Icelandic Volcano Research Articles

A peculiar cluster of microearthquakes on the eastern flank of Katla volcano, southern Iceland

A peculiar cluster of seismicity near the tip of Sandfellsjökull on the eastern flank of Katla volcano in southern Iceland has been analyzed in detail using data from a temporary seismic network. A total of 300 events were detected between July 2011 and August 2013, most of them from a swarm between December 4th and 12th, 2011. The sparser permanent network detected a small fraction of these events, but also a larger swarm in November 2010. When seismic activity started in this area is uncertain because of changes in the detection capability of the network over time. The events are of low magnitude (–0.5 < $M_L$ < 0.5) and the b-value of their magnitude distribution is high (1.6±0.1). Based on their frequency content (4–25 Hz) and clear P and S arrivals, the events are classified as volcano–tectonic. Two multiplets probably with different source mechanism are identified in their population. The events locate at approximately 3.5 km depth. Most of them are tightly clustered according to double difference relative locations in a volume that is only about 400 m in diameter in all directions. Several events are scattered up to 800 m beneath this volume. There is some suggestion of elongate structure in the cluster with a NNE/SSW strike and a dip of 60 degrees. We argue that these events cannot be due to a glacial or a broad tectonic process. Possibly, a localized source of fluid pressure, e.g., a small magma body at depth may be the source of these events.

Interaction between central volcanoes and regional tectonics along divergent plate boundaries: Askja, Iceland

Activity within magmatic divergent plate boundaries (MDPB) focuses along both regional fissure swarms and central volcanoes. An ideal place to investigate their mutual relationship is the Askja central volcano in Iceland. Askja consists of three nested calderas (namely Kollur, Askja and Oskjuvatn) located within a hyaloclastite massif along the NNE-SSW trending Icelandic MDPB. We performed an extensive field-based structural analysis supported by a remote sensing study of tectonic and volcanic features of Askja’s calderas and of the eastern flank of the hyaloclastite massif. In the massif, volcano-tectonic structures trend N 10° E to N 40° E, but they vary around the Askja caldera being both parallel to the caldera rim and cross-cutting on the Western side. Structural trends around the Oskjuvatn caldera are typically rim parallel. Volcanic vents and dikes are preferentially distributed along the caldera ring faults; however, they follow the NNE-SSW regional structures when located outside the calderas. Our results highlight that the Askja volcano displays a balanced amount of regional (fissure-swarm related) and local (shallow-magma-chamber related) tectonic structures along with a mutual interaction among these. This is different from Krafla volcano (to the north of Askja) dominated by regional structures and Grimsvotn (to the South) dominated by local structures. Therefore, Askja represents an intermediate tectono-magmatic setting for volcanoes located in a slow divergent plate boundary. This is also likely in accordance with a northward increase in the spreading rate along the Icelandic MDPB.

Reconfiguration of Financial System Elements to Restore Economic Growth: The System Simplicity and Transformation towards State-Based and Corporate-Based Types

Highlight The analysis indicates that credit in general have been driving the long-term economic growth more than diversity of financial systems or financial innovations. However, the driver becomes a drug as GDP growth needs a several times faster growth of credit. The scholastic review of the traditional system characteristics (functional, intermediation, institutional) stresses the characteristics as different sides of one coin and the characteristics conventional simplicity cannot explain the system little contribution to economic growth. The research also stresses practical complexity of the financial system, not only the problematic of "too-big-to-fail" banks, but also interrelations of such seemingly uncorrelated natural and social disasters as the Iceland volcano and the Arab Spring, Obama care and military tensions in Ukraine. Conventional market-based or bank-based approaches are criticized as staying too far from primary distribution of money by corporate finances and secondary redistribution by public finances, based on statistics of fixed capital investments and its sources. The article collects opinions and evidences that the financial system simplicity should become a conventional trend combined with the financial instruments approach. The only few leading financial instruments should be offered widely, but others should service the niches to decline an excessive burden of the financial sector for economies. The important contribution of public finances to long-term economic growth is not only visible by sovereign borrowings and infrastructure investments, but also by income redistribution, optimization of consumption and maximization of output by the current budget. The article also collects the evidences and explanations that large non-financial corporations effectively invest in fixed capital and support credit sales without real financial intermediation, and also that many financial services are now provided by IT companies without banks. Problem set and research methodology Financial system, the system types and elements and the country specific features are one of the most popular topics for scientific articles. At the same time, the publications rarely stress the reality that financial system is neither the economic driver, at least in 2008-2016, nor the accumulator of financial sources for economic growth. The mainstream economic thought points that major economies face cyclical crisis, not systematic, and only the time is needed. Economic history of the 20th century shows that financial systems of major economies changed noticeably during every financial crisis and economic cycle. Such system elements as commercial banks, financial markets, public budgets, corporate finance practices fundamentally act without any significant changes. However, economies are really driven by few of the most influential financial institutions and financial instruments, which have been changing from one generation or a long economic cycle to another. Hence, providing many historic analogues of the past transformation of financial system seems to be an important illustration of modern challenges and proposed shifts. The bulk of literature is written about the financial system nature and its role, about two conventionally popular market-based and bank-based models, as well as about the system complex approach. The review of such literature forms a first third of this article and allows shaping the analytical approaches to another proposed system types, such as state-based and corporate-based. Avoiding a wide observation of conventional thought, only several articles were segregated for the review, either from the respective international finance organizations or highly ranked by citations. Financial system has been developing by bright economic events. Thus, the article mainly interprets them and specifies their influence, along with the system shift to unconventional state-based and corporate-based types. …

Assessment of the potential respiratory hazard of volcanic ash from future Icelandic eruptions: a study of archived basaltic to rhyolitic ash samples

BackgroundThe eruptions of Eyjafjallajökull (2010) and Grímsvötn (2011), Iceland, triggered immediate, international consideration of the respiratory health hazard of inhaling volcanic ash, and prompted the need to estimate the potential hazard posed by future eruptions of Iceland’s volcanoes to Icelandic and Northern European populations.MethodsA physicochemical characterization and toxicological assessment was conducted on a suite of archived ash samples spanning the spectrum of past eruptions (basaltic to rhyolitic magmatic composition) of Icelandic volcanoes following a protocol specifically designed by the International Volcanic Health Hazard Network.ResultsIcelandic ash can be of a respirable size (up to 11.3 vol.% < 4 μm), but the samples did not display physicochemical characteristics of pathogenic particulate in terms of composition or morphology. Ash particles were generally angular, being composed of fragmented glass and crystals. Few fiber-like particles were observed, but those present comprised glass or sodium oxides, and are not related to pathogenic natural fibers, like asbestos or fibrous zeolites, thereby limiting concern of associated respiratory diseases. None of the samples contained cristobalite or tridymite, and only one sample contained quartz, minerals of interest due to the potential to cause silicosis. Sample surface areas are low, ranging from 0.4 to 1.6 m2 g−1, which aligns with analyses on ash from other eruptions worldwide. All samples generated a low level of hydroxyl radicals (HO•), a measure of surface reactivity, through the iron-catalyzed Fenton reaction compared to concurrently analyzed comparative samples. However, radical generation increased after ‘refreshing’ sample surfaces, indicating that newly erupted samples may display higher reactivity. A composition-dependent range of available surface iron was measured after a 7-day incubation, from 22.5 to 315.7 μmol m−2, with mafic samples releasing more iron than silicic samples. All samples were non-reactive in a test of red blood cell-membrane damage.ConclusionsThe primary particle-specific concern is the potential for future eruptions of Iceland’s volcanoes to generate fine, respirable material and, thus, to increase ambient PM concentrations. This particularly applies to highly explosive silicic eruptions, but can also hold true for explosive basaltic eruptions or discrete events associated with basaltic fissure eruptions.

Detrital zircon resolve longevity and evolution of silicic magmatism in extinct volcanic centers: A case study from the East Fjords of Iceland

Breiðuvik and Kaekjuskorð are two neighboring extinct eruptive centers in the East Fjords of Iceland. Together, they compose the second-largest volume of silicic rock in the country (after Torfajokull, an active volcanic system in southern Iceland). We use ages and compositions of detrital zircon collected from two riv- ers, the Storaa and Krossa-Kaekjudalsa, to investigate the origins and longevity of silicic magmatism at Breiðuvik-Kaekjuskorð. Zircon populations from the two catchments have identical median U-Pb dates (12.9 Ma), O isotopes (d 18 O Vienna standard mean ocean water = 3.1‰ versus 3.3‰), and Hf isotopes ( I Hf = 14.7). We interpret coherence of zircon elemental and isotopic compositions to indicate that a signifi cant volume of relatively uniform silicic material was produced in close temporal and spatial proximity between 11.2 ± 0.7 Ma and 15.0 ± 0.9 Ma (all errors are 1 i ), dominated by assimilation–fractional crystallization processes. To test the robustness of this longevity estimate, we applied Monte Carlo modeling to the Breiðuvik-Kaekjuskorð detrital zircon results and found the age span to be statistically resolvable at ³2.8 m.y. While this lifespan is comparable to those of large mafi c-silicic volcanic systems that have described in other settings glob- ally, it is the longest reported estimate for any Icelandic volcano, where typical longevity is thought to be ~0.5–1.5 m.y. The ³2.8 m.y. lifespan we present for Breiðuvik-Kaekjuskorð is a conservative assessment, because the dates used in this study only represent the zircon-saturated period of magmatic activity. This study demonstrates that detrital zircon analysis of volcanigenic sediment pro- vides an effi cient and powerful tool that can illuminate histories of zircon-satu- rated magmatism at targeted volcanic centers and systems. This approach can be particularly valuable in dominantly mafi c provinces where silicic material is subordinate (e.g., ocean islands, fl ood basalt provinces), where glaciation, ero- sion, or alteration has transformed the landscape, or in areas that are inaccessi- ble (e.g., obscured by glacial ice)

Surface air quality implications of volcanic injection heights

Air quality implications of volcanic eruptions have gained increased attention recently in association with the 2010 Icelandic eruption that resulted in the shut-down of European air space. The emission amount, injection height and prevailing weather conditions determine the extent of the impact through the spatio-temporal distribution of pollutants. It is often argued that in the case of a major eruption in Iceland, like Laki in 1783–1784, that pollutants injected high into the atmosphere lead to substantially increased concentrations of sulfur compounds over continental Europe via long-range transport in the jet stream and eventual large-scale subsidence in a high-pressure system. Using state-of-the-art simulations, we show that the air quality impact of Icelandic volcanoes is highly sensitive to the injection height. In particular, it is the infinitesimal injections into the lower half of the troposphere, rather than the substantial injections into the upper troposphere/lower stratosphere that contribute most to increased pollutant concentrations, resulting in atmospheric haze over mainland Europe/Scandinavia. Besides, the persistent high pressure system over continental Europe/Scandinavia traps the pollutants from dispersing, thereby prolonging the haze.

High-resolution geochemistry of volcanic ash highlights complex magma dynamics during the Eyjafjallajökull 2010 eruption

The April to May 2010 eruption of Eyjafjallajokull (Iceland) volcano was characterized by a large compositional variability of erupted products. To contribute to the understanding of the plumbing system dynamics of this volcano, we present new EMPA and LA-ICP-MS data on groundmass glasses of ash particles and minerals erupted between April 15 and 22. The occurrence of disequilibrium textures in minerals, such as resorption and inverse zoning, indicate that open system processes were involved in determining the observed compositional variability. The variation of major and trace element data of glasses corroborates this hypothesis indicating that mixing between magma batches with different compositions interacted throughout the whole duration of the eruption. In particular, the arrival of new basaltic magma into the plumbing system of the volcano destabilized and remobilized magma batches of trachyandesite and rhyolite compositions that, according to geophysical data, might have intruded as sills over the past 20 years beneath the Eyjafjallajokull edifice. Two mixing processes are envisaged to explain the time variation of the compositions recorded by the erupted tephra. The first occurred between basaltic and trachyandesitic end-members. The second occurred between trachyandesite and rhyolites. Least-squares modeling of major elements supports this hypothesis. Furthermore, investigation of compositional histograms of trace elements allows us to estimate the initial proportions of melts that interacted to generate the compositional variability triggered by mixing of trachyandesites and rhyolites.

Visualizing Volcanic Ash Forecasts: Scientist and Stakeholder Decisions Using Different Graphical Representations and Conflicting Forecasts

Abstract During volcanic eruptions, Volcanic Ash Advisory Centres issue ash advisories for aviation showing the forecasted outermost extent of the ash cloud. During the 2010 Icelandic volcano Eyjafjallajökull eruption, the Met Office produced supplementary forecasts of quantitative ash concentration, due to demand from airlines. Additionally, satellite retrievals of estimated volcanic ash concentration are now available. To test how these additional graphical representations of volcanic ash affect flight decisions, whether users infer uncertainty in graphical forecasts of volcanic ash, and how decisions are made when given conflicting forecasts, a survey was conducted of 25 delegates representing U.K. research and airline operations dealing with volcanic ash. Respondents were more risk seeking with safer flight paths and risk averse with riskier flight paths when given location and concentration forecasts compared to when given only the outermost extent of the ash. Respondents representing operations were more risk seeking than respondents representing research. Additionally, most respondents’ hand-drawn no-fly zones were larger than the areas of unsafe ash concentrations in the forecasts. This conservatism implies that respondents inferred uncertainty from the volcanic ash concentration forecasts. When given conflicting forecasts, respondents became more conservative than when given a single forecast. The respondents were also more risk seeking with high-risk flight paths and more risk averse with low-risk flight paths when given conflicting forecasts than when given a single forecast. The results show that concentration forecasts seem to reduce flight cancellations while maintaining safety. Open discussions with the respondents suggested that definitions of uncertainty may differ between research and operations.

The 2011 unrest at Katla volcano: Characterization and interpretation of the tremor sources

A 23-hour tremor burst was recorded on July 8–9th 2011 at the Katla subglacial volcano, one of the most active and hazardous volcanoes in Iceland. This was associated with deepening of cauldrons on the ice cap and a glacial flood that caused damage to infrastructure. Increased earthquake activity within the caldera started a few days before and lasted for months afterwards and new seismic activity started on the southern flank. No visible eruption broke the ice and the question arose as to whether this episode relates to a minor subglacial eruption with the tremor being generated by volcanic processes, or by the flood. The tremor signal consisted of bursts with varying amplitude and duration. We have identified and described three different tremor phases, based on amplitude and frequency features. A tremor phase associated with the flood was recorded only at stations closest to the river that flooded, correlating in time with rising water level observed at gauging stations. Using back-projection of double cross-correlations, two other phases have been located near the active ice cauldrons and are interpreted to be caused by volcanic or hydrothermal processes. The greatly increased seismicity and evidence of rapid melting of the glacier may be explained by a minor sub-glacial eruption. A less plausible interpretation is that the tremor was generated by hydrothermal boiling and/or explosions with no magma involved. This may have been induced by pressure drop triggered by the release of water when the glacial flood started. All interpretations require an increase of heat released by the volcano.

Phase petrology reveals shallow magma storage prior to large explosive silicic eruptions at Hekla volcano, Iceland

Understanding the conditions that culminate in explosive eruptions of silicic magma is of great importance for volcanic hazard assessment and crisis mitigation. However, geological records of active volcanoes typically show a wide range of eruptive behavior and magnitude, which can vary dramatically for individual eruptive centers. In order to evaluate possible future scenarios of eruption precursors, magmatic system variables for different eruption types need to be constrained. Here we use petrological experiments and microanalysis of crystals to clarify the P–T–x state under which rhyodacitic melts accumulated prior to the H3 eruption; the largest Holocene Plinian eruption of Hekla volcano in Iceland. Cobalt-buffered, H2O-saturated phase equilibrium experiments reproduce the natural H3 pumice phenocryst assemblage (pl>fa+cpx>ilm+mt>ap+zrc) and glass chemistry, at 850±15°C and PH2O of 130 to 175 MPa, implying shallow crustal magma storage between 5 and 6.6 km. The systematics of FeO and anorthite (CaAl2Si2O8) content in plagioclase reveal that thermal gradients were more important than compositional mixing or mingling within this magma reservoir. As these petrological findings indicate magma storage much shallower than is currently thought of Hekla's mafic system, we use the constrained storage depth in combination with deformation modeling to forecast permissible surface uplift patterns that could stem from pre-eruptive magma intrusion. Using forward modeling of surface deformation above various magma storage architectures, we show that vertical surface displacements caused by silicic magma accumulation at ∼6 km depth would be narrower than those observed in recent mafic events, which are fed from a lower crustal storage zone. Our results show how petrological reconstruction of magmatic system variables can help link signs of pre-eruptive geophysical unrest to magmatic processes occurring in reservoirs at shallow depths. This will enhance our abilities to couple deformation measurements (e.g. InSAR and GPS) to petrological studies to better constrain potential precursors to volcanic eruptions.

Subdiffusion of volcanic earthquakes

A comparative study is performed on volcanic seismicities at Icelandic volcano, Eyjafjallaj\"okull, and Mt. Etna in Sicily from the viewpoint of complex systems science, and the discovery of remarkable similarities between them is reported. In these seismicities as point processes, the jump probability distributions of earthquakes (i.e., distributions of the distance between the hypocenters of two successive events) are found to obey the exponential law, whereas the waiting-time distributions (i.e., distributions of inter-occurrence time of two successive events) follow the power law. A careful analysis is made about the finite size effects on the waiting-time distributions, and the previously reported results for Mt. Etna (Abe and Suzuki 2015) are reinterpreted accordingly. It is shown that the growth of the seismic region in time is subdiffusive at both volcanoes. The aging phenomenon is commonly observed in the "event-time-averaged" mean-squared displacements of the hypocenters. A comment is also made on (non-)Markovianity of the processes.

Estimating the frequency of volcanic ash clouds over northern Europe

Fine ash produced during explosive volcanic eruptions can be dispersed over a vast area, where it poses a threat to aviation, human health and infrastructure. Here, we focus on northern Europe, which lies in the principal transport direction for volcanic ash from Iceland, one of the most active volcanic regions in the world. We interrogate existing and newly produced geological and written records of past ash fallout over northern Europe in the last 1000 years and estimate the mean return (repose) interval of a volcanic ash cloud over the region to be 44±7 years. We compare tephra records from mainland northern Europe, Great Britain, Ireland and the Faroe Islands, with records of proximal Icelandic volcanism and suggest that an Icelandic eruption with a Volcanic Explosivity Index rating (VEI) ≥ 4 and a silicic magma composition presents the greatest risk of producing volcanic ash that can reach northern Europe. None of the ash clouds in the European record which have a known source eruption are linked to a source eruption with VEI < 4. Our results suggest that ash clouds are more common over northern Europe than previously proposed and indicate the continued threat of ash deposition across northern Europe from eruptions of both Icelandic and North American volcanoes.

Introducing cybernomics: A unifying economic framework for measuring cyber risk

This is the first in a series of papers on the risk measures and unifying economic framework encompassing the cross-disciplinary field of “Cybernomics”. This is also the first academic paper to formally propose measurement units for cyber risk. In this paper, multidisciplinary methodologies are used to apply proven risk measurement methods in finance and medicine to define novel risk units central to cybernomics. Leveraging established risk units – MicroMort (MM) for measuring medical risk and Value-at-Risk (VaR) for measuring market risk – BitMort (BM) and hekla (named after an Icelandic volcano) are defined as cyber risk units. Risk calculation methods and examples are introduced in this paper to measure cost-effectiveness of control factors, articulate an entity's “willingness-to-pay” (risk pricing) for cyber risk reduction, cyber risk limit, and cyber risk appetite. Built around BM and hekla, cybernomics integrates cyber risk management and economics to study the requirements of a databank in order to improve risk analytics solutions for: 1) the valuation of digital assets; 2) the measurement of risk exposure of digital assets; and 3) the capital optimization for managing residual cyber risk. Establishing adequate, holistic and statistically robust data points on the entity, portfolio and global levels for the development of a cybernomics databank are essential for the resilience of our shared digital future. This paper explains the need to establish data schemes such as International Digital Asset Classification (IDAC) and International Classification of Cyber Incidents (ICCI).

Phase Estimation for Distributed Scatterers in InSAR Stacks Using Integer Least Squares Estimation

In recent years, new algorithms have been proposed to retrieve maximum available information in synthetic aperture radar (SAR) interferometric stacks with focus on distributed scatterers. The key step in these algorithms is to optimally estimate single-master (SM) wrapped phases for each pixel from all possible interferometric combinations, preserving useful information and filtering noise. In this paper, we propose a new method for SM-phase estimation based on the integer least squares principle. We model the SM-phase estimation problem in a linear form by introducing additional integer ambiguities and use a bootstrap estimator for joint estimation of SM-phases and the integer unknowns. In addition, a full error propagation scheme is introduced in order to evaluate the precision of the final SM-phase estimates. The main advantages of the proposed method are the flexibility to be applied on any (connected) subset of interferograms and the quality description via the provision of a full covariance matrix of the estimates. Results from both synthetic experiments and a case study over the Torfajokull volcano in Iceland demonstrate that the proposed method can efficiently filter noise from wrapped multibaseline interferometric stacks, resulting in doubling the number of detected coherent pixels with respect to conventional persistent scatterer interferometry.

The Katla volcanic system imaged using local earthquakes recorded with a temporary seismic network

AbstractKatla is one of the most active subglacial volcanoes in Iceland. A temporary seismic network was operated on and around Katla for 2.5 years. A subset of ~800 analyzed local earthquakes clustered geographically in four regions: (1) the caldera, (2) the western region, (3) the southern rim, and (4) the eastern rim of the glacier. Based on the frequency content of recorded seismograms, each event was labeled as volcano tectonic (VT), long period (LP), or ‘Mixed’. The southern cluster consists of LP events only, and the eastern cluster consists of VT events, while the western cluster is ‘Mixed’ although primarily LP. The caldera seismicity is confined to a subregion centered in the northeastern part of the caldera above 1 km below sea level (bsl) and gradually deepens away from its center to about 4 km depth. Deeper events are almost all VT, whereas LP events in the center of caldera locate at shallow depths. This is also where the velocities are lowest in the top 3 km of the crust of our 3‐D tomographic model. A high‐velocity core (~6.5 km/s) is found at 4 km bsl beneath this low‐velocity zone. We propose that a “subcaldera” may be developing within the present caldera and suggest a conceptual model for Katla volcano with a thin volume (~1 km thick) that may host hot rhyolitic material in the shallow crust below the relocated seismic activity and above the high‐velocity core. We interpret this core to consist of mafic cumulates resulting from fractionation of mafic intrusions and partial melting of subsiding hydrothermally altered rocks.

Introduction to integrated environmental modelling to solve real world problems: methods, vision and challenges

Across the world, stakeholders are asking questions of their governments and decision makers to quantify the risks of environmental threats to their well-being. These questions manifest themselves as ‘deceptively simple questions’, which are easy to articulate but difficult to solve. An example of which is: ‘how much will the eruption of an Icelandic volcano cost the UK economy’. Answering these questions requires predictions of the interaction of multiple environmental processes, this requires the development and maintenance of systems that allow these processes to be simulated, and that is the nascent science of integrated environmental modelling (IEM). Such processes may be long-term (e.g. those that are impacted by climate change) or short-term threats, such as the impact of drought on UK agriculture or the impact of space weather on energy supply systems.

Dispersal of key subplinian–Plinian tephras from Hekla volcano, Iceland: implications for eruption source parameters

Hekla is the most active silicic volcano in Iceland, with 18 subplinian–Plinian eruptions since AD 1104. In the period 1970 to 2000, the frequency of such eruptions increased to once every decade. Hekla is currently inflated to above the levels observed prior to the most recent eruptions in 1991 and 2000. The next eruption could pose a hazard to air traffic between North America and Europe because explosive eruptions of Hekla, independent of size, typically start with a subplinian or Plinian phase that produces a sustained ash plume. We present an overview of five of the largest historical Hekla eruptions (taking place in 1104, 1158, 1300, 1693, and 1766). These eruptions cover a compositional range of rhyolite to andesite, previously estimated Volcanic Explosivity Index (VEI) values of 4–5 and are characterised by contrasting wind dispersal (dispersal axes NW–NE). New isopach maps show both greater deposit thicknesses in the proximal region and wider dispersal than previously inferred, resulting in different volume estimates (minimal values ranging between 0.18 and 0.91 km3). New isopleth maps were also compiled and resulted in inferred plume heights of about 13–25 km. These changes in the estimated values of volume and mass eruption rates have large implications on the forecasting and impacts of future Hekla eruptions.

Long-term health effects of the Eyjafjallajökull volcanic eruption: a prospective cohort study in 2010 and 2013

ObjectivesTo examine the long-term development of physical and mental health following exposure to a volcanic eruption.DesignPopulation-based prospective cohort study.SettingIn spring 2010, the Icelandic volcano Eyjafjallajökull erupted. Data were collected at...

Water‐rich and volatile‐undersaturated magmas at Hekla volcano, Iceland

AbstractOlivine‐hosted melt inclusions from four eruptions at Hekla volcano in Iceland were analyzed for their dissolved H2O, CO2, S, and Cl contents. A positive correlation among the repose interval, magmatic evolution, and volatile contents of magmas is revealed. H2O is the dominant volatile species; it behaves as an incompatible component, increasing in concentration over time as a result of fractional crystallization in the magma. The full suite of H2O contents ranges from a low of 0.80 wt % in basaltic andesites to a maximum of 5.67 wt % in rhyolites. Decreasing H2O/K2O at fixed major element compositions suggests that syneruptive degassing reduces H2O contents significantly. Hekla magmas are CO2 poor, with very low concentrations present only in the most evolved compositions (∼20–30 ppm or less). The decrease in S content from basaltic andesite to rhyolite demonstrates that sulfide saturation is attained when the melt composition reaches basaltic andesite, resulting in the precipitation of pyrrhotite. Low CO2/Nb ratios suggest that vapor saturation is most likely reached during an early period of cooling and solidification in the crust. Fresh injections of mafic magma interact with previously solidified intrusives, producing new melts that are volatile undersaturated. Vapor saturation pressures obtained using the most volatile‐rich melt inclusions suggest the presence of a magma chamber at a minimum depth of ∼7 km. This is in agreement with geophysical observations from recent small‐volume eruptions, but given the possibility of volatile‐undersaturated melts, some of the magmas may reside at greater depths.

Long-period seismic events with strikingly regular temporal patterns on Katla volcano's south flank (Iceland)

Katla is a threatening volcano in Iceland, partly covered by the Mýrdalsjökull ice cap. The volcano has a large caldera with several active geothermal areas. A peculiar cluster of long-period seismic events started on Katla's south flank in July 2011, during an unrest episode in the caldera that culminated in a glacier outburst. The seismic events were tightly clustered at shallow depth in the Gvendarfell area, 4km south of the caldera, under a small glacier stream at the southern margin of Mýrdalsjökull. No seismic events were known to have occurred in this area before. The most striking feature of this seismic cluster is its temporal pattern, characterized by regular intervals between repeating seismic events, modulated by a seasonal variation. Remarkable is also the stability of both the time and waveform features over a long time period, around 3.5years. We have not found any comparable examples in the literature. Both volcanic and glacial processes can produce similar waveforms and therefore have to be considered as potential seismic sources. Discerning between these two causes is critical for monitoring glacier-clad volcanoes and has been controversial at Katla. For this new seismic cluster on the south flank, we regard volcano-related processes as more likely than glacial ones for the following reasons: 1) the seismic activity started during an unrest episode involving sudden melting of the glacier and a jökulhlaup; 2) the glacier stream is small and stagnant; 3) the seismicity remains regular and stable for years; 4) there is no apparent correlation with short-term weather changes, such as rainstorms. We suggest that a small, shallow hydrothermal system was activated on Katla's south flank in 2011, either by a minor magmatic injection or by changes of permeability in a local crack system.