David A. Budd’s research while affiliated with Uppsala University and other places

Quartz is a common phase in high-silica igneous rocks and is resistant to post-eruptive alteration, thus offering a reliable record of magmatic processes in silicic magma systems. Here we employ the 75 ka Toba super-eruption as a case study to show that quartz can resolve late-stage temporal changes in magmatic δ¹⁸O values. Overall, Toba quartz crystals exhibit comparatively high δ¹⁸O values, up to 10.2‰, due to magma residence within, and assimilation of, local granite basement. However, some 40% of the analysed quartz crystals display a decrease in δ¹⁸O values in outermost growth zones compared to their cores, with values as low as 6.7‰ (maximum ∆core−rim = 1.8‰). These lower values are consistent with the limited zircon record available for Toba, and the crystallisation history of Toba quartz traces an influx of a low-δ¹⁸O component into the magma reservoir just prior to eruption. Here we argue that this late-stage low-δ¹⁸O component is derived from hydrothermally-altered roof material. Our study demonstrates that quartz isotope stratigraphy can resolve magmatic events that may remain undetected by whole-rock or zircon isotope studies, and that assimilation of altered roof material may represent a viable eruption trigger in large Toba-style magmatic systems.

Measurement of oxygen isotope ratios in common silicate minerals such as olivine, pyroxene, feldspar, garnet, and quartz is increasingly performed by Secondary Ion Mass Spectrometry (SIMS). However, certain mineral groups exhibit solid solution series, and the large compositional spectrum of these mineral phases will result in matrix effects during SIMS analysis. These matrix effects must be corrected through repeated analysis of compositionally similar standards to ensure accurate results. In order to widen the current applicability of SIMS to solid solution mineral groups in common igneous rocks, we performed SIMS homogeneity tests on new augite (NRM-AG-1) and enstatite (NRM-EN-2) reference materials sourced from Stromboli, Italy and Webster, North Carolina, respectively. Aliquots of the standard minerals were analysed by laser fluorination (LF) to establish their δ¹⁸O values. Repeated SIMS measurements were then performed on randomly oriented fragments of the same pyroxene crystals, which yielded a range in δ¹⁸O less than ± 0.42 and ± 0.58‰ (2σ) for NRM-AG-1 and NRM-EN-2, respectively. Homogeneity tests verified that NRM-AG-1 and NRM-EN-2 do not show any crystallographic orientation bias and that they are sufficiently homogeneous on the 20 μm scale to be used as routine mineral standards for SIMS δ¹⁸O analysis. We subsequently tested our new standard materials on recently erupted pyroxene crystals from Merapi volcano, Indonesia. The δ¹⁸O values for Merapi pyroxene obtained by SIMS (n = 204) agree within error with the LF-derived δ¹⁸O values for Merapi pyroxene but differ from bulk mineral and whole-rock data obtained by conventional fluorination. The bulk samples are offset to higher δ¹⁸O values as a result of incorporation of mineral and glass inclusions that in part reflects crustal contamination processes. The Merapi pyroxene SIMS data, in turn, display a frequency peak at 5.8‰, which is allows us to estimate the δ¹⁸O value of the primary magma of ~ 6.1‰, assuming differentiation in a closed system.

Recent seismic unrest and a persistent Holocene eruption record at Katla volcano, Iceland indicate that a near-future eruption is possible. Previous petrological investigations suggest that Katla is supplied by a simple plumbing system that delivers magma directly from depth, while seismic and geodetic data also point towards the existence of upper-crustal magma storage. To characterise Katla's recent plumbing system, we established mineral-melt equilibrium crystallisation pressures from four age-constrained Katla tephras spanning from 8 ky BP to 1918. The results point to persistent shallow- (≤8 km depth) as well as deep-crustal (ca. 10 – 25 km depth) magma storage beneath Katla throughout the last 8 ky. The presence of multiple magma storage regions implies that mafic magma from the deeper reservoir system may become gas-rich during ascent and storage in the shallow crust and erupt explosively. Alternatively, it might intersect evolved magma pockets in the shallow-level storage region, and so increase the potential for explosive mixed-magma ash eruptions. This article is protected by copyright. All rights reserved.

Merapi volcano is among the most hazardous volcanoes on the planet. Ancient Javanese folklore describes Merapi's activity as the interaction between the Spirit Kings that inhabit the volcano and the Queen of the South Sea, who resides at Parangtritis beach, 50 km SSE of Merapi. The royal palace in Yogyakarta is located halfway along the hypothetical line between Merapi and Parangtritis (the Merapi–Kraton–South Sea axis) to bring balance between these mystical forces. In 2006 and 2010, Merapi erupted explosively and on both occasions, earthquakes shook the region and the eruptions grew more violent in response. These earthquakes appear to influence the sub-volcanic magma supply of Merapi and a positive feedback loop has recently been postulated between the volcano and local earthquake patterns. The 2006 earthquakes clustered along the Opak River fault to the south of the volcano, which trends NE–SW, and reaches the southern sea at Parangtritis beach, the fabled residence of the Queen of the South Sea. Our interpretation of the Merapi–Kraton–South Sea axis is that local folklore was used by ancient people to describe and rationalize the complex interplay between geological processes. We suggest that Merapi displayed volcano– earthquake interaction many times in the past, and not only during its most recent eruptive cycle. Although now shrouded in mystery, these oral traditions can be thought of as an ancient hazard mitigation tool, which makes them likely useful in helping to foster effective dialogues with a variety of target parties and interest groups around the volcano's slopes.

The archipelago of Indonesia is formed from several highly active volcanic arcs, including the Island of Sumatra, located in the west Sunda Arc. Although thirty-four, mainly andesitic, volcanoes exist on Sumatra, most of the volcanological research in the area has been focussed on mount Toba, which produced the largest known volcanic eruption on Earth within the last 2 Ma. The ongoing eruption of Mount Sinabung coupled with continued unrest at Mount Kerinci, which erupted in 2009, indicates the need for further research into eruption timescales and the hazards posed by these volcanoes. Along arc variation of whole rock andesite samples have been observed in Sumatra; Mg concentrations are high in the north of the island, yet low in the south. The data further stresses the need for detailed research into each separate volcano, in order to understand the genesis of each volcano. Mount Sorik Marapi is a 600m wide stratovolcano, located around 200km south of the well-known Mount Toba. The edifice hosts a large crater lake, solfatara fields and a small parasitic volcano (Danau Merah) on its southeastern flank. Although it seemed quite active during the 19th and early 20th century, with several phreatic eruptions, it has not erupted since 1996. Seismic unrest was detected in late 2011, however no eruption occurred. Samples taken from the area are moderately to highly vesicular with a porphyritic texture. They contain abundant plagioclase and pyroxenes, moderate Fe-Ti oxides, sparse olivine crystals and abundant crystals clots. Rare occurrences of amphibole are noted in some of the sampled lavas. Plagioclase, pyroxene and olivine are texturally zoned and often host melt inclusions. Multiple plagioclase populations are observed. Crystals and melt inclusions will be characterised for major and trace elements to investigate magma source and depth of crystallising magma body. In addition, diffusion modelling of pyroxene will provide insights into eruption timescales, in order to gain new understanding of the development of Mount Sorik Marapi and Sunda Arc volcanism as a whole.

We present a review of advances made in the last decade concerning the effects of CO2-rich basement on the composition and style of explosive eruptions at Merapi volcano, Central Java. Partially reacted calc-silicate inclusions are frequent in pre-2010 Merapi block-and-ash flows (BAFs), providing direct evidence for magma-carbonate interaction beneath the volcano. Indeed, 87Sr/86Sr and δ18O values for feldspar and pyroxene in recent Merapi eruptions, including the latest in 2010, support a model of limestone and calc-silicate assimilation in which shallow-grown plagioclase are most affected, whereas pyroxene tends to record the deep magmatic signals. This model is also consistent with recently acquired δ11B data on fused Merapi basaltic-andesite. Merapi’s plumbing system consists of a plexus of interconnected magma reservoirs that are partly emplaced into upper crustal CO2-rich sedimentary rocks, thus promoting crustal heat flow and magma-carbonate interaction in the uppermost parts of the system. Experiments show that break-down of carbonate in magma produces voluminous CO2 over geologically rapid timescales (hours to days), which would likely place acute unsustainable pressure on the magmatic system, especially if efficient removal of CO2 from the reaction site is limited by magma viscosity or impermeable country rock. Localized pockets of gas over-pressure may then develop and drive intermittent explosions at the surface, as reflected in elevated δ 13CCO2 values in fumarole gas at Merapi, which furthermore suggest that magma-carbonate interaction is exacerbated by regional seismic activity. Earthquakes can cause mechanical disruption of the crust and allow trapped gas pockets to escape. This process temporarily creates increased surface area for reaction, hence causing a peak in extra CO2 production which can, in turn, fuel further eruptive activity. CO2-driven eruptions at Merapi can therefore be erratic with only short warning times, and represent a challenge for civil protection authorities, especially regarding the people living in Merapi’s direct vicinity.

No abstract available.

A submarine eruption started off the south coast of El Hierro, Canary Islands, on 10 October 2011 and continues at the time of this writing (February 2012). In the first days of the event, peculiar eruption products were found floating on the sea surface, drifting for long distances from the eruption site. These specimens, which have in the meantime been termed "restingolites" (after the close-by village of La Restinga), appeared as black volcanic "bombs" that exhibit cores of white and porous pumice-like material. Since their brief appearance, the nature and origin of these "floating stones" has been vigorously debated among researchers, with important implications for the interpretation of the hazard potential of the ongoing eruption. The "restingolites" have been proposed to be either (i) juvenile high-silica magma (e.g. rhyolite), (ii) remelted magmatic material (trachyte), (iii) altered volcanic rock, or (iv) reheated hyaloclastites or zeolite from the submarine slopes of El Hierro. Here, we provide evidence that supports yet a different conclusion. We have analysed the textures and compositions of representative "restingolites" and compared the results to previous work on similar rocks found in the Canary Islands. Based on their high-silica content, the lack of igneous trace element signatures, the presence of remnant quartz crystals, jasper fragments and carbonate as well as wollastonite (derived from thermal overprint of carbonate) and their relatively high oxygen isotope values, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary layers that were picked up and heated by the ascending magma, causing them to partially melt and vesiculate. As they are closely resembling pumice in appearance, but are xenolithic in origin, we refer to these rocks as "xeno-pumice". The El Hierro xeno-pumices hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies beneath the Canary Islands as well as in similar Atlantic islands that rest on sediment-covered ocean crust (e.g. Cape Verdes, Azores). The occurrence of "restingolites" indicates that crustal recycling is a relevant process in ocean islands, too, but does not herald the arrival of potentially explosive high-silica magma in the active plumbing system beneath El Hierro.

The Indonesian island of Sumatra, located in one of the most active zones of the Pacific Ring of Fire, is characterized by a chain of subduction‐zone volcanoes which extend the entire length of the island. As a group of volcanic geochemists, we embarked upon a five‐week sampling expedition to these exotic, remote, and in part explosive volcanoes (SAGE 2010; Sumatran Arc Geochemical Expedition). We set out to collect rock and gas samples from 17 volcanic centres from the Sumatran segment of the Sunda arc system, with the aim of obtaining a regionally significant sample set that will allow quantification of the respective roles of mantle versus crustal sources to magma genesis along the strike of the arc. Here we document our geological journey through Sumatra's unpredictable terrain, including the many challenges faced when working on active volcanoes in pristine tropical climes.