Valentin Troll

Uppsala University, Department of Earth Sciences, Faculty Member

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My research aims to better understand the dynamic interplay of magma generation, magma chamber processes, magma transport, and eruptive behaviour. We use a number of different approaches to investigate the various aspects that influence magmas from their source to the surface, including field-work, experimental and numerical simulations and petrological, geochemical and isotope studies, ranging from a tens of kilometre scale in regional tectonic and geochemical approaches down to the sub-micrometer-scale in crystal analysis and imaging.
Address: Dept. of Earth Sciences
Villavägen 16
75226 Uppsala

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Employing ancient oral traditions in Central Java to warn of volcano&#8211;earthquake interaction

Concealed hydrothermal alteration zones provide mechanical weaknesses within lava domes

Messages from the past; the petroglyphs of El Hierro Island

Ancient cultures have frequently made use of stone surfaces to carve and engravesymbols, letters ... more Ancient cultures have frequently made use of stone surfaces to carve and engravesymbols, letters and messages for others. These petroglyphs usually have a lastingcharacter and are frequently preserved well beyond the survival of the culture thatproduced the petroglyphs. In this article we focus on the written and pictorial testimonyof the pre-Hispanic era of the island of El Hierro (Canary Islands, Spain), whichexploited a series of volcanic rock features to create a written testimony of theirpresence and their way of life. This specific cultural heritage has been adapted to thespecific geological features on the island and the emerging stone masonry skill of theaboriginal culture of the original islander, creating a unique and lasting record of theirability to use geological elements for cultural development.

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Characterization of Xeno-pumices from Harrat Rahat, SaudiArabia: Understanding magma-crust interaction

Goldschmidt2022 abstracts, 2022

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Lava compositions of the 2021 La Palma eruption reflect magma recharge and mixing processes in the lithosphere

Goldschmidt2022 abstracts, 2022

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Diverse mantle components with invariant oxygen isotopes; the 2021 Fagradalsfjall eruption, Iceland

Goldschmidt2022 abstracts, 2022

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Ancient oral tradition in Central Java warns of volcano–earthquake interaction

Goldschmidt2022 abstracts

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Porosity, strength, and alteration – Towards a new volcano stability assessment tool using VNIR-SWIR reflectance spectroscopy

Earth and Planetary Science Letters

Volcano slope stability analysis is a critical component of volcanic hazard assessments and monit... more Volcano slope stability analysis is a critical component of volcanic hazard assessments and monitoring. However, traditional methods for assessing rock strength require physical samples of rock which may be difficult to obtain or characterize in bulk. Here, visible to shortwave infrared (350-2500 nm; VNIR-SWIR) reflected light spectroscopy on laboratory-tested rock samples from Ruapehu, Ohakuri, Whakaari, and Banks Peninsula (New Zealand), Merapi (Indonesia), Chaos Crags (USA), Styrian Basin (Austria) and La Soufrière de Guadeloupe (Eastern Caribbean) volcanoes was used to design a novel rapid chemometricbased method to estimate uniaxial compressive strength (UCS) and porosity. Our Partial Least Squares Regression models return moderate accuracies for both UCS and porosity, with R 2 of 0.43-0.49 and Mean Absolute Percentage Error (MAPE) of 0.2-0.4. When laboratory-measured porosity is included with spectral data, UCS prediction reaches an R 2 of 0.82 and MAPE of 0.11. Our models highlight that the observed changes in the UCS are coupled with subtle mineralogical changes due to hydrothermal alteration at wavelengths of 360-

format_quoteVNIR-SWIR reflectance spectroscopy offers a rapid, cost-effective method for estimating UCS and porosity of volcanic rocks.format_quote

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Iron isotopes constrain sub-seafloor hydrothermal processes at the Trans-Atlantic Geotraverse (TAG) active sulfide mound

Communications Earth & Environment

Sub-seafloor hydrothermal processes along volcanically active plate boundaries are integral to th... more Sub-seafloor hydrothermal processes along volcanically active plate boundaries are integral to the formation of seafloor massive sulfide deposits and to oceanic iron cycling, yet the nature of their relationship is poorly understood. Here we apply iron isotope analysis to sulfide minerals from the Trans-Atlantic Geotraverse (TAG) mound and underlying stockwork, 26°N Mid-Atlantic Ridge, to trace hydrothermal processes inside an actively-forming sulfide deposit in a sediment-free mid-ocean ridge setting. We show that data for recently formed chalcopyrite imply hydrothermal fluid–mound interactions cause small negative shifts (<−0.1‰) to the δ56Fe signature of dissolved iron released from TAG into the North Atlantic Ocean. Texturally distinct types of pyrite, in turn, preserve a δ56Fe range from −1.27 to +0.56‰ that reflects contrasting precipitation mechanisms (hydrothermal fluid–seawater mixing vs. conductive cooling) and variable degrees of progressive hydrothermal maturation dur...

format_quoteThe study measured δ56Fe values in TAG sulfides ranging from -1.27 to +0.56‰, highlighting significant variation across sulfide textures.format_quote

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Whole-rock oxygen isotope ratios as a proxy for the strength and stiffness of hydrothermally altered volcanic rocks

Bulletin of Volcanology

Hydrothermal alteration is considered to increase the likelihood of dome or flank collapse by com... more Hydrothermal alteration is considered to increase the likelihood of dome or flank collapse by compromising stability. Understanding how such alteration influences rock properties, and providing independent metrics for alteration that can be used to estimate these parameters, is therefore important to better assess volcanic hazards and mitigate risk. We explore the possibility of using whole-rock δ 18 O and δD values and water contents, metrics that can potentially track alteration, to estimate the strength (compressive and tensile) and Young's modulus (i.e. "stiffness") of altered (acid-sulfate) volcanic rocks from La Soufrière de Guadeloupe (Eastern Caribbean). The δ 18 O values range from 5.8 to 13.2‰, δD values from -151 to -44‰, and water content from 0.3 to 5.1 wt%. We find that there is a good correlation between δ 18 O values and laboratory-measured strength and Young's modulus, but that these parameters do not vary systematically with δD or water content (likely due to their pre-treatment at 200 °C). Empirical linear relationships that allow strength and Young's modulus to be estimated using δ 18 O values are provided using our new data and published data for Merapi volcano (Indonesia). Our study highlights that δ 18 O values can be used to estimate the strength and Young's modulus of volcanic rocks, and could therefore be used to provide parameters for volcano stability modelling. One advantage of this technique is that δ 18 O only requires a small amount of material, and can therefore provide rock property estimates in scenarios where material is limited, such as borehole cuttings or when sampling large blocks is impracticable.

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Characterising ice-magma interactions during a shallow subglacial fissure eruption: northern Laki, Iceland, a case study

&amp;lt;p&amp;gt;Iceland has the largest variety of subglacially formed volcanic edifices... more &amp;lt;p&amp;gt;Iceland has the largest variety of subglacially formed volcanic edifices worldwide, given the extensive glacial cover during the Pleistocene and its frequent volcanic activity. As substantial parts of the volcanic zones are presently ice-covered, eruptions beneath glaciers are common.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Phreatomagmatic activity and flood deposits have been hypothesised for shallow subglacial fissure eruptions, at or within a glacial margin. However, to date, no historical examples that did not immediately break through the ice, resulting in dry magmatic activity, have been directly observed. Also, at dynamic ice-margin settings, no extensive resultant formations from shallow subglacial fissure eruptions formed in older historic eruptions have been studied until now.&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The final fissure from the 1783&amp;amp;#8211;84 CE Laki basaltic flood lava event in the S&amp;amp;#237;&amp;amp;#240;a highlands of Iceland, fissure 10, provides a perfect natural laboratory to understand the eruptive dynamics of a shallow subglacial or intraglacial fissure eruption. Fissure 10 is a 2.5 km long formation, which constitutes the final phase of activity on the 29 km long Laki crater row, formed as eruptive activity from the Laki eruption propagated under S&amp;amp;#237;&amp;amp;#240;uj&amp;amp;#246;kull, an outlet glacier from the Vatnaj&amp;amp;#246;kull ice-cap. The resultant eruptive sequences display evidence of the increasing influence of ice when traced along strike from SW to NE, with the eruption transitioning to a predominantly phreatomagmatic phase with increasing degrees of lateral confinement. The sequence is dominated by volcanoclastic units, formed by multiple phreatomagmatic and magmatic phases suggestive of fluctuating water levels, intercalated with hackly jointed intrusions, hackly jointed lobate lava flows and debris flows. Repeating units of agglutinated spatter and spatter-fed lava flows cap the sequence, suggesting decreasing influence of external water with stratigraphic height and towards the end of the fissure&amp;amp;#8217;s eruptive activity. A thin layer of glacial till coats the top of the fissure 10 sequences. The margin of S&amp;amp;#237;&amp;amp;#240;uj&amp;amp;#246;kull has since fully receded from the formation.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Our model for the eruptive dynamics of the northern Laki fissure 10 formation is based on field mapping, a drone photogrammetry survey, petrological observations and EMP analysis of glassy tephra and lava selvages to gain a full understanding of the activity and how eruptive activity progressed. The Laki eruption benefits from a wealth of previous studies on the magmatic phases from the other 9 subaerially eruptive fissures, to the SW of fissure 10, allowing for the effects of the glacier on this fissure&amp;amp;#8217;s activity to be isolated and defined.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Fissure 10 allows for an approximate reconstruction of the ice margin and glacier slope at the time of eruption, adding valuable information on the extent of the glaciers in SW-Vatnaj&amp;amp;#246;kull in the late 18&amp;lt;sup&amp;gt;th&amp;lt;/sup&amp;gt; century, and during the Little Ice Age. These shallow subglacially erupted deposits are the only fully accessible intraglacial eruptive vents, from a known historical eruption, on Earth. Detailed mapping and petrological analysis of deposits like these is important for interpreting landforms in paleo-ice margins, where transitional activity occurs.&amp;lt;/p&amp;gt;

Iron Isotopes Constrain Sub-Seafloor Hydrothermal Processes at the TAG Active Sulfide Mound, 26°N Mid-Atlantic Ridge

Sub-seafloor hydrothermal processes along volcanically active plate boundaries are integral to th... more Sub-seafloor hydrothermal processes along volcanically active plate boundaries are integral to the formation of seafloor massive sulfide (SMS) deposits and to oceanic Fe cycling, yet their nature is poorly understood. Here we apply Fe isotope analysis to sulfides from the TAG mound and underlying stockwork, 26°N Mid-Atlantic Ridge, to trace hydrothermal processes inside an actively-forming SMS deposit in a sediment-free mid-ocean ridge setting. We show that data for recently formed chalcopyrite imply fluid–mound interactions cause small negative shifts (< -0.1‰) to the δ56Fe signature of dissolved Fe released from TAG into the North Atlantic Ocean. Texturally resolved pyrite, in turn, preserves a δ56Fe range from − 1.27 to + 0.56‰ that reflects contrasting modes of formation (fluid–seawater mixing vs. fluid conductive cooling) and variable degrees of progressive hydrothermal maturation during the > 20 kyr evolution of the TAG complex. The identified processes may explain Fe is...

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Direct Observation of Spallation Bombs During The 2021 La Palma Eruption, Canary Islands, Spain

Expulsion of incandescent pyroclasts of >64 mm from active volcanoes are known as ‘volcanic bo... more Expulsion of incandescent pyroclasts of >64 mm from active volcanoes are known as ‘volcanic bombs’1-3, which can pose significant hazards to life and manmade structures. Most volcanic bombs are considered to fall ballistically, enabling the prediction of a volcanic hazard radius4,5. Here we describe a bomb type that was ejected ballistically, but subsequently travelled downslope a steep volcanic flank, posing an important but hitherto unrecognized impact and fire hazard. The volcanic bombs were observed to fall from the summit of the newly formed La Palma cone in late October 2021 and fell on a soft tephra substrate, travelling downhill for over a kilometer in some instances. The bombs spalled incandescent lava fragments en route, creating a significant fire hazard far beyond the range of ballistic transport. Spallation bomb hazards ought to be considered in volcanic risk assessment, necessitating an increase of hazard radius exceeding a factor of two on steep-sided volcanoes wit...

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Imaging the structural changes and instability of the Merapi dome

Actively growing volcano domes may gradually oversteepen, which can lead to catastrophic collapse... more Actively growing volcano domes may gradually oversteepen, which can lead to catastrophic collapse and associated block and ash flows. Here we test how the structural architecture of such instability is initiated and gradual altered by volcanic activity. After the climactic 2010 eruption, the dome at Merapi volcano has been regrown and partially destroyed again during several eruptions that occurred between 2012 and 2014. At least 6 eruptions produced 1 to 2 km high ash columns and three major fractures formed that split the dome into several segments. Here we elaborate the geometric details of these structural continuing changes.

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Exotic, Frothy Xenoliths in Recent and Historical Ocean Island Eruptions

Goldschmidt Abstracts, 2020

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Volatile dilution during magma injections and implications for volcano explosivity

Geology, 2016

Magma reservoirs underneath volcanoes grow through episodic emplacement of magma batches. These p... more Magma reservoirs underneath volcanoes grow through episodic emplacement of magma batches. These pulsed magma injections can substantially alter the physical state of the resident magma by changing its temperature, pressure, composition, and volatile content. Here we examine plagioclase phenocrysts in pumice from the 2014 Plinian eruption of Kelud (Indonesia) that record the progressive capture of small melt inclusions within concentric growth zones during crystallization inside a magma reservoir. High-spatial-resolution Raman spectroscopic measurements reveal the concentration of dissolved H 2 O within the melt inclusions, and provide insights into melt-volatile behavior at the single crystal scale. H 2 O contents within melt inclusions range from ~0.45 to 2.27 wt% and do not correlate with melt inclusion size or distance from the crystal rim, suggesting that minimal H 2 O was lost via diffusion. Instead, inclusion H 2 O contents vary systematically with anorthite content of the host plagioclase (R 2 = 0.51), whereby high anorthite content zones are associated with low H 2 O contents and vice versa. This relationship suggests that injections of hot and H 2 O-poor magma can increase the reservoir temperature, leading to the dilution of melt H 2 O contents. In addition to recording hot and H 2 O-poor conditions after these injections, plagioclase crystals also record relatively cold and H 2 O-rich conditions such as prior to the explosive 2014 eruption. In this case, the elevated H 2 O content and increased viscosity may have contributed to the high explosivity of the eruption. The point at which an eruption occurs within such repeating hot and cool cycles may therefore have important implications for explaining alternating eruptive styles.

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Magma plumbing for the 2014-2015 Holuhraun eruption, Iceland

Geochemistry, Geophysics, Geosystems, 2016

The 2014–2015 Holuhraun eruption on Iceland was located within the Askja fissure swarm but was ac... more The 2014–2015 Holuhraun eruption on Iceland was located within the Askja fissure swarm but was accompanied by caldera subsidence in the Bárðarbunga central volcano 45 km to the southwest. Geophysical monitoring of the eruption identified a seismic swarm that migrated from Bárðarbunga to the Holuhraun eruption site over the course of two weeks. In order to better understand this lateral connection between Bárðarbunga and Holuhraun, we present mineral textures and compositions, mineral‐melt‐equilibrium calculations, whole rock and trace element data, and oxygen isotope ratios for selected Holuhraun samples. The Holuhraun lavas are compositionally similar to recorded historical eruptions from the Bárðarbunga volcanic system but are distinct from the historical eruption products of the nearby Askja system. Thermobarometry calculations indicate a polybaric magma plumbing system for the Holuhraun eruption, wherein clinopyroxene and plagioclase crystallized at average depths of ∼17 km and ∼5 km, respectively. Crystal resorption textures and oxygen isotope variations imply that this multilevel plumbing system facilitated magma mixing and assimilation of low‐δ18O Icelandic crust prior to eruption. In conjunction with the existing geophysical evidence for lateral migration, our results support a model of initial vertical magma ascent within the Bárðarbunga plumbing system followed by lateral transport of aggregated magma batches within the upper crust to the Holuhraun eruption site.

Persistent multitiered magma plumbing beneath Katla volcano, Iceland

Geochemistry, Geophysics, Geosystems, 2016

Recent seismic unrest and a persistent Holocene eruption record at Katla volcano, Iceland indicat... more 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 toward the existence of upper‐crustal magma storage. To characterize Katla's recent plumbing system, we established mineral‐melt equilibrium crystallization pressures from four age‐constrained Katla tephras spanning from 8 kyr 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 kyr. 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 stora...

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Geological constraints on the dynamic emplacement of cone-sheets – The Ardnamurchan cone-sheet swarm, NW Scotland

Journal of Structural Geology, 2015

Cone-sheets are a significant constituent of many central volcanoes, where they contribute to vol... more Cone-sheets are a significant constituent of many central volcanoes, where they contribute to volcano growth by intrusion and through flank eruptions, although the exact emplacement mechanisms are still controversially discussed. In particular, it is not yet fully resolved whether cone-sheets propagate as magma-driven, opening-mode fractures or as shear fractures, and to what extent pre-existing host-rock structures and different stress fields influence cone-sheet emplacement. To shed further light on the role of these parameters in cone-sheet emplacement, we use detailed field and remote sensing data of the classic Ardnamurchan cone-sheet swarm in NW-Scotland, and we show that the cone-sheets primarily propagated as opening-mode fractures in the s1es2 plane of the volcanic stress field. In addition, more than one third of the Ardnamurchan cone-sheet segments are parallel to lineaments that form a conjugate set of NNW and WNW striking fractures and probably reflect the regional NWeSE orientation of s1 during emplacement in the Palaeogene. Cone-sheets exploit these lineaments within the NE and SW sectors of the Ardnamurchan central complex, which indicates that the local volcanic stress field dominated during sheet propagation and only allowed exploitation of host-rock discontinuities that were approximately parallel to the sheet propagation path. In addition, outcrop-scale deflections of conesheets into sills and back into cone-sheets (also referred to as "staircase" geometry) are explained by the interaction of stresses at the propagating sheet tip with variations in host-rock strength, as well as the influence of sheet-induced strain. As a consequence, cone-sheets associated with sill-like segments propagate as mixed-mode I/II fractures. Hence, cone-sheet emplacement requires a dynamic model that takes into account stress fields at various scales and the way propagating magma interacts with the host rock and its inherent variations in rock strength.

format_quote88.7% of cone-sheets intersected metasedimentary rocks, indicating significant geological relationships between rock types and cone-sheets.format_quote

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Low Pressure"(P>= 150 MPa) Experiments in the Piston Cylinder Apparatus

ABSTRACT The piston cylinder apparatus is one of the most versatile instruments operating in labo... more ABSTRACT The piston cylinder apparatus is one of the most versatile instruments operating in laboratories of experimental petrology because it provides a safe, inexpensive, and easy-to-use technique for accessing high-pressure and high-temperature phases and processes. The operating pressure of the piston cylinder usually ranges between 0.5 and 5 GPa, which allows Earth scientists to investigate materials and processes occurring at deep crustal to upper mantle levels. Incomplete compaction of the assembly and thermocouple failure are typical problems in experiments performed at pressures lower than 0.5 GPa. In this work, we present new calibration data that demonstrates that the piston cylinder apparatus is suitable for experiments at pressure as low as to 150 MPa. Two new designs for the 25 mm assembly have been developed and calibrated using two different calibration methods: the NaCl melting curve and the solubility of H2O in albite and rhyolite melts. NaCl calibration data shows that positive friction corrections of 45, 55, and 60 MPa applied to the force of the piston are necessary to establish sample pressures of 300, 200, and 150 MPa respectively. The H2O solubility experiments in albite and rhyolite not only confirm the corrections determined using the NaCl calibration method, but also indicate that the friction correction is the same even when operating at temperatures higher than 800°C and for 24-hour durations. The accuracy of the pressure estimate associated with the calibration methods is ±25 MPa. The major advantage of using the new design assemblies in the piston cylinder apparatus is that experiments for which low-pressure conditions as well as very fast heating and quenching rates are required (e.g. volcanic and hydrothermal systems), can be performed with the same ease and precision as for the pressure ranges for which piston cylinders are routinely employed.

Valentin Troll

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