –4 –8

S.L. –4 –8 –12 S.L.

–12 Elevation, km Elevation, A Figure 6. Cross sections illustrating interpreted long east rift of Kohala, onlapped by Mauna Kea (V.E.—verti- sections illustrating interpreted 6. Cross Figure longitudinal profi Arcuate 1. (A) shown on Figure cal exaggeration). Locations of sections are the crest of Kohala and its rift zones. Basal surface of Mauna Kea is constrained by the interpreted contact of Kohala and its rift zones. Basal surface Mauna Kea is constrained by the interpreted the crest meters below sea level along Hilo Ridge (Holcomb et al., 2000). S.L.—sea level. at 1100 at the slope break (B) Radial profi subaerial; SM—submarine. et al. (1997, their fi et al. (1997, their

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Age and Volume Dates from subaerial samples of the waning- alkalic stage document a broad transition from tholeiitic eruptions at ca. 350–300 ka and probable termination of Kohala volcanism at ca. 120 ka (Sherrod et al., 2007). Interpretation of Hilo Ridge as the distal east rift of Kohala (Holcomb et al., 2000), in conjunction with ages of transitional-composition basalt at its toe (ca. 1150 ka; Lipman and Calvert, 2011), allows the fi rst estimated duration for the sustained- tholeiite stage (~800–850 k.y.) of a Hawaiian volcano. This duration is substantially longer than that inferred from prior plate-motion models (~500 k.y. [Moore and Clague, 1992]; 600 k.y. [DePaolo and Stolper, 1996]). These results also imply that the 135-km- long east rift zone developed to near-total length early during growth of Kohala and imply a volume (Table 2) substantially larger than the prior estimate of 36,000 km3 (Robinson and Eakins, 2006). Any geometrically simple topographic profi le connecting Hilo Ridge to Kohala requires the rift zone to have been subaerial at shallow depth beneath the north fl ank of Mauna Kea, limiting Mauna Kea to a much smaller volcano perched on the south slope of the large Kohala rift zone (Fig. 6). Kohala would have begun largely or entirely on ocean fl oor as an elongate northwest-southeast edifi ce without signifi cant interference from pre-existing volcanoes. Rapid early growth of Hilo Ridge (Lipman and Cal- vert, 2011) suggests that at least distal parts of Kohala reached near-present size prior to major growth of Mauna Kea. Late interfi ngering of lavas from these volcanoes may have been relatively minor, as Kohala eruptions increasingly Figure 7. Bathymetric map of Japan Agency for Marine-Earth Science and Tech- became focused closer to its present summit. nology dive site K215, along pillow lavas on the south fl ank of distal Hilo Ridge, A more modest addition to the total volume showing locations of dated transitional-alkalic basalt and overlying >600 m of of Kohala results from reduced estimates for tholeiitic picrite, and interpreted geologic relations (Lipman and Calvert, 2011). Mahukona, as discussed for that volcano. If Non-shaded areas are inferred to be largely exposed pillow basalt. Water depth the volume of Mahukona is ~6000 km3 (Garcia contour interval is 10 m. Location shown on Figure 1. et al., 2012), or if this construct were the distal

TABLE 5. ALTERNATIVE KOHALA GROWTH MODELS, AT 100 K.Y. INTERVALS, CONSTRAINED BY ESTIMATED TOTAL VOLUME OF 64 × 103 KM3 A. Sustained-tholeiite magma supply B. High peak-tholeiite magma supply Age Magma supply Volume Cumulative Magma supply Volume Cumulative (ka) Event (km3/yr) (103 km3) (103 km3) (km3/yr) (103 km3) (103 km3) 1300 Inception (alkalic) 0.001 0.001 1200 Transition to tholeiite, ~ 1150 ka 0.011 0.60 0.6 0.013 0.70 0.7 1100 Begin tholeiite 0.078 4.45 5.1 0.075 4.40 5.1 1000 Sustained tholeiite 0.100 8.90 14.0 0.200 13.75 18.9 900 Sustained tholeiite 0.105 10.25 24.2 0.140 17.00 35.9 800 Sustained tholeiite 0.100 10.25 34.5 0.085 11.25 47.1 700 Sustained tholeiite 0.085 9.25 43.7 0.056 7.05 54.2 600 Sustained tholeiite 0.075 8.00 51.7 0.036 4.60 58.8 500 Sustained tholeiite 0.055 6.50 58.2 0.020 2.80 61.6 400 Sustained tholeiite 0.025 4.00 62.2 0.010 1.50 63.1 300 Transitional volcanism, after ~ 340 ka 0.004 1.45 63.7 0.003 0.65 63.7 200 Hilo Ridge submerged, after 130 ka 0.001 0.25 63.9 0.001 0.20 63.9 100 Termination at 120 ka 0.000 0.05 64.0 0.000 0.05 64.0 0 0.000 0.0 64.0 0.000 0.00 64.0 Note: Bold indicates best-constrained events and ages, and total cumulative volumes. Shading indicates duration of sustained-tholeiite stage.

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HA Subaerial Hana Ridge Submarine K

Laupahoehoe Slump M-G M-C KO Kiholo R Hilo Ridge N Kona Slump MK H HU Puna Ridge ML KL

100100 kmkm N

19° 156° LO 154°

Figure 8. Diagram comparing the geometry of Hilo Ridge with Hana Ridge of Haleakala. Solid line is the construc- tional base of Hana Ridge; dotted line is the slope break marking the original submarine-subaerial shoreline at the end of shield growth; dashed line is the crest of the rift zone. South ﬂ ank of Hana Ridge is embayed by landslide scars and partly covered by deposits of the Laupahoehoe Slump. Geometry is similar when these features of Hana Ridge are juxtaposed onto Kohala, Hilo Ridge, and the rift crest beneath Mauna Kea. Abbreviations as in Figure 1.

west rift zone of Kohala onlapped by a Hualalai strained by the recent ages from the Hilo Ridge (Fig. 9B) that could persist for only a brief rift, then half or more of its previously estimated (Lipman and Calvert, 2011), in conjunction with interval without exceeding the total volume of volume (15,500 km3; Robinson and Eakins, prior K-Ar dating of its late-alkalic stage and this volcano. Even Mauna Loa, with its greater 2006) becomes part of Kohala. Based on a analogy with duration of the early-alkalic stage total volume, yields a compressed growth simple geometric model of elongate ellipsoidal at Kilauea. The Kohala ages provide the only curve at such magma production rates. Such a prisms for Hilo Ridge and northwest rifts of measured duration for the main-tholeiite stage short-duration high magma supply would also Kohala, while retaining the smaller Mahukona at a Hawaiian volcano, and simple geometric be inconsistent with a large-diameter hotspot estimate from Garcia et al. (2012), a revised vol- modeling of its growth as dominated by a mildly source (100–150 km), as commonly inferred for ume for Kohala is ~64,000 km3 (Table 2; Appen- asymmetric trend of sustained tholeiite erup- the Hawaiian chain from diverse geochemical dix B, Table B2), nearly as large as previously tions (Fig. 9A) yields peak magma-supply rates and geophysical evidence (e.g., Ribe and Chris- estimated for Haleakala (69,800 km3; Robinson of ~0.10 km3/yr that are similar to estimates of tensen, 1999; DePaolo et al., 2001). and Eakins, 2006). Of this increased Kohala long-term historical rates at Kilauea (Swanson, No estimates have been published for vol- volume, 7500 km3 was previously included with 1972; Dzurisin et al., 1984; Wright and Klein, umes of the late-alkalic lavas at Kohala, but no Mahukona and 20,000 km3 with Mauna Kea 2013). A rate this high can characterize only a more than a few hundred cubic kilometers seems (Hilo Ridge and landward continuation). fraction of Kohala’s tholeiite stage; otherwise, likely, judging by the widely exposed transitional its total volume would be even larger than the and tholeiitic ﬂ ows low on subaerial slopes and Growth Model 64,000 km3 estimated here (Table 2). An alter- absence of alkalic clasts or sand grains in land- By these volume interpretations, Kohala is native growth model, in which magma supply slide and turbidite deposits sampled on the north among the largest Hawaiian volcanoes. Its life- becomes comparable to the 0.20 km3/yr peak submarine ﬂ ank during the JAMSTEC dives. span (~1200 k.y.) and duration of main-tholeiitic rate during recent Kilauea activity, produces a For a volume of ~300 km3, erupted between 350 stage (~800–850 k.y.) are relatively well con- high-amplitude short-wavelength growth curve and 120 ka, average late-alkalic magma supply

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A Sustained growth B High peak-tholeiite growth—linear (Kilauea @ 0.1 km3/yr) (Kilauea @ 0.2 km3/yr) 0.25 0.25 Kilauea 0.20 0.20 Mauna Loa A /yr (linear) /yr (linear) 3 3 0.15 0.15

0.10 Figure 9. Age and magma-sup- 0.10 ply growth models for Kohala, 0.05 at 100 k.y. intervals, in com- 0.05 Magma supply, km Magma supply, km parison to Kilauea (Fig. 5) and 0.00 Mauna Loa (Fig. 12). (A) Sus- 0.00 1000 500 0 tained-tholeiite growth (Kilauea 1400 1200 1000 800 600 400 200 0 at 0.1 km3/yr). (B) High peak- tholeiite growth (Kilauea at 0.2 km3/yr). The semi-log scale better illustrates variations during intervals of low magma supply. 0.10 0.10 Data are from Table 5, which

also lists interval and cumula- /yr (semi--log) /yr (semi--log) 3 tive volumes. 3

0.01 0.01 Magma supply, km Magma supply, km

0.00 0.00 1400 1200 1000 800 600 400 200 0 1000 500 0 Age, ka Age, ka

would have been ~0.0013 km3/yr, signifi cantly which onlaps the fl ank of a much larger Kohala. entire 3.1 km tholeiitic sequence accumulated lower than for the shorter duration of waxing- The late eruptive record of Mauna Kea has been at an average rate of 8–9 mm/yr. Above 352 m alkalic eruptions at Kilauea or Loihi. deciphered in detail, both from surface geology to the top of the Mauna Kea section at 245 m Despite uncertainties, the time-volume plots (Wolfe et al., 1997) and from the impressively (>200 ka), interlayered alkalic to tholeiitic lavas for Kohala provide a possible template for documented HSDP holes targeted to penetrate (Hamakua Volcanics) defi ne evolution from the inferring growth rates at other less-constrained Mauna Kea lavas near Hilo (DePaolo and Stol- main-stage tholeiite to more uniform late-alkalic volcanoes. Based on its interpreted inception per, 1996; Sharp and Renne, 2005; Stolper et al., lavas and tephra (Laupahoehoe Volcanics) that at ca. 1300 (± 50?) ka, and that of Kilauea at 2004; Rhodes and Vollinger, 2004; Stolper et al., are largely confi ned to upper subaerial slopes of 275 ka, the distance between these two vol- 2009; among many publications). In contrast, the volcano. These compositionally transitional canoes (88 km) yields a propagation rate of the early growth history of Mauna Kea remains fl ows accumulated at a much lower average rate, 8.6 ± ~0.4 cm/yr. This rate, similar to that for the poorly known. ~0.9 mm/yr (Sharp and Renne, 2005), and were entire Hawaiian Ridge (8.6 ± 0.2 cm/yr; Clague The 3506 m HSDP2 hole (Stolper et al., 2009) capped at ca. 100 ka by Mauna Loa lavas in the and Dalrymple, 1987) and to current motion of contains an ~500 k.y. record of upper parts of upper 245 m of the hole. the Pacifi c plate (~7 cm/yr; http://sideshow.jpl the sustained-tholeiite stage and the change to The oldest subaerial lavas on Mauna Kea, .nasa.gov/post/series.html), can then be used to late-alkalic lavas. The lowermost 2 km of the the Hamakua Volcanics, include interbedded infer inception ages for other volcanoes along HSDP hole consist of submarine-emplaced tholeiitic and alkalic fl ows with ages (K-Ar the Kea trend. As discussed later, interpretation tholeiitic pillow lavas and hyaloclastite brec- determinations only) of ca. 300–65 ka (Wolfe of propagation rates is more complex for vol- cias, all tholeiitic but including more variable et al., 1997; Sherrod et al., 2007). The Hamakua canoes of the Loa trend. compositional subgroups than characterize Volcanics therefore are at least largely correla- other main-stage tholeiites such as at Mauna tive with the transitional-composition lavas at Mauna Kea Loa (Stolper et al., 2004; Rhodes and Vollinger, 352–245 m in the drill hole. The alkalic Laupa- 2004). Extrapolation of 40Ar/39Ar ages suggests hoehoe Volcanics on upper slopes of Mauna Kea Based on reinterpretation of the size and shape that the submarine section accumulated from ca. have ages from 65 ka to 4–5 ka (summarized by of Kohala including the Hilo Ridge, Mauna 635 to 400 ka (Sharp and Renne, 2005), when Sherrod et al., 2007); no deposits in the HSDP Kea is interpreted as a topographically high (at 1080 m depth in the hole) an abrupt change hole are equivalent to the Laupahoehoe rocks. edifi ce (4205 m) of relatively modest volume to subaerial lavas of similar tholeiitic com- Diverse compositional, morphologic, and (22,000 km3) among the volcanoes of Hawaii, position continues to 352 m (ca. 330 ka). The structural features of Mauna Kea are consistent

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with its interpretation as a relatively small vol- on land, quenched at the shoreline) interfi nger in the sustained-tholeiite stages. In addition, cano in volume, despite the high elevation of its with pillow lavas that erupted underwater. The Mauna Loa as the larger volcano may have a summit. Without Hilo Ridge (here interpreted Hilo Ridge crest, projected 15 km north of the longer overall life span, and initial eruptions as a distal part of Kohala), Mauna Kea lacks HSDP site, would have been near sea level in there could have begun earlier than projected morphologically or geophysically defi ned siz- the vicinity of the drill site during formation of from simple plate-motion models. Finally, able rift zones. Late-alkalic vents scatter widely the bench at 1100 mbsl (425–450 ka, estimated because of higher magma-supply rates, Mauna on its fl anks without clear alignment that might from isostatic subsidence at 2.4–2.6 mm/yr Loa would likely have grown more rapidly and refl ect rift geometry, in contrast to more lin- [Moore, 1987]). Hyaloclastites in the drill hole may have encroached on a concurrently active ear trends of late vents on volcanoes such as could have come from the shoreline of one vol- Mauna Kea. Haleakala, Kohala, and Hualalai. The volume cano, while pillow lavas erupted from the other A relatively minor uncertainty involves the of waning-stage alkalic lavas on Mauna Kea, (Lipman and Calvert, 2011). High-Si tholeiites probability that deep solidifi ed intrusions of estimated at 875 km3 (Wolfe et al., 1997), also of Kea-trend volcanoes are petrologically simi- Mauna Kea magma, which generate the positive seems large relative to overall size of this vol- lar, making sources challenging to distinguish, gravity anomaly below the summit, continue cano, in contrast to 300 km3 for the much big- but isotopic studies also suggest lavas from at depth into the underlying fl ank of Kohala. ger Haleakala edifi ce (Sherrod et al., 2003). more than one volcano in the drill hole: the “lost Assuming that the total thickness of the Kohala The apparent less-complete development of a volcano” of Blichert-Toft and Albarede (2009). fl ank could be as much as 10 km, reaching as sustained-tholeiite stage at Mauna Kea, in com- shallow as sea level (Fig. 6), and that intrusive parison to other Hawaiian volcanoes, may be Age and Volume feeders and solidifi ed tholeiite-stage reservoirs related to the lower magma-supply rates mod- Based on results from subaerial and the HSDP were as much as 5 km in radius beneath Mauna eled in following sections. samples (Wolfe et al., 1997; Sharp and Renne, Kea, this volume could be ~800 km3, but well Additionally, the HSDP hole encountered 2005), Mauna Kea progressed from main- within uncertainties for the total volume. In the compositional complexities in the 3.1 km main- tholeiite to late-alkalic stage during a lengthy absence of geophysically detectable rift zones, tholeiite sequence (Stolper et al., 2004; Rhodes transition interval from 330 to 65 ka, and is now no sizable volume of deep dike intrusions seems et al., 2012) that could be consistent with rela- near the end of its lifetime, at least in terms of likely beneath the Mauna Kea edifi ce. tively small edifi ce volume, low magma supply, total eruptive volume. The subaerial edifi ce con- or interfi ngering with concurrently growing tinued to grow during much of this interval, as Growth Models Kohala (compare projected location of Hilo indicated by the submerged offshore slope break As a mid-sized volcano, for which age and Ridge’s south fl ank beneath Mauna Kea, at that marks decline in growth, at a water depth volume are well constrained only for late growth, the HSDP site; Fig. 8). Almost a third (31%) of 400 mbsl with an estimated age of 130 ka the early history of Mauna Kea is modeled by of the submarine glass samples from the drill (Moore and Clague, 1992). The prolonged analogy with information from other Hawaiian

hole are low-Si tholeiite (<50% SiO2) that are transitional volcanism and delayed decline in volcanoes. Based on propagation of 8.6 cm/yr atypical in the main-tholeiite stage at Kilauea subaerial growth at Mauna Kea is in contrast to along the Kea trend as bracketed by results from and Mauna Loa (<1% of the analyses for these these events at Kohala, where the compositional Kilauea and Kohala (Table 3), volcanism at volcanoes, as tabulated by Wolfe and Morris change and shoreline submergence appear to Mauna Kea is modeled to have begun at 850 ka, [1996b]). Only about a third of the section, at have been nearly concurrent at ca. 350 ka. with a relatively brief ~400 k.y. duration for its 800–1950 m depth corresponding to ages of ca. The downward-revised volume estimate, sustained-tholeiite stage, and a likely peak erup- 380–515 ka (Sharp and Renne, 2005), consists from ~42,000 to 22,000 km3 (Table 2; Appen- tion rate of ~0.07 km3/yr (Table 6; Fig. 10A). mainly of high-Si tholeiite; within this interval dix B, Table B3), results mainly from exclu- Alternatively, if overall lifespan (1100 k.y.) are two excursions to low-Si tholeiite. Deeper sion of Hilo Ridge and its landward projection and duration of the sustained-tholeiitic stage in the hole, proportions of high- and low-Si beneath Mauna Kea. Also excluded is the (700 k.y.) were closer to that for Kohala, the tholeiite are subequal, and the longest inter- Laupahoehoe slump area, depicted as part of peak eruption rate would have been lower, val without low-Si samples (2650–2800 m) Mauna Kea by Robinson and Eakins (2006) ~0.06 km3/yr (Fig. 10B). Such an early incep- has been interpreted to span only ~20 k.y. (ca. but interpreted here, and by Smith et al. (2002), tion and long lifespan, however, would require 595–615 ka; Stolper et al., 2004; Sharp and as the northeast fl ank of Kohala overlain at a divergent propagation rates between Mauna Renne, 2005). These tholeiites are composi- submerged slope break (1100 mbsl) by Mauna Kea and adjacent volcanoes, rapid from Kohala tionally more variable than thick main-stage Kea lavas. The southwestern boundary between and much slower to Kilauea. In either case, the sequences where sampled on other volcanoes Mauna Kea and Hualalai is inferred to involve highest eruption rate is about two-thirds the such as Mauna Loa (Garcia et al., 1995b) or steep interfi ngering, because these two vol- 0.1 km3/yr inferred for peak 100 k.y. intervals Kilauea (Quane et al., 2000). The abundance of canoes are interpreted to have grown concur- at Kohala or observed at present-day Kilauea. low-Si tholeiite at Mauna Kea is consistent with rently, at similar distance along the trend of the For Mauna Kea to have achieved even a brief lower partial melting and magma supply during Hawaiian Ridge, and with similar ages of erup- interval of tholeiitic eruptions at a rate as high as shield growth than typical of other Hawaiian tive decline as marked by 130 ka submerged 0.1 km3/yr, its modeled eruptive duration would volcanoes (Sisson et al., 2002). slope breaks (400 mbsl). Geometry of the deep have been shorter, ~700 k.y. with a sustained- These compositional variations, and repeated boundary with Mauna Loa to the south is less tholeiite stage of only 250–300 k.y. (Fig. 10C), alternation of subaerially erupted hyaloclastites certain, but also inferred to be steep in most timing that appears inconsistent with the ages with pillow basalts in the drill hole, might also in sectors. Mauna Loa is only 25 km farther along from deep in the HSDP hole (Sharp and Renne, part result from interfi ngering with another con- the Hawaiian Ridge propagation trend, and the 2005). With an estimated volume of 875 km3 currently growing volcano. In the drill hole at volcano-propagation model developed in a later (Wolfe et al., 1997) and a 330 k.y. duration for 2000–2900 m depth (ca. 520–625 ka; Sharp and section predicts nearly concurrent inception of the prolonged transitional and waning-alkalic Renne, 2005), degassed hyaloclastites (erupted these two volcanoes, resulting in large overlap stage at Mauna Kea (Sharp and Renne, 2005),

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TABLE 6. ALTERNATIVE MAUNA KEA GROWTH MODELS, AT 50 TO 100 K.Y. INTERVALS as 1 km thick but only ~300 km3 in volume Age Magma supply Volume Cumulative (Sherrod et al., 2007). No distinct time break (ka) Event (km3/yr) (103 km3) (103 km3) accompanies the compositional shift from lavas A. Kea-trend propagation at 8.6 cm/yr, volcano inception at 850 ka designated “postshield” (Kula Volcanics) to the 850 Inception (alkalic), high on Kohala 0.001 0.40 0.40 800 Waxing alkalic 0.015 1.50 1.90 more alkalic Hana Volcanics (Sherrod et al., 750 Transition, to tholeiite 0.045 2.88 4.78 2003), which previously had been interpreted as 700 Emergence 0.070 6.35 11.13 600 Sustained tholeiite 0.057 5.10 16.23 a “rejuvenated stage” (Clague and Dalrymple, 500 Sustained tholeiite 0.045 3.50 19.73 1987). The average magma supply for this pro- Shore at HSDP site 400 0.025 1.60 21.33 longed interval of late-alkalic volcanism is only Transitional compositions, starting at 330 ka 3 300 Transitional alkalic 0.007 0.45 21.78 0.0003 km /yr, almost three orders of magnitude Equilibrium shoreline? 200 0.002 0.15 21.93 lower than during the main-tholeiite stage. Submergence, at 130 ka 100 Only alkalic, <60 ka 0.001 0.06 21.98 0 0.0001 LOA-TREND VOLCANOES B. Near-constant lifespan, volcano inception at 1100 ka 1100 Inception (alkalic), high on Kohala 0.001 0.55 0.6 Growth and magma supply for the Loa-trend 1000 Waxing alkalic 0.010 2.50 3.1 volcanoes are discussed separately from the Kea 900 Transition, to tholeiite 0.040 5.00 8.1 800 Sustained tholeiite 0.060 5.50 13.6 trend, because the two groups appear to have 700 Emergence 0.050 4.00 17.6 contrasting eruptive histories, propagation rates, 600 Sustained tholeiite 0.030 2.25 19.8 and inception ages that diverge on Hawaii (see 500 Sustained tholeiite 0.015 1.10 20.9 Shore at HSDP site Discussion, especially Table 11 and Fig. 15). 400 0.007 0.55 21.5 Transitional compositions, starting at 330 ka A common propagation rate for the two trends 300 Transitional alkalic 0.004 0.30 21.8 Equilibrium shoreline? would require the younger volcanoes along the 200 0.002 0.15 21.9 Submergence, at 130 ka Loa trend (Loihi, Mauna Loa) to have begun 100 Only alkalic, <60 ka 0.001 0.06 21.96 more recently than seems possible, as evaluated 0 0.0001 in a later section. C. High peak-tholeiite magma supply, volcano inception at 750 ka 750 Inception (alkalic), high on Kohala 0.001 0.05 0.1 700 Waxing alkalic 0.013 0.65 0.70 Loihi Seamount 650 Transition, to tholeiite 0.070 3.50 4.20 600 Sustained tholeiite (oldest HSDP date) 0.090 9.00 13.20 500 Sustained tholeiite 0.055 5.50 18.70 Upper slopes of Loihi, the youngest and Shore at HSDP site smallest of the clustered volcanoes that form 400 0.025 2.50 21.20 Transitional compositions, starting at 330 ka Hawaii Island, with a summit about a kilome- 300 Transitional alkalic 0.005 0.50 21.70 Equilibrium shoreline? ter below sea level, contain interlayered alkalic , 200 0.002 0.20 21.90 Submergence, at 130 ka transitional, and tholeiitic basalts. These pro- 100 Only alkalic, <60 ka 0.001 0.10 22.00 vided the fi rst compelling evidence for a wax- 0 0.001 Note: Shading indicates durations of sustained-tholeiite stage; italics indicate interval of compositional transition; ing-alkalic stage in Hawaii and showed that this HSDP—Hawaii Scientifi c Drilling Program. volcano is currently in early transition to the sustained-tholeiite stage (Moore et al., 1982; Garcia et al., 1995a, 2006). No lavas have thus far been sampled at Loihi that are as mafi c and its late-stage eruption rate is 0.003 km3/yr, 1–2 1000 k.y. tholeiite stage ended at ca. 1000 ka, primitive as the nephelinites and other highly orders of magnitude lower than that modeled for with estimated peak magma supply at ~0.12 alkalic rocks from the submarine south fl ank of its earlier tholeiite stage (Table 6). km3/yr. Lava compositions alternated for at Kilauea, and the increased proportions of Loa- least 100 k.y. during the shift to waning-alkalic trend tholeiite high on Loihi suggests a stage Haleakala stage on land (available dates, 1100–970 ka; comparable to that of Kilauea at ca. 100–125 ka. Chen et al., 1991), after which only alkalic Many published Loihi glass analyses that have As the youngest volcano north of Hawaii and lavas erupted. A widespread submerged slope been described as tholeiite are less silicic (<50%

the largest ediﬁ ce in the Kea trend, Haleakala break, at ~2000 mbsl, is interpreted to record SiO2, ~3% total alkalis) than typical Loa-trend provides a framework for interpreting growth of submergence of the subaerial shoreline at ca. tholeiites from Mauna Loa or Hualalai; these the younger Kea-trend volcanoes. Haleakala has 950 ka (Faichney et al., 2009), near the end of would be classed as transitional or low-Si tho- a volume estimated at ~70,000 km3 (Robinson the tholeiite stage (Moore et al., 1990a; Eakins leiites in plots for other Loa or Kea volcanoes and Eakins, 2006), an original summit probably and Robinson, 2006). In contrast to Mauna Kea, (Sisson et al., 2002; Stolper et al., 2004). 4–5 km above sea level—1–2 km higher than some tholeiitic volcanism continued after incep- the present summit (3055 m) as result of sub- tion of shoreline submergence, as indicated by Age and Volume sidence, and an exceptionally long rift zone— dredged tholeiitic hyaloclastite along the ridge Inception of volcanism at Loihi was estimated the 150 km Hana Ridge (Fig. 1). crest (Moore et al., 1990a). at ca. 100 ka by Moore and Clague (1992), No observational data bear on early growth, Diverse alkalic lavas then erupted for more based on plate-motion modeling and inferred but based on the size of Haleakala, propaga- than 900 k.y. at Haleakala (youngest ﬂ ow, ca. duration of early-alkalic volcanism. In contrast, tion rate along the Kea trend, and analogy A.D. 1600). The waning-alkalic rocks on Halea- from unspiked K-Ar age determinations (Guil- with younger volcanoes like Kohala, volcano kala, accumulating concurrently with growth lou et al., 1997b), Garcia et al. (2006) inferred inception is modeled at 2000–2200 ka. A 900– of Hawaii, formed a subaerial cap as much that Loihi eruptions had already begun on the

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A Near-constant volcano-progression B Near-constant lifespan C High peak-tholeiite magma supply

0.15 0.20 Mauna Kea Mauna Kea Mauna Kea Kohala 0.20 0.15 Kohala 0.10 Mauna Loa–B /yr (linear) /yr (linear) /yr (linear) 3 3 3

0.10 0.10 0.05 0.05 Magma supply, km Magma supply, km Magma supply, km 0.00 0.00 0.00 1400 1200 1000 800 600 400 200 0 1400 1200 1000 800 600 400 200 0 1400 1200 1000 800 600 400 200 0

0.10 0.10 0.10 /yr (semi-log) 3 /yr (semi-log) /yr (semi-log) 3 3 0.01 0.01 0.01

Magma supply, km 0.00 0.00

0.00 Magma supply, km 1400 1200 1000 800 600 400 200 0 1400 1200 1000 800 600 400 200 0 Magma supply, km 1400 1200 1000 800 600 400 200 0

Age, ka Age, ka Age, ka

Figure 10. Age and magma-supply growth models for Mauna Kea, at 50 and 100 k.y. intervals. (A) Near-constant volcano-propagation model. (B) Near-constant lifespan model. (C) High peak-tholeiite model. The semi-log scale better illustrates variations during intervals of low magma supply. Data are from Table 6, which also lists interval and cumulative volumes. Growth curves for Kohala and Mauna Loa are from Figures 9 and 12, respectively.

sea fl oor at depths of ~5000 m by 330–400 ka. grown over lower fl anks of the large Punaluu the waxing-alkalic stage (Fig. 11). Its in-prog- Some reported Loihi ages are internally incon- slump derived from the south fl ank of Mauna ress shift to main-tholeiite stage, after erupting sistent with sample depth, however, and ages Loa, where the latest major downslope move- only about half the total volume as Kilauea at obtained by this method for young basalts can ment is recorded by faulting in the Ninole Hills a similar stage, suggests that it may become a be too old because of potential effects of excess at 100–200 ka (Lipman et al., 1990; Jicha et al., smaller or shorter-lived volcano. Loihi’s current Ar (Calvert and Lanphere, 2006). Alternatively, 2012). If constructed on the Punaluu slump, volume would be comparable in size to Kilauea based on rates of volcano propagation discussed much less of Loihi’s lower slopes would be con- at ca. 150 ka (125 k.y. after initial Kilauea in a later section and analogy with duration cealed by younger volcaniclastic deposits, the growth), and an inception age of 125 ka is mod- of the early-alkalic stage at Kilauea, Loihi is erupted volume of the volcano would be signifi - eled for Loihi (Table 7). For an earlier inception inferred to have commenced at ca. 100–150 ka. cantly smaller at ~800 km3 (Appendix B, Table at 150–175 ka that would be most comparable Although no 40Ar/39Ar isotopic ages have been B4), and it could have grown to present size in to the early-alkalic duration at Kilauea, Loihi’s determined yet for Loihi basalts, alkalic rocks 125 k.y. or less. This smaller volume estimate magma supply would be lower and seemingly from deep on the landslide-scarred eastern and neglects dense olivine-rich cumulates within the less likely to have begun to erupt tholeiite. More western fl anks could be suffi ciently old to yield Mauna Loa fl ank beneath the summit of Loihi. recent inception at 100 ka would be consistent reliable dates. As discussed for Kilauea, such deep cumulate with a rapidly increasing magma supply, per- The volume of Loihi has been estimated as may be as much as 20% of total magma supply, haps more appropriate for the shift to tholeiite. 1700 km3, with lower parts of the edifi ce con- and accordingly, the estimated total Loihi vol- No data exist for present-day magma supply at cealed beneath the volcaniclastic apron derived ume is reduced to 1000 km3 (Table 2). Because Loihi, but by analogy with Kilauea’s transition from subaerial Hawaii Island (Garcia et al., Loihi is relatively young, its volume small, and to tholeiitic eruptions, the modeled rate of 0.03 2006; Robinson and Eakins, 2006). By analogy magma supply low, such volume uncertainties km3/yr seems plausible. with age-volume parameters for the waxing- play little role in modeling the overall growth A more signifi cant problem in relation to alkalic volcanism at Kilauea, however, this of Hawaii. Kilauea is the volcano-propagation rate; Loihi is volume at Loihi could have accumulated within too distant for its inferred age. Projected along 150 k.y. or less, also suggesting that the unspiked Growth Model the composite Kea-Loa trend (N35°W), Loihi is K-Ar ages are too old. In addition, the Loihi vol- With likely inception at 100–150 ka, and a 45 km southeast of Kilauea. Based on an incep- ume estimate seems high. Rather than initiated volume of ~1000 km3, Loihi’s growth would be tion age (125 ka) only 150 k.y. younger than directly on deep-sea fl oor, Loihi appears to have dominated by increasing eruption rates during for Kilauea, the propagation rate between these

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0.12 trends (Wright, 1971; Garcia et al., 1995b; Rhodes and Vollinger, 2004). No deep samples recovered to date provide compositional or age Loihi 0.09 information bearing on an early-alkalic stage. Kilauea While Mauna Loa continues to erupt frequently, /yr (linear)

3 diverse evidence suggests it is late in its main- 0.06 tholeiite stage (Moore et al., 1990b; Lipman, 1995). Only three subaerial lavas (of 468 analyses; Wolfe and Morris, 1996b) have transitional 0.03 compositions, but several young-appearing underwater cones on Mauna Loa’s west sub- Magma supply, km marine ﬂ ank are alkalic (Wanless et al., 2006), 0 hinting that a transition to late-alkalic volcanism 300 250 200 150 100 50 0 may be imminent. Additional evidence for eruptive decline comes from ages and lava-accumulation rates in relation to island subsidence.

0.1 Age and Volume Loihi Several hundred surface ﬂ ows from Mauna Kilauea Loa have radiocarbon ages back to 30–40 ka,

/yr (semi-log) the effective resolution for this method (Lock- 3 0.01 wood, 1995), but older tholeiites have been a geochronometric challenge. Early attempts to analyze tholeiitic samples by K-Ar methods yielded ages with large analytical uncertainties, as well as some dates that are spurious on Magma supply, km 0.001 geologic grounds (Dalrymple and Moore, 1968; 300 250 200 150 100 50 0 Lipman et al., 1990). Age, ka Recent results by 40Ar/39Ar methods have met with greater success, although analyses of low-K Figure 11. Age and magma-supply growth model for Loihi (esti- tholeiites remain diffi cult and uncertainties large. mated inception at 125 ka), at 25 k.y. intervals, and comparison A fl ow from the base of the Mauna Loa section with Kilauea (at 0.1 km3/yr) (Fig. 5). As with other fi gures, the semi- in the HSDP core yielded a groundmass date of log scale better illustrates variations during intervals of low magma 132 ± 32 ka (Sharp et al., 1996), consistent with supply. Data are from Table 7, which also lists interval and cumula- the age (ca. 100 ka) inferred from lava-accumu- tive volumes. lation and coastal-subsidence rates at this site (Lipman and Moore, 1996). In the most substantial effort thus far, 11 dates on submersible volcanoes would be an improbable 30 cm/yr Kilauea (Lipman et al., 2006). Despite its size and dredge samples from the 1.6-km-long scarp (see Discussion, especially Table 11B). Even for amounting to 35%–50% of the volcanic volume along Ka Lae Ridge (underwater southwest rift inception of Loihi at 75 ka, the propagation rate of Hawaii, and in part because of it, the growth zone, Fig. 1) are broadly consistent with strati- would be 22.5 cm/yr. Alternatively, at the Kea- history of Mauna Loa is perhaps the least con- graphic position, defi ning slowing of eruptions trend propagation rate of 8.6 cm/yr, activity at strained of the island’s volcanoes. at ca. 400 ka while documenting that Mauna Loihi should not have commenced until 525 k.y. Historical eruptions, surface exposures of Loa was already a large subaerial volcano by after Kilauea, ~250 k.y. in the future (see Dis- lavas as old as several hundred thousand years, that time (Jicha et al., 2012). A deeper sample cussion, especially Table 11A). A related prob- on-land and underwater fault and landslide dredged from the distal ridge yielded an age of lem with propagation rates between Mauna Loa scarps as much as 1.6 km high, and the 245 m 657 ± 175 ka, further helping delimit inception and Kilauea is discussed next. Mauna Loa section in the HSDP drill core, of tholeiitic volcanism at Mauna Loa. On the expose only tholeiitic lavas that have similar submarine west fl ank, a few ages in the range Mauna Loa compositions modulated by olivine-control 240–460 ka, with large analytical uncertainties ,

As the largest volcano on Earth, rising ~15 km above oceanic crust down-bowed beneath TABLE 7. MAGMA-SUPPLY GROWTH MODEL FOR LOIHI , AT 25 K.Y. INTERVALS Age Event Magma supply Volume Cumulative the Hawaiian Ridge, Mauna Loa dominates (ka) (inception at 125 ka) (km3/yr) (103 km3) (103 km3) growth models for Hawaii. Its volume has been 125 Inception 0.001 approximated at 80 × 103 km3 (Lipman, 1995), 100 Waxing alkalic 0.0015 0.03 0.03 as much as 105 × 103 km3 (Garcia et al., 1995b), 75 Waxing alkalic 0.003 0.06 0.09 50 Waxing alkalic 0.006 0.11 0.20 3 3 and as little as 74 × 10 km (Robinson and 25 Alkalic-transitional 0.014 0.25 0.45 Eakins, 2006) by a model that did not include 0 Transitional-tholeiite 0.030 0.55 1.00 the substantial subsurface ﬂ ank onlapped by Note: Intervals are constrained by estimated total volume of 1.0 × 103 km3.

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have been obtained from tholeiites that have alternative would transfer volume to an older In addition to isotopic and historical age data, compositions similar to recent Mauna Loa lavas adjacent edifi ce, thereby augmenting conclu- coastal lava-accumulation rates and ages of sub- (Morgan et al., 2007). In addition, two tholeiite sions concerning timing of peak overall growth merged shorelines and coral reefs provide evi- samples from the Ninole Hills on Mauna Loa’s of Hawaii. dence for decline in magma supply late during south fl ank yielded ages of 227–108 ka, demon- An additional proposal, that an ancient buried the tholeiite stage. While Mauna Loa has been strating that by this time, the subaerial Mauna “Ninole rift zone” underlying the south fl ank of interpreted to be continuing vigorous growth Loa edifi ce was approaching its present size. Mauna Loa predates the present-day confi gura- because its historical lava volume (4.1 km3), This geochronologic evidence for early rapid tion of the southwest rift (Morgan et al., 2010), if spread uniformly over the subaerial volcano growth to form Ka Lae Ridge, followed by a is inconsistent with isotopic ages that are older (5125 km2), would have an average lava-accu- lengthy period of eruptive decline later during for distal southwest rift lavas (400–650 ka) than mulation rate of ~5 mm/yr (Jicha et al., 2012), the main-tholeiite stage at Mauna Loa, support a for the Ninole Basalt (100–200 ka; Lipman coastal accumulation has been insuffi cient to general model of asymmetric growth during the et al., 1990; Jicha et al., 2012). Profi les of high grow the subaerial edifi ce. About a quarter of lifespan of Hawaiian volcanoes, as initially dia- seismic velocity and positive gravity, cited as historically erupted lava has ponded within the grammed perceptively by Wise (1982). evidence for a Ninole rift (Morgan et al., 2010, summit caldera (Lockwood and Lipman, 1987), The volume of Mauna Loa, estimated here as their fi gures 2 and 4), appear to have juxtaposed some historical eruptions crossed the shore- 83 × 103 km3 (Appendix B, Table B5), adjusts the large velocity/density anomaly associated line to deposit on submarine slopes, and much the Robinson and Eakins (2006) value of 74 × with the summit magma reservoir of Mauna of the on-land lava accumulated preferentially 103 km3, based on a substantially reduced vol- Loa and analogous geophysical expression of in proximity to vents high on the edifi ce. With ume of Kilauea and increased volume of Hua- Kilauea’s distal southwest rift. adjustments for these factors, overall coverage lalai. Because Kilauea onlaps the south fl ank of rates for subaerial slopes during the historical Mauna Loa (Lipman et al., 2006), the volume Growth Models period averages only ~3 mm/yr, and coastal of Kilauea is here estimated at 11 × 103 km3, in Multiple scenarios are possible for Mauna rates would necessarily be lower. With shoreline contrast to the previous 32 × 103 km3 (Robin- Loa’s growth, depending on estimates of its subsidence at ~2.6 mm/yr (Moore, 1970, 1987; son and Eakins, 2006). Inferred to offset some lifespan. As the largest Hawaiian volcano, Ludwig et al., 1991), the historical period thus of this component, however, is evidence from would duration of its growth also be relatively provides little evidence for continued vigorous gravity data that the south rift zone of Hualalai lengthy? The recent 40Ar/39Ar ages from Ka Lae growth, or even maintaining the subaerial size continues beneath the west fl ank of Mauna Loa Ridge (Jicha et al., 2012) appear to document of the edifi ce. for at least 20 km beyond any surface outcrops 600 k.y. or more of sustained eruption of com- Along much of the present coastline, aver- of Hualalai lavas (Kauahikaua et al., 2000). positionally similar tholeiite, without any hint age lava accumulation is only approximately Accordingly, Hualalai is interpreted to be larger of inception. If a duration of 100–150 k.y. is keeping pace with subsidence (Lipman, 1995), than previously estimated, at the expense of assumed for an early-alkalic stage by analogy even though the on-land area of Mauna Loa Mauna Loa volume (Table 2). with Loihi and Kilauea, and a future late-alkalic has decreased by ~20% as Kilauea has grown Two additional diffi cult-to-evaluate uncer- stage of ~200 k.y., the lifespan of Mauna Loa above sea level and overlapped the south fl ank tainties further complicate these volume esti- would be at least 900 k.y. of its large neighbor. The low rate of subaerial mates: (1) a plausible but untested inference Mauna Loa and Kilauea are the only Hawai- lava accumulation for Mauna Loa is well docu- that the relatively short present northeast rift ian volcanoes for which historical records and mented in the HSDP core, where average accu- of Mauna Loa formerly may have continued geologic mapping of young prehistoric fl ows mulation has been balanced by subsidence since beneath the east rift and Puna Ridge of Kilauea provide quantitative data on eruption rates and at least ca. 100–120 ka (Lipman and Moore, (Lipman, 1980b, p. 772; Flanigan and Long, magma supply. Total lava output for the 170 1996), despite funneling of Mauna Loa fl ows 1987), and (2) a proposal that Hualalai’s south years of historical record (A.D. 1843–2012) is toward the drill site, from its northeast rift into rift zone might once have continued as far south ~4.1 km3 (Lockwood and Lipman, 1987), or the broad valley between Mauna Kea and the as Ka Lae Ridge (Holcomb et al., 2000). Neither 0.024 km3/yr. Detailed mapping of prehistoric growing Kilauea shield. of these alternatives can be evaluated unambigu- lava fl ows on Mauna Loa suggests a roughly The dated decline in lava accumulation at ca. ously from available data. As possible support similar rate for at least the past 3000 years 400 ka along the submarine southwest rift zone for alternative 2, a drowned seacliff along Ka (Trusdell, 2010). (Jicha et al., 2012) may result mainly from the Lae Ridge (Moore et al., 1990b; Garcia et al., Intrusive contributions to the recent magma apparent tendency for Hawaiian rift zones to be 1995b) is similar in depth (430–450 m) to a sub- supply of Mauna Loa are diffi cult to estimate established early during volcano growth, then merged reef that drapes the northwest (Kiholo but seem likely to be less than at Kilauea where to become less active (“drying up”) as tholeiite Ridge) of Hualalai (Moore and Clague, 1992). the rift-bounded south fl ank is spreading sea- eruptions become focused higher on the grow- Alternative 1 would further increase the vol- ward much more rapidly than its geometric ing edifi ce (Moore and Clague, 1992; Lipman ume of Mauna Loa relative to that of Kilauea counterpart on Mauna Loa (Miklius et al., 1995; and Calvert, 2011). Alternatively, reduced activ- because much of Kilauea’s volume as currently Miklius and Cervelli, 2003). The long-term ity along the lower southwest rift may have interpreted resides in its long east rift zone intrusive contribution to Kilauea’s magma sup- been caused by dislocations in response to (~3000 km3, 30% of total Kilauea volume in just ply has been estimated at 30%–50% (Dvorak large-scale landslides and slumps along Mauna the submarine Puna Ridge; Lipman et al., 2006). and Dzurisin, 1993; Cayol et al., 2000; Wright Loa’s west fl ank (Lipman, 1980b; Lipman et al., Alternative 2, discussed further in the section on and Klein, 2013; Poland et al., in press); an 1990). Whatever the initial cause, decline in Hualalai, if valid, would increase that volcano’s assumed 30% for Mauna Loa would yield a lava-accumulation rate along the lower south- volume substantially and reduce Mauna Loa’s. historical magma supply of ~0.035 km3/yr, only west rift is further documented by a submerged If both alternatives were valid, impact on the about a third of the estimated average historical paleo-shoreline, marked by an ~10-m-high sea volume of Mauna Loa could be modest. Either rate at Kilauea (~0.1 km3/yr). cliff with wave-rounded boulders at its base, 450

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mbsl, with an interpreted age of 170 ka (Moore TABLE 8. ALTERNATIVE MAUNA LOA MODELS AT 50 TO 100 K.Y. INTERVALS et al., 1990b; Garcia et al., 1995b). Age Magma supply Volume Cumulative (ka) Event (km3/yr) (103 km3) (103 km3) Growth of the submarine Ka Lae Ridge A. Near constant Loa-trend propagation (10.6 cm/yr), inception at 800 ka (Fig. 1) to near present size by 400 ka (Jicha 800 Inception 0.001 et al., 2012) and maintenance of its subaerial 750 Waxing alkalic 0.016 0.03 0.03 shoreline 8.5 km seaward of the present one until 700 Transition, to tholeiite 0.135 0.43 0.45 600 Sustained tholeiite 0.200 16.75 17.20 ca. 170 ka demonstrate that Mauna Loa already 500 Sustained tholeiite 0.180 19.00 36.20 was a large subaerial edifi ce by these times, with 400 Sustained tholeiite 0.140 16.00 52.20 topographic profi les projecting close to its pres- 300 Equilibrium shoreline? 0.100 12.00 64.20 200 Equilibrium shoreline? 0.070 8.50 72.70 ent slopes. Accordingly, growth models devel- 100 Waning tholeiite 0.050 6.00 78.70 oped here (Table 8) assume substantial decline in 0 Incipient alkalic submarine, South Kona 0.035 4.25 83.0 tholeiite eruption rates, starting ca. 400 ka. Even B. Near-constant lifespan, volcano inception at 950 ka if volcano inception began as early as ca. 950 ka, 950 Inception 0.001 900 Waxing alkalic 0.010 0.28 0.3 about concurrently with Mauna Kea (and requir- 800 Transition, to tholeiite 0.120 6.50 6.8 ing a long gap before initial volcanism at Kilauea 700 Sustained tholeiite 0.160 14.00 20.8 at ca. 275 ka), peak sustained magma supply for 600 Sustained tholeiite 0.170 16.50 37.3 500 Sustained tholeiite 0.140 15.50 52.8 100 k.y. periods at Mauna Loa likely approached 400 Sustained tholeiite 0.075 10.75 63.5 0.17 km3/yr (Fig. 12B), 50% greater than for 300 Equilibrium shoreline? 0.055 6.50 70.0 present-day Kilauea. Alternately, if inception 200 Equilibrium shoreline? 0.045 5.00 75.0 100 Waning tholeiite 0.040 4.25 79.3 of Mauna Loa were younger, at ca. 850 ka, to 0 Incipient alkalic submarine, South Kona 0.035 3.75 83.0 allow for a more nearly constant age progression C. High peak-tholeiite magma supply, volcano inception at 550 ka among the island’s volcanoes, the time interval 550 Inception: early alkalic 0.001 for main-stage tholeiite magma supply becomes 500 Transition, to tholeiite 0.100 2.53 2.5 450 Sustained tholeiite 0.500 15.00 17.5 shorter and the estimated peak rate higher, ~0.20 400 Sustained tholeiite 0.350 21.25 38.8 km3/yr (Fig. 12A). 350 Sustained tholeiite 0.200 13.75 52.5 The timing of volcano inception at Mauna 300 Equilibrium shoreline? 0.120 8.00 60.5 200 Equilibrium shoreline? 0.090 10.50 71.0 Loa, as at Loihi, is a special problem in rela- 100 Waning tholeiite 0.055 7.25 78.3 tion to propagation along the Kea trend. While 0 Incipient alkalic submarine, South Kona 0.040 4.75 83.0 Loihi is too distant from Kilauea to have a Note: Intervals constrained by estimated total volume of 83 × 103 km3. Southwest rift zone (SWR) submergence, after ca. 400 ka. Shading indicates duration of sustained-tholeiite stage. propagation rate consistent with motion of the Pacifi c plate, the proximity of Mauna Loa to Kilauea (23 km, along the composite volcano trend) would imply volcano inception at only rather than on the fl ank of another volcano, and ciated gravity high continues to the Mahukona ca. 540 ka, at the average progression rate (8.6 its estimated volume is larger than Mauna Kea. platform (Garcia et al., 2012). The south rift cm/yr) for the Kea trend (see Discussion, espe- Its relatively small surface exposures are decep- zone can be traced for at least 40 km, including cially Table 11). Modeling of young inception tive because of widespread cover by Mauna its gravity expression beyond exposed Hualalai of Mauna Loa (at ca. 540 ka) would also require Loa, probable submarine overlap of Mahukona, lavas (Kauahikaua et al., 2000). extremely high magma production during the and large-scale fl ank failure along the west peak-tholeiitic stage (~0.5 km3/yr at 450 ka) that coast. Hualalai remains active, in its late-alkalic Age and Volume then declined rapidly to the present-day rate of stage (Moore et al., 1987), but the relatively As for most old volcanoes on the island, ~0.035 km3/yr (Fig. 12C). Such a recent incep- infrequent eruptions are not keeping pace with direct information is unavailable for inception tion for Mauna Loa seems inconsistent, how- shoreline subsidence (Moore and Clague, 1992). of the early-alkalic stage or the change to tho- ever, with dates as old as 657 ± 175 ka (Jicha Future volumetric growth will be modest. leiitic volcanism. A submerged slope break and et al., 2012) on submarine tholeiite from Ka Subaerial Hualalai exposes only waning- coral reef, widely traceable at ~400 mbsl and Lae Ridge. Alternatively, Mauna Loa and Loihi stage alkalic lavas, but tholeiite crops out off- dated at ca. 130 ka, mark decline in main-stage could record volcano inception asynchronously shore and has been penetrated above sea level in activity at Hualalai, although some tholeiitic older by several hundred thousand years than water wells (Moore et al., 1987; Cousens et al., fl ows drape the reef (Moore and Clague, 1987). for counterparts along the Kea trend. Such an 2003). The topographic summit of alkalic basalt Trachyte lavas at Puu Waawaa on Hualalai’s interpretation seems required by the young ages lies 5–7 km north of the gravity maximum that north fl ank, inferred to record beginning of the for waxing-alkalic growth of Kilauea (Calvert likely images intrusions associated with the tho- waning-alkalic stage, have K-Ar ages as old as and Lanphere, 2006). leiitic stage (Kauahikaua et al., 2000), perhaps 114 ka (Clague, 1987; Cousens et al., 2003). refl ecting late vent migration in response to but- The shift from tholeiite to waning alkalic stages Hualalai tressing by Mauna Loa (Lipman, 1980b). North- is thus closely bracketed, <130 to >114 ka. west- and south-trending rift zones are marked The volume of Hualalai, previously esti- Hualalai appears to have begun growing by late-alkalic vents that coincide with residual- mated at 14,200 km3 (Robinson and Eakins, before Mauna Kea even though it has erupted gravity highs, in contrast to absence of similar 2006), is particularly uncertain because of cover more frequently in recent time. The location alignments on Mauna Kea. The underwater by Mauna Loa lavas, gravitational failure of of Hualalai slightly farther northwest along the continuation of the northwest rift zone (Kiholo its southwest fl ank (North Kona slump), diffi - Hawaiian Ridge suggests earlier inception, it Ridge) has bathymetric expression for >70 km culty in tracing extent of rift zones, and likely appears to have grown mainly on ocean fl oor from the subaerial summit (Fig. 1), and the asso- complex interfi ngering with Mauna Kea to the

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A Near-constant Loa-trend propagation (10.6 cm/yr), B Near-constant lifespan, C High peak-tholeiite magma supply, volcano inception at 800 ka volcano inception at 950 ka volcano inception at 550 ka

0.25 0.25 0.50

0.20 0.20 0.40 /yr (linear) /yr (linear) /yr (linear) 3 3 0.15 3 0.15 .030

0.10 0.10 .020

0.05 0.05 0.10 Magma supply, km Magma supply, km Magma supply, km

0.00 0.00 0.00 1000 500 0 1000 500 0 1000 500 0

1.00

0.10 0.10

0.10 /yr (semilog) /yr (semilog) 3 /yr (semilog) 3 3

0.01 0.01 0.01 Magma supply, km Magma supply, km Magma supply, km 0.00 0.00 0.00 1000 500 0 1000 500 0 1000 500 0 Age, ka Age, ka Age, ka

Figure 12. Age and magma-supply growth models for Mauna Loa, at 100 k.y. intervals. (A) Near-constant volcano-propagation model (10.6 cm/yr). (B) Near-constant lifespan model (volcano inception at 950 ka). (C) High peak-tholeiite model (volcano inception at 550 ka). The semi-log scale better illustrates variations during intervals of low magma supply. Data are from Table 8, which also lists interval and cumulative volumes.

east. A larger estimate of 26,000 km3 (Table 2; numerous giant landslides and slumps. If Ka thousand years shorter than at Kohala (Table Appendix B, Table B6) is based on assump- Lae Ridge were part of Hualalai, its volume 9B; Fig. 13B). With a rough volume estimate of tion that the perimeter of subaerial Hualalai lies would be considerably larger, perhaps 45,000– 500 km3 and a 115 k.y. duration for the waning- 5–15 km beyond present exposures, onlapped 50,000 km3, and that of Mauna Loa accordingly alkalic stage at Hualalai, the late-stage eruption by Mauna Loa ﬂ ows, and that distal rift zones smaller. Broader implications of this uncertain rate averages 0.004 km3/yr, similar to that for continue farther than estimated by Robinson hypothesis (Holcomb et al., 2000) are consid- Mauna Kea but an order of magnitude or more and Eakins (2006). ered further in the section on overall assembly lower than during the sustained-tholeiite stage. An additional uncertainty is the speculative of Hawaii. proposal that deeper parts of Ka Lae Ridge Mahukona could be the distal continuation of Hualalai’s Growth Models south rift (Holcomb et al., 2000). No petrologic As a mid-sized volcano, for which age and The broad Kohala platform extending ~50 km distinctions are known between Mauna Loa ver- volume are well constrained only for late growth, offshore from northwest Hawaii (Fig. 1), ﬁ rst sus Hualalai tholeiites that could help evaluate Hualalai’s earlier eruptive history is modeled by proposed as the site of a submarine volcano this alternative, but a Hualalai connection could analogy with other volcanoes. Based on dis- by Stearns and Macdonald (1946, p. 56), was be consistent with the abrupt decline in eruption tance from Mauna Loa (37 km) and a Loa-trend named Mahukona volcano and inferred to mark rate at ca. 400 ka at Ka Lae Ridge (Jicha et al., propagation rate (10.6 cm/yr), Hualalai would initial volcanism of Hawaii (Moore and Camp- 2012). Gravity data show a density gap between have begun at ca. 1100 ka, with a relatively long bell, 1987). Dredging and submersible sam- Hualalai and the southwest rift of Mauna Loa sustained-tholeiite stage (Table 9A; Fig. 13A). pling have recovered tholeiitic, transitional, and (Kauahikaua et al., 2000); however, making Without inclusion of Ka Lae Ridge, peak tho- weakly alkalic basalt along the broad ridge at such an interpretation seem improbable. In leiitic magma supply would have been ~0.05 the west end of the platform, which has been addition, a lengthy south rift of Hualalai all the km3/yr (Fig. 13A), about half that inferred for interpreted as the “missing volcano” along the way to Ka La Ridge would likely have formed peak 100 k.y. intervals at Kohala or observed Loa trend between Kahoolawe and Hualalai a structural barrier to large slope failures (as on at present-day Kilauea. For Hualalai to have a (Garcia et al., 1990; Clague and Moore, 1991). the northeast side of Mauna Kea), but the west tholeiitic stage approaching 0.1 km3/yr, its erup- Most sites yielded tholeiite; transitional to side of Mauna Loa instead has been the site of tive duration would have been several hundred weakly alkalic basalt has been recovered mainly

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TABLE 9. ALTERNATIVE HUALALAI GROWTH MODELS, AT 50 TO 100 K.Y. INTERVALS et al., 2012), but other Hawaiian volcanoes, and Age Magma supply Volume Cumulative even the relatively small Loihi Seamount at an (ka) Event (km3/yr) (103 km3) (103 km3) early growth stage, have large positive gravity A. Near-constant Loa-trend propagation (10.6 cm/yr), volcano inception at 1100 ka 1100 Inception (alkalic) 0.001 anomalies associated with summits and proxi- 1000 Early alkalic 0.005 0.30 0.30 mal rift zones (Kinoshita et al., 1963; Strange 900 Transition to tholeiite 0.014 0.95 1.25 et al., 1965; Kauahikaua et al., 2000). Absence of 800 Increased tholeiite 0.05 3.20 4.45 700 Sustained tholeiite 0.065 5.75 10.20 a positive anomaly marking a Mahukona summit 600 Sustained tholeiite 0.045 5.50 15.70 would seem especially problematic for a rela- 500 Sustained tholeiite 0.03 3.75 19.45 400 Sustained tholeiite 0.02 2.50 21.95 tively large edifi ce hosting a summit caldera and 300 Sustained tholeiite 0.015 1.75 23.70 accompanying shallow magma chamber, such as 200 Alkalic after ~ 130 ka 0.01 1.25 24.95 proposed by Clague and Moore (1991). In addi- 100 Late alkalic 0.005 0.75 25.70 0 Late alkalic 0.001 0.30 26.00 tion, the broad Kohala platform seems puzzling B. High peak-tholeiite magma supply, volcano inception at 750 ka morphologically for a waning-alkalic stage of a 850 Inception (alkalic) 0.001 Hawaiian volcano; such late volcanism typically 800 Early alkalic 0.005 0.15 0.15 generates steeper slopes than the tholeiite stage. 700 Transition to tholeiite 0.040 2.25 2.4 As an additional complexity, tholeiitic lavas 600 Sustained tholeiite 0.100 7.00 9.4 500 Sustained tholeiite 0.060 8.00 17.4 attributed to Mahukona are unusually diverse 400 Sustained tholeiite 0.025 4.25 21.7 in elemental and isotopic composition, includ- 300 Sustained tholeiite 0.015 2.00 23.7 200 Alkalic after ~ 130 ka 0.010 1.25 24.9 ing subequal proportions of Loa and Kea types 100 Late alkalic 0.005 0.75 25.7 (Clague and Moore, 1991; Garcia et al., 2012). 0 Late alkalic 0.001 0.30 26.0 This variability, which differs from the other 3 3 Note: Constrained by estimated total volume of 26 × 10 km . Shading indicates duration of volcanoes of Hawaii Island, might be related to sustained-tholeiite stage. Bold indicates best constrained events and ages. a diffuse magmatic system without a long-lived central reservoir, or possibly to overlapping by nearby volcanoes. For this last speculative from the large cone that forms the youngest part that contains a fi lled caldera. These contrasting alternative, based on geometry of the gravity of Mahukona as currently interpreted. The east- views are closely tied to alternative interpreta- anomaly and the mixture of Kea and Loa com- ern extent of Mahukona is hidden beneath the tions of the submarine slope breaks that mark positions, no discrete Mahukona volcano need Kohala platform, which contains a stepped suc- the end of sustained-tholeiitic growth in relation exist. Instead, the western ridge of the Kohala cession of at least six drowned coral reefs. Iso- to ages of coral reefs on the platform (Fig. 1). platform perhaps could be an early-formed topic ages from the coral constrain late growth Clague and Moore (1991) interpreted reef 6 and broad rift zone from Kohala (Kea composition), and termination of volcanism at Mahukona, associated slope break as the paleo-shoreline of onlapped by continuation of the northwest rift as well as island subsidence rates (Moore and Mahukona, and correlated the Kohala tholeiitic zone from Hualalai (Loa composition). A larger Campbell, 1987; Moore and Clague, 1992). shoreline with a shallower coral reef at 950 mbsl analog for such distal widening of a submarine (reef 4) on the platform. They also interpreted rift could be the landside-modifi ed tip of the Is Mahukona Really a Volcano? “trains of basalt rubble in chutes” (Clague and Hana Ridge of Haleakala (Eakins and Rob- Despite much elemental and isotopic chem- Moore, 1991, p. 161) on an intermediate-depth inson, 2006). If part of the Mahukona edifi ce istry, 40Ar/39Ar age determinations, and detailed reef (~1150 mbsl, reef 5) as erupted from Mahu- were a west ridge of Kohala, this rift would be bathymetric and gravity surveys, uncertainty kona, requiring that its summit lay to the east. ~100 km long, and Kohala in broad form would continues about the shape and volume of the All the reefs on the Kohala terrace are tilted be a 230-km-long ridge, paralleling the arcuate Mahukona construct, location of its summit, southward in response to volcanic loading on south fl ank of the clustered older volcanoes of whether the edifi ce ever rose above sea level, the Hawaiian Ridge (Moore and Campbell, Maui Nui (submerged platform of Maui, Molo- causes of compositionally diverse lavas, tim- 1987), however, and the deeper reefs (5–6) rise kai, Lanai, Kahoolawe). ing of the change from tholeiitic to late-alkalic and merge northward with a single slope break stages, and even whether this feature constitutes at a depth of ~1000 mbsl. This break continues Volume and Age a discrete volcano. Analogous interpretive ambi- clockwise around the north fl ank of Kohala vol- The volume of any Hawaiian volcano is guities and possible alternative origins also exist cano and marks the decline of tholeiitic eruptions inherently diffi cult to determine, because of for several other shallow elongate platforms (Moore and Clague, 1992; Smith et al., 2002). uncertainties about edifi ce overlaps and effects offshore of older Hawaiian islands: Penguin Recent geophysical, bathymetric, and petro- of crustal subsidence beneath the Hawaiian Bank southwest of Molokai, Kaena and Waialu logic data provide additional perspectives on Ridge. For Mahukona, these complexities are Ridges west of Oahu, and Pauwela Ridge north complexities and uncertainties concerning the augmented by the uncertainties concerning of Maui (Robinson et al., 2006). summit location and shape of Mahukona. An volcano area, summit location, and origin. Pos- Garcia et al. (1990, 2012) inferred a relatively elliptical positive residual-gravity anomaly that sible alternatives include: (1) small western edi- small Mahukona seamount, having an area of trends northwest from Hualalai (Garcia et al., fi ce, volume of ~6000 km3 (Garcia et al., 1990, ~1600 km2, and a summit location marked by 2012, their fi gure 4) coincides with neither of the 2012); (2) larger edifi ce with summit farther a large steep-sided cone that grew only to ~270 proposed summit locations nor the morphologi- east and a concealed fl ank onlapped by Kohala mbsl. In contrast, Clague and Moore (1991) and cally expressed west-trending Mahukona ridge. (Clague and Moore, 1991; Clague and Calvert, Clague and Calvert (2009) interpreted a larger Absence of a dense core suffi cient to generate 2009), volume here estimated as ~20,000 km3; edifi ce that formerly rose above sea level, as now a gravity anomaly at Mahukona was inferred to or speculatively (3) even absence of Mahukona marked by a submerged platform ~30 km across result from slow growth and small size (Garcia as a discrete volcano. In absence of positive

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A Loa-trend propagation at 10.6 cm/yr, B High peak-tholeiite magma supply, volcano inception at 850 ka volcano inception at 850 ka

0.25 0.50

0.20 Mauna Loa A 0.40 Hualalai Mauna Loa C Hualalai /yr (linear)

/yr (linear) 0.30 0.15 3 3

0.10 0.20

0.10

0.05 Magma supply, km Magma supply, km

0.00 0.00 1400 1200 1000 800 600 400 200 0 1400 1200 1000 800 600 400 200 0

0.10 Mauna Loa A Mauna Loa C Hualalai 0.10 Hualalai /yr (semi-log) /yr (semi-log) 3 3

0.01 0.01 Magma supply, km Magma supply, km

0.00 0.00 1400 1200 1000 800 600 400 200 0 1400 1200 1000 800 600 400 200 0 Age, ka Age, ka

Figure 13. Age and magma-supply growth models for Hualalai and comparisons with Mauna Loa, at 100 k.y. intervals. (A) Near-constant volcano-propagation model (10.6 cm/yr; near-constant lifespan model is the same). (B) High peak-tholeiite model (volcano inception at 850 ka). The semi-log scale better illustrates variations during intervals of low magma supply. Data are from Table 9, which also lists interval and cumulative volumes. Growth curves for Mauna Loa are from Figures 12A and 12C.

evidence for alternative 3, or gravity data in sup- cia et al., 2012), probably representing the near parable to volcanoes such as Kohala (~1200 port of alternative 2, models for this overview termination of eruptions. An age of 481 ± 37 ka k.y.), then even with prolonged (100–200 k.y.) are based conservatively on the ~6000 km3 for transitional basalt from deeper on the ﬂ ank waxing and waning stages, peak magma supply estimate of Garcia et al. (2012). Because the of the same cone suggests a possibly prolonged would have been ~0.01 km3/yr, an order of mag- volume of the Mahukona construct would be interval of waning volcanism, but no highly nitude less than for larger volcanoes or present- relatively small by whatever alternative, none of alkalic lavas have been sampled at Mahukona. day Kilauea. Peak tholeiite activity at even half them substantially affects broad conclusions of An age of 654 ± 36 ka on tholeiite from a deeper the rate of larger volcanoes would require a overall magma supply and eruption rates during cone farther west provides another limit on late much briefer lifespan (600 k.y. or less), but this composite growth of Hawaii, discussed later. activity (Garcia et al., 2012). Generalizing from would delay inception of Mahukona until ~400 Age estimates are also problematic, because these results, the putative Mahukona volcano is k.y. later than initial activity at adjacent Kohala of uncertainties concerning which dates are reli- interpreted to have changed from main-tholeiite or predicted from geodynamic models of vol- ably associated with growth at Mahukona. Based to late-alkalic stage at ca. 400–450 ka and to cano propagation. on a coral age from the 1350-mbsl shelf break have terminated by 300 ka. No data exist for at reef 6, Clague and Moore (1991) estimated waxing-alkalic stage at Mahukona, but the bulk Kahoolawe that tholeiite-stage eruptions began to decline of this ediﬁ ce must be tholeiite; only two sites by ca. 470 ka but persisted to at least 430 ka, have yielded transitional samples. In parallel to Haleakala on Maui Nui, the the coral age of reef 5 that is draped by tho- growth history of Kahoolawe bears on initia- leiitic rubble inferred from Mahukona. Recent Growth Model tion of the Loa trend on Hawaii, but modern 40Ar/39Ar ages from transitional basalt on the A 6000 km3 volume for Mahukona would geologic data are sparse because of island use shallow cone along the western Mahukona ridge imply growth markedly different from larger as a military bombing range. Available K-Ar are 300–350 ka (Clague and Calvert, 2009; Gar- Hawaiian volcanoes. If its lifespan were com- ages roughly define the end of sustained-

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tholeiite eruptions at ca. 1200 ka, followed by TABLE 10. VOLCANO-GROWTH MODELS, WITH VOLUMES (103 KM3) AT 100 K.Y. INTERVALS, late-alkalic volcanism until ca. 900 ka (Sherrod FOR COMPOSITE ASSEMBLY OF THE ISLAND OF HAWAII Time Total et al., 2007); analogies with other volcanoes (ka) Mahukona Kohala Hualalai Mauna Kea Mauna Loa Kilauea Loihi island suggest inception at 2100–2250 ka (Table 3). A. Near-constant propagation of volcano inception (difference between Kea and Loa trends) 1600 — ASSEMBLY OF THE ISLAND 1500 0.1 0.1 1400 0.2 0.2 OF HAWAII 1300 0.3 — 0.3 1200 0.5 0.6 1.1 Composition, age, and volume data for indi- 1100 0.8 4.5 — 5.3 1000 1.0 8.9 0.3 10.2 vidual volcanoes, while of uneven quality, quan- 900 1.0 10.3 1.0 — 12.2 tity, and completeness, provide a framework 800 0.6 10.3 3.2 0.40 — 14.5 for modeling the composite growth of Hawaii 700 0.5 9.3 5.8 4.38 0.48 20.4 600 0.4 8.0 5.5 6.35 16.75 37.0 Island. Ages and volumes have been combined 500 0.3 6.5 3.8 5.10 19.00 34.7 for three alternative magma-supply models for 400 0.2 4.0 2.5 3.50 16.00 26.2 300 0.1 1.5 1.8 1.60 12.00 — 16.9 100 k.y. intervals from each volcano: (1) near- 200 0.0 0.3 1.3 0.45 8.50 0.3 — 10.8 constant propagation of volcano inception; 100 0.0 0.1 0.8 0.15 6.00 2.3 0.1 9.4 (2) near-equal lifespan, varied peak-tholeiite 0 0.0 0.0 0.3 0.05 4.25 8.4 0.9 13.9 Total 6.0 64.0 26.0 22.0 83.0 11.0 1.0 212.9 rate; and (3) varied duration, high peak-tholeiite B. Near-constant long lifespan (~1.1 m.y.); variably lower tholeiite rates rate (Table 10). These models then can gener- 1400 ate age-volume growth plots for the entire island 1300 — — 0.0 (Fig. 14). 1200 0.1 0.6 0.7 1100 0.3 4.5 —— 4.8 Somewhat unexpectedly, the three growth 1000 1.0 8.9 0.3 0.55 — 10.8 models yield generally similar results despite 900 1.5 10.3 1.0 2.5 0.3 15.5 the varied assumptions and inputs. Each model 800 1.2 10.3 3.2 5.0 6.5 26.2 700 0.8 9.3 5.8 5.5 14.0 35.3 has a broad peak of high magma supply (20– 600 0.5 8.0 5.5 4.0 16.5 34.5 35 × 103 km3/100 k.y.) from ca. 400 to 800 ka, 500 0.3 6.5 3.8 2.3 15.5 28.3 when four Hawaiian volcanoes (Kohala, Hua- 400 0.2 4.0 2.5 1.1 10.8 18.6 300 0.1 1.5 1.8 0.6 6.5 — 10.4 lalai, Mauna Kea, Mauna Loa) were erupting 200 0.0 0.3 1.3 0.3 5.0 0.3 — 7.1 tholeiite voluminously. The lower magma vol- 100 0.1 0.8 0.2 4.3 2.3 0.1 7.6 0 0.0 0.3 0.1 3.8 8.4 0.9 13.4 umes for earlier time intervals refl ect ramping Total 6.0 64.0 26.0 22.0 83.0 11.0 1.0 212.9 up of volcanism at Hawaii as it waned on Maui C. Variable volcano lifespan; high peak-tholeiite eruption Nui, and an interval of diminished magma sup- 1400 ply along the Hawaiian Ridge as recorded by 1300 — 0.0 the inter-island channel. The lower volumes 1200 0.7 0.7 1100 4.4 4.4 for younger intervals largely refl ect existence 1000 13.8 13.8 of only a single volcano, Kilauea, with a recent 900 — 17.0 — 17.0 3 800 0.1 11.3 0.2 — 11.5 magma supply of 0.1 km /yr or higher. For the 700 0.8 7.1 2.3 0.2 10.3 other two highly active volcanoes, Loihi is tran- 600 4.0 4.6 7.0 2.6 — 18.2 sitioning from its waxing-alkalic stage while 500 1.0 2.8 8.0 8.0 2.5 22.3 400 0.1 1.5 4.3 7.3 36.2 49.3 tholeiitic eruption rates have been declining at 300 0.0 0.7 2.0 3.1 21.7 ——27.5 Mauna Loa, resulting in lower overall magma 200 0.2 1.3 0.5 10.5 0.3 — 12.8 supply. Because Kilauea only entered its main- 100 0.1 0.8 0.3 7.3 2.3 0.1 10.8 0 0.0 0.3 0.1 4.8 8.4 0.9 14.5 tholeiite stage at ca. 100 ka or more recently, Total 6.0 64.0 26.0 22.0 83.0 11.0 1.0 212.9 magma volumes were lower for the preceding Note: Bold indicates best constrained age intervals; italics indicate volumes during peak of sustained-tholeiite few hundred thousand years as tholeiite erup- stage; dashes indicate time interval before volcano inception. Based on small Mahukona (Garcia et al., 2012). Shading indicates duration of sustained-tholeiite stage. tions diminished at Kohala, Hualalai, Mauna Kea, and Mauna Loa. In comparison to the near-constant propagation plot (Table 10A; Fig. 14A), the age-volume distribution of magma supply shifts to a slightly in this model is dominated by Mauna Loa input, the Hawaii construct thus broadly mirror, on earlier peak time for near-constant volcano a result probably inconsistent with available different scales, the growth histories of the indi- life spans (Table 10B), because these mod- ages as discussed earlier. Although the differ- vidual component volcanoes (Figs. 3A, 9–10, els lengthen eruptive duration and lower peak ences among the plots are relatively modest, 12–13), and defi ne an intense pulse of magma magma supply for volcanoes with small total they incorporate substantially different growth supply that has diminished during the last few volume. In contrast, models of higher tholeiite models for some volcanoes. For example, the hundred thousand years. production and variable lifespan (Table 10C) inception age for Mauna Kea varies from 1100 The growth models for individual volcanoes shift peak magma supply to younger times, to 750 ka, and duration of its main-tholeiite can be adjusted to varying degrees without vio- because the reduced life spans require younger stage 650–300 k.y.; for Mauna Loa, 950–550 ka, lating available age data and uncertainties in inception ages and reduced durations of the and 850–450 k.y., respectively (Table 3). These volume estimates, and multiple iterations were main-tholeiite stage. The high volume at 400 ka time-volume plots for composite assembly of explored. However, no seemingly reasonable

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A HAWAII ISLAND, ALL VOLCANOES: ALTERNATIVE GROWTH MODELS

NEAR--CONSTANT PROPAGATION

NEAR-CONSTANT LIFESPAN

VARIABLE HI-THOLEIITE LIFESPAN /100 ka 3 km 3 VOLUME, 10 0 102030405060 1400 1200 1000 800 600 400 200 0 AGE, ka

B Cumulave volcano volume (near-constant propagaon)

200 Loihi

Kilauea

Mauna Loa 150 Mauna Kea 3 Hualalai km 3

100 Kohala

Mahukona Volume, 10

0 1600 1400 1200 1000 800 600 400 200 0 Years, ka

Figure 14 (on this and following page). Volcano-growth models, at 100 k.y. intervals, for composite assembly of the Island of Hawaii. Volume versus age data are from Table 10. (A) Time-volume plot, illustrating three alternative growth models (near-constant propagation, near-constant lifespan, high peak-tholeiite).(B) Time-volume plot (near-constant propagation), illustrating cumulative contributions of each volcano.

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C 40 GROWTH OF HAWAII ISLAND

Near-constant volcano propagation; Total island volume, 213 km3; average eruption rate, ~0.14 3 30 km /yr

[Lighter shades of colors: transitional & alkalic lavas]

/100 ka 3 Mauna Loa

Mauna Kea

Loihi

VOLUME, kmVOLUME,

Hualalai 10 Kilauea

Kohala

Mahukona 0 1,500 1,000 500 0 AGE, ka

Figure 14 (continued). (C) Time-volume plot (near-constant propagation), illustrating contributions of each volcano.

models produced substantial changes to the Loa were drastically in error. No obvious alter- In this seemingly extreme model (not illus- growth geometries plotted in Figure 14, and natives seem adequate. Even if Mauna Loa trated separately), the main-tholeiite stage dur- some adjustments lead to improbable models. were much younger than the models preferred ing sustained growth of Mauna Loa would have For example, models that raise peak-tholeiite here or previously proposed (800–900 ka; Lip- been atypically brief (400–450 k.y.) compared magma supply for smaller-volume vol canoes, man, 1995; DePaolo et al., 2001), with incep- to that documented for Kohala, and the island- closer to the current 0.1 km3/yr rate for tion as recent as 550 ka and thereby requiring wide magma supply would still have peaked Kilauea and that modeled for large volcanoes very high tholeiite-stage magma supply (up to at ca. 400 ka with a rate more than double that like Kohala, reduce the time span for this stage 0.5 km3/yr; Table 8C; Fig. 12C), the island-wide since 200 ka. and yield a narrow steep growth curve, rather magma-supply rate (at 300–500 ka) would still Magma-supply and eruption rates change by than a broad plateau of sustained growth (e.g., be about triple that since 200 ka (Table 10C; an order of magnitude or more at some individ- Mauna Kea, Fig. 10C; Mauna Loa, Fig. 12C). Fig. 14A). An even more speculative alterna- ual volcanoes and between adjacent ones dur- Such abbreviated intervals of peak growth tive might be the previously noted possibility ing the tholeiite stage, despite relatively uniform would likely require a hotspot magma source that Ka Lae Ridge could be the distal south rift major-element melt compositions. These ranges of much smaller magma-capture diameter of Hualalai (Holcomb et al., 2000), thereby suggest near-constant proportions of melt- than the 100–150 km inferred for the Hawai- permitting eruptive decline at Mauna Loa to ing but large changes in source volume. Such ian Ridge, based on duration of activity at have begun as recently as 100 ka, rather than source variations are likely recorded by more individual volcanoes and distribution of con- decreasing in growth at ca. 400 ka as implied subtle trace-element and isotopic variations dur- currently active ones (Ribe and Christensen, by age determinations at Ka Lae (Jicha et al., ing tholeiitic growth (Frey and Rhodes, 1993; 1999; Quane et al., 2000; DePaolo et al., 2012). This interpretation, although seemingly Rhodes and Hart, 1995; Pietruszka and Garcia, 2001). A small hotspot locus would also make inconsistent with gravity expression for the rift 1999; Marske et al., 2007; Weis et al., 2011). the sustained compositional contrast between zones of these volcanoes (Kauahikaua et al., the Kea and Loa trends (Weis et al., 2011) 2000), could lower peak magma production DISCUSSION even more difﬁ cult to interpret, as well as the and broaden the time span for growth at Mauna cause for eruptive loci along separate trends Loa, especially if combined with a young Major results from this summary include rec- rather than a single one centralized over the inception age as in Figure 12C. Such a model ognition that no one-size-ﬁ ts-all growth model propagation axis. would also reduce the total volume of Mauna accounts for the diverse age, volume, compo- Evidence for decline in the overall magma Loa and greatly augment that of Hualalai, how- sition, and magma-supply variations among supply during the last few hundred thousand ever, precluding large increase in total magma Hawaiian volcanoes. Volumes of the older vol- years seems robust unless the models for Mauna supply for the island in the interval 400–100 ka. canoes that have nearly completed their growth

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TABLE 11. MODELED VOLCANO-INCEPTION AGES, PROPAGATION RATES, AND DURATIONS OF MAIN-THOLEIITE STAGE, KEA AND LOA TRENDS Distance between Cumulative Propagation rate, from Volcano-to-volcano Duration of the main volcanoes* distance† Inception age§ Kilauea propagation rate tholeiite stage# Volcano (km) (km) (ka) (calculated, cm/yr) (calculated, cm/yr) (calculated, k.y.) A. Calculated inception and main-tholeiite ages, based on Kilauea to Kohala propagation rates (8.6 cm/yr) Loihi –45 –248 8.6 — 45 8.6 Kilauea 0 275 — — 23 8.6 Mauna Loa 23 542 8.6 442 25 8.6 Mauna Kea 48 833 8.6 403 12 8.6 Hualalai 60 973 8.6 703 28 8.6 Kohala 88 1300 8.6 800 24 8.7 Mahukona 112 1577 8.6 977 60 8.6 Haleakala 172 2275 8.6 1125 6 8.6 Kahoolawe 178 2345 8.6 1095 B. Calculated propagation rates: distance from Kilauea, and volcano to volcano Loihi –45 125 30.0 — 45 30.0 Kilauea 0 275 — — 23 8.7 Mauna Loa 23 540 8.7 440 25 8.8 Mauna Kea 48 825 8.7 395 12 8.0 Hualalai 60 975 8.6 705 28 8.6 Kohala 88 1300 8.6 800 24 8.0 Mahukona 112 1600 8.5 1000 60 10.0 Haleakala 172 2200 8.9 1050 6 12.0 Kahoolawe 178 2250 10.4 1000 C. Kea trend only, ﬁ xed Kilauea-Kohala propagation (8.6 cm/yr) Kilauea 45 275 >100 48 8.7 Mauna Kea 93 850 8.7 345 40 8.4 Kohala 133 1300 8.6 850 84 8.8 Haleakala 217 2250 8.7 1100

Mean: Kilauea to Haleakala 8.67 8.66 D. Loa trend only, inception of Loihi Seamount, at 125 ka Loihi 0 125 10.5 — 68 Mauna Loa 68 775 10.5 11.4 675 37 Hualalai 105 1100 10.8 10.4 830 52 Mahukona 157 1600 10.6 10.2 1000 66 Kahoolawe 223 2250 10.5 900

Mean: Loihi to Kahoolawe 10.6 10.6 Note: Loa-trend volcanoes in blue. Best-constrained ages in bold. Anomalous values in italics. Dashes indicate sustained-tholeiite stages at Kilauea and Loihi that continue long into the future. *Projected along trend N 35° W. †For A. and B., distances are from Kilauea; for C. and D., distances are from Loihi. §A. Calculated, assuming constant propagation, extrapolated from early-akalic ages for Kilauea and Kohala (in bold). B. and D. Estimated inception ages, ﬁ xed rather than calculated. #Calculated: inception ages, minus duration of early-alkalic stage, minus inception date for late-alkalic stage.

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(Table 2) vary by up to an order of magnitude duration of growth stages, and propagation over yields an impossible future inception age for (if Mahukona is a separate edifi ce), volcano a fi xed hotspot, thus are diffi cult to reconcile in Loihi Seamount (-248 ka; Table 11A) and an spacing along the Kea and Loa trends by a detail with even the limited age and volume data implausibly young age for Mauna Loa (540 ka; factor of two (Tables 11C and 11D), and peak now available. The constant propagation rate Table 11B), younger than some isotopic ages magma supply probably by a factor of fi ve or and growth-stage duration model for Hawaii on main-stage tholeiite from the distal Ka Lae more during the tholeiite stage that accounts for by Moore and Clague (1992) required propaga- Ridge (Jicha et al., 2012). At the best estimate of the bulk of each volcano. The growth models tion at 13 cm/yr (Fig. 3C) that is much faster inception age for Loihi (ca. 125 ka), the propa- also show that the evolutionary stages during than present-day or longer-duration Pacifi c plate gation rate from Kilauea would be an improb- volcano growth are more varied than previ- motion (7–9 cm/yr), inception ages for Kohala ably rapid 30 cm/yr (Table 11B). If Loihi were ously discussed, demonstrate inconsistencies and Mauna Loa that are younger than can be older than 125 ka (e.g., 330–400 ka, as inferred with prior geodynamic models, indicate that reconciled with recent 40Ar/39Ar dates, and dura- by Garcia et al. [2006]), the divergence between composite volcanic growth at Hawaii peaked tion of the main-tholeiite stage of only 500 k.y. trends would be even greater. ca. 800–400 ka, and suggest that current island that would require magma supply at the larger Alternatively, a separate distance-inception growth is at reduced rates. volcanoes to be much higher than at present- age plot for Loa-trend volcanoes, both projected Variable durations of growth stages are well day Kilauea (fi ve times as high for Mauna Loa; from Loihi inception at 125 ka and for individ- documented for the waning-alkalic stage on Table 8C). Geometric models for the varied size ual volcano pairs, yields more rapid propagation the older volcanoes: commonly a few hundred and duration of Hawaiian volcanoes in relation rates of 10.5–10.7 cm/yr (Table 11D; Fig. 15B). thousand years, but ranging from >950 k.y. to location along the trace of the hotspot by This rate produces offsets to earlier inception at Haleakala to absent at Lanai (Moore and DePaolo and Stolper (1996) led to inference of ages for the younger Loa-trend volcanoes, rela- Clague, 1992; Sherrod et al., 2007). Much vari- a 600 ka inception age for Kilauea, more than tive to distance along the Kea trend, that reduce ability also seems likely for the earlier growth twice that implied by recent isotopic ages (Cal- or eliminate inconsistencies in age-distance plots stages, for which age data are sparse. The wax- vert and Lanphere, 2006). Their steady-state for these two volcano groups (Fig. 15B). Most ing-alkalic stage is ~50% longer at Kilauea than geometric model, which related volcano life- importantly, the model inception age for Mauna at Loihi. Modeling suggests that durations of span and size to varied distance from the axis of Loa becomes geologically more plausible (ca. tholeiitic activity were briefer at smaller-volume hotspot progression, also lacks an explanation 800 ka). Such an average Loa-trend rate (~10.6 volcanoes like Mauna Kea than at larger ones for alternation of large and small volcanoes cm/yr) would converge with the Kea trend on such as Kohala (Table 3). As a result, the shifts on both the Kea and Loa trends. The uniform Maui Nui, yielding near-concurrent distances between growth stages correlate inconsistently growth curves (Fig. 3B) modeled by Holcomb and ages for Haleakala and Kahoolawe. with propagation and inception rates estimated et al. (2000) are incompatible with the order- A semi-constant Loa-trend propagation rate from volcano spacing and plate motion. For of-magnitude variation in volume among the (10.6 cm/yr) yields an inception age of 2250 ka example, the tholeiite–late alkalic transition was island’s volcanoes (Table 2). (Table 11) and a sustained-tholeiite stage of nearly concurrent at ca. 330–350 ka for Kohala No single propagation rate works for the ~900 k.y. for Kahoolawe, consistent with the and Mauna Kea, 40 km distant. For Mauna Kea combined volcanoes of the two trends, either. slightly younger age (by only 50 k.y.) esti- and Hualalai, the decline in morphologic shield The best-constrained rate for any of the Kea mated independently for Haleakala, based on growth (shoreline subsidence) was nearly con- or Loa volcanoes is 8.6 cm/yr (Table 11; Fig. the lower propagation rate for the Kea trend. current at ca. 130 ka, while their tholeiite stages 15), calculated from time-distance relations for These inception ages for volcanoes on Maui ended asynchronously at ca. 330 and ca. 120 ka, the waxing-alkalic and volcano-inception ages Nui may be somewhat old, generating dura- respectively. at Kilauea and Kohala (Calvert and Lanphere, tions of 900–1000 k.y. for their main-tholeiite Interpretations that have modeled growth at 2006; Lipman and Calvert, 2011). In contrast, stage (Table 11, models C–D), and suggesting near-constant values for total volcano lifespan, a propagation rate of 8.6 cm/yr from Kilauea that propagation rates across the Maui Channel

Figure 15 (on following page). Modeled volcano propagation rates and inception ages, illustrating divergence between younger volcanoes of the Kea and Loa trends, Hawaii Island and Maui Nui. (A) Modeled volcano-inception ages versus distance from Kilauea (Kea and Loa trends plotted together; data from Table 11B), illustrating divergence of Loihi from the best-ﬁ t trend anchored by dated rocks from Kilauea and Kohala. The propagation rate of 8.6 cm/yr for the Kea trend is calculated from the time-distance relation for the dated volcano inception and the early-alkalic transition at Kilauea and Kohala (Tables 11A and 11C). For the Loa trend to converge with the better-constrained Kea trend, anchored by Kilauea inception at 275 ka, Loihi activity should not begin until ~250 k.y. in the future, and inception of Mauna Loa at ca. 540 ka would be younger than some dated tholeiite pillow lavas from Ka Lae Ridge (Jicha et al., 2012). Alternatively, an estimated 125 ka inception age for Loihi would require an implausibly rapid propagation rate (~30 cm/yr) from Kilauea (Table 11B). Alternatively, if volcano inception is plotted separately along the Kea and Loa trends, the plots are linear but divergent (shown in B). (B) Modeled volcano- inception ages versus distance from Loihi (Kea and Loa trends plotted separately; data from Table 11C–D), illustrating divergence between younger volcanoes of the Kea and Loa trends, Hawaii and Maui Nui. The best-ﬁ t rate of 10.6 cm/yr for the Loa trend is based on an estimated 125 ka inception age for Loihi, projected to converge with near-concurrent distances and ages for Haleakala and Kahoolawe on Maui Nui (Table 11D). If Loihi commenced earlier (e.g., 330–400 ka, as proposed by Garcia et al. [2006]), the propagation from Kilauea would be negative (Loihi older than Kilauea), and the divergence between the two trends would become even greater. Major results from plotting the Loa trend separately are the more consistent propagation rate, both progressing from Loihi inception at 125 ka and for individual volcano pairs, and the offset to an older inception age for Mauna Loa (ca. 800 ka) that is more geologically reasonable. Abbreviations: H—Hualalai; HA—Haleakala; KI—Kilauea; KO—Kohala; L—Loihi; MK—Mauna Kea; ML—Mauna Loa.

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0 A KL Kea and Loa Trends Combined LO

500 ML MK

1000 HU KO

1500 8.6 cm/yrM

2000 Modeled volcano incepon age, ka HA

K 2500 200 150 100 50 0 –50 Distance from Kilauea, km

0 B KL LO 500 Kea Trend

Loa Trend MK 10.6 cm/yr ML 1000 KO 8.6 cm/yr HU

1500

Modeled volcano incepon age, ka 2000 HA Modeled propagation: separate Kea and Loa trends, distance from Loihi K 2500 250 200 150 100 50 0 Distance from Loihi, km

Figure 15.

Geosphere, October 2013 1375

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may have been more rapid, perhaps ~11 cm/yr longer-term growth of the Hawaiian chain as Garcia, Jack Lockwood, Jim Moore, Bill Normark, for both trends. The combined average Kea and discrete islands rather than a continuous ridge, Tom Sisson, Don Swanson, and Bob Tilling. Much appreciated are thoughtful comments on an early draft Loa propagation rates agree reasonably with may record strongly pulsed magma fl ow in the by Bob Tilling, Jim Moore, Tom Sisson, and Brian a prior estimate of 9 cm/yr by DePaolo and hotspot/plume source, similar to that recorded Jicha, and helpful reviews for the journal by Dennis Stolper (1996), but are lower than the 13 cm/yr in tomographic images of the mantle beneath Geist and Dave Clague. suggested by Moore and Clague (1992). How- Yellow stone (Schmandt et al., 2012). For the ever, such comparisons are based on limited growth of Hawaii, the magma pulse took ~500– APPENDIX A. GEOCHRONOLOGY data: ages and volumes are less known for the 600 k.y. to reach maximum supply, then was sus- older Loa-tend volcanoes, and interpretation of tained for ~400 k.y. before diminishing steeply. Geochronology of Hawaiian lavas is extremely dif- the Kohala terrace (Mahukona) is especially Peak growth of Hawaii Island between ca. 400 fi cult due to modest K contents, diffi cult rock textures, problematic . and 800 ka was probably preceded by another and tropical weathering. Early results were often plagued by excess argon (implausibly old ages), nega- Inception ages and sites for new volcanoes period of high magma supply at ca. 1.5–2.0 Ma tive or zero ages, and results that violated superposi- along the Hawaiian Ridge, rather than follow- during composite growth of Maui Nui. Such tion. Recent studies using careful sample selection, ing any simple geometric propagation, are episodic magma fl ux and island growth along preparation, and analytical techniques have obtained likely nonlinear in detail, jumping ahead of the the Hawaiian chain thus may constitute an intra- promising results. 40Ar/39Ar results from relatively high-K, crystalline-lava groundmass concentrates plate-motion progression or lagging behind in oceanic analog to the intermittent recurrence of separated from submarine and borehole samples are response to availability of favorable structures in ignimbrite super-eruptions and attendant caldera reproducible, satisfy stratigraphic constraints, and the oceanic lithosphere or in adjacent volcanoes. formation along the Snake River–Yellowstone appear reliable. Unspiked K-Ar samples using novel Perhaps volcano inception can be triggered by hotspot track (Pierce and Morgan, 2009). methods yield promising results, though occasion- 40 39 controls other than just location relative to the The conclusions presented here are largely ally in confl ict with Ar/ Ar results. Tholeiitic lavas continue to yield little useable data, due to low potas- melting zone. Some volcanoes could be con- based on sparse results from rocks that are chal- sium (K2O generally <0.4 wt%) and diffi cult textures, ceived in the headwalls of slumps or slides on lenging to date, while volume estimates remain although Jicha et al. (2012) managed to produce 14 older volcanoes; Kilauea and Loihi both could poorly constrained because of limited control reasonable ages from 41 candidate tholeiitic lavas. All have started this way. Complexities of the geo- on dimensions of volcano onlap, the component known published 40Ar/39Ar and unspiked K-Ar results for the Island of Hawaii are compiled in Table A1, metric models explored here may be indicating of intrusive and cumulate bodies at depth below along with representative radiogenic argon yields and that other factors are involved in inception and the associated volcano construct, and even bulk-rock potassium contents. growth of Hawaiian volcanoes. Although exist- uncertainty about the existence of Mahukona Armed with this improved chronologic framework ing age data are inadequate to evaluate such volcano. Inconsistent relations between loca- and understanding of rock samples and analytical alternatives, they demonstrate that volcano tion and inception age among the youngest vol- techniques necessary for reliable ages, we recommend inception cannot be rigorously modeled based canoes on Hawaii (Loihi, Kilauea, Mauna Loa), several directions for future research: leading to interpreted offset between the Kea (1) Loihi samples dated by Guillou et al. (1997a) solely on motion of the Pacifi c plate. In addition, should be analyzed using 40Ar/39Ar incremental-heat- absolute southwestward motion of the hotspot at and Loa trends, suggest that comparable com- ing techniques, such as employed in laboratories at the 4–5.5 cm/yr seems required by the divergence plexities probably characterize the older edifi ces Berkeley Geochronology Center, University of Wis- of direction and velocity for volcano propaga- for which early growth is even less constrained. consin, Oregon State University, and U.S. Geological Survey. This sample suite contains 0.6–1 wt% K O tion along the Kea and Loa trends on Hawaii Particularly needed are additional ages from 2 and yielded reproducible but stratigraphically incon- (N35°W, 8.6–10.6 cm/yr) from the longer-term early-alkalic basalts on other volcanoes, per- sistent ages. 40Ar/39Ar techniques may solve those trend of the Hawaiian chain (N65°W, 9.6 cm/yr; haps from submarine samples low along land- issues. Clague and Dalrymple, 1987) and from pres- slide scarps or distal rift zones, and controls on (2) Mauna Loa’s Ninole Hills have produced com- ent GPS-measured motion of the Pacifi c plate rate of main-stage tholeiite lava accumulation plicated K-Ar (Lipman et al., 1990) and 40Ar/39Ar (N65°W, ~7 cm/yr; http://sideshow.jpl.nasa sampled from drill holes or submarine scarps. results (Jicha et al., 2012) that suggest eruption at 100–200 ka. Further careful sample collection and .gov/post/series.html). This hotspot motion Much more could be learned from such addi- analysis may yield more reliable results for these thus would be about three-quarters as large as tional sampling, along with efforts to improve Mauna Loa units. the plate motion, contributing signifi cantly to capacity to determine reliable isotopic ages for (3) Subaerial transitional and alkalic rocks from the geometry of volcano propagation. Recent low-K basalt (discussed further in Appendix A). Kohala (Pololu and Hawi Volcanics) should be ana- southwestward motion of the Hawaiian hotspot, lyzed using 40Ar/39Ar techniques. also inferred from trends of isotopic and seismic Finally, we encourage full disclosure of future Hawaii geochronologic work to help understand limi- ACKNOWLEDGMENTS data (DePaolo et al., 2001; Wright and Klein, tations of the techniques. It is tempting to publish only 2006), could account for the change in trend of data that yield positive or stratigraphically consistent the Hawaiian Ridge at Maui Nui. This overview, initiated as an invited keynote talk ages; however, Hawaiian rocks are unusually diffi cult The variable growth histories of individual at the 2012 American Geophysical Union Chapman to date and eventual success will require a collective Conference on Hawaiian Volcanoes, has roots in effort. While discussing problematic samples often volcanoes, divergent propagation rates along decades of interactions with colleagues too numer- complicates and lengthens manuscripts, authors and the Kea and Loa trends, discontinuous magma ous to acknowledge, but especially including Dave editors are encouraged to present all data, not only fl ux during assembly of Hawaii Island, and Clague, Michelle Coombs, Don DePaolo, Mike those that yield satisfactory results.

1376 Geosphere, October 2013

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Unspiked K/Ar — — — Rejected by authors, no data reported 2 S S S S S S S S S S S S S S S S S S S Ar AND SOME RECENT K/Ar AGE DETERMINATIONS USED FOR ESTIMATING VOLCANO GROWTH RATES, ISLAND OF HAWAII AND UNDERWATER SLOPES AND UNDERWATER ISLAND OF HAWAII VOLCANO GROWTH RATES, USED FOR ESTIMATING Ar AND SOME RECENT K/Ar AGE DETERMINATIONS 39 Ar/ 40 o a a a a a a a a a a a a a a a a a a a a a a a a n l l e e e e e e e e e e e e e e e e e e e e e e i i i i i a a a u u u u u u u u u u u u u u u u u u u u u u c h h h h h h h l i i i i i a a a a a a a a a a a a a a a a a a a a a a l l l l l l l l l l l l l l l l l l l l l l i i i i i i i i i i i i i i i i o o i i i i i i o o o o o o Kilauea K K K K K K K K K K K K K K K K K L K V L L L K K K K K K L APPENDIX TABLE A1. ALL PUBLISHED APPENDIX TABLE r e b 1 m 7 4 1 2 9 6 5 u 3 4 3 9 0 5 5 B N 2 9 5 6 1 7 4 B A 4 A B B C A 0 A ------e 7 4 4 5 2 1 2 4 2 6 2 1 2 4 1 1 2 4 l 1 1 1 1 1 1 1 ------1 5 6 6 2 - - - - - p - - 8 7 4 8 8 8 9 9 5 5 5 4 8 8 0 5 7 - - - - - H H H H H H H 0 0 0 0 0 0 0 0 0 1 1 0 0 1 0 0 0 6 7 8 8 m 6 O O O 2 2 5 5 O 2 O 2 2 5 5 5 O 2 2 2 5 5 a O 7 5 8 8 5 5 8 S S 7 samples not reported S S KK ank –2372 144 25 ank –2883 65 28 S S ank –3954 234 9 S S K ank –2472 138 30 1 K ank –2539 159 19 K ank –2080 166 26 SS ank ank –4132 –4013 280 248 20 150 R174-8.3 Kea Mauna (subaerial fl HSDP-1 S ank –4599 192 111 S 1 ank –1475 201 7 Unspiked K/Ar 0.677, 0.686% 0.7 0.89 mean of two splits, rejected by authors Weighted 5 1 K K ank –2935 67 29 K F288HW-D18-R3 Mahukona Submarine Mahukona –1425 306 26 S S 1 R177-6.0 Kea Mauna (subaerial fl HSDP-1 159-6 Mahukona Submarine Mahukona –1685 480 74 S R164-1.6-plag Mauna Kea HSDP-1 (subaerial fl S ank –4122 212 38 S F288HW-D18-R7F288HW-D18-R9F288HW-D18-R11MVD6-R2MVD6-R6 Mahukona160-5 Mahukona Mahukona Mahukona Mahukona Submarine Mahukona Mahukona Submarine Mahukona Submarine Mahukona –1425 –1425 280 –1425 Submarine Mahukona 312 36 237 Submarine Mahukona 30 32 –2990 Submarine Mahukona –2990 285 329 42 –1200 38 350 33 161-2R158-0.1 Kea Mauna Mahukona (subaerial fl HSDP-1 Submarine Mahukona –1970 654 72 R164-1.6 Kea Mauna (subaerial fl HSDP-1 1

Geosphere, October 2013 1377

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Guillou et al. (1997), 6. Clague and Calvert (2009), 7. Garcia et al. (2012), 8. Sharp d Calvert (2011), 5. Guillou et al. (1997), 6. Clague and (2009), 7. Garcia r r r r r r r r r r r r r r r r r r r r r r r r r r r r r A A Ar Ar Ar Ar ArAr n.a. n.a. n.a. — n.a. 0.27 mean of composite isochron ages Weighted mean of isochron ages Weighted 9 9, 14 A A A A A A A A A A A A A A A A A A A A A A A A A A A Ar — — — Rejected by authors, no data reported 10 r r r r 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 A A A A / / / / K K K K 6), 14. Rhodes and Vollinger (2004), 15. M.J. Rhodes, 2013, written commun. *Glass composition. 6), 14. Rhodes and Vollinger Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ Ar/ 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 3 5 0 4 4 8 2 3 1 7 1 1 ±2s 2 1 4 2 (ka) Technique %radiogenic 7 8 2 4 2 8 2 0 5 1 2 7 Age 2 1 3 1 3 3 (ka) 0 8 0 7 2 5 1 9 0 7 6 7 (m) 1 – – – – Elevation ) ) ) ) w w w w o o o o ow) –946 ow) 550 320 –1010 1080 1040 ow) –513 500 320 ow) –984 370 180 ow) –797 ow) 760 ow) 280 –995 –995 391 385 80 112 ow) –984.2 364 93 ow) –277 236 16 ow) –416 326 46 ow) –748 550 280 ow) –720 790 360 ow) –1052 780 220 ow) –935 400 52 t t n l l o a a i t s s a a a c B B o e e L l l o o n n i i N N Ar AND SOME RECENT K/Ar AGE DETERMINATIONS USED FOR ESTIMATING VOLCANO GROWTH RATES, ISLAND OF HAWAII AND UNDERWATER SLOPES ( AND UNDERWATER ISLAND OF HAWAII VOLCANO GROWTH RATES, USED FOR ESTIMATING Ar AND SOME RECENT K/Ar AGE DETERMINATIONS 39 Ar/ 40 ow) HSDP-2 (subaerial fl a a o o L L o a a n n n a c u u l a a o V Mauna Loa M M r APPENDIX TABLE A1. ALL PUBLISHED APPENDIX TABLE e b m u References for ages, K2O content: 1. Calvert and Lanphere (2006), 2. Quane et al. (2000), 3. Hanyu (2010), 4. Lipman an N e l 5 7 p 4 7 - - Note: m a W W R243-8.4 Mauna Kea (subaerial fl HSDP-1 R428-2.8R452-5.9 Mauna Kea Mauna Kea (subaerial fl HSDP-1 (subaerial fl HSDP-1 R208-5.0 Mauna Kea (subaerial fl HSDP-1 S R153-3.0 Loa Mauna HSDP-1 –268 132 64 SR0860-8.1SR0907-1.6-plag Kea Mauna Mauna Kea (submarine) HSDP-2 (submarine) HSDP-2 –2614 –2789 560 760 150 380 SR0413-4.0 Kea Mauna (subaerial fl HSDP-2 SR0781-21.2 Mauna Kea (submarine) HSDP-2 –2242 482 67 R340-5.1R371-0.3R446-3.6R446-3.6II Mauna Kea Mauna Kea Mauna Kea Mauna Kea (subaerial fl HSDP-1 (subaerial fl HSDP-1 (subaerial fl HSDP-1 (subaerial fl HSDP-1 SR781-21.2 Kea Mauna (submarine) HSDP-2 –2242 488 75 M1203 Mauna Loa South Kona landslide –3700 247 56 SR0907-1.6 Kea Mauna (submarine) HSDP-2 –2789 683 82 R315-3.6 Mauna Kea (subaerial fl HSDP-1 R452-5.9 Mauna Kea (subaerial fl HSDP-1 SR413-4.0 Mauna Kea (subaerial fl HSDP-2 SR0132-1.5 Kea (subaerial fl Mauna J2-20-22 Mauna Loa Ka Lae Ridge Submarine –501 59 16 (1996), 9. Sharp and Renne (2005), 10. Jicha et al. (2012), 11. Coombs (2006), 12. Lipman 13. Rhodes (199 R371-0.3 Mauna Kea (subaerial fl HSDP-1 SR0121-1.0 Loa Mauna HSDP-2 –245 122 86 R350-5.0 Mauna Kea HSDP-1 (subaerial fl 184-13J2-20-20 J2-20-17 Mauna Loa Mauna Loa Mauna Loa Submarine Ka Lae Ridge Ka Lae Ridge Submarine Ka Lae Ridge Submarine –550 –600 –668 120 196 273 43 12 55 R340-5.1 Mauna Kea HSDP-1 (subaerial fl R466-5.0 Mauna Kea HSDP-1 (subaerial fl J2-20-14184-8J2-24-01 Mauna Loa Mauna Loa31 samples not reported Mauna Loa Ka Lae Ridge Submarine Submarine Ka Lae Ridge –857 474 –1020 27 461 Ka Lae Ridge Submarine 36 –4537 657 175 R423-7.2 Mauna Kea HSDP-1 (subaerial fl 183-4J2-19-10J2-16-04J2-24-14 Mauna Loa Mauna Loa Mauna Loa Mauna Loa Ka Lae Ridge Submarine Submarine Ka Lae Ridge Ka Lae Ridge Submarine –1753 Ka Lae Ridge Submarine –1075 –2112 463 468 –3963 470 28 38 543 74 150 S S

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APPENDIX B. ESTIMATED VOLUMES OF VOLCANOES

The following tables (Tables B1–B6) summarize geometric assumptions and other approaches used to estimate volumes for the individual volcanoes on the Island of Hawaii. Most revisions involve adjustments for inferred sloping onlap contacts between ediﬁ ces, while constrained by the estimated overall island volume of 213 × 103 km3 (Robinson and Eakins, 2006). Uncertainties vary among volcanoes, but likely are about ±10% for most. Uncertainties are probably largest for the older volcanoes of the Loa trend.

APPENDIX TABLE B1. KILAUEA VOLUME ESTIMATES A. Total volume of dikes along rifts (model as rectangular prism) Length, E rift: 50 on land, 65 submarine: total 115 km Length, SW rift: 35 on land, 10 submarine: total 45 km Total rift length: 160 km Dike height: max 6 km (Cayol et al., 2000), tapers to 0 at distal edge of rift km3 A1. Maximum horizontal intrusion width, S of summit: 5 km* (10 km total spreading, 50% intrusion: Lipman et al., 2006) 1600 10 km (10 km total spreading, 100% intrusion) 3200 20 km (20 km total spreading, 100% intrusion) 6400 40 km (40 cm/yr, 100% intrusion: Cayol et al., 2000) 12,800

*Preferred model: geometrically similar to Koolau (Walker, 1987) A2. Maximum horizontal intrusion width, S of summit, taper 50% vertically 5 km (10 km total spreading, 50% intrusion: Lipman et al., 2006) 800 10 km (10 km total spreading, 100% intrusion) 1600 20 km (20 km total spreading, 100% intrusion) 3200 40 km (40 cm/yr, all intrusion: Cayol et al., 2000) 6400 B. Summit intrusions (deep feeders, magma reservoir, and cumulate) Assume cylinder: R=5 km, H=9 km, V=710 km3 710

Inferred total intrusion: 2310 (~20% total volcano volume: 11,100 km3) C. Deep-intrusion volume (within underlying Mauna Loa) Summit (50% within Mauna Loa) 355 Rift zones (33% in Mauna Loa: most of SW rift, minor E rift) 533

Inferred total deep intrusion: 888 D. Estimated total volume of Kilauea: Ediﬁ ce (from Lipman et al., 2006): 10,200 km3 Deep-intrusion volume: 888 km3 TOTAL: 11,100 Note: Alternative estimates: Kilauea intrusion volumes during tholeiite stage (100 ky)

APPENDIX TABLE B2. KOHALA VOLUME ESTIMATES PREFERRED MODEL: Kohala entirely on ocean ﬂ oor; adjacent to small Mahukona (Garcia et al., 2012)

Triaxial ellipsoid: = (h*l*w)*4π/3, or h*l*w*4.187; half segment for rift model Elevation at summit Elevation at toe Base, below summit Summit height Length Center half width Volume (km) (km) (km) (h) (km) (l) (km) (w) (km) (km3) Southeast Rift 1.8 –5 –11 12.8 135 25 45,220 Northwest rift 1.8 –4 –11 12.8 55 25 18,423

TOTAL: 63,642

ALTERNATE MODEL: Kohala onlaps larger eastern Mahukona (Clague and Moore, 1991)

Triaxial ellipsoid: = (h*l*w)*4π/3, or h*l*w*4.187; half segment for rift model Elevation Elevation Base, Summit height Length Central half width Volume [All km] at summit at toe below summit (h) (l) (w) (km3) Southeast Rift 1.8 –5 –11 12.8 135 25 45,220 Northwest rift 1.8 –4 –11 12.8 55 25 18,423 Correction for onlap NW ﬂank of larger Mahukona (Clague and Moore, 1991): (6,000) TOTAL: 57,642 Note: Model long SE rift and shorter NW rift as half of triaxial-ellipsoid. Infer both Pololu and Laupahoehoe slumps are Kohala tholeiite; MK lavas deposited later at paleoshore.

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APPENDIX TABLE B3. MAUNA KEA VOLUME ESTIMATES PREFERRED MODEL: Kohala entirely on ocean ﬂ oor; adjacent to small Mahukona (Garcia et al., 2012) Triaxial ellipsoid: = (h*l*w)*4π/3, or h*l*w*4.187 Elevation at summit Elevation at SW base Elevation at NE base Average summit height Center half length Center half width Volume (km) (ML-Hual) (km) (Kohala) (km) (h) (km) (l) (km) (w) (km) (km3) 4.2 –9 –1 9.2 45 25 21,668 TOTAL: 21,668

Alternative volume estimate: 103 Km3 Prior volume estimate (Robinson and Eakins, 2006): 41.9

Additional calculated volume of Kohala, with Hilo Ridge (Table A2): =64-36.4 27.6 Additional volume of Kohala, from smaller Mahukona (Garcia et al., 2012): =13.5-6 7.5 Additional volume of Kohala, from smaller Mauna Kea: 20.1

Resulting net volume of Mauna Kea: = 41.9 – 20.1 TOTAL: 21.8 Note: Model as triaxial-ellipsoid, with, SE-sloping axial plane (against ﬂ ank of Kohala), approximated by averaged summit elevation. Infer both Pololu and Laupahoehoe slumps are Kohala tholeiite; MK lavas deposited later at paleoshore.

APPENDIX TABLE B4. LOIHI VOLUME ESTIMATE Ellipsoid segment: = (h*l*w)*4*π/3, or h*l*w*4.187; quarter segment for rift model Elevation at summit Elevation at toe Base, below summit Summit height Length Center half width Volume (km) (km) (km) (h) (km) (l) (km) (w) (km) (km3) South Rift –1 –4.5 –3 2 22 10 461 North rift –1 –2 –3 2 14 10 293

Burial/compaction* South rift (10%) 46 North rift (25%) 73 TOTAL: 873

Deep dike intrusions (within underlying fl ank of Mauna Loa): Estimated additional ~15%, as for Kilauea 131 TOTAL: 1004 Note: Model long S rift and shorter N rift as quarter-ellipsoid segments. (Ocean-floor subsidence considered minor, because of volcano youth and distal location.) *Loihi built on Punaluu slump (relatively dense substrate: dive S507); assume burial decreases down slope. Longitudinal profile of Loihi: shield shape, with avg. 10° dip on south rift crest; ~5° on north rift. Estimated growth to sea level: 250 ky, Moore and Clague (1992); 50 ky, DePaolo and Stolpber (1996); 200 ky (Clague and Sherrod (in press).

APPENDX TABLE B5. MAUNA LOA VOLUME ESTIMATES GEOMETRIC MODEL: Oblate spheroid: = (h*l*w)*4π/3, or h*l*w*4.187 Elevation at summit Depth to ocean ﬂ oor Average summit height Center half length Center half width Volume (km) (km) (h) (km) (l) (km) (w) (km) (km3) 4 –12 16 50 50 83,740

TOTAL: 83,740

ALTERNATIVE VOLUME ESTIMATE: 103 Km3 Prior volume estimate (Robinson and Eakins, 2006): 74.0 Additional volume, from smaller Kilauea Lipman et al., 2006; Table A1): = 31.6-11.1 20.5 Reduced volume, from larger Hualalai (Robinson and Eakins, 2006; Table A6): = 26.0-14.2 11.8

Resulting net volume of Mauna Loa: TOTAL: 82.7 Note: Highly simplified model as obllate spheroid, with growth from deeply subsided ocean floor. Infer Mauna Loa interfingers with concurrently growing Hualalai and Mauna Kea.

APPENDIX TABLE B6. HUALALAI VOLUME ESTIMATES GEOMETRIC MODEL: Triaxial ellipsoid: = (h*l*w)*4π/3, or h*l*w*4.187 Elevation at summit Depth to ocean ﬂ oor Average summit height Center half length Center half width Volume (km) (km) (h) (km) (l) (km) (w) (km) (km3) 2 –9 11 45 25 25,907

TOTAL: 25,907

ALTERNATIVE VOLUME ESTIMATE: 103 Km3 Prior volume estimate (Robinson and Eakins, 2006): 14.2 Estimated increase, hidden by onlap of Mauna Loa ﬂows (Table B5): = +11.8 11.8

Resulting net volume of Hualalai: TOTAL: 26.0 Note: Highly simplifi ed model as triaxial-ellipsoid, with growth from deeply subsided ocean fl oor. Infer Hualalai interfi ngers with concurrently growing Mauna Kea and Mauna Loa, complicated by (1) onlap by young Mauna Loa fl ows,(2) uncertain distal extent of south rift, and (3) uncertain distal extent of Kiholo rift. As result, volume highly uncertain.

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