Volcanology

Concordant U–Pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth. Advances in zircon TIMS analysis and geochronological studies by SIMS on zircon from young volcanic rocks, along with evolving views of the evolution of magmatic systems, makes it necessary to revaluate this interpretation. Assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton. Distinctions must be made between true inherited zircon, xenocrystic zircon derived from host rocks during magma ascent and/or emplacement, and multi-stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons. These complications are exemplified by recent high-precision U–Pb zircon age dating from the Cretaceous Tuolumne and Mt. Stuart batholiths, which clearly show that the timeframe of pluton assembly was long (> 5 Ma for Mt. Stuart and > 8 Ma for Tuolumne). Zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon (several 105 yr up to 2 × 106 yr), and assignment of statistically valid rock solidification ages is not possible from these data. Low Zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent. Recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages, and is compatible with progressive growth of a large, long-lived, crystal mush body. Because eruption of magma requires low to moderate crystal fraction and high temperatures (relative to stored crystal mushes), zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions.

The Taupo Volcanic Zone (TVZ) of New Zealand is characterised by extensive volcanism and by high rates of magma production. Associated with this volcanism are numerous high-temperature ( > 250°C) geothermal systems through which the natural heat output of 4200 f 500 MW is channelled. Outside the geothermal fields the heat flow is negligible. The average heat flux from the central 6000 km2 of the TVZ, which contains most of the geothermal fields, is 700 mW/m3. This heat flux appears to be more concentrated along the eastern margin of the TVZ.

The Neapolitan Yellow Tuff (NYT) is the product of the largest known trachytic phreatoplinian eruption. It covered an area larger than 1000 km 2 with an estimated volume of about 40 km 3 of erupted magma. During the course of the eruption a caldera collapsed within the previously formed Campanian Ignimbrite caldera. The resulting nested structure strongly influenced the following volcanic activity in the Campi Flegrei caldera. As previous dating of the NYT does not converge toward a unique result, a new set of 40 Ar/ 39 Ar age determinations has been carried out to better constrain the age of the eruption. Two variants of the 40 Ar/ 39 Ar dating method were applied to determine the age of the NYT eruption: (1) single-crystal total fusion (SCTF), on an individual phenocryst of feldspar, and (2) laser incremental heating (LIH), on bulk aliquots of feldspar phenocrysts. The results of the SCTF analyses show that the overall sample weighted mean age, derived from the conventional age calculation, is 15.6 þ 0.8 ka. A weighted mean of the isochron age is 15.3 þ 1.2 ka (2c), and has been assumed as the best indicator of age to be derived from the SCTF analyses. The LIH analyses results show that plateau ages vary from 15.4 þ 0.5 to 14.5 þ 0.5 ka. The overall weighted mean age of the isochron results is 14.9 þ 0.4 ka (2c). This result has been assumed as the reference age for the NYT eruption, and agrees with the SCTF age. The new age obtained for the NYT deposits is of great relevance for the understanding of the evolution and the present state of the Campi Flegrei caldera and collocates the NYT in a crucial stratigraphical position to date the climatic oscillations that occurred between the Late Glacial and the Holocene.

We report new major element, trace element, isotope ratio, and geochronological data on the Galfipagos Archipelago. Magmas erupted from the large western volcanos are generally moderately fractionated tholeiites of uniform composition; those erupted on other islands are compositionally diverse, ranging from tholeiites to picritic basanitoids. While these volcanos do not form a strictly linear age progressive chain, the ages of the oldest dated flows on any given volcano do form a reasonable progression from youngest in the west to oldest in the east, consistent with motion of the Nazca plate with respect to the fixed hotspot reference frame. lsotope ratios in the Galfipagos display a considerable range, from values typical of mid-ocean ridge basalt on Genovesa (87Sr/86Sr: 0.70259, end: +9.4, 206pb/204pb: ! 8.44), to typical oceanic island values on Floreana (87Sr/86Sr: 0.70366, oeNd: +5.2, 206pb/204pb: 20.0). La/Sm N ranges from 0.45 to 6.7; other incompatible element abundances and ratios show comparable ranges. Isotope and incompatible element ratios define a horseshoe pattern with the most depleted signatures in the center of the Galfipagos Archipelago and the more enriched signatures on the eastern, northern, and southern periphery. These isotope and incompatible element patterns appear to reflect thermal entrainment of asthenosphere by the Galfipagos plume as it experiences velocity shear in the uppermost asthenosphere. Both north-south heterogeneity within the plume itself and regional variations in degree and depth of melting also affect magma compositions. Rare earth systematics indicate that melting beneath the Galfipagos begins in the garnet peridotite stability field, except beneath the southern islands, where melting may occur entirely in the spinel peridotite stability field. The greatest degree of melting occurs beneath the central western volcanos and decreases both to the east and to the north and south. Sis. 0, FeB. 0, and NaB. 0 values are generally consistent with these inferences. This suggests that interaction between the plume and surrounding asthenosphere results in significant cooling of the plume. Superimposed on this thermal pattern produced by plume-asthenosphere interaction is a tendency for melting to be less extensive and to occur at shallower depths to the south, presumably reflecting a decrease in ambient asthenospheric temperatures away from the Galfipagos Spreading Center.

RED SEED stands for Risk Evaluation, Detection and Simulation during Effusive Eruption Disasters, and combines stakeholders from the remote sensing, modelling and response communities with experience in tracking volcanic effusive events. The group first met during a three day-long workshop held in Clermont Ferrand (France) between 28 and 30 May 2013. During each day, presentations were given reviewing the state of the art in terms of (a) volcano hot spot detection and parameterization, (b) operational satellite-based hot spot detection systems, (c) lava flow modelling and (d) response protocols during effusive crises. At the end of each presentation set, the four groups retreated to discuss and report on requirements for a truly integrated and operational response that satisfactorily combines remote sensors, modellers and responders during an effusive crisis. The results of collating the final reports, and follow-up discussions that have been on-going since the workshop, are given here. We can reduce our discussions to four main findings. (1) Hot spot detection tools are operational and capable of providing effusive eruption onset notice within 15 min. (2) Spectral radiance metrics can also be provided with high degrees of confidence. However, if we are to achieve a truly global system, more local receiving stations need to be installed with hot spot detection and data processing modules running on-site and in real time. (3) Models are operational, but need real-time input of reliable time-averaged discharge rate data and regular updates of digital elevation models if they are to be effective; the latter can be provided by the radar/photogrammetry community. (4) Information needs to be provided in an agreed and standard format following an ensemble approach and using models that have been validated and recognized as trustworthy by the responding authorities. All of this requires a sophisticated and centralized data collection, distribution and reporting hub that is based on a philosophy of joint ownership and mutual trust. While the next chapter carries out an exercise to explore the viability of the last point, the detailed recommendations behind these findings are detailed here.

[1] A global compilation of 170 time-averaged volumetric volcanic output rates (Q e ) is evaluated in terms 12 of composition and petrotectonic setting to advance the understanding of long-term rates of magma 13 generation and eruption on Earth. Repose periods between successive eruptions at a given site and 14 intrusive:extrusive ratios were compiled for selected volcanic centers where long-term (>10 4 years) data 15 were available. More silicic compositions, rhyolites and andesites, have a more limited range of eruption 16 rates than basalts. Even when high Q e values contributed by flood basalts (9 ± 2 Â 10 À1 km 3 /yr) are 17 removed, there is a trend in decreasing average Q e with lava composition from basaltic eruptions (2.6 ± 18 1.0 Â 10 À2 km 3 /yr) to andesites (2.3 ± 0.8 Â 10 À3 km 3 /yr) and rhyolites (4.0 ± 1.4 Â 10 À3 km 3 /yr). This 19 trend is also seen in the difference between oceanic and continental settings, as eruptions on oceanic crust 20 tend to be predominately basaltic. All of the volcanoes occurring in oceanic settings fail to have 21 statistically different mean Q e and have an overall average of 2.8 ± 0.4 Â 10 À2 km 3 /yr, excluding flood 22 basalts. Likewise, all of the volcanoes on continental crust also fail to have statistically different mean Q e 23 and have an overall average of 4.4 ± 0.8 Â 10 À3 km 3 /yr. Flood basalts also form a distinctive class with an 24 average Q e nearly two orders of magnitude higher than any other class. However, we have found no 25 systematic evidence linking increased intrusive:extrusive ratios with lower volcanic rates. A simple heat 26 balance analysis suggests that the preponderance of volcanic systems must be open magmatic systems with 27 respect to heat and matter transport in order to maintain eruptible magma at shallow depth throughout the 28 observed lifetime of the volcano. The empirical upper limit of $10 À2 km 3 /yr for magma eruption rate in 29 systems with relatively high intrusive:extrusive ratios may be a consequence of the fundamental 30 parameters governing rates of melt generation (e.g., subsolidus isentropic decompression, hydration due to 31 slab dehydration and heat transfer between underplated magma and the overlying crust) in the Earth. 32 41 [2] Despite the significant impact of volcanic sys-42 tems on climate, geochemical cycles, geothermal 43 resources and the evolution and heat budget of the 44 crust, surprisingly little is known regarding the 45 systematics of long-term rates of magma genera-46 tion and eruption on Earth. Global rates of magma 47 generation provide insight regarding the planetary-48 scale energy budget and thermal evolution of the 49 Earth. Rates of magma generation and eruption are 50 key factors affecting the petrological and geochem-51 ical evolution of magma bodies as well as eruptive 52 styles due to the intrinsic coupling between magma 53 recharge, fractional crystallization, wall rock as-54 similation and melt volatile saturation [Shaw, 1985; 55 Spera et al., 1982]. Volcanoes and formation of 56 intrusive bodies such as sill complexes have been 57 suggested to play a role in global climate change 58 and perhaps even trigger 59 biotic extinctions. In addition, global rates of 60 magmatism may have important implications for 61 seismic energy release [Shaw, 1980] and the mag-62 netic geodynamo by modulating heat transfer from 63 the core-mantle boundary and the concomitant 64 development of deep mantle plumes [Olson, 65 1994]. Rates of magmatism on Earth are also used 66 in planetary research as analogues to constrain 67 magmatic and thermal models. In summary, there 68 is an exhaustive set of reasons for developing 69 systematic knowledge regarding the rates of mag-70 matism on Earth including the effects of magma 71 composition and petrotectonic environment on vol-72 umetric rates. 73 [3] One of the key factors in understanding mag-74 matism is a quantitative evaluation of the extent to 75 which magmatic systems operate as open or closed 76 systems. These alternatives have significantly dif-77 ferent implications for magma evolution. However, 78 the openness of magmatic systems is difficult to 79 determine since there is no unambiguous way to 80 track magma transport from the generation and 81 segregation through the crust to volcanic output. 82 On balance, many magma systems are thought to 83 be open systems in that they receive additional 84 inputs of heat and mass during magmatic evolution 85 [Davidson et al., 1988; 86 Gamble et al., 1999; Petford 87 and Gallagher, 2001]. Closed magmatic systems 88 which exchange heat but little material with their 89 surroundings (i.e., neither assimilation nor recharge 90 is important) may be rather uncommon. What is 91 more likely is that specific systems may behave as 92 closed systems for restricted portions of their 93 history [e.g., Singer et al., 1992; Zielinski and 94 Frey, 1970]. It is important to note, however, for 95 the olivine basalt-trachyte series at Gough Island 96 where fractional crystallization appears dominant, 97 Pb and Sr isotopic data indicates that assimilation 98 of hydrothermally altered country rock and/or 99 recharge of isotopically distinct magma has taken 100 place [Oversby and Gast, 1970]. 101 [4] In this paper, time-averaged volcanic output for 102 periods >10 3 years are evaluated. Volcanic output 103 rates for individual eruptions may vary wildly 104 about some norm, but evidently settle to a repre-105 sentative ''average'' value when time windows on 106 the order of 10 times the average interval of 107 eruptions are considered [Wadge, 1982]. Crisp 108 [1984] conducted a similar study of magmatic rates 109 published between 1962 and 1982 and established 110 some basic relationships between volcanic output 111 and associated factors such as crustal thickness, 112 magma composition, and petrotectonic setting. 113 This work updates and extends that earlier compi-114 lation with 98 newly published volcanic rates and 115 volumes from 1982 -2004 for a total of 170 116 estimates (see auxiliary material 1 Tables S1 and 117 S2). We also endeavor to establish some scaling 118 relationships based primarily on the compilation 119 and some simple energy budget considerations 120 with the goal of discovering possible systematic 121 trends in the data. 122 2. Sources and Quality of the Data 123 [5] The data presented here are volumetric volca-124 nic or intrusive rates published from 1962-2005, 125 including data from the compilation by Crisp 126 [1984] of rates published from 1962-1982 where 127 these data have not been superseded by more 128 recent studies. We have also reviewed the rate data 129 presented by Crisp [1984] and corrected or re-130 moved several references as appropriate. Thus the 131 data presented here is a completely updated com-132 pilation of volumetric rates of eruption. 133 [6] Most volcanoes have cycles of intense activity 134 followed by repose. Comparing volcanic systems 135 at different stages in their eruptive cycles can lead 136 to erroneous conclusions, if the duration of activity 137 is not long enough to average the full range of 138 eruptive behavior over the lifetime of the volcano.

The April–May 2010 volcanic eruptions of Eyjafjallajökull, Iceland caused significant
economic and social disruption in Europe whilst state of the art measurements and ash
dispersion forecasts were heavily criticized by the aviation industry. Here we demonstrate for the first time that dramatic improvements can be made in quantitative predictions of the fate of volcanic ash emissions, by using an inversion scheme that couples
a priori source information and the output of a Lagrangian dispersion model with satellite data to estimate the volcanic ash source strength as a function of altitude and time.
From the inversion, we obtain a total fine ash emission of the eruption of 8.3 ± 4.2 Tg for particles in the size range of 2.8–28 µm diameter and extrapolate this to a total ash
emission of 11.9 ± 5.9 Tg for the size range of 0.25–250 µm. We evaluate the results
of our a posteriori model using independent ground-based, airborne and space-borne
measurements both in case studies and statistically. Subsequently, we estimate the
area over Europe affected by volcanic ash above certain concentration thresholds relevant for the aviation industry. We find that during three episodes in April and May,
volcanic ash concentrations at some altitude in the atmosphere exceeded the limits for
the “normal” flying zone in up to 14% (6–16%), 2% (1–3%) and 7% (4–11%), respectively, of the European area. For a limit of 2 mg m−3
only two episodes with fractions of 1.5% (0.2–2.8%) and 0.9% (0.1–1.6%) occurred, while the current “no-fly” zone criterion of 4 mg m−3 was rarely exceeded. Our results have important ramifications for
determining air space closures and for real-time quantitative estimations of ash concentrations. Furthermore, the general nature of our method yields better constraints
on the distribution and fate of volcanic ash in the Earth system.

The field occurrence, age, classification and geochemistry of the Mesozoic volcanic rocks of Patagonia and West Antarctica are reviewed, using published and new information. Dominated by rhyolitic ignimbrites, which form a bimodal association with minor mafic and intermediate lavas, these constitute one of the largest silicic igneous provinces known, equivalent in size to many mafic LIPs. Diachronism is recognized between the Early–Middle Jurassic volcanism of eastern Patagonia (Marifil and Chon Aike formations) and the Middle Jurassic–earliest Cretaceous volcanism of the Andean Cordillera (El Quemado, Ibañez and Tobı́fera formations). This is accompanied by a change in geochemical characteristics, from relatively high-Zr and -Nb types in the east to subalkaline arc-related rocks in the west, although the predominance of rhyolites remains a constant factor. All of the associated mafic rocks are well fractionated compared to direct mantle derivatives. Petrogenetic models favour partial melting of immature lower crust as a result of the intrusion of basaltic magmas, possibly with some hybridisation of the liquids and subsequent fractionation by crystal settling or solidification and remelting. The formation of large amounts of intracrustal silicic melt acted as a density barrier against the further rise of mafic magmas, which are thus rare in the province.

Pierson, T.C., Janda, R.J., Thouret, J.-C. and Borrero, C.A., 1990. Perturbation and melting of snow and ice by the 13 November 1985 eruption of Nevado del Ruiz, Colombia, and consequent mobilization, flow and deposition of lahars. In: S.N. Williams (Editor), Nevado del Ruiz Volcano, Colombia, I. J. Volcanol. Geotherm. Res., 41: 17-66.

Kimberlite volcanism involves the ascent of low viscosity (0.1 to 1 Pa s) and volatile-rich (CO 2 and H 2 O) ultrabasic magmas from depths of 150 km or greater. Theoretical models and empirical evidence suggest ascent along narrow (∼1 m) dykes at speeds in the range >4 to 20 m/s. With typical dyke breadths of 1 to 10 km, magma supply rates are estimated in the range 10 2 to 10 5 m 3 /s with eruption durations of many hours to months. Based on observations, theory and experiments we propose a four-stage model for kimberlite eruptions to explain the main geological relationships of kimberlites. In stage I magma reaches the Earth's surface along fissures and erupts explosively due to their high volatile content. The early flow exit conditions are overpressured with choked flow conditions; an exit velocity of ∼200 m/s is estimated as representative. Explosive expansion and near surface overpressures initiate crater and pipe formation from the top downwards. In stage II under-pressures (the difference between the lithostatic pressure and pressure of the erupting mixture) develop within the evolving pipe causing rock bursting at depth, undermining overlying rocks and causing down-faulting and crater rim slumping. Rocks falling into the pipe interior are ejected by the strong explosive flows. Stage II is the erosive stage of pipe formation. As the pipe widens and deepens larger under-pressures develop enhancing pipe wall instability. A critical threshold is reached when the exit pressure falls to one atmosphere. As the pipe widens and deepens further the gas exit velocity declines and ejecta becomes trapped within the pipe, initiating stage III. A fluidised bed of pyroclasts develops within the pipe as the eruption wanes to form typical massive volcaniclastic kimberlite. Marginal breccias represent the transition between stages II and III. After the eruption stage IV is a period of hydrothermal metamorphism (principally serpentinisation) and alteration as the pipe cools and meteoric waters infiltrate the hot pipe fill. Following an eruption an open crater can be filled by kimberlite-and country-rock derived sediments, forming the crater-facies.

The study of peperite is important for understanding magma^water interaction and explosive hydrovolcanic hazards. This paper reviews the processes and products of peperite genesis. Peperite is common in arc-related and other volcano-sedimentary sequences, where it can be voluminous and dispersed widely from the parent intrusions. It also occurs in phreatomagmatic vent-filling deposits and along contacts between sediment and intrusions, lavas and hot volcaniclastic deposits in many environments. Peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal, but other shapes occur and mixtures of different clast shapes are also found. Magma is dominantly fragmented by quenching, hydromagmatic explosions, magma^sediment density contrasts, and mechanical stress as a consequence of inflation or movement of magma or lava. Magma fragmentation by fluid^fluid shearing and surface tension effects is probably also important in fluidal peperite. Fluidisation of host sediment, hydromagmatic explosions, forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed. Factors which could influence fragmentation and mingling processes include magma, host sediment and peperite rheologies, magma injection velocity, volatile content of magma, total volumes of magma and sediment involved, total volume of pore-water heated, presence or absence of shock waves, confining pressure and the nature of local and regional stress fields. Sediment rheology may be affected by dewatering, compaction, cementation, vesiculation, fracturing, fragmentation, fluidisation, liquefaction, shear liquification and melting during magma intrusion and peperite formation. The presence of peperite intraclasts within peperite and single juvenile clasts with both sub-planar and fluidal margins imply that peperite formation can be a multi-stage process that varies both spatially and temporally. Mingling of juvenile clast populations, formed under different thermal and mechanical conditions, complicates the interpretation of magma fragmentation and mingling mechanisms. ß

Quench fragmentation is a non-explosive process that occurs when molten magma is super-cooled to glass upon contact with ambient water. This occurs when coherent lavas are erupted subaqueously, when they flow into water, when magma intrudes into water-saturated sediments, and when magma and water interact explosively during phreatomagmatism.  Quench fragmentation also occurs alongside explosive phreatomagmatic activity. Although products of quench fragmentation (hyaloclastite sensu stricto) have been discussed qualitatively in the volcanological literature, compared to explosive fragmentation processes very little is known about the exact dynamics of quench fragmentation of magma and how this relates to the rheology and physical properties of volcanic glass. Based on literature from materials engineering, we present a detailed review of the processes by which glass forms, the properties of glass, and the fracture mechanics that cause it to fragment non-explosively. We also consider how this can be applied to understanding the dynamics behind the volcanological processes of in-situ glass fragmentation during quenching in wet environments and phreatomagmatism. Important parameters for the occurrence of quench fragmentation are the temperature difference between the magma and the ambient water and how much the ambient water is superheated above its Leidenfrost temperature. The geometry of the lava or magma intrusion, the thermal conductivity and the thermal expansion are also of great importance. The resistance of the magma against fragmentation can be increased with the presence of crystals provided the thermal expansion of the crystals does not greatly exceed that of the glass; vesicles have the opposite effect, unless the magma is highly vesicular. This overview then provides a solid basis for further quantitative study of quench fragmentation and hyaloclastite formation.

Subduction zones modulate the global carbon cycle. Carbon is transported into the mantle by the subducting slab and returned to the surface by degassing at arc volcanoes above the subduction zone 1,2 . However, the mechanisms for the transfer of carbon from the subducting slab and sediments into the overlying mantle wedge are poorly understood. Decarbonation-a metamorphic reaction between silicate and carbonate minerals that releases CO 2 -was thought to be the primary mechanism. Yet, thermodynamic models show that decarbonation occurs at much greater pressures and temperatures than those found in typical subduction zones 3-6 . Carbon should therefore be retained in the slab and transported to great depths in the mantle, rather than supply the arc volcanoes. Here we identify diamonds in ultrahigh-pressure rocks from the Italian western Alps that have an oceanic origin. We assess the geochemistry of diamond-bearing fluid inclusions and find that they contain bicarbonate, carbonate and sulphate ions, silica monomers, and crystals of carbonate and silicate. This fluid geochemistry indicates that carbon was released from the slab at relatively shallow depths through dissolution, not decarbonation. We conclude that dissolution, driven by fluids released from the subducted slab, is an important mechanism for the transfer of carbon into the mantle and ultimately back into the atmosphere, helping to balance the carbon flux.

We present studies on the physical volcanology of the -15 Ma Roza Member of the Wanapum Formation in the Columbia River Basalt Group. The Roza Member represents a compound pahoehoe flood basalt lava flow field, with an area of-40,300 km 2 and a vol-3 ß . .

Volcanic eruptions are commonly preceded, accompanied, and followed by variations of a number of detectable geophysical and geochemical manifestations. Many remote sensing techniques have been applied to tracking anomalies and eruptive precursors, and monitoring ongoing volcanic eruptions, offering obvious advantages over in situ techniques especially during hazardous activity. Whilst spaceborne instruments provide a distinct advantage for collecting data remotely in this regard, they still cannot match the spatial detail or time resolution achievable using portable imagers on the ground or aircraft. Hand-held infrared camera technology has advanced significantly over the last decade, resulting in a proliferation of commercially available instruments, such that volcano observatories are increasingly implementing them in monitoring efforts. Improved thermal surveillance of active volcanoes has not only enhanced hazard assessment but it has contributed substantially to understanding a variety of volcanic processes. Drawing on over a decade of operational volcano surveillance in Italy, we provide here a critical review of the application of infrared thermal cameras to volcano monitoring. Following a summary of key physical principles, instrument capabilities, and the practicalities and methods of data collection, we discuss the types of information that can be retrieved from thermal imagery and what they have contributed to hazard assessment and risk management, and to physical volcanology. With continued developments in thermal imager technology and lower instrument costs, there will be increasing opportunity to gather valuable observations of volcanoes. It is thus timely to review the state of the art and we hope thereby to stimulate further research and innovation in this area.

advances that characterise each of these periods, and their causes and influences, are described with reference to contemporary scientists and their publications. Period 1: determination by dendrochronology of first numerical age of a prehistorical eruptive (Burrell Lapilli); first isopach map (Tarawera Tephra). Period 2: first tephra mapping in central North Island (for soil survey). Period 3: first use of I4 C dating; establishment of late Quaternary tephrostratigraphic framework by 'hand-over-hand' mapping in central North Island and Taranaki; initial development of tephra 'fingerprinting' using laboratory methods; application of tephrochronology to many disciplines. Period 4: revision and refinement of proximal stratigraphy, particularly in central TVZ calderas and on Mayor Island; extension of tephra mapping to distal regions, on and offshore, and to older deposits; advances in tephra correlation and dating methods; new tephrochronological applications; revolutionary studies of pyroclastic deposits for determining nature and effects of eruptions (physical volcanology and petrology); renewed awareness of volcanic hazards associated with tephra eruptions. The advances relate to indigenous, external, and 'individualistic' factors. They generally parallelled overseas trends but in some topics preceded or lagged behind them. Tephra studies, or "tephrology", may be regarded as having "come of age" early in the 1980s, about 100 years after the first tephrostratigraphic studies in New Zealand.

The Earth's magmatism produces both volcanic and plutonic rocks. These two rock types share many similarities, but also display significant differences that have led to a tendency to view (and study) them as separate realms. This review tries to bridge the gap to provide more incentive to integrate data from all magmatic rocks in a hope to better understand the processes that led to the differentiation of the Earth and generation of a silicic continental crust. We strongly reinforce recent statements made in the literature suggesting that most disparities between volcanic and plutonic rocks can be resolved if volcanic rocks are seen as erupted melt-rich regions (magma "chambers") expelled from crystal-rich (mushy) reservoirs, which later crystallize to form plutons.

During the eruption of Redoubt Volcano from December 1989 through April 1990, the Alaska Volcano Observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long-period (LP) seismic events (dominant period of about 0.5 s). The initial eruption on December 14 occurred after 23 years of quiescence and was heralded by a 23-hour swarm of LP events that ended abruptly with the eruption. After a series of vent-clearing explosions over the next few days, dome growth began on December 21. Another swarm, with LP events similar to those of the first, began on the 26th and ended in a major tephra eruption on January 2. Eruptions continued over the next two weeks and then ceased until February 15, when a large eruption initiated a long phase of repetitive dome-building and dome-destroying episodes that continued into April. Warnings were issued before the major events on December 14 and January 2, but as the eruptive sequence continued after January 2, the energy of the swarms decreased and forecasting became more difficult. A significant but less intense swarm preceded the February 15 eruption, which was not forecast. This eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until March 4, when the first of three new stations was installed within 3 km of the active vent. From March 4 to the end of the sequence on April 21, there were eight eruptions, six of which were preceded by detectable swarms of LP events. Although weak, these swarms provided the basis for warnings issued before the eruptions on March 23 and April 6. The initial swarm on December 13 had the following features: ( 1 ) short duration (23 hours); (2) a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm, followed by a decline of activity during the 5 hours preceding the eruption; (3) a magnitude range from -0.4 to 1.6; (4) nearly identical LP signatures with a dominant period near 0.5 s; (5) dilatational first motions everywhere; and (6) a stationary source location at a depth of 1.4 km beneath the crater. This occurrence of long-period events suggests a model involving the interaction of magma with groundwater in which magmatic gases, steam and water drive a fixed conduit at a stationary point throughout the swarm. The initiation of that sequence of events is analogous to the failure of a pressurerelief valve connecting a lower, supercharged magma-dominated reservoir to a shallow hydrothermal system. A three-dimensional model of a vibrating fluid-filled crack recently developed by Chouet is found to be compatible with the seismic data and yields the following parameters for the LP source: crack length, 280-380 m; crack width, 140-190 m; crack thickness, 0.05-0.20 m; crack stiffness, 100-200; sound speed of fluid, 0.8-1.3 km/s; compressional-wave speed of rock, 5.1 km/s; density ratio of fluid to rock, ~ 0.4; and ratio of bulk modulus of fluid to rigidity of rock, 0.03-0.07. The fluid-filled crack is excited intermittently by an impulsive pressure drop that varies 0377-0273/94/$07.00 SSDIO377-O273(93)EO090-O 96 B.A. Chouet et aL/ Journal ot ~ Olcanology and Geothermal Resear~'h t~2 ~ I t)94~ 95 t 3)

What influence did climate have on disease in Late Antiquity? Natural archives of pre-instrumental temperature indicate significant summer cooling throughout the period. The coolest stretch spanned the 6th and 7th c., and corresponds startlingly to the appearance of the Justinianic Plague in the Mediterranean region. Drawing on principles from landscape epidemiology, this paper marries textual evidence for disease with palaeoclimatic data, in order to understand how gradual and dramatic climatic change, the 535-50 downturn especially, may have altered the pathogenic burden carried in Late Antiquity. Particular attention is paid to the Justinianic Plague, but the potential impacts of a changing climate on malaria and non-yersinial, non-plague, epidemics are not overlooked.

The reconstruction of magma pathways at active volcanoes is of paramount importance for the comprehension of their structure and for geohazard assessment. Magma plumbing systems at volcanic arcs may be particularly complicated since the magma rises along fractures that can be consistent with the coeval regional state of stress, the local state of stress, or can form dykes that instead follow pre-existing structures. Magma path orientation can be stable over time or can vary as the consequence of external events like large earthquakes or important modifications in volcano morphology. In order to advance understanding of these issues, we reviewed all available information on the Holocene volcano-tectonics of the Alaska-Aleutian arc and back-arc zones, based on published seismological, interferometric and geological-structural data, geological maps, and official reports. We completed our review with some new measurements of Holocene eruptive fissures, faults, dykes, and morphometric characteristics of pyroclastic cones and volcanic domes aimed at better defining the possible shallow magma paths of the recent-active volcanoes. Finally, we reviewed the possible parameters and models that explain the path configurations. At 32 volcanoes, magma paths strike NW-SE, perpendicular or oblique to the arc but parallel to the regional greatest principal stress. At 20 volcanoes magma paths are parallel to the arc, and 19 volcanoes form rows of coalescent cones that also suggest ascent of magma parallel to the arc. Eight volcanoes display both directions (normal and parallel to the arc), and seismological data indicate that at some volcanoes there has been a rotation of the magma pathway over time. Integration of all data shows that the regional ambient tectonic stress field promotes dyke intrusions normal to the trench. Dykes can also intrude parallel to the trench following stress unclamping from large earthquakes. Trench-parallel dykes and rows of volcanoes can be generated by magma batches that are aligned parallel to the trend of the subduction zone. Once a dyke or a sill is intruded, it locally perturbs the stress field facilitating successive intrusion along a perpendicular direction.

Measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics, as well as for monitoring efforts during on-going eruptions. However, its exact definition remains a source of confusion, and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales, or measured using different approaches. Thus our aims are to: (1) define effusion rate terminology; and (2) assess the various measurement methods and their results. We first distinguish between instantaneous effusion rate, and time-averaged discharge rate. Eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began. The ultimate extension of this is mean output rate, this being the final volume of erupted lava divided by total eruption duration. Whether these values are total values, i.e. the flux feeding all flow units across the entire flow field, or local, i.e. the flux feeding a single active unit within a flow field across which many units are active, also needs to be specified. No approach is without its problems, and all can have large error (up to ∼50%). However, good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here. There are three important factors to consider and state when measuring, giving or using an effusion rate. First, the time-period over which the value was averaged; second, whether the measurement applies to the entire active flow field, or a single lava flow within that field; and third, the measurement technique and its accompanying assumptions.

Vesicles in volcanic rocks are frozen records of degassing processes in magmas. For this reason, their sizes, spatial arrangements, numbers and shapes can be linked to physical processes that drive magma ascent and eruption. Although numerous techniques have been derived to describe vesicle textures, there is no standard approach for collecting, analyzing, and interpreting vesicular samples. Here we describe a methodology for techniques that encompass the entire data acquisition process, from sample collection to quantitative analysis of vesicle size and number. Carefully chosen samples from the lower, mean and higher density/vesicularity endmembers are characterized using image nesting strategies. We show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes. A new program (FOAMS) was designed to perform the quantification stage, from vesicle measurement to distribution plots. Altogether, this approach allows substantial reduction of image acquisition and processing time, while preserving enough user control to ensure the validity of obtained results. We present three cameo investigations — on basaltic lava flows, scoria deposits and pumice layers — to show that this methodology can be used to quantify a wide range of vesicle textures, which preserve information on a wide range of eruptive conditions.

Recently measured partition coecients for Rb, Th, U, Nb, La (Ce), Pb, Sr, Sm, Zr, and Y between lherzolite assemblage minerals and H2O-rich fluid (Ayers et al. 1997; Brenan et al. 1995a,b) are used in a two-component local equilibrium model to assess the eff€ects of interaction between slab-derived aqueous fluids and wedge lherzolite on the trace element and isotopic composition of island arc basalts (IAB). The model includes four steps representing chemical processes, with each process represented by one equation with one adjustable parameter, in which aqueous fluid: (1) separates from eclogite in the subducted slab (Rayleigh distillation , mass fraction of fluid released Ffluid); (2) ascends through the mantle wedge in isolated packets, exchanging elements and isotopes with depleted lherzolite (zone refining, the rock/fluid mass ratio n); (3) mixes with depleted lherzolite (physical mixing, the mass fraction of fluid in the mixture Xfluid); (4) induces melting to form primitive IAB (batch melting, mass fraction of melt Fmelt). The amount of mantle lherzolite processed by the fluid in step (2) determines its isotopic and trace element signature and the relative contributions of slab and wedge to primitive IAB. Assuming an average depleted lherzolite composition and mineralogy (70% olivine, 26% orthopyroxene, 3% clinopyroxene and 1% ilmenite) and using nonlinear regression to adjust parameter values to obtain an optimal fit to the average composition of IAB (McCulloch and Gamble 1991) yields values of Ffluid ˆ 0.20, n ˆ 26, Xfluid ˆ 0.17, and Fmelt ˆ 0.15, with r2= 0.995 and the average relative error in trace element concentration ˆ 6%. The average composition of IAB can also e€ffectively be modeled with no contribution from the slab other than H2O (i.e., skip model step 1): n ˆ=27, Xfluid= 0.21, Fmelt= ˆ 0.17, with r2= 0.992. By the time the fluid reaches the IAB source, exchange with depleted wedge lherzolite reduces the 87Sr/86Sr ratio isotopic composition to near-mantle values and the slab contribution to <50% for all but the most incompatible elements (e.g., Pb). The IAB may retain the slab signature for elements such as B and Be that are highly incompatible and that have very low concentrations in the depleted mantle wedge. The relatively high equilibrium D mineral/fluid values measured by Ayers et al. (1997), Brenan et al. (1995a) and Stalder et al. (1998) suggest that large amounts of fluid (>5 wt%) must be added to lherzolite in the IAB source. Decreasing Xfluid below 0.05 causes model results to have unacceptably high levels of error and petrologically unreasonable values of F melt. That H2O contents of IAB are generally <6 wt% suggests that not all of the H2O that metasomatizes the IAB source remains in the source to dissolve in the subsequently formed melt. Modeling of the compositions of specific primitive IAB from oceanic settings with low sediment input and depleted mantle wedges (Tonga, Marianas) shows a generally lower level of fluid-wedge interaction (low n), and therefore a larger slab component in primitive IAB.

The combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands. This method has been successfully applied on the island of El Hierro, the westernmost island of the Canaries Archipelago. For the emerged part of this island, built in the last 1.2 Ma, magnetic stratigraphy and mapping show the presence of four consecutive subchrons. K-Ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy. The ages show that the magnetic polarity zones correlate to the upper part of the Matuyama and to the Brunhes chrons. The Jaramillo normal polarity subchron of the upper part of the Matuyama reverse polarity Chron is recorded in one of the lava sequences. The lower limit of this event is constrained by two ages of 1.04 k 0.02 Ma and one of 1.05 * 0.02 Ma, close to the value deduced from the astronomically tuned magnetic polarity time scale (APTS).

The Eastern Anatolia Region exhibits one of the world's best exposed and most complete transects across a volcanic province related to a continental collision zone. Within this region, the Erzurum-Kars Plateau is of special importance since it contains the full record of collision-related volcanism from Middle Miocene to Pliocene. This paper presents a detailed study of the volcanic stratigraphy of the plateau, together with new K-Ar ages and several hundred new major-and trace-element analyses in order to evaluate the magmatic evolution of the plateau and its links to collision-related tectonic processes. The data show that the volcanic units of the Erzurum-Kars Plateau cover a broad compositional range from basalts to rhyolites. Correlations between six logged, volcano-stratigraphic sections suggest that the volcanic activity may be divided into three consecutive Stages, and that activity begins slightly earlier in the west of the plateau than in the east. The Ž . Early Stage mostly from 11 to 6 Ma is characterised by bimodal volcanism, made up of mafic-intermediate lavas and acid pyroclastic rocks. Their petrography and high-Y fractionation trend suggest that they result from crystallization of anhydrous assemblages at relatively shallow crustal levels. Their stratigraphy and geochemistry suggest that the basic rocks erupted ) Corresponding author. 0377-0273r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.

Flood volcanic provinces are assumed generally to consist exclusively of thick lavas and shallow intrusive rocks (mostly sills), with any pyroclastic rocks limited to silicic compositions. However, mafic volcaniclastic deposits (MVDs) exist in many provinces, and the eruptions that formed such deposits are potentially meaningful in terms of potential atmospheric impacts and links with mass extinctions. The province where MVDs are the most voluminous-the Siberian Traps-is also the one temporally associated with the greatest Phanerozoic mass extinction. A lot remains to be learned about these deposits and eruptions before a convincing genetic link can be established, but as a first step, this contribution reviews in some detail the current knowledge on MVDs for the provinces in which they are better known, i.e. the North Atlantic Igneous Province (including Greenland, the Faeroe Islands, the British Isles, and tephra layers in the North Sea basin and vicinity), the Ontong Java plateau, the Ferrar, and the Karoo. We also provide a brief overview of what is known about MVDs in other provinces such as the Columbia River Basalts, the Afro-Arabian province, the Deccan Traps, the Siberian Traps, the Emeishan, and an Archean example from Australia.

From 1986 to 1997, the Pu'u 'O'o-Kupaianaha eruption of Kilauea produced a vast pahoehoe flow field fed by lava tubes that extended 10-12 km from vents on the volcano's east rift zone to the ocean. Within a kilometer of the vent, tubes were as much as 20 m high and 10-25 m wide. On steep slopes (4-10 ø) a little farther away from the vent, some tubes formed by roofing over of lava channels. Lava streams were typically 1-2 m deep flowing within a tube that here was typically 5 m high and 3 m wide. On the coastal plain (< 1 ø), tubes within inflated sheet flows were completely filled, typically 1-2 m high, and several tens of meters wide. Tubes develop as a flow's crust grows on the top, bottom, and sides of the tubes, restricting the size of the fluid core. The tubes start out with nearly elliptical cross-sectional shapes, many times wider than high. Broad, flat sheet flows evolve into elongate tumuli with an axial crack as the flanks of the original flow were progressively buried by breakouts. Temperature measurements and the presence of stalactites in active tubes confirmed that the tube walls were above the solidus and subject to melting. Sometimes, the tubes began downcutting. Progressive downcutting was frequently observed through skylights; a rate of 10 cm/d was measured at one skylight for nearly 2 months. constraints on, flow advance, tube formation, tube stability, and other unsteady aspects, all of which need to be incorporated to develop a truly predictive model of pahoehoe flow behavior. Paper number 97JB03576 Hawaiian lavas were observed to travel in subsurface tubes by the earliest Western observers of pahoehoe flows. Coan [1844] observed flowing lava through a skylight during the 1843 Mauna Loa eruption and coined the term pyroduct for the conduit. He estimated that the fluid was traveling at a speed of 9 m/s through the 10-m-wide lava tube and observed that rocks thrown into the stream were carried out of sight before sinking. Skylights (openings in the roof of a tube) were noted by sightseers in all the subsequent major pahoehoe flows from Mauna Loa and Kilauea in the nineteenth century. Wentworth and Macdonald [1953], in their summary of work done on lava forms in the first half of the twentieth century, outlined two ways that lava tubes form: chilling of skin around protruded lava toes, and crusting over of the main lava river or channel. More substantive work was begun during the Mauna Ulu eruption of Kilauea between 1969 and 1974 [Greeley, 1971, 1972, 1987; Peterson and Swanson, 1974; Peterson et al., 1994]. These references detailed three ways that channels may roof over: (1) growth of rooted crusts, (2) accretion on levees to build an arch, and (3) aggregation of floating crustal rafts, in addition to the other manner of tube formation, progressive extension of pahoehoe lobes. Many of the Mauna Ulu tube observations cited previously were made near the vents on a moderately sloping surface, and we might conclude that roofing of channels is most important in that region of the flow field. 27,303 27,304 KAUAHW•,UA ET AL.: OBSERVATIONS ON BASALTIC LAVA STREAMS Observations of the current Pu'u 'O'o-Kupaianaha eruption form the basis of our ongoing studies [Kauahikaua et al., 1990; Mattox et al., 1993; Hon et al., 1994]. Compared to the studies from Mauna Ulu and earlier eruptions, our observations are (1) more quantitative, (2) representative of the entire flow field, and (3) representative of prolonged tube occupation. The Kupaianaha and episodes 51-53 flow fields were built by numerous tubes, and we had repeated opportunities to view their formation and evolution. In addition, numerous eruptive pauses [Heliker and Wright, 1991] allowed a further experimental element in that the supply to the tube system was repeatedly turned off and on, so that the response of the tube system could be noted. We made many measurements and observations on most of the tubes formed between 1990 and 1997. This paper describes what we have learned about the formation and evolution of lava tubes and about the behavior of the lava that flows through them.

. The extensive, complex, continental flood basalt CFB province which occurs in Ethiopia and Yemen consists of Oligocene prerift volcanism related to the Africa-Arabia continental break-up. Basalts from the northwestern Ethiopian Plateau exhibit a particularly large range of compositions and, for the first time in the Afro-Arabian CFB province, low-Ti basalts have been encountered. Major and some trace element data have been used to identify distinct geochemical groups Ž and evaluate the role of differentiation processes. Three magma types have been distinguished: two high-Ti groups HT1 and . Ž . Ž . ) Ž . HT2 and one low-Ti group LT . The transitional to tholeiitic LT suite exhibits low TiO 1-2.6% , Fe

Peperites formed by mixing of magma and wet sediment are well exposed along Punta China, Baja California, Mexico, where two sills intrude a section of lava flows, limestones, and volcaniclastic rocks. Irregular lobes and dikes extend from the sills several meters into host sediments, including highly comminuted flow top breccias (lithic lapilli tuff breccias) and shelly micrites, whereas intrusive contacts with lava flows are sharp and planar. Where one sill intruded both coarse-grained volcaniclastic rock and finegrained limestone, textural differences between the hosts produced strikingly different styles of peperite. Blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias; the blocks consequently underwent in situ fragmentation as they were rapidly quenched. The high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse-grained permeable host. Elutriation of fine-grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter-scale fluidization of the host. The contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous, immiscible fluids (fluidal peperite). Intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off "grain by grain" as magma advanced into the host. Thinsection-scale elutriation pipes formed. Microglobular peperite represents a "frozen" example of a fuel-coolant interaction (FCI) between basaltic magma and fluidized micrite host. The intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma-vapor-host interface.

Volcanic islands pose several major types of natural hazards, often interconnected and concentrated in relatively small areas. The quantification of these hazards must be framed from a multi-hazard perspective whilst building on existing single-hazard analyses. Ischia is a densely inhabited volcanic island with a long eruptive history lasting more than 150 ka (last in 1302 AD) characterized by the significant asymmetric resurgence of a caldera block. Here, we review the state-of-art of the natural hazards of Ischia, aiming at building a solid base for future holistic multi-hazard quantifications. We frame our analysis in three steps: i) review of geological, historical and current activity; ii) review of available hazard models and analyses; iii) development of an interpretative framework for the interdependent hazards. The results highlight that volcanic activity has been quite intense and many volcano-related hazardous phenomena have affected the island including in very recent times, both for eruptive (phreatic or magmatic eruptions) and non-eruptive (earthquakes, landslides, and tsunamis) phenomena. The effects of some of them (e.g. tsunamis, tephra) are also relevant beyond the island territory. Quantitative hazard assessments are almost absent and should be developed in the future considering the evident interconnections between hazards. To this end, we propose a conceptual interpretative multi-hazard framework that highlights the fundamental role played by the resurgent block in controlling and connecting the different hazards, in terms of both spatial distribution of the sources and temporal clustering.

The understanding of processes within the root zone of maar-diatreme volcanoes is important for the interpretation of the geology, volcanology and even hazard assessment of these volcanoes. In the phreatomagmatic model of pipe formation, the irregularly shaped root zone is the site of the phreatomagmatic explosions, and thus functions as the "engine" for pipe formation. In this model the root zone grows over a period of time in a series of many single thermohydraulic, i.e. phreatomagmatic, explosions. The explosions initially occur close to the surface and with ongoing explosive activity penetrate towards deeper levels. The ejection of country rock clasts from the root zone results in a mass deficiency in the root zone that causes the overlying tephra and the adjacent country rocks to subside passively in a sinkhole-like fashion into the root zone. Many phreatomagmatic eruptions consequently result in the formation of a cone-shaped diatreme. Thus with ongoing eruptions the cone-shaped diatreme has to grow systematically both in depth and diameter. During its growth, processes in the lower diatreme levels successively destroy the upper levels of the evolving root zone. At the surface, the maar crater in turn reacts to the underlying subsidence processes and also grows both in depth and diameter.

Water dissolved in a silicate melt can strongly influence its physical properties and thus magma behavior during crystallization, degassing, foaming and fragmentation. Etna is a basaltic volcano whose activity is dominated by effusive eruptions which have long represented a threat to the densely populated, surrounding area. Recently, recognition of the products of a Plinian eruption (122 B.C.) has raised further issues for hazard assessment at Etna and other basaltic volcanoes. Constraining the behavior of Etna magma under conditions relevant to both effusive and explosive hazards requires viscosity data under conditions near the glass transition. Here we have investigated the viscosity of hydrous Etna lava in order to better understand eruptive processes which characterize this volcano. The experimental methods which have been used include piston cylinder synthesis of the hydrated melts, micropenetration viscometry for low-temperature viscosity measurements, and near-infrared spectroscopy for the evaluation of sample homogeneity and measurements of water content. Additionally, scanning calorimetric determinations were performed to check whether incipient crystallization had occurred. Sample compositions were determined using electron microprobe analysis and 57Fe Mössbauer spectroscopy. Results from this study are compared with previous reports of trachytic, phonolitic and model calc-alkaline rhyolite (HPG8) compositions. The viscosity of the basaltic melt (dry and wet) has been parameterized in terms of temperature and water content via the non-Arrhenian equation: log10η=–4.643+(5,812.44–427.04×H2O)/(T(K)–499.31+28.74×ln(H2O)) where η is the viscosity in Pa s, H2O is the water content in wt%, and T is the temperature in Kelvin. We observe that the viscosity of alkali basalt (at more than 0.5 wt% H2O) is similar to that of an alkaline trachyte (Agnano–Monte Spina eruption, Phlegrean Fields) and much higher than that of a peralkaline phonolite (Teide, Tenerife) at similar silica contents and NBO/T. For water contents above 1.5 wt%, the viscosity of the basalt is similar to that of rhyolitic melts with similar water contents. At temperatures ranging from 1,050 to 1,150 °C and with water contents between 0.5 and 2.3 wt% (eruptive conditions), the viscosities calculated using the equation defined in this study are (1) in reasonable agreement with those calculated using Shaw's model, and (2) much lower than those experimentally determined in a previous study. However, outside these temperature and water content ranges, the agreement with Shaw's model (1972) breaks down.

Campi Flegrei is an active, resurgent caldera that is located a few kilometres west of the city of Naples, a densely populated urban settlement in southern Italy. Identifying, locating at depth and better defining the geometry of the magma feeding system of the caldera is highly relevant for assessing and monitoring its volcanic hazard. Based on a high resolution seismic reflection dataset, we investigated the deep structure of the volcano. Here we show that seismic wave amplitude variations with distance from the radiating source provide clear evidence for large amplitude seismic reflections from the top of an extended gas- and/or brine-bearing rock formation at about 3000 m and of an about 7500 m deep, low velocity layer, which is associated with a mid-crust, partial melting zone beneath the caldera. The modeling of magma properties based on measured seismic velocities indicates a relatively high melt percentage (in the range 80-90%). These new data suggest that a large magmatic sill is present well within the basement formations, which is possibly linked to the surface through a system of deep fractures bordering the caldera. The lateral extension and similar depth of the melt zone observed beneath the nearby Mt. Vesuvius support the hypothesis of a single continuous magma reservoir feeding both of these volcanoes.

The extensive harrat lava province of Arabia formed during the past 30 million years in response to Red Sea rifting and mantle upwelling. The area was regarded as seismically quiet, but between April and June 2009 a swarm of more than 30,000 earthquakes struck one of the lava fields in the province, Harrat Lunayyir, northwest Saudi Arabia. Concerned that larger damaging earthquakes might occur, the Saudi Arabian government evacuated 40,000 people from the region. Here we use geologic, geodetic and seismic data to show that the earthquake swarm resulted from magmatic dyke intrusion. We document a surface fault rupture that is 8 km long with 91 cm of offset. Surface deformation is best modelled by the shallow intrusion of a north-west trending dyke that is about 10 km long. Seismic waves generated during the earthquakes exhibit overlapping very low-and high-frequency components. We interpret the low frequencies to represent intrusion of magma and the high frequencies to represent fracturing of the crystalline basement rocks. Rather than extension being accommodated entirely by the central Red Sea rift axis, we suggest that the broad deformation observed in Harrat Lunayyir indicates that rift margins can remain as active sites of extension throughout rifting. Our analyses allowed us to forecast the likelihood of a future eruption or large earthquake in the region and informed the decisions made by the Saudi Arabian government to return the evacuees.

This study presents new geochemical data for Mutnovsky Volcano, located on the volcanic front of the southern
portion of the Kamchatka arc. Field relationships show that Mutnovsky Volcano is comprised of four distinct
stratocones, which have grown over that past 80 ka. The youngest center, Mutnovsky IV, has produced basalts
and basaltic andesites only. The three older centers (Mutnovsky I, II, III) are dominated by basalt and basaltic andesite
(60–80% by volume), but each has also producedsmall volumes of andesite and dacite. Across centers of all
ages, Mutnovsky lavas define a tholeiitic igneous series, from 48–70% SiO2. Basalts and basaltic andesites have
relatively low K2O and Na2O, and high FeO* and Al2O3 compared to volcanic rocks throughout Kamchatka. The
mafic lavas are also depleted in the light rare earth elements (REEs), with chondrite-normalized La/Sm b 1.0. Andesites
have generally higher REE abundances and are more enriched in light REEs, some showing negative Eu
anomalies. All samples are depleted in field strength elements (HFSEs) relative to similarly incompatible REEs
(e.g., low La/Ta, Nd/Hf compared to MORB), similar to island arc volcanic rocks worldwide. Radiogenic isotope
ratios (Sr, Nd, Pb, Hf) are similar for samples from all four eruptive centers, and indicate that all samples were
produced by melting of a similar source mixture. No clear age-progressive changes are evident in the compositions
of Mutnovsky lavas. Mass balance and assimilation-fractional crystallization (AFC) modeling of major and
rare earth elements (REEs) indicate that basaltic andesites were produced by FC of plagioclase, clinopyroxene
and olivine froma parental basalt, combinedwith assimilation of a melt composition similar to dacite lavas present
at Mutnovsky. This modeling also indicates that andesites were produced by FC of plagioclase from basaltic
andesite, combinedwith assimilation of dacite. Dacites erupted fromMutnovsky I and II have lowabundances of
REEs, and do not appear to be related to mafic magmas by FC or AFC processes. These dacites are modeled as the
products of dehydration partial melting at mid-crustal levels of a garnet-free, amphibole-bearing basaltic rock,
which itself formed in the mid-crust by emplacement of magma that originated from the same source as all
Mutnovsky magmas. Lead isotope data indicate that subducted sediment is likely present in the source beneath
Mutnovsky and most Kamchatka volcanoes, but uniformly radiogenic Hf and Nd in mafic samples (εNd= 8.7–
9.3, εHf = 15.4–15.9), and significant variation in trace element ratios at nearly constant εNd and εHf, indicate
that sediment plays a minor roll in controlling subduction trace element patterns in Mutnovsky lavas. Mafic
lavas with Ba/Th N 450 require an aqueous fluid source component from subducting oceanic crust, but mixing
patterns in isotope versus trace element ratio plots for Hf and the REEs (εNd and εHf vs. ratios with Ce, Nd and
Hf) demonstrate that a source component with radiogenic Nd and Hf, and fractionated (arc-type) trace element
ratiosmust be present in the source ofMutnovsky lavas. This source component,which is interpreted to be a partial
melt of subducted basalt in the eclogite facies (eclogite melt source component), appears to be present in the
source of all Kamchatka volcanoes. Cross-arc geochemical patterns at Mutnovsky and in other arc systems (Isu-
Bonin, Tonga-Kermadec) suggest that the aqueous fluid component diminishes and the eclogite melt component
is increased from volcanoes at the arc front compared to those in rear-arc positions.

Rowe, G.L. Jr., Brantley, S.L., Fernandez, M., Fernandez, J.F., Borgia, A. and Barquero, J., 1992. Fluid-volcano interaction in an active stratovolcano: the crater lake system of Po~is volcano, Costa Rica. J. Volcanol. Geotherm. Res., 49: 23-51.

l Tungurahua, one of Ecuador's most active volcanoes, is made up of threc volcanic edifices. Tungurahua I was a 14-km-wide andesitic stratocone which experienced at least one sector collapse followed by the extrusion of a dacite lava series. Tungurahua II, mainly composed of acid andesite lava flows younger than 14,000 years BP, was partly destroyed by the last collapse event. 7955 f 90 years ago, which left a large amphitheater and produced a -8 -h 3 debris deposit. The avalanche collided with the high ridge immediately to the west of the cone and was diverted to the northwest and southwest for -15 km. A large lahar formed during this event, which was followed in turn by dacite extrusion. Southwestward, the damming of the Chambo valley by the avalanche deposit resulted in a -10-km-long lake, which was subsequently breached. generating another catastrophic debris flow. The eruptive activity of the present volcano (Tungurahua III) has rebuilt the cone to about 50% of its pre-collapse size by the emission of -3 km3 of volcanic products. Two periods of construction are recognized in Tungurahua's III history. From -2300 to -1400 years BP, high rates of lava extrusion and pyroclastic flows occurred. During this period, the magma composition did not evolve significantly, remaining essentially basic andesite. During the last -1300 years, eruptive episodes take place roughly once per century and generally begin with lapilli fall and pyroclastic flow activity of varied composition (andesite 4-dacite), and end with more basic andesite lava tlows or crater plugs. This pattern is observed in the three historic eruptions of 1773, 1886 and 1916-1918. Given good age control and volumetric considerations, Tungurahua III growth's rate is estimated at -1.5 X lo6 m3/year over the last 2300 years. Although an infrequent event, a sector collapse and associated lahars constitute a strong hazard of this volcano. Given the -3000 m relief and steep slopes of the present cone, a future collapse, even of small volume, could cover an area simil? to that affected by the -3000-year-old avalanche. The more frequent eruptive episodes of each century, Fonds Documentaire OWSTOM 2 ML. Hail et al./Joumal of Volcanology and Geothermal Research 91 (19991 1-21 characterized by pyroclastic flows, lavas, lahars. as well as tephra falls, directly threaten 25,000 people and the Agoyan hydroelectric dam located at the foot of the volcano. O

Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and
eruption. We use multiparameter geophysical and geochemical data to show that the 110-square kilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014–2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, nearexponential decline of both collapse rate and the intensity of the 180-day- long eruption.

The way that faults transport crustal fluids is important in many fields of earth sciences such 15 as petroleum geology, geothermal research, volcanology, seismology, and hydrogeology. For 16 understanding the permeability evolution and maintenance in a fault zone, its internal 17 structure and associated local stresses and mechanical properties much be known. This 18 follows because the permeability is primarily related to fracture propagation and their linking 19 up into interconnected clusters in the fault zone. Here we show that a fault zone can be 20 regarded as an elastic inclusion with mechanical properties that differ from those of the host 21 rock. As a consequence, the fault zone develops its own local stresses which differ from the 22 associated regional stresses. The local stresses, together with fault-rock heterogeneities and 23 interfaces (discontinuities; fractures, contacts), determine fracture propagation, deflection 24 (along discontinuities/interfaces), and arrest in the fault zone and, thereby, its permeability 25 development. We provide new data on the internal structure of fault zones, in particular the 26 fracture frequency in the damage zone as a function of distance from the fault core. New 27 numerical models show that the local stress field inside a fault zone, modelled as an 28 inclusion, differ significantly from those of the host rock, both as regards the magnitude and 29 the directions of the principal stresses. Also, when the mechanical layering of the damage 30 zone, due to its variation in fracture frequency, is considered, the numerical models show 31 Manuscript Click here to view linked References 2 abrupt changes in local stresses not only between the core and the damage zone but also 32 within the damage zone itself. Abrupt changes in local stresses within the fault zone generate 33 barriers to fracture propagation and contribute to fracture arrest. Also, analytical solutions on 34 the effects of material toughnesses (critical energy release rates) of layers and their interfaces 35