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

1A1_3B-O1

Room A5

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

Episodic triggering of the rise of resident small-scale basaltic magmas from the mantle
Ian E M Smith1 , Lucy E McGee1 , Shane J Cronin2 , Jan M Lindsay1
1

Geology-School of Environment, University of Auckland, New Zealand, 2 Institute of Natural
Resources, Massey University, New ZealandE-mail: ie.smith@auckland.ac.nz

Small scale basaltic magmatic systems are expressed at the Earth’s surface as fields of individual volcanoes, each
representing a discrete batch of magma erupted within a defined period of time (weeks to years). Characteristicallyeach volcano shows chemical compositions that are distinct from that of other volcanoes in the field and this can be
explained in terms of variation in the parameters of magma generation, specifically depth and proportion of melting.
Fundamental to an understanding of the behaviour of such systems is the behaviour of their mantle source. The
scale of these systems precludes large scale plume related processes such as those implicated in the origin oflarge igneous provinces. Rather, adiabatic melting linked to small scale mantle convection can explain both thesize and longevity (up to 10 Ma) of these systems. However, the important questions are does each volcano in afield represent a single melting event and what triggers each event? To address these questions we investigate theQuaternary Auckland Volcanic Field (AVF) in northern New Zealand. The field exhibits the common volcanologicaland chemical behaviour of classic monogenetic volcanic systems. However, a notable feature is the eruptionof compositionally discrete magma batches within a very short interval. Paleomagnetic measurements indicate
eruption of at least 5 distinct magma batches within a period of about 100 years at about 36 ka. Geochemical
modelling shows that these discrete magma batches are not linked by fractionation processes to a single parental
composition. The physics of mantle behaviour and melting processes suggest that it is unlikely that each batch
represents a separately triggered melting event within a small isolated source volume. We therefore suggestthat the origin of compositionally discrete magma batches is not separate melting events but separate extraction
events from a source that is partially molten but heterogeneous in terms of melting proportion and therefore melt
composition. This is analogous to the model of crustal hot zones invoked to explain variation in magmas within thecrust. The final question is what triggers a series of individual extraction events. Here we invoke tectonic forcing
from the convergent plate boundary 400 km distant in the central North Island of New Zealand as indicated bycorrelations between major events on this boundary and flare-ups of volcanic activity in other NZ volcanoes as wellas the AVF.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

741

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

1A1_3B-O2

Room A5

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

Depth of melt segregation below the Nyos maar-diatreme volcano (Cameroon,West-Africa): major-trace element evidence and their bearing on the origin of CO2 in
Lake Nyos
Festus Tongwa AKA1 , Tetsuya YOKOYAMA2 , Asaah Elvis Nkenmatia ASOBO2 , Issa ISSA3 , Takeshi
OHBA3 , Minoru KUSAKABE4 , Sigha NKAMDJOU1 , Gregory TANYILEKE1 , Joseph HELL1
1

Institute for Geological and Mining Research, Cameroon, 2 Tokyo Institute of Technology, Japan, 3 Tokai
University, Japan, 4 University of Toyama, Japan
E-mail: midissa17@yahoo.fr

The Nyos maar-diatreme volcano on the Oku Volcanic Group (OVG) in NW Cameroon carries yet the most infamous
maar lake in the world because the lake exploded in 1986 releasing CO2 that killed about 1750 people and over3000 livestock. A process of safely getting rid of accumulated gas from the lake started in 2001. Even though
about 40 per cent of it has been removed, gas continues to seep into the lake from the mantle, so the lake still
poses a thread. Available data on basaltic lava from the maar-diatreme volcano and other volcanoes of the OVG
are used here to determine the depth and location where the magmas are produced, and to make inferences on thegeneration of CO2 in the Nyos mantle. Fractionation-corrected major element data agree well with experimental
data on mantle peridotite and suggest that Lake Nyos magmas formed at pressures of 2-3 GPa in the garnetstability field. This inference is corroborated by trace element models that indicate small degree (1-2 per cent)partial melting in the presence of residual garnet (2-3 per cent). The basalts have elevated High Field Strength
Element (HFSE) ratios (Zr/Hf = 48.5 + 1.2 and Ti/Eu = 5606 + 224) which cannot be explained by any reasonablefractional crystallization model. A viable mechanism would be melting of a mantle that was previously spiked
by percolating carbonatitic melts. It is suggested that small degree partial melting of this metasomatised mantle
produces the lavas with super chondritic HFSE ratios, and is generating the CO2 that seeps into and accumulates
in the lake, and which asphyxiated people and animals during the 1986 gas disaster. This finding requires thatcurrent efforts to degas Lake Nyos should take into account the fact that CO2 will continue to seep into the lake fora yet undetermined but long time in the future. A viable solution would be to avoid renewed stratification of the lake,by (somehow) safely and permanently bringing bottom gas-charged waters to the surface to release gas, even after
the gas currently stocked in the lake has been completely removed.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

742

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

1A1_3B-O3

Room A5

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

Petrology and geochemistry of the New Tolbachik Fissure Eruption volcanic rocks andtheir evolution during the first two weeks of eruption
Anna O. Volynets1 , Dmitry Melnikov1 , Anton Yakushev2 , Maria Tolstykh3
1

Institute of volcanology and seismology FED RAS, Petropavlovsk-Kamchatsky, Russia, 2 Institute ofGeology of Ore Deposits, Petrography, Mineralogy and Geochemistry RAS, Moscow, Russia,
3
Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Russia
E-mail: a.volynets@gmail.com

The New Tolbachik Fissure Eruption started on 27.11.2012. Plosky Tolbachik is a stratovolcano, active in Holocene;
it is intersected by Tolbachinsky Dol - the monogenetic lava field, formed by numerous cinder cones and lava flows
eruptions which repeatedly took place for the last 10 Ka. Most of all cinder cones are concentrated in the narrow
axial zone responding to the fault zone location (Fedotov et al., 1984). The last big fissure eruption in this region
occurred 37 years ago and lasted for 2 years; the volume of erupted material was 2.2 km3, lava flows covered thearea of 45 km2; magnesian, alumina and transitional basalts were erupted. Besides, a new caldera was formed at
the summit crater of Plosky Tolbachik (Fedotov et al., 1984).
The New Tolbachik Fissure Eruption began from the effusion and explosion of high-K Ti-rich aluminous
trachy-basaltic andesites, black, sub-aphyric, with rare phenocrysts of Pl, Ol and Cpx. Microlites of the groundmass
with pilotaxitic and hyalopilitic structures are mainly Pl, dovetail shaped, and, to a lesser extent, Ol and Cpx; Mt
is abundant; the areas with hyaline groundmass compositionally similar to the whole rocks are confined to thehighly-porous parts of the rock. The petrography of the volcanic rocks of the first days of eruption attests very
rapid cooling, high rates of eruption and high mobility of the lava. Composition of Ol varies from Fo64 to 80, Pl
is An41 to 62; Cpx are Augites and Salites. The average content (wt.percent) of SiO2 in the whole rock fromthe first days of eruption is 54.57, Al2O3 16.6, K2O 2.5, MgO 3.36, TiO2 1.8 (for comparison, the eruption in1975 started from high-Mg medium-K basalts and was continued by high-Al high-K basalts, which are close incomposition to the newly erupted basaltic andesites, but have lower content of silica, alkalis and TiO2 at higher
MgO and CaO). During the next two weeks bigger plagioclase crystals appeared as phenocrysts (up to 1 cm indiameter); also Ol became more abundant and bigger in size (up to 3 mm in diameter) in comparison to the lavasof the beginning of this eruption. The composition of rocks gradually changed to more mafic: after 10-14 days
silica content (wt.percent) dropped to 52.79, while MgO increased to 4.08, TiO2 to 2.03, Al2O3 decreased to 15.8
and K2O remained roughly the same. The trace elements content also changes regularly with the shifting of themain oxides content. Overall, the incompatible trace elements content in lavas of the first portions of new eruption
is higher than in all previously studied volcanic rocks of Tolbachinsky Dol; the distribution of trace elements on
spidergrams and REE on REE-diagrams forms sub-parallel trends, indicating possible derivation of these rocks
through fractional differentiation processes of parent magmas, responsible for the formation of basalts of the Northand South Vents of the Great Fissure Tolbachik Eruption in 1975-76.
This work is supported by FED RAS grant 12-III-A-08-165.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

743

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

1A1_3B-O4

Room A5

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

Magma ascent and fragmentation in a silica-undersaturated monogenetic volcanic field:
evidence from textural analysis of pyroclasts from the Gregory Rift (East African Rift
System)Hannes B Mattsson
Institute of Geochemistry and Petrology, ETH Zurich, Switzerland
E-mail: hannes.mattsson@erdw.ethz.ch

Pyroclasts formed in eruptions involving high CO2 , silica-undersaturated, magmas in the Gregory Rift of northern
Tanzania show distinct textural and morphological characteristics when compared to the more common basaltic
equivalents. Overall the shape of all pyroclasts (independent of size) is sub-rounded to near spherical and evidenceof broken bubble walls or blocky fragments is extremely rare. This applies to all melilititic eruptions, but do also occur
in the eruptions of more primitive nephelinitic magmas erupted in the area. Many of the volcanic landforms within
this monogenetic field would classify as maars and tuff rings/cones based on morphology alone, yet the availabilityof external water required to drive phreatomagmatic fragmentation is scarce as most of these "phreatomagmatic"
landforms are located on a horst structure 200-300 meters above the surrounding sedimentary basins and in
an arid climate (where evaporation greatly exceeds rainfall on an annual basis). The melilititic pyroclasts aremoderately vesiculated (around 30-40%), which is a considerably higher value than what would be expected inphreatomagmatic deposits. Analysis of vesicle size distributions and vesicle number densities also show minor
differences between melilititic pyroclasts in scoria cones and those found within tuff rings as well as maar-diatreme
volcanoes. From this, in combination with the observed morphologies, it is clear that there is no clear difference
between inferred "magmatic" and "phreatomagmatic" pyroclasts of melilititic compositions.
The ascent rate must have been high for the melilititic magmas, and calculations show that these magmas probably
ascended with a rate of 8-35 ms-1 from an upper-mantle source to the surface (i.e., less than one day), with anabsolute minimum speed of <1 ms-1 required in order to keep the mantle debris entrained with the rising magma.
This essentially excludes any possibility of long-time ponding, and associated degassing, of the melilititic magmas
during ascent. Previous studies have shown that melilititic melts can hold >18 wt.% of CO2 dissolved within the melt
structure at upper-mantle pressures, and it is here proposed that the sub-rounded to spherical melilititic pyroclasts
form as a result of rapid exsolution of CO2 during ascent, and that this fragmentation level (controlled by theincreasing gas fraction-volume) is located at depth within the conduit. A deep fragmentation level and transport
as an aerosol-type gas jet would imply significant cooling of pyroclasts (also within the conduit itself) and this may
explain the absence of agglutination/welding even at the crater rim of the melilititic deposits.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

744

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

1A1_3B-O5

Room A5

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

Chemical variation in an historical monogenetic eruption (1256 AD Al-Madinah eruption)in the Kingdom of Saudi Arabia: Identifying magma sources
Hugo F Murcia1 , Jan M Lindsay1 , Ian EM Smith1 , Mohammed R Moufti2 , Karoly Nemeth2 , Shane J
Cronin3 , Nabil N El-Masry2
1

School of Environment, The University of Auckland, Auckland, New Zealand, 2 Geologic Hazards
Research Unit, King Abdulaziz University, Jeddah, Saudi Arabia, 3 Volcanic Risk Solutions, Massey
University, Palmerston North, New ZealandE-mail: hmur591@aucklanduni.ac.nz

The study of monogenetic volcanism has become increasingly important over the past decade, particularly inareas where small-scale but frequent volcanism can pose a threat to highly populated or culturally significant areas.
Combined physical volcanology and geochemical studies have the potential to provide insights into the occurrenceof future eruptions, and the study of well-preserved historical eruptions is particularly useful in this regard. We
examined the most recent eruption of the Al-Madinah Volcanic Field in Saudi Arabia, which occurred in 1256 AD,
20 km from the centre of Al-Madinah City. This eruption created seven isolated and nested cones (cones 1-7,
from S to N), along a ca.2 km-long fissure associated with a 56 km²pahoehoe-and-aa lava flow field. Cones 1
to 4 are isolated and cones 5 to 7 are nested and the largest. Cone 1 original edifice was modified by repeatedrafting while the others are well-preserved. Volcanological facies variations indicate that the eruptions were most
explosive in the nested cones and Strombolian activity was the dominant style. The products generated werealkali basalts and hawaiites (SiO2 45-47wt%) with some variation in composition, although all show trace element
characteristics that lie between typical OIB and MORB. Three compositional groups can be identified: Group 1
has higher abundances of compatible elements (MgO 8-9.4wt%; Mg# 58-63; CaO 10-11wt%; Sc 29-34ppm; V
255-277ppm; Cr 139-329ppm; Ni 118-189ppm), Group 3 has lower abundances of compatible elements (MgO
5.6-6.3wt%; Mg# 46-51; CaO 8-9wt%; Sc 24-29ppm; V 190-217ppm; Cr 69-137ppm; Ni 45-76ppm), and Group 2lies between these two compositions. Group 1 compositions are from cone 1 and rafted material >1 km from thecone. Group 2 compositions are from cone 2; and Group 3 compositions are from cones 3 to 7. These groups
correlate with three groups of lava flows defined as erupting simultaneously in a previous study and described
as Low-K, High-K and hybrid basalts. Preliminary results suggest polybaric melting with trace element behaviour
indicating a spinel peridotite source for Group 1 (Tbn /Ybn =1.62-1.8; (La/Yb)n /(Sm/Yb)n =1.38-1.71) and a garnet
peridotite source for Groups 2 and 3 (Tbn /Ybn =1.9-2.1; (La/Yb)n /(Sm/Yb)n =1.56-1.96) with variations in the degrees
of melting: Group 1, Lan /Lun =3.1-4.8; Lan /Smn =1.5-2; Gdn /Ybn =1.8-2.2; Group 3, Lan /Lun =4-6.8; Lan /Smn =1.3-1.7;
Gdn /Ybn =2-2.7; and Group 2 compositions lying between these values. This study contributes to the understandingof the temporal evolution of magma compositions and gives new insights into the origin of the magma(s), which isvital information for creating realistic hazard scenarios in this culturally important area.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

745

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

1A1_3B-O6

Room A5

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

Mantle domain boundary beneath the Jicin Volcanic Field, Czech Republic: evidence
from isotopic composition of primitive alkaline basaltic rocks
Vladislav Rapprich1 , Vojtech Erban1 , Jitka Mikova1 , Tomas Magna1 , Julia Kocergina1 , Jakub Haloda1 ,Lukas Ackerman1 , Zoltan Pecskay2
1

Czech Geological Survey, Klarov 3, 118 21 Praha, Czech Republic, 2 Inst. Nuclear Res., Hun.
Academy of Sci., Bem ter 18/C, H-4001 Debrecen, Hungary
E-mail: vladislav.rapprich@geology.cz

The Jicin Volcanic Field is situated on the southern shoulder of the Oligocene-Miocene Eger Rift, some 30-60
km from its southern margin and is dominated by scattered erosional remnants of monogenetic volcanoes in NE
Bohemia (Czech Republic). The volcanic field mostly consists of scoria- and tuff-cones, a handful of lava flows andlava lakes filling phreatomagmatic craters, and several dykes exposed by selective erosion. Volcanic activity in thisarea took place in two distinctive periods. Most volcanoes were formed during the Miocene (16-19 Ma) whereas
few cones grew up during the Pliocene (4-5 Ma). Primitive members predominate among the erupted magmas ofwithin-plate alkaline character. These are represented by olivine nephelinites and basanites/limburgites with rare
picrobasalts. Models of mineral composition suggest that the picrobasalts are derived from basanites throughaccumulation of ca 15% olivine. Despite relatively uniform major and trace element compositions, significant
differences in radiogenic isotopic compositions are observed. The 87 Sr/86 Sr (present-day) ratios for the southernpart of the volcanic field are higher than 0.7035 whereas they are strictly limited to lower than 0.7035 in the northern
part. In parallel, 143 Nd/144 Nd ratios are higher than 0.51285 for magmas erupted in southern part and lower than thisvalue in the northern part. Collectively, magmas erupted in the northern part of the Jicin Volcanic field are isotopicaly
similar to main volcanic complexes of the Eger Rift, whereas the southern part is obviously derived from a more
depleted mantle source. Both groups of basaltic rocks erupted in the Jicin volcanic field are also distinguished bytheir Pb isotopic compositions. Both suites plot in two parallel trends in the 208 Pb/204 Pb vs. 206 Pb/204 Pb diagram,where the northern part is relatively enriched in 208 Pb compared to the southern part. We explain more depletedcharacter of the source mantle for the southern part of the Jicin Volcanic field in the context of greater distance fromthe Eger Rift and, therefore, also from the Variscan suture between Saxothuringian and Bohemian domains, which
could modify the mantle composition in the zone of Eger Rift.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

746

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

1A1_3B-O7

Room A5

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

Small calc-alkaline volcanoes from the Oas-Gutâi Neogene volcanic area, Eastern
Carpathians, Romania; contribution to the controversial monogenetic versus
polygenetic classification
Marinel Kovacs1 , Alexandrina Fülöp2 , Zoltan Pécskay3
1Tech.Univ.Cluj-Napoca, North Univ.Center Baia Mare, Baia Mare, Romania, 2 De Beers Canada Inc.,
Toronto, Ontario, Canada, 3 Institute of Nuclear Research of the Hungarian Academy of Sciences,
Debrecen, Hungary
E-mail: marinelkovacs@yahoo.com

The Oas-Gutâi Neogene volcanic area (OG) belongs to the inner volcanic arc of the Eastern Carpathians built
up during complex Miocene subduction processes developed in the Carpathian-Pannonian region. A complex
volcanism developed in OG during Miocene (15.4-7.0 Ma). The dominant intermediate calc-alkaline volcanic rocks(predominant medium-K andesites) are overlapping the previous felsic volcanic rocks (rhyolite ignimbrites). The
small-sized volcanic forms (200 m to 5 km) related to the intermediate volcanism are mainly represented by solitary
volcanoes surrounded by Neogene-Quaternary sedimentary deposits, generally emplaced outside of the main
volcanic area, or by small volcanoes spatially associated with the large-sized, complex volcanic structures. Theseare extrusive domes, dome-coulées and cryptodomes comprised of andesites to rhyolites. The majority of thesolitary volcanoes are monogenetic (simple-shape, small volume of magma, single petrographic rock-type) as thosefrom Oas Mts., subaqueously emplaced along certain alignments (possibly tectonically-controlled fissures) oriented
parallel with the volcanic arc. Others show petrographic complexity raising questions about the monogenetic or
polygenetic genesis. In Oas Mts., the steep conical Jeleznic dome of ca. 4 km diameter, shows a discontinuouscomposition with pyroxene andesite in the western side and pyroxene hyalodacite in the eastern side. Two verysmall volcanic forms (ca. 300 m all together) joined in an extrusive dome (Turulung) are comprised of biotite dacite
and pyroxene hyalodacite, respectively. In Gutâi Mts., two interconnected extrusive domes (Piatra Rosie-Dănesti),surrounded by Neogene-Quaternary sedimentary deposits, are comprised by pyroxene dacite and biotite dacite/
rhyolite, respectively. In the case of the small volcanoes developed inside the volcanic area and classified as"monogenetic", these show a well-defined morphology and specific volcanological and petrological features (e.g.
Gutin and Breze extrusive domes). Others raise the question whether these are monogenetic or polygenetic: theLaleaua Albă small-sized (ca. 800 m) dome is comprised of a core of macroporphyric sanidine dacite (8.42±0.33Ma) surrounded by an envelope of aphyric andesite (8.47±0.42 Ma); the Plesca Mare large-sized (ca. 3.5 km)
dome is comprised of a well-developed biotite dacite (68.2 SiO2 ) core, bordered by a biotite andesite (58.7 SiO2 ).
Although these features are the result of magma-mixing and -mingling processes, their eruptive history suggests atleast two magmatic pulses/events possibly developed during the same near-continuous, short-lived volcanic activity.
The problem of the "monogenetic" volcanoes in OG is aligned with the ongoing discussion about the criteria to be
used to separate monogenetic versus polygenetic, as well as to define the size of so called "small monogenetic"
volcanoes.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

747

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

1A2_3B-O8

Room A5

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

The eruptive history of the small and isolated andesitic Caraci Volcano, developed
adjacent to Zărand Basin, South Apuseni Mountains, Romania.
Răzvan-Gabriel Popa, Ioan Seghedi
Institute of Geodynamics of the Romanian Academy, Romania
E-mail: razvangabriel.popa@yahoo.com

Caraci Volcano has a slightly asymmetrical buttressed edifice with an ellipsoidal dome structure (D/H ratio 10.7) on
top and a total height of 420m, covering a surface estimated at 22km2 . It is located in a small Miocene tectonic basinthat has developed adjacent to Zărand Basin, in the South Apuseni Mountains of the Carpathian-Pannonian Region.
It was active at around 12.5Ma. Most of the volcanic structure overlies the pre-Neogene basement made of ophiolitic
basalts and intruded by younger igneous bodies, while the northern part of the edifice covers Miocene sedimentarydeposits (coarse quartz gravel, shales and weakly consolidated sandstone). 3D modeling of the surface of thebasement reveals a wedge like basin delimited by normal faults and cut by transversal adjustment normal faults
that facilitated volcanic activity. The first volcanic deposits consist of highly fragmented tuffs (sometimes up to
40m thick), covered on the northern slope by a hornblende-plagioclase-phyric andesitic lava flow, and on thesouthern slope by a highly fragmented breccia of phreatomagmatic origin. The volcanic activity continues witha hornblende-plagioclase-phyric andesitic lava flow sequence that comprises most of the volume generated by
Caraci and which spreads over most of the surface covered by the volcanics; flow units juxtapose to a maximum
thickness of 100m and slight, but consistent geochemical and petrological variations are observed from bottom totop. Two more, less voluminous andesitic effusions add up to the volcano, one with entirely opacitised hornblendeand the latter with almost completely disintegrated opacite and microcrysts of clino- and ortho-pyroxenes. The
final effusion consists in the growth of the central dome structure, made of two-pyroxene-plagioclase-phyric basaltic
andesites. The southern slope and in less extend the northern, are covered by breccias of pyroclastic origin, madeof centimeter-to-meter sized basaltic andesite fragments bounded together in cineritic material; they are interpreted
as block-and-ash deposits resulted from dome collapsing events. Meter sized angular basaltic andesite blocks are
spread over the eastern, southern and western slopes of the volcano.
From a petrological view, feldspars from each sample show disequilibrium textures and overgrowths that createa variety of patterns, consistent with temperature rise, depressurization or undercooling. These patterns become
more complex with each new eruption, until the effusion of the dome-building basaltic andesites that show again
simpler patterns. Hornblende also develops thicker reaction rims and more profound opacitisation and resorbtion
until it is completely replaced by pyroxenes. This is interpreted as evidence for magma mixing and it is consistent
with geochemical modeling that suggests mixing with a more primitive batch of magma. Magnetic susceptibility
variations are supporting the petrological assumptions.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

748

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

1A2_3B-O9

Room A5

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

Targeting monogenetic volcanoes from different angles to enhance our understanding of
the complex eruption dynamics: case study Mt. Gambier, S.E. Australia (VEI 4)
Jozua van Otterloo, Ray A.F. Cas
Monash University, Australia
E-mail: jozua.vanotterloo@monash.edu

Monogenetic volcanoes can be very complex requiring a multidisciplinary approach to fully understand theirdynamics. Here we present the improved understanding of the eruption dynamics of monogenetic volcanoes
based on such an approach, with the 5 ka Mt Gambier Volcanic Complex in the Newer Volcanics Province ofsouth-eastern Australia being the case study. This maar-cone complex is marked by the alternating magmatic andphreatomagmatic deposits reflecting multiple changes in eruption styles.
Detailed mapping was integrated with borehole data into a 3D model, so that the volumes of the different pyroclastic
deposits and lava flows related to different eruption styles could be determined. In total a minimum volume of 3.25 x
108 m3 of material was erupted with a minimum dense-rock equivalent volume of 1.97 x 108 m3 of magma involved.
These volumes are not only indicative for the VEI of this prehistoric eruption, which was 4, but also correspond to
the amount of energy for this eruption stored as heat, and using these an estimate can be made of the minimum
volume of groundwater necessary in order to produce the phreatomagmatic explosions and deposits.
Based on groundwater models and parameters from the local aquifers these volumes can be tested from ahydrodynamic point of view. This shows that with the aquifer conductivities or flow rates, K, ranging from 1.7- 3.3 x 10-4 m s-1 , the available groundwater could not continuously recharge the root zones and diatremes ofthe maar-diatreme structures of Mt. Gambier, causing the strong alternations in magmatic and phreatomagmatic
deposits observed at this volcanic centre. The control of the aquifer dynamics on the eruption dynamics is confirmedby the fact that the magmatic properties (i.e. viscosity, temperature, crystallinity, vesicularity and apparent ascentrate) are not different for the distinct magmatic and phreatomagmatic deposits.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

749

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

1A2_3B-O10

Room A5

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

Using substrate geology to delimit the spectrum of phreatomagmatic eruptive scenarios
for the Auckland Volcanic Field (AVF), New ZealandJavier Agustin-Flores1 , Karoly Nemeth1 , Shane Cronin1 , Gabor Kereszturi1 , Jan Lindsay2
1

Volcanic Risk Solutions, Massey University, New Zealand, 2 School of Environment, The University of
Auckland, New ZealandE-mail: J.AgustinFlores@massey.ac.nz

Evidence of phreatomagmatic phases is found in 39 of the c. 50 volcanic centres in the AVF. Most of these arelocated along stream valleys or lowlands especially in the southern part of the field. Phreatomagmatic craters
vary from 200 to 1 600 m in diameter and are surrounded by tephra rings up to tens of metres high, comprising
pyroclastic surge and subordinated fall successions. Although most of the phreatomagmatic vents have not beenstudied in detail, the reconstruction of the eruptive histories of few of the volcanoes (Crater Hill, Maungataketake,
Motukorea, North Head, Orakei, Pupuke) point to a broad array of distinct eruptive event sucessions.

The

juvenile fragment content of these deposits range between sites from 30 to 90 vol%. The accidental clasts are
made up of fragments from the Miocene Waitemata Group and/or the Plio-Pleistocene Tauranga and Kaawa
Formations. The Waitemata Fm is a poorly consolidated, turbiditic sandstone and siltstone succession, upliftedin the Auckland Isthmus area but down-faulted in the Manukau lowlands and capped by 50-100 m-thick sequenceof the unconsolidated Plio-Pleistocene sediments. Jointed, low transmissivity, confined aquifers occur in the
Waitemata, whereas Kaawa Fm. has good hydraulic conductivity and the impermeable sediments of Tauranga
Fm. conform an aquiclude. Maungataketake and Crater Hill tuff rings were excavated mainly within Tauranga
and Kaawa. The others were built by explosions through the Waitemata group. Only one example of emergent
phreatomagmatic volcanism occurs, the North Head tuff cone (<10 % in vol. of accidental content), which could
be an important eruptive style scenario in a near future eruption due to present high sea levels. The most criticalfactors that control small basaltic phreatomagmatic eruptions are magma flux rates, total erupted volume, substraterheology, hydrogeological conditions and paleotopography. Assessing quantitative proportions of each factor isdifficult. However, a qualitative approach can be developed by associating the stratigraphic, sedimentary andgrain/fragmentation characteristics, with the paleo-hydrological/geological conditions of the substrate, as well as
sea level. Assuming that substrate and tectonic conditions remain the same in future, as well as considering thehigh present sea level ( 1/5 of AVF area is submerged in up to 40 m-depth water) and that the Plio-Pleistocene
sediments cover 30 to 40 % of AVF area, future phreatomagmatic eruptions in most parts of the field will have initial
phases ranging from emergent-type to base-surge dominated eruptions of brief duration (hours to days). These willproduce base surge runouts from several hundreds of meters up to 4 km from the vent. This clearly shows that thesubstrate conditions play a highly relevant dominant role in guiding the type of phreatomagmatic eruptions in AVF.
Shifts of activity to purely magmatic conditions is most likely under eruption scenarios of greater magma volumes©IAVCEI 2013 Scientific Assembly. All rights reserved.

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IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
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1A2_3B-O11

Room A5

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

Factors influencing effusive and explosive eruptions of trachytic-phonolitic magmas, anexample suite from Harrat Rahat, Saudi Arabia
Shane J Cronin1 , M. Rashad H Moufti2 , Marco Brenna1 , Ian E.M. Smith3 , Karoly Nemeth1
1Institute of Agriculture and Environment, Massey University, New Zealand, 2 Faculty of Earth Sciences,King Abdulaziz University, Saudi Arabia, 3 School of Environment, University of Auckland, New ZealandE-mail: s.j.cronin@massey.ac.nz

The 20,000 km2 intraplate field of Harrat Rahat in Saudi Arabia hosts >1000 volcanic structures erupted between
c.10 Ma to 1256AD. Alkali basaltic volcanism dominates, but in the central northern areas of the field (where
the lava pile is thickest), more evolved magmas erupted, including benmoreitic, and trachytic compositions. Thesemost evolved products exhibit a range of eruption styles that appear to represent a combination of controlling factors
including: eruptive volume, compositional variation, mafic magma intrusion and dissolved gas content. The effusive
volcanic suite ranges from simple cryptodome/dome formation, to larger-volume eruptions of large, complex
multi-stage domes with temporal variations in magma composition. These produced flank-collapse pyroclastic flows
up to 1 km from the flanks. In the parallel explosive sequence, small-volume magma intrusions encountered groundwater at depths of 100-300 m and resulting phreatomagmatic explosions formed deep maar craters with minor ringsof explosion breccias. In larger volume examples, initial explosions were followed by pyroclastic surges, with further
larger volume events producing tephra columns and fountain-collapse pyroclastic flows, deposited up to 4 km fromsource. In the largest-volume cases, larger pyroclastic flows (>7 km runout), surges and falls were generated incomplex eruption sequences that may have lasted several weeks. The most complex eruptive sequences show
trends from early near-phonolitic compositions, to later more-primitive compositions. Some sequences were also
apparently interrupted by eruption of hotter more mafic magmas. These mafic magmas may be the cause of
instability of mid-crustal trachytic magmas, leading to their rise and eruption. Early erupted units are completely
crystalline with trachytic textures and no residual glass. Later products contain glass between phenocrysts andvesicles with rounded, but highly deformed margins where they were restricted by the crystalline network. Latest
stage eruptives show very small isolated vesicles also restricted by the crystalline mush. Hence, expansion was
late-stage, indicating rapid unroofing of very crystal rich magma bodies.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

751

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

1A2_3B-O12

Room A5

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

Highly explosive basaltic eruptions: the case of the sunset crater (az, usa)
Fabrizio Alfano1 , Laura Pioli2 , Amanda B. Clarke1 , Michael H. Ort3 , Kurt Roggensack1 , Stephen Self4
1

SESE, Arizona State University, USA, 2 Dep. Mineralogy, University of Geneva, Switzerland, 3 SESES,
Northern Arizona University, USA, 4 CEPSAR, The Open University, UK
E-mail: fabrizio.alfano@asu.edu

Volcanic eruptions involving basaltic magma usually produce low explosivity events characterized by lava flow
effusion, lava fountains and/or small Strombolian explosions. However, more explosive eruptions, ranging fromviolent Strombolian to sub-Plinian and Plinian events, are not uncommon and can represent a serious threat forto nearby populated areas. The study of highly explosive mafic eruptions thus provides an important test of ourunderstanding of eruptive processes. The eruption of Sunset Crater volcano represents an interesting case in thatit produced highly explosive eruptions, up to sub-Plinian in scale, that heavily affected the pre-historic communities
in the area, and also produced intermittent episodes of lava effusion. Sunset Crater is a >300 m high scoria cone
located ∼25 km northeast of Flagstaff, AZ (USA), in the San Francisco Volcanic Field. The eruption produced
three lava flows that cover ∼8 km2 , a scoria-fall blanket up to 12 m thick covering an area of about 500 km2 ,and minor spatter cones and ramparts that marked the onset of the eruption. The tephra sequence consists ofat least eight fall units associated with major explosive phases, mainly dispersed to the east. The total volume
of individual fall units varies between 0.02 and 0.08 km3 DRE. The maximum is estimated for the Unit 3 deposit(0.08 km3 DRE) and the total cumulative volume is ∼0.3 km3 DRE. This value is close to the volume calculated
based on the total deposit isopach map from Ort et al. (2008, JVGR 176(3): 363-376) (∼0.4 km3 DRE). Associatedcolumn heights, calculated based on the maximum clast-size distribution of Amos (1986, ASU MS Thesis), arebetween 7 km (Unit 2) and 25 km (Unit 3). Sunset Crater scoria are characterized by a density of 1.2-1.9 x 103
kg m-3 , which corresponds to 35%-67% vesicularity. The chemical composition is nearly uniform (∼47 wt.% SiO2 )for all eruptive units. Two textural endmembers, intimately intermingled at the mm-scale within a single clast, wereidentified: one endmember (sideromelane) is characterized by higher vesicularity, with large regular sub-sphericalvesicles (modal diameter 0.6 mm), a glass-rich groundmass and evidence of post-fragmentation vesicle expansion;
the second endmember texture (tachylite) is characterized by lower vesicularity, with small highly irregular vesicles(modal diameter 0.3 mm) that result in a higher vesicle number density than the sideromelane, and a groundmass
rich in microcrysts, mainly Fe-oxides. Scoria compositions and textural characteristics suggest interaction between
magmas stored at different depths. The crystalline tachylite texture is interpreted as shallower magma that mixed,in the upper conduit, with more rapidly cooled and decompressed magma (sideromelane) sourced from deeper
crustal levels.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

752

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

1A2_3B-O13

Room A5

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

Submarine fire-fountaining eruptions: monogenetic scoria cone construction and clast
vesicularity (Nishiizu, Izu Peninsula, Japan)
Martin Jutzeler, James DL White
University of Otago, New ZealandE-mail: jutzeler@gmail.com
The Nishiizu Member is a ∼12x106 m3 , half-dissected coastal remnant of a submarine monogenetic scoria conein the overall andesitic Matsuzaki Formation (Shirahama Group), on the western side of the Izu Peninsula, Japan.
The volcanogenic Shirahama Group is the youngest uplifted section of the Izu-Bonin arc from subduction of thePhilippine plate under Japan. The brown scoria cone consists of tens to hundreds of thin to very thick beds of grey
scoria lapilli and subordinate water-chilled bombs that are radially dipping (15 to 40 degrees dip) outwards a single
area, considered to be the vent source. The beds of brown scoria are massive, ungraded, network-supported
and overall monomictic; beds are defined by differences in grain size, and contacts are weak or indistinct. The
bombs are fluidal, have thick quenched margins and some are folded and agglutinated. Lapilli and coarse ash
chiefly consist of fragments of water-chilled bombs; fine ash is absent. Lithic clasts are extremely rare overall, butcommon (up to 10 vol.%) in the oldest beds closer to vent. Grading in vesicularity and bubble number density is
ubiquitous in bombs, with overall increase in size and abundance of vesicles towards the clast core. This grading inclast vesicularity suggests submarine eruptions by volatile-coupled fire-fountaining, followed by vesicle ripening andmoderate coalescence. The very thick, ungraded, poorly defined beds do not match deposition from conventional
subaqueous grain flows or density currents, and may reflect a variety of primary and syn-eruptive resedimentationon unstable slopes of the scoria cone, including discrete clast rolling and sliding, and short-lived grain flows.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

753

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

1A2_3B-O14

Room A5

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

Variations in eruptive style of mexican basaltic maar volcanoes
Gerardo Carrasco-Nunez1 , Michael H. Ort2 , Pablo Davila-Harris3
1

Centro de Geociencias, Universidad Nacional Autonoma de Mexico, Mexico, 2 SESES, Northern
Arizona University, USA, 3 IPICYT, Mexico
E-mail: gerardoc@geociencias.unam.mx

Maars are a special type of volcano that represent extreme conditions of explosivity due to the sudden conversionof thermal to mechanic energy during the interaction of ascending magma with water. Variations in the eruptive
style can be attributed to several factors such as magma extrusion rate, explosion depth variation, water/magma
ratio, increasing cratering, and viscosity, among others. In Central Mexico, monogenetic volcanism is extensive,
and, although scoria cones are dominant, maars form small volcanic fields such as Valle de Santiago (Guanajuato)
and Serdan-Oriental Basin (Puebla). In these volcanic fields, maars of basaltic composition are characterized
by deep craters that reach the local water table, forming a crater lake; they are by far the most abundant, incomparison with volcanoes of rhyolitic composition, which instead form tephra rings. Based on the stratigraphic
fluctuations on their eruptive style, basaltic maars in Central Mexico can be grouped into two main groups: a) Hoya
Cintora-Joyuela type volcanoes are characterized by an entirely dry magmatic activity starting from hawaiian lava
flows, followed by strombolian scoria and a transitional explosive phase that changes to wet phreatomagmatic
maar-forming activity, which includes the periodic injection of juvenile material, particularly at the end of theeruptive phase. b) Atexcac type volcanoes characterized by an evolution from highly fragmented surge-dominatederuptions to coarse brecciated deposits followed by an alternation of wet and dry layers in the upper part of thesequence. This reveals a general drying trend, with the periodic injection of new magma as well as the abrupt
fluctuations in water/magma ratios during the construction of the eruptive succession sequence. Perhaps initial
magma extrusion rates played an important role in producing these different maar volcanoes, with higher rates forthe first type that inhibited phreatomagmatic activity at the beginning. Also, the location of the explosions within theupper unconsolidated granular aquifer (brown tuff) or the deeper highly-fractured bedrock aquifer may control theefficiency of the explosions. Deepening and lateral migration of explosion loci are observed in both maar types, andthe lateral migration is strongly controlled by the regional stress regime.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

754

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

1P1_3B-O15

Room A5

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

Comparison of the volcanic geology of the Tacambaro-Puruaran (arc front) and theZacapu (arc inland) areas in the Michoacan Guanajuato volcanic field, Mexico
Claus Siebe1 , Marie-Noelle Guilbaud1 , Sergio Salinas1 , Paul W Layer2
1

Departamento de Vulcanologia, Instituto de Geofisica, Universidad Nacional Autonoma de Mexico,
Mexico, 2 Geophysical Institute, University of Alaska Fairbanks, USA
E-mail: csiebe@geofisica.unam.mx

The highest concentration of monogenetic volcanoes in the subduction related Mexican Volcanic Belt (MVB) occurs
in its western-central part, where the arc reaches a maximum width of 150 km. This 40,000 km2 area, theMichoacan-Guanajuato Volcanic Field (MGVF), hosts more than 1000 monogenetic volcanoes and vents, and theonly two of the MVB born in historical times: Jorullo and Paricutin. The 690 km2 Tacambaro-Puruaran area (TAC) is
located at the volcanic front while the 2310 km2 Zacapu area (ZAC) lies more inland, 60 km to the N, in a direction
parallel to the subduction vector. The systematic comparison of the two areas allows for inferences regarding to
the subduction process and associated magma genesis, and might help explain the unusual number of vents thatcomprise the MGVF.
Based on detailed mapping, volumes of erupted products were estimated with the aid of a Digital Elevation Model.
Compositional and new 40Ar-39Ar and 14C data allowed us to estimate magma eruption rates and to determine
variations in the relative proportion of different magma types erupted during the course of time. Our results indicatethat MVB volcanism has been present in both areas since 5 Ma, but eruptions have become more frequent at thearc front. In the Holocene, at least 13 eruptions occurred in the TAC (average recurrence interval of 800 years,
one of the highest monogenetic eruption frequencies detected within such a small area in a subduction-setting)while only 10 eruptions occurred in the much larger ZAC. Thus, volcanism has not migrated southward in thisregion, as often postulated, but rather has become more intense at the arc front. Compositions of erupted products
are distinctly more diverse and less evolved at the arc front (high proportion of basaltic andesites and occurrenceof exotic alkaline compositions in the TAC) than at greater distances from the trench (mostly andesites, but also
dacites and rhyolites in the ZAC). Volcanic centers are preferentially aligned along SW-NE directions in the TAC
compared to WSW-ENE in the ZAC, consitent with local fault strikes. A higher rate of lithospheric extension in thesouth during the Quaternary seems to have allowed a larger number of small, poorly evolved, and compositionallydiverse dikes to reach the surface during this period.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

755

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

1P1_3B-O16

Room A5

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

Experimental craters formed by single and multiple buried explosions and implications
for volcanic craters with emphasis on maars
Greg A. Valentine1 , James D.L. White2 , Pierre-Simon Ross3 , Jacopo Taddeucci4 , Ingo Sonder1 , Jamal
Amin1 , Peter Johnson1
1

University at Buffalo, USA, 2 University of Otago, New Zealand, 3 Institut national de la recherche
scientifique, Canada, 4 Istituto Nazionale di Geofisica e Vulcanologia, Italy
E-mail: gav4@buffalo.edu

Craters at many volcanoes, including most maars, are formed by multiple subsurface explosions. Experiments
compared the crater formed by a single large, buried explosion, with craters formed by multiple explosions withthe same cumulative energy. Explosive charges were detonated in pads composed of layered aggregates, in three
configurations: (1) a single large charge buried near its optimal crater excavation depth; (2) three charges, each with
1/3 the energy of the first one, buried at approximately the same depth with respect to the original pad surface; (3)the same three charges buried successively deeper. Final crater size in the multiple explosion cases is not a good
indicator of the energy of individual explosions. However, crater morphology, and ejecta volume and distribution canbe good indicators of explosion energy and depth. The experimental explosions also demonstrate a mechanism forformation of dilute, fine-grained pyroclastic density currents driven by the collapse of a coarse mixture and lateralexpulsion of dusty gas. These results directly impact the estimate of the energy released by past maar eruptions
and future hazard assessments.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

756

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

1P1_3B-O17

Room A5

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

Magma withdrawal below ground-water table as a trigger to form large maars over highmagma discharge rate fissure-fed lava spatter/scoria cones: the Al Wahbah Crater(Harrat Kishb, Saudi Arabia)
Karoly Nemeth1 , Mohammed Rashad Moufti2 , Nabil El-Masry2 , Atef Qaddah2
1Institute of Agriculture and Environment, Massey University, Private Bag 11222, Palmerston North,
New Zealand, 2 Faculty of Earth Sciences, King Abdulaziz University, P.O. Box 80200, Jeddah, 21589,
Saudi Arabia
E-mail: k.nemeth@massey.ac.nz

Al Wahbah Crater is one of the largest and deepest Quaternary maar crater (NW-SE-elongated, appx.2.3-km
wide and 250-m deep with an irregular near-perpendicular crater wall) not only in the Arabian Peninsula but
also among other craters of volcanic fields on Earth. It is located in the SW edge of the bimodal (alkali olivine
basalt/phonolite) Harrat Kishb (2Ma-Recent) that formed lava flows over 6000-km2. Al Wahbah Crater cuts deeply
into the pre-eruptive surface exposing the Proterozoic diorite basement that is covered by at least two basanitic
lava sheets and a lava spatter/scoria cone defining the crater as a maar. The half-sectioned pre-maar cone in the
NW demonstrate that the maar collapse post-date the lava schield and cone formation. The lack of evidences
to support significant time break between the pre-maar cone-building pyroclastic beds and the dune-bedded
accidental lithic-rich pyroclastic beds that form the tuff ring suggests that the pre-maar cone (and its lava flow)
and the tuff ring formation is in a time-continuum and they formed in the same eruptive episode. In this respect
Al Wahbah’s eruption is unique and differs from maar formation that implies initial magma-water interaction-driven
explosions near surface followed by gradual explosion locus down-migration as a result of gradual exhaustionof ground-water sources (Lorenz’s model). Al Wahbah seems to have been followed an opposite eruption pathstarted with an initial lava shield and cone-building phase that have been intervened by phreatomagmatic explosive
eruptions that have been culminated in a maar collapse and tuff ring formation. This scenario can be best explainedby the drop of the magma discharge rate causing magma withdrawal below regional ground-water table. The drop in
the magmatic pressure in the conduit due to the decrease in magma rise speed enhanced ground-water to enter tothe top of the withdrawn magma column through cracks along the unsupported solidified mnargin of the conduit wall.
As a result, effective thermohydraulic explosion took place initially in the time when the same volcanic system still
emitted lava flows that rafted cone material and damping tuff breaccia on top of the still moving lava flows allowing
protrusions of lava into the freshly deposited wet pyroclastic blanket. In the main phase of the maar-forming eventthe reduced magma discharge rate shifted the efficiency of the explosive phreatomagmatic magma fragmentation
to its maximum to produce base surges that were travelled radially at least 2-km from their source leaving behind aquickly thinning blanket of dune-bedded pyroclastic deposit that covered, plastered and engulfed everything aroundthe newly formed maar. It seems Al Wahbah represents a rare but potentially one of the most hazardous volcanic
phenomena documented in the Harrat Kishb that is essential to understand to develop accurate volcanic hazard
scenarios at the Harrat Kishb and elsewhere.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

757

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

1P1_3B-O18

Room A5

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

Submarine monogenetic volcanism
Ken H Rubin1 , Robert W Embley2
1

Dept. of Geology and Geophysics, Univ. of Hawaii, Honolulu, HI 96822, USA, 2 NOAA-PMEL, Hatfield
Marine Science Center, Newport, OR 97365, USA
E-mail: krubin@hawaii.edu

Monogenetic volcanism is a widespread phenomenon recognized to occur in a range of terrestrial settings. By
comparison, very few observations of submarine volcanism have been interpreted as monogenetic, particularly inthe vast expanse of the deep sea, which forms Earth’s volumetrically dominant volcanic province. The purpose ofthis presentation is to consider the types of landforms, eruption products and vent geometries one might anticipate
for deep sea monogenetic fields in the context of what is known from direct and remote observations of deep sea
volcanism. We discuss several settings in which submarine monogenetic volcanism is likely to be common andexplore examples using a generic definition (small magma batches, small volume eruptions, isolated/dispersed
magmatic systems, and no link of eruption deposits to pre-existing polygenetic volcanic structures but structuralcontrol on the locus of volcanism is permissible). These settings include extensional basins (particularly in backarcs), near-spreading-center seamount fields, and mid-plate settings. Examples will be compared to subaerial
settings (e.g., Michoacan-Guanajuato and Auckland volcanic fields). For example, apparently short-lived volcanism
at discrete, closely spaced elongate volcanic cones and low lying lava flows in the NE Lau backarc basin
shares many characteristics with subaerial monogenetic fields, including the size and spacing of volcanic ventsand edifices. Geological, morphological, petrological, and geochemical observations made over six research
expeditions since 2008 have been used to characterize this volcanic field and to test for a monogenetic or
polygenetic classification. Volcanoes in the group are as close as 1.5 km apart (summit to summit) and 450-1400m
tall. They are formed predominantly of low effusion rate pillow lavas with variable amounts of pyroclastic deposits,
suggesting relatively long-lived volcanism (ca 100-200 yrs) at each edifice, similar to large lava shields in Iceland(e.g., skjaldbreidur). ROV and near-bottom photographic surveys do not indicate the types of structures expected
for a protracted, many-eruption volcanic history at a single volcano, although there is some evidence for syn or post
eruptive tectonism. At least three of the (the now inactive) volcanoes support black smoker hydrothermal chimneys,
suggesting relatively recent volcanism and a crustal magma body remains to generate these high temp systems.
Terrestrial monogenetic fields can also support robust geothermal systems. All but one of the cones are built of
broadly boninitic volcanic products yet major and trace element compositions are distinct enough to imply thateach is fed by separate, poorly mixed, small magma batches. Rapid extension combined with thin lithosphere andepisodic and dispersed magma supply from the nearby subduction system appears to promote conditions favoring
dispersed monogenetic volcanism over longer lived volcanic edifices or ridges at this site.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

758

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

1P1_3B-O19

Room A5

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

The complex geometries of maar-diatremes determined from geophysical modelling
techniques. Examples from the Newer Volcanics Province of south-eastern Australia
Teagan N Blaikie, Laurent Ailleres, Peter G Betts, Ray A F Cas
School of Geosciences, Monash University, Australia
E-mail: teagan.blaikie@monash.edu

The Cainozoic Newer Volcanics Province (NVP) of south-eastern Australia is an intraplate, basaltic volcanic
province comprised of over 400 monogenetic eruptive centres. Approximately 40 maar volcanoes have been
identified, typically displaying well preserved edifices with no exposure of the underlying diatreme, so geophysicalmodelling techniques are applied to understand the morphology of their subsurface structures.

High resolution gravity and magnetic surveys were conducted across several maar volcanoes located within
the NVP, including the Ecklin maar, Red Rock Volcanic Complex (RRVC), Mount Leura Volcanic Complex(MLVC) and the Anakie maar. The maar volcanoes surveyed display simple (Ecklin and Anakie) and complex(RRVC, MLVC) morphologies and eruption styles, representing a range of the different sizes and eruption styles
observed within maar volcanoes of the NVP. Within this region, volcanic rocks tend to have a high petrophysicalcontrast (higher magnetic susceptibility, lower density pyroclastic deposits and higher density lava flows) with thesurrounding host rock (carbonates, siliciclastics and granite (Anakie)), making maar volcanoes ideal for geophysicalmodelling. The depth, geometry and petrophysical property distributions of the volcanoes diatreme and feeder
dykes were determined by 2D forward and 3D inverse modelling techniques.

The Ecklin and Anakie maars display relatively simple geophysical signatures.

Long wavelength gravity

lows with corresponding magnetic highs are observed across the craters and were reproduced during modellingwith the presence of a shallow maar-diatreme structure at Anakie and two coalesced diatreme structures containing
a denser central vent at Ecklin. The RRVC and MLVC have more complex geophysical signatures, consisting of
short wavelength gravity and magnetic highs superimposed on longer wavelength gravity lows. These anomalies
are reproduced during modelling with multiple shallow coalesced diatremes containing dykes and magma ponds.

The complex diatreme geometries revealed from forward and inverse modelling suggest that the eruption
histories of these volcanoes are more complex than their relatively simple morphology would suggest. Multiple
coalesced diatreme structures indicate complex eruption histories involving vent migration, while preserved dykes
within the diatreme suggest short-lived fluctuations between phreatomagmatic and magmatic eruption styles.
The shallow diatreme structures observed suggest that soft-substrate behaviour influenced the geometry of thediatreme, and likely contributed to the migration of vents observed at Ecklin, RRVC, and MLVC. The shallow
diatreme observed within the Anakie maar is attributed to a short-lived eruption and low water content within the
granitic host rock.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

759

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

1P1_3B-O20

Room A5

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

Fly By Numbers: Using Mercury-DPM to explore the in-flight particle-particle interactionsof ’ballistic’ volcanic blocks
Leah M Courtland1 , Thomas Weinhart2 , Anthony Thornton2
1

University of South Florida, USA, 2 University of Twente, Netherlands
E-mail: courtland@mail.usf.edu

Particles ejected in Strombolian-type eruptions typically follow ballistic trajectories through the atmosphere before
coming to rest at the Earth’s surface. However, Vanderkluysen et al. (2012) have observed particles colliding
mid-air, resulting in deviations from standard ballistic trajectories that, in some instances, allow particles to exceed
the maximum distances attainable by their previously assumed ballistic trajectories.

Mercury-DPM, a code for discrete element simulations, is here used to investigate the prevalence and effects ofparticle collisions numerically. Once particle parameters (e.g. size, density), exit conditions (e.g. ejection angle,
ejection speed), external body forces (e.g. gravity, air drag), and particle-particle interactions (elastic, plastic,
viscous, frictional) are defined, Mercury computes the translational and rotational evolution of particles by solving
Newton’s second law. Thus it is an ideal tool for exploring the reltionships between the exit conditions of particles,
including the concentrations of particles within eruptive bursts and the time periods between bursts, and how thesefactors affect both the prevalence of particle collisions and the resultant translations of the particles involved. By
exploring the range of scenarios documented for actual eruptions, we are able to quantify the anticipated effects ofparticle-particle interactions due to Strombolian-type volcanic activity.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

760

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

1P1_3B-O21

Room A5

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

Space–time evolution of monogenetic basaltic volcanism in the Garrotxa Volcanic Field,
NE Iberian Peninsula.
Corrado Cimarelli1 , Federico Di Traglia2 , Guillem Gisbert Pinto3 , Meritxell Aulinas Juncá3 , Donatella De
Rita4 , Domingo Gimeno Torrente3
1

Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universitaet Muenchen,
Munich, Germany, 2 Dipartimento di Scienze della Terra, Universitá di Pisa, Pisa, Italy, 3 Department
Geoquimica, Petrologia i Prospecció Geològica, Universitat de Barcelona, Barcelona, Spain,
4
Dipartimento di Scienze Geologiche, Universitá Roma Tre, Rome, Italy
E-mail: cimarelli@min.uni-muenchen.de

We reconstructed the space-time evolution of the central Garrotxa monogenetic Volcanic Field (GVF), theyoungest volcanic area of the Iberian Peninsula, by integrating stratigraphy, petrography, geomorphology, andwell-log stratigraphy of the volcanic products. The mapping and the study of the volcanic succession has been
conducted following the Unconformity Bounded Stratigraphic Units criteria applied to volcanic terrains. The detailed
stratigraphy of the volcanic successions shows that the central GVF evolved through four main periods of volcanic
activity (Synthems) represented by the eruptive products of the mafic monogenetic volcanoes (Eruptive Units)
and by their reworked syn- and inter-eruptive (epiclastic) deposits. The morphology and the architecture of themonogenetic eruptive centres suggest that feeder dykes emplaced responding to the orientation of local structurallineaments according to the present stress tensor, which determines the strike-slip tectonic regime active inthe region since the Pliocene-Pleistocene. The facies analysis of the deposits and their distribution show that
migration of volcanism toward the center of the basin coincided with a trend of increasing explosivity. Episodichydromagmatism in the central Garrotxa occurred without a specific neither geographic nor temporal correlation.
Basic lava flow units in this sector have been systematically sampled and petrographically and geochemicallystudied in order to obtain a complete dataset useful for correlation purposes. Finally, integrating field data with thestratigraphy of water wells, we determined the volume of the volcanic deposits. The low average volume of products
emitted during each eruptive period and the long quiescence separating them allows classifying the GVF as a low
output rate volcanic field.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

761

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

1P2_3B-O22

Room A5

Date/Time: July 21 17:00-17:15

Structural controls of monogenetic volcanism
Joan Marti, Xevi Bolos, Stephanie Barde-Cabusson, Dario Pedrazzi, Stefania Bartolini, Laura Becerril,
Adelina Geyer
Institute of Earth Sciences Jaume Almera, CSIC. Lluis Sole Sabaris s/n, 08028 Barcelona, Spain
E-mail: joan.marti@ictja.csic.es

The factors controlling the precursory activity in monogenetic volcanic fields are still poorly understood, whichmeans that eruption forecasts in these systems are not very accurate. The fact that in monogenetic volcanism
each eruption has a different vent suggests that volcanic susceptibility has a high degree of randomness, so that
accurate forecasting is subjected to a very high uncertainty. Recent studies on monogenetic volcanism reveal how
sensitive magma migration may be to the existence of changes in the regional and/or local stress field produced
by tectonics or lithological contrasts (i.e., intrusion of magma bodies), which may induce variations in the pattern offurther movements of magma, thus changing the location of future eruptions. This implies that a precise knowledgeof the stress configuration and distribution of rheological and structural discontinuities in such regions is crucial toforecast monogenetic volcanism.

We use the Garrotxa Volcanic Field (NE Spain) as a case study to improve our understanding of the local
3D geology of monogenetic volcanic fields. We have used a combination of high precision geophysical techniques,
including gravimetry, self-potential and electrical resistivity tomography, in order to investigate the relationshipbetween local tectonics and the spatial distribution of monogenetic volcanoes in the Garrotxa. Our results showthat this volcanic field is underlain by low-density material, which partly can be interpreted as the roots of surface
manifestations of volcanic activity. They also show that most of the eruptive fissures which have controlled thevolcanic activity in this area for more than 300 ka correspond to NE-SW and NW-SE oriented tectonic structures.
This suggest that ascent and eruption of magmas in this volcanic field has been controlled by the same regional
normal faults bounding the horsts and grabens of the area and which seems to be related to the origin of magmas
at the base of the lithosphere. This explains the high magma ascent velocities (0.2- 2m/s) found in these volcanoes,
which together with the presence of mantle xenoliths and lower crust cumulates, suggest that some of the eruptive
fissures and faults reached quite deep in the lithosphere. The occasional diversification of magma at the upper
part of the crust towards secondary fractures of the same structural system seems due to stress barriers causedby the presence of intrusive bodies from previous eruptions and stratigraphic discontinuities in the substrate.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

762

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

1P2_3B-O23

Room A5

Date/Time: July 21 17:15-17:30

Integrating temporal and spatial patterns of Quaternary Cascades eruptions with
geochemistry, tomography and heat flow
Leif Karlstrom1 , Lah Kuan Loh1 , David Ramsey3 , Heather MN Wright2
1

Stanford University, USA, 2 USGS Menlo Park, USA, 3 USGS Cascades Volcano Observatory, USA
E-mail: leifk1@stanford.edu

Volcanism in the Cascades arc, USA, is episodic in both space and time. The modulation of time-varying mantle
melt influx by crustal magmatic plumbing drives much of this unsteadiness. However the relative contributionsof source time-variation versus crustal control are poorly constrained. Here we synthesize a number of datasets
relevant to Holocene and Quaternary Cascades magmatism, to identify patterns in preserved eruptions andvalidate models for crustal magma transport.

Our database contains >2200 published Quaternary Cascades volcanic vent locations, vent types, ages, andmajor element geochemistry of erupted lavas. Major element geochemistry is obtained from USGS professional
papers and the American Volcanic and Intrusive Rock Database (NAVDAT). We also include arc-wide heat flow
data, modeled seismic tomography and crust thickness beneath vents. Eruption ages are less well constrained
than other parameters, and we focus on variation between major geologic Epochs and their subdivisions.

We perform Spectral Clustering on vent locations to define volcanic centers for each Epoch and for theentire Quaternary.

Centers found through Spectral Clustering reproduce the major loci of volcanism in the

cascades, and identify time-varying structure in the number and distribution of monogenetic eruptions. Concentric
zonation of SiO2 content within many clusters reflects a bimodal distribution of eruptions, between compositionally
evolved central vent eruptions and mafic regional monogenetic vents. There is significant North-South structure invent type and distribution that correlates with variations in heat flow and average crustal shear velocity.

Although precise eruption ages for the complete dataset are not currently available, certain volcanic centersare quite well constrained and allow further analysis. The time history of eruptions <400 ka at Mazama, OR, showsthat the spatial distribution of eruptions does not follow a Poisson distribution when well-resolved in time, but rather
clusters around an evolved center. Monogenetic eruptions preceding the 7.8 ka Crater Lake eruption define aspatial and temporal pattern that is consistent with stress focusing of rising dikes by a growing and pressurizing
magma chamber over 20-25 kyr.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

763

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

1P2_3B-O24

Room A5

Date/Time: July 21 17:30-17:45

Spatial and temporal variations in volcanism younger than 4.5 ka in the Campi Flegrei
active volcanic field
Roberto Isaia1 , Enrico Iannuzzi1 , Mauro Rosi2 , Carlo Scirocco3 , Francesco D. A. Tramparulo3 , Stefano
Vitale31Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Napoli, Italy, 2 Universita diPisa, Dip.to di Scienze della Terra, Pisa, Italy, 3 Universita di Napoli Federico II, Dip.to di scienze della
Terra, Ambiente e Risorse, Napoli, Italy
E-mail: roberto.isaia@ov.ingv.it

The Campi Flegrei caldera is an active volcanic field in one of the most densely populated and high-risk volcanic
areas in the world. Volcanological, structural and geochemical research documents an intense volcanism with aseries of 15 explosive and effusive eruptions over a 200-300 years period following less than 2 centuries of repose
after the Agnano-Monte Spina Plinian eruption (about 4.5 ka). The renewal of volcanism was preceded by an upliftof a few tens of meters, triggered by mafic refilling of reservoirs at depths of 3 km or less. The repose was ended bya sequence of about 15 eruptions, twelve of the events were of low magnitude and involved some combination ofphreatomagmatic, strombolian and effusive activity. All but one of the eruptions occurred in the eastern-central partof Campi Flegrei, which coincided with the area of maximum deformation and seismic and hydrothermal energy
release inside the caldera.
The activity began with the SMG explosive event which erupted latites and include a sequence of ash surge layers
beneath a strombolian scoria fallout deposit that formed a small scoria cone with a feeder conduit exposed southof the Solfatara crater. Subsequently close to SMG scoria cone growth the Olibano lava dome which was overlain
by a sequence of volcanic breccias and fine-ashes generated by phreatic explosions from the southeastern cornerof the present Solfatara crater. Later a lava dome forming eruption laid down several layers of scoria breccias at
the base of the Accademia lava dome which shortly preceded the vulcanian activity of the Solfatara maar. The
SMG, Olibano, Accademia and Solfatara eruptions were clustered along NW-SE-trending faults at the boundary of
the minor Agnano Monte Spina caldera. Similar trending faults were also activated during the seven eruptions of
Astroni followed by the Fossa Lupara event which was erupted from a vent along the same NW-SE eruptive fissure
as Astroni. The exception to the clustering was the Averno event, in the western sector of the caldera, located along
an old NNW-SSE structure, outlined by several eruptive centres active from ca. 14 to ca. 4 ka. Tephra from the
Averno eruption was deposited while Solfatara was still active and provides the first direct evidence that concurrent
explosive activity has occurred in two different sectors of the caldera.
The presented data show that eruptions may cluster at intervals of a few years to decades and also occurred
simultaneously in the eastern and western sectors of the caldera, providing insight into future eruption scenarios in
CF for hazard-mitigation plans.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

764

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

1P2_3B-O25

Room A5

Date/Time: July 21 17:45-18:00

Volcanic hazard mapping based on eruptive histories and eruptive volumes - A casestudy from the Auckland Volcanic Field (New Zealand)
Gabor Kereszturi1 , Karoly Nemeth1 , Shane J. Cronin1 , Javier Agustin-Flores1 , Ian E. M. Smith2 , Jan
Lindsay2 , Mark Bebbington1
1

Volcanic Risk Solutions, Massey University, Palmerston North, New Zealand, 2 School of Environment,
The University of Auckland, Auckland, New ZealandE-mail: kereszturi_g@yahoo.com

Volcanic field-scale spatial and temporal magma fluxes are often used to express the long-term volcanic hazard
associated with monogenetic volcanic fields.

In addition, the temporally ordered eruptive volumes are key

information to assess the field’s long-term eruptive behaviour (i.e. ascribe time or volume predictability). However,these descriptions of volcanic hazard and volcanic field evolution provide only limited information about theedifice-scale volcanic hazard related to a future vent opening. The eruptive volume, as an important parameterfor long-term volcanic hazard assessment, is also essential for the edifice-scale hazard classification. However,
the accuracy of this parameter is hampered by the high susceptibility of volcanic edifices to significant erosion
in a relatively short time (e.g. 1 000 to 100 000 yr) after their eruption. The remobilization of tephra after
an eruption also creates uncertainty in eruptive volume calculations. Determination of eruption style is also
important for better understanding of area will be area affected by future volcanism (e.g. difference in distributionof phreatomagmatic pyroclastic density current deposits versus scoria fall deposits). All these input data should
be applied when quantifying likely eruptive scenarios and describing the spatial context of volcanic hazards inmonogenetic volcanic fields. In this study, an edifice-scale investigation of eruptive volumes and eruption histories
was performed on the Quaternary Auckland Volcanic Field with the aim of constructing volcanic hazard maps.
The eruptive volumes, which were corrected to Dense Rock Equivalents (DREs), were interpreted and assigned todominant eruption styles recorded for the specific edifices such as phreatomagmatic and magmatic. These volumes(genetic-unit-based eruptive volumes) were used subsequently to understand the proportion of magma fragmented
by a certain eruption style. Four eruptive scenario types were distinguished: (1) pure magmatic volcanoes (e.g.
scoria cones with lava flows), (2) volcanoes with short-lived phreatomagmatic eruptions and long-lived magmatic
phases, (3) volcanoes with long-lived phreatomagmatic, and short-lived magmatic, stages (e.g. tuff rings with an
intra-crater lava lake and scoria cone), and (4) pure phreatomagmatic volcanoes (e.g. maars). These groups forma gradual transition from one to another that reflects the variable influences of climate, topography, and substrategeology, across different spatial locations and over time during the life of the field. Within each of these groups,
there is a wide range of volumetric variability from 0.001 to 0.6 cubic km, with an average of 0.03 cubic km. Thisapproach can be adapted to improve the volcanic hazard mapping of monogenetic volcanic fields worldwide, which
ideally could be further developed by building a database of individual eruption properties from a range of similarfields in other areas.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

765

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

1P2_3B-O26

Room A5

Date/Time: July 21 18:00-18:15

Multidisciplinary approach to the hazard assessment for the Holocenic Tenerife flank
eruptions
CLAUDIA PRINCIPE1 , MARIA J BLANCO2 , DANIELE GIORDANO3 , GIANLUCA GROPPELLI4 , JOAN
MARTI MOLIST5 , STAVROS MELETLIDIS2
1

Istituto di Geoscienze e Georisorse, CNR, Pisa, ITALIA, 2 Instituto Geografico Nacional, Calle La
Marina 20. Santa Cruz de Tenerife., Espana, 3 Dipartimento di Scienze della Terra, Universita degli studi
di Torino, ITALIA, 4 Istituto per la Dinamica dei Processi Ambientali, Milano, CNR, ITALIA, 5 Instituto deCiencias de la Tierra Jaume Almera, CSIC, Barcelona, Espana
E-mail: c.principe@igg.cnr.it

A multidisciplinary approach has been applied to assess the hazard related to the eruptive fissures on the slopesof the main volcanic edifices in Tenerife. We concentrated on the historical eruptions and on the whole frameworkof the NW rift. Tenerife is a complex volcanic area in which long-lived volcanic centers coexist with a number ofdifferent-age scoriae and spatter cones. Our work concentrated on the youngest portion of these cones, their age,and distribution. In order to achieve this goal, a detailed fieldwork has been carried out by means of a 1:5,000
scale cartography of volcanic deposits and structural feature. An area of about 10 sq km has been surveyed up to
now. Archaeomagnetic method has been used to elucidate age relations of the main recent volcanic record (last
8.000 yrs BP) and a suitable field work was done. Chronostratigraphic characterization of 42 different localities (i.e.
590 archaeomagnetic measurements) was performed. In addition, petrochemical and rheological analyses are in
progress. The present data set allows us to point out some important findings that depict a new scenario for the flank
activity in Tenerife with strong implication for hazard assessment. At present, we are able to produce the complete
cartographic and chronostratigraphic sequence of two famous and distinct areas, Fasnia-Siete Fuentes-Arafo andChinyero volcanic fields, that probably represent the "general behavior" of the up to known monogenetic activity
on Tenerife. Polygenetic cones, instead of monogenetic scoriae cones, seem to be the main character of the
Holocene activity in Tenerife. No previous investigations have ever evidenced this aspect. In the Fasnia area werecognized the effect of at least two volcano-tectonic trends (one 120N oriented and the other one 50N) resulting inthree different lava flows outpouring, in stratigraphic order, from two dismantled scoriae cones and from an eruptive
fissure oriented 30N. Three orders of lava levees are well exposed in the southern portion of the lava field. Only the
1km long and last emitted lava flow belongs to the 1704-05 eruptive episode. Scoriae ramparts, pit craters and asmall cover of lapilli fallout complete the deposits associated to 1704-05 eruption. The contemporaneous presenceof big scoriae cones and small scoriae ramparts has been frequently recognized elsewhere in Tenerife and is acharacteristic of the Chinyero volcanic field too, where the 1909 volcanics are mantling two previous scoriae cones.
These observations have implications on the hazard assessment for opening of eruptive fissures in Tenerife andhazard maps have to be deeply revised taking into account that large older scoriae cones are related to a vigorous
Strombolian activity, characterized by high explosivity (highly vesicular lapilli and bombs) and long lasting lava flows,
while the real historical activity expressed only scoriae ramparts along eruptive fissures and moderate lava flows.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

766

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

1P2_3B-O27

Room A5

Date/Time: July 21 18:15-18:30

Mathematical Coupling of Geological Data as an Approach to Volcanic Hazard Analysis;
Harrat Rahat, Saudi Arabia
Melody G Runge1 , Mark Bebbington2 , Shane J Cronin2 , Jan M Lindsay1 , Mohammed R Moufti3 , Talal
Mokhtar3
1

University of Auckland, New Zealand, 2 Massey University, New Zealand, 3 King Abdulaziz University,
Saudi Arabia
E-mail: mhum400@aucklanduni.ac.nz

The monogenetic volcanic field of Harrat Rahat in Saudi Arabia is a highly complex volcanic system with 1000+
volcanic cones or craters distributed over 20,000 km2 and with evidence of volcanic activity spanning from >10
Ma to eruptions in 641AD and 1256AD. This record, and a possible recent stalled eruption in 1999, drives a needto quantify the likelihood and magnitude of future eruptions. This has stimulated research about the controlling
subsurface processes essential for estimating eruption frequency, magnitude, and style of distributed alkali-basaltic
intraplate volcanism, as well as the probable location of a future event.

Observable data for this field include:

vent locations, volumes and spatial distributions of past eruptive

products, aeromagnetic and seismic interpretations of sub-surface structure, regional tectonic models, along withpetrographic and geochemical analyses of some the erupted products.

To obtain spatio-temporal recurrence rate estimates for volcanic fields that exhibit both natural variability
and highly complex dynamics, a method is presented which determines probable relationships between data sets.
The ultimate goal is to determine which, if any, of the currently observable data and geophysical/geological models
are related to the locations and timings of eruptive events.

Data sets are arranged as spatially (and if applicable, temporally) constrained layers and training and validation
procedures used to determine the most probable relationships between data sets and consequently which
geophysical properties best explain the surface expression of volcanism©IAVCEI 2013 Scientific Assembly. All rights reserved.

767

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

1P2_3B-O28

Room A5

Date/Time: July 21 18:30-18:45

Using a Monte Carlo event-order model to compare spatio-temporal eruption forecasts ina monogenetic volcanic field
Mark S Bebbington
Massey University, New ZealandE-mail: m.bebbington@massey.ac.nz

Many spatio-temporal models have been proposed for forecasting the location and timing of the next eruption in amonogenetic volcanic field. These have almost invariably been fitted retrospectively. That is, the model has been
tuned to all of the data, and hence an assessment of the goodness of fit has not been carried out on independentdata. The low rate of eruptions in monogenetic fields means that there is not the opportunity to carry out a purely
prospective test, as thousands of years would be required to accumulate the necessary data. This leaves open thepossibility of a retrospective sequential test, where the parameters are calculated only on the basis of prior eventsand the resulting forecast compared statistically with the location and time of the next eruption. In general, events involcanic fields are not dated with sufficient accuracy and precision to pursue this line of investigation; An exception
is the Auckland Volcanic Field (New Zealand), consisting of c. 50 centers formed during the last c. 250,000 years,
for which an age-order model exists in the form of a Monte Carlo sampling algorithm, facilitating repeated sequential
testing. I examine a suite of spatial, temporal and spatio-temporal hazard models, comparing the degree of fit, andattempt to draw lessons from how and where each model is particularly successful or unsuccessful. It is found thata relatively simple (independent) combination of a renewal model (temporal term) and a spatially uniform ellipse(spatial term) performs as well as any other model. Both avoid over fitting the data, and hence large errors, when
the spatiotemporal occurrence pattern changes.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

768

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

3W_3B-P1

Date/Time: July 23 Poster

Petrology of the melilititic and nephelinitic rock suites in the Lake Natron-Engaruka
monogenetic volcanic field, northern Tanzania
Hannes B Mattsson, Rohit H Nandedkar, Peter Ulmer
Institute of Geochemistry and Petrology, ETH Zurich, Switzerland
E-mail: hannes.mattsson@erdw.ethz.ch

The Lake Natron - Engaruka Monogenetic Volcanic Field (LNE-MVF) in northern Tanzania consists of more than
150 vents of Upper Pleistocene to Holocene age that are scattered over an area of 2500 km2 . Here we describe thepetrological characteristics of these eruptions in detail and link the magma chemistry to eruptive behaviour when themagmas reach the surface. Erupted magmas are predominantly of melilititic or nephelinitic compositions (70 and
25%, respectively), together with minor amounts of basanites (5%). The melilititic magmas form by small degrees(1-2%) of partial melting of a metasomatized upper mantle source (containing 1-4% garnet together with both
amphibole and phlogopite). The melilitites ascend very rapidly through the lithosphere prior to eruption minimizing
the effect of fractional crystallization and/or crustal contamination. These eruptions also frequently carry relatively
large amounts of mantle debris to the surface. The nephelinitic rock suite, on the other hand, form by larger degrees
of melting (2-4%) at higher levels of the sub-continental lithosphere containing less garnet (<1%). The scarcity ofmantle debris in the nephelinitic eruption deposits, combined with the more evolved magma chemistry indicatesponding in crustal reservoirs en-route to the surface. For many of the nephelinitic magmas this ponding resulted in
fractional crystallization of predominantly olivine, which is also one of the main phenocryst phases in these rocks.
However, these periods of ponding in the crust must have been short as none of the investigated rocks show any
clear evidence of being affected by crustal contamination.
Within the LNE-MVF there is a rough correlation between magma chemistry and the resulting volcanic landforms.
Large maar volcanoes and tuff cones/rings are predominantly of melilititic composition, whereas the nephelinites
typically form scoria cones. This is attributed to the fact that melilititic magmas can hold more CO2 dissolved in themelt structure compared to nephelinites, in combination with a rapid ascent from the upper mantle to the surface
for the melilitites (<1-2 days). We interpret violent exsolution of CO2 (in response to rapid decompression) to be
responsible for the higher explosivity of the melilititic eruptions compared to the nephelinitic magmas within the
LNE-MVF.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

769

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

3W_3B-P2

Date/Time: July 23 Poster

Seismological evidences o a potential birth of a monogenetic volcano
Denis Legrand1 , Klaus Bataille2 , Jose Cembrano3 , Pavez Andres4 , Kundu Bhaskar5 , Vineet Gahalaut5 ,Raul PÃl’rez-LÃşpez6
1

Universidad Nacional Autonoma de Mexico, Instituto geofisica, Mexico, 2 Universidad de Concepcion,
Departamento de Ciencias de la Tierra, Concepcion, Chile, 3 Pontificia Universidad Catolica de Chile,
Departamento de Ingenieria Estructural y Geotecnica, Chile, 4 Universidad de Chile, Departamento deGeofisica, Chile, 5 National Geophysical Research Institute, Hyderabad, India, 6 IGME- Instituto
Geologico y Minero de EspaÃśa, Spain
E-mail: denis@geofisica.unam.mx

Some monogenetic volcano fields are very close to cities, such as in New Zealand or in Mexico. A new monogenetic
volcano may appear at any place and at any time, which could be potentially hazardous for nearby regions. The
ability to detect a new one in advance is obviously very important and challenging. The existence of nearby
seismometers may help for such detection. Magma sometimes reaches the surface with the birth of a volcano which
can be monogenetic, but in other cases the magma does not reach the surface How to detect such movements?
How to be sure the magma will reach the surface? Some observations may detect them, such as seismicity which
is distributed as a swarm, with a very peculiar distribution in time and magnitudes. In particular, it is important
to distinguish between a tectonic swarm and a volcanic swarm. Scaling laws of seismicity in magnitude and time
help to perform such a distinction. We show three cases: a seismic swarm in Chile, in the 2007 Aysen crisis,
corresponding to an aborted birth of a monogenetic volcano; a seismic swarm triggered after the 2004 great Mw 9.2
Sumatra-Andaman earthquake over an old monogenetic volcano; and a spatial study of monogenetic volcanoes in
Mexico (Michoacan) showing the difficulty to forecast the place and time of the birth of a monogenetic cone without
seismological records.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

770

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

3W_3B-P3

Date/Time: July 23 Poster

Eruptive Event Determination; Harrat Rahat, Saudi Arabia
Melody G Runge1 , Mark Bebbington2 , Shane J Cronin2 , Jan M Lindsay1 , Mohammed R Moufti3 , Talal
Mokhtar3
1

University of Auckland, New Zealand, 2 Massey University, New Zealand, 3 King Abdulaziz University,
Saudi Arabia
E-mail: mhum400@aucklanduni.ac.nz

The monogenetic volcanic field of Harrat Rahat in Saudi Arabia is a highly complex volcanic system with 1000+
volcanic cones and craters distributed over 20,000 km2 and with evidence of volcanic activity spanning from >10
Ma to eruptions in 641AD and 1256AD. This record, and a possible recent stalled eruption in 1999, drives a needto quantify the likelihood and possible location and magnitude of future eruptions. This has stimulated research
about the controlling subsurface processes influencing distributed alkali-basaltic intraplate volcanism.

Within volcanic fields around the world, particularly in rifting or extensional environments, magma reaches
the surface through dykes that may erupt through multiple vents within a brief period (hours to months). Thisis observed at the surface as temporal and spatial clustering of vents, on a variety of scales as seen by chainsof cones/craters, overlapping cones and/or closely clustered structures. From a long term hazards perspective,these multiple vent eruptions should be considered as single eruptive events to avoid overestimation of temporal
recurrence rates and/or bias of the hazard, and hence the consequent risk. This definition of an eruptive event,with varying spatial and temporal components, also allows model validation to a greater extent. It is simpler tomodel the area where a dyke may reach the surface than an exact location at which a vent may appear.

In the absence of detailed site-by-site mapping, few have attempted to disentangle multiple-vent eruptions
to develop a field-wide volcanic event/episode record. Here, eruptive events are determined using expert elicitation
to obtain a priori event dimension distributions. These were adapted via Bayes to well-informed distributions withthe likelihood function based on observed eruptive events in Harrat Rahat.

Probabilities for each vent grouping across the volcanic field were then obtained by comparison of the potential
event dimensions with this a posteriori distribution. Results were validated by field mapping and petrographic study
for several of the identified events.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

771

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

3W_3B-P4

Date/Time: July 23 Poster

Karioi volcano, western North Island, New Zealand: a behind arc polygenetic
intraplate-convergent margin volcanic complex
Roger M Briggs1 , Gordon G Goles2 , Roland Maas3
1

University of Waikato, New Zealand, 2 University of Oregon, USA, 3 University of Melbourne, Australia
E-mail: r.briggs@waikato.ac.nz

Karioi is a 756 m high Late Pliocene to Early Pleistocene basaltic shield volcano surmounted by a low-angle
composite cone. It is situated 130 km behind the active Taupo Volcanic Zone (TVZ) and 250 km above thesubducted Pacific slab, at the northwestern end of a 65-km long chain of volcanoes on the Tasman Sea coastof western North Island, New Zealand. Karioi volcano is constructed of lavas derived from two contrasting basalt
magma series: an arc magma series, and an alkalic intraplate series. Both series of lavas are stratigraphicallyintercalated, with no evidence of any significant time break between them. The alkalic basalts have geochemicalcompositions typical of other intraplate basalt volcanic fields of western and northern North Island, i.e. steep
REE patterns indicating derivation from a garnet peridotite source, low LIL/HFS element ratios, and Sr, Nd and Pb
isotopic compositions with a HIMU-OIB source. The arc lavas are primitive low SiO2 ankaramites with compositions
typical of subduction-derived convergent margin magmas, i.e. high LIL/LREE and LIL/HFS element ratios, and Sr,
Nd, and Pb isotopic compositions derived from a depleted mantle component, a component from subducted oceanic
lithosphere, and possibly a minor component from subducted sediments. Some stratigraphically younger lavas on
the summit cone of Karioi have more evolved high-K andesitic compositions, but others are basaltic and havetransitional compositions, possibly representing mixing of intraplate and arc type magmas. Although Karioi volcano
is surrounded by a contemporaneous monogenetic volcanic field, the intraplate lavas of Karioi have constructed abasal polygenetic lava shield sequence. Also, since they are intercalated and contemporaneous with arc lavas, theycannot be derived from a recent deep mantle plume source because of the existence of the underlying subductedslab.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

772

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

3W_3B-P5

Date/Time: July 23 Poster

Insights into volcanic fissure eruption dynamics based on detailed field mapping andgeochemical analysis: A case study of the Mt. Eccles Volcanic Complex, south-eastern
Australia
Janine L Kavanagh1 , Julie Boyce2 , Ray A F Cas2 , Rebecca Trowbridge2
1

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

The Mt. Eccles Volcanic Complex (MEVC; 38° 3.66’S, 141° 55.34’E) forms part of the Newer Volcanics province(NVP) of south-eastern Australia, which is the site of Australia’s most recent volcanic activity. The MEVC is the only
known exposed fissure vent system in Australia and represents a ’snap-shot’ into the intermediate stages of shield
volcano development. The MEVC has been dated as young as 7 ka, and comprises a spectacular NW-SE trending
fissure vent system that is aligned with several small cinder and spatter cones to the south, forming a ∼2 km longarray. The strong alignment of the MEVC fissure vent and cone array suggests dykes utilized pre-existing structuresduring magma ascent, a hypothesis supported by co-alignment with large-scale Paleozoic basement faults in thearea. Partial collapse of the vent walls reveals excellent exposure of the internal structure of the fissure, which
comprises alternating horizons of lava and spatter sequences. The fissure vent is breached to the north by a
substantial lava field, the longest of these lavas extends over 50 km in length reaching the current coastline tothe south. These sizable flows indicate a sustained high effusive phase in the MEVC eruption that allowed thedevelopment of an extensive lava tube network, which is preserved as numerous lava caves, channels and tumuli.
Quarrying of scoria cones to the south of the array has provided excellent exposure of their internal structure, down
to the lava flows on which the cones were built. Stratigraphic logging of the quarry walls and detailed mapping of
the quarry floor provides insights into the growth of cinder cones and the nature of the shallow feeder system. Field
relations suggest the volcanism started in the north of the area and moved progressively southwards. Hawaiian
fire-fountaining was a dominant eruptive style at the MEVC, with minor Strombolian and phreatomagmatic behaviour
to the south. XRF analyses of stratigraphically constrained samples show the erupted products comprise hawaiite,
nepheline-hawaiite, basanite and alkali-olivine basalt, with a strong Ocean Island Basalt character that is consistent
with other erupted products in the NVP. The MEVC eruptive period was likely short-lived, with punctuated events
lasting in total several weeks to months.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

773

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

3W_3B-P6

Date/Time: July 23 Poster

Understanding geomorphic data of monogenetic scoria cones
Gabor Kereszturi, Karoly Nemeth
Volcanic Risk Solutions, Massey University, Palmerston North, New ZealandE-mail: kereszturi_g@yahoo.com

The definition of a scoria (or cinder) cone traditionally refers to any kind of volcanic landform that has conicalgeometry, is dominantly composed of fragmented rocks (coarse ash to lapilli) of low silica content of any type (e.g.
basalt) and that is small in edifice volume (e.g. 0.1 to 0.00001 cubic km). Geomorphic data of scoria cones are often
used for understanding eruptive and degradation processes quantitatively and as discrimination factors for relative
age dating. One of the most common interpretations of scoria cones’ geomorphic data is that these geomorphic
parameters gradually decrease with age as the erosion processes smooth the cone morphology away from the
Earth surface. Recently, an increasing number of studies have found evidence for a significant eruptive-control
on the morphology of scoria cones. This study aims to give a summary of the possible interpretations of thegeomorphic data of scoria cones in the light of the findings of new studies. Morphometric data extracted fromany source (e.g. Digital Elevation Models) carry information about both syn-eruptive and post-eruptive processes.
Therefore, the traditional morphology-based discrimination of edifice degradation stages and relative age groupingsof volcanic cones should be avoided; a distinction should be made between the syn-eruptive contribution andthe post-eruptive contribution before any further interpretation is carried out. For discrimination purposes, known
absolute ages should be used, thus the likely effect of erosion on the primary, syn-eruptive morphology can bequantified. Here we suggest that prior to any detailed morphological study on a cone-dominated field, a preliminary
assessment of the cone (e.g. eruption history) needs to be performed and cones grouped following their genetic(syn-eruptive) origin. If the grouping of edifices is based on eruptive similarities, then the initial morphologies should
be similar to each other and their subsequent degradation will likely follow the same pattern over time. Here we
provide numerous examples to support the syn-eruptive controls on scoria cone morphology and their long-term
effect on degradation rates and patterns under different climatic settings. A theoretical degradation model, by the
combination of long-term (e.g. rain splash erosion) and short-term (e.g. debris flow) mass wasting processes, isestablished to help the interpretation of geomorphic data. Due to the coupling mechanism between the eruptive
diversity and the degradation path of individual volcanoes, it is proposed that volcano degradation is not only theconsequence of age and climate, but of many other processes, such as number of ’event’ degradations and theerosion-resistance of pyroclastic materials exposed to the environment.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

774

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

3W_3B-P7

Date/Time: July 23 Poster

Uranium series - size correlations in intraplate basaltic volcanic fields: source control on
physical parameters
Lucy E McGee1 , Heather K Handley2 , Christoph Beier3 , Ian E M Smith1 , Jan M Lindsay1
1

University of Auckland, New Zealand, 2 GEMOC, Macquarie University, Australia, 3 GeoZentrum
Nordbayern, Universitaet Erlangen-Nuernberg, Germany
E-mail: l.mcgee@auckland.ac.nz

Small volume basaltic eruptions within volcanic fields have the potential to reveal subtle features of magmatic
processes which are overwhelmed in larger systems such as central continental volcanoes, ocean island basalts
and large igneous provinces. One of the major findings of recent research has been that such volcanic fields canreveal the fine detail of source heterogeneity both on whole field and single volcano scales. Because small volume
centres often display almost complete volcanic sequences within a range of eruptive styles and sizes, opportunities
are presented whereby correlations between physical features and chemical compositions can be investigatedin detail. The Auckland Volcanic Field (AVF) in northern New Zealand is one of the best-sampled cases of abasaltic volcanic field; the volcanoes comprising the field show a spectrum of sizes and compositions from small
volume nephelinitic maars and tuff dominated centres, through medium sized alkalic basanitic and basaltic scoria
cones, to larger volume subalkalic basalt scoria and lava dominated centres. We focus on four eruptions whichdisplay a size and compositional spectrum: Purchas Hill (11ka, the smallest sampled volcanic centre in the AVF,
nephelinitic in composition), Mt Wellington (10ka, medium sized, alkalic basalt) and the two eruptions of Rangitoto(Rangitoto 1: 552yrs BP, medium sized, alkalic basalt, and Rangitoto 2: 502yrs BP, the largest volcanic centre in
the AVF, subalkalic basalt). U series and other isotopic data for the largest, smallest and two medium sized volcanic
centres in the field show strong correlations between eruptive volume and isotopic composition. Preliminary data
show that the volcanic centres display a spectrum of compositions in U-Th isotopic, Pb isotopic and SiO2 vs.
Total Alkali space, with the smallest centre (Purchas Hill) displaying the highest (230Th/232Th) (1.38), the mostradiogenic 206Pb/204Pb (19.416) and 208Pb/204Pb (39.009), the lowest SiO2 (39 wt%) and highest total alkalis(6 wt%). The largest centre displays the lowest (230Th/232Th) (1.14), the least radiogenic 206Pb/204Pb (19.039)
and 208Pb/204Pb (38.781), the highest SiO2 (49.5 wt%) and lowest total alkalis (3 wt%). Other isotopic and traceelement parameters tentatively show similar correlations. The observed differences in the chemical parameters canbe attributed to melting of a heterogeneous source, where the heterogeneity results in varying magmatic processes.
These results suggest that physical parameters of individual centres in intraplate volcanic fields may dominantly be
dictated by processes in the deep asthenosphere.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

775

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

3W_3B-P8

Date/Time: July 23 Poster

Unraveling the eruption dynamics of the complex volcanology at the 5 ka Mt. Gambier
Volcanic Complex, south-eastern Australia
Jozua van Otterloo, Ray A.F. Cas, Massimo Raveggi
Monash University, Australia
E-mail: jozua.vanotterloo@monash.edu

The 5 ka, basaltic, multi-vent and polymagmatic Mt. Gambier Volcanic Complex (MGVC) is a complex of maars,
tuff, scoria and spatter cones. It occurs within the late Cainozoic basaltic intraplate Newer Volcanics Provinceof south-eastern Australia. Field mapping, stratigraphy and facies analysis, component analysis, whole rockgeochemistry and electron microprobe and Fourier Transform IR analyses were used to constrain the eruption
dynamics of the MGVC. The eruption styles range from magmatic to phreatomagmatic with varying intensities in
explosivity. The analyses indicate that the highly variable eruption styles in this complex monogenetic system
resulted from a combination of magmatic variables (magmatic effusive vs.

magmatic explosive styles) andthe dynamics of interaction between the rising magma and the two underlying aquifers (one confined and one
unconfined).
Magmatic variables are crystallinity, vesicularity, temperature, density, viscosity, rise rate, pre-eruptive volatile
contents and degassing. The aquifer dynamics are related to the aquifer properties - grainsize distributions,permeability, recharge rates, hydraulic conductivity (i.e. horizontal flow rate) - as well as the behaviour of thewater itself and how these properties rheologies change with the introduction of rising hot magma. Also the conduitproperties related to the aquifers are important (i.e. sealing of the conduit walls and liquifaction). The rising magma,
at each eruption point, first interacted with the upper unconfined aquifer and then later with the deeper confined
aquifer as the diatreme was progressively excavated deeper.
This poster provides insight in how these variables and dynamics are constrained and what the results are to dateof the different methods. It should trigger a discussion about the way hydrodynamics are perceived when studying
eruption dynamics.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

776

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

3W_3B-P9

Date/Time: July 23 Poster

New insight into the timing of volcanism at Salton Buttes, California from 40 Ar/39 Ar dating
and paleomagnetism
Heather M Wright, Margaret T Mangan, Duane E Champion, Andrew T Calvert
U.S. Geological Survey, U.S.A.
E-mail: hwright@usgs.gov

Five Quaternary rhyolite domes lie along the southern margin of the Salton Sea, California. The domes are aligned
parallel to the axis of spreading along the boundary between the Pacific and North American plates in the Salton
Trough pull apart basin. These volcanic domes are spatially associated with a broad area of high heat flow (tens ofkilometers wide) and active geothermal energy production in the Salton Sea Geothermal Field. Magmatic rocks in
the Salton Trough are bimodal in composition, including rhyolites and subsurface diabase dikes. Volcanism at the
Salton Buttes is characterized by both magmatic and phreatomagmatic activity, where explosive activity preceded
an effusive phase in at least two cases.

Given the surface expression of the low profile domes in an area of rapid sedimentation and subsidence(∼0.2-2 cm/yr; Schmitt and Hulen 2008; Brothers et al. 2009) and <15 ka U-Th ages for the rims of zircon
crystals from two of the domes (Schmitt and Vazquez 2006; Schmitt et al. 2013), the domes are likely all latest
Pleistocene to Holocene in age. Here, we add U-Th zircon rim ages for all of the domes and a new 40 Ar/39 Ar
age for anorthoclase from Obsidian Butte, confirming latest Pleistocene to Holocene eruption ages. Further, bycomparing independent paleomagnetic remanent directions from sites drilled in the domes with geomagnetic
secular variation, we find that there were at least three distinct eruption periods. These distinct eruption dates arecoincident with small variations in glass and whole-rock composition of domes.

Finally, over a longer timespan, volcanism in the Salton Trough apparently is markedly sporadic. The mostrecent known volcanism (small volume rhyolite domes akin to surface domes discovered by geothermal exploration
drilling) occurred >420 ka (now at >1.6 km depth beneath the ground surface, Schmitt and Hulen 2008). We
speculate that volcanism is reserved to periods when magma production rate outpaces extension rate.

Brothers, Driscoll, Kent, Harding, Babcock, Baskin (2009) Tectonic evolution of the Salton Sea inferred fromseismic reflection data, Nature Geoscience 2: 581-584.
Schmitt and Hulen (2008) Buried rhyolites within the active, high-temperature Salton Sea geothermal system,
Journal of Volcanology and Geothermal Research 178: 708-718.
Schmitt and Vazquez (2006) Alteration and remelting of nascent oceanic crust during continental rupture: Evidence
from zircon geochemistry of rhyolites and xenoliths from the Salton Trough, California, Earth and Planetary Science
Letters 252: 260-274.
Schmitt, Martin, Stockli, Farley, Lovera (2013) (U-Th)/He zircon and archaeological ages for a late prehistoric
eruption in the Salton Trough (California, USA), Geology 41: 7-10.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

777

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

3W_3B-P10

Date/Time: July 23 Poster

Abu monogenetic volcano group in SW Japan Arc: its characteristic landforms, eruption
types, and magma genesis
Takashi Nagao1 , Koji Kiyosugi2 , Yoshiyuki Horikawa1 , Susumu Kakubuchi3
1

Yamaguchi University, Japan, 2 University of Tokyo, Japan, 3 Saga University, Japan
E-mail: taknagao7@gmail.com

Late Cenozoic Abu monogenetic volcano group (AMVG) consists of 56 volcanoes and is distributed over an areaof 400km2 in SW Japan Arc. Some of the 56 volcanoes are located within the sea. The volcanic activity is classified
into an alkaline basalt-dominated early period (2-1.6Ma), and a calc-alkaline andesite to dacite dominated lateperiod (<0.8Ma). The early activity took place about 0.4 mys, during which time 0.3 km3 of alkaline basalt alone
was erupted to form lava flow with scoria cone and small lava plateaus. The late activity produced alkaline basalt
consisting of small lava plateau and lava flows with scoria cone. Smallest basaltic lava plateau, Nakanodai volcano(0.19Ma), is 600m x 450m in basal distance and 50m in height. Dominant calc-alkaline andesite to dacite also
flooded from the fissure to build lava plateaus or flat lava domes. Largest lava plateau, Ooshima volcano (0.19Ma),
is 2400m x 1500m in basal distance and 170m in height. The andesite to dacite lavas formed the lava plateaus
might be higher temperatures and effusive rates. The largest basaltic monogenetic volcano, Iraoyama volcano(0.4-0.32Ma), erupted thick fallout deposits (<30m in thickness) from central vent and simultaneous scoria cone
formation. Then large volume of lava flows oozed out two directions from the base of the scoria cone. The east lava
flow formed the lava plateau surrounding country rock. The northern lava flow followed a former river valley to reachthe lowland 14km away. The solidified long lava flow (<100m in depth) is eroded and exhibits spectacular columnar
jointing along cliffs in valleys. These landmarks are named Dragon’s Causeway related to the tradition of this area.
These suggest that Iraoyama volcano might be constructed by violent strombolian eruption such as production oflarge amount of fallout deposit, simultaneous scoria cone formation and large volume of lava effusion from the baseof the scoria cone. The basalts in early activity show the OIB type signature. On the other hand, basalts in lateactivity have the OIB- and island-arc type signatures. They might be derived from heterogeneous mantle diapir.
The calc-alkaline andesite and dacite might be produced by magma mixing between primitive basaltic and felsicmagmas. Magmatism of AMVG suggests that heating induced by intrusion of basalt magma resulted in partial
melting of the crust, thus producing felsic calc-alkaline magmas.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

778

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

3W_3B-P11

Date/Time: July 23 Poster

Petrography and Ar isotopic information of nosean in the phonolite in East Eifel volcanic
field, Germany: investigation of the source of excess 40 Ar
Masafumi Sudo, Uwe Altenberger
University of Potsdam, Institute of Earth and Environmental Science, Germany
E-mail: msudo@geo.uni-potsdam.deSince the reports of the 40 Ar/39 Ar analyses and excess 40 Ar on Quaternary Eifel monogenetic volcano field inGermany from 1985 to 1990 by the group of Lippolt of the University of Heidelberg, hauyne and nosean in certain
phonolites from the northwest of East Eifel volcanic field were known to contain significant amounts of excess 40 Ar
and show apparent older ages. However, its petrographic meaning was not well known. The group of Sumino of
the University of Tokyo has clarified the source for excess 40 Ar in plagioclase phenocrysts from the historic Unzen
dacitic lava flows as the melt inclusions shown as zones in plagioclase by in-situ laser Ar isotope analysis.
In order to investigate the source of excess 40 Ar in hauyne/nosean from the phonolite in the East Eifel by in-situ
Ar isotope analysis with UV pulse laser (wavelength 266 nm) and 40 Ar/39 Ar dating system at the University of
Potsdam, we collected phonolites from the East Eifel and investigated their petrography, mineral composition and Ar
isotopes. The rock collected from Olbrueck contains nosean, leucite and sanidine phenocrysts. Nosean contained
fine inclusions with a size of less than 5 micrometer which are distributed linearly, but not as zones. For manynosean grains resorbtion occurred, although no inclusions or resorption are shown from the leucite and sanidine
phenocrysts. The analysis by SEM-EDS showed that the resorbtion was caused by carbonates or carbonate melts.
The chemistry at inclusions or in holes where the inclusions probably located showed higher Cl and S content,
which could be derived from volcanic volatile elements. The in-situ Ar isotopic analyses were performed on thepolished surface of small rock plates (less than 1cm size and less than 1mm thickness) with UV pulse laser by
100 or 200 micrometer beam size. Obtained results are: (1) carbonate in/around the nosean only show nearly theatmospheric Ar isotope ratios, (2) the in-situ analyses of nosean and leucites showed clearly higher 40 Ar/36 Ar ratios
up to 460 (nosean) or 600 (leucite), (3) the correlation of the 40 Ar/36 Ar ratios with or without apparent involvementof linear distribution of inclusions in the spot areas was not clear. It was mostly difficult to analyze inclusion-freeareas. (4) From the K-Ar isochron plots of the results considering potassium contents for nosean and leucites,
nosean clearly shows the older age than leucite. This data set implies that the nosean surely has the apparent
older ages than leucite as the previous reports by the group of Lippolt. Therefore presently the influences to the
Ar isotope from the inclusions are not yet clear. As other rock plates were also irradiated by the fast neutron in thereactor at Petten, Netherlands, the discussion will continue with the results by in-situ 40 Ar/39 Ar analyses of thosesamples.

©IAVCEI 2013 Scientific Assembly. All rights reserved.

779

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

3W_3B-P12

Date/Time: July 23 Poster

Complex interaction between Strombolian and phreatomagmatic eruptions in the
Miocene monogenetic volcanism of the Harrat Shama Volcanic Field (SW of Sauda
Arabia)Ezz El Din Abdel Hakim Khalaf1 , Ali Abdel Motelib2
1

Associate professor, Egypt, 2 Associate professor, Egypt
E-mail: E.2012_khalaf@hotmail.com

The Harrat Shama volcanic Field (HSVF) is a well-exposed, intra-continental extensional basin during the openingof the Red Sea, containing 5 km of Miocene preserved and uplifted bimodal volcanics and interbedded volcaniclastic
rocks. The HSVF comprises proximal wall deposits with a well defined crater wall unconformity and crater-filldeposits. The style of volcanic activity was mainly explosive and was reinforced by hydrovolcanic processes.
The Shama deposits can be divided into two sequences depending on the field observations and the main
depositional characteristics: lower sequence represents volcanic aggradational processes that constructed thecrater, and is composed of hyaloclastites, zeolite-bearing bedded tuffs, and explosively fragmented accretionary
bedded lapillituffs of wet surge facies and an upper sequence, made up of ash flow deposits and peperitic brecciasthat are capped by basaltic lava flows. The differences between the two sequences are reflected in both eruption
dynamics and fragmentation mechanisms as well as the overall characteristics of the deposits. Fluvial erosion anddeposition completed the evolution of the emerged marginal part of the basin.
The two complex volcanic successions that show evidence of several eruptive episodes, were built by magmaticand hydrovolcanic explosions of different styles (Strombolian, sub-Plinian and phreato-Strombolian) generated
from a common source. They formed a dynamic closed intra-continental sedimentary system that experienced
a successive subsidence. The initial eruptions are interpreted to have been dominated by discrete, highly efficient,phreatomagmatic fall deposits, which are attributed to an overall high eruption rate in a deep lacustrine setting(lower sequence), followed by a transition to dominantly subaerial ash-flow deposits and volcaniclastic sediments
sited in the upper part of the basin. The Phreatomagmatism has contributed to the construction of more than a halfof this volcanic edifice, frequently associated with the Strombolian activity but also independently, giving rise to alarge variety of eruptive sequences. Dome growth occurred at the end of the eruption, but subsequent retrogressive
explosions triggered by external water destroyed all trace of the original dome morphology. We find that the maincause of such complex eruptive behaviour resides in the stratigraphic, structural and hydrogeological characteristicsof the substrate above which the volcanoes were emplaced, rather than on the compositional characteristics of theerupting magma, as they do not show significant variations among the different deposits studied.

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