IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_1D-O1

Room B1

Date/Time: July 24 8:45-9:00

Radiometric constraints on timescales of degassing and crystallization for lavas fromarcs, ridges, rifts, and ocean islandsMark K Reagan
University of Iowa, Iowa CIty, IA 52242, USA
E-mail: mark-reagan@uiowa.edu

The relative activities of short-lived radionuclides (e.g. 210Pb T1/2 =22.6 y and 210Po T1/2 = 138 d) in lavas
are revealing contrasts in late-stage magmatic processes for different tectonic settings. Most basalts erupted fromocean islands and continental rifts have (210Pb/226Ra) < 1. Although 210Pb deficits in some of these lavas havebeen attributed to magma genesis or differentiation, most are caused by degassing of 222Rn in a CO2-dominatedvapor phase as magmas decompress over periods of years to decades (e.g. Turner et al., 2012, G-cubed). Some
small volume trachytes and phonolites can have (210Pb/226Ra) >1 as a result of removal of 226Ra during rapid
fractionation of amphibole and K-feldspar (e.g. Reagan et al., 2008, GCA). Lavas ejected from a large and growing
phonolite magma body at Erebus have 210Pb-226Ra equilibrium (Sims et al., 2013, J.Pet). Although arc lavas
can have significant excesses or deficits of 210Pb, they more commonly have (210Pb/226Ra) within 10 percent ofequilibrium. These near equilibrium values illustrate that water-rich arc magmas tend to degas for short periodsof time, causing crystallization, higher viscosities, and magma stagnation. Excesses of 210Pb in arc magmas arecommonly associated with magma intersection, and likely result from 222Rn transfer in a vapor phase from larger
volumes of intruding magmas into smaller volumes of previously stagnated magmas, a process that can lead totheir defrosting. Deficits of 210Pb in some arc magmas show that these magmas did not stagnate either due tolatent heat inhibiting crystallization or to a more CO2-enriched volatile content. The lavas erupted in 2004-2008
from Mount St. Helens had progressively greater 210Pb deficits with time, illustrating that the entire magma body
lost what little gas it had for the entire eruption. Mid-ocean ridge basalts have 210Pb deficits and excesses likearc lavas. Small 210Pb deficits have been attributed to melting and rapid melt migration to the surface (Rubin etal. 2005, Nature). However, the 210Pb excesses found in some MORB illustrate that gas loss and accumulation
also play a role in their genesis (Waters et al., submitted, EPSL). Most subaerially erupted lavas from all settings
degas more than 90 percent of their 210Po before eruption, providing a way to detect juvenile versus older ejecta.
Exceptions to this rule include rare lavas erupted from Mount St. Helens between 2004 and 2008 that ceased
open-system degassing weeks to months before eruption due to their extreme viscosity and low overall volatile
contents.

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IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_1D-O2

Room B1

Date/Time: July 24 9:00-9:15

Are high magma supply mid-ocean ridge magma chambers open or closed-system?
Ken H Rubin1 , Chris J Russo1 , Mike R Perfit2 , John M Sinton1
1

Dept. of Geology and Geophysics, Univ. of Hawaii, Honolulu, HI 96822, USA, 2 Department of
Geological Sciences, Univ. of Florida, Gainesville Fl 32611, USA
E-mail: krubin@hawaii.edu

Mid ocean ridge (MOR) volcanism at high magma supply is often thought of as a near steady-state process, withfrequent magma supply from below and relatively frequent eruptions. Repeat eruptions at several MOR sites overthe past several decades allow one to probe this assumption using radioactive disequilibrium between 210Pb and226Ra, which is governed by a 22 year half-life. There are multiple possible causes of 210Pb-226Ra radioactive
disequilibria in magmas, but in magnesian (>7 wt o/o MgO) tholeiites, this is thought to be produced primarily bymantle melting, followed by decay during melt transport and pre-eruptive storage. Petrological, geochemical andU-series data on four mapped eruption sequences at two sites on the East Pacific Rise (at 9.8 deg N in 1991-92 and2005-06, and at 17.5 deg S in ca 1990 and ca 1980) demonstrate that successive eruptions separated by 10-20
yrs were fed by the same mantle-derived magma batches that had resided in the crust and lost 210Pb-226Ra
radioactive disequilibria by decay, under nominally closed-system conditions. All of the erupted magmas were >7
wt o/o MgO and only sparsely plagioclase phyric. At both sites, crustal magma residence timescales must bevery short for the component of the melt that caries live Pb-Ra disequilibrium to be preserved in erupted magmas.
On the N-EPR, the two eruptions produced lava flows with only small amounts of compositional variability, but
the magmas of the later eruptions were more differentiated (by ca 1wt o/o MgO). On the S-EPR, two eruptions ofchemically heterogeneous magmas have variable but indistinguishable ranges of 210Pb-226Ra, MgO, Pb isotopic
characteristics, and other geochemical tracers, indicating that they both probably represent mixes of the same two
distinct magma batches in the crust. Several things are learned from this study: (a) Erupted magmas resided
in the crust for no more than several decades, but longer than the 1-2 decade repose interval at both sites; (b)Erupted magmas are mixtures of melts that act as closed-systems during the repose period, only one of whichneeds to carry Pb-Ra disequilibrium (the other could be in secular equilibrium); (c) not every MOR eruption at highmagma supply ridges requires new magma input from the mantle; (d) mush zone interactions did not induce 210Pb
excesses, and (e) crustal melts can differentiate along a range of P-T paths over these short time intervals. Magmachamber thermal modeling indicates that to continually supply heat to observed high temperature hydrothermal
systems, magma chambers need to be replenished on decadal timescales if hydrothermal systems are driven byheat from only the small shallow melt lenses detected seismically at ridges. Resupply of magma to these lenses
from deeper melt segregations or a crystal mush zone during the repose interval can supply the heat and still allow
for the apparent U-series closed-system behavior if the same mantle-derived magma batches are involved.

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157

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_1D-O3

Room B1

Date/Time: July 24 9:15-9:30

Li-Pb and U-Th-Ra isotope systematics in metasomatised harzburgite xenoliths from
Batan Island, Philippines
Simon Turner1 , Janne Blitchert-Toft2 , Raul Brens1 , Xiaoming Liu3 , Roberta Rudnick3 , Tracy Rushmer11Macquarie University, Australia, 2 Ecole Normale Superieure de Lyon, France, 3 University of Maryland,USAE-mail: simon.turner@mq.edu.au

Subduction delivers sediment and hydrated oceanic lithosphere into the convecting mantle. Some of thesematerials are involved in magma generation and returned to the surface as arc volcanism.

The remainder

continues into the deeper mantle contributing to long-term heterogeneity that may be later sampled by mantle
plumes. In order to understand the global cycling of volatiles in subduction zones it is essential to understand thephysical and chemical processes of fluid release and melting. Significant debate remains on the role of aqueous
fluids versus wet melts and the release of fluids and melting are both strongly dependent on slab temperatures.
Metasomatised xenoliths from Batan Island, Philippines, represent unique samples of the sub-arc mantle. They
have incompatible trace element and radiogenic isotope characteristics typical of their host lavas and arc lavasin general. Li concentrations in the xenoliths and host lavas range from 1.2 to 8.2 ppm whilst Li isotopes show
a significant range from -1.3 to 2.2 and correlate positively with Sr isotopes. Pb isotopes range from 18.37 to
18.50, from 15.60 to 15.72 and from 38.48 to 38.75. These data cannot be explained by addition of a single
subduction component to the mantle wedge but arguably require both fluid and sediment addition. The xenoliths
also, remarkably, preserve extreme U-Th-Ra disequilibria. These disequilibria do not result from either infiltrationby the host magma, steady-state diffusion in the mantle or subsequent crustal level processes. Rather, thexenoliths provide the first direct evidence that such signatures originate in the mantle and that contributions fromboth wet sediment melts and aqueous fluids were separately delivered from the slab. The data also require thatmetasomatism was ongoing at the time of their incorporation in the host magmas.

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158

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_1D-O4

Room B1

Date/Time: July 24 9:30-9:45

On the timescales of magma accumulation and evolution at Tambora (Sumbawa,
Indonesia) prior to the 1815 eruption
Ralf Gertisser1 , Stephen Self2 , Heather Handley3 , Louise Thomas2 , Peter van Calsteren2 , John Wolff4
1School of Physical and Geographical Sciences, Keele University, Keele, ST5 5BG, UK, 2 Department ofEarth and Environmental Sciences, The Open University, Milton Keynes, MK7 6AA, UK, 3 GEMOC,
Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia,
4
School of Earth and Environmental Sciences, Washington State University, Pullman, WA 99164-2812,
USA
E-mail: r.gertisser@keele.ac.uk

The great Tambora eruption in 1815 has been one of the largest explosive eruptions in historic time. It produced
extensive pyroclastic fall and density current deposits from the evacuation of a 30-33 km3 trachyandesite totephriphonolite magma body [1, 2]. Geochemical modelling suggests that the parental trachybasalt of the evolved
1815 magma may be produced by 2% partial melting of a garnet-free, I-MORB-like mantle source contaminatedwith 3% fluids from altered oceanic crust and < 1% subducted sediment, preserving the small 238 U excesses
observed in the 1815 Tambora rocks.

Magmatic differentiation from primary trachybasalt to trachyandesite

and tephriphonolite occurred during two-stage, polybaric differentiation at depth(s) around the Moho and in ashallow-level crustal magma reservoir emplaced at a maximum depth of 7.5 km, but with a degassed cap possibly
extending to depths as shallow as 2.3 km below the summit. This crustal reservoir grew by influx of basaltic
trachyandesite magma, which is interpreted to have formed predominantly by partial crystallisation of primarytrachybasalt in the inferred deep reservoir or hot zone [3]. Subsequent magmatic differentiation dominated byfractional crystallisation, magma recharge/mixing and convection over timescales of 4000-4500 years led to thetrachyandesitic (and ultimately tephriphonolitic to phonolitic) melts that erupted in 1815. Highly calcic, in somecases corroded, plagioclase and other mineral phases in 226 Ra-230 Th equilibrium (> 8000 years old) provide
physical evidence for incorporation of antecrystic material into the 1815 magma. Magma accumulation anddifferentiation at shallow depth prior to the eruption were accompanied by continuous degassing of sulphur andother volatile species, which appear not to have accumulated within or towards the top of the magma reservoir tocontribute to the volatile budget of the eruption, but to have escaped to the surface passively through permeable
wall rocks.

References: [1] Self et al. (2004). Geophys. Res. Lett., 31, doi:10.1029/2004GL020925; [2] Gertisser etal. (2012). J. Petrol., 53, 271-297; [3] Annen et al. (2006). J. Petrol., 47, 505-539.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

159

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_1D-O5

Room B1

Date/Time: July 24 9:45-10:00

Evolution of magma plumbing system of the Iwate Volcano, Northeast Japan,
constrained by chronological relationship of the bulk chemical and isotopic composition
Jun’ichi ITOH, Isoji MIYAGI, Nguyen HOANG
Geological Survey of Japan, AIST, Japan
E-mail: itoh-j@aist.go.jp

Iwate Volcano is one of the active volcanoes in the NE Japan Arc Quaternary volcanic front. The volcanic activity
started about 300 ka, however, most active only since the last 120 ka. Topographically, the volcano is divided into
two bodies: Higashi-Iwate (HI) forming a stratocone and Nishi-Iwate (NI) having a 2.5 by 1.5 km caldera. Eruption
activities of the Iwate Volcano are divided into 4 stages for NI and 3 stages for HI. The chronological relationshipof these stages is interfingered. Eruptive rocks of Iwate volcano are composed mainly of low-K tholeiitic basalt toandesite. Calc-alkaline andesite to dacite are rare component.
Low-K tholeiite from the two volcanic bodies (NI and HI) are interpreted to be derived from different sources and/or
different magma chambers based on the major and trace element compositions. In the case of NI, interaction ofprimitive magma with heterogeneous crustal assimilant (assimilation and fractional crystallization: AFC) in crustal
magma chambers would explain the chemical and Sr-Nd-O isotopic compositions. Whereas, chemical variationsof the HI volcanic rocks are controlled mainly by fractional crystallization (FC).
AFC process gradually progressed in the NI magma chamber, and the injection of the newly arrived primitive
magma renewed the chamber. Drastic change of chemical and isotopic compositions are observed before andafter the caldera forming stage. The fact that the most geochemically enriched volcanic rocks erupted only before
the caldera forming, while the volcanics produced after the depression were isotopically depleted. We suggest thecaldera formation may relate to activities of shallower crustal magma chamber where crustal material may be moreenriched than those deeper, formed after the collapse.
Bulk chemical compositions of HI eruptive rocks show two chemical trends; High-Si and Low-Si type. High-Si typeshows significantly increase in SiO2 (51 to 55) with the increase in FeO/MgO ratios (1 to 2). SiO2 contents of the
Low-Si range between 51 and 53. Comparison of the bulk chemical trend between the two chemical types and
MELTS (Ghiorso and Sack, 1995) model variation trend suggest that the High-Si type is formed at lower pressures(ca. 0.5-1 kb) than the Low-Si type (ca. 3-7 kb). The temporal chemical variation of the Low-Si type rocks shows
MgO decrease with eruptive sequence. This compositional cycle lasted about 3-4 thousand years. Whereas theHigh-Si type volcanics occurred in the later stages of the composition cycle. We proposed that the magma plumbing
system in the HI main magma chamber was stored at 3-7kb condition and FC process controlled the change oferuptive products. The injection of more primitive magma into main magma chamber renewed the chemical cycle of
HI volcanics. In contrast, the High-Si magma was operated by FC process in shallow magma pocket where magma
being stored at lower pressures (0.5-1 kb).

©IAVCEI 2013 Scientific Assembly. All rights reserved.

160

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_1D-O6

Room B1

Date/Time: July 24 10:00-10:15

The post-Minoan plumbing system behaviour at Santorini Volcanic field: implications forthe current unrest phase
Chiara Maria Petrone1 , Lorella Francalanci2 , Georges E. Vougioukalakis3
1

Natural History Museum, Department of Earth Sciences, Cromwell Road, SW7 5BD London, United
Kingdom, 2 Dipartimento Scienze Terra, Università di Firenze, Via La Pira 4, 50121 Firenze, Italy,
3
I.G.M.E., 3rd Entrance Olympic Village, Athens, Greece
E-mail: C.Petrone@nhm.ac.uk

Explosive volcanic eruptions are often triggered by replenishment of the magma chamber by new magma. In thecase of the historical eruptions at Santorini extremely short residence time has been recently estimated for the
intrusion of basaltic andesitic magma in the dacitic reservoir. Understanding the occurrence of replenishment andthe dynamics of magma mixing is thus crucial to a correct evaluation of the risk of explosive volcanoes.
The post-caldera islets of Palea- and Nea-Kameni formed as result of nine eruptive events from A.D. 46-47 till 1950
in the center of the Santorini Minoan caldera. These nine eruptive events lead to the emplacement of dacitic lava
flows and domes also characterised by the presence of basalts to andesites mafic magmatic enclaves.
Dacitic rocks have low porphyritic index that increases with time. Plagioclase is the prevalent mineral phase,
followed by clinopyroxene, orthopyroxene and opaque minerals. Few resorbed xenocrysts of olivine with coronaeof pyroxene are also present. Basalts to andesites mafic enclaves have variable texture spanning from cumulate toaphyric. Porphyritic enclaves with olivine in groundmass are also found. Mafic enclaves have ellipsoidal or cuspateshape, with some chilled margins clearly suggesting their molten state at time of incorporation in the host magmas.
Host lavas show a general decrease of the evolution degree with time, at the same time enstatite contentsof pyroxenes and anorthite contents of plagioclase decrease from mafic enclaves to host lavas. Sr isotopes
systematically increase with time and thus toward the less evolved compositions of lavas and mafic enclaves.
The latter, along with mineral separates, generally show slightly more enriched radiogenic compositions in respectwith host lavas, with the exception of 46-47 A.D. eruptive events.
All data point to mixing/mingling between mafic and dacitic magmas and enclave crumbling processes. The
increases in Sr isotope ratios with time and toward more mafic magmas suggest crustal contamination of mafic
magmas. Our data suggest the existence of a shallow layered reservoir with dacitic magmas overlaying lower mafic
magmas. Cumulitic processes, crystal fractionation eventually accompanied by variable degree of assimilationof crustal country rocks, also characterised the lower part of the plumbing system allowing further layering andevolutionary processes of the mafic magmas which, in turn, generate the complex and variable textures shownby mafic enclaves. Type, composition and distribution of mafic enclaves change in different eruptions suggestingthat different part of the layered reservoir where frequently and variably sampled during time. This clearly points
to periodic arrival of more mafic magmas during the post-Minoan activity of Santorini suggesting a still very active
magma source in agreement with data available for the current unrest phase at Santorini Volcanic field.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

161

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_1D-O7

Room B1

Date/Time: July 24 10:15-10:30

Processes leading up to the 22 ka silicic caldera-forming eruption of Santorini (Greece):
Constraints from crystal trace-element fingerprinting and diffusion chronometry
Gareth N Fabbro1 , Timothy H Druitt1 , Fidel Costa2
1

Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, BP 10448, France,
2
Earth Observatory of Singapore, Nanyang Technological University, Singapore
E-mail: g.fabbro@opgc.univ-bpclermont.fr

Caldera-forming eruptions are amongst the most destructive phenomena on this planet.

Constraining theprocesses that occur before these eruptions, as well as the timescales of those processes, is vital for forecasting
the behaviour of the volcanoes responsible for them. The 21.7±0.2 ka caldera-forming Cape Riva eruption of
Santorini Volcano discharged at least ∼10 km3 of dacitic magma (along with a minor basalt-dacite hybrid andesitic
component), and caused caldera-collapse. The eruption was preceded by a ∼13 ky period of dacitic effusive andminor explosive volcanism. This effusive activity constructed the 1-2 km3 , <200-m-thick Therasia dome complex,
centred on the site of the subsequent Cape Riva caldera. The major element geochemistry of the Therasia dacite
is very similar to that of the Cape Riva dacite, but its lower incompatible element concentrations (e.g. K, Zr, Rb, La,
Ce and Nb) demonstrate that it is a different magma batch. This difference is also apparent in the concentrationsof La and Ce in plagioclase crystals from the two magmas. La and Ce diffuse very slowly through plagioclase(<100 µm in 107 y at 900°C), and therefore reflect the concentration of those elements in the parent magma on
the timescale of our system (<105 y). The contrasting trace element compositions of the whole rocks and crystals
seem to rule out a simple interpretation that the Therasia dacites were leaks from the growing Cape Riva magma
chamber. Modelling of diffusion gradients of relatively fast-diffusing elements such as Mg and Sr in plagioclase
crystals provides estimates of the residence times of those crystals at magmatic temperatures. Preliminary results
also show that plagioclase crystals in the Therasia dacites have maximum residence times of the order of 102 -103
years. This is short compared to the total 13 ky duration of effusive volcanism, suggesting that the Therasia lavas
may represent the repeated ascent, partial crystallisation and eruption of multiple, small parcels of dacitic magma
over a long period of time. Field and 40 Ar/39 Ar constraints tie down the arrival of the Cape Riva dacite batch inthe shallow plumbing system less than 4000 y prior to the Cape Riva eruption. Preliminary diffusion chronometry
results for Cape Riva crystals suggest residence times for some plagioclase crystals as short as 10-102 years. This
supports the idea that major influx of new, silicic magma occurred shortly before the eruption, and possibly provides
more a precise constraint on the timing of this influx.

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162

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A2_1D-O8

Room B1

Date/Time: July 24 10:45-11:00

Exsolution lamellae in volcanic pyroxenes as an indicator of cooling times and sizes ofmagma reservoirs
Fidel Costa1 , Jason S Herrin2
1

Earth Observatory of Singapore, Nanyang Technological University, Singapore, 2 Facility for Analysis,
Characterisation, Testing, and Simulation, Nanyang Technological University, Singapore
E-mail: fcosta@ntu.edu.sg

Magma residence times below active volcanoes are crucial for understanding the processes of magma evolution
and for proper assessment of volcano related hazards. Major progress has been made in the last decades by
a combined approach of modeling zoning patterns of crystals, bulk-rock and single mineral analyses of U-Th
disequilibria isotope series, and in-situ determination of crystallization ages of zircon. Here we explore anotherapproach that can potentially lead to new insights into the, sizes, residence times and internal processes of magma
bodies that is based on the existence of solvus relations in several mineral groups. Clino- and orthopyroxenes forexample may start crystallizing at high magmatic temperature, and new compositions will grow with decreasing thetemperature. But once the system intercepts the solvus, early-formed pyroxenes will tend reequilibrate throughformation of exsolution lamellae.

The size, spacing, and composition of the lamellae depend on the initial

temperature, cooling rate, and bulk composition. This means that the characteristics of exsolution lamellae arepotentially a record of the cooling history which can be related to the size, growth styles (single batch vs. pulses),and cooling rates of the magma. This type of information has been exploited in several studies of plutonic bodies.
However, exsolution lamellae have been rarely documented in volcanic pyroxenes (except for plutonic xenocrysts),
probably because of faster cooling rates and shorter magma residence times. Using a new Field Emission Gun
Electron Microprobe (EM), and electron backscattered diffraction we have found micro to submicron exsolution
lamellae subparallel to the [001] plane (e.g., high-T exsolution) on clinopyroxene from dacites and andesites fromvolcanoes in Chile and Indonesia. The size of the lamellae is too small to fully characterize with the EM so we haveused the Focused Ion Beam technique to extract cross-sectional slices of lamellae in clinopyroxenes perpendicular
to the 001 plane. We obtained element maps and traverses using energy dispersive spectrometry and electronenergy loss spectroscopy with an Analytical Transmission Electron Microscope. We found that the width of thelamellae vary from about 50 nm to a few hundred nm, and thus near the resolution of backscattered electron maps
produced by the EM. Using experimentally calibrated growth rates of exsolution lamellae in clinopyroxene, andsimplified cooling models of magma reservoirs of various sizes, we find that the observed lamellae require timescales of formation of a few thousand years from a reservoir of a few to tens of km3 . Given the small sizes ofthe lamellae that we observed, it seems likely that they have been overlooked in other volcanic systems, but the
information they could provide is difficult to obtain by other approaches and should lead to better understanding of
the growth rates and sizes of subvolcanic magma reservoirs.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

163

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A2_1D-O9

Room B1

Date/Time: July 24 11:00-11:15

How do quartz watches compare?: glass inclusion faceting versus Ti diffusion profiles
Ayla S Pamukcu1 , Guilherme AR Gualda1 , Florence Begue2 , Darren M Gravley2
1

Department of Earth and Environmental Sciences, Vanderbilt University, United States, 2 Geological
Sciences, University of Canterbury, New ZealandE-mail: ayla.s.pamukcu@vanderbilt.edu

Constraining the timescales over which magma bodies accumulate and erupt is critical to developing methods
to effectively monitor and prepare for future eruptions. There are many methods used to assess timescales(radiometric dating, geospeedometry, textural analysis), but results often conflict, and our ability to directly compare
timescales obtained from different methods is debated. Here we assess the use of glass inclusion facetingas a geospeedometer. Glass inclusions change from rounded to increasingly faceted over time at magmatic
temperatures through dissolution and re–precipitation. Thus, the degree of faceting is a possible measure ofresidence time. Our prior work on faceting revealed residence times that compare well with those suggested
by other methods; however, the results depend on crude estimates of critical parameters such as size, shape,and position of inclusions using optical microscopy. We have started using propagation phase contrast x–ray
tomography, which enhances object edges, to image glass inclusions within quartz crystals. We use image
processing techniques to find a 3D hull that envelopes the inclusion, and we fit an equal volume ellipsoid tothe hull. We compute the volume diffused during faceting as the volume of the ellipsoid that protrudes from theinclusion hull. We also assess size and position of the inclusion within the crystal. This improved characterization
allows a more critical evaluation of the applicability of glass inclusion faceting as a measure of residence time. We
compare results from glass inclusion faceting with those from diffusional relaxation of Ti in quartz. Variations incathodoluminescence (CL) intensity correlate well with variations in Ti contents in quartz, so we use CL profiles
as a proxy for Ti zoning. We employ a 1D diffusion model along selected CL profiles to find the best fit relaxation
length scale, from which we can calculate residence times–taking advantage of experimentally determined diffusion
coefficients for Ti in quartz. We are documenting textures of multiple glass inclusions located in distinct zones withinquartz crystals to directly compare timescales from faceting and diffusional relaxation. We obtain tomograms ofquartz crystals containing inclusions at GSECARS (Advanced Photon Source). We then select grains with multiple
inclusions, particularly those with inclusions near the center (along the c axis) of the crystal, which we polishand image with SEM-based panchromatic CL. We have so far imaged crystals from 5 pumice clasts of different
compositions of the 240 ka Ohakuri–Mamaku ignimbrites (Taupo Volcanic Zone, New Zealand). Results fromthe two methods are comparable, lending support to faceting as a geospeedometer. Both methods suggest thesemagma bodies were short lived, crystallizing over 10s–100s of years prior to eruption, consistent with recent results
obtained for crystallization timescales of other giant magma bodies (e.g. Bishop Tuff).

©IAVCEI 2013 Scientific Assembly. All rights reserved.

164

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A2_1D-O10

Room B1

Date/Time: July 24 11:15-11:30

Tracking pre-eruptive degassing at Laki, Iceland, through diffusion modelling
Margaret E Hartley1 , Dan J Morgan2 , David A Neave1 , John Maclennan1 , Marie Edmonds1 , Thor
Thordarson3
1

University of Cambridge, UK, 2 University of Leeds, UK, 3 University of Iceland, IcelandE-mail: meh43@cam.ac.uk

Information on the timescales of magma ascent, mixing and degassing in volcanic plumbing systems provides
important constraints on the interpretation of seismic, geodetic and gas monitoring data prior to and during large
fissure eruptions. The AD 1783 Laki eruption, southeast Iceland, produced over 15 km3 of basaltic lava and tephra,and led to three years of extreme climatic variability in Europe and North America. We quantify the timescales ofdegassing in the Laki magma system, and determine the potential flux of CO2 to the surface in the premonitory
phases of the Laki eruption.

Olivine-hosted melt inclusions from Laki range from volatile-rich (5000 ppm CO2) to almost completely degassed(<50 ppm CO2). Volatile saturation models suggest that these melt inclusions were trapped at pressures from
<0.1 to >7 kbar, and the melt inclusions preserve a record of concurrent degassing and crystallisation. The total
CO2 mass release from the Laki magma is on the order of 370 Mt. Diffusion modelling techniques applied tocompositional profiles across olivine and plagioclase phenocrysts enable the timescales of magmatic processes in
the run up to the Laki eruption to be constrained.

Olivine crystals from rapidly-cooled tephra samples display up to three distinct compositional zones linked
by diffusion profiles, indicative of crystallisation and storage in different magmatic environments. Preliminarymodelling suggests that the diffusion profiles reflect timescales on the order of 100 days. These residence times
apply to magma storage in a shallow reservoir immediately prior to eruption, thus providing a minimum bound on
the timescale of melt inclusion entrapment.

Plagioclase macrocrysts from Laki often have high-anorthite (An84-89) cores surrounded by oscillatory-zoned(An74-80) mantles.

The high-anorthite core compositions cannot be reproduced by fractional crystallisation

modelling of the Laki carrier melt, and may have grown from depleted melts of the shallow mantle that were mixed
into the Laki carrier liquid during the earliest stages of magmatic evolution. The growth of the zoned plagioclase
mantles thus represents one of the earliest magmatic processes in the history of the Laki magma. Crystallisation ofplagioclase mantles occurred concurrently with the crystallisation of the melt inclusion-bearing olivine macrocrysts.
Diffusion of Mg and Sr between plagioclase cores and mantles is expected to provide information on the timescalesof processes occurring early in Laki’s magmatic history, including the deep degassing of CO2. Suitably-zoned
plagioclase macrocrysts are used to obtain direct estimates for the timescales between crystal growth, melt
inclusion entrapment and eruption. The timescale estimates are linked to the evolution of the Laki magma bodyby integrating the diffusion modelling results with the record of cooling and crystallisation preserved in the melt
inclusion compositions.

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IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4A2_1D-O11

Room B1

Date/Time: July 24 11:30-11:45

Short time scales of pre-eruptive magma mixing processes: petrographic evidence fromthe 2011 eruptions of Shinmoedake volcano, Kirishima volcanic group, southern
Kyushu, Japan
Akihiko Tomiya, Isoji Miyagi, Genji Saito, Nobuo Geshi
Institute of Geology and Geoinformation, AIST, Japan
E-mail: a.tomiya@aist.go.jp

We estimated the time scales of magma mixing processes prior to the 2011 sub-Plinian eruptions of Shinmoedake
volcano, Kirishima volcanic group, southern Kyushu, Japan, to constrain the triggering process of the eruptions, on
the basis of zoning profiles of magnetite phenocrysts and diffusion calculations.
The eruptive products are comprised mainly of phenocryst-rich (28 vol%) gray pumice (SiO2 = 57 wt%) with minor
amount of white pumice (SiO2 = 62 wt%) (Geshi et al., 2011). We found that the gray pumice was formed by mixing
between high-temperature nearly aphyric magma (basalt or basaltic andesite) and low-temperature mushy magma(andesite) (e.g., Saito et al., 2011). The depth of the magma chamber, at which the magma mixing occurred, wasabout 6 to 8 km, deduced from MELTS calculation (Miyagi et al., 2011).
Most of the magnetite phenocrysts (type-A1 ) were originated from the low-temperature magma and their zoning
profiles showed considerable increase in Mg and Al contents toward the rims of the phenocrysts, due to mixing withthe high-temperature mafic magma. We calculated the time for diffusion to form these zoning profiles (i.e., the timefrom the magma mixing to the eruption) to be only about 1-2 days. The short time scale suggests that the mixingof high-temperature magma triggered the sub-Plinian eruptions.
This mixing process was not accompanied by a significant change in the volume of the magma chamber because
no significant crustal deformation was observed several days before the eruptions (Japan Meteorological Agency,2011). We propose magmatic overturn or melt accumulation within the magma chamber as a possible process.
Some magnetite phenocrysts (type-A0 ) showed almost no increase in Mg and Al, indicating that they were notaffected by the magma mixing and were incorporated in the magma during the ascent. The time for diffusion of
type-A0 magnetite was less than 0.4 days. This time scale corresponds to the duration of magma ascent from themagma chamber to the surface. This means that the average ascent velocity was more than 15 to 20 km/day.

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IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4A2_1D-O12

Room B1

Date/Time: July 24 11:45-12:00

On the longevity of large upper crustal silicic magma reservoirs
Sarah E Gelman1 , Francisco J Gutierrez2 , Olivier Bachmann3
1

University of Washington, USA, 2 Universidad de Chile, Chile, 3 ETH Zurich, Switzerland
E-mail: baolivie@ethz.ch

Understanding the timescales and processes involved in the formation and maturation of upper crustal magma
reservoirs, ultimately sourcing the largest volcanic eruptions on Earth, is one of the most fundamental goals of
volcanology. While such reservoirs are known to assemble incrementally over extended periods of time, debate
persists regarding the timescales of melt preservation in the cold upper crust. If rapid cooling individually freezes
incoming replenishing intrusions, accumulations of eruptible magma are impossible, precluding caldera-forming
eruptions for all but the highest magma emplacement rates. Recent numerical thermal models have been used toassess the viability of upper crustal silicic magma survival, and have suggested that supervolcanic reservoirs must
form in geologically short timescales with anomalously high injection rates, and subsist only ephemerally, making
them less predictable. Motivated by geological observations suggesting the contrary, we have improved upon thesemodels by incorporating two fundamental features of natural systems not previously considered: (1) a non-linear
crystallization-temperature relationship adapted for upper crustal silicic magmas and (2) a temperature-dependent
thermal conductivity. We demonstrate that the incorporation of both of these properties can allow an upper
crustal reservoir to remain above its solidus for hundreds of thousands of years, on par with estimates fromzircon crystallization histories, when fed by magma fluxes typical of large magmatic provinces.

While thecrystallization-temperature path plays the most significant role in maintaining a large pool of eruptible magma, theincorporation of temperature-dependent thermal properties, together with a deeper emplacement level, significantly
extends the lifetime of such reservoirs. These results provide strong support for long-lived upper crustal mushes
as a staging ground for accumulation of highly eruptible, crystal-poor silicic magmas, and further assert theevolutionary link between volcanic and plutonic systems©IAVCEI 2013 Scientific Assembly. All rights reserved.

167

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4A2_1D-O13

Room B1

Date/Time: July 24 12:00-12:15

Petrogenetic process controlling explosivity at an intraplate volcano: a case study from
Ulleung Island, Republic of Korea
Marco Brenna1 , Shane J Cronin1 , Ian E M Smith2 , Richard C Price3 , Young Kwan Sohn4
1

Massey University, New Zealand, 2 University of Auckland, New Zealand, 3 University of Waikato, New
Zealand, 4 Gyeongsang National University, Republic of Korea
E-mail: m.brenna@massey.ac.nz

Ulleung Island represents the top of a 3000 m (from sea floor) intraplate alkali volcanic edifice in the East Sea/Sea
of Japan. The emergent section of the volcano consists of a basaltic lava and agglomerate succession intruded
and tilted by a younger trachytic core. Younger eruptions at c. 20 ka and 8-5 ka generated thick tephra sequencesof phonolitic composition and carried to the surface intrusive syenitic accidental clasts. In major element space,
there is a continuous spectrum of compositions from trachyte to phonolite but offset trace element trends exclude a
direct relationship between these two end member compositions. Within the phonolitic tephras two subgroups canalso be distinguished. The early erupted tephras are considerably enriched in incompatible elements and chondrite
normalised rare earth element (REE) patterns display negative Eu anomalies. Later tephras have compositions
intermediate between the early tephras and the trachyte/syenite samples and their REE patterns do not havesignificant Eu anomalies. Petrographic evidence and mineral chemistry suggest a genetic relationship between
the syenitic xenoliths and their host phonolitic pumices. The c. 20 ka eruption was fed by a phonolite magma
enriched in incompatible elements, possibly by fluids from the crystallizing portion of the hosting shallow magma
reservoir; these fluids caused alteration, which gives the lower tephras an orange colour. The subsequent c. 8-5
ka eruption was fed by a new magma batch, which evolved through crystal fractionation but also assimilated partsof the previous reservoir. The phonolite erupted explosively as opposed to the trachytes, which erupted effusively
or formed cryptodomes. The differences in eruption style are mainly due to different degrees of fractionation andenrichment in a shallow magma reservoir.

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IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4A2_1D-O14

Room B1

Date/Time: July 24 12:15-12:30

Shallow crustal magma residence times and storage conditions revealed through in situ
zircon chemistry at the Pastos Grandes Caldera Complex in SW Bolivia
Jason F Kaiser1 , Shanaka de Silva1 , Axel K Schmitt2 , Mayel Sunagua3
1

Oregon State University, USA, 2 University of California Los Angeles, USA, 3 Formerly Servicio
Nacional De Geologia Y Tecnico De Minas Sergeotecmin, Bolivia
E-mail: geojason.kaiser@gmail.com

The Pastos Grandes Caldera Complex in the Central Andes of southwest Bolivia provides the unique opportunity
to study a young volcanic terrain along with its associated plutonic record. Studying both records together can
expound the relationship between volcanic activity and pluton emplacement and evolution. The multicyclic caldera
has erupted over 2500 km 3 of high K dacite and rhyolite ignimbrite from at least two caldera-forming supereruptions
depositing the 5.45 +/- 0.02 Ma Chuhuilla, and the 2.89 +/- 0.01 Ma Pastos Grandes Ignimbrites (PGI). The
much younger Chascon dome (85-94 ka) formed inside the margins of the Pastos Grandes Caldera and contains
granodiorite plutonic xenoliths. Similar xenoliths have also recently been discovered in the intracaldera facies of the
PGI. Together, the ignimbrites, post-collapse lava domes, and xenoliths provide a complete view of the magmatic
cycles associated with a silicic, caldera-forming, eruption.
U-Pb zircon crystallization ages of the ignimbrites, collected via SIMS, reveal the pre-eruption magmatic histories.
Weighted average U-Pb zircon ages from the Chuhuilla and PGI are 6.04 +/- 0.06 Ma (MSWD = 2.53; n = 45)
and 3.36 +/- 0.037 Ma (MSWD = 5.79; n = 64), respectively. From a comparison of the zircon crystallization anderuption ages, minimum residence times of magmas associated with the ignimbrites are 0.59 Ma and 0.47 Ma for
the Chuhuilla and PGI, respectively.
The plutonic xenoliths of the Chascon dome have a weighted average zircon crystallization age of 2.64 +/- 0.906
Ma (MSWD = 4.54; n = 54). Preliminary trace element concentrations, collected from the same spots as the U-Pb
data, provide a chronologic view of magma chemistry and conditions in the ignimbrites and xenoliths. REE patterns
are nearly identical in both the PGI and the xenoliths representing the remnant pluton. Many other elements suchas Th, Hf, and Ti also remain constant with time. The uniform Ti concentrations indicate that temperature andcomposition remained uniform (650-700 C) throughout the span of zircon crystallization during the Pastos Grandes
magma cycle. Collectively, these data connote that the xenoliths represent remnant magma after the PGI andrecord a total magmatic cycle time (minimum) of 1.60 Ma.
Post-collapse lava domes yield zircon crystallization ages in agreement with both the PGI and the plutonic xenoliths,
suggesting that they represent effusive "leaks" from the solidifying post-climactic pluton.
Granodiorite xenoliths present in the intracaldera facies of the PGI likely represent the remnant magma after
eruption of the Chuhuilla Ignimbrite.

These xenoliths are currently under investigation, and can provide an

integrated view into the magmatic evolution of a multi-cycle caldera system.

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IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4P1_1D-O15

Room B1

Date/Time: July 24 15:00-15:15

Volcanic and compositional evolution of Nemrut stratovolcano over ca. 550,000 years as
reflected on land and in tephra layers drilled into adjacent huge Lake Van (Eastern
Anatolia)
Mari Sumita1 , Hans-Ulrich Schmincke1 , PaleoVan scientific team
1

GEOMAR Helmholtz-centre for ocean research Kiel, Germany
E-mail: msumita@geomar.de

We have analyzed the evolution of explosive volcanism (stratigraphy, volcanology, composition) of a large,
previously poorly studied stratovolcano by studying both land deposits and several hundred tephra layers drilled
at Lake Van, the largest saline lake in the world (130 km WSW-ENE extent, max. depth 450 m). One of our aims
is to reconstruct the evolution of one or more theoretical stratovolcano based entirely on the tephra layers drilled in2010 in the ICDP PaleoVan project - pretending the source to be unknown. This model is then compared with thetephra studies of two real volcanoes: Historically active alkalic Nemrut (2,948 m asl), famous for its caldera, rises
west and neighboring calcalkalic larger Suphan (4,058 m asl) north/northeast of Lake Van. This approach should
aid in reconstructing volcano evolution based entirely on drill data. Another goal is to understand the interaction ofclimate - paleoclimate being the rationale of the Paleovan project - volcanism and tectonism, the Van basin being
located in the collision zone between the Arabian and Eurasian plates.
We have recognized ca. 40 variably peralkaline trachytic and rhyolitic fallout tephra units on land, some of large
magnitude (up to ca. 30 km3 DRE), and ca. 12 slightly welded and slightly more mafic ignimbrites. Rhyolitic activity
increased strongly during the past 200 ka, major eruptions occurring in intervals of 20-40,000 years. Axes of major
fallout fans are oriented dominantly west-southwest, the main reason for the dominance of Nemrut-sourced tephrasin the cored section. Basaltic tephras are next to absent.
Results from drilled tephra deposits: (1) Explosive eruptions began ca. 550,000 years ago dominantly from nearby
sources. (2) Calcalkalic dacite-rhyolite tephras are more common among older tephras while the upper ca 100 m ofthe 220 m cored section are almost exclusively peralkaline trachyte and rhyolite. (3) Basaltic tephra is common in
the lower ca. 80 m (older than ca. 400 ka), common sideromelane shards indicating subaqueous eruption. Basaltic
eruptions dominantly occurred at low altitudes possibly also in the early lake stage. (4) Fallout tephras dominate
but ca. 10-12 thicker (up to 6 m) and poorly sorted tephras are interpreted as syn-ignimbrite turbites suggesting
several caldera stages. (5) The overall volcanic evolution began with a dominantly basaltic stage accompaniedby 2 or more explosive volcanoes, beginning with the calcalkalic one. (6) Compositions changed significantly,
the calkalkalic center prevailing early, the alkalic later. (7) At least 2 different centers are involved because oflack of overlap in mineralogy and bulk chemistry (fayalite, hedenbergite, sporadic aenigmatite, anorthoclase in thealkalic volcano and plagioclase, hypersthene, clinopyroxene and olivine all in partial disequilibrium in the calcalkalic
center). (8) The alkalic volcano was either much larger (more active), younger or located more upwind than thecalcalkalic one.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

170

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4P1_1D-O16

Room B1

Date/Time: July 24 15:15-15:30

Understanding regular variability in magma composition and eruption frequency throughhigh-precision, long tephra records
Shane J. Cronin1 , Ian E.M. Smith2 , Mark S. Bebbington1 , Michael B. Turner3 , Gert Lube1
1

Volcanic Risk Solutions, Massey University, New Zealand, 2 School of Environment, Auckland
University, New Zealand, 3 Department of Geology, Macquarie University, Australia
E-mail: s.j.cronin@massey.ac.nz

It has long been recognized that reawakening stratovolcanoes have a semi-regular pattern of activity, with return
periods of large, destructive eruptions at many volcanoes around the world on the order of 200-500 years. This may
be driven by magma-production rates, heat flow or mantle fertility of various volcanic settings, or simply represent
the time taken for the filtering and processing of magma as it makes its way through the crust to eruption. Plaguingthe quest for a deeper understanding of the processes leading to regular large eruptions at stratovolcanoes isthe need for a complete record of volcanic output over time. We attempt to fill this gap by building the highest
possible resolution records of volcanic activity for the longest possible periods at individual volcanoes. We present
here our results from two tephra records containing more than 160 eruption events, one from Mt. Taranaki, New
Zealand that extends for 32 ka and the other from Gunung Merapi, Java, Indonesia that spans 10 ka. Both records
show regular variations in dome-building vs. explosive eruptions, the former represented by fall and surge layers
dominated by dense juvenile lithics and the latter by lapilli-dominated pumice fall and pyroclastic flow deposits.
Both records also show regular cycles in variations of eruption frequency. Glass and titanomagnetite chemistry (viaElectron microprobe) shows regular variations in erupted composition that match with eruption frequency cycles.
Titanomagnetite Ti, Al and Mg contents show strong correlation with eruption style and frequency. Mg and Al
contents of titanomagnetite and glasses of each record indicate cycling between the eruption of mafic and evolved
andesitic magmas. Variability in Ti concentrations primarily reflects late-stage solid-state exolution in magmas
stored in shallow conduits and domes. By contrast, homogenous Ti, Al and Mg contents of titanomagnetites
reflect the initial partial melting, fractional crystallization, assembly and mixing of multiple magma sub-batches at
mid to lower crustal depths before sudden eruption via sub-plinian processes. Contrasting in these two records,
however, is the overall frequency of eruptions and the nature of long-term geochemical changes. The Taranaki
system shows an increasing average Ti content in titanomagnetites, corresponding with higher alkali (especially K)
contents in glasses and whole-lapilli compositions. By contrast, the Merapi system appears relatively more stable
over time. Comparing and contrasting these two long records, along with the assembling of similar detailed eruption
sequences at other stratovolcanoes, can provide improvements to the hazard assessment at such volcanoes
through the more robust informed application of probabilistic methods. This research direction can also provide new
insights into the magmatic and eruptive dynamics of stratovolcanoes, and especially transitions between various
eruption mechanisms and magnitudes.

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171

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4P1_1D-O17

Room B1

Date/Time: July 24 15:30-15:45

Effect of volatiles, crystallization, and lava dome effusion rate on pyroclastic surge
dispersal at Merapi volcano, Java, Indonesia
Kimberly Genareau1 , Shane J. Cronin2 , Gert Lube2
1

Lehigh University, U.S.A., 2 Massey University, New ZealandE-mail: kig210@lehigh.edu

The behavior of volatile elements in an erupting magma will have direct effects on the rheology of effused lavas
and the dynamic properties of pyroclastic density currents resulting from dome collapse and explosive activity.
Pyroclastic density current deposits from the October/November 2010 surge-producing events at Merapi volcano,Java, Indonesia were examined using a combination of scanning electron microscopy (SEM), stereo-scanningelectron microscopy (SSEM), secondary ion mass spectrometry (SIMS), and electron microprobe (EMP) analyses.
Samples from the two climactic and lethal surge events on 26 October and 5 November were examined, in addition
to several intermediate surges, taken from a series of transects between 3 and 8 km from source. Microtextural andgeochemical properties of the tephras reveal variations in volatile behavior that influenced the physical propertiesof the resulting pyroclastic surges. The number density of plagioclase feldspar microlites is ten times higher inthe 5 November event, while the number of pyroxene/Fe-oxide microlites is fifteen times higher compared to the
26 October event. SSEM analyses of the intermediate surges reveal variations in vesicle morphology during thetransition between the two main surge-producing events. EMP analyses indicate synchronous growth of feldspar
microlites and phenocryst rims in both phases of dome effusion. Degassing of the 26 October dome at relatively
greater depths in the plumbing system lead to a significant shift of the feldspar liquidus, resulting in alkali-richcompositions compared to the dominantly plagioclase compositions found in the 5 November lava crystals. Despite
efficient degassing of the earlier dome, enough volatiles remained in the interstitial melt to cause sudden, significant
vesiculation of the residual melt following decompression. In addition, CO2 contents of groundmass glasses in the
26 October dome material is significantly higher (2-3 times) than that of the 5 November lavas. Textures within lapilliof the 5 November surge deposits revealed the development of permeable vesicle pathways, enabling efficientdegassing and decompression-induced crystallization of phenocryst rims and microlite phases in the shallow
conduit in a few days prior to collapse. Trends in volatile elements during the final stage of feldspar phenocryst
growth will be presented. Variations in lava textural and chemical characteristics are a function of lava effusion rateand decompression path between the different effusive stages. The behavior of volatile elements, mainly H2 O, CO2 ,and Li, between the main surge-producing events of 26 October and 5 November, 2010, affected magma rheology
over several days during an increased rate of lava dome effusion, altering the composition of the products, thegeneration of fine ash, and the transport properties (total volume, run-out distance) of resulting pyroclastic density
currents.

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172

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4P1_1D-O18

Room B1

Date/Time: July 24 15:45-16:00

Understanding the volcanic activity at Popocatepetl Volcano, Mexico from 1997 to 2010
Julie Roberge1 , Severine Moune2 , Angel Briseno-Arellano3
1

ESIA-Ticoman, Instituto Politecnico Nacional (IPN), Mexico, 2 Laboratoire Magmas et Volcans,
Universite Blaise Pascal, Clermont Ferrand, France, 3 Facultad de Ingeniera, UNAM, Mexico
E-mail: robergejulie@gmail.com

Popocatepetl volcano located southeast of Mexico City has been the site of open vent degassing since late 1994.
The products of these eruptions show evidence of a mixture of siliceous and mafic magmas shortly before eruption.
We present a qualitative analysis of the activity of Popocatepetl from 1997 to 2010 based on the daily reports from
CENAPRED (National Center for Disaster Prevention). The daily reports are a compilation of the number of gas/gas
and ash emissions and number and intensities of tremors and volcanotectonic earthquakes events. Gas and ash
emissions, tremors and volcanotectonic earthquakes were plotted in number of events against time for each month,year and the total of the years studied. In addition, the earthquakes were further characterized according to theirintensity and location around the volcano. All the combined data display trends showing that the volcanic activity
increases at the end of each year and gradually decreases in March, with even lower activity during the summer.
In January 2010, videos of the degassing activity were taken while measuring SO2 fluxes with a DOAS (Differential
Optical Absorption Spectroscopy). The video clearly shows two types of degassing: 1) diffuse degassing fromthe central vent of the volcano where the lava dome is emplaced, and 2) jet-like degassing from fumaroles at theEastern side of the crater. These fumaroles form a degassing site with very rare lava emission. It was observedthat when the degassing activity intensifies at one site, it decreases at the other. However, preliminary data indicate
similar SO2 fluxes which imply that the source of gas is the same for both types of degassing activities and only theemission site changes.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

173

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4P1_1D-O19

Room B1

Date/Time: July 24 16:00-16:15

Relationships between mafic replenishment and eruption triggering at silicic systems:
Insights from time scales of magma interactions
Caroline Bouvet de Maisonneuve1 , Fidel Costa1 , Christian Huber2
1

Earth Observatory of Singapore, Nanyang Technological University, Singapore, 2 School of Earth andAtmospheric Sciences, Georgia Tech., USA
E-mail: carolinebouvet@ntu.edu.sg

In silicic systems (dacites to rhyolites), evidences of mixing/mingling with a mafic component (basalts tobasaltic-andesites) are frequently observed. The time scales for mixing prior to eruption have been inferredusing the presence of disequilibrium mineral assemblages and applying reaction and diffusion-based models.
Interestingly, these time scales are often on the order of a few hours to months, and the usual interpretation isthat the intrusion of mafic magma triggered the silicic eruption. However, given the complexity of fluid dynamic
interactions between magmas of contrasting physical properties it is unclear whether these time scales accurately
record the arrival of mafic magma in the system, or if there is a delay between replenishment and mixing that is notregistered by the crystals and their reactions.
The efficiency with which two magmas interact and mix depends on several factors, including the mafic injection
rate, the Ra number (i.e. the ability to convect), and the viscosities of both magmas. In the case of large injection
rates, low magma viscosities, and the presence of a large reservoir (i.e. large Ra), silicic and mafic magmas will
mix rapidly. Therefore the time scales recorded by reaction and zoning of mafic minerals will accurately report thetime between mafic injection and eruption. On the other hand, if the injection rates are low and the viscosity of theambient silicic magma is high (i.e. low Ra), the mafic magma can pond at the base of the reservoir rather than mix.
In this case, the zoned mafic minerals record a time scale that can be significantly shorter than that of injection,and thus lead to erroneous interpretation of eruption triggers.
We investigate the likelihood and implications of each scenario by combining theoretical arguments and thermal
modelling with petrological investigations. We consider the case of the Rabaul caldera where above backgroundseismic and deformation signals started in 1971, and peaked between 1983 and 1985, but the onset of eruptive
activity only occurred in 1994.

Evidence for basaltic injection into a dacitic reservoir is preserved in the

1994-to-present eruptive products. A textural maturation from fine, acicular to large, blocky mafic crystal clots
implies different relative ages of formation. Modelling the trace element zoning in plagioclase yields two contrastingtime scales of mixing. One event occurred a couple of decades prior to the 2006 eruption and coincides with thepeak of unrest. The other occurred a few days to weeks prior to the 2006 eruption, which could imply that mafic
injections were the trigger for this eruption. We explore the range of mechanical parameters pertinent to the Rabaulsystem to address whether (i) all the basaltic replenishment occurred in 1983-85 and mixing occurred subsequently
as a number of discrete events, or (ii) multiple replenishment events are required to produce the observed sample
textures and characteristics.

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174

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4P1_1D-O20

Room B1

Date/Time: July 24 16:15-16:30

Late stage assembly of a voluminous ignimbrite from multiple magma batches asrevelaed by in-situ Sr isotopic measurements
Ben S Ellis1 , Darin M Schwartz2 , William M Phillips3 , Dawid Szymanowski1 , Olivier Bachmann11Institute for Geochemistry and Petrology, ETH Zurich, Switzerland, 2 Geological Sciences, University of
Idaho, USA, 3 Idaho Geological Survey, USA
E-mail: ben.ellis@erdw.ethz.ch

The Heise caldera complex of the Yellowstone hotspot track represents a multi-cyclic caldera which was active
between about 6.6 and 4.5 Ma. The youngest explosive eruption of the centre produced the 1,800 km3 , rhyolitic
Kilgore Tuff which is exposed to the north and south of the Snake River Plain. As part of a new mapping initiative andbuilding on previous work in the region we are characterising the mineral componentry of the Kilgore Tuff. Previous
work has shown that Kilgore Tuff represents the largest low-18 O rhyolite known with O isotopes homogeneous inquartz and feldspars yet heterogeneous in zircon. Here we investigate multiple mineral phases to decipher themagmatic processes occurring prior to this catastrophic event. In feldspars we analysed major and trace elements
and 87 Sr/86 Sr ratios via in-situ LA-ICPMS, our results show that multiple populations of plagioclase exist within the
Kilgore Tuff. The main plagioclase population is between 0.7116 and 0.7118, which is more radiogenic than thereported bulk values of 0.7103-0.7107. The variability observed in plagioclase in the Kilgore Tuff is in contrast bothwith the hotter rhyolites of the central Snake River Plain further west, and with the older explosive deposits from theHeise centre. Such compositional variety is surprising given the oxygen isotope evidence for magma homogeneity
prior to eruption and the relatively high magmatic temperatures (estimated between 800-900 o C) which should act
to homogenise isotopic variability. Under such conditions, Sr isotopic homogeneity in plagioclase is likely achievedin 5 mm grains within <10 kyr. The observed Sr isotope heterogeneity in Kilgore Tuff plagioclase may result fromisolation of magma batches until shortly before eruption. Such rapid priming of the magma reservoir is increasingly
being observed and may be a common occurrence in large-volume volcanic systems.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

175

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4P1_1D-O21

Room B1

Date/Time: July 24 16:30-16:45

Deformation of Cordon Caulle Volcano (Chile) measured by InSAR from 2007 to 2011
Jennifer A Jay1 , Matthew E Pritchard1 , Fidel Costa2 , Luis E Lara3
1

Cornell University, USA, 2 Earth Observatory of Singapore, Singapore, 3 SERNAGEOMIN, Chile
E-mail: jaj88@cornell.edu

We combine petrological and ground deformation data to constrain the subsurface magmatic and hydrothermal
processes related to the 2011-2012 rhyodacite eruption of Cordon Caulle volcano in southern Chile.

The

geochemical data indicate that the phenocryst-poor rhyodacite erupted in 2011-2012 is very similar to that of
the 1960 and 1921-1922 eruptions. The calculated pre-eruptive conditions for the 3 erupted magmas are also
indistinguishable: 900 +/- 20 deg C, 4 +/- 0.5 wt percent H2O, and 150 +/- 20 MPa. This implies that either(1) there has been no significant intrusion of magma in about 100 years while still erupting about 2 km3 (DRE)in the 3 eruptive periods, or (2) that all new additions are rhyodacitic melt that are indistinguishable from that in
the shallow reservoir and is probably generated much deeper, in the lower crust. Using InSAR, we have founda complex history of ground deformation preceding the eruption at Cordon Caulle, and the nature of the several
distinct inflation events are informed by this petrological data. This is one of the few large rhyodacite eruptions withdetailed images of ground deformation in the years before the eruption.
InSAR studies show that Cordon Caulle has undergone episodes of deformation since at least 1996 and has varied
between subsidence and uplift in different locations of the volcanic complex. Between 2007 and 2009 we observe
two distinct uplift episodes, both with a maximum uplift signal of 18.5 cm at the center of deformation. We also findan episode of deformation occurring sometime between Feb-Mar 2010 located in the Cordillera Nevada caldera
with 10 cm uplift within the caldera and 10 cm subsidence on the eastern rim of the caldera. This deformation
episode is likely related to the nearby Trahuilco hot springs, which is fed by a shallow steam-heated aquifer and is
the main outflow of the Cordon Caulle geothermal system. We do not observe any deformation from late 2010 toearly 2011, when the ALOS satellite ceased operation. Petrological studies of the clinopyroxene exsolution lamellaein the 2011 eruptive products indicate the existence of a large (10 km3) long-lived (5 ka) shallow magma reservoir.
We hypothesize that the 2007-2009 uplift episodes could have resulted from an injection of magma into the base ofa pre-existing rhyodacite magma reservoir with minimal interaction between the 2 magma sources. Initial modelingof the 2008-2009 deformation pattern using one inflating point source puts the deformation source at about 7 km
depth with a volume change of 0.03 km3. Assuming an appropriate value for magma compressibility, the combinedmodeled reservoir volume change from 2007-2009 could account for the volume of the 2011-2012 DRE erupted
material of 0.8 km3. However, this simple model does not provide an accurate fit to all available ascending anddescending interferograms, suggesting that a more complicated source may be involved, such as a prolate spheroid
or faulting.

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176

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P1

Date/Time: July 24 Poster

Magmatic control on volcanic activity at Volcan de Colima, Mexico
Reubi Olivier1 , Blundy Jon2 , Pickles Joe2 , Varley Nicholas3
1

Institut des sciences de la Terre, Universite de Lausanne, Switzerland, 2 School of Earth Sciences,
University of Bristol, UK, 3 Facultad de Ciencias, Universidad de Colima, Colima, Mexico
E-mail: olivier.reubi@unil.ch

Volcan de Colima historical activity is characterized by periods of intermittent effusive and Vulcanian eruptions
punctuated by major sub-Plinian to Plinian eruptions, the most recent of which occurred in 1913.

The

effusive-Vulcanian phases are dominated by andesitic lavas with 61 wt% SiO2 , when the Plinian eruptions involve
more mafic andesites with 58 wt% SiO2 . The systematic shifts in compositions associated with the Plinan eruptions
indicate a link between the eruptive cycles and the magmatic dynamics.

Detailed petrological and geochemical investigations of the magmas erupted during the effusive and Vulcanianactivity between 1998 and 2010 enable us to constrain the storage conditions and pre-eruptive evolution ofthese magmas. The melt inclusions exhibit compositional trends consistent with up to 40% crystallization undervapour-statured conditions at pressures <1.5 kbar. Decompression induced dehydration is driving crystallisationin the sub-volcanic magmatic systems. Compositional zoning of phenocrysts indicates that, in addition to magma
mingling in the ascending dacite melt of mafic crystals, magma mixing was important in the 1998-2010 magmatic
system but involved predominantly dacitic magmas with limited compositional variability. The range of (210 Pb/226 Ra)
activity ratios and the width of amphibole reaction rims indicate that the feeding magmatic system comprised
several magma batches with residence and degassing times in the vapour-saturated section of the system ranging
from several days to 7 years. No significant differences in petrology, volatile contents, degassing paths and timescales are observed between the Vulcanian and effusive eruptions, implying that these shifts in eruption style are
principally related to conduit dynamics. The most vigorous effusive phases may, nonetheless, be related to influxof undegassed dacitic magmas.

The last major Plinian eruption, in 1913, erupted magmas clearly distinct from those of 1998-2010 in termsof storage conditions and pre-eruptive magmatic evolution. The most distinctive features of the 1913 magmas
are the higher H2 O contents (and storage pressures) of the melt inclusions, the textural and chemical evidences
for magma mixing with mafic melts shown by some phenocrysts, and the more mafic compositions of thegroundmass glasses compared to the melt inclusions. Taken together this indicates that the Vulcanian-effusive
activity characteristic of the 1998-2010 period and the 1913 Plinian eruption represent clearly distinct pre-eruptive
scenarios rather than a continuum. Influx and mixing of mafic magmas in the dacitic subvolcanic reservoir was
important prior to the 1913 eruption and most likely caused the shift in eruptive style. The rates and periodicity ofreplenishment of the subvolcanic system by, respectively, dacitic and mafic magmas appear to be key parameters
controlling the eruptive cycles at Volcan de Colima.

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177

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P2

Date/Time: July 24 Poster

The 1707 AD eruption of Fuji Volcano, Japan: Magmatic Processes and Timescales
Elisabeth Widom, David C Kuentz
Dept. of Geology and Environmental Earth Science, Miami University (Ohio), USA
E-mail: widome@MiamiOH.edu

Fuji Volcano, one of the most hazardous volcanoes in Japan, has erupted primarily basaltic magmas throughout
its history. However, the most recent eruption in 1707 AD produced a chemically zoned deposit with compositions
ranging from basalt to dacite. This eruption was one of the largest (0.7 km3 d.r.e.) and most explosive eruptions
in Fuji’s history, and related tephra deposits a few centimeters in thickness reached as far as Tokyo, approximately
100 km from the vent [1-3]. Prior studies have proposed a variety of processes to explain the chemical variations inthis deposit, including liquid immiscibility [4], magma mixing involving magmas from discrete magma chambers[2], and fractional crystallization with minor crustal assimilation and basaltic magma injection [5]. In order tofurther constrain the timescales of magma evolution leading to the 1707 eruption, we have evaluated a suiteof samples from throughout the 1707 AD deposit for 238U-230Th-226Ra and Ba systematics. Major and traceelement variations, as well as constant Sr, Nd and Pb isotopes throughout the Fuji 1707 AD deposit are consistent
with fractional crystallization of plagioclase, pyroxene, olivine and magnetite, and minor apatite as the dominant
process leading to chemical variations. U-series disequilibria data show that all samples are U-enriched, consistent
with derivation from a mantle wedge that has been fluxed by hydrous slab fluids [6; this study]. Essentially constant
230Th/232Th, but decreasing 238U/232Th with increasing SiO2 and 230Th/238U close to radioactive equilibrium inthe most evolved samples could be explained by assimilation of old, low U/Th crust with a 230Th/232Th ratio similar
to the Fuji basalts. However, Os isotope variations indicate that the most evolved samples have been affectedby less than 0.2 percent crustal assimilation, which should have an insignificant effect on the U-Th disequilibria.
Fractionation of apatite during magma differentiation can alternatively explain the variations in 238U/232Th. The
constant 230Th/232Th requires this fractionation to take place over a timescale of less than 10 ka. However, activity
ratios of 226Ra/230Th greater than 1 in all samples [6; this study] indicate that magma fractionation timescales
may be substantially shorter. Decreasing 226Ra/230Th with increasing SiO2 can be explained by instantaneous orcontinuous fractionation models, and indicate timescales of magma fractionation from parental basalts to dacite on
the order of 103 years. References: [1] Miyaji (1984), Bull. Volcanol. Soc. Japan 29, 17-30. [2] Yoshimoto et al.
(2004), Proc. Japan Acad., Ser. B 80, 103-106. [3] Miyaji et al. (2011), JVGR 207, 113-129. [4] Kawamoto (1992),
Int. Geological Congress Abs. 29, 558. [5] Watanabe et al. (2006), JVGR 206, 1-19. [6] Kurihara et al. (2008),
Radioisotopes 57, 471-483.

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178

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P3

Date/Time: July 24 Poster

Uranium-series timescale constraints on recent changes in the eruptive behaviour of
Merapi Volcano, Java, Indonesia
Heather Handley1 , Ralf Gertisser2 , Mark Reagan3 , Katie Preece4 , Kim Berlo5 , Jenni Barclay4 , Richard
Herd4
1

Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia,
School of Physical and Geographical Sciences, Keele University, Keele, ST5 5BG, UK, 3 Department ofGeoscience, The University of Iowa, Iowa City, IA 52242, USA, 4 School of Environmental Sciences,
University of East Anglia, Norwich, NR4 7TJ, UK, 5 Department of Earth Sciences, University of Oxford,
Oxford, OX1 3AN, UK

2E-mail: heather.handley@mq.edu.au

The 2010 eruption Merapi volcano (Central Java, Indonesia) was the volcano’s largest eruption in 140 years
and was much more violent than expected. Prior to 2010, for example in 2006, volcanic activity at Merapi wascharacterised by several months of slow dome growth punctuated by gravitational dome failures, generatingsmall-volume pyroclastic density currents. We present new uranium-series (U-Th-Ra-Pb) isotope data for the
volcanic products of both the 2006 and 2010 eruptions at Merapi to investigate the driving forces behind the recent
unusual explosive behaviour and their timescales. The 2006 and 2010 volcanic rocks display 238 U excess andsuggest variable enrichment by a U-rich fluid or melt (e.g., subducted slab or crustal assimilant) within the last 380
kyr. The 2010 deposits display a slightly wider range in (238 U/232 Th) (0.671 to 0.723) compared to those of 2006
(0.702 to 0.720). A negative correlation is observed between (226 Ra/230 Th) and Th (as index of differentiation).
Assuming that the degree of disequilibria in the sample with the highest (226 Ra/230 Th) (3.28) represents that at theonset of differentiation, 226 Ra excesses implicate short timescales for magmatic differentiation at Merapi of < 750
years for the 2006 and < 300 years for the 2010 volcanic rocks, noting that apart from one 2006 sample, the volcanic
rocks of both eruptions have similar (226 Ra/230 Th) activity ratios. However, it is unlikely that the U-series data at
Merapi can be interpreted within the context of simple closed-system evolution due to the previous recognition of
open-system processes, such as magma recharge, magma mixing and mingling processes and assimilation ofcrustal carbonates. The 2006 and 2010 volcanic rocks have initial (210 Pb) values of 2.66 to 3.04 dpm/g and 2.22 to
3.08 dpm/g and (210 Pb/226 Ra)0 ratios of 0.81 to 0.95 and 0.72 to 0.96, respectively and may suggest persistent andcomplete 222 Rn degassing over a few years to a decade prior to eruption possibly related to the time for magma
ascent from a deeper crustal reservoir. The 2010 volcanic rocks show the largest 210 Pb deficits suggesting longer
timescales of degassing prior to eruption compared to the 2006 eruption. However, volcanic rocks of both eruptions
display relatively similar range in (210 Pb/226 Ra)0 ratios.

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179

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P4

Date/Time: July 24 Poster

Magma-mixing and -mingling as key magmatic processes controlling the development of
the volcanic events in the Gutâi Neogene Volcanic Zone, Eastern Carpathians, Romania
Marinel Kovacs1 , Alexandrina Fülöp2 , Zoltan Pécskay3 , Maria Jurje4
1

Tech.Univ.Cluj-Napoca, North Univ.Center Baia Mare, Baia Mare, Romania, 2 DeBeers Canada Inc.,
Toronto, Ontario, Canada, 3 Institute of Nuclear Research of the Hungarian Academy of Sciences,
Debrecen, Hungary, 4 Mineralogy Museum of Baia Mare, Baia Mare, Romania
E-mail: marinelkovacs@yahoo.com

The Gutâi Volcanic Zone (GVZ) belongs to the Neogene-Quaternary volcanic chain of the Carpathians developedon the north-western part of the Romanian territory. A calc-alkaline intermediate volcanism represented by a seriesof rocks ranging from basalts to rhyolites (andesites are the prevalent ones) took place during Miocene (13.4-7.0
Ma). The mineralogical, textural and geochemical features of many of the igneous rocks from GVZ suggest thatmagma-mixing and -mingling processes were involved during their genesis (e.g. the large-sized embayed sanidine
crystals coexisting with high Mg# (85-90) chromian-diopside and high amount of gabbroic-type MME in the same
biotite dacite and the large-sized sieve-textured or strong reverse zoned plagioclases together with large-sized
embayed quartz crystals in the same andesite rock). Most of the rock types are dacites and subordinately
andesites mainly related to extrusive domes (13.2-8.0 Ma). In some cases, two different but co-genetic rocktypes appear spatially and temporally associated as a result of magma-mixing and -mingling (e.g. biotite dacite
and biotite andesite). Sometimes, one of the rocks is a hybrid rock such as a MME-hosting dacite and the otherone is compositionally close to the potential basic end-member such as a basaltic andesite with 51.5-54.3 SiO2 .
Some of the magma-mixing and -mingling products show compositions matching with the acidic end-members(e.g. the biotite dacites/rhyolites with glassy, perlitic groundmass texture). The mineralogical and geochemicalsimilarities between the MME of the dacite rocks and some of the basaltic rocks from GVZ suggest the involvementof such basaltic magmas as basic end-members. These features enable the reconstruction of the magmatic
processes developed in the crustal magma chambers or in the volcanic conduit, processes which controlled theemplacement of these rocks. Many volcanic events controlled by repeated magma-mixing and -mingling processes
took place during the volcanic activity of GVZ and conducted to the emplacement of important volcanic structures bytriggering the eruption events timewise in different locations of the area. The different PT parameters of the mineralphases contained in the hybrid rocks, suggest different conditions of evolution of the magma-mixing and -mingling
processes involving different magmatic sources. The small-volume acidic MME-hosting volcanic rocks (e.g. theDănesti dacite/rhyolite -11.6 Ma, Valea Morii dacite -10.1 Ma and Laleaua Albă dacite -8.0 Ma) resulted frommagma-mixing and -mingling processes developed in small-sized, shallow level evolved/silicic reservoirs. Opposite
to these, some hybrid rocks which represent one of the dominant volcanic phases in GVZ (e.g. the large-spreadquartz andesite complexes – 11.3-10.5 Ma) resulted from magma-mixing and -mingling processes developed inlarge-sized differentiated magma chambers with near-continuous replenishment by new basaltic magmas.

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180

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P5

Date/Time: July 24 Poster

Evolution of magma plumbing system of Miyakejima volcano
Masashi Ushioda1 , Eiichi Takahashi1 , Toshihiro Suzuki2 , Morihisa Hamada1
1

Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Japan, 2 IFREE,
JAMSTEC, Japan
E-mail: ushioda.m.ab@m.titech.ac.jp

Miyakejima is an active tholeiitic volcanic island located at about 200 km south of Tokyo in Izu-Mariana arc.
Miyakejima is a typical volcano in immature arc crust. Tsukui et al. (2001) divided the volcanic activity of the last
10,000 years into four stages: 10-7ka (Ofunato Stage), 4-2.5ka (Tsubota Stage), 2.5ka to AD1154 (Oyama Stage)
since AD1469 (Shinmio Stage). According to Niihori et al.(2003), products of the Ofunato Stage were basalts andthey were relatively primitive basalts. On the other hand, products in Tsubota Stage were andesites and thosein the latter two stages were mixed products of basalt and andesite. Precise knowledge of depth, temperature,
water content and fO2 of magma chamber are essentially important in discussing evolution of magma plumbing
system. The purpose of this study is to investigate the evolution of the magma plumbing system in Miyakejima in
the last 10ka based on high-pressure experiments and petrology. We show that a simple system in the Ofunato
Stage developed into a complex one and this accounts for the change in chemical and petrological features in thesubsequent stages of Miyakejima volcano.
To understand the evolution of the magma plumbing system, first we studied the magma chamber in Ofunato Stageby high-pressure experiments. Experiments were performed at 1.0-2.5kbar with various H2O content using IHPVs
at the Magma Factory, Tokyo Tech. Based on the experimental results and petrology of products in Ofunato Stage,
magma chamber in Ofunato Stage was reconstructed. The magma chamber was located at 5-6km depth (about
1.5kbar) and water-rich (about 3wt.%) basalt magma crystallized olivine and calcic plagioclase (which is the typicalphenocryst assemblage throughout Ofunato Stage). Volatile content (H2O, CO2, S and Cl) of melt inclusions wereanalyzed by FTIR and EPMA. Maximum H2O and CO2 content of a melt inclusion in olivine are 3.3wt.% and160wt.ppm, respectively. The gas saturation pressure of magma indicates that the pressure of magma chamber inOfunato Stage should be at least 1.5kbar.
Whole rock compositions in Ofunato and Tsubota stage was analysed by XRF. A series of crystallization trends
were calculated using MELTS program (Ghiorso and Sack, 1995), and it is found that andesites erupted in Tsubota
Stage can be formed by fractional crystallization of OFS basalt at pressure less than 1.5kbar which correspondswith that of shallow level chamber in the two-layered magma chamber after Sinmio stage (e.g. Amma-Miyasaka
and Nakagawa, 2003). Postulated water content in magma (about 0.6 wt.%; water-saturated pressure of basalt forthis water content is less than 1.0kbar), however, is much lower than in Ofunato Stage (about 3 wt.

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181

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P6

Date/Time: July 24 Poster

Magma mixing indicated by heterogeneous structure in the Mikurasawa lava, theTaisetsu volcano, in central Hokkaido, Japan
BABA HIKARU1 , WADA KEIJI1 , SATO EIICHI2
1

Hokkaido University of Education at Asahikawa, Japan, 2 Kobe University, Japan
E-mail: hikaru.baba@gmail.com

The eruption products of the Taisetsu volcano in central Hokkaido show the heterogeneous structures such as
mafic inclusions and banded lavas, caused by magma mixing. The Mikurasawa lava erupted from a vent of outside
the Ohachidaira caldera (about 30 Ka) at a younger stage (<10-20 Ka) of the Taisetsu volcano. This andesitic
host lava has various types of mafic inclusions, and both dacitic and mafic elongated parts make up the banded
structure. These heterogeneous structures in the Mikurasawa lava are the most case of characterizing the Taisetsu
volcano particularly. The key to elucidating magma mixing processes with petrological technique is to understandthe factors of forming heterogeneous structures in the Mikurasawa lava.
The host lava is characterized by coexisting phenocrysts which crystallized from different end-member magmas.
The plagioclase phenocryst is classified into three types by An content of the core. Type-A plagioclase phenocryst(An>82) indicates no zoning in the core, but indicates strong normal zoning in the rim. Type-B plagioclase
phenocryst (58<An<82) indicates heterogeneous zoning in the core; the compositional range is from An=47 toAn=82. The core composition partially overlaps with that of type-C plagioclase phenocryst. Type-C plagioclase
phenocryst (An<58) indicates continuous zoning overall phenocryst; this characters are good agreement withthose of the dacitic part. Type-C phenocryst in the host lava indicates reverse zoning in the rim. The augite andorthopyroxene phenocrysts are classified into two types based on Mg# versus Ti and Al content respectively. Using
two pyroxene thermometer (Wells, 1977), temperatures of felsic and mafic end-member magmas were estimated
900°C and 1000°C.
Mafic inclusions in the host lava are classified into two types by the color of the interstitial glass; clear glass andbrown glass. Each type of mafic inclusions is classified into two sub-types by granularity of groundmass minerals;
fine-type and coarse-type.
Heterogeneous structures at the outcrop, phenocrysts compositional variety in the host lava, and diversity of mafic
inclusions suggest that three mixed (andesitic, dacitic and mafic) magmas were erupted, those from different stageof mixing events in the zoned magma chamber with mush layers injected by two kinds of mafic end-member
magmas.

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182

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P7

Date/Time: July 24 Poster

Evolution of magma plumbing system of Sakurajima volcano in the last 50 years:
Frequent vulcanian eruptions controlled by basalt injection
Kaho Ebihara1 , Mitsuhiro Nakagawa1 , Akiko Matsumoto1 , Mizuho Amma-Miyasaka1 , Masato Iguchi2
1

Hokkaido University, Japan, 2 Kyoto University, Japan
E-mail: shrimp@mail.sci.hokudai.ac.jp

Sakurajimna volcano, a post-caldera volcano of Aira caldera in South Kyushu, has repeated plinian eruptions
three times since 1471 and effused lava in 1946. Vulcanian eruptions have continued since 1955 until now.
Nakagawa et al. (2011) concluded that three end-member magma mixing have occurred in 1914, 1946, 1958
and 1990; basaltic magma (B) inject into mixed magma of silicic (S) and andesitic (A) just before eruption. We
develop petrological study of the vulcanian eruptions in the last 50 years to investigate temporal change of magma
plumbing system in detail. Whole-rock SiO2 content of erupted materials in the last 50 years are 58-64% (andesitic).
Although these rocks have gradually changed to become more mafic with time since 1914, their compositional
trends in SiO2 -variation diagrams are consistent with those of 1914 and 1946. All the ejecta contain plagioclase,
orthopyroxene, clinopyroxene and magnetite as phenocrysts, and sometimes accompanying olivine. Plagioclase
phenocrysts show compositionally bimodal distributions (An60 and An80), and sometimes there exist compositional
peaks of An90. Orthopyroxene phenocrysts show unimodal or bimodal distribution in the range of Mg#65-75,
and clinopyroxene phenocrysts similarly in Mg#70-80. Furthermore, normally and reversely zoned phenocrystsof plagioclase and pyroxene usually coexist in a single sample. Olivine phenocrysts are mainly divided into two
types, one is Fo70 (surrounded by thick pyroxenes), and another is Fo80 (surrounded by microlites, have noreaction rims). Bimodal distribution of plagioclase phenocrysts, coexistence of normally and reversely zoned
phenocrysts and presence of Mg-rich olivines that compositionally disequilibrium with pyroxenes suggested thatmagma mixing also occurred in the last 50 years. S-magma: plagioclase (An=46-64), orthopyroxene (Mg#=60-68),
clinopyroxene (Mg#=66-72) and magnetite, and A-magma: plagioclase (An=64-86), orthopyroxene (Mg#=68-76),
clinopyroxene (Mg#=72-79) and magnetite, and B-magma: plagioclase (An=86-94) and olivine (Fo=75-82). The
end-member magmas of these vulcanian eruptions are similar to those of Nakagawa et al.(2011). The relationships
between ratios of these phenocrysts and whole-rock SiO2 suggests that whole-rock compositional variations ofjuvenile materials since 20th century should be formed by injection of B-magma into the mixed magma of S and A(Nakagawa et al., 2011). The level of eruptive activity would correlate to whole-rock chemistry of juvenile materials.
During the periods, in 1914 and from the late 1970’s to 1980’s, which the level of the activity increased, whole-rock
SiO2 contents of the juveniles had also decreased. This fact suggests that the scale and/or frequency of theinjection of B-magma would control the level of eruptive activity. In other word, we suggest that monitoring of the
B-magma might be essential to forecast future eruptive activity in Sakurajima volcano.

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183

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P8

Date/Time: July 24 Poster

Magma process and systems of the Kyoho eruption of Shinmoe-dake volcano in
Kirishima volcanoes, Japan
Tsuyoshi Miyamoto
Center for Northeast Asian Studies, Tohoku University, Japan
E-mail: t-miya@cneas.tohoku.ac.jp

Shinmoe-dake volcano in Kirishima volcanoes at south Japan has erupted in January 2011. This activity has
been in about 300 years since the Kyoho eruption (AD1716-17). From the similarities in the magma composition
and the eruption sequence between the 2011 eruption and the early stage of the Kyoho eruption, it is importantto understand the magma process of the Kyoho eruption. But the 2011 eruption after the first stage has a longer
dormancy than the Kyoho eruption. Thus I examined the Kyoho eruption products to understand the difference ofmagma systems between two episodes.
The Kyoho eruption products are classified into eight units (Sm-KP1 to Sm-KP7, and Sm-MP) (Imura andKobayashi, 1991; Tsutsui and Kobayashi, 2011). Pumice clasts in all units are dark-gray and rare yellow. Dark-graypumices have lower bulk-rock SiO2 content (57-58.5 wt.%) than the yellow ones (62 wt.%). Almost pumice show
the heterogeneous texture on a scale from millimeters to tens of micrometers. Mineral assemblages of phenocrysts
in all pumices are composed of plagioclase, orthopyroxene (Opx), clinopyroxene (Cpx), and Fe-Ti oxides. Olivine
phenocrysts are contained only in the dark-gray pumice of Sm-KP4.
In dark-gray pumices, the distribution of the core Mg-value in Opx is bimodal in the range of 64-66 and 73-76.
Low-Mg core Opx has thick rim of 72-74 with reverse zoning. The other mineralogical features in the dark-graypumice also show the mixing of mafic and felsic magmas. But the olivine (Fo77-80) in Sm-KP4 is not in equilibriumwith high-Mg core Opx. This indicates that high-Mg pyroxene was derived from mixed magma without mafic magma,
whereas the low-Mg pyroxene was from felsic magma.
Mafic magma did not erupt independently in both eruptions. The heterogeneous texture in pumice indicates that
two magmas ascended in conduit at the same time. In addition, the absence of isolated olivine and a thickreverse-zoned rim of Opx in mixed magma show that mixed magma was already produced before the magma
ascent. The strong chemical zoning and the various zoning profiles of the Usp component in a magnetite phenocryst
indicate that mafic injection occurred repeatedly before eruption. The magnetite phenocrysts have significant
compositional variation, which is larger than the zoning within each phenocryst. In spite of mingling magmas
on the ascent, the bulk chemical compositions lie in a narrow range; these imply that the heterogeneity is derived
not from the chemical composition but from physical conditions such as temperature and oxygen fugacity. The 2011
pumice are similar to the Kyoho products. However, whereas the olivine is rare in Kyoho pumice, 2011 eruption
products almost contain the olivine without pyroxene reaction rim. This discrepancy would indicate that the mixed
magma produced before eruption decreases, and at the next stage the activity might change to the other eruptionstyle for an increase of the ratio of mafic magma.

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184

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P9

Date/Time: July 24 Poster

Changes in magma composition and formation process of Minamidake stratovolcano, at
Sakurajima volcano, Kyushu, Japan; inferred from paleomagnetic age estimate andchemical composition analysis.
Daisuke Miki1 , Kozo Uto2 , Nguyen Hoang2 , Kazuhiro Ishihara1
1

Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University,
Japan, 2 National Institute of Advanced Industrial Science and Technology, Japan
E-mail: dmiki@svo.dpri.kyoto-u.ac.jp

Sakurajima volcano is a stratovolcano complex situated in south Kyushu, Japan. Fukuyama (1978) divided
lava flows of Minamidake stratovolcano which distributed south part of Sakurajima, into M1-M4 in order fromthe lower. Paleomagnetic ages of M1 and M2 lava were obtained by Miki (1999) as 4 ka, and, 2 ka or 3 ka,
respectively. Samples for paleomagnetic measurements and XRF analysis collected from mainly M3 and M4
lava distributed in south and southeast slope of Minamidake. Paleomagnetic age is estimated by comparison
between known geomagnetic secular variation and measured paleomagnetic direction and paleointensity. As aresult, paleomagnetic ages of M3 and M4 are estimated as about 2.9 ka and about 1.0 ka, respectively. From
results of XRF analysis, M4 lava shows 65 wt% of SiO2 and relatively high P2 O5 and TiO2 contents, where about
62 wt% of SiO2 and relatively low P and Ti contents are observed from lower lavas (M1-M3). These facts are
consistent with that products of recent 2000 years in Sakurajima volcano show higher P and Ti contents, pointed
out by Uto et al. (2005). It is considarable that the main body of Minamidake stratovolcano, consists of M2 andM3 lavas, was formed during several hundred years around 3000 years ago. And, no lava whose age is between
about 3 ka and late 8th century is found. Chemical composition of lavas of high P and Ti group including "histriclavas" seems to change systematically, where that of low P and Ti group is uniform. During recent 1300 years, SiO2
content increased until Bunmei eruption (late 15c), then decreased until present. This may an important information
to consider about evolution process of magma chamber of Sakurajima volcano.

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185

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4W_1D-P10

Date/Time: July 24 Poster

Dynamics of magma mixing and structure of silicic magma chamber: Evidence frompetrogenesis of two types of mafic inclusions of Kurodake volcano, Central Hokkaido,
Japan
Eiichi Sato1 , Keiji Wada2
1

Institute for Promotion of Higher Education, Kobe University, Japan, 2 Hokkaido University of Education
at Asahikawa, Japan
E-mail: esato@people.kobe-u.ac.jp

Kurodake volcano was formed about 0.2 Ma with andesitic lava flows and dome. The lavas contain a numberof mafic inclusions (< 20 vol.%) ranging in size from < 1 cm to about 30 cm in diameter. The mafic inclusions
have typically rounded to ellipsoidal shapes, and have sharply defined smooth contacts with the host lavas. The
mafic inclusions are classified into two types, referred to as Fine-type and Coarse-type, on the basis of size ofgroundmass. The groundmass of the Fine-type inclusions is composed of acicular minerals (0.1 to 0.3 mm in size).
On the other hand, the groundmass of the Coarse-type inclusions is composed of considerable tabular minerals(> 85 vol.% and 0.2 to 0.5 mm in size). The plagioclase phenocryst, microphenocryst, and groundmass corecompositions of the host lavas have a large variation in composition from An38 to An90 . They can be classified
into three groups based on their core compositions: An-rich (An > 80), intermediate (60 < An < 80), and An-poor(An < 60). The plagioclase phenocrysts have various core compositions ranging from An-poor to An-rich. The
An-rich and An-poor plagioclase phenocrysts show normal zoning and reverse zoning, respectively. The plagioclase
microphenocrysts and groundmass have narrowly core compositions than the phenocrysts. Most of plagioclase
microphenocrysts and groundmass are classified into the intermediate. In the Fine-type inclusions, An-rich andAn-poor plagioclase phenocrysts coexist, and most of plagioclase microphenocrysts and groundmass are classified
into the intermediate. While, in the Coarse-type inclusions, most of plagioclase phenocrysts, microphenocrysts, andgroundmass are classified into the An-poor. These features suggest that the Fine-type inclusions are formed fromhybrid layer between mafic and silicic magmas, whereas, the Coarse-type inclusions are formed by undercoolingaround margin of silicic magma chamber. We presume that the margin of the silicic magma chamber is highly
crystalline. When the host magma included the Fine-type inclusions uprises, the host magma engulfs the highly
crystalline part as the Coarse-type inclusions.

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186

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4W_1D-P11

Date/Time: July 24 Poster

Sulfur-rich basaltic magma injection into the magma plumbing system of Asama 2004
eruption: Melt inclusion study for magma compositions, the timing of degassing andmixing, and sulfur supply
Yoshiaki Yamaguchi1 , Tamami Yamaguchi2 , Yasushi Ohta3 , Toshisuke Kawasaki4
1

Shinshu university, Japan, 2 Kawasaki Municipal Science Museum, Japan, 3 Pacific Metals Co., Ltd.,
Japan, 4 Ehime University, Japan
E-mail: yoshia_ygutti@d4.dion.ne.jp

In the evolution of Asama volcano, most of the erupted materials have andesitic compositions, however, melt
inclusion studies found no sign of primary andesitic melt and revealed that basaltic liquid formed a part of theejecta. Melt inclusion study of 2004 scoria (23 September) (SiO2 61 wt%) revealed that sulfur-rich basaltic magma(SiO2 52 wt%, S <2600 ppm) injected into the reservoir beneath the volcano and mixed with a long-lived crystal-richfelsic-magma (SiO2 64 wt%) in the ratio 36 : 64. Diffusion profiles of Fo composition in olivine phenocrysts suggest ashort period (<a few months) from the basaltic magma injection to the eruption. There is no trace of new phenocryst
growth from the mixed magma.
Olivine phenocrysts include ferric-bearing crystalline phases together with the basaltic melt, suggesting a highoxygen fugacity condition of the basaltic magma. Measured sulfur X-ray peak shifts for the trapped melt indicatethat the dominant sulfur-bearing species is SO4 2- (>NNO + 1), corresponding with high sulfur solubility in themagma. This initial high sulfur concentration has, however, mostly been diminished (from 2600 to 1300 ppm orlower) before the melt entrapment, due to magma boiling and sulfide phase precipitation. The melt inclusions
commonly show various petrological features of the heterogeneous trapping (melt plus bubbles) of vesiculated
magma. There are only a few pre-boiling melt inclusions. Further, common sulfide inclusions in olivine suggest that
sulfur precipitations decreased continuously in sulfur concentration of magma during the crystallization. Hence, themost mafic (SiO2 -poor) and pre-boiling melts have the highest sulfur concentration (2600 ppm). These data provide
us a valuable source of information about the primary sulfur budget and the sulfur supply systems in arc magmas
in central-northeastern Japan.

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187

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4W_1D-P12

Date/Time: July 24 Poster

Olivine residence times for historical lavas of Chokai volcano, NE Japan: Estimation by
Fe-Mg and Ni diffusions in olivine crystals
Takanori Sato1 , Masao Ban2 , Tsukasa Ohba3 , Shintaro Hayashi4
1

Graduate School of Science and Engineering, Yamagata University, Japan, 2 Faculty of Science,
Yamagata University, Japan, 3 Faculty of Science, Akita University, Japan, 4 Faculty of Science, Akita
University, Japan
E-mail: s12e105m@st.yamagata-u.ac.jp

Chokai volcano is an active strato-volcano situated in the rear arc side of northeast Japan arc. Chokai volcano
erupted more than ten times in historic period. The magmatic activity occurred at least three times between AD
871 and 1801. Based on petrologic data of the historical lavas, it has been proposed that the erupted products
were formed by magma mixing. However, little is known about time intervals between mixing and eruption. Here
we estimate the time intervals based on Fe-Mg and NiO zoning of olivine phenocrysts in the historical lavas.
Samples for this study are from the Senjadani lower and upper lavas (AD871), the Kohjingatake lower lavas (someperiod between AD 871 and 1801). Phenocryst assemblages are similar in all samples, and the phenocrysts are
divided into mafic magma derived (An-rich plg and olv) and felsic magma derived ones (An-poor plg, opx, cpx, andhbl). Silica contents of the lavas are 56-58% and in the Senjadani lower lavas, ca. 51% in the upper lavas, 59-60%
in the Kohjingatake lower lavas.
Olivine phenocrysts are less than 1.2 mm in size and subhedral in shape. Most olivine crystals have the reaction
rim of orthopyroxene but some do not. These olivines have broad homogeneous cores and narrow, normally zoned
rims. Fo content of core typically spans 74 to 79, and that of rim decreases to be around 64. In addition, NiO
content of core is ca. 0.02 wt% and that of rim decreases to be ca. 0.002 wt%. We calculated residence times forthe olivine crystals on the assumption that the zoning was produced by diffusion of the elements after the magma
mixing event.
We used diffusion coefficients for Fe-Mg and Ni calculated by the equations of Costa et al. (2008) and Petry et al.
(2004). We selected olivine crystals without reaction rim and whose crystal orientations are easily determinable in
the thin section. We measured compositional profiles across these zoned olivine crystals by electron microprobe.
Using the methods of Costa and Chakraborty (2004), we compared modeled diffusion profiles with the observed
ones, and determined the times required to produce the measured profiles. The obtained olivine residence times
were one month to one year for the Senjadani lower lavas, one year to one year and a half for the Senjadani upperlavas and two months to eight months for the Kohjingatake lower lavas.

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188

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P13

Date/Time: July 24 Poster

Depths of two magma chambers of the Fuji 1707 eruption
Toshitsugu Fujii1 , Atsushi Yasuda2 , Akiko Yasuda2
1

Crisis and Environment Management Policy Institute (CeMI), Japan, 2 Earthquake Research Institute,
University of Tokyo, Japan
E-mail: fujii@eri.u-tokyo.ac.jp

Fuji volcano dominantly consists of basalt; however, several lines of evidence indicate existence of differentiated
SiO2 -rich magma beneath. The olivine-hosted melt inclusions clearly show the existence of andesitic liquid.
Phenocrystic plagioclase generally show bimodal distributions in compositional frequency, while most olivine
phenocrysts show unimodal distribution with reverse zoning and frequently contain andesitic melt inclusion. Thesesuggest that erupted magmas of Fuji are generated through mixing between basalt and more SiO2 -rich magmas.
It has been argued that the SiO2 -rich magmas evolved within a shallow magma chamber is mixed with the newly
ascended basalt magma which have differentiated in a deep magma chamber (e.g. Kaneko, et al., 2010).
The depth of the deep magma chamber has been estimated to be deeper than 20 km based on the compositionalvariation of basalt magmas (Fujii, 2007) and to be 25 km by high pressure melting experiments on the basalt scoriaof the 1707 eruption (Ushioda et al., 2012).
The depths of the shallow chambers, however, have not been well constrained because the SiO2 -rich end member
magma has been usually dissolved in the mixed basalt magma and is obtained only as a melt inclusion inphenocryst.
Among the eruption history of Fuji volcano, the 1707 eruption was peculiar because the SiO2 -rich end member
magma was extremely differentiated to dacite composition and resulted in unmixing with the basalt magma. This isa rare case we can obtain the composition of the SiO2 -rich magma as dacite pumice erupted at the beginning.
Recent finding of hornblende phenocryst in the dacite pumice of the 1707 eruption gives constraint on the depth
estimation of the evolved magma chamber. The pressure estimated is below 200 MPa and is almost 100 MPa. The
melt inclusions hosted in hypersthene phenocryst in dacite contain around 4 wt% of H2 O, indicating a crystallizationpressure around 100-150 MPa. These suggest the shallow magma chamber is around 4-6 km in depth. Thisestimation is consistent with the volatile concentration of olivine-hosted melt inclusions in basalt scoria of 1707
eruption. The most volatile-rich melt inclusion in olivine shows basaltic composition which indicates unmixing
nature and contains 3wt% H2 O and 300 ppm CO2 , suggesting the depth of crystallization of 6km or deeper.
The evidence described above indicates that a shallow and a deep reservoir are involved in the 1707 eruption. The
first is shallow as well as 4-6 km, and the deeper is around 25km. As most basalts of Fuji volcano show evidence of
mixing between a SiO2 -rich melt such as andesite, and a basalt magma, the magma plumbing system derived fromthe analysis of the 1707 eruption might be applied to the usual eruptions through the development of Fuji volcano.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

189

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P14

Date/Time: July 24 Poster

Processes leading up to the 22 ka silicic caldera-forming eruption of Santorini (Greece):
Constraints from field, 40 Ar/39 Ar and chemical data
Gareth N Fabbro1 , Timothy H Druitt1 , Stephane Scaillet2
1

Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, BP 10448, France,
2
Institut des Sciences de la Terre d’Orléans (ISTO), INSU-CNRS, Université d’Orléans, France
E-mail: g.fabbro@opgc.univ-bpclermont.fr

Large caldera-forming eruptions are commonly preceded by effusive eruptions whose magma chemically andpetrologically resembles that of the climatic eruption. Studying these lavas can reveal processes that occur in thebuild-up to these often-catastrophic eruptions. On Santorini, the 21.7±0.2 ka caldera-forming Cape Riva eruption
produced at least 10 km3 of dacitic magma, along with a minor andesitic component. It was preceded by a periodof effusive volcanism that discharged 1-2 km3 of magma and built up the so-called Therasia dome complex. The
Therasia dome complex is dominated by at least 12 different dacitic coulées and domes, which total up to 200 m inthickness. These are intercalated with the dacitic products of sub-plinian explosive activity, and are capped by anandesitic lava flow (the upper Therasia andesite). The Therasia lavas were fed by dykes, with vents located within
the area that subsequently collapsed to form the Cape Riva caldera. The majority of the Therasia dome complex
was erupted in a period of about 13 ky, starting 36.0±2.8 ka. The youngest lava has an age of 23.2±2.3 ka, lessthan 4000 y before the Cape Riva eruption. The Therasia dacites contain between 65 and 69 wt% SiO2 , and have
1-17 wt% phenocrysts of plagioclase, orthopyroxene, clinopyroxene and Fe-Ti oxides. This closely resembles theCape Riva dacite, which has a similar phenocryst assemblage and 64-67 wt% SiO2 . The upper Therasia and Cape
Riva andesites are also similar to each other. They are both hybrid andesites (60-62 wt% SiO2 ) with crystals ofplagioclase, orthopyroxene, olivine and Fe-Ti oxides, and formed by mixing ∼60 wt% dacite with ∼40 wt% basalt.
The occurrence of hybrid andesites at the top of the Therasia sequence suggests that, for the first time since∼36 ka, mafic magma was reaching shallow levels of the plumbing system under Santorini. Despite the similarities
in the petrology and major-element chemistry of the Therasia and Cape Riva magmas, however, the Cape Riva
dacite is depleted in incompatible elements such as K, Zr, Rb, La, Ce and Nb. This fits with the long-term trend
towards more depleted magma compositions on Santorini, and implies that the Cape Riva and Therasia magmas
were distinct batches. The two hybrid andesites (Therasia and Cape Riva) also exhibit the same differences intrace element composition. This could be explained by a large influx of silicic magma (and accompanying basaltic
magma) into the shallow plumbing system in the short period between the end of the construction of the Therasia
dome complex and the onset of the Cape Riva eruption. One implication of this interpretation is that the transition
from prolonged effusive to major explosive activity coincided with this upward transfer.

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190

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P15

Date/Time: July 24 Poster

A combined mineral and melt inclusion study of the Nea Kameni dacites
Ben S Ellis1 , Michael C Rowe2 , Kostas Kyriakopoulos3
1

Institute for Geochemistry and Petrology, ETH Zurich, Switzerland, 2 School of Environment, Universityof Auckland, New Zealand, 3 Department of Geology and Geoenvironment, National and Kapodistrian
University of Athens, Greece
E-mail: ben.ellis@erdw.ethz.ch

Since the voluminous 3.6 ka Minoan eruption, the Santorini volcano has been periodically erupting small volumes ofdacitic magma. This study examines mineral and melt inclusions geochemistry of lavas spanning from 1573 to 1950
from Santorini volcano. Unlike the larger explosive events which commonly contain clasts of multiple compositions,the eruptions of Nea Kameni have been compositionally monotonous in bulk terms. The Kameni dacites do
however contain two populations of feldspar, one An38-65 interpreted as crystallising from the dacitic liquid and asecond An86-94 interpreted as xenocrystic. The two populations are distinct in terms of 87 Sr/86 Sr as determined via
LA-ICPMS with the higher anorthite plagioclase having higher 87 Sr/86 Sr. The larger dataset provided by LA-ICPMS(albeit with reduced precision) indicates that plagioclase grains within the Kameni dacites are isotopically morevariable than existing data for the preceding explosive volcanism. Further differences are observed in the traceelement compositions of the plagioclase grains, with the higher-anorthite population having systematically lower
Sr and Ba abundances than the lower-anorthite plagioclase. The mafic and silicic plagioclase compositions
appear to have remained approximately constant throughout the last 500 years of volcanism on the Kameni
islands. Groundmass glass compositions are rhyolitic (SiO2 73.5-73.8 wt.%) and melt inclusion compositions
hosted within plagioclase exhibit two compositional populations which are related to the host composition. Highanorthite plagioclase contains less evolved melt inclusions (SiO2 51.2-58.1 wt.%) whereas the lower anorthiteplagioclase contains melt inclusions more similar to the groundmass glass (SiO2 63.6-71.4 wt.%). Water contentsof the dacitic inclusions as determined via SIMS are slightly less than predicted via plagioclase-melt hygrometry(4-5 wt.%) but consistent with previous estimations.

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191

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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4W_1D-P16

Date/Time: July 24 Poster

Evolution of the Austurhorn Intrusive Complex revealed by zircon elemental and isotopic
geochemistry and geochronology
Abraham J Padilla1 , Tamara L Carley1 , Calvin F Miller1 , Joseph L Wooden2 , Rita C Economos3 , Axel K
Schmitt3 , Chris M Fisher4 , John M Hanchar5
1

Vanderbilt University, United States, 2 Stanford University-USGS MAC, SHRIMP-RG Lab, UnitedStates, 3 University of California-Los Angeles, United States, 4 Washington State University, UnitedStates, 5 Memorial University of Newfoundland, Canada
E-mail: a.padilla@vanderbilt.edu

The Austurhorn Intrusive Complex (AIC) is a small silicic intrusion along the SE coast of Iceland comprising large
bodies of granophyre, gabbro, and a mafic-felsic composite zone that exemplifies mafic-felsic interactions common
in Icelandic silicic systems. Despite being one of Iceland’s best-studied intrusions (Blake 1966; Furman et al
1992a,b; Thorarinsson and Tegner 2009), zircon studies are notably lacking for the AIC, as well as for other Iceland
plutons. The value of zircon as a tracer of the history and evolution of its parental magma(s) has been widely
recognized. Here, we present the first detailed chronologic, elemental, and isotopic study of Icelandic plutonic
zircon, likely Iceland’s dominant zircon population.
The elemental composition of AIC zircons form a broad but coherent array that partly overlaps with thewell-constrained signature of zircons from Icelandic silicic volcanic rocks (Carley et al 2011). The broader rangeof AIC zircon is likely due to the effect of crystallization down to the solidus in plutonic environments (absent
in volcanic environments). With some exceptions (see below), Ti concentrations range from 6-25 ppm (Ti-zirctemperatures 730-870 deg.C), and Hf concentrations are low (below 10,000 ppm), typical of Iceland zircon.
Epsilon-Hf values are well-constrained at +13(+/-)1 epsilon units, falling between epsilon-Hf for Iceland basalts
from rift and off-rift settings and suggesting a single source for the different units of the AIC. Similarly, d18O values
are generally well-constrained at +3 to +4 per mil, consistent with Icelandic magmatic zircon (Bindeman et al 2012)and suggesting contribution from hydrothermally-altered crust to the petrogenesis of the parental silicic magmas.
The notable exceptions to the trends described above are analyses of zircons from a high-silica miarolitic
granophyre that display CL-dark zones with convolute and irregular zoning. These fall well outside the AIC
elemental and isotopic arrays, and are primarily distinguished by extreme Hf (up to 24,000 ppm) and lower Ti(down to 2 ppm [630 deg.C]), far higher and lower, respectively, than other analyzed Icelandic zircon, as well as
generally higher U and Th. Their d18O values range from normal (+4) to extremely low (-6 per mil). We interpretthese unusual analyses to reflect hydrothermal recrystallization.
Field relationships provide clear evidence that the AIC was constructed by repeated mafic and felsic intrusions.
In-situ (SHRIMP) dating of 5 zircon samples yields a pooled age of 6.43(+/-)0.04 Ma for the entire complex.
However, the relatively high MSWD (1.6) suggests real spread in ages, and UNMIX analyses and subtle peaks inprobability-density plots are consistent with multiple ages ranging from 6.3 to 6.6 Ma. Assuming this interval is real,
it may reflect prolonged lifetime of a periodically rejuvenated mush, or re-melting events that revived earlier-solidified
magmatic increments to the AIC.

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192

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P17

Date/Time: July 24 Poster

Post-supereruption reconstruction of Taupo volcano (New Zealand) through systematic
crystallization episodes
Simon J Barker1 , Colin J.N Wilson1 , Bruce L.A Charlier2 , Wooden D Joseph3
1

School of Geography, Environment and Earth Sciences, Victoria University of Wellington, New
Zealand, 2 CEPSAR, The Open University, Walton Hall, Milton Keynes, UK, 3 SUMAC, Department of
Geological and Environmental Sciences, Stanford University, USA
E-mail: smnbarker@gmail.com

Large explosive silicic supereruptions have received much attention because of the challenges in explaining how
such large volumes of magma are accumulated and stored, and over what time intervals. The processes that follow
supereruptions are less fully documented and, in particular, how and on what time scales the overall magma systemmoves into a post caldera mode of activity. The 530 km³Oruanui eruption from Taupo volcano, New Zealand, is theworlds youngest (25.4 ka) supereruption. Following this event and after only 5 kyr of quiescence, Taupo volcano
erupted three dacitic pyroclastic units of modest volume (<0.1 km³), followed by another 5 kyr year time break, andthen eruption of the modern sequence of rhyolitic units starting at 12 ka. Here we present U/Th model age datingof zircons extracted from the post Oruanui eruption products to investigate how Taupo’s magmatic system wasreactivated following a supereruption. Zircon model ages in first erupted rhyolites indicate that there is minimal or
no inheritance of crystals from either of the two dominant age modes (35 and 90 ka) in the Oruanui magma source.
Post Oruanui age spectra are typically centered close to eruption ages with subordinate pre 300 ka plutonic andpre 100 Ma greywacke grains. In addition, there is consistent inheritance of grains between the temporally spaced
but geographically overlapping post Oruanui eruption groups, allowing the identification of systematic dominant age
peaks since the Oruanui supereruption. We interpret this consistent and repeated pattern to result from recycling of
crystals from post supereruption episodic heating and cooling cycles, reflecting periods of magmatic rejuvenationand eruption, versus cooling and crystallization, acting within a crustal protolith independent of that which was
dominant in the Oruanui system.

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193

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P18

Date/Time: July 24 Poster

Experimental constraints on mixing between basaltic and rhyolitic magmas along theNorris Mammoth Corridor in the Yellowstone National Park (USA)
Daniele Morgavi1 , Diego Perugini2 , Chad J. Pritchard3 , Cristina P. De Campos1 , Peter B. Larson4 ,Donald B. Dingwell1
1

Dept. Earth and Environmental Sciences, Ludwig Maximilian University (LMU), Munchen, Germany,2
Dept. Earth Sciences, University of Perugia, Piazza Universita, 06100 Perugia, Italy, 3 Geology
Department, Eastern Washington University, Cheney, Washington 99204, USA, 4 School of Earth andEnvironmental Sciences Washington State University, Pullman, Washington„ USA
E-mail: morgavi@min.uni-muenchen.de

The magma mixing process in the Norris Mammoth Corridor in Yellowstone National Park (USA) is observed
at different scales, including variable structural and textural patterns, as well as morphologies such as filament
like structures, enclaves, and mineral phases showing physicochemical disequilibrium. The type and geometry ofthese structures strongly depends on the mixing dynamics (e.g. Perugini et al., 2012; Morgavi et al., 2013). The
quantification of the morphology and the compositional variability of these structures are essential to understandthe mixing process and require detailed analytical and experimental studies.
We present the first set of chaotic mixing experiments performed using natural basaltic and rhyolitic melts fromthe Yellowstone Norris-Mammoth Corridor. The mixing process is triggered by a recently developed apparatus thatgenerates chaotic streamlines in the melts, mimicking the development of magma mixing in nature. The study of theinterplay of physical dynamics and chemical exchanges between melts is carried out performing time series mixing
experiments under controlled chaotic dynamic conditions. The variation of major and trace elements is studied indetail by electron microprobe (EMPA) and Laser Ablation ICP MS (LA ICP MS).
The mobility of each element during mixing is estimated by calculating the decrease of concentration variancein time. Both major and trace element variances decay exponentially, with the value of the exponent of the
exponential function quantifying the element mobility. Our results confirm and quantify how different chemicalelements homogenize in the magmas at differing rates. These results constitute a robust basis for determining thetimescale of the mixing process at Yellowstone volcano using the differential mobility of chemical elements.

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194

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P19

Date/Time: July 24 Poster

Magma mixing/mingling and viscous fingering: Analogue experiments and geometry ofinterfaces
Nodoka Takada1 , Eiichi Sato2 , Kazuhito Yamasaki1
1

Department of Earth and Planetary Sciences, Graduate School of Science, Kobe University, Japan,
2
Institute for Promotion of Higher Education, Kobe University, Japan
E-mail: esato@people.kobe-u.ac.jp

Magma mixing/mingling is common in the dynamics of volcanic eruptions and igneous activities, and its processes
have been investigated by petrological, experimental and theoretical studies.

Especially, the morphology ofinterfaces between the two magmas having different viscosities shows the various complex patterns due to thedifferences in physical and chemical conditions under the mixing/mingling process (e.g., Wada, 1995; Perugini
et. al., 2005; Sato and Sato, 2009). Since the quantity that we can observe easily is the geometrical patterns of
the interfaces, it is important to express this physical phenomenon in terms of the geometrical quantities of theinterfaces.
The geometry of interfaces enables us to extract the useful information of the mixing/mingling process from themorphological analysis of the interfaces of rocks in nature (Perugini and Poli, 2005; Sato and Yamasaki, 2012).
However, few attempts have been made to consider how the dynamic quantities such as the growth rate of theinterfaces affect the geometry of the interfaces in the mixing/mingling process.
In this work, to simulate the replenishment of felsic magma chamber by continuous inputs of mafic magmas, we
perform the analogue experiment in which we inject air or water into glycerin using the Hele-Shaw cell. In this case,the mixing/mingling process can be described by the DLA model (e.g., Nittmann et al., 1985), and the interfaces
show the viscous fingering pattern due to the instability of the interfaces that also occur in the natural cases (e.g.,
Perugini and Poli, 2005). The following results were obtained.
1. We estimate the three fractal dimensions: the interfaces Di, the area of the high viscosity fluids Dh and that of
the low viscosity fluids Dl. We find that the sum of Dh and Di is the conserved quantity, and the Di is proportional to
Dl. This implies that the fractal dimension of the interfaces (easily observed quantities) enables us to estimate thefractal dimension of the area of the felsic or mafic magma (hardly observed quantities).
2. We find that the radius of curvature of the viscous fingerling depends on the growth rate of the interfaces. This isagreed with the solutions of the development equation of the curvature in the differential geometry (e.g., Nakamura
and Wadati, 1993). This implies that we can estimate the growth rate of the interfaces by the radius of curvature of
the mafic magmas.
3. In the case of colorless water and black-colored glycerin experiments, the interface of the two fluids shows lightto dark gray color. We measure the fractal dimensions of the gray levels classed into several groups to estimate thedegree of mixing. We find that the fractal dimensions correlate with the degree of mixing. This implies that we canestimate the degree of mixing from natural mixed rocks.

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195

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P20

Date/Time: July 24 Poster

The role of bubble ascent in magma mixing
Sebastian Wiesmaier1 , Daniele Morgavi1 , Diego Perugini2 , Cristina De Campos1 , Kai Uwe Hess1 , Yan
Lavallee3 , Donald B Dingwell1
1

Ludwig-Maximilians-University Munich, Earth and Environmental Sciences, Germany, 2 University of
Perugia, Department of Earth Sciences, Italy, 3 University of Liverpool, School of Environmental
Sciences, United Kingdom
E-mail: sebastian.wiesmaier@min.uni-muenchen.de

Understanding the processes that affect the rate of liquid state homogenization provides fundamental clues on
the otherwise inaccessible subsurface dynamics of magmatic plumbing systems. Compositional heterogeneities
detected in the matrix of magmatic rocks represent the arrested state of a chemical equilibration. Magmatic
homogenization is divided into a) the mechanical interaction of magma batches (mingling) and b) the diffusive
equilibration of compositional gradients, where diffusive equilibration is exponentially enhanced by progressive
mechanical interaction (1). The mechanical interaction between two distinct batches of magma has commonly
been attributed to shear and folding movements between two distinct liquids. A mode of mechanical interaction
scarcely invoked is the advection of mafic material into a felsic one through bubble motion. Yet, experiments withanalogue materials demonstrated that bubble ascent has the potential to enhance the fluid mechanical componentof magma mixing (2).
Here, we present preliminary results from bubble-advection experiments. For the first time, experiments of this kind
were performed using natural materials at magmatic temperatures. Cylinders of Snake River Plain (SRP) material
were prepared for a static layered set-up, with basalt glass placed underneath rhyolite glass. Upon heating, airtrapped in the interstices between glass cylinders and the crucible expanded, forming bubbles in the now molten
basalt. The bubbles rose, thus entraining a portion of basaltic material into the rhyolite.
The plume-like structure that the advected basalt formed within the rhyolite was characterized by microCT andsubsequent high-resolution EMP analyses. The diffusional gradient around the plume tail showed a progressive
diffusional equilibration from top to bottom, consistent with increasing time of interaction towards the bottom endof the plume tail. Furthermore, single protruding filaments at the bottom end of the plume tail indicate that theplumous structure is a composite of many smaller plume tails. Possibly, the first bubble rising created a preferential
pathway for bubble ascent thereafter. The normalised variance, which serves as a proxy of cation diffusion rate
at the interface of rhyolite and basalt, is unsystematic. This is most likely a result of the many small plume tails
combined in the hybridised region. In turn, stretching and folding experiments produce very systematic normalised
variances. The normalised variance measured in natural magma mixing structures may thus provide characteristic
evidence to distinguish between mixing induced by bubble action or scenarios of stretching and folding.
(1) De Campos et al. (2011) Enhancement of magma mixing efficiency by chaotic dynamics: an experimental
study, Contrib. Mineral. Petrol., 161(6), 863-881.
(2) Thomas et al. (1993) Mixing of stratified liquids by the motion of gas bubbles: application to magma mixing,
Earth Planet. Sci. Lett., 115(1-4), 161-175.

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IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P21

Date/Time: July 24 Poster

Amphibole Reaction Rim Development: EBSD insights into crystal nucleation and growth
Sarah Henton De Angelis1 , Yan Lavallee1 , Jessica Larsen2 , Elisabetta Mariani1
1

University of Liverpool, United Kingdom, 2 University of Alaska Fairbanks, United States
E-mail: pelee83@gmail.com

This study employed electron backscatter diffraction (EBSD) to examine the development of anhydrous reaction
rims around magmatic amphiboles. Sample materials from the 2006 eruption of Augustine Volcano, Alaska were
utilised. EBSD analysis was performed on 3 sample types: 1) naturally produced amphibole reaction rims; 2)reaction rims produced experimentally by heating; 3) reaction rims produced experimentally by decompression.
Amphibole, a hydrous mineral, decomposes to form rims of anhydrous minerals when removed from its
thermobarometric stability field. The thickness, texture, and mineralogy of these rims are thought to be reflective of
the process driving amphibole disequilibrium (e.g. heating, decompression). However, experimental results showthat reaction rim formation is also dependent on the magnitude and duration of amphibole disequilibrium. Further,significant overlap in reaction rim thicknesses and reaction rim microlite textures means that distinguishing between
heating and decompression is not simple. EBSD data have demonstrated differences in volcanic plagioclase
microlite textures as a function of reaction conditions. We collected crystal orientation maps of amphibole reaction
rims to investigate how processes of reaction rim microlite crystal nucleation, rim growth and microlite coarsening
vary with changing disequilibrium conditions, magnitudes, and durations. This work aims to show that different
disequilibrium conditions result in different crystallisation regimes. Consequently, the results provide further insight
into the classification of natural reaction rims on the basis of formation processes.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

197

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P22

Date/Time: July 24 Poster

DIPRA: A new user-friendly program to determine the timescales of magmatic processes
from diffusion modelling of multiple elements in olivine
Társilo Girona, Fidel Costa
Earth Observatory of Singapore, Nanyang Technological University, Singapore
E-mail: tarsilo.girona@gmail.com

One recent advance in igneous petrology has been to be able to quantify the timescales and rates of magmatic
processes. This provides a lot of valuable information about a wide range of phenomena, such as the residence
times of magmas in shallow reservoirs before eruptions. A methodology to determine these timescales is modellingthe concentration of different elements in minerals, which is based on chemical diffusion within the crystals.
However, despite the good knowledge of diffusion coefficients and the ease of measurements of chemical gradients,
the use of this technique is not widespread yet. This could be due in part to the lack of a user-friendly tool thatallows modelling the chemical zonings in crystals easily. We have developed an interface-based computer program(DIPRA: Diffusion Process Analysis) that allows modelling intuitively the diffusion of Fe, Mg, Mn, Ni, and Ca inolivine (one of the most widespread minerals in igneous rocks) by performing an automatic and quick fit to thenatural chemical profiles. DIPRA accounts for most variables that affect diffusivity, such as temperature, oxygen
fugacity, and anisotropy, and initial and boundary conditions can be chosen as complex as the user requires. The
program also calculates the uncertainties of the diffusion time based on the uncertainty of the data and temperature.
DIPRA is very versatile and, besides being a working tool for petrologists, it could also be useful for teaching kinetics
of chemical re-equilibration and timescales of magmatic processes in higher education courses. The program canbe downloaded from www.tgirona.com.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

198

IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P23

Date/Time: July 24 Poster

Identifying transitions in activity and precursors to major eruptive events at Mt. Taranaki,
New Zealand
Kimberly Genareau1 , Shane J. Cronin2 , Thomas Platz3
1

Lehigh University, U.S.A., 2 Massey University, New Zealand, 3 Freie Universitat Berlin, Germany
E-mail: kig210@lehigh.edu

Mt. Taranaki, located in the western North Island of New Zealand is an andesite stratovolcano which has been in astate of quiescence for the last >200 years. Its record of >100 eruptions over the last 12,000 years and its upwind
position with respect to the largest populated areas of the country means that it presents a significant hazard withany re-awakening. Volcanic activity at Taranaki is characterized by periods of hundreds of years dominated byrepeated lava dome growth and collapse, interspersed semi-regularly at 300 year intervals with large sub-Plinian
explosive events. In addition to widespread tephra falls, Taranaki has produced hazardous pyroclastic density
currents in the form of surges, block-and-ash flows, and column collapse pyroclastic flows that reach run-out
distances of up to 15 km from the summit. This study focuses on the sequence of pyroclastic deposits thatstratigraphically precede the 1655 AD Burrell Lapilli unit, which was the latest sub-Plinian eruption of Taranaki.
This eruption culminated a period of repeated lava effusion and dome growth that lasted roughly 1000 years.
The pre-Burrell pyroclastic sequence is comprised of several, fall, flow, and surge units and these tephras wereanalyzed using a combination of scanning electron microscopy, stereo-scanning electron microscopy, secondary
ion mass spectrometry (SIMS), and electron microprobe analyses. SIMS analyses of oscillatory-zoned plagioclase
phenocrysts from the Burrell Lapilli show increasing Li contents in crystal rims compared to cores. Profiles acrossphenocrysts show that Li increases substantially even when An contents increase, decrease, or remain relatively
constant, indicating that Li variations reflect properties of the ascending magma parcel rather than local chemical
gradients at the melt-crystal interface. In addition, thin (10-20 microns), decompression-induced breakdown rims on
amphibole crystals and extensive groundmass crystallization of plagioclase microlites in the indicate changes in thevolatile content of the magma leading up to the Burrell explosive phase, and thus, Li trends may allow quantificationof the timescale during the final stage of magma ascent prior to the Burrell sub-Plinian explosion. Microtexturaland geochemical trends in the pre-Burrell sequence will be compared to those of the subsequent Burrell Lapilli
unit to highlight the evolution of magma properties during transitions from effusive to explosive activity. Quantifying
physical parameters within conduits and understanding how they vary over time to cause dome collapse events andexplosive activity will allow researchers to more accurately model (and ideally, with ongoing analysis of samples
collected during an eruption crisis, forecast) volcanic behavior. This will lead to improved hazard assessment
strategies for >100 andesitic volcanoes worldwide that show regular variations in effusive and explosive activity likethose observed at Taranaki.

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