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

3A1_2J-O1

Room A6

Date/Time: July 23 8:45-9:00

Do high lava-dome extrusion rates foreshadow explosive eruptions?
John S Pallister1 , Christopher G Newhall2
1

USGS Cascades Volcano Observatory, USA, 2 Earth Observatory of Singapore, Singapore
E-mail: jpallist@usgs.gov

Satellite radar, LIDAR, and photogrammetry provide improved measurements of erupting lava domes. Data fromthese sources combined with petrologic data and historical records raise the question of whether high extrusion
rates can be used to forecast explosive eruptions.
Lava dome extrusion takes place both before and after large explosive eruptions (as well as interspersed between
explosive eruptions). Examples include Pinatubo (1991), Chaitén (2008-2009), and Merapi (2010). At Pinatubo,
mingled magma lava domes were extruded both before and a year after the paroxysmal Plinian eruption on 15
June 1991 (Daag et al., 1996; Pallister et al., 1996). At Chaitén, rapid (>45 m3s-1 extrusion of low viscosity rhyolite
followed an initial Plinian eruptive phase (Pallister et al., in press). At Merapi, rapid (25 m3s-1) lava extrusion
followed an initial phreatomagmatic eruption on 26 October 2010 and formed a 5 Mm3 lava dome before the main
Plinian eruption on 5 November 2010. Rapid (35 m3s-1) extrusion then resumed for a brief period on 6 November,forming a 1.5 Mm3 lava dome that initially inflated and then subsided as the eruption waned (Surono et al., 2012;
Pallister et al., 2013).
At both Pinatubo and Merapi intrusion of new gas-rich magma into pre-existing crustal reservoirs triggered theeruptions, and in both cases, ascent was retarded by transit through these viscous crystal-rich reservoirs. However,there are distinct differences in the Pinatubo and Merapi situations. Prior to 1991, Pinatubo was a closed system
lacking a conduit to the surface. Gas-rich recharging basalt magma mingled with crystal-rich dacite in Pinatubo’s
crustal reservoir. It was this mingled magma that augered a new conduit to the surface to form the 7-12 June
1991 lava dome (extrusion rate unknown) and it was dacite that powered the paroxysmal eruption. At Merapi, an
unusually large and gas-rich batch of magma invaded and pressurized a dominantly andesitic magmatic systemwith a pre-existing conduit to the surface. In both cases, the erupted magmas bear petrologic evidence of a difficult
passage (e.g., mingled or mixed magmas with varied crystal cargos). Consequently, large or particularly gas-richreplenishing magma batches are most likely to break through these shallow crustal filters (Costa et al, 2013) andtrigger eruptions. Such magmas are the vanguards that create and pressurize conduits and thereby generate
seismic swarms and near-surface deformation.
Anomalously high rates of dome extrusion, accompanied by increasing and accelerating levels of shallow seismicity
and inflation (as seen at Merapi) are a warning sign that a more explosive eruption may ensue. However, whenseismicity and inflation are flat or declining, despite a high rate of extrusion (as seen at Chaitén and Merapi following
their initial Plinian phases), pressure in the conduit system has declined and the threat of a more explosive eruption
has diminished.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

644

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

3A1_2J-O2

Room A6

Date/Time: July 23 9:00-9:15

Revealing shallow magmatic ascent processes during the 2006 and 2010 eruptions ofMerapi volcano: evidence from textural and compositional variations of feldspar
microlites
Katie Preece1 , Ralf Gertisser2 , Jenni Barclay1 , Richard Herd1
1

School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK, 2 School ofPhysical and Geographical Sciences, Keele University, Keele, Staffordshire, ST5 5BG, UK
E-mail: K.Preece@uea.ac.uk

The interplay between magma ascent, degassing and changing magmatic properties are widely recognized as
critical factors controlling the style of silicic volcanic eruptions. Microlite textures in samples from the prolonged
dome-forming eruption of Merapi in 2006 provide a record of changing magmatic ascent conditions and shallow
conduit processes throughout the eruption. Analysis of microlite textural parameters, including measurements ofareal number density (NA ), mean microlite size, crystal aspect ratio and groundmass crystallinity (φ), combinedwith the monitoring record and field observations, indicate that magma ascent paths change between continuous
ascent at varying rates from a deeper magma storage region, to ascent being temporarily stalled at shallow depths
in the latter stages of the eruption [1]. Plagioclase microlite compositions show evidence of decompression-induced
degassing, often displaying rims of anorthoclase and more K-rich alkali feldspar (sanidine). Anorthite contents
also support the textural data of later erupted magma being temporarily stalled at shallow depths. Crystal size
distributions (CSDs) are interpreted to show that both growth-dominated and nucleation-dominated crystallisation
regimes existed during the 2006 eruption, resulting from changing conditions of undercooling (∆T) during variablemagma ascent paths. By contrast, microlite textural analysis and feldspar microlite compositions of samples
from the fast-growing lava dome of the second phase of the 2010 eruption prior to the cataclysmic events on 5
November indicate faster ascent rates, a crystallisation regime more strongly dominated by nucleation due to high∆T and possible interaction of the 2010 magma with more mafic magma from depth.
The differences in ascent processes have key implications for determining the eruptive behaviour at Merapi, i.e.
effusive vs. explosive activity, as well as the associated hazards.

Reference: [1] Preece et al., (2013) J. Volcanol. Geotherm. Res. (in press)©IAVCEI 2013 Scientific Assembly. All rights reserved.

645

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

3A1_2J-O3

Room A6

Date/Time: July 23 9:15-9:30

Petrology and geochemistry of the large-magnitude 2010 eruption of Merapi volcano,Central Java, Indonesia: insights into magma dynamics
Ralf Gertisser1 , Katie Preece2 , Heather Handley3 , Mark Reagan4 , Kim Berlo5 , Jenni Barclay2 , Richard
Herd2
1

School of Physical and Geographical Sciences, Keele University, Keele, ST5 5BG, UK, 2 School ofEnvironmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK, 3 GEMOC, Department ofEarth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia, 4 Department ofGeoscience, The University of Iowa, Iowa City, IA 52242, USA, 5 Department of Earth Sciences,
University of Oxford, Oxford, OX1 3AN, UK
E-mail: r.gertisser@keele.ac.uk

The devastating eruption of Merapi that started on 26 October 2010 was the volcano’s largest since 1872 and thedeadliest event since 1930. The eruption was unusual in many respects: (1) it started, after nearly two months
of increased seismicity and summit deformation, with an explosive phase that was not preceded by lava dome
extrusion at the summit; (2) between 30 October and 4 November, a lava dome appeared and grew rapidly within
the newly formed summit crater, exceeding growth rates observed at the peak of the penultimate eruption in 2006
by a factor of 7.5 [1]; (3) during the paroxysmal eruption phase on 5 November, high-energy PDCs were generated
and at least one PDC travelled more than 15 km (more than twice the distance of the largest flows in 2006) beyond
the summit along the Gendol river valley, causing widespread devastation on Merapi’s south flank [2, 3]; (4) in alater phase on 5 November, PDCs were produced that incorporated conspicuous light-coloured pumice clasts; (5)ash emissions from sustained eruption columns resulted in ash fall tens of kilometres from the volcano, affecting,amongst other areas, the city of Yogyakarta 25 km to the south of Merapi; and (6) the total non-DRE volume in2010 is thought to have been at least 4 times higher than that of the preceding 2006 eruption [3, 4]. Despite
the unusual eruptive behaviour of Merapi in 2010, whole-rock major and trace element compositions, Sr-Nd-O
isotopic data, pre-eruptive melt volatile concentrations, as determined by electron and ion microprobe analysis
of pyroxene-hosted melt inclusions, for the eruptive products from the various stages of the 2010 eruption are
remarkably similar to other recent and historical eruptions, which were predominantly characterised by periods ofslow lava dome extrusion punctuated by gravitational dome failures. By contrast, notable petrographical differences
are the presence of unaltered amphibole phenocrysts and microphenocrysts without reaction (breakdown) rims aswell as variations in groundmass textures in the juvenile component(s) of the 2010 eruption, which, in combination
with short-lived U-series isotope systematics (210 Po-210 Pb-226 Ra), provide a detailed picture of pre-eruptive magma
dynamics characterized by fast ascent and temporary shallow stalling of magma (or batches of magma) that fed
the eruption.

References: [1] Pallister et al. (2013). J. Volcanol. Geotherm. Res., doi:10.1016/j.jvolgeores.2012.07.012.
[2] Komorowski et al. (2013). J. Volcanol. Geotherm. Res., doi: 10.1016/j.jvolgeores.2013.01.007. [3] Charbonnier
et al. (2013). J. Volcanol. Geotherm. Res., doi:10.1016/j.jvolgeores.2012.12.021. [4] Charbonnier and Gertisser(2011). Sedimentology, 58, 1573-1612.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

646

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

3A1_2J-O4

Room A6

Date/Time: July 23 9:30-9:45

Modelling the frequent transitions between explosive and effusive activity at Volcán de
Colima, Mexico
Nick Varley1 , Yan Lavallée2 , William Hutchinson3 , Erica Webb3 , Gabriel Reyes1
1

Universidad de Colima, Mexico, 2 Liverpool University, UK, 3 University of Oxford, UK
E-mail: nick@ucol.mx

During the past 14 years Volcan de Colima has transitioned between a large variety of eruptive styles whilst
showing a remarkable consistency in the magma composition. The volcano has produced 6 distinct periods ofdome growth with mean effusion rates varying over 2 orders of magnitude from 0.02 to 8 m3 s-1. Several domes
were destroyed by subsequent Vulcanian explosions with a variation in the interval dividing the two types of activity(from days to several months). In 2005 the explosions were of sufficient magnitude to produce pyroclastic density
currents from column collapse which reached up to 5.4 km. However, the largest run-out distances (6.1 km) wereachieved by flows resulting from dome collapse in Oct. 2004. Superimposed on top of this activity the volcano
has demonstrated a very efficient sealing mechanism preventing continuous gas release and resulting in small
Vulcanian explosions on the time-scale of a few hours.

Different data has been used to understand the upper edifice processes controlling magma degassing andcrystallization. Seismicity has enabled the tracking of magma ascent rates with precursory swarms of LP events
associated with brittle fracturing along the margins of fractures. Variation in fumarole temperatures has reflected
the variation in degassing pathways and magma ascent rates, whilst thermal images of domes has given an
insight into their emplacement mechanism. The SO2 flux has shown a decreasing trend throughout the 1998-2013
eruptive period, however, there is evidence for relatively large volumes of gas-rich magma which decompressed todrive the sporadically occurring larger explosions. Further insight has been obtained from the comparison between
column ascent rate of the explosions and associated seismic and thermal energy release.

Physical evidence in the form of widespread tuffesites found on the dome gives us further insight into the
explosive mechanism. These represent fractures that were filled with gas-rich magma prior to the eruption. Failureof the capping dome-rock, lead to rapid decompression and fragmentation within these zones. Some ash entered
the eruption column, whilst some re-crystallized to close the cracks, increasing the permeability once more witha new Vulcanian sequence following. A slow growing dome was emplaced between 2007 and June 2011, when
there was a moderate explosion, which destroyed a portion and marked the end of its growth. Then there wasa remarkable quiet period, but after only a 1.5 year hiatus, it resumed activity during January 2013, with further
moderate explosions with magma emplacement within the newly formed crater.

Volcan de Colima represents an excellent case study due to its frequent transitions and interplay between
explosive activity of different magnitudes and effusive eruptions. The understanding of these transitions is critical
for the interpretation of precursory signals and the evaluation of possible eruptive scenarios and their associatedhazards.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

647

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

3A1_2J-O5

Room A6

Date/Time: July 23 9:45-10:00

Does magma rheology control eruption style? The case of Fuego, Guatemala
Alan Whittington1 , Thais Magaldi2 , Amilcar Calderas3 , Gustavo Chigna3 , Rudiger Escobar-Wolf4 , John
Lyons5 , Otoniel Mathias3 , Genevieve Robert1 , Sheila Seaman6
1

Department of Geological Sciences, University of Missouri, USA, 2 Instituto de Geociencias,
Universidade de Brasilia, Brazil, 3 INSIVUMEH, Guatemala, 4 Department of Geological and Mining
Engineering and Sciences, Michigan Technological University, USA, 5 Alaska Volcano Observatory, US
Geological Survey, USA, 6 Department of Geosciences, University of Massachusetts, USA
E-mail: whittingtona@missouri.edu

Volcán Fuego, Guatemala, is a basaltic andesitic stratovolcano that has been in semi-continuous eruption for
more than 500 years. The past decade has been characterized by vulcanian explosions with minor ash emission,
punctuated by strombolian episodes with extrusions of lava flows and rare larger eruptions with pyroclastic flows,
most recently in September 2012. We have investigated 9 samples (4 lava flows, 1 air-cooled bomb, and 4 blocks
transported in pyroclastic flows) erupted or deposited in 2003 and in 2008-9, and all collected from the Barranca
Santa Teresa on Fuego’s western flank, to see if the type of activity (lava flow vs pyroclastic flow generation) can
be correlated with varying physical and chemical properties of the magma. In particular we test the hypothesis thatmagma rheology controls eruptive style, i.e. blocks and bombs should be more viscous than lava flows.

All the samples are highly crystalline, with similar basaltic andesite bulk compositions (52-53 wt.% SiO2 )comprising matrix glass of andesitic to dacitic composition (62-67 wt.% SiO2 ) with abundant plagioclase, olivine
and pyroxene phenocrysts together with minor Fe-Ti oxides. One lava flow "2003c" has a rhyolitic matrix glass(∼74 wt.% SiO2 ). Phenocryst compositions vary little, and show no systematic variation with eruption style. The
matrix (dense-rock) density of the samples also varies little, from ∼2810-2850 kgm-3 ), while bulk density varies
from ∼1480 to ∼2680 kgm-3 , due to porosity. Lava flow samples contain 11-16 vol.% vesicles, while the bombcontains 16 vol.% and blocks range from 5 vol.% (dense) to 48 vol.% (vesicular). Water contents of matrix glasses
vary from ∼0.25 wt.% (bomb) to less than 500 ppm (breadcrust block in a pyroclastic flow). The rheology ofall samples was measured by uniaxial compression at ∼1020°C and 1 atm. In all experiments, regardless ofporosity, the viscosity increased from ∼1010 to ∼1012 Pa.s in a few hours, then increased only slightly for the next
∼80 hours. Lava flow sample 2003c has a slightly (∼0.5 log unit) higher viscosity than other samples. Theseexperiments never exceeded 2% total strain, and overall changes in porosity were negligible, but the proportion ofisolated porosity increased during the experiment, which we attribute to early crack closure.

Despite large variations in vesicularity, and modest variations in matrix glass chemistry and dissolved watercontent, the rheology of blocks, bombs and lava flows is generally identical. We conclude that changes in eruptionstyle do not reflect changes in magma properties. The most likely alternative controls are magma supply rate,
and/or mechanisms related to how lava and hot erupted material accumulates near the summit region, and how
this material may be remobilized as either lava or pyroclastic flows.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

648

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

3A1_2J-O6

Room A6

Date/Time: July 23 10:00-10:15

Reassembling a volcanic conduit using bombs at Cordón Caulle, Chile
Jonathan M Castro1 , C. Ian Schipper3 , Hugh Tuffen2 , Mike James2 , Annemarie Militzer1
1

University of Mainz, Germany, 2 University of Lancaster, UK, 3 Victoria University Wellington, NZ
E-mail: castroj@uni-mainz.de

Active volcanic conduits are not directly observable, however, snapshots of the state of magma feeding varied
eruption styles can be reconstructed from pyroclasts. During the opening weeks of the June, 2011 Cordón Caulle
eruption, hundreds of large (cm’s to m’s) bombs were ejected and deposited up to 2.5 km from the vent. At thistime, activity changed from being explosive to hybrid, involving effusion of obsidian lava along side a pyroclastic
fountain. The bombs at El Caulle provide an unprecedented view into an active conduit that fostered simultaneous
explosive and effusive volcanism.

We examined the physical characteristics of >70 bombs from the flanks of Cordón Caulle, and based onthese observations group them into two general categories. Type I bombs were erupted as dense magma andquenched to form either obsidian or breadcrusted blocks. The dense, flow banded blocks have incipient surface
cracks and etched outer surfaces. Type I breadcrusted bombs occur as many separate fragments that individually
vesiculated after the bomb impacted and broke. Both dense and breadcrusted bombs have white, ash- andpumice-laden tuffisite veins (mm to cm’s) adjoined to their surfaces, indicating that some of the Type I bombs wereactually composites of dense obsidian and juxtaposed ash and pumice domains at the time of their eruption.

Type II bombs are pumiceous with <5 vol% obsidian clasts. These bombs may be partly or wholly brecciated,comprising angular pumice clasts (cm to dm’s) suspended in fine to coarse ash and pumice lapilli. Some Type IIbombs are homogenous pumice blocks that also contain red tuffisite veins cutting through them. Pumice breccia
bombs often have large (dm’s) coalesced vesicles at their centers that cracked the outer bomb surface due to their
expansion after the bomb erupted. These features indicate that despite the bomb’s clastic and porous nature,
brecciated conduit magma must weld to the point of having low permeability—this may, in turn, impede outgassing
to the point of explosive release in the conduit.

The glassy and pumiceous bombs found at Cordón Caulle represent juxtaposed regimes of magma movement anddegassing. Type I facies develops during coherent magma flow through the conduit, while Type II records multiple
fragmentation events and gas-driven flow of clastic bubbly magma. That overlap exists between these facies—thisevidenced by the mixing (inclusion) of pyroclastic and dense elements in Type I and II bombs—suggests that thebombs are sourced from a boundary zone/layer that separates effusively and explosively erupting magma. Thisboundary zone must allow not only physical exchange of pyroclastic and coherent elements, but also chemicaltransfer of exsolved gases between the different magma domains.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

649

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

3A1_2J-O7

Room A6

Date/Time: July 23 10:15-10:30

Explosive expansion of a slowly-decompressed magma analog: evidence of delayed
bubble nucleation
Eleonora Rivalta1 , Karen Pascal2 , Jeremy Phillips3 , Alessandro Bonaccorso4
1

GFZ-Potsdam, Germany, 2 University of Leeds, UK, 3 University of Bristol, UK, 4 INGV, Italy
E-mail: rivalta@gfz-potsdam.de

Slow decompression of magma generally results in an effusive or mildly explosive expansion of the magma,
but counterexamples of sudden switches from effusive to explosive eruptive behaviour have been documented
at various volcanoes worldwide. The mechanisms involved in this behavior are currently debated, in particularregarding basaltic magmas. Here, we explore the interplay between decompression rate and vesiculation vigour bydecompressing a magma analog obtained by dissolving pine resin into acetone in varying proportions. Our mixturescontain solid particles and upon decompression experience the nucleation of acetone bubbles. We find mixtureshigh in acetone, containing smaller and fewer solid particles, experience strong supersaturation and fragment forvery slow decompressions, despite having low viscosity, while mixtures low in acetone, with more and larger solid
particles degas efficiently. We interpret our results in terms of delayed bubble nucleation due to a lack of efficient
nucleation sites. We discuss how a similar mechanism might induce violent, explosive expansion in volatile-richand poorly crystalline low-silica magmas, by analogy to previous inferences for rhyolitic magmas©IAVCEI 2013 Scientific Assembly. All rights reserved.

650

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

4W_2J-P1

Date/Time: July 24 Poster

Explosive versus effusive eruptive activity at Merapi volcano, Java, Indonesia.
Mary-Ann del Marmol1 , Bruce D. Marsh2 , Ralf Gertisser3 , Chris Newhall4 , Supriyati Andreastuti51Dept. of Geology and Soil Science, Ghent University, Belgium, 2 Earth & Planetary Sciences, Johns
Hopkins University, U.S.A., 3 School of Physical and Geographical Sciences and Geography, Keele
University, U.K., 4 Earth Observatory of Singapore, Nanyang Technological University, Singapore,
5
Center for Volcanology and Geological Hazard Mitigation, Indonesia
E-mail: maryann.delmarmol@ugent.be1872 Merapi volcanic activity was even more violent and explosive than the 2010 events (VEI 4). Here we examine
Merapi past explosive versus effusive activity through a detailed analysis of selected lava flows and domes, juvenile
components from different types of pyroclastic flow deposits and lapilli ejecta from sub-plinian-style eruptions,
ranging in age from Proto-Merapi to the recent activity.

The textures, petrology and geochemistry of the older Merapi units are revisited giving particular attention
to the contrast in crystal sizes of the volcanics relative to those of the inclusions and xenoliths as well as to theassociated mineral assemblages and compositions in order to identify the various stages of magma genesis andevolution. Moreover, special attention is given to the 1872 eruptive products and their comparison to the 2010
ejecta.

Crystal size distribution (CSD) theory is applied to obtain information on growth and residence times ofplagioclase crystals in the various magma storage zones in the sub-volcanic plumbing system and to gain
insight on open-system processes such as the frequency of magma replenishment and possible rates of crustal
assimilation. From Intercept-Slope (I-S) relations, in comparison to other large magmatic systems, the staging
zones for some Merapi eruptives appear to be similarly extensive in terms of volume and longevity. This suggests
that, in addition to understanding eruption mechanics, the eruptive record of Merapi may also be valuable inunderstanding the ongoing evolution of other major magma chambers.

Coupled with petrographic results, like a freshly-crystallized amphibole observed in the 2010 deposits (Costa etal., 2013 and Preece et al., 2013) and in older deposits, it may provide a clue to the identification of precursors
for very explosive events (VEI 4) by carrying the signature of a large, undegassed magmatic batch from a source
deeper than where 20thcentury lava dome magmas were stored before extrusion.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

651

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

4W_2J-P2

Date/Time: July 24 Poster

Textural and Mineral Chemistry Constraints On Evolution of Merapi Volcano, Indonesia
Sabrina Innocenti2 , Mary-Ann del Marmol1 , Barry Voight2 , Supriyati Andreastuti3 , Tanya Furman2
1

Dept. of Geology and Soil Science, Ghent University, Belgium, 2 Dept of Geosciences, Pennsylvania
State University, U.S.A., 3 Center for Volcanology and Geological Hazard Mitigation, Indonesia
E-mail: maryann.delmarmol@ugent.be

We analyze and compare the textures of Merapi lavas (basalts and basaltic andesites) ranging in age fromProto-Merapi through modern activity, with the goal of gaining insights on the temporal evolution of Merapi magmatic
system. Analysis of textural parameters, such as phenocryst and microphenocryst crystallinity, coupled with crystal
size distribution theory, provides information about the storage and transport of magmas. We combine textural
analyses with geochemical investigations for a comprehensive comparison of erupted lavas over time. The chemical
analyses identify crystal growth processes in the magma chamber and underline differences between sample
groups. We analyze also the textures and mineralogy of Merapi tephra generated during explosive eruptions with
VEI 3-4, and compare these data to those observed for Merapi dome and flow lavas. We find that the Merapi tephra
and lava textures differ significantly with respect to small-size crystal populations, but that phenocryst textures are
generally similar. A similar initial phase of crystallization is indicated for tephras and lavas in mid-crustal reservoirs.
Subsequent textural differences are mainly affected by ascent rate and degassing during ascent, and, for dome
lavas, with temporary storage in a shallow reservoir. These differences correspond to different eruptive styles.
In general, comparison of the crystal size distributions and calculated residence times among the effusive andexplosive eruptive styles indicates that the two magma types resided for a similar length of time in a mid-crustal
reservoir, before ascending toward the surface and either erupting (tephra), or stagnating in a shallow magma
chamber (lava). The interpretation is supported by the occurrence of amphibole in pristine condition (tephra) or
altered state (lava). Dome lavas from the 20th century eruptive activity indicate steady-state, open-system behavior,
while samples from the stratigraphic history of Merapi record both repeated attainment and loss of steady-state
conditions. This observation suggests that the relatively benign activity of the 20th century will be interrupted fromtime to time by more explosive eruptions such as that of 2010.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

652

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

4W_2J-P3

Date/Time: July 24 Poster

Effects of magma and conduit conditions on transitions between effusive and explosive
activity: A numerical modeling approach to illuminate the 2006-2010 activity at Merapi
Volcano, Indonesia
Brett B. Carr1 , Amanda B. Clarke1 , Mattia De’ Michieli Vitturi2 , Barry Voight3
1

SESE, Arizona State University, Tempe, AZ, United States of America, 2 Sezione di Pisa, Instituto
Nazionale di Geofisica e Vulcanologia, Italy, 3 Department of Geosciences, Pennsylvania State
University, University Park, PA, United States of America
E-mail: bbcarr@asu.edu

Transitions between effusive and explosive eruptions, common at silicic volcanoes, can occur between distinct
eruptive episodes or can occur with switches between effusive and explosive phases in a single episode. The
precise causes of these transitions are difficult to determine due to the multitude of mechanisms and variables that
can influence fragmentation thresholds. Numerical modeling of magma ascent within a volcanic conduit allows theinfluence of key variables to be extensively tested. We use a conservative, 1-D, two-phase, steady-state modelthat allows for lateral gas loss at shallow depths to study the effect of different variables on the mass eruption
rate at the vent. We use a fragmentation criteria based on gas volume fraction. We are able to generate anumber of regime diagrams for a variety of magma and conduit conditions that constrain transitions from effusive
to explosive episodes. For constant conduit geometry, initial magma crystal content and chamber overpressure
have the greatest effect on the mass eruption rate. We apply our model to the recent activity at Merapi Volcano
in Indonesia. We constrain model input and output parameters using current petrologic, seismic, and geodetic
studies of the Merapi system, and vary critical parameters over reasonable ranges as documented in the literature.
Our model is able to reproduce eruption rates observed during both the 2006 effusive and 2010 explosive/effusive
eruptions. Our modeling suggests a combination of overpressure, increased volatile content, and decreased crystal
content due to the voluminous injection of new magma into the shallow Merapi system is the plausible cause of
explosivity in the 2010 eruption, the most violent at Merapi since 1872. Transitions in eruptive activity were also
observed during the 2010 eruptive sequence, where explosive episodes lasting on a scale of hours alternated withlonger periods of rapid effusive dome growth. Our modeling suggests these transitions can be plausibly controlledby (1) the degassing behavior of the shallow conduit system without needing to change the magma supply rate
into the conduit from the chamber, or (2) alternating conduit magma batches with different H2O content that reflect
converging extraction patterns in a volatile-heterogeneous chamber. The latter condition reflects the inevitability fora large eruption to sample, nearly simultaneously, from a wide vertical and horizontal range of locations in a zoned
chamber.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

653

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

4W_2J-P4

Date/Time: July 24 Poster

Evolution of conduit flow during the 2011 eruption of Shinmoe-dake, Japan-insights into
cyclic sub-Plinian activity and shifting eruption style of andesite magma
Yuki Suzuki1 , Fukashi Maeno1 , Masashi Nagai2 , Setsuya Nakada1 , Mie Ichihara1
1

Earthquake Research Institute, Univ. of Tokyo, Japan, 2 National Research Institute for Earth Scienceand Disaster Prevention, Japan
E-mail: ysuzuki@eri.u-tokyo.ac.jp

The climactic phase of the 2011 eruption of Shinmoe–dake is characterized by sub–Plinian eruptions (Jan 26–27)
and lava accumulation in the crater (Jan 28–31), both of which accompanied vulcanian eruptions (Nakada et al., inreview). Referring real–time observatory data on crater image, tremor and infrasound (Ichihara et al., in review) andtilt variation (e.g. Kozono et al., in review), a geological study (Maeno et al., in review) showed three sub–Plinian
events (26PM, 27AM and 27PM, the most intense phase of each lasted 2.5–1.7 hours) occurred every 12 hours
with a decrease of erupted magma volume and with a constant mass discharge rate. This study reveals evolutionof conduit flow through the climactic phase, by combining, a) records in groundmass microlite and vesicle texturesand b) the above–mentioned, time–resolved observatory results. Based on a petrological result (Suzuki et al.,in review JVGR), we judge that variable groundmass textures among the samples reflect different conditions insyneruptive magma ascent, not different characteristics of the magma at the reservoir. Although most ejecta (grayand brown ones as to pumice clasts) are products of magma mixing that resulted from syneruptive injection ofbasaltic andesite magma into a silicic andesite magma reservoir, the mixed magmas were homogeneous in thereservoir (SiO2 57–58 wt.%, 30vol.% phenocrysts, 960–980C, 4wt.% H2 O) owing to constant mixing ratio. The
volcanological questions we would like to address after we reveal evolution of conduit flow through the climactic
phase are, 1) mechanisms that led to the cyclic sub–Plinian eruption, including triggering processes of each event,2) timing and conditions of syneruptive magma ascent that are responsible for the shifting eruption intensity andthe eruption style (explosive and effusive). We expect this groundmass textural study also helps us newly define aboundary between the 26PM and 27AM pumice deposits. The corresponding deposit exhibits reverse and normal
gradings, as if it was generated in a single event (Maeno et al., in review, Nakada et al., in review). Regardlessof that, the groundmass textures of the samples may record waxing and waning phases of conduit magma flow ineach sub-Plinian event.

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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_2J-P5

Date/Time: July 24 Poster

Unsteady and steady phases of the Kaharoa 1314 eruption, Tarawera volcano, New
ZealandRebecca J Carey1 , Bruce F Houghton2 , Samantha J Weaver2 , Steve Self3
1

ARC Centre of Excellence in Ore Deposit Research, School of Earth Sciences, University of
Tasmania, Australia, 2 Dept. Geology and Geophysics, University of Hawaii at Manoa, Hawaii, USA,
3
Volcano Dynamics Group, The Open University, UK
E-mail: rebecca.carey@utas.edu.au

The 5 km3 Kaharoa eruption of AD1314 was a prolonged rhyolitic eruption (ca. 5 years) involving at least
7 source vents located along an 8 km long fissure transecting a pre existing dome complex. Following ventopening explosions, seven early powerful pyroclastic fall phases formed tephra lobes dispersed to the SE withminor pyroclastic explosive activity. The eruption deposits have characteristics typical of both subplinian-Plinian(absolute intensity, duration) and Vulcanian styles (multiple explosive phases, dense juvenile clasts, grain sizefluctuations). These characteristics are not compatible with end-member models of either rapid ascent (Plinian),or short lived, low intensity (Vulcanian) explosions. Each pumice fall unit is separated by partings rich in fineash, interpreted to represent short quiescence intervals between eruptive phases. Within fall units, grainsize andjuvenile clast density measurements taken on a bed by bed basis provide a high-resolution eruption chronologythat implies the degree of "steadiness" (or instantaneous mass discharge rates) of the eruptive phases.Two fallout
units were chosen to represent "unsteady" and "steady" eruption conditions. We use clast microtextures combined
and analytical measurements to evaluate the parameters that drive steady vs. unsteady silicic explosive eruptions.
Initial microtextural observations reveal that the partial outgassing of the magma column in the conduit was a criticalfactor in driving unsteady eruptions. Additionally, high density (greater than 1600 kgm-3) juvenile clasts increasein size and abundance during unsteady phases suggesting evacuation of stagnant melt within the conduit, plug ordome. Our juvenile clast density analysis also shows evidence for the existence of a protodome or plug in the active
vent at an earlier stage of the eruption than initially postulated.

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