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

0P1_3D-O1

Room B1

Date/Time: July 20 14:30-14:45

Eruption model of bromo volcano, east java, indonesia, in the 2011 eruption
Akhmad Zaennudin
Geological Agency of Indonesia, Indonesia
E-mail: azaennudin@gmail.com

Bromo volcano is one of six volcanic cones inside the Sand Sea Caldera of Tengger volcanic complex. It is one of
the most active volcanoes in Indonesia since four decades ago. The eruption gab time is between several months
up to 16 years with duration in several days until several months. The eruption of 2011 was six years dormant after
the phreatic eruption of June 8, 2004, and it took place about eight months as the longest period of eruption inhistorical time record. In this eruption period at least there were three times of new injected magma recognized
as long as in one year before triggering the eruption. The first eruption occurred in late of November 2010 until
the middle of December 2010 by mild phreatic eruptions and then followed by phreatomagmatic eruptions for the
next step. The phreatomagmatic eruption ejected continually of the fine materials dominated and deposited insurrounding area up to 40 km from the crater, but the worst area that covered by thick ash deposit is only 10 km
in radius with 50 cm thick. The eruption was reflected by mixture of lithic and juvenile fragments together in theejected materials of the eruption as the fragmentation of magma due to contacted with ground water beneath. The
eruption sequence was the main eruption step of 2011 Bromo eruption. A big eruption on February 5, 2011 is as
the end of the phreatomagmatic eruption that was reflected by destroying of a lava plug. The fragments of lava
plug of 50 cm in diameter were landed around 1,200 m from the crater. Due to damaging of lava plug in the conduit
finally movement of magma from beneath is undisturbed and on February 8, 2011 was shown a fire sparkles like a
big fire fox on the Bromo crater. It is the beginning of the strombolian eruptions until the end of the Bromo eruptionin July 2011.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

840

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

0P1_3D-O2

Room B1

Date/Time: July 20 14:45-15:00

Drilling of a volcanic conduit beneath the Hiyoriyama Cryptodome, Kuttara Volcano,
Hokkaido, Japan
Yoshihiko Goto1 , Setsuya Nakada2 , Hiroaki Sato3 , Sumio Sakuma4
1

Muroran Institute of Technology, Japan, 2 University of Tokyo, Japan, 3 Kobe University, Japan,
4
Geothermal Engineering, Co., Ltd., Japan
E-mail: ygoto@mmm.muroran-it.ac.jp

Hiyoriyama, located in Kuttara Volcano, Hokkaido, Japan, is a Quaternary dacitic cryptodome (350-550 m across,
130 m high), with active fumaroles at the summit. The cryptodome consists of augite-hypersthene dacite (SiO2:
70 wt. percent) that contains abundant mafic enclaves (SiO2: 57-59 wt. percent). Fission-track dating of thedacite suggests that the dome formed at 15 ka. In FY 2009-2010, a 350-m-long hole (the MIT-NB-5 hole) was
drilled on a slanted trajectory passing beneath the centre of the cryptodome to study its feeder conduit. The drill
rig was set at 200 m northeast of the dome, and the angle of the drilling was 41-50 degree from vertical. The
drilling succeeded to penetrate the conduit zone at 300-310 m in drilled depth, and to recover boring cores between
18 and 350 m (core recovery 97 percent). The principal lithofacies of the MIT-NB-5 cores are pyroclastic deposits,
coherent andesite and volcaniclastic veins (tuffisite veins). The pyroclastic deposits occur at 18-300 m and 310-350
m and comprise a succession of pumice flow deposits, pumice fall deposits, and base surge deposits. These
pyroclastic deposits are inferred to have exploded from the Kuttara Volcano at 40 ka. The coherent andesite facies
occurs at 300-310 m and has sharp contacts with the pyroclastic deposits. The andesite is massive, porphyritic,hydrothermaly altered and contains 57-62 wt. percent in SiO2. This facies is interpreted as a dyke intruded into the
pyroclastic deposits. The dyke width, calculated from the core length (9.8 m) and drill-hole angle (41 degree), is 6.4
m. The volcaniclastic veins occur within the coherent andesite and in the pyroclastic deposits between 291 and 315
m. The total number of the veins is 30. The volcaniclastic veins are platy, zigzag or Y-shaped, up to 20 cm wide,and composed of subangular lithic and mineral fragments up to 2 cm across. They are hydrothermaly altered andcommonly have pyrite-rich, alteration zones on either side of the veins. The volcaniclastic veins are inferred to haveformed by injection of high-temperature fluid and entrained particles into temporally opening fractures. Despite thecompositional contrast between the dome dacite (SiO2: 70 wt. percent) and the coherent andesite (SiO2: 57-62
wt. percent), we infer that the coherent andesite facies is the feeder conduit (dyke) of the dome, because (1)this facies is positioned just below the summit of the dome; (2) this facies and the adjacent pyroclastic deposits
contains numerous volcaniclastic veins; and (3) this facies is almost identical in composition to the mafic enclaves(SiO2: 57-59 wt. percent) in the dome dacite. The compositional contrast between the dome (mainly dacite) andthe feeder dyke (andesite) can be explained by magma ascent from a zoned magma chamber, consisting of upper
dacitic magma and lower andesitic magma.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

841

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

0P1_3D-O3

Room B1

Date/Time: July 20 15:00-15:15

The fissure eruptions of Fuji Volcano, Japan, during the last 10,000 years
Akira Takada, Takahiro Yamamoto, Yoshihiro Ishizuka, Shun Nakano
Geological Survey of Japan, AIST, Japan
E-mail: a-takada@aist.go.jp

Fuji Volcano, 3776m high, Central Japan, is the largest basaltic volcano in Japan, and located at the plate boundary
between the North American Plate and Eurasian Plate. The magma plumbing system develops in the Philippine
Sea Plate subducting beneath the above two plates. This paper discuss the effect of the stress field beneath
Fuji volcano using eruptive fissures. The fissure eruption sites are good indicators to know the local stress filed
in and beneath the volcano as well as the regional stress one. The local stress makes the feedback system onmagma supply system in the shallow crust. The evolution of distribution on fissure eruption sites of Fuji Volcano
suggests the restriction of eruption sites, that is, producing the more compressive condition around its own magma
plumbing system. The fissure eruption sites younger than Cal BC 10,000 are easy to recognize on outcrops orusing trenching survey. GSJ determined the ages of fissure eruption sites using trenching survey with 14C ages
(Takada et al., 2007; Ishizuka et al., 2007; Nakano et al., 2007, Suzuki et al., 2007; Kobayashi et al, 2007). Fissure
eruptions occurred at various azimuths during the period of Cal BC 10,000-6,000. The volcano became active
again after a low activity period during the period of Cal BC 6,000-3,600 to construct the recent edifice with flank
eruptions of various azimuths during the period of BC 3,600-1,500 (Yamamoto et al., 2005). The eruption sites
became restricted to the summit to cause explosive eruptions during the period of Cal BC 1,500-300. The lastsummit explosive eruption was followed only by flank eruptions on the restricted flanks during the last 2,300 years.
The dominant trend of the eruptive fissures is generally NW-SE, which is concordant to the axis of the regional
maximum horizontal compressive stress filed. The eastern flank, however, caused a lot of fissure eruptions during
the period of Cal BC 300-1100 (Yamamoto et al., 2011). In addition to the easter flank, the frequency of flank
eruption became high on the NW and SE flanks during the Cal AD 700-1100 (Takada et al., 2007). After theeffusive Jogan 864-866 eruption at the restricted vent, the eruptive fissures shifted its trend to NS during Cal AD
900-1100 (Yamamoto et al.,2005; Takada et al., 2007). The existence of high-level magma head is supported byhigh-level fissure eruption site up to 3,500 m-high just beneath the summit crater. Some of the fissure eruptions
may have been caused by drain back. A decrease in explosively has relation to continuous degassing at the summit
during AD 700-1200. The volcanic activity became low during Cal AD 1200-1700 before the last Hoei explosive
eruption.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

842

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

0P1_3D-O4

Room B1

Date/Time: July 20 15:15-15:30

Numerical simulations of magma intrusion into crust near the surface by means of
discrete element method
Shigekazu Kusumoto
Graduate School of Science and Engineering for Research, University of Toyama, Japan
E-mail: kusu@sci.u-toyama.ac.jp

We employed the software PFC2D (Particle Flow Code in 2 Dimensions) based on the discrete element method
and attempted to simulate magma intrusion into crust near the surface. Although behaviors (e.g., initiation of ashallow magma chamber and formation of a sill) of the intruded magma depend on various factors, here we paid
attention to the intrusion magma velocity, which reflects overpressure conditions.
In discrete element modeling, all materials are approximated as assemblies of many particles, and each particle
is connected by two elastic springs (having normal and shear stiffness). In addition, "contact bond" parameters
for determining the strength of material (rock) must be set between all adjacent particles. By trial and error, theseparameters are determined by biaxial test in a computer. A Young modulus of 16 GPa and a Poisson ratio of
0.21, as elastic constants of the surface crust, and viscosities in range of 107 - 1010 Pa s, for middle-high viscousmagma, were assumed in this study. The normal and shear contact bonds for intruded magma were not set inorder to maintain fluidity.
Before applying the above-mentioned magma model to simulations of magma intrusion into the crust, extrusions
to the surface of these magma were simulated in order to confirm whether the magma model behaves realistically.
As a result, it was shown that the shape of extruded magma (lava) depends on the viscosity of the magma and its
flow velocity in the conduit. The high viscous magma makes a lava dome at the surface and its interior structure is
distorted concentric circle patterns. These structures due to the high viscous magma have been simulated by someanalogue experiments. From these pre-simulation results, it was concluded that the developed magma model was
suitable for simulations of magma intrusion.
As a preliminary simulation model for magma intrusion, we modeled the surface crust by a rectangle of widthand depth 5 and 1.6 km, respectively. The radius and density of the particles constituting the model crust wereassumed to be 4.8 - 6.4 m and 2500 kg/m3 , respectively. The radius and density of the particles constituting themodel magma were assumed to be 0.8 - 0.96 m and 2200 kg/m3 , respectively, and a probable intrusion velocity
was given to the particles. The volume of the intruded magma was set to 2 105 m3 in all simulations. As a result,it was found that the shape of the intruded magma was circular at an initial stage of intrusion, and that this initial
shape did not depend on the intrusion velocity. However, the subsequent change in the shape over time did dependon the velocity. A low velocity made the intruded magma become elliptical, elongating upward and deforming thesurface greatly over a wide area. In contrast, a high velocity made the magma intrude into a circular shape, thelower parts of which elongated sideways, or in a rounded triangular shape.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

843

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

0P1_3D-O5

Room B1

Date/Time: July 20 15:30-16:00

Stress and strain distribution in the shallow crust during dyke and sill emplacement
Janine L Kavanagh1 , David A Boutelier2 , Alexander R Cruden2
1

University of Liverpool, UK, 2 Monash University, Australia
E-mail: janine.kavanagh@liverpool.ac.uk

The mechanics of sill formation are important for understanding magma distribution within the shallow crust andthe tendency for these magmas to intrude or erupt. We present a series of layered gelatine analogue experiments
monitored with a Particle Image Velocimetry (PIV) system to document the small-scale deformation processes in thehost material during dyke and sill emplacement. Experiments are prepared comprising multiple layers, with small
strength contrasts (comparable to those between crustal strata) created by varying the gelatine concentration andallowing sufficient time for it to reach its Young’s modulus plateau. Injection of dyed water (the magma analogue)
into the solid gelatine from below causes a vertically propagating penny-shaped experimental dyke to form. A
horizontal sill then forms along a weak contact beneath a more rigid layer. To monitor displacements within thegelatine using the PIV technique, neutrally buoyant fluorescing particles are added to the gelatine during experimentpreparation. Two high-speed cameras are positioned outside the tank in a plane perpendicular to the strike of theexperimental feeder dyke, and parallel to a vertical high-power laser sheet that fluoresces the particles in thegelatine with short intense pulses. The cameras and laser sheet are triggered so that images are recorded at
known time intervals. Incremental displacement vectors are calculated by cross-correlation between successive
images. Spatial derivatives of the velocity field yield map the gelatine’s 2-D strain components within the laser
sheet. As the gelatine deforms elastically, the calculated strain correlates with the stress distribution. PIV provides
new insights into the dynamics of sill formation by allowing small-scale stress and strain perturbations within thehost gelatine layers to be measured for the first time at the time of sill inception. These experiments highlight thestress and strain partitioning that occurs between layers of contrasting elastic properties during intrusion, and theimportant role this plays in sill initiation.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

844

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

0P1_3D-O6

Room B1

Date/Time: July 20 16:00-16:15

Energy sources, behaviour, and durations of volcanic eruptions
Agust Gudmundsson1 , Nahid Mohajeri2
1

Department of Earth Sciences, University of London Royal Holloway, UK, 2 Department of Geography,
University College London, UK
E-mail: rock.fractures@googlemail.com

Why are some eruptions of long duration and others of very short duration? Why do some eruptions of shortduration produce much more eruptive materials than other eruptions of much longer duration? Why do mostvolumetric flow rates (effusive rates in the case of lava production) decline rapidly after the peak, whereas somedecline much more slowly? These are all fundamental questions in theoretical and applied volcanology that need
to be answered in order to forecast the likely behaviour and duration of an eruption once it has started.
Thermodynamically, all volcanoes are open systems; they exchange heat and materials with their surroundings. Foran eruption to occur, there must be sufficient energy within the volcano to propagate a feeder dyke to the surface.
Furthermore, for a significant volume of magma to be issued during an eruption, there must be energy available topress the magma out of the chamber and to the surface. Here we provide energy models to explain (1) the durationof eruptions, as well as their (2) volumetric flow rates, (3) behaviour, and (4) the eruptive-volume size distributions.
We show that the primary energy responsible for feeder-dyke formation is elastic energy, which consists of twoparts: (1) the strain energy stored in the volcano before magma-chamber rupture and (2) the work done throughdisplacement of the flanks of the volcano and the expansion/shrinkage of the magma chamber itself. Largevolumetric flow rates are related to the size of the aperture of volcanic fissure, the magmatic overpressure, andthe work done through the displacement of the flanks of the volcano.
In the absence of a collapse caldera formation, the duration of an eruption (from a chamber of a given size) is
primarily related to the chamber excess pressure, which can be maintained for a considerable time (giving rise toeruptions of long duration) depending on several factors. These factors include (1) flow of new magma (from adeeper reservoir) into the shallow chamber during the eruption; (2) gas exsolution and expansion in the chamber
during the eruption; and (3) shrinkage (volume reduction) of the chamber during the eruption.
Normally, the rate of inflow of new magma into a shallow chamber is too low to have significant effects on the
duration of the eruption. Gas exsolution and expansion is certainly one of the fundamental factors for determining
the duration and volumetric flow rate of eruptions issuing evolved magmas, but is much less so for primitive magmas.
Elastic, and inelastic, shrinkage of the magma chamber is a major factor contributing to the duration and volumetricflow rate of an eruption. The rate and size of shrinkage depends on the strain energy stored in the volcano before
the eruption. We show that stratovolcanoes generally store more elastic energy, per unit rock volume, than basaltic
edifices, a fact that partly explains their commonly widely different behaviour during eruptions.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

845

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

0P2_3D-O7

Room B1

Date/Time: July 20 16:30-16:45

Structural variation of the feeder dikes of explosive eruptions in Miyakejima, Japan
Nobuo Geshi, Teruki Oikawa
Geological Survey of Japan, AIST, Japan
E-mail: geshi-nob@aist.go.jp

Basaltic eruptions exhibit wide variation about its explosivity, from stable lava effusion, mild-violent strombolian
eruption, to plinian eruption. Complex behavior of magma during flow within the conduit may one of the controls of
the style of the eruption activities, and the structure of the conduit may also control the behavior of the ascending
magma through the conduit.
We describe various type of the cross section of vent, from feeder dike to its surface products, in the caldera wall of
Miyakejima, Japan. Many basaltic dikes fed fissure eruptions in Miyakejima during the last 10,000 years. The AD
2000 caldera truncated a basaltic stratovolcano with numerous feeder and non-feeder dikes. The depth of diatreme
and the horizontal size of its pyroclastic cone represent the difference of explosivity. Some feeder dikes connect
directly to the lava flow without any pyroclastic cone, indicating the effusive eruption. Some feeder dikes connect
to pyroclastic deposit, indicating pyroclastic eruption. Some feeder dikes connect to the base of small and conicalscoria cone, with 100- 200 meters across and several tens meters high. Size and internal structure of the scoria
cone indicates the mild strombolian activity. Uppermost ten meters of these feeder dikes shows upward-flaring(widen the dike thickness to the surface), which infers the magmatic erosion of the dike wall by explosive activities
within the conduit. More explosive activities formed some diatremes. The depth of these diatreme reaches 100
meters from the original ground surface. Typically, these diatremes connect to very-flat scoria cone and wide-spreadthick scoria-fall deposit, which indicates the highly explosive activities. The sizes of these flat scoria cones arecomparable to that of the scoria cones which was built by sub-plinian eruption (e.g., Izu-Oshima 1986). Upward
flaring structure of the diatreme indicates the effective mechanical erosion of the dike wall by the explosive activities.
The wider feeder dikes for lager diatreme suggests the higher magmatic overpressure for the explosive activities
in comparison to the less-explosive feeder dikes. Comparison of the structures of these feeder dikes indicatesthat the variation of the depth of fragmentation (or explosion) controls the explosivity of the basaltic eruption.
The fragmentation depth of mild strombolian feeders are relatively shallow (<10 m), whereas the deep rooted
diatreme of the sub-plinian feeders indicates the deep fragmentation more than 100 meters from the original groundsurface. The structural variation of feeder dikes suggests that the differences of magmatic overpressure and thefragmentation depth may control the eruption behavior.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

846

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

0P2_3D-O8

Room B1

Date/Time: July 20 16:45-17:15

Physical characteristics of kimberlite and basaltic intraplate volcanism, and implicationsof a biased kimberlite record
Richard J Brown1 , Greg A Valentine2
1

Durham University, UK, 2 University of Buffalo, USA
E-mail: richard.brown3@durham.ac.uk

Kimberlite volcanoes are rarely preserved in the geological record and much of what we understand about theeruption of kimberlite magmas has been deduced from studies of sub-volcanic structures and deposits. This
presents us with problems because the surface products that are commonly used to infer eruptive processes atother volcanoes have been removed. We have investigated bias in the record of kimberlite volcanism by using
newly acquired size data on over 900 kimberlite bodies from 12 kimberlite fields eroded to depths estimated to be
between 0 m to 1200 m, and by a cautious comparison with intraplate monogenetic basaltic volcanic fields. Eroded
kimberlite fields are composed of pipes, or diatremes, and dikes and within any one kimberlite field, regardless oferosion level, kimberlite bodies vary in area at the Earth’s surface over 2 to 3 orders of magnitude. Typically 60 to 70
percent of the bodies are less than 10 percent of the area of the largest body in the field. The data indicate that the
selective removal of surface volcanic structures and deposits by erosion may have distorted the geological record ofkimberlite volcanism. Selective mining of preferentially large, diamondiferous kimberlite pipes and underreportingof small kimberlite pipes and dikes adds further bias. A comparison of kimberlite volcanic fields with intraplatemonogenetic basaltic volcanic fields indicates that both types of volcanism overlap in terms of field size, volcano
number and size, and typical erupted volumes. Eroded monogenetic basaltic fields comprise dikes that fed effusive
and weakly explosive surface eruptions, and diatremes generated during phreatomagmatic eruptions, and are
structurally similar to eroded kimberlite fields. Published data suggests that kimberlite magmas can erupt in a variety
of ways and that most data, gathered from the largest kimberlite pipes, may not be representative of kimberlite
volcanism as a whole.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

847

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

0P2_3D-O9

Room B1

Date/Time: July 20 17:15-17:30

Fragments within fragments: are composite bombs hints of weakness or sustained
violence?
James D L White
University of Otago, New ZealandE-mail: james.white@otago.ac.nz

Bombs and lapilli containing or consisting of smaller fragments are composite clasts, and are produced in many
mafic eruptions. They have been attributed to accretion of highly fluid pyroclasts in gas suspensions of either
conduits or plumes, to hot-state vent/conduit recycling of pyroclasts, and depositional amalgamation. It is important
to distinguish composite clasts formed within sustained eruption columns from the others because the hazard anddepositional footprint of the former is much larger. Bombs in some inferred gas-rich systems are argued to growby particle collisions under thermal conditions that allow surface-tension reshaping, requiring assembly of bombs
while immersed in a gas jet. The jet is also considered to elutriate, rather than accrete, fine ash. Suspension of a
20 cm bomb in gas-rich particle-poor conduit flow or in gas-thrust regions of plumes requires sustained velocities
associated with "violent Strombolian" eruptions that blanket many tens of square kilometres with decimetres-thickdeposits. Basaltic to nephelenitic bombs formed by discrete explosions in conduits characteristicstically containwallrock fragments. The explosions fragment fluid magma and wallrock but are ineffective in clearing the material
from the conduit or vent. This general mechanism requires discrete explosions, and implies limited particle
dispersal. Composite fragments from maar-diatreme environments of nephelenitic to basaltic tholeiitic compositions
are typically country-rock rich and display a variety of textures, surface features, and styles of assembly. Bombs at
Rotomahana incorporated many fragments that show minimal thermal alteration and must have been assembled
and cooled over short timescales. Associated with fragmentation zones in Hopi Buttes maar-diatremes, arecomposite bombs and a variety of clastogenic lithic-rich coherent rocks, whereas in the Karoo province suchcomposite clasts accompany lithic-rich lava flows. Composite fragments in the Antaractic Ferrar province arepresent in pyroclastic flow deposits of substantial extent, but also with locally dispersed layers; plume-fed fall
deposits are not significant. The most consistent feature of reported composite clasts is their occurrence inmafic-intermediate to ultramafic cones or maar/diatremes, and not associated with dispersed fall deposits. The
range of magma types and volcanic environments with composite bombs argues against an origin dependent on
unusually fluid magmas or extreme eruption conditions. Weak dispersal of fragments formed in discrete explosions
allows fallback and amalgamation or re-incorporation into magma of first-generation fragments, re-ejected bysubsequent explosions as lapilli or bombs. Where fragmentation also produces wallrock fragments, these areincorporated into the composite fragments.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

848

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

0P2_3D-O10

Room B1

Date/Time: July 20 17:30-17:45

Linking maar eruptions with diatremes: experimental insights from single and multiple
buried explosions
Pierre-Simon Ross1 , James D.L. White2 , Greg A. Valentine3 , Jacopo Taddeucci4 , Ingo Sonder3 , Robin
G. Andrews2
1

Centre Eau Terre Environnement, Institut national de la recherche scientifique (INRS), Canada,
Geology Department, University of Otago, New Zealand, 3 Department of Geology and Center for
Geohazards Studies, University at Buffalo, USA, 4 Istituto Nazionale di Geofisica e Vulcanologia (INGV),
Italy
2

E-mail: rossps@ete.inrs.ca

Maar-diatreme eruptions are hazardous to people and infrastructure; kimberlitic diatremes can also containdiamonds so they are economically important. Yet processes occurring in the subsurface diatreme and theirrelation to surface eruptions are not yet well understood. Previous laboratory studies have addressed different
types of potential ’diatreme-forming’ processes, whereas previous field-scale experimental studies have addressed
cratering but without significant focus on sub-crater deposits, and only for single explosions. We conducted
field-scale experiments at the Geohazards Field Station (University at Buffalo, NY) using single and multiple buried
chemical explosions in a prepared, layered granular substrate. The explosions produced craters, extra-crater
deposits and sub-crater deposits analogous to volcanic maar craters, tephra rings and incipient diatremes.

We excavated a series of vertical cross-sections through the deposits after the explosions. This revealed asignificant zone of sub-crater deposits, extending several decimeters below the post-shot craters. Videos of theexperiments show vertical ejection and fallback of material, especially for the explosions that occurred below
optimal depth of burial. In other words, the majority of the material which formed these eruptive plumes fell backdirectly into the transient explosion craters. The sub-crater deposits have an upper zone containing domains
sourced from different substrate depths, and an underlying zone distinguished primarily by being more loosely
packed than the original substrate. We infer that much of the loosely packed material was disassembled, verticallytransported to different heights during the explosions, then fell back without significant relative lateral movement ofgrains. One explosion ejected material from the deepest substrate horizon, but it was redeposited only within thecrater and is unrepresented in the ejecta ring.

Implications of the experiments for maar-diatreme volcanoes are as follows: (1) vertical focusing of deep
explosions in the diatreme explains the deficit of deep wallrock lithics observed at maar volcanoes; (2) direct
vertical fallback is possibly a major process forming diatreme deposits; (3) direct fallback from numerous explosions
at various depths and lateral positions would eventually produce a diatreme fill that looks "well mixed" overall; (4)even in our limited simulation the number and scaled depth of explosions clearly affect diatreme size and structure.
While representing a pilot study, these initial results already advance our understanding of explosive cratering andhave implications for understanding how some features of maar-diatreme volcanoes and some kimberlite pipes
form.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

849

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

0P2_3D-O11

Room B1

Date/Time: July 20 17:45-18:15

Volcanic jets, plumes and collapsing fountains: evidence from large-scale experiments,
with particular emphasis on the entrainment rate.
Pierfrancesco Dellino1 , Fabio Dioguardi1 , Daniela Mele1 , D’addabbo Maria1 , Bernd Zimanowski2 , Ralf
Buettner2 , Domenico M Doronzo3 , Ingo Sonder3 , Roberto Sulpizio1 , Tobias Duerig2 , Luigi La Volpe1
1

Dipartimento di Scienze della Terra e Geoambientali, Italy, 2 University of Wuerzburg, Germany,3
University of Buffalo, USA
E-mail: pierfrancesco.dellino@uniba.it

The source conditions of volcanic plumes and collapsing fountains are investigated by means of large-scale
experiments. On experiments, gas-particle jets issuing from a cylindrical conduit are forced into the atmosphere bya variable mass flow rate. Dense jets (high particle volumetric concentration) generate collapsing fountains whose
height scales with the squared exit velocity. This is consistent with Bernoulli’s equation and means that kinetic
energy is transformed into potential energy without loss against friction with the atmosphere. The dense collapsing
fountain, on hitting the ground, generates an intense shear flow similar to pyroclastic density currents. Dilute
hot jets (low particle volumetric concentration) reach a height much smaller than that resulting from Bernoulli’s
equation, meaning that part of the kinetic energy is lost through friction with the atmosphere. This causes a
significant air entrainment and dilution, which leads to the formation of a buoyant column (plume) resulting inparticles settling from its margin, similar to pyroclastic fallout. By means of the functional relationship between theinitial densiometric Froude number and normalized height, the scaling of experiments is compared with data of therecent fluid-dynamics literature.
In order to assess the different entrainment rate between collapsing fountains and plumes, experiments were
investigated by quantitative video analysis. Results show that dense collapsing fountains are formed only when
air entrainment is not significant. Cold dilute experiments result in an entrainment coefficient of about 0.06, which
is typical of pure jets in fluid-dynamics. Hot dilute runs result in an entrainment coefficient of about 0.11, which istypical of plumes.
An initial densiometric Froude number of 3 sets the limit between dense collapsing fountains and dilute jets-plumes.
We use this value for obtaining a diagram of the stability fields of pyroclastic density currents and pyroclastic fallout.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

850

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

1W_3D-P1

Date/Time: July 21 Poster

Insights on a new pattern of dyke propagation in volcanic edifices
Claudia Corazzato1 , Alessandro Tibaldi1 , Fabio Luca Bonali1 , Federica Lanza2
1

Department of Earth and Environmental Sciences, University of Milan-Bicocca, Italy, 2 Department of
Geological and Mining Engineering and Science, Michigan Technological University, United States
E-mail: claudia.corazzato@unimib.it

Dyke intrusions in volcanoes contribute to edifice internal growth and feed flank and summit eruptions.
Understanding the control factors on dyke paths is thus critical to assess areas prone to vent formation, and for thegeneral understanding of how volcanoes work.
As a contribute to this wide topic, we present our field and laboratory results dealing with an understudied magma
path system, characterized by a central summit rectilinear volcanic rift zone that turns into an outward-widening,
fan-arranged pattern of eruptive fissures and dykes at two opposite volcano flanks, giving an overall “hourglass”
configuration.
We identified nine elongated volcanoes in different tectonic settings showing evidence of this pattern, andwe analysed their geological, structural and morphometric characteristics, highlighting those volcanic-structuralfeatures that depict this configuration.
Then, in order to constrain the relation between the state of stress in the edifice and dyke propagation, we developed
a series of scaled analogue models. Volcanic edifices were reproduced in gelatine with defined geometries basedon field data, while sheet intrusions were simulated by injecting coloured water at different locations below thevolcano respect to its flanks and elongation axis.
Our results suggest that this “hourglass” configuration of magma paths in volcanoes can result from the dominanceof stress tensors with different geometries in diverse parts of the edifice. These stresses should also have diverse
origins; while regional tectonics might exert a control on the orientation of the central part of the rift system, thegeometry of the edifice (with defined ranges of elongation and volume) can reorient the local stress field and dictate
the pattern of dyke propagation at the volcano edges. These findings complete and integrate previous works on thedevelopment of volcanic rift zones, contributing to the assessment of volcanic hazards associated to the opening ofdyke-fed eruptive fissures on the volcano flanks.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

851

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

1W_3D-P2

Date/Time: July 21 Poster

The tertiary volcanic sub-marine formation of kuta-beach, lombok, indonesia, ageological and educational site of high patrimonial value
Indyo Pratomo1 , Patrick Wassmer2 , Sam Permanadewi1
1

Geological Agency, Minist. of Energy and Mineral Resources, Indonesia, 2 Univ. Paris 1
Pantheon-Sorbone, Lab. de Geographie Physique, France
E-mail: indyopratomo@gmail.com

At the South of Lombok Island, Indonesia, the morphology of the coast corresponds to a succesion of indented
bays interupted by eroded Tertiary volcanic remnants. The distribution of the old volcanic cones that underwent
hydrothermal alterations corresponds to the presence of feeder dikes of basltic andesite lava oriented ESE.
This Late Oligocene to Early Miocene submarine volcanic deposit is constituted by volcanic breccias, tuffs andbasaltic andesites lavas, with intercalations of marine deposits lenses of Oligo to Miocene limestones. A large
bloc of hyaloclastite displaying radial cracks linked to a contraction during the process of cooling. Numerous
cavities due to the gas trapping during the sudden cooling. On large surfaces of the abrasion platform, a loose
network of perpendicular cracks underlined by recristallisation due to fluid movements, attests the importance ofcontaction during cooling. The result of auto-brecciation of basaltic lava flow can be observed locally as well as
pyroclastic flows constituted of oriented hyaloclastite-peperite fragments displaying a reverse grading. A submarine
volcanic edifice can hardly be found onshore in the Indonesian archipelago. Identification of the morphologicalfeatures and study of the characteristic of products resulting of sub-aqueous volcanic activities will allow to better
understand the eruptive mechanisms. A good exposure of dikes, fragmented sub-marine lava flows, hyaloclastite
and peperitic deposits, supported by a rare and beautiful beach composed exclusively by foraminifera fossils-sandsof Schlumbergerella floresiana contribute to confer to this geological and educational site a high patrimonial value.
Key words : Kuta beach Lombok, Submarine Tertiary volcanism, hyaloclastites, peperites©IAVCEI 2013 Scientific Assembly. All rights reserved.

852

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

1W_3D-P3

Date/Time: July 21 Poster

Finite element analysis of conduit wall rock stresses associated with steady flow models
Jonathan B Hanson1 , Alison C Rust1 , Martyn J Pavier1 , Jeremy C Phillips1 , Antonio Costa2
1

University of Bristol, United Kingdom, 2 INGV - Bologna, Italy
E-mail: jonathan.hanson@bristol.ac.uk

Conduit erosion (i.e. the permanent removal of wall-rock) modifies conduit geometry during eruptions and affects
eruption dynamics. However, there has been very little modelling of conduit wall-rock failure and none couplingerosion and fluid dynamic models.

Finite element analysis is a powerful tool to elucidate the behaviour of the wall-rock during both dynamic
and static loading and is capable of dealing with inherently non-linear and complex systems. Initial investigations
using the FEA package Abaqus have focused on conduit wall-rock loading based on the pressure profiles
determined by the steady 1-D explosive eruption dynamics models of Costa et al., 2009. Their models assume a
6000 m conduit linking the chamber (of variable pressure) to the vent with a cylindrical, dyke-like or hybrid (dikethat transitions to a cylinder) geometry. The fluid pressures in their set of simulations range from +30MPa to-106MPa, with respect to lithostatic.

FE models loading the conduit walls with the stress from the simulated fluid pressures suggest significant
wall-rock failure would occur for all geometries modelled. For example, the pressure profile for a cylindricalconduit in an elastic medium (Youngs modulus = 40 GPa, Poissons ratio = 0.25, and yield strength = 20 MPa)
results in damaged volumes of 107 m3 . Damage is focused around, and particularly important in, areas of conduit
underpressures, as this material will implode into the conduit; erosion of damaged overpressured areas requires afurther mechanism to remove material (e.g. magmatic shear stress or particle collisions). The forecasted yielded
volumes exceed that of the conduit by an order of magnitude, suggesting that significant wall-rock failure would
inhibit the development of the modelled steady flow pressure profiles. FE analyses with a dyke-like geometry
suggest that significant failure would be focused near the dyke tips. Results for a dyke underpressure of 50 MPa(properties as above) indicate yielded cross-sectional areas of hundreds of square meters. Due to the spatial
relationship between this damaged material and the dyke, this material would not easily be removed, although
increased permeability through damage could be important in promoting magma-water interaction.

The amount of damaged material strongly depends on the initial size of the conduit and the assumed rockrheology. For increasingly complicated, quasi-steady models coupling 1-D flow and evolving conduit geometry
based on FE wall-rock failure, an elastic-plastic wall-rock rheology may be more appropriate. In the static loading
done to date, adjusting the rheology from elastic to elastic-plastic increases the damaged volume by orders ofmagnitude.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

853

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

1W_3D-P4

Date/Time: July 21 Poster

From dike to plug: critical physical transitions in the evolution of sustainable basaltic
volcanism
Meredith R Townsend, David D Pollard
Stanford University, USA
E-mail: mtown@stanford.edu

Basaltic volcanic eruptions commonly are characterized by three stages. In the upper few kilometers of the crust,magma rises in planar dikes, resulting in fissure eruptions when they intersect the surface. In some cases, thefissures may not feed significant eruptions and may quickly (within hours) die out. In other cases, magma continues
to erupt and localizes into discrete vents, until the flow is sustained through a central vent, which is able to carrymuch greater volumes of magma to the surface. These types of eruptions have been well documented in places
like Kilauea volcano in Hawaii and are inferred to have operated in ancient systems like Ship Rock, New Mexico.
However, the physical processes governing the evolution of conduit geometry from dike-like to plug-like and theassociated eruptive dynamics are poorly understood. Field evidence from Ship Rock provides insights we use
to develop a framework for what processes may have caused the evolution of dikes into plugs. Ship Rock is amaar-type diatreme standing 600 m above the surrounding land surface, with minette dikes extending radiallyaway. Systematic joint sets in the host rock (Mancos shale) adjacent to dike contacts and the presence of breccias
along the margins of the dikes and around plugs suggests that brittle deformation and subsequent erosion of thehost rock was primarily responsible for changing conduit geometry. Fracture orientations and petrographic analysisof the breccias have allowed us to construct a conceptual model for what style of deformation has taken place, thesequence of these deformational events, and the stress state that gave rise to this deformation. We hypothesize
the following order of events: 1) dike-parallel fractures form in the host rock ahead of the propagating crack tip;2) magma intrudes and solidifies at the contact and oxides and calcite fill in pore space in the adjacent hostrock; 3) dike-perpendicular fractures form in the host rock; 4) solidified magma fractures and host rock partially
fluidizes; 5) fractured magma is eroded by the flow of molten magma; 6) fractured host rock is eroded by the flowof molten magma. An analysis of the state of stress around a dike identifies the primary controls on the various
styles of deformation. The stress state includes mechanical stresses from dike opening, thermoelastic stresses
from heat transfer, and pore pressure increases from coupled heat transfer and groundwater flow. We present thefield evidence for the conceptual model and preliminary results from the stress analysis. Ultimately, physics-based
numerical models will be developed to test which physical mechanisms primarily control the evolution of fissure- tocentral- type eruptions, and under what conditions this transition is likely to take place.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

854

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

1W_3D-P5

Date/Time: July 21 Poster

Structure of phreatomagmatic crater rows from gravity surveying. Conduit shapecomparisons between the fissures of the 871 AD Vatnaoldur and 1477 AD Veidivotn
eruptions, south central Iceland
Jeanne M. Giniaux, Magnus Tumi Gudmundsson, Gudrun Larsen, Thorbjorg Agustsdottir, Thordis
Hognadottir
Institute of Earth Sciences, University of Iceland, IcelandE-mail: contact@jeanneginiaux.com

The 60 km long Vatnaoldur and Veidivotn volcanic fissures in south central Iceland belong to the same SW-NE
trending fissure swarm that is part of the Bardarbunga volcanic system. Eruptions on the fissure swarm havein postglacial times been both effusive, producing large lava fields, and explosive, producing the largest known
basaltic tephra layers in Iceland. Ground water level is high within the southwestern part of the fissure swarm anda large river flows through the volcanic area.
The two most recent eruptions on the southwestern part of the fissure swarm occurred in 871 ±2 AD when the craterrow of Vatnaoldur was formed, and in 1477 AD, when the Veidivotn fissure was active. Both eruptions produced
basaltic tephra layers of several cubic kilometres. Minor effusive phase at the end of the Veidivotn eruption, filled
the bottom of the large phreatomagmatic craters from the main phase, while only tephra was produced in the earlier
Vatnaoldur eruption.
The aim of the project is to model the structure of some volcanic conduits from both fissures, in order to figure out
their filling materials and understand better their process of formation. A large density contrast is to be expected
between the crater rims made of tephra (density 1200-1900 kg/m3) and the lavas that fill the Veidivotn craters(2300-2700 kg/m3). Therefore the gravity method was chosen to figure out the volcanic structures.
Six profiles were surveyed across six explosive craters using a LaCoste Romberg gravity meter and kinematic GPS.
Complete Bouguer anomalies were obtained by integrating the gravitational effects of the mass of the topographyusing a high resolution DEM. Two profiles cross the Veidivotn fissure whereas the other four cross Vatnaoldur.
Preliminary results do not indicate gravity anomalies associated with the conduit of the fully phreatomagmatic
Vatnaoldur crater row, suggesting that the crater fill has the same density as the surrounding bedrock of tephra,
hyaloclastite and lava. In contrast, the lava-filled craters of Veidivotn show up as gravity highs. Forward models of
the craters indicate the existence of a few hundred meters wide and >100 m deep lava fill in the phreatomagmatic
Veidivotn craters. The results therefore indicate considerable excavation of the pre-existing uppermost part of the
bedrock in these powerful phreatomagmatic eruptions.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

855

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

1W_3D-P6

Date/Time: July 21 Poster

Eruption of crystal-rich basalts following a large sector collapse: Evidence from IODP
cores sampled offshore Montserrat
Michael Cassidy1 , Sebastian F.L Watt1 , Peter Talling2 , Shipboard scientists aboard IODP 3403
1

University of Southampton, UK, 2 National Oceanography Centre, Southampton, UK, 3 Integrated
Ocean Drilling Program (IODP), International
E-mail: m.cassidy@soton.ac.uk

Recently sampled IODP leg 340 cores sampled offshore Montserrat in the Lesser Antilles have recovered alarge amount of marine sediment, which is intercalated with tephra fallout deposits, reworked volcaniclastic andbioclastic turbidites sequences resulting from large landslides. This information will provide a wealth of information
about the mechanisms of these volcanic island landslides as well as the evolution of the style and compositionof the volcanoes through time. In recent years we have discovered more about Montserrat’s geomorphological,
chemical and eruptive history through information gained from shallow marine cores, subaerial work and now
deep IODP cores. Montserrat comprises 4 volcanic centres dating back to 2.6 Ma, including the presently active,
Soufrière Hills volcano. As with most subduction zone volcanoes, the majority of the volcanoes on Montserrat erupt
andesite, which has ideal density and viscosity qualities which facilitate ascension and eruption of this intermediate
composition. The presence of a basaltic volcanic centre at Montserrat at 130 ka (South Soufrière Hills) is therefore
puzzling. However new data from the IODP cores find thick basaltic (46% SiO2 ) fallout units, which overly one of
the largest sector collapses discovered offshore Montserrat (8 km3 ). This basaltic unit is crystal-rich and contains
normally zoned phenocrysts of plagioclase, olivine and two-pyroxene. This study uses geochemical, textural andpetrological work to explore whether this represents an unloading and decompression event, which led to theeruption of these dense and crystal-rich basaltic magmas.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

856

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

1W_3D-P7

Date/Time: July 21 Poster

Evolution of the phreatomagmatic Cova de Paul eruption, Santo Antao, Cape VerdeIslands: links between the development of the eruption and the growth of the crater.
Robert W Tarff1 , Simon J Day2
1

Birkbeck University of London, United Kingdom, 2 University College London, United Kingdom
E-mail: ucfbsjd@live.ucl.ac.uk

Episodes of hazardous phreatomagmatic explosive activity that excavate large deep craters occur within otherwise
less dangerous effusive to mildly explosive magmatic eruptions at high-elevation vents on many oceanic island
volcanoes. The water driving these explosions is sourced from freshwater aquifers within the volcanic edifices,
whose location and other characteristics will influence crater growth and final geometry. Here we describe crater
wall sequences and near-vent deposits around the large Cova de Paul crater on the island of Santo Antao,
Cape Verde Islands, which provide some insights into a transition from mild magmatic to violently explosive
phreatomagmatic activity in one such eruption. This pre-historic but well-preserved crater formed in a single
eruption that produced extensive low-temperature, lithic-rich phreatomagmatic ignimbrites and surge deposits;these are interbedded in proximal outcrops with airfall to mixed fall and flow breccia and ash beds containing
varying proportions of lithic and juvenile clasts, pointing to a series of climactic explosions within an extended
period of milder phreatomagmatic explosive activity.

Prior to the transition to phreatomagmatic activity, the eruption had been characterized by mild Strombolian activity
that produced scoria and spatter deposits of broadly tephritic composition. The upper parts of the Stromboliansequence contains distinctive flow-banded angular sub-glassy juvenile clasts, compositionally identical to theStrombolian scorias, that become larger and more abundant just below the transition to phreatomagmatic activity.
We interpret these as fragments of flow-banded chilled margins from the walls of the eruptive conduit. Thermal
shattering of these margins to produce the angular sub-glassy clasts may have allowed increased groundwaterflows into the conduit, attainment of a critical coolant input ratio, and the onset of the phreatomagmatic explosions.
The lack of angular sub-glassy clasts in the rest of the eruptive sequence suggests that the chilled margins neverre-established and that subsequent variations in the intensity of phreatomagmatic activity were controlled by waterflow to the conduit as the crater was excavated to deeper levels and different aquifers were tapped and depleted.
We find that whereas most of the lithic clasts in the mixed units can be matched with rock units in the exposed
crater walls, implying widening of the crater during periods of low-level explosivity, the ignimbrite and surge units
contain hydrothermally altered clasts that appear to have originated from deeper in the volcanic edifice implyingthat during these climactic episodes the crater vent walls were being actively excavated to as much as several
hundred metres below the surface of the volcano.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

857

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

1W_3D-P8

Date/Time: July 21 Poster

Dolerite sill body inferred from bore hole investigation in the Yufutsu Oil and Gas Field,
Hokkaido, North Japan
Satoshi Okamura1 , Sakura Onodera2 , Takahiro Torigoe3
1

Hokkaido Education University, Sapporo, Japan, 2 Hokkaido Education University, Sapporo, Japan,
3
Japan Petroleum Exploration Co., Ltd., Japan
E-mail: okamura.satoshi@s.hokkyodai.ac.jp

Petrographic study of the dolerite intrusions in the Yufutsu well, drilled over 5 km depth revealed that the dolerite
multiple sills up to 1 km in total thickness intruded into the Mid Eocene coal-bearing Formations of the IshikariGroup and the Late Eocene fine-grained marine strata of the Poronai Formation. The thickness of each sill
ranges from several m to over 30 m. The dolerite rocks are characterized by variable textures ranging fromtypical coarse-grained dolerite texture to porphyritic texture with fine-grained crystal and /or glassy groundmass.
Plagioclase size distribution indicates small and needle form at the levels of the Poronai Formation and bottom of
the Ishikari Group, and large and square form at the middle of the Ishikari Group. The dolerite rocks have basaltic
andesite to andesite compositions (54-59 SiO2 wt percentage). Main mineral assemblages of the dolerite rocks
are divided into plagioclase (SiO2 rich rocks) and plagioclase + clinopyroxene (SiO2 poor rocks). Upper most andbottom part of sills consist of mafic rocks, middle part of sills repeated layers of felsic and mafic rocks. Thesefeatures suggest that the multiple sills body may indicate marginal facies of the cross section of magma chambercharacterized by layering in gabbro plutons.
Among the igneous rocks in the Yufutsu Oil and Gas Field, a subset of the Oligocene volcanic rocks in the
Minami-Naganuma Formation underlain by the Late Eocene Poronai Formation is distinctive on the basis ofmarkedly high incompatible element abundances. The dolerite rocks also show an enrichment in incompatible
elements. The similarity of geochemical signature in the Oligocene volcanic rocks and the dolerite sills suggeststhat the former exhibits effusive facies and the latter has played the role of parent magma chamber emplacing in
the Poronai Formation and the Ishikari Group.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

858

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

1W_3D-P9

Date/Time: July 21 Poster

2012 Copahue volcano eruption (Argentina)
Alberto T Caselli1 , Mariano R Agusto2 , Maria L Velez2 , Pablo Euillades3 , Cintia L Bengoa2 , Pablo B
Forte2 , Franco Tassi4 , Bruno Capaccioni5
1

GESVA - Universidad nacional de Rio Negro, Argentina, 2 GESVA - Universidad de Buenos Aires CONICET, Argentina, 3 CEDIAC, Universidad de Cuyo - CONICET, Argentina, 4 Universidad deFlorencia, Italia, 5 Universidad de Bolonia, Italia
E-mail: atcaselli@gmail.com

Copahue volcano (37,8°S, 71,2°W, 2997 masl) is one of the major examples of active volcanism in Argentina. Thisbasaltic-andesitic stratovolcano is located on the western edge of the Caviahue caldera in the Andes. The volcano
summit has nine craters aligned in the N60 °E direction, the eastern crater is the active one and it currently hosts
an acidic crater lake (pH ∼1) with a diameter close to 250 m and 40 m depth. During the last 250 years this volcano
has experienced at least 12 low intensity phreatic and phreatomagmatic eruptions. The last eruptive cycles took
place from the active crater, during 1992 and 1995 characterized by phreatic eruptions and from July to October2000 with a phreatomagmatic eruptive type, all of them with VEI 1-2. After the 02-27-2010 Maule earthquake(Chile, Mw 8.8), several variations were observed related to the local seismicity, primarily associated with anincrease in the amount and type of signals Later, on 12-01-2011 a seismic swarm was registered and gaseousemissions from the crater lake started to increase in both temperature (62 °) and acidity (pH<0). Deformation
measurements were made by processing Envisat images available from January 2011 until April 2012 allowing theconstruction of 33 interferograms. The analysis of temporal deformation series indicate an inflation process startingon November-December 2011, located mostly on the northern slope of the volcano edifice. After April 2012 thesatellite was out of operation.The 07/16/2012, after a marked increase in seismic activity from 07/09/2012, somephreatic events were observed and two days later a phreatic explosion throws pyroclastic sulfur from deposits of thecrater lake bottom. The phreatic manifestations produced by degassing continued until December 2012, decreasing
the volume of water from the crater lake. Finally, on 12-22-2012 at 9:15 pm a phreatic eruption began, vaporizing
the crater lake waters and the hydrothermal system in a few minutes. At 9:40 hs it became phreatomagmatic withgeneration of a convective cloud and emission of blocks and bombs in ballistic projection outflow of the plume.
Diluted pyroclastic flows were observed during this eruptive phase. Several hours later (15:30 hs) burning clouds
were viewed getting out of the crater produced by combustion of volcanic gases. Thus, an eruptive strombolian
phase began, with the emission of elongated volcanic bombs, up to 1.5 m in length. This eruption ended in a few
hours, continuing to the present with gas emissions.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

859

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

1W_3D-P10

Date/Time: July 21 Poster

Petrographic characterization of material ejected during eruptive phases of Copahue
volcano (Argentina) in 2012
Alberto T Caselli1 , Romina Daga2 , Juan M Albite3 , Mariano R Agusto3
1

GESVA - Universidad Nacional de Rio Negro, Argentina, 2 Laboratorio Analisis por ActivaciÃşn
Neutronica (CAB-CNEA) âĂŞ CONICET, Argentina, 3 GESVA - Universidad de Buenos Aires, Argentina
E-mail: atcaselli@gmail.com

Copahue volcano is an Andean active basaltic-andesitic stratovolcano. The crater currently hosts an hot and acidic
crater lake. On July 19, 2012 a phreatic explosion occurred with emission of pyroclastic material, producing a small
plume that extended 18 km on ESE direction. A sample of this event, recovered from the crater, was constituted
mainly by sulphur pyroclasts, with low proportion of pumice and scoriae fragments, irregular argillaceous whitematerial and accidental/accessory fragments. Sulphur pyroclastic material have variable sizes (3-4 mm), mostly
globular morphology with vesicles, like perfect spheres or elongated forms in some cases, and like deformed ’drops’in others. On December 22, 2012 a new magmatic pulse initiated with a rapid vaporization of the Crater Lake anda phreatic eruption. Minutes later it became in phreatomagmatic with convective cloud generation and ballistic
emission of blocks and bombs, and pyroclastic fall of ash, mainly dark brown pumice fragments, from the plume.
Several hours later the eruptive phase turned to strombolian style, with emission of elongated volcanic bombs.
The emitted material sampled 9 km far from the volcano corresponds to lapilli-sized tephra. It is mainly composedby irregularly to subrounded shaped dark gray scoria with moderate vesicularity. Another abundant component
corresponds to dark brown pumice, with both fluidal and vesicular textures and high vesicularity degree. Bothscoria and brown pumice contain mafic and felsic crystals in the glassy matrix. An argillaceous white material isalso present in the sample, less abundant than the previous components. Accidental/accessory fragments together
with mafic and felsic crystals and crystal fragments are present in the sample. The andesitic volcanic bombs
reach 1.5 km away and have elongated shapes with moderate vesicularity; microscopically they are characterized
by a porphyritic texture. The observed phenocrysts are euhedral oligoclase, clinopyroxene and alkali feldspars;the hialopilitic matrix is almost completely made of glass with microlites of plagioclase, alkali feldspars andclinopyroxenes. The dark brown pumiceous fragments are flat and reach up to 10 cm length. They are characterizedby light weight because of their high vesicularity. Under the microscope, the dark brown pumice showed porphyritic
texture, where phenocrysts represent less than 1 Percent, all euhedral and fragmented phenocrysts (oligoclase andclynopiroxene). Due to its light weight, ability to float, and mineralogy it might be named pheno-andesitic scoria.
According to field observations, this ejects were thrown up by a grey plume that preceded the strombolian event.
According to the preliminary study of the emitted material and the observations made during the eruption, we caninfer an andesitic composition for the magma and vesiculated pumice fragments, which correspond to the initial
phase, accumulated at the top of the conduit.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

860

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

1W_3D-P11

Date/Time: July 21 Poster

Eruptive history of long-lived active Tokachidake volcano group, southwestern Kurile arc
Yoshihiro Ishizuka1 , Mitsuhiro Nakagawa2
1

Geological Survey of Japan, AIST, Japan, 2 Hokkaido University, Japan
E-mail: y.ishizuka@aist.go.jp

Detailed geologic mapping supported by radiometoric age deteminations is important tool to clarify the eruptive
history of long-lived arc active volcanoes. Tokachidake is one of the most active volcanoes in Japan, and is acluster of Quaternary volcanoes. It overlies Late Pliocene to Early Pleistocene rhyolite ignimbrites. The volcanogroup extends 25 km mainly in the NE-SW direction, consisting of at least twelve volcanic edifices which are 5 to
10 km in diameter. Using detailed mapping and stratigraphy, airborne laser scanner data, and new 33 K-Ar and 16
radiocarbon ages determinations, and geochemical data, we have mapped the 55 geologic units in the area of 270
km2 centered on the volcano group.
The Tokachidake volcano group can be divided the volcanic evolution spanning approximately 1.0 Ma into threestages -Older, Middle and Younger- on the basis of their radiometric ages, eruption centers and petrologic features.
(1) In the Older stage, the products have limited distribution and consist mainly of andesite lava flows that erupted
during 1.0 Ma to 500 ka. (2) The Middle stage activity occurred during 300 to 70 ka, and had increased extensively.
Five basaltic stratovolcanoes were built in the margins of the volcano group, whereas six andesite stratovolcanoes
and a dacite lavas erupted around its center. (3) The Younger stage began around 60 ka, and the active region
is concentrated in the central part of the volcano group. The topographical features of each volcanic unit arepreserved. The products are composed of basalt to andesite lava flows and pyroclastic fall, pyroclastic flow anddebris avalanche deposits with a dacite lava dome. These products are enriched in K2 O relative than those of the
Middle stage.
The most characteristic of the eruptive history of the Tokachidake volcano group is that the activity expanded
approximately 300 ka and gradually contracted to the center. Then mafic magmas were erupted in the whole areaof the volcano group, whereas the intermediate to felsic magmas were only around the center. We could evaluate
the long-term volcanic activity in the point of view of this geologic mapping.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

861