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

1A1_1E-O1

Room A3

Date/Time: July 21 8:45-9:00

When circulation gets tough, the TOUGH gets going.
Modeling of hydrothermal fluid circulation in active volcanic areas
Micol Todesco
Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna, Italy
E-mail: micol.todesco@bo.ingv.it

Numerical modeling of hydrothermal fluid circulation has been prompted by a wide variety
of industrial needs, ranging from nuclear waste disposal and geothermal energy
exploitation, to the more recent applications devised for environmental remediation andcarbon sequestration. Volcanological applications had a later start, hindered by theformidable challenges posed by poorly-constrained and extreme system conditions,joined with a chronic lack of founding and good-quality, modeling-oriented data sets.
Nevertheless, as the volcanological implications of hydrothermal activity are important,modeling of fluid circulation in active volcanic system has become more popular in recent
times. Modeling results provided useful hints on the evolution of active volcanic systems,
by illustrating the role of an evolving source of volcanic gases and showing the diversity of
the geochemical and geophysical signals that can be generated by fluid circulation.
Numerical simulations also showed how these signals can be modulated by the propertiesof the rocks, and by their temporal and spatial evolution. This talk will provide an overview
of the volcanological applications of hydrothermal circulation models, highlighting the strength
and weaknesses of this approach, and discussing future developments. In particular, apromising research direction is the application of inverse modeling of hydrothermal fluid
circulation as a tool for the assessment of volcanic system conditions. Preliminary resultsfrom the first application to the well known Campi Flegrei caldera will provide an opportunity
to discuss potential and problems of the inverse approach to the interpretationof monitoring signals.

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200

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

1A1_1E-O2

Room A3

Date/Time: July 21 9:00-9:15

Estimation of carbon dioxide emission from Kuju Volcano, Japan, and its numericalmodeling
Yasuhiro Fujimitsu1 , Norihide Maeda2 , Sachio Ehara3 , Tetsuro Noda3
1

Faculty of Engineering, Kyushu University, Japan, 2 Graduate School of Engineering, Kyushu
University, Japan, 3 Institute for Geothermal Information, Japan
E-mail: fujimitsu@mine.kyushu-u.ac.jp

Kuju Volcano is located in Kyushu and one of the active volcanoes in Japan. In order to infer the mass balance andenergy balance of the hydrothermal system in the Kuju volcanic area, we tried to estimate volcanic CO2 emission
and to construct a numerical model of the hydrothermal system of Kuju Volcano.
We considered four forms of volcanic CO2 emission; from the fumaroles, the bare area around the fumaroles, theflank by the soil gas, and some hot springs at the foot of the volcano. We adopted the value of about 166 t/day fromthe plumes of Kuju Volcano estimated by Ehara et at. (1981). On the other hand, Itoi (1993) shows the distributionof soil gas CO2 concentration in the bare area around the fumaroles. In our previous study (Araragi et al., 2008),
the relationship between soil gas CO2 concentration measured by the Kitagawa Gas Detector Tube System andCO2 flux measured by a CO2 flux meter in Kuju Volcano was found. Therefore, the CO2 concentration values
shown by Itoi (1993) were converted into the CO2 flux values, and about 0.8 t/day of the volcanic CO2 emission
was estimated. We measured soil gas CO2 concentration at 60 points on the flank of the volcano by the Kitagawa
Gas Detector Tube System and collected 15 soil gas samples to conduct the carbon isotope analysis to identify
the origin of the CO2 . As a result, we concluded that the volcanic CO2 emission from the flank was 0 t/day. And
for the CO2 emission from the hot springs at the foot of the volcano, the hot water discharge rate and the average
CO2 concentration in the carbonated water of the Nagayu Hot Springs area was adopted. Then about 5.0 t/dayof the volcanic CO2 emission from Nagayu Hot Springs was estimated. These results show that the volcanic CO2
emissions by the plumes from the fumaroles and by the carbonated water from a hot springs area are dominant in
Kuju Volcano.
In order to construct a numerical model of the hydrothermal system of Kuju Volcano, we used a geothermal
simulator STAR Version 9 (Pritchett, 1989) that can treat the components of H2 O and CO2 but has the limitations oftemperature from 0 to 350 deg. C and pressure from 1 to 600 bars. The modeling area has a horizontal extensionof 25 km (E-W) and 15 km (N-S), and a vertical extension from -500 m asl to the ground surface. Finally, weconstructed a numerical model, which explains the heat discharge rate and CO2 emission rate by the plumes fromthe fumaroles and the CO2 emission rate from the Nagayu Hot Springs area, by trial and error. This numericalmodel also indicates that the volcanic CO2 emission is dominated by the gas from the fumaroles and hot waterfrom Nagayu Hot Springs.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

201

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

1A1_1E-O3

Room A3

Date/Time: July 21 9:15-9:30

The bolsena-torre alfina geothermal field (Italy): a case of caldera-related blindgeothermal resource
GUIDO GIORDANO1 , GABRIELE BERARDI1 , CLAUDIO CHIARABBA3 , ARNALDO DE BENEDETTI1 ,MARINA PASTORI3 , ANNAMARIA PINTON1 , FEDERICO ROSSETTI1 , ANDREA SCHITO1 , MICHELESOLIGO1 , INES TESCIONE1 , MICOL TODESCO2 , GIANLUCA VIGNAROLI1
1

UNIVERSITA’ ROMA TRE, ITALY, 2 INGV - BOLOGNA, ITALY, 3 INGV - ROMA, ITALY
E-mail: guido.giordano@uniroma3.it

The Torre Alfina geothermal field is located about 10 km north of the Quaternary Bolsena caldera. The
reservoir is a buried structural high made of Mesozoic-Cenozoic carbonatic sequences characterised bydiscontinuous secondary permeability and sealed by clay-rich alloctonous syn-orogenic flysch successions
and Pliocene neo-authoctonous marine clays. The reservoir is locally highly productive, water-dominated
and CO2-rich, with T at its top of 120 degrees C. The origin of the heat source was not investigated in detail but
generally attributed to some unidentified deep magmatic body. Our field structural data document fracturing
and faulting that affect both the reservoir and the seal units with dominant NE-SW and a subordinate E-W as
maximum extension directions. The surface pattern and kinematics indicate that fault systems are part of the
Pliocene-Quaternary tectonic episode in Central Italy, where strike-slip kinematics transfers deformation
between main extensional shear zones. The fault network controls intense hydrothermal manifestations andtravertine deposition north of the Torre Alfina area. 230Th/234U dating allows distinguishing three different
stages of hydrothermal pulses bracketed between 200 and 90 ka. To improve the current understanding of
the geometry and density of subsurface fracture system we applied the Shear Wave Splitting (SWS)
technique studying the waveforms from local microearthquakes recorded in the area from 2008 to 2011. The
analysis of SWS provides parameters directly related to the strike of the subsurface fluid-filled fractures andtheir density. According to the extensive-dilatancy anisotropy hypothesis (Crampin, 1984) SWS is generated
by propagation through distributions of fluid-filled cracks, microcracks, and preferentially oriented porespace aligned according to the active stress field in the area.
The analysis was made using the software ANISOMAT and gives a major direction NW-SE. The results
agree both with structural data and with the focal mechanism of the earthquakes collected in the area
between years 1977 and 1992. From the analysis on the crack density our data gives
as result a good index of fracture for the reservoir’s rocks. Based on the updated conceptual model we
performed numerical simulations in TOUGH2 code. Results indicate that deep circulation is forced by thegeometry of the reservoir and by T and P gradients. We interpret the Torre Alfina field as a "blind" system,
formed dominantly by lateral advection of heat and mass from the Bolsena caldera deep system driven bothby high T and by the greater depth at which reservoir rocks are downthrown by the volcano-tectonic
collapse. Preferential fracture fabric in the deep carbonates allows the lateral heat transfer. The cap-rocks
have excellent sealing characteristics allowing the preservation of heat in correspondence with positive
structural traps.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

202

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

1A1_1E-O4

Room A3

Date/Time: July 21 9:30-9:45

U-Pb dating of zircon as an aid in interpretation of geothermal systems: a case study
from the Kawerau Geothermal Field, New Zealand
Sarah D Milicich1 , Colin JN Wilson1 , Greg Bignall2 , Ben Pezaro3 , John Clark3
1

SGEES, Victoria University of Wellington, Wellington, New Zealand, 2 GNS Science, Wairakei
Research Centre, Taupo, New Zealand, 3 Mighty River Power Ltd, Auckland, New ZealandE-mail: s.milicich@gns.cri.nz

Exploration and development of geothermal resources for electrical power generation and direct heat use requires
an understanding of the geology that hosts the geothermal system. Key to this understanding is being able to dateand correlate marker horizons to link permeable formations, constrain displacement history of faults and time thepresence of local heat sources.

The Kawerau Geothermal Field is the most northeasterly of high-temperature geothermal systems in the
Taupo Volcanic Zone (TVZ, New Zealand), an active Quaternary arc locus of rhyolitic volcanism and thermal
output. The reservoir rocks are a 1 km thick pile of lava, pyroclastic rocks and sediments, supplied with fluid
circulating through faulted Mesozoic basement greywacke. Here, where correlation solely by petrographic andtextural observations was ambiguous due to hydrothermal alteration, we show the value of U-Pb age information oninterpreting geothermal systems. U-Pb age determinations on zircons from extensively altered lithologies provide
estimates of crystallisation and eruption ages that allow depositional and faulting histories of rocks hosting thegeothermal system to be reconstructed. These histories may be linked to evidence for episodic local magmatism
beneath the field and to changes in regional tectonic stress patterns.

Prior to the 0.32 Ma Matahina ignimbrite (a regional marker plane), deposition of ignimbrites occurred in
short-lived episodes around 1.45, 1.0, and 0.55-0.6 Ma, separated by thin sediment-dominated intervals whichaccumulated at average rates of 0.06 mm/yr. The ignimbrites represent marker horizons from other volcanic
centres and do not reflect the presence of local magmatic heat sources. Net subsidence rates inferred from
depths to these marker planes do not reflect the present-day situation. Modern rates of subsidence (2+/-1 mm/yr)
associated with TVZ rifting processes can have been active for no more than 50,000 years in the area of the field,
based on elevation differences of the Matahina ignimbrite top surface.

Bodies of coherent rhyolite (i.e., lava or intrusive material) occur at multiple intervals in the volcanic/sedimentary
cover and basement greywacke. Age dating resolves these multiple bodies as either domes or intrusions: twopetrographically contrasting magma types with associated tuffs were emplaced as domes and sills at 0.36+/-0.03
Ma, and a third type at 0.138+/-0.007 Ma as dikes, and domes exposed at surface. Heat sources beneath thefield resulted from these local magma intrusions, together with that feeding the Holocene eruptive activity of
Putauaki andesite/dacite volcano. Of these, the last is responsible for the thermal and alteration characteristicsof the modern field. We infer that only at long-spaced intervals is there evidence of magma at shallow enoughcrustal levels beneath the field to generate vigorous hydrothermal activity (as at the present day); at other times noKawerau geothermal system’ existed.
©IAVCEI 2013 Scientific Assembly. All rights reserved.

203

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

1A1_1E-O5

Room A3

Date/Time: July 21 9:45-10:00

Concept of the Japan Beyond-Brittle Project (JBBP) for new forntier of geothermal power
generation
Hiroshi ASANUMA1 , Hirofumi MURAOKA2 , Noriyoshi TSUCHIYA1 , Hisao ITO3
1

Tohoku University, Japan, 2 Hirosaki University, Japan, 3 JAMSTEC, Japan
E-mail: asanuma@geoth.kankyo.tohoku.ac.jp

New conventional geothermal energy projects have not been actively promoted in Japan for the last decade
because of perceptions of high relative cost, limited electricity generating potential and the high degrees
of uncertainties and associated risks of subsurface development.

More recently however, EGS (Enhanced

Geothermal System) geothermal has been identified as a most promising method of geothermal development
because of its potential applicability to a much wider range of sites, many of which have previously been considered
to be unsuitable for geothermal development. Meanwhile, some critical problems with EGS technologies havebeen experimentally identified, such as low recovery of injected water, difficulties in establishing universal
design/development methodologies, and the occurrence of induced seismicity, suggesting that there may belimitations in realizing EGS in earthquake-prone compression tectonic zones.

We propose a new concept of engineered geothermal development where reservoirs are created in ductile
basement. This potentially has a number of advantages including: (a) simpler design and control of the reservoir,(b) nearly full recovery of injected water, (c) sustainable production, (d) lower cost when developed in relatively
shallower ductile zones in compression tectonic settings, (e) large potential quantities of energy extraction fromwidely distributed ductile zones, (f) the establishment of a universal design/development methodology, and (g)suppression of felt earthquakes from/around the reservoirs.

To further assess the potential of EGS reservoir development in ductile zones we have initiated the "Japan
Beyond-Brittle Project (JBBP)". It is intended that the first few years of the JBBP will be spent in basic scientificinvestigation and necessary technology development, including studies on rock mechanics in the brittle/ductile
regime, characterization of ductile rock masses, development of modeling methodologies/technologies, andinvestigations of induced/triggered earthquakes. We expect to drill a deep experimental borehole that will penetrate
the ductile zone in northeast Japan after basic studies are completed.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

204

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

1A1_1E-O6

Room A3

Date/Time: July 21 10:00-10:15

The preliminary conceptual model of Tolehu geothermal resource based on geology,
geochemistry and MT data
Asnawir Nasution1 , Endro Supriyanto2 , Tjahjo Sasmojo3 , Matsuru Honda4 , Miman Aviff5 , Sigid
Nugroho6 , Yudistian Yunis7 , Zulkarnain Nasution8
1

Faculty of Earth Science and Technology, ITB. Bandung, Indonesia, 2 PT.PLN Geothermal, Jakarta,
Indonesia, 3 PT.PLN Geothermal, Jakarta, Indonesia, 4 West Japan Engineering Consultants, Inc„ Japan,
5
PT.PLN Geothermal, Jakarta, Indonesia, 6 PT.PLN Geothermal, Jakarta, Indonesia, 7 PT.PLN
Geothermal, Jakarta, Indonesia, 8 PT.Excavindo Pratama, Bandung, Indonesia
E-mail: nasution@gc.itb.ac.id

The Tolehu Geothermal area Ambon (70 m asl.), which had initially been studied more than fifteen years ago wasresurveyed by additionalMT-TDEM method and an exploration well in 2010 and 2011 to constrain a conceptualmodel for the prospect area. Based on those conceptual model that integrated the 1D and 2D MT inversion images
with data from existing wells and geochemistry, six gradient thermal wells with the maximum depth 150 m andone exploration well of about 930 m depth had indicated over 200 degree Celsius resource. The deep well was
drilled to confirm the elements of the model and extended the proven geothermal reservoir 1.5 km to 2.5 km to thesouth an old volcanic complex. Shallow cores and deeper cuttings were analyzed by using petrography and x-ray
methods. They had confirmed that the low resistivity detected by MT and TDEM surveys closely correlated with the
distribution of low temperature smectite and high temperature of illite and chlorite clay alteration. Due to the greater
tendency of clay minerals (smectite, illite, phyrophlite, chlorite clay) to inhibit the formation of fracture permeability
relative to more brittle clays, the top of the permeable reservoir generally conformed to the geometry of the base of
the low resistivity clay alteration. The rough correlation of the 200 degree Celsius geothermometry with the 5 and10 ohm-m contours below the transition from smectite,illite, illite to chlorite clay were used to predict the depth ofcap rocks.The extreme temperature of thermal gradient is 123 degree Celsius at the depth of 150 m and the water
dominated system with Chloride concentration lower than 5000 ppm at 930 m depth, indicate sea water uninvolved
to the geothermal system.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

205

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

1A1_1E-O7

Room A3

Date/Time: July 21 10:15-10:30

A business model of hot spring power generation and its current progress in Japan
Hirofumi Muraoka1 , Seiichiro Ioka1 , Norio Yanagisawa2 , Munetake Sasaki2 , Hajime Sugita2 , Masatake
Sato3 , Kazumi Osato3
1

North Japan Research Institute for Sustainable Energy (NJRISE), Hirosaki University, Japan, 2 Institutefor Geo-Resources and Environment (GREEN), AIST, Japan, 3 Geothermal Energy and Development
Co., Ltd. (GERD), Japan
E-mail: hiro@cc.hirosaki-u.ac.jp

A business model of hot spring power generation was proposed by Muraoka (2007) and Osato and Muraoka(2008) to efficiently utilize low-temperature hydrothermal resources such as the numerous hot springs in Japan.
About 28,000 hot spring sources are distributed all over Japan and their pre-existence is one of the serious
barriers to develop new geothermal power plants in Japan. However, current binary cycle technology enables
power generation by hot spring water even less than 100°C. Most of high-temperature hot springs are mainly used
for bathing in Japan until the present where they have to be cooled down to the adequate bath temperature 42°C
without any serious dilution of balneological constituents. It means that high-temperature hot springs need moreworks in terms of the bath use compared to the moderate-temperature hot springs. Then, we proposed to introducea very small binary cycle in the upper reach of high-temperature hot springs. If we do that, we could make power
generation with the high-temperature range above the bath-use temperature and we could make the cooling down
to the adequate bath use temperature without any serious dilution of balneological constituents at the same time.
This is our business model of hot spring power generation. This business model gives a further merit, that is, if hot
spring owners adopt the business model of hot spring power generation, the conflict between hot spring owners
and geothermal power development will be gradually reduced, because the hot spring power generation itself issome sort of geothermal power development. At the time of the proposal, we did not have any small binary cycle
power generation systems suitable for the small discharge rate of hot springs and therefore we made our efforts
to develop a 50 kW class Kalina cycle hot spring power generation system. This system was almost completed
and is now under the operation experiment in the Matsunoyama hot spring field, Niigata Prefecture. In addition tothis, many makers recently manufactured small-scale binary cycle power generation systems such as 70 kW, 50
kW, 20 kW and 3 kW classes in Japan. The feasibility studies of hot spring power generation are recently made in
Niigata, Shizuoka, Nagasaki, Oita, Nagano, Toyama and Aomori Prefectures. The profitability of hot spring power
generation is still marginal even by the new Feed-in Tariff system at 42 Yen/kWh introduced in July 2012, but the
hot spring power generation market will be established within the coming ten years.
References: Muraoka, H. (2007) Current withering and possible future revival of geothermal energy development
in Japan. Journal of the Japan Institute of Energy, 86, 153-160 (in Japanese with English abstract). Osato, K. andMuraoka, H. (2008) Hot spring binary cycle power generation. Journal of the Japan Institute of Energy, 87, 812-818(in Japanese with English abstract).

©IAVCEI 2013 Scientific Assembly. All rights reserved.

206

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

1A2_1E-O8

Room A3

Date/Time: July 21 10:45-11:00

Magmatic and Hydrothermal Activity in the East African Rift
Juliet Biggs1 , William Hutchison2 , Matthew Wilks1 , Elspeth Robertson1 , Andrew Nowacki1 , David Pyle2 ,Tamsin Mather2 , Marie Edmonds3 , Michael Kendall1 , Atalay Ayele4 , Elias Lewi4
1

University of Bristol, UK, 2 University of Oxford, UK, 3 University of Addis Ababa, Ethiopia, 4 University ofCambridge, UK
E-mail: juliet.biggs@bristol.ac.uk

The caldera volcanoes of the East African Rift are among some of the most dangerous volcanoes in the world(Aspinall et al, 2011), since they have had eruptions within the very recent past, are close to densely populatedareas and are un-monitored. However, they also contain significant geothermal resources and are therefore subjectof large infrastructure investment. There is a critical lack of understanding of the current activity of the magmaticand hydrothermal system, and the potential volcanic hazards. To address this we are engaged in active research
projects on two young volcanoes, Alutu, Ethiopia and Longonot, Kenya. Both of these volcanoes are currently
undergoing active deformation, identified by InSAR during the period 1997-2010 (Biggs et al, 2011). Alutu iscurrently the location of the only major geothermal power plant in Ethiopia and drilling is about to start at Longonot,
Kenya. Naturally occurring changes in the volcano affect the operation of the plant while the production itself maychange the state of stress in the reservoir and surroundings, influencing the seismic and volcanic hazard. This
project involves seismic monitoring, MT and geodetic measurements and well as airborne imagery , field mappingand sampling. The opportunity to obtain such a multi-disciplinary dataset offers the potential to transform ourunderstanding of the status of ongoing magmatic and hydrothermal activity associated with these active volcanic
systems and their current and future volcanic hazards.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

207

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

1A2_1E-O9

Room A3

Date/Time: July 21 11:00-11:15

Magmatic vapor plumes in active volcanoes: dynamics, discharge and disasters
Richard Henley
The Australian National University, Australia
E-mail: r.143.henley@gmail.com

Magmatic gas mixtures released by crystallizing intrusives expand across permeability discontinuities fromlithostatic to near-hydrostatic pressure within volcanic systems. In arc volcanoes they provide most of the heat
energy that is widely dispersed as extensive geothermal systems or released directly through the surface as hightemperature, high enthalpy fumaroles and extensive solfatara and as gas plumes.Modeling of their expansion to thesurface and their interaction with groundwater to form magmatic vapor plumes is compromised by the difficulties ofdealing with compressible fluids. Data from fossil plumes (for example, porphyry and high sulfidation copper-gold
deposits) however provide evidence of their scale and internal structure that may then be used to constrain modeling(Henley and McNabb, 1978).
A general approach to analysis of the dynamics of magmatic vapor plumes is outlined here based on simple phaserelations and Markov principles and shows that one of the principle controls on plume architecture is the ratio,Kp,of vertical to horizontal permeability (Hurwitz et al., 2003). In low Kp systems, phase separation to form envelopeson the margins of plumes is a consequence of the net decrease in enthalpy due to groundwater mixing and has
implications for hydrothermal alteration and mineralisation, and the evolution of geothermal systems. Where Kp
is large, high energy discharges are maintained. In addition to input power, their periodicity is related primarily tochanges in fracture permeability due to mineral deposition and depletion of the source magmatic gas reservoir.
Understanding of the behavior of magmatic vapor plumes may contribute to the analysis of the history of volcanic
systems and their energy flux. It may also provide a basis for forecasting and tracking Plinean eruptions and theirlinkage to major seismic events in tectonically-challenged crust.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

208

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

1A2_1E-O10

Room A3

Date/Time: July 21 11:15-11:30

Understanding phreatic & hydrothermal explosion dynamics: insights into the energy
conversion based on lab experiments
Bettina Scheu, Donald B Dingwell
Earth and Environmental Sciences, LMU Munich, Germany
E-mail: b.scheu@lmu.dePhreatic eruptions are amongst the most common and most diverse eruption types on earth. Often they areprecursory to another type of volcanic activity but they can stand as well on their one. Phreatic explosions occur
for instance when subsurface water or water on the surface is heated by magma, lava, hot rocks, or fresh volcanic
deposits and result in craters, tuff rings and debris avalanches. Another wide and important field affected by steam
explosions are hydrothermal areas; here hydrothermal explosions might occur every few months creating explosion
craters and resemble a significant hazard to hydrothermal power plants as well as visitor parks. Despite of theirhazard potential, phreatic explosions have so far been overlooked by the field of experimental volcanology. A partof their hazard potential in owned by the fact that phreatic explosions are hardly predictable in occurrence time andsize as they have manifold triggers. The diversity of phreatic and hydrothermal eruptions arises from the variety of
host rocks, ways to seal possible degassing pathways, and to alter this material depending on the composition of
volcanic gases and the hydrothermal fluids.

We conduct rapid decompression experiments on a variety of natural samples from igneous rocks to sedimentaryrocks; consolidated and unconsolidated. The setup used can be operated with gas and/or vapour overpressureof up to 20 MPa and in a temperature range from range from 20°C to 400°C, further we vary the degree ofwater saturation of the samples. The experiments are monitored with a set of pressure and temperature sensors,synchronized to high-speed video recording of the particle ejection. The resulting particles are recovered andtheir grain size distribution are analysed. This together allows us to constrain the fragmentation behaviour and theefficiency of the fragmentation in phreatic explosions. We observe that the threshold for fragmentation is slightly
lowered whereas the propagation speed of the fragmentation process through the sample is comparable to dry
magmatic experiments. A clear contrast is seen for the ejection speed of the clasts: phreatic clasts can be ejected
at almost double the speed as their magmatic counterparts under similar overpressure conditions. Further theejection speed depends on the ratio of superheated water to vapour and argon gas. This ratio controls also theefficiency of fragmentation as well as the grain shapes.

Our experiments and results enable us to better understand the dynamics of phreatic and hydrothermal
explosions and associated risks. Here we present insights into the energy conversion during phreatic eruptions,based on various starting scenarios. This will provide vital information for the hazard assessment of hydrothermally
active areas.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

209

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

1A2_1E-O11

Room A3

Date/Time: July 21 11:30-11:45

New Insights on the structure and dynamics of geysers
Jean Vandemeulebrouck1 , Shaul Hurwitz2 , Philippe Roux4 , Robert Sohn3 , Estelle Cros1
1

ISTerre, Universite de Savoie, CNRS, France, 2 U.S. Geological Survey, Menlo Park, USA, 3 Woods
Hole Oceanographic Institute, Woods Hole, USA, 4 ISTerre, CNRS, Grenoble, France
E-mail: jvand@univ-savoie.fr

Recent experiments performed at Lone Star Geyser and the reprocessing of seismic ambient noise data collected
at Old Faithful Geyser (OFG), both at Yellowstone Nat. Park (USA) provide new insights on the structure anderuption dynamics of these geysers.
Seismic data obtained in 1992 with a dense array around Old Faithful Geyser have been re-processed using
acoustic localization techniques (beamforming) to characterize the spatial and temporal patterns of seismic sources
inside the geyser conduit. The remarkably energetic, seismo-acoustic activity at OFG is induced by the continuous
cavitation of steam bubbles, which occurs in the upper one meter of the water column. Time-dependent localizationof this powerful acoustic source during the eruption cycle allows us to track water level and phase separation in the
conduit, which in turn provides new insights on the dynamics of the geyser. The distribution of the dominant noise
sources at OFG highlights two distinct structures in the geyser subsurface where water boiling is concentrated:the cylindrical geyser conduit, and a previously unknown lateral reservoir. This reservoir is activated during therecharge period at the beginning of each geyser eruption cycle and plays a major role in the oscillatory behavior of
the water level in the conduit before each eruption.
Geophysical experiments have been carried out during one week in 2011 at Lone Star geyser, during which seismic
ambient noise, ground deformation, acoustic, Infra-red and water flow data from 30 eruptions were collected. We
focus here on the dynamics of the pre-play preceding the eruption, in which the conditions required to initiate theeruption are slowly reached. During the pre-play, thermal expansion and oscillation of the fluid into the conduit
induces several episodes of water overflow, which are followed after some delay by a very energetic pulse of
seismic noise indicating boiling at depth. Eruption starts when these two processes are synchronous.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

210

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

1A2_1E-O12

Room A3

Date/Time: July 21 11:45-12:00

Eruptions at Lone Star Geyser, Yellowstone National Park, USA: Energetics and Eruption
Dynamics
Leif Karlstrom1 , Shaul Hurwitz2 , Robert Sohn3 , Jean Vandemeulebrouck4 , Fred Murphy2 , Maxwell L
Rudolph5 , Malcolm JS Johnston2 , Michael Manga5 , R. Blaine McCleskey2
1

Stanford University, USA, 2 USGS Menlo Park, USA, 3 Woods Hole Oceanographic Institute, USA,
4
ISTerre, Universite de Savoie, France, 5 UC Berkeley, USA
E-mail: leifk1@stanford.edu

Geysers provide a unique natural laboratory to study multiphase eruptive processes. We present results from afour day experiment at Lone Star geyser in Yellowstone National Park, USA. We measured simultaneously water
discharge, acoustic emissions, infrared intensity, and visible and infrared video to quantify the energetics anddynamics of eruptions, occurring approximately every three hours. We define four phases in the eruption cycle:
1) a 28 ± 3 minute phase with liquid and steam fountaining, maximum jet velocities of 16–28 m/s, steam massfraction of 0.5–2.5%, intermittently choked flow, and unsteady flow oscillations with periods increasing from 20 to
40 s, coincident with a decrease in jet velocity and an increase of steam fraction, 2) a 26 ± 8 minute post-eruption
relaxation phase with no fluid discharge from the vent, infrared (IR) and acoustic power oscillations gliding between
30 and 40 s, and ∼ 8 s lag between the peak in acoustic and IR signals, 3) a 59 ± 13 minute recharge period
during which the geyser reservoir progressively refills, and 4) a 69 ± 14 minute pre-play period characterized bya series of 5–10 minute–long steam puffs, small volumes of liquid water discharge, 50–70 s oscillations, and nolag between IR and acoustic signals. The erupted waters ascend from a 163 ± 5◦ C – 186 ± 2◦ C reservoir and thevolume discharged during the entire eruptive cycles is 20.8 ± 4.1 m3 . Assuming isentropic expansion, we calculatea heat output of 1.5–1.7 MW, which is < 0.1% of the total heat output from Yellowstone Caldera.

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1A2_1E-O13

Room A3

Date/Time: July 21 12:00-12:15

Imaging seismic source variations throughout the eruptive sequences of volcanoes andgeysers using back-projection methods
Cyndi L Kelly, Jesse F Lawrence
Stanford University, USA
E-mail: cyndi@stanford.edu

Our understanding of the mechanisms, dynamics, and plumbing networks that characterize volcanic andhydrothermal systems is limited by our ability to remotely observe weak motions related to dynamic processes at
depth. Seismic records from these systems are typically extremely noisy, making it difficult to utilize traditional
seismic methods to resolve 3D subsurface structures. High-amplitude bursts within the noise (i.e. eruptions),
which might be suitable for use with traditional seismic methods, occur infrequently compared to the length ofthe entire eruption cycle. Therefore, while these events may help us understand the dynamics of a particular
eruption, they shed little insight into the mechanisms and dynamics that occur throughout the entire eruption
sequence. Without a continuous temporal sampling we cannot characterize the system as a whole. However, it
has been shown that much more abundant low-amplitude “noise” in these records actually represents a series ofoverlapping low-magnitude displacements that can be directly linked to magma and fluid movement at depth. Thisdata, ignored by most prior studies, contains valuable information about the processes occurring in the volcanic orhydrothermal system before, during and after eruptions. New array processing has the potential to provide crucial
insight into the overall behavior of the volcanic or hydrothermal system.

In this study, we present a new method that seeks to comprehensively study how the seismic source distributionof all events - - including micro-events - - evolves through a volcanic or hydrothermal systems entire eruption
cycle. We apply a back-projection search algorithm to image sources of seismic “noise” at different stages in theeruptive cycle of a volcano (Sierra Negra, Galapagos) and hydrothermal system (El Tatio Geyser Field, northern
Chile). By analyzing coherent seismic energy from all possible events to all available receivers, we determine
how the seismic source location changes through time. This approach utilizes data from the entire seismic record
before, during and after eruptions and thus allows for a more complete understanding of how seismic sourceschange throughout an eruptive sequence rather than only during a particular high-magnitude event or eruption.
This information will help 1) answer fundamental geologic questions about volcano-tectonic processes, 2) makemore accurate assessments of volcanic and hydrothermal hazards, and 3) improve our understanding of how
geothermal reservoirs evolve.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

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1A2_1E-O14

Room A3

Date/Time: July 21 12:15-12:30

First results from the broadband seismological network at Wayang Windu geothermalarea, West Java, Indonesia
Philippe Jousset1 , Andri Hendriyana1 , Makky Jaya1 , Wahyuddin Diningrat2 , Rachmat M. Sule3 , Devy
Syahbana4 , Benjamin Braeuer1 , Christopher Otto1 , Michaela Merz1 , Muksin Umar1 , Yosep Kusnadi2 ,Yudi Indrianto2 , Kemal Erbas1
1

Helmholtz Centre Potsdam GFZ, Germany, 2 Star Energy, Geothermal (Wayang Windu) Limited,Indonesia, 3 Institut Teknologi Bandung, Indonesia, 4 Royal Observatory Belgium, Belgium
E-mail: pjousset@gfz-potsdam.de

The understanding of structure and dynamics of geothermal reservoirs for geothermal exploration and asustainable use of the resource requires assessment using multidisciplinary approach. We deployed a temporary
network of 30 broadband and 4 short-period seismic stations with Güralp and Trillium sensors (0.008 - 100 Hz)
since October 2012 which is still recording in West Java, Indonesia. The two phase liquid/vapor geothermal field
is situated inside the volcanic zone in the center of West Java. The presence of a complex tectonic setting may
explain the co-existence of a large variety of intense surface manifestations like geysers, hot-steaming grounds,
hot water pools, and active volcanoes (including Papandayan volcano). These co-existent features around the twophase geothermal field suggest an intimate coupling between volcanic, tectonic and hydrothermal processes in thisarea. We describe the set-up of the broadband network and discuss first observations and results.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

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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

1P1_1E-O15

Room A3

Date/Time: July 21 15:00-15:15

Reconstructing the volcanological and paleoenvironmental setting of an Archean
Hollandaire Cu-Au volcanic hosted massive sulphide deposit, Murchison Domain,
Yilgarn Craton, Western Australia
Raymond A.F. Cas1 , Patrick C. Hayman1 , Sarah Hull1 , Edward Summerhayes2 , David Price2
1

School of Geosciences, Monash University, Clayton, 3800, Australia, Australia, 2 Silver Lake
Resources, South Perth, Western Australia, 6951, Australia, Australia
E-mail: ray.cas@monash.edu

Discovered in late 2011, Hollandaire is a Cu-Au VMS deposit situated near the town of Cue within the Archean
Murchison Domain of the Youanmi Terrane, Western Australia, and occurs within the Greensleeves Formationof the Polelle Group (2820-2735 Ma). Host rocks are variably silicified, chloritised and sericitised, have been
metamorphosed to upper greenschist facies, and have a pervasive foliation (S1) that is crenulated (S2) in places.
As a result, primary textures are obscured. From stratigraphic logging of 31 diamond drill holes, geochemistry(major and trace elements), petrography and geochronology, we reconstruct the paleo volcano-sedimentary setting.
Host rocks consist dominantly of either quartz-chlorite-muscovite schists (andesitic to dacitic in composition) or
quartz-chlorite-muscovite schists with larger blue quartz crystals (rhyolitic). The former lithofacies, where least
deformed and altered, consists of thin interbedded fine and coarse layers up to 100 m thick, as well as intervals offine-grained carbonaceous black material. This lithofacies is interpreted as a metasedimentary, below wave-base,deep water, distal turbidite succession. The rhyolitic schist lithofacies, with evenly dispersed quartz crystals, ranges
up to 300 m thick, and even within less deformed domains is massive and uniform. Fragmentation is absent at
the margins of this lithofacies, indicating it is a high-level intrusion. The lone breccia interval ( 1 m), consistingof cobble-size clasts of coherent rhyolite in a metasedimentary matrix, is interpreted as reworked autoclastic
volcanic debris. Undeformed dacite porphyries cross-cut the stratigraphy and clearly post-date deformation, andbased on our preliminary geochronological work, are 2780 Ma. Sulphide mineralisation ranges from massiveintervals of mainly pyrite and chalcopyrite (up to 14 m thick) to stringers and disseminated styles. Massiveintervals are restricted to the metasedimentary lithofacies, while disseminated sulphides are found within boththe metasediments and high-level rhyolite intrusion and rarely within the younger dacite porphyries. We interpret
much of this as remobilisation but are uncertain to what extent the primary mineralisation reflected seafloorvs sub-seafloor emplacement. We interpret the setting as a rhyolitic cryptodome with VMS mineralisation ina deep-water setting that was pervasively deformed by both S1 and S2 and subsequently intruded by dacitic
porphyries. We know of no clear evidence for an arc, however, the tectonic setting remains unclear. Voluminous
volcanic events contemporaneous with Hollandaire include the nearby Eelya plutonic complex (2750 Ma), which
has similar geochemistry to the high-level rhyolitic intrusion, and the mafic-ultramafic Gnanagooragoo Igneous
Complex. This study highlights some of the difficulties in working with Archean deposits and adds to the small
database of VMS deposits within the Yilgarn Craton.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

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IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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1P1_1E-O16

Room A3

Date/Time: July 21 15:15-15:30

Understanding the volcanic processes, stratigraphy and mineralization of the archeanteutonic bore, jaguar and bentley volcanic massive sulphide deposits, yilgarn craton,
western australia.
Ritipurna Das1 , Ray Cas1 , Patrick Hayman1 , James Bell2 , Steve Lynn2 , Paull Parker2
1

Monash University, Australia, 2 Independence Group NL, Australia
E-mail: ritipurna.das@monash.edu.au

Teutonic Bore, Jaguar and Bentley volcanic hosted massive sulphide deposits are situated in the Eastern
Goldfields of the Archean Yilgarn Craton, Western Australia. The VMS complex is situated in the Gindalbie Terrane
which is a linear belt (2695-2680 Ma). This bimodal rhyolite-basalt volcanic belt enriched in high field strength
elements, consists of felsic calc-alkaline volcanic rocks, quartz rich sedimentary rocks, layered mafic complexes
and mafic sills, formed during a period of regional extension in a back arc setting. The VMS deposits are hosted
by a bimodal mafic and felsic volcanic succession with associated volcaniclastics and mudstones, and are locatedalong strike over a 12 km distance. The rocks are metamorphosed to lower greenschist facies and have undergone
moderate deformation.

The stratigraphy is divided into a hanging wall facies association and a footwall facies association, which
are commonly separated by sulphide mineralization.

The dominant lithofacies are coherent basalt, rhyolite,

andesite and dolerite, which form concordant, tabular bodies black mudstone, with minor graded bedded
sandstones (turbidites) and rare polymictic conglomerates, represent the ambient deep water facies that areintercalated with the volcanic units. The basalt is present in both the hanging wall and footwall and contains both
massive and pillow basalt facies, indicating that at least some basalts were seafloor lavas. However, monomictic
volcanic breccia, commonly with peperitic textures, occurs at the tops and bottoms of many basalt units, indicatingthat they intruded into unconsolidated sediments. The rhyolite is mainly present in the footwall and is highly altered.
Dolerite occurs as late intrusions with coarse crystalline textures.

The Teutonic Bore consists of one steeply dipping lens of massive polymetallic sulphide underlain by stringer
mineralization. The Jaguar and Bentley deposit consists of three lenses of massive sulphide that are split by alate dolerite intrusion. The massive sulphide consists of pyrite, sphalerite and chalcopyrite. The mineralization ismainly hosted by black mudstone but also occurs in pillowed basalt above the rhyolites. The sulphide lens occurs
as: 1. massive bodies without any dominant fabric; 2. banded bodies of pyrite and sphalerite and chalcopyrite
replacing the pyrite at places; and 3. stringer and disseminated patches. The sulphide shows replacement textureswith basalt and black mudstone, and therefore represents sub-seafloor mineralization that postdates sedimentation
and basalt emplacement. The disseminated sulphide occurs both in the hanging wall and footwall as patches andblebs. Hydrothermal alteration extends into the hanging wall, which also supports a late mineralizing event.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

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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

1P1_1E-O17

Room A3

Date/Time: July 21 15:30-15:45

Magma-related hydrothermal system in volcanic terrain: An example of the alteration in
Unzen USDP-4 scientific drilling
Satoshi Hamasaki1 , Masaru Kurokawa2 , Hideo Hoshizumi1 , Setsuya Nakada2
1

Geological Survey of Japan, AIST, Japan, 2 Earthquake Research Institute, University of Tokyo, Japan
E-mail: hamasaki-st@aist.go.jp

Magmatic heat sources form hydrothermal systems in volcanic areas. Magmatic fluids transport various elements
and produce secondary minerals as a result of reactions with surrounding rocks. For describing the hydrothermal
system inside volcanic terrain, this study examines the characteristics of the hydrothermal alteration undergone
by sample drilled cores and cuttings. The samples were taken from a site located about 840 m above sea levelon the northern side of Mt. Heisei-shinzan. The conduit drilling USDP-4, International Cooperative Research with
Scientific Drilling, began here in 2003. In July 2004, the drilling head reached the conduit zone corresponding to the
1990-1995 eruption (Nakada et al., 2005). The total length of the USDP-4 drilling hole is 1995.75 m. Cuttings were
sampled every 2 m along the drilled hole, and sixteen cores named C1 to C16 were sampled at depths exceeding
1582 m. The drilled cores consist of hornblende-bearing andesite to dacite lavas or pyroclastic rocks.
According to the cutting samples, fresh volcanic rocks can be found at depths less than 200 m. Smectite and pyrite
occur at depths of more than 1100 m and 1400 m, respectively. Smectite disappears at a depth of 1600 m in both
cuttings and core samples. Chlorite appears at depths more than 1700 m in the core samples. The occurrence of
these alteration minerals shows generally good correlation with those expected at these depth. On the other hand,some minerals such as kaolinite occur along fractures or faults. Therefore, it is considered that a relatively hightemperature solution rose along the fractures or faults, which provided good pathways for hydrothermal fluids. In
addition, hydrothermal breccia-bearing veins up to 1 m wide can be observed, indicating that some hydrothermal
solution rose explosively. Tuffisite veins are chlorite-altered with green color, which suggests that these veins madegood pathways for the migration of volcano-related fluids. Calcites occur as veinlets at depths of less than 1900 m inthe drilled cores. The calcite veins often cut through the tuffisite veins, suggesting that the calcite was precipitatedat the latest hydrothermal period.
Inside the Unzen volcanic terrain, the hydrothermal alteration is very similar to those of epithermal vein-type gold
deposits or geothermal fields. According to the alteration minerals, it can be estimated that the smectite zone
shallower than 1600 m was formed at 100 to 150°C, while the chlorite zone deeper than 1700 m was formed attemperatures higher than 190°C. These mineral assemblages correspond to II to IV zones (Izawa et al., 1990) in
the hydrothermal systems such as Hishikari, Kushikino gold deposits, and Ogiri geothermal field in Kyushu.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

216

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

1P1_1E-O18

Room A3

Date/Time: July 21 15:45-16:00

Age dating volcanic springs in the Western Highlands of Cameroon, along the Cameroon
Volcanic Line: a multi-tracer approach
Mengnjo Jude Wirmvem1 , Takeshi Ohba1 , Wilson Yetoh Fantong2 , Samuel Ndonwi Ayonghe3 , JusticeYuven Suila4 , Asobo Nkengmatia Elvis Asaah5 , Kazuyoshi Asai6 , Gregory Tanyileke2 , Joseph Victor
Hell2
1

Tokai University, Japan, 2 Institute of Mining and Geological Research, Cameroon, 3 University of Buea,
Cameroon, 4 G.B.H.S. Atiela, Cameroon, 5 Tokyo Institute of Technology, Japan, 6 Geo-Science
Laboratory Co. Ltd, Japan
E-mail: judevom@yahoo.co.uk

The Western Highlands of Cameroon (WHC) is located mid-way along a chain of volcanoes (ca. 1600 km), cutting
diagonally across Cameroon, called the Cameroon Volcanic Line (CVL). The area forms the main watershed in
the country and consists of mineralised springs (MS) and numerous less mineralised springs (LMS). Despite thesignificance of such subsurface waters in volcanic processes, little hydrological data is available on the origin
and age of these fluids along the CVL. Such data can provide information on the interaction of subsurface fluids
along the CVL. In this study, a preliminary multi-tracer technique has been conducted on 18 LMS (mean TDSof 1542 mg/l) and 6 MS (TDS of 45 mg/l) in the WHC to determine their origin and time of circulation in theupper crust. Except for one MS (hot spring, T >33oC), all other springs are cold (T <27oC). Field observations
revealed emanations of an unknown gas at the MS, which may be CO2 based on related studies along the CVL.
Regardless of their discharge at relatively low altitudes, all MS are isotopically depleted (mean delta O-18 of -5.67
per-mille) in relation to high altitude discharging LMS (mean delta O-18 of -4.04 per- mille) suggesting recharge ofMS under relatively cold climatic conditions. However, both plot along the Local Meteoric Water Line, suggesting
their meteoric origin. Tritium values in MS are low, ranging from >0.3 TU (4 samples) to 2.3 TU, compared to 2.4
to 3.1 TU in LMS, mainly indicating pre-1957 recharge of the former and post-1957 recharge of the later. The
CFC-12 (like CFC-11 and CFC-113) and SF6 in MS are low, ranging from 6 to 85 pk/kg and from 0 to 0.34 fmol/lg,
respectively. On the contrary, LMS show high values in CFC-12 and SF6, ranging from 28 to 239 pk/kg and 1.01 to
7.23 fmol/lg, respectively. Based on the known concentrations of CFCs and SF6 in the atmosphere, CFC-12 versus
CFC-11, CFC-113 and SF6 plots of samples show a binary mixing model in MS and mainly an exponential mixing
model, of uniform areal recharge, in LMS. CFC-12 versus 3H and delta O-18 versus delta-D plots show different
degrees of binary mixtures of old MS and young LMS. Thus, based on the multi-tracer approach, the estimatedages of MS and LMS range from 51 to 35, and 45 to 19 years, respectively, indicating the long residence timeand deep circulation of MS which may explain their enriched mineralization. Conclusively, the MS may represent
a portion of magmatic fluid that mixes with old deep circulating groundwater, upon its upward movement it further
mixes with shallow and cold young groundwater.

Key words: spring water origin, residence time, subsurface circulation, The Cameroon Volcanic Line

©IAVCEI 2013 Scientific Assembly. All rights reserved.

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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

1P1_1E-O19

Room A3

Date/Time: July 21 16:00-16:15

Chemical evolution within a hydrothermal fluid circulation system at the Aira caldera,
Kyushu, Japan
Jun-ichiro Ishibashi1 , Shingo Hirao1 , Tatsuaki Ono1 , Toshiro Yamanaka2
1

Graduate School of Science, Kyushu University, Japan, 2 Graduate School of Natural Science andTechnology, Okayama University, Japan
E-mail: ishibashi.junichiro.779@m.kyushu-u.ac.jp

A caldera structure provides a geological setting suitable for development of a hydrothermal fluid circulation system,
since it is equipped with a heat source magma and fluid conduit of fault networks. The Aira caldera is one of
Quaternary calderas which formed within the Kagoshima graben in south Kyushu. At present, most part of the Airacaldera (30 km x 20 km in size) is submerged to be a part of Kagoshima Bay.
The Wakamiko submarine crater is considered as the volcanic center of the past giant eruption that formed the Airacaldera. On the seafloor of 200 meters water depth at the Wakamiko submarine crater, venting of high temperature
fluid (around 200 degC) was observed during dive expeditions using ROV (Remote Operation Vehicle). On the other
hand, along the shoreline at northern part of the Kagoshima Bay where corresponds to the rim of the Aira caldera,
some hot springs are pumped up from the aquifers situated at 650-1100 m depth. The hot spring waters showedtemperature of 40-80 degC and NaCl-rich chemistry. In order to reveal similarities in these fluids, geochemical
studies were conducted for submarine hydrothermal fluid and onshore hot spring waters.
Relationships among delta-D and chloride concentration of these fluids are commonly explained by around 1:1
mixing of the meteoric water and seawater. This result implies they share the same fluid reservoir that may
distribute across subbasement of the caldera floor. Comparison of water chemistry would provide important keys
to understand how fluid chemistry evolves during fluid circulation from a recharge zone to discharge zone.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

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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

1P1_1E-O20

Room A3

Date/Time: July 21 16:15-16:30

Geochemistry of geothermal fluids in the active Liquiñe-Ofqui Fault System (Southern
Andes Volcanic Zone, Chile).
Daniele Tardani1 , Pablo Sanchez1 , Pamela Perez2 , Martin Reich1 , Franco Tassi3 , Bruno Capaccioni4 ,Giovanni Chiodini5 , Orlando Vaselli3
1

Departamento de Goelogia, Universidad de Chile, Santiago, Chile, 2 Pontificia Universidad Catolica deChile, Santiago, Chile, 3 Department of Earth Sciences, University of Florence, Florence, Italy,
4
Department of Earth and Geological-Environmental Sciences, Bologna, Italy, 5 Istituto Nazionale diGeofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy
E-mail: tardaniele@gmail.com

The nature of the interplay between tectonics and the chemical composition and circulation of geothermal
fluids is a major question in active continental margins (Cox, 2010; Rowland and Simmons, 2012).

The

intra-arc, strike-slip Liquiñe-Ofqui Fault System (LOFS) in the Southern Andes Volcanic Zone (SAVZ) of Chile
offers a unique opportunity to address this question because of evident changes in tectonic style related withchanges in geochemical signature of volcanic products (Lopez Escobar, 1995; Lara et al., 2006). Two main
volcano–tectonic features have been recognized by Cembrano and Lara (2009): 1) kinematically coupled systems
directly related to the current dextral transpressional tectonic regime, including NE–trending volcanic alignments ofstratovolcanoes and monogenetic cones of primitive, basaltic compositions; 2) kinematically uncoupled systems,
including NW–trending of stratovolcanoes associated with ancient reverse faults of the volcanic arc basement.
Within this context, one lesser known but relevant aspect of the evolution of geothermal systems associated to the
LOFZ is the relation between these volcano–tectonic features and fluid geochemistry.
This study focus on the chemical and isotopic composition of gases and waters in selected volcanoes in the SAVZ.
The NE–trending volcanic alignment Callaqui–Copahue is investigated at the northern termination of the LOFS,
where the spatial distribution of the hydrothermal discharges is controlled by a NW–trending faults (Nakanishi etal., 1995). South of this area, two additional systems are studied: the Tolhuaca volcano, whose geothermal systemseems to be related to an active NW–trending fault, and the NE–trending systems that control the active Lonquimay
volcano.
Previous works in Copahue volcano shows a variability in He concentration between the two, NW and NE, structurallineation that control the geothermal system (Agusto 2011). We are using He, O, H and N isotopes able to provide
insights about fluid sources, gas–water–rock interactions and their relation with the volcano–tectonic structures,
mentioned above.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

219

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

1P1_1E-O21

Room A3

Date/Time: July 21 16:30-16:45

The Source to Surface Project: what are geochemical proxies really telling us aboutmagmatic-hydrothermal systems in the Taupo Volcanic Zone, New Zealand?
Joshua M Blackstock1 , Darren Gravley1 , Simon Bloomberg1 , Travis W Horton1 , Kevin Brown2 , Clinton
Rissmann3
1

University of Canterbury, New Zealand, 2 GEOKEM, New Zealand, 3 Environment Southland, New
ZealandE-mail: joshua.blackstock.canterbury@gmail.com

The uses of geochemical proxies both to describe and quantify heat and mass fluxes are important tools in
understanding hydrothermal systems globally. Information derived from these proxies is crucial for geothermal
resource characterization and management, studying ore-forming processes, understanding geochemical cycling,
and the assessment for both hydrothermal and volcanogenic hazards. Over the past half-century, hydrothermal
systems in the Taupo Volcanic Zone, New Zealand (TVZ) have been extensively studied to which numerous
inferences have been presented describing the origin, flow paths, and heat and mass flux through fluid
geochemistry. In this study, we have compiled and compared published, unpublished, and our own data for
liquid, gas, and soil-gas surveys in the TVZ hydrothermal systems. We describe here an updated model for theorigin, flow paths, and heat and mass transport for fluids in the TVZ. Numerous relationships between elements
and compounds show evidence for a geochemically distinct single-parent fluid. However, the ultimate origin(s)or end-member(s) for the elements and compounds comprising this fluid is not known. New interpretations arepresented regarding three unique groupings based on B/Cl relationships. Where these groupings occur, they do not
spatially correlate with any particular tectonomagmatic setting, as inferred by previous authors. We propose these
relationships to be the result of water-rock interaction and phase separation and not from multiple fluid sources.
We also show from soil-gas surveys, that ’blind’ structural components are a significant factor in detecting upflow
zones that are not readily apparent from either structural mapping or temperature profiles. Spatial correlations
also exist between geophysical data and our soil-gas surveys demonstrating a powerful new combined method in
the identification of upflow. Finally, from our soil CO2 studies we demonstrate that for high-resolution surveys, a
CO2 -based method incorporating the carbon isotopic signature of CO2 may provide a more accurate heat flux value
than existing chloride models which may not always be reliable throughout the TVZ (Bibby et al., 1995). This has
implications for reassessing the heat flux for the entire TVZ (currently accepted to be 4500 MW) and ultimately thescale of modern crustal magmatism. Our findings are of particular interest for similar arc- and rift-type systems alikeand our methods are likely applicable outside the TVZ for both assessment and monitoring of magmatic-geothermal
systems.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

220

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

1W_1E-P1

Date/Time: July 21 Poster

Eruption due to depressurization: Numerical simulation by VERA code
Eisuke Fujita
National Research Institute for Earth science and Disaster prevention, Japan
E-mail: fujita@bosai.go.jp

Magma and hydrothermal systems are more or less stable under lithostatic and hydrostatic circumstance, however,in case of some pressure condition, the system becomes unstable and even a tiny perturbation can trigger acatastrophic instability, which may lead to an eruption. In a hydrothermal system and shallow volcanic fluid system,
the gas-liquid interaction controls the activities, and the instability of two-phase flow dynamics is essential torecognize the eruption mechanism.
There are several candidates as "tiny perturbation", for example, new magma intrusion from deeper part, magma
mixing, etc. One of the important triggering mechanisms is depressurization, which occurs in many situations:the opening of a "plug" which is keeping a pressurized gas-water system would disturb a hydrothermal system.
For magma plumbing system, magma ascends and reduces the pressure itself, then the bubbling is promoted.
Once the volume fraction of gas component overcomes a threshold, the fragmentation occurs and we can detect
as an explosive eruption. This series of phenomena from depressurization to fragmentation is controlled by manyfactors. We developed a numerical simulation code "VERA", by which volcanic eruption is simply simulated asa phenomenon triggered by pressure release due to an opening of a conduit cap at the top. In VERA code,
we formulate gas-liquid flow by the expanded two-phase flow model and adopt VOF scheme for free surface
evaluation. The subsurface plumbing system is modeled to consist of cylindrical conduit and spherical reservoir
with an adequate length and/or diameter. As an initial condition, we assume an initial radius of a bubble in themagma reservoir, bubble number density, and excess pressure in reservoir. Opening of the conduit cap releases
fluid pressure and enhances the growth of bubbles. When the void ratio exceeds a threshold, fluid is fragmented.
The fluid viscosity is also an important factor, and in case of large viscosity, the fluid is very hard to be fragmented,
since the bubbles cannot expand easily. This model is also applied to the Mount Fuji magma system depressed aslarge as 1MPa due to the enormous ground deformation by Tohoku megathrust earthquake. Our simulation code
VERA reveals the details of the fragmentation phenomena, significant heterogeneous distribution of gas and liquidcomponents as well as pressure perturbation in the conduit and reservoir.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

221

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

1W_1E-P2

Date/Time: July 21 Poster

Features of geyser’s eruptive activity in broadband seismic records (Valley of Geysers,
Kamchatka)
Vadim Saltykov, Yulia Kugaenko
Geophysical Survey of Russian Academy of Sciences, Kamchatkan Branch, Russia
E-mail: salt@emsd.ru

Valley of Geysers on Kamchatka Peninsula is one of the world’s major geyser areas, in a league with Yellowstone,
El Tatio in Chile, Waiotapu on New Zealand’s North Island, and Iceland. We use seismic method for detection of
possible hidden feature of geyser’s eruptive activity in Valley of Geysers in Kamchatka.
A geyser is a spring characterized by intermittent discharge of water ejected turbulently and accompanied by avapor phase (steam). The reasons of geyser periodicity and specifics of the activity for every particular geyser are
not completely clear yet. So almost for all known geysers it is necessary to develop the personal model.
We obtained broadband seismic records of geyser generated signals in Valley of Geysers hydrothermal field by
24-bit digital output broadband seismometers GURALP CMG-6TD (0.033-50 Hz). Three geysers were surveyed:
the fountain type Big and Giant geysers and the cone type Pearl geyser. Seismometers were set as close as
possible to the geyser’s surface vent (usually at the distance near 3 m).
For the large Big and Pearl geysers low-frequency seismic response on geyser’s eruption was detected.
Seismometers showed surface deformation caused by water-steam burst from the vent (or geyser eruption) withthe period about 10-12 min. It was shown, that eruptions of the Big geyser are not constant at different frequency
bands. Some eruptions are weaker than other in low-frequency band (lesser then 0.01 Hz), but approximately
similar for the range 20-50 Hz. It means possible deep variations of thermal supply.
The most important result is the detection of hidden underground geyser in the area of the Giant geyser. Its
deep activity is recorded by seismic and mass position channels as very stable quasi-periodic oscillations withperiod 16-18 min. It caused quasi-harmonic displacements of surface with amplitude about 5-6 mm. Earlier the
existents of the underground geyser was assumed due to observation of intense bursts with such periodicity duringboiling-effusion mode before every eruption. So the supposed underground geyser was accounted as the mainheat provider and the principal cause of the Giant geyser eruptions. We named this deep quasi-periodic source ofseismic signal (underground geyser) Heart of Giant.

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IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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1W_1E-P3

Date/Time: July 21 Poster

Characterization and quantification of geyser eruptions: insights from infrasoundmonitoring at Yellowstone National Park
Philippa J Demonte, Jeffrey B Johnson
Boise State University, United States
E-mail: philippademonte@u.boisestate.edu

This study investigates the infrasound emissions from geysers in Yellowstone National Park to characterize andquantify eruption parameters. Geysers are hot springs, which intermittently erupt hot water and steam. Theireruption phenomena include bubble bursts and two-phase fluid jets, which are strong emitters of near-infrasound(1-20 Hz) and low frequency audible airwaves.

During a field campaign in August 2011, a 2-element and two 4-element MEMS transducer arrays were
installed to continuously record the infrasound generated by three distinctive geysers: Sawmill Geyser, Great
Fountain Geyser and Lone Star Geyser. The infrasound waveforms are diverse and distinct. We highlight thecomparison of their spectral content and acoustic power. Time-synched video observations reveal how the geysers’
eruptive behaviors relate to their waveform characteristics.

Great Fountain Geyser (GFG) typically produces episodic bi-modal pressure pulses (compression-rarefaction),
which we interpret as bubble or gas slug bursts leading to two-phase fluid ejections. Characterizing GFG as
a monopole source, we calculate that the largest excess pressures recorded correspond to cumulative fluid
ejections on the order of 50 m3 . In contrast to GFG, the periodic (0.7 s) pressure pulses of Sawmill Geyser (SMG)
commence with a rarefaction, which we interpret as the collapse or implosion of steam bubbles. Lone Star Geyser(LSG) eruptions consist of ~30-minute episodes of continuous broadband tremor. We observe from the recorded
signals that LSG displays a distinct change in behavior from a relatively low frequency water-dominated phase(20-60 Hz) to a higher frequency pure steam-jet-dominated phase (40-85 Hz).

The two-phase (water and steam) eruptions of geysers provide a useful intermediary in the comparison of
analogue laboratory experiments and silicic magmatic eruptions. Geysers are easily accessible for observation,
erupt often, and display a wide range of behaviors. Hence, despite differences in scaling and materials erupted, weconclude that geysers and their eruption dynamics could be useful analogues for the interpretation of infrasoundgenerated by volcanoes.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

223

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

1W_1E-P4

Date/Time: July 21 Poster

Estimates of Heat output from the Yellowstone Plateau Volcanic Field using different
approaches
Shaul Hurwitz, R Greg Vaughan, Jacob B Lowenstern
US Geological Survey, USA
E-mail: shaulh@usgs.gov

Yellowstone is one of the largest and most restless calderas on Earth and its magmatic system is one of the most
focused heat sources on Earth. The most recent caldera-forming eruption occurred around 0.64 Ma ago, thoughsmaller explosive and lava-effusing eruptions have continued up until approximately 70 ka. The magmatic systemremains active as manifested by abundant seismicity, deformation and the presence of more than 10,000 thermalfeatures. Quantifying heat flux through the ground surface can provide insight into magma intrusion rates andhydrothermal flow, but is a daunting task because of the vast extent of thermal areas in and around the Yellowstone
Caldera. Nevertheless, obtaining such data could provide an improved understanding of magmatic processes,
which in turn, allows for a better estimate of hazards. Heat is transported to the surface by conduction and by
advection of liquid water and steam. Heat is transported away from the surface by evaporation from lakes, pools,
and rivers, conduction to the atmosphere, and radiation. Diverse methods are used to quantify heat discharged
through these various modes. Estimates in the early 20th century that were based on the integration of discharge
and temperature measurements of individual thermal features throughout Yellowstone yielded a total heat output of
about 1 GW [Allen and Day, Carnegie Inst. Publication, 1935]. The chloride-inventory method, which was initiallyapplied to Yellowstone in the 1970s, assumes that all the chloride discharged by rivers draining Yellowstone isderived from a single deep parent fluid [Fournier, AREPS, 1989]. With this method and a set of plausible parametervalues, estimates of heat output vary by a factor of two. A minimum output of 4 GW corresponds to a chloride
concentration of 450 mg/L, a temperature of 320 C, and a chloride flux of 45 kt/yr, and a maximum output of 8 GW
corresponds to a Cl concentration of 350 mg/L, 360 C, a flux of 55 kt/yr Shallow conductive temperature gradientmeasurements and evaporation from thermal pools are restricted to very small areas [Morgan et al., JGR, 1977;
Hurwitz et al., JGR, 2012] and the extrapolation of these data to the entire Yellowstone Plateau incorporates many
assumptions. Extrapolation of the average heat flux from two small vapor dominated areas to the approximately 35
km2 of vapor dominated areas in Yellowstone yields more than 3.6 GW [Hurwitz et al., JGR, 2012]. Satellite-based
thermal infrared (TIR) remote sensing methods provide estimates for the entire Yellowstone thermal anomaly, but
measure only the radiative component of heat output. For example, nighttime ASTER TIR data were used toestimate a radiative heat output of about 2.0 GW [Vaughan et al., JVGR, 2012]. Future studies aimed at integratingthese disparate approaches and characterizing temporal variations will require a combination of ground-based
methods, airborne infrared, and improved satellite radiometers.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

224

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

1W_1E-P5

Date/Time: July 21 Poster

The response of geysers to stress and weather perturbations
Robert A Sohn1 , Karen Luttrell2 , Shaul Hurwitz2
1

Woods Hole Oceanographic Institute, USA, 2 US Geological Survey, USA
E-mail: shaulh@usgs.gov

Geysers are rare with less than 1,000 worldwide, of which between 200 and 500 occur in the geyser basins of
Yellowstone National Park. Their rarity reflects a delicate balance between supply of water, a large supply of heat,
and a unique geometry of fractures and porous rocks. Because of the delicate balance between these controllingparameters, only a few geysers display relatively constant intervals between eruptions. Analyzing the sensitivityof geysers to stress perturbations from earthquakes and Earth tide and weather variations, including barometricpressure, precipitation, and wind can yield significant information on cause and effect relationships in thesesystems, and on the threshold stress perturbation amplitude required to trigger eruptions. Previous studies thatexamined geyser response to external forcing were based either on sub annual or discontinuous geyser eruption
records, and therefore have resulted in conflicting interpretations. To overcome these shortfalls, we analyzed nearlycontinuous records of eruption patterns of Daisy and Old Faithful geysers in the Upper Geyser Basin of Yellowstone
National Park for the period between 2001 and 2011 available from the Geyser Observation Society of America.
Geyser eruption times are determined from continuously recording temperature sensors in the geysers outflow
channels, and are compared with data on regional and remote earthquakes, barometric pressure, precipitation,wind storms, and calculated theoretical Earth tides. Daisy and Old Faithful geysers were selected for the analysis
because they have relatively uniform eruption intervals and long-term records are available. Preliminary results
indicate that eruption intervals at Old Faithful slightly shortened in response to the passage of surface waves fromonly a few large global earthquakes. Daisy Geyser eruption intervals were only modulated after the passage of
surface waves from the November 2002 Denali earthquake. Eruption intervals of both geysers are not modulated
by earth tides. The results of this study have implications for studying the triggering of volcanic eruptions by external
forces. As with volcanoes, stress perturbations in hydrothermal systems can either perturb the nearly saturated
fluid, and thus enhance or suppress phase separation and bubble formation, or perturb the surrounding rocks
and fractures, both of which may lead to, or delay an eruption. Because geyser eruptions are more frequent anduniform than volcanic eruptions, statistical analysis linking external forces with geyser eruptions rely on much larger
datasets, and thus may provide more robust insight on the sensitivity of multiphase erupting systems.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

225

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

1W_1E-P6

Date/Time: July 21 Poster

Filling geyser conduits between eruptions, as revealed by acoustic measurements in the
El Tatio Geyser Field, Chile
Atsuko Namiki1 , Carolina Munoz2 , Shaul Hurwitz3 , Max Rudolph2 , Eric King2 , Michael Manga2
1

University of Tokyo, Japan, 2 UC Berkeley, USA, 3 USGS, USA
E-mail: namiki@eps.s.u-tokyo.ac.jp

We performed the acoustic and temperature measurements, correlated with visual observations, at the El Tatio
Geyser Field, at an elevation of ca.4300 m in the Northern Chilean Andes. We focused on two geyser systems,
named El Jefe and El Cobreloa.

El Jefe Geyser erupts every 2 minutes lasting for 15 seconds.

We confirmed that acoustic measurements

are useful for monitoring the sequence of eruptions during at night. When eruptions occur, documented by risingtemperatures in the conduit, high frequency sound is recorded. Sound may be generated by water droplets
landing on the ground surface. Between eruptions, sounds with a characteristic frequency approximately 100 Hz
are recorded. This may be originated from the air column resonance within the conduit. During the day time it
was windy, and acoustic measurements do not show a correlation with eruption activity. We also confirmed thatmeasurements of ground temperature can detect the flowing hot water associated with eruptions.

We applied these methods to the other target, El Cobreloa Geyser, which erupts in two ways: vigorous
major eruptions, and less energetic minor eruptions. We monitor major eruptions measuring ground temperatureand minor eruptions acoustically. We found that major eruptions occur at regular intervals of approximately 4
hours and 40 minutes. During the inter eruption period, minor eruptions also occur regularly, with an interval of
approximately 13 minutes. The observations suggest that filling of the conduit is a complex process.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

226

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

1W_1E-P7

Date/Time: July 21 Poster

A physical model for the phreatic explosion on July 15, 1888 at Bandai volcano,northeastern Japan
Hamaguchi Hiroyuki1 , Ueki Sadato2 , Nakamichi Haruhisa3
1

Tohoku Univ., Japan, 2 Graduate School of Sciences, Tohoku Univ., Japan, 3 Graduate School ofEnvironmental Studies, Nagoya Univ., Japan
E-mail: hamaguti@cello.ocn.ne.jp

The 1888 eruption at Bandai volcano, Japan, has been well known as one of the most gigantic historical phreatic
explosions. The precise nature of the explosion mechanism, however, has not been quantitatively clarified until
now. It is due to the statements and interpretations in the leading article of Sekiya and Kikuchi (1890) were mainly
based on the various circumstantial evidences that were collected by seeing of authors’ selves and local habitants.
They inferred that the hydrothermal fluid triggering the explosion and rock avalanche might have been locatedbeneath the exploded peak called Kobandai-san and that the depths of the earthquakes immediately preceding
the eruption might be very shallow in the volcano. These naive inferences have been left without any quantitative
examination for more than one century. We re-examined their ambiguous inferences about the explosion source
and the earthquakes preceding the eruption. We analyzed primarily the following two observational data: The
one is the shallow bulge structure beneath the old crater that is recently deduced from the seismic tomography
and the other is the isoseismal map drawn from questionnaire by Sekiya and Kikuchi. The map showed that theperceptible area of the biggest preceding earthquake had a shape of an ellipsoid elongated in the direction of N25E
and its intensity at the boundary was assigned to 1 on the JMA scale which was equivalent to ca. 2 gal. The
characteristics of the observed isoseismal were compared with those calculated as a function of source depth anddirectivity under several reasonable assumptions. Referring to the observed 3D bulge structure beneath the oldcrater, an explosion source was modeled by a pressurized spherical cavity with a radius of 0.5 km located at a
depth of 1.0 km. The numerical analysis revealed that the fluid pressure would escape from the cavity through two
tensile fractures oriented in different directions; one is oriented upward from the apex of the cavity and the other is
at an oblique angle of 30 degrees with the ground surface at a horizontal distance of about 1.8 km from the apex.
We concluded that the explosion source with a radius of 0.5 km was located beneath Numanotaira (the old crater)
at a shallow depth of 1.0 km but not beneath Kobandai-san (the collapsed mountain) and that two tensile fracturesin directions of N20W and N100E were simultaneously opened due to an excess pressure, resulting the dynamic
collapse with large rock avalanche into the north and the steam-jet burst with mud flow into the south-east. The
seismic moment and magnitude of the biggest earthquake immediately preceding the explosion were estimated tobe 10**16 Nm and M4.6, respectively. These results provided a counter-evidence for the traditional inference by
Sekiya and Kikuchi.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

227

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

1W_1E-P8

Date/Time: July 21 Poster

Experimental constraints of phreatic eruptions at Solfatara volcano, Campi Flegrei
Cristian Montanaro1 , Bettina Scheu1 , Klaus Mayer1 , Giovanni Orsi2 , Donald B. Dingwell1
1

Ludwig Maximilians Universitat (LMU), Germany, 2 National Institute of Geophysics and Volcanology(INGV), Italy
E-mail: cristian.montanaro@min.uni-muenchen.de

The Phlegraean Fields caldera, a nested and resurgent structure, is amongst the most dangerous volcanic areasin the world, enclosing part of the city of Naples, the town of Pozzuoli and numerous densely inhabited villages.
The relationship between resurgence and volcanism in the past 15 ka is manifested by an intense volcanic activity
preceded and accompanied by important phases of ground deformation [Orsi et al., 2004]. A complex interaction
between the deep magmatic source and the shallow hydrothermal system seems to have driven most of the recent
unrest episodes, during which ground uplift and seismic activity affected Pozzuoli City and the near fumarolic field of
Solfatara. The latter represents the most active hydrothermal site of Phlegraean Fields; here historical chronicles
report the occurrence of a phreatic event in the 12th century. Phreatic eruptions usually occur with little or no
warning and are able to create substantial explosion craters. Additionally they are often precursory to a new cycleof volcanic activity as was the case during the 1538 Monte Nuovo eruption.
We present an experimental approach based on a shock-tube apparatus [Alidibirov and Dingwell, 1996, Spieler et
al. 2004, Scheu et al. 2008] to investigate different scenarios likely for phreatic eruptions in the Solfatara area. This
technique allows producing fragmentation from a combination of Argon gas overpressure and steam flashing within
the connected pore space of the tested samples at varying PT conditions. Neapolitan Yellow Tuff is used as sample
material for the study as it is the stratigraphic unit of the expected source region for phreatic explosions [Orsi et al.
1996].
The hydrothermal system below Solfatara is thought as a gas plume with a shallow single phase gas zone anda deeper mixing zone. The latter occur at depth between 1000 and 1500 m (20-25 MPa), where temperature
conditions are close to the critical point of water (>360°C) [Caliro et al., 2007].
We focused in a first case study on the deeper system, therefore a pressure and temperature range of 15-20
MPa and 300-350°C were chosen mimicking the natural conditions. The entire experiments were monitoredwith temperature and pressure sensors, the latter were also used to determine the speed of fragmentation. The
generated fragments were fully recovered and the grain-size distribution and thus the efficiency of fragmentation
were determined. Further different degrees of water saturation and variably tempered samples have been used inorder to investigate strength reduction due to both water weakening effects and the zeolite dissolution.
The study’s aim is to raise awareness of the hazard potential of phreatic explosions in Solfatara area. It also
represents the first part of an experimental data base we are aiming to construct and that will enable us to constrain
the phreatic eruption scenarios in Solfatara area as well as other sites in Phlegraean Fields.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

228

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

1W_1E-P9

Date/Time: July 21 Poster

Experimental approach to constrain phreatic eruption processes on White Island, New
ZealandKlaus Mayer1 , Bettina Scheu1 , Yan Lavallée2 , Ben Kennedy3 , H. Albert Gilg4 , Michael Heap5 , Mark
Letham-Brake3 , Cristian Montanaro1 , Laura Jacquemard5 , Noémie Pernin5 , Donald B. Dingwell1
1

LMU Munich, Germany, 2 University of Liverpool, Great Britain, 3 University of Canterbury, New
Zealand, 4 TUM Munich, Germany, 5 University of Strasbourg, France
E-mail: klaus.mayer@min.uni-muenchen.de

White Island is New Zealand’s most active volcano and primarily characterised by phreatic and phreatomagmatic
eruptions. A phreatic eruption on August 2nd, 2012 ended an eleven year quiescence. More than 100 years ofintense hydrothermal activity from magmatic fluids and groundwater has created a weak and unstable volcanic
edifice highly susceptible to sector collapses and landslides. Here, we constrain the influence of alteration onphreatic eruption conditions and on the stability of an edifice subjected to an active hydrothermal system. A
hydrothermally altered lava flow and four lithified pyroclastic rocks with different grades of alteration, together withunconsolidated material and sulfur- and iron-rich crusts from the crater-fill were sampled and investigated.
The lava flow is primarily composed of plagioclase, K-feldspar and pyroxene, but alteration has also lead to thepresence of cristobalite, amorphous silica, gypsum and jarosite. The pyroclastic rocks do not contain any primaryminerals or glass and consist instead of amorphous silica, alunite, jarosite, gypsum and kaolinite.
The lava flow with a low porosity (6.6-8%) was found to be moderately strong (110-140 MPa) when deformed inuniaxial compression tests, although we find that the presence of macroscopic fractures can lower the strength to
60 MPa. The altered pyroclastic rocks are more heterogeneous, porous (32-48%) and weaker, with unconfinedcompressive strengths ranging between 3 and 20 MPa. Our uniaxial experiments also show that the alteredpyroclastic rocks are weakened when saturated with water.
Conditions for phreatic eruptions were constrained by fragmentation experiments on dry and water-saturated
samples due to rapid decompression (from 9 MPa to atmospheric pressure) at temperatures of up to 300°C.
This provided information about the energy threshold, fragmentation efficiency, the maximum speed and evolutionof particle ejection velocities. The fragmentation threshold ranges between 5.1 MPa and 3.8 MPa for samples
with a connected porosity of 32% to 48% , which is in agreement with the trend for pristine volcanic rocks. The
fragmentation efficiency generally increases with higher applied energy but also if the sample is saturated. The
particle ejection velocity after fragmentation increases with the applied pressure and porosity. For experiments ondry consolidated samples, where the fragmentation occurs at an argon gas overpressure of 6.5 MPa and 300°C,
the ejection speed (45 m/s) is significantly lower than for fully water-saturated samples (145 m/s). Unconsolidated
samples with connected porosities of 35% show a similar effect of sample saturation on the ejection.
Our study suggests that hydrothermal alteration and fluid-saturation associated with the presence of a hydrothermal
system weakens the rocks (over a range of strain rates), which may result in slope destabilisation, lateral/sector
collapse and further phreatic eruptions.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

229

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

1W_1E-P10

Date/Time: July 21 Poster

Campi Flegrei Deep Drilling Project and geothermal activities in Campania Region(Southern Italy)
Giuseppe De Natale, Claudia Troise, Stefano Carlino, Renato Somma, Antonio Troiano, Maria Giulia Di
Giuseppe, Angela Mormone, Anna Tramelli, Monica Piochi
Istituto Nazionale di Geofisica e Vulcanologia - Osservatorio Vesuviano, Italy
E-mail: stefano.carlino@ov.ingv.it

Recent studies of Campanian volcanic geothermal systems have shown a large geothermal potential (Carlino etal., 2012), similar to the Larderello-Radicondoli-Amiata region, in Tuscany (Central Italy), which has been the firstsite in the World exploited for electric production. Recently, the Campi Flegrei Deep Drilling Project (CFDDP),
sponsored by ICDP and devoted to understand and mitigate the extreme volcanic risk in the area, has also raised
new interest for geothermal exploration in several areas of Italy. Following the new Italian regulations which favor
and incentivize innovative pilot power plants with zero emission, several geothermal projects have started in theCampania Region, characterized by strict cooperation among large to small industries, Universities and public
Research Centers. INGV department of Naples (Osservatorio Vesuviano) has the technical/scientific leadership ofsuch initiatives. We intend to show the present state of art of the researches, new insights and ongoing geothermal
projects in Campanian region. Among the most important results of geothermal interest, determined by recent
research projects, we also show here new computations of in-situ permeability at Campi Flegrei caldera, obtained
during the drilling of CFDDP pilot hole.

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230

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

1W_1E-P11

Date/Time: July 21 Poster

Geophysical changes and hydrothermal activity at the early stage of the White Island
2012 unrest episode
Lauriane Chardot1 , Bruce W. Christenson2 , Micol Todesco3 , Tony Hurst4 , Nicolas Fournier5
1

Dept. Geol. Sci., University of Canterbury, Private Bag 4800, Christchurch, New Zealand, 2 National
Isotope Centre, GNS Science, Private Bag 31-312, Lower Hutt, New Zealand, 3 INGV Sezione di
Bologna, via D. Creti 12 40128 Bologna, Italy, 4 GNS Science, PO Box 30368, Lower Hutt 5040, New
Zealand, 5 GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo, New ZealandE-mail: l.chardot@gns.cri.nz

White Island volcano, one of the most active volcanoes in New Zealand, is experiencing an elevated level of unrest
at the time of writing, after more than 10 years of relatively low hydrothermal activity. Some sustained periods of
volcanic tremor started in June 2012, later accompanied by fluctuations of the crater lake level in July and minor
eruptions from August. A small lava dome was first observed in November within the crater and the activity extended
to the remnant crater lake location where currently, venting occasionally occurs. This activity is accompanied by
rapid variations in the level of volcanic tremor.
The volcano hydrothermal system has most likely been disturbed by this new magmatic activity, potentially before
the magma even reached the surface. It is then of paramount importance to better understand the hydrothermal
system fingerprint in the early signals of volcanic unrest to better detect future activity at the volcano.
We present results from three magnetic and gravity surveys acquired prior to this unrest episode, between May
2011 and June 2012. Data were collected at the volcano crater floor on 67 magnetic pegs and 10 gravity tiles. We
then compare these results with other monitoring datasets and present some preliminary results from numericalmodelling (e.g. TOUGH2) in order to assess potential relationships between recorded geophysical signals and themagmatic-hydrothermal processes.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

231

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

1W_1E-P12

Date/Time: July 21 Poster

Characteristics of seismicity within proximity to active geothermal and volcanic areas
Xiaowei Chen
University of California, San Diego, USA
E-mail: Xiaowei.fengr@gmail.com

Geothermal energy is renewable, clean, and has been utilized worldwide. Exploitation of geothermal energy
involves fluid injection for heat circulation purposes and increasing permeability. Increased fluid pore pressure will
accelerate the failure process under Coulomb failure criteria. Thus, correlations between seismicity and injection
activities are identified at most geothermal reservoirs; one famous example is the Geysers. The triggering frontof seismicity due to fluid is controlled by the pore pressure diffusion process in space and time. The hydraulicdiffusivity can be obtained from the spatial-temporal pattern of seismicity, which is usually between 0.01 to 10 m2/s,
and varies among different regions with generally higher values in geothermal and volcanic areas. California has
ample natural resources for geothermal energy. Here, we try to understand the relationship among seismicity,
tectonic environments and injection activities. The current study region is the Salton Trough; future analysis will
include Coso area. In the Salton Trough, the first-order correlation is strong spatial clustering around injection
wells, and temporal correlation between increased seismicity and increased injection. The pore pressure changes
likely couple with tectonic applied shear stress, and with affect earthquake stress drop. Some correlation has been
identified for hydraulic fracturing experiments. In the Salton Trough, we also find that the stress drop is correlatedwith distance from injection wells. We will investigate the variation in the Coso geothermal field, and compare
seismicity with injection history. In the future, I will apply the analysis method in California to Japan earthquake
catalog, to learn about the seismicity pattern in different tectonic environments using high-precision differential time
relocation. A comparison of fluid properties will be synthesized based on results in California and Japan.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

232

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

1W_1E-P13

Date/Time: July 21 Poster

Stress Distribution in the Rotokawa Geothermal Field, New Zealand and implications for
fluid flow through brittle crust
Jonathan R J Davidson1 , Paul Siratovich1 , Irene Wallis2 , Darren Gravley1 , David McNamara3
1

University of Canterbury, New Zealand, 2 Mighty River Power, New Zealand, 3 GNS Science, New
ZealandE-mail: jrjdavidson@gmail.com

Quantifying the stress field is a vital tool for mapping and determining how to maintain the pathways thathydrothermal fluids follow in a naturally fractured geothermal system. Permeability in the Rotokawa Geothermal
Reservoir, located in the Taupo Volcanic Zone (TVZ), is primarily fracture hosted and is influenced by the activityof large faults. Thus permeability preservation in the reservoir relies on cyclical reactivation of these structures.
The magnitude and orientation of the principal stress axes will influence fault mechanics and how fracture-hosted
permeability operates in geothermal reservoirs. Slip on faults and fractures can depend heavily on their orientation
relative to that of the stress field and the relative magnitude of the principal stresses.
Leak-off Tests (LOTs), density models and borehole images are used to constrain stress magnitudes at depth in the
Rotokawa Geothermal Reservoir. In the extensional tectonic setting of the TVZ, the vertical stress axis coincides
with the maximum principal stress. As this is dependent on the weight of the overburden, we employed extensive
lab-based density measurements that have been performed on core from Rotokawa and other geothermal fields toderive a vertical stress model. Using this data, the vertical stress across the Rotokawa Field has been modeledtaking into account the variable lateral thicknesses of different lithologies. Data from LOTs and the observationof drilling induced tensile fractures (DITFs) on borehole acoustic images are used to quantify the minimum andmaximum horizontal stresses respectively.
The differential between the vertical and minimum horizontal stresses corresponds to a crust in frictional equilibrium.
Results of this study indicate that spatial variation in the vertical stress magnitude due to lateral variation in the
thickness of the overlying stratigraphy may be an important factor in maintaining permeable fractures. For example,
the presence of a young andesitic cone in the strata causes a local increase in the vertical stress. This may have a
local effect on the permeability of the underlying rocks.
Another key outcome of this study is that a portion of the fractures imaged in boreholes is exploiting weaknesses
in an otherwise strong rock. The range of fractures observed suggest that the fractures were activated undercompressional shear conditions, yet the strength of the rock measured suggest that is difficult to initiate such
fractures. It is likely that the rock is weaker due to the presence of primary fractures (i.e., created when the rockwas emplaced) or fractures due to subsequent volcanic activity. It is therefore crucial to have a good grasp on the
volcano-tectonic history of the region in order to understand the pathways that fluids take to reach the surface.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

233

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

1W_1E-P14

Date/Time: July 21 Poster

Geological and geophysical model of cap rock of the Karymshinskaya hydrothermal
system (Kamchatka)
Veronika Yu. Pavlova, Ivan F. DelemenInstitute of Volcanology and Seismology FEB RAS, Russia
E-mail: sacura17041988@mail.ru

Karymshinskaya hydrothermal system is located to the west of the volcanoes of the Eastern Kamchatka volcanic
belt within the valley of the rivers Paratunka and Karymshina and is part of the Upper Paratunka geothermal system,
dedicated to the area of the giant caldera of an extinct ancient supervolcano, which lies between the mountains ofBerry, Fat Point, Hot, Baby Stone (Leonov and Rogozin, 2007). Structural position of the system is determined by
the intersection of the strike slip fault, extends along the axis of the valley with a transverse fault to him. Thermal
waters are confined to the tank represented fractured vein zone within the volcanic deposits of miocene-pliocene
age (acid tuffs). Results of integrated geophysical studies in the area (Melnikova, Shulzhenkova and others, 2011),
in addition to the GPR and well logging GK-5, which is the object of routine observations of the Kamchatka branchof the Geophysical Service RAS (KB GS RAS), allowed us to construct geological and geophysical model of cap
rock of the Karymshinskaya hydrothermal system. Cap rock these rocks are massive tuffs, and a violation of thesetuffs fractured zones are thermal-water discharge. Discharge zone extends along the fault. In this case, we have a
medium-temperature system, dedicated to the same faults.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

234

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

1W_1E-P15

Date/Time: July 21 Poster

The structure of iron-silica rich chimney in shallow marine hydrothermal environment at
Iwo-Jima Island, Kikai caldera, southern Japan
Takashi Kuratomi1 , Shoichi Kiyokawa1 , Minoru Ikehara2 , Syusaku Goto3 , Fumihiko Ikegami1 , Yuto
Minowa1
1

Kyushu university, Japan, 2 Kochi core center, Japan, 3 GSJ, Japan
E-mail: t.kuratomi.0808@gmail.com

Satsuma Iwo-Jima is a volcanic island in the northwestern rim of Kikai caldera. Two post-caldera volcanoes
exist, so one has volcanic and hydrothermal activity at the present. Nagahama bay where the orange-brownish
discoloration is taken place is locatd in the southwestern island. The bay is half-closed environment and separated
into two parts of East and West-site. The origin of the discoloration is ferrous rich hot spring (pH=5.5, 55-60 degree
Celsius) (Shikaura and Tazaki, 2001). Kiyokawa et al. (2012) reported the fast deposition of about 1 m per ten
years at West-site which is under control of tide, rain and wind. East-site is distinct because of the presence ofchimney mounds, but yet studied in detail.
Samples were the massive chimney (20-30cm) and the floating particle divided from the sea water. We observed
the structure of chimney with X-ray CT scan, thin section and FE-SEM, as well as EDS for composition analysis.
The massive chimney is classified into two parts: black high-density hard layer and brownish low-density soft layer.
The result of X-ray CT scan shows that the chimney is constructed by the aggregation of convex structures (3-4cm).
Low-density layer has many pipes (radius of 1mm). Petrographic observations indicate that both high- and low-density layers have the filament-like form, and the form at the low-density layer is vertical to outer rim. In the
low-density layer, the number of particles attaching to the filament-like form increases toward the high-density
layer. FE-SEM observation shows that the filament-like form at the high-density layer is consists of aggregation of
bacillus-like structure that looks the chain of particles (about 2µm). At low-density layer, bacteria-like form attachedparticles (<1µm) existed and this form is classed into 3 types (helix, ribbon-like, twisted). The floating particles were
aggregation of fine particles (<0.5µm) has no bacteria-related form. All particles consist of Fe, Si and O, and thoseparticles are chemically homogeneous by EDS.
According to the observation results above, we present a hypothesis of growth process of a chimney-complex
mound in Nagahama bay. The chimney is constructed by aggregation of convex structure with many pipes probably
work as the hydrothermal vent. All grains are consist of Fe, Si and O. Bacteria-like form resembles Gallionella spp.
as iron-oxidizing bacteria. The bacteria is known as neutrophilic bacteria and prefers to living at redox interface(Weber et al., 2012). The activity of bacteria around hard rim makes high density layer. The chimney is likely to be
influenced by activity of microbe.
Shikaura.T and Tazaki.K (2001), clay mineral 40,4,229-241.
Kiyokawa S., Ninomiya T., Nagata T., Oguri K., Ito T., Ikehara M. and Yamaguchi K. (2012), Island Arc 21. 66-78.
Karrie A. Weber, T.L. Spanbauer, D. Wacey, M.R. Kilburn, D.B. Loope, and R.M. Kettler (2012), Jornal of Geology
40. 8. 747-750©IAVCEI 2013 Scientific Assembly. All rights reserved.

235

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

1W_1E-P16

Date/Time: July 21 Poster

Hydrochemical properties of thermal and cold mineral waters of Khnagay Mountain
Region, Mongol
D. Oyuntsetseg1 , D. Ganchimeg1 , G. Odontuya1 , A. Ueda2
1

Institute of Chemistry, Chemical Technology, Mongolian, 2 University of Toyama, Japan
E-mail: akira@sci.u-toyama.ac.jp

Hydrochemical properties were studied for thermal and cold mineral waters in Khangay mountain region, central
Mongolia. The eastern part of Khangay hydro-geothermal system is one of the most energetically powerful on thequality of the fluid heat-carrier (temperatures of the geothermal water at ground surface are up to 92 degree) withthe high yield of thermal sources and on the area of deep magma chamber and high activity of Cenozoic volcanism.
Chemical ompositions of 14 water samples in which 8 samples were analyzed. The Cl-SO4-HCO3 and Na-K-Mg
ternary diagrams and mixing models were used to characterize the water chemistry and estimate their subsurface
temperatures. The results show that most of the thermal waters are in partial equilibrium with the surroundingrocks. The hot waters in the study area can be classified into Na-HCO3 and Na-SO4 types.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

236

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

1W_1E-P17

Date/Time: July 21 Poster

Geochemical flow model of groundwater in Sho River fan, Toyama Prefecture for heatusage by geothermal heat
Kaname Iwatake1 , Akira Ueda1 , Shingo Tomiyama2
1

University of Toyama, Japan, 2 Mitsubishi Materials Techno Corporation, Japan
E-mail: akira@sci.u-toyama.ac.jp

Groundwater flow model is discussed with chemical and isotopic (D, O) compositions of 56 water samples in Sho
River fan, Toyama, northern part of central Japan to apply to geothermal heat usage for room air-conditioning
and melting of road snow by geothermal heat pump (Geo-HP). Groundwaters are a mixture of two big riverwaters (Sho and Oyabe) and precipitation. Deep groundwaters from observation wells are characterized to behigh pH and enriched in HCO3 compared to the shallow groundwaters. These features may indicate that shallow
groundwater originated from a mixture of river water and precipitation moving to the north and becoming confineddue to the presence of an impermeable layer. Groundwaters become high pH due to ion exchange reaction withrocks containing clay minerals, where HCO3 concentration also increases.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

237

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

1W_1E-P18

Date/Time: July 21 Poster

Geochemical study of hot springs for new geothermal exploration in eastern part ofToyama Prefecture, Japan
Kohei Sasaki1 , Akira Ueda1 , Soichiro Kageyama2 , Takehiro Koseki2 , Hirofumi Muraoka3
1

University of Toyama, Japan, 2 Mitsubishi Materials Techno Corp, Japan, 3 North Japan ResearchInstitute for Sustainable Energy, Hirosaki University, Japan
E-mail: sptw5769@jewel.ocn.ne.jp

Chemical and H and O isotopic compositions of 13 hot spring waters in eastern part of Toyama Prefecture wereanalyzed to examine their chemical characteristics and estimate the underground temperature for new geothermal
exploration. On the basis of chemical and isotopic compositions, hot spring waters can be divided into two groups;
low and high salinities. The low salinity group is of meteoric origin and high one is a mixture of sea water andmeteoric water with oxygen isotope shift. The latter may be geopressured fluid, which is characterized by the highdelta-D values of ca. -20 permil and medium Cl concentrations of ca. 6,000 mg/L as reported elsewhere. The
results of estimated underground temperature support the view that the area along Kurobe River has one of thehighest geothermal potential in the studied fields.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

238

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

1W_1E-P19

Date/Time: July 21 Poster

GEOCHEMICAL EXPLORATION FOR GEOTHERMAL RESOURCES AT THE SE ZONE OF
GRAN CANARIA ISLAND (ATIDAMA MINING GRID), CANARY ISLANDS.
Fatima Rodriguez1 , Nemesio Perez2 , Pedro Hernandez2 , Raul Hidalgo3 , Eleazar Padron2 , Gladys
Melian2 , Dacil Nolasco2 , German Padilla2 , Jose Barrancos2 , Samara Dionis1 , Inigo Hernandez1 , David
Calvo1 , Cayetano Guillen1
1Instituto Volcanologico de Canarias, Spain, 2 Instituto Tecnologico y de Energias Renovables, Spain,
3
Petratherm Hispania s.l., Spain
E-mail: fatima@iter.es

Very few efforts have been done to date in the Canary Islands to develop the potential geothermal energy resourcesin the archipelago. Between seventies and nineties, the Geological Survey of Spain performed intense researchon geothermal resources in the country due to the oil crisis of the 70s. Later geothermal research declined sharply
and only a few projects on geothermal resources were active in Spain from 1994 to 2006, compared with the many
projects carried out during the previous two decades. This overall picture has changed dramatically in recent years
and geothermal has become a new source of scientific research activity. In 2011 ITER, University of La Laguna,PETRATHERM Spain and the University of Barcelona started a joint research project (GEOTHERCAN), aimed todevelop an experimental study of 3D models to characterize geothermal reservoirs in the subsurface of Tenerife,
Gran Canaria and La Palma (Canary Islands), which enables further development of geothermal energy in theArchipelago. The multidisciplinary approach of this project, composed by different methodologies and techniques(geochemical, geophysical, and geological) allow us to address the definition of the geothermal potential in the
Canary Islands under the framework of this comprehensive and ambitious project.
Under the framework of this project soil gas geochemistry studies will be carried out at different areas of La
Palma, Tenerife and Gran Canaria Islands. In recent years soil gas surveys have become increasingly common in
geoscientific studies. Among the objectives of these studies are the quantification of gas and heat flux from volcanicand geothermal systems and the identification and delineation of active faults. Both topics are of central importanceto investigations of geothermal resources. In this abstract we are presenting the results of a geochemical surveyof soil gases and volatiles that was carried out by ITER during summer 2012 in Atidama area (around 100 km2),
located at the SE of Gran Canaria island. 600 sampling sites were selected to measured soil CO2 efflux, 222Rn
and 220Rn activities, Hg0 and H2S concentrations and soil temperature at 40 cm depth. Soil gas samples werecollected at same depth for chemical analysis (He, H2, N2, CO2, CH4 and Ar). Relatively low CO2 efflux values
were measured, ranging from non-detected up to 52.9 g m-2 day-1, with an average value of 1.9 g m-2 day-1. The
total diffuse CO2 output was estimated in 144 +- 3 t/d. Significant trends observed in the concentration of otherchemical components, suggest the presence of vertical permeability structures in the studied area.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

239

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

1W_1E-P20

Date/Time: July 21 Poster

Fluid geochemistry of the vicano-cimino hydrothermal reservoir (central italy):
implications for geothermal exploration
Daniele Cinti1 , Franco Tassi2 , Monia Procesi1 , Marco Bonini2 , Francesco Capecchiacci2 , Orlando
Vaselli3 , Fedora Quattrocchi1
1

INGV (Istituto Nazionale di Geofisica e Vulcanologia), Rome, Italy, 2 University of Florence Dipartimento di Scienze della Terra, Florence, Italy, 3 CNR-IGG Istituto di Geoscienze e Scienze della
Terra, Florence, Italy
E-mail: daniele.cinti@ingv.it

The Vicano-Cimino Volcanic District (VCVD), located in the peri-Tyrrhenian sector of central Italy, is characterized
by Pleistocenic volcanic products derived from two different magmatic cycles: i) the acid cycle, consisting ofa SiO2-rich magma of the Tuscan Magmatic Province, encompassing the Cimino Volcanic District, and ii) theK-alkaline cycle of the Roman Magmatic Province, encompassing the Vicano Volcanic District. The volcanic
products overlie a sedimentary sequence constituted by Plio-Pleistocene clays, Cretaceous-Oligocene flyschoid
sediments and a thick Mesozoic carbonate-evaporite formation containing a pressurized hydrothermal reservoir.
Extensive exploration surveys were carried out in this area in the seventies to nineties for geothermal purpose
although the VCVD is presently not exploited. The presence of thermal waters and of anomalous heat flow, together
with demographical growing in the last years, makes this site a suitable location for applications of the geothermal
resource.
On the whole, 333 fluid discharges (cold waters, thermal waters and bubbling pools) and 25 gas emissions werecollected for chemical and isotopic compositions. Water chemistry points out the presence of two main reservoirs at
different depths. The deepest one is hosted in the Mesozoic formation and shows a Ca-SO4(HCO3) composition,
likely produced by high temperature fluid-rock interaction involving Triassic anhydrite layers at the base of the
carbonates. The shallow aquifer is hosted within the volcanic domain and has a Ca-HCO3 composition. deltaD anddelta18O values suggest that both reservoirs are fed by meteoric waters.
Carbon dioxide, largely dominating the free gas phase associated to both cold and thermal springs, has a twofold
origin, being related to i) mantle degassing and ii) thermo-metamorphic reactions occurring in the carbonate
reservoir. The R/Ra values range from 0.41 to 1.14 and suggest relatively low contribution of mantle-derived fluidswith respect to those gases produced in the crust. The 13C/12C ratios of CH4 and 34S/32S ratios of H2S are likely
indicating an origin for these two gas species mainly controlled by high temperature reactions occurring within the
Mesozoic reservoir and involving the reduction of CO2 and that of the Triassic anhydrites, respectively. Furthermore,delta15N-N2 isotopic data point out to a non-atmospheric source for N2 likely related to high-temperature alterationof organic-rich meta-sedimentary rocks of the Palaeozoic basement below the Mesozoic reservoir.
Gravimetric and structural data suggest that the spatial distribution of the deep-originated fluid discharges
corresponds to the boundaries between positive and negative gravity zones, which are interpreted as extensional
faults bordering buried structural highs of the carbonate basement.
Gas geothermometric calculations have allowed to estimate reservoir temperature in a range between 250 and 300
degrees.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

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