Shallow Hydrothermal System Research Articles

The thermal regime in the resurgent dome of Long Valley Caldera, California: Inferences from precision temperature logs in deep wells

Long Valley Caldera in eastern California formed 0.76 Ma ago in a cataclysmic eruption that resulted in the deposition of 600 km 3 of Bishop Tuff. The total current heat flow from the caldera floor is estimated to be ~ 290 MW, and a geothermal power plant in Casa Diablo on the flanks of the resurgent dome (RD) generates ~40 MWe. The RD in the center of the caldera was uplifted by ~ 80 cm between 1980 and 1999 and was explained by most models as a response to magma intrusion into the shallow crust. This unrest has led to extensive research on geothermal resources and volcanic hazards in the caldera. Here we present results from precise, high-resolution, temperature–depth profiles in five deep boreholes (327–1,158 m) on the RD to assess its thermal state, and more specifically 1) to provide bounds on the advective heat transport as a guide for future geothermal exploration, 2) to provide constraints on the occurrence of magma at shallow crustal depths, and 3) to provide a baseline for future transient thermal phenomena in response to large earthquakes, volcanic activity, or geothermal production. The temperature profiles display substantial non-linearity within each profile and variability between the different profiles. All profiles display significant temperature reversals with depth and temperature gradients <50 °C/km at their bottom. The maximum temperature in the individual boreholes ranges between 124.7 °C and 129.5 °C and bottom hole temperatures range between 99.4 °C and 129.5 °C. The high-temperature units in the three Fumarole Valley boreholes are at the approximate same elevation as the high-temperature unit in borehole M-1 in Casa Diablo indicating lateral or sub-lateral hydrothermal flow through the resurgent dome. Small differences in temperature between measurements in consecutive years in three of the wells suggest slow cooling of the shallow hydrothermal flow system. By matching theoretical curves to segments of the measured temperature profiles, we calculate horizontal groundwater velocities in the hydrothermal flow unit under the RD that range from 1.9 to 2.8 m/yr, which corresponds to a maximum power flowing through the RD of 3–4 MW. The relatively low temperatures and large isothermal segments at the bottom of the temperature profiles are inconsistent with the presence of magma at shallow crustal levels.

Modeling of unrest signals in heterogeneous hydrothermal systems

Monitoring of quiescent volcanoes, such as Campi Flegrei (Italy), involves the measurement of geochemical and geophysical parameters that are expected to change as eruptive conditions approach. Some of these changes are associated with the hydrothermal activity that is driven by the release of heat and magmatic fluids. This work focuses on the properties of the porous medium and on their effects on the signals generated by the circulating fluids. The TOUGH2 porous media flow model is applied to simulate a shallow hydrothermal system fed by a source of magmatic fluids. The simulated activity of the source, with periods of increased fluid discharge, generates changes in gas composition, gravity, and ground deformation. The same boundary conditions and source activity were applied to simulate the evolution of homogeneous and heterogeneous systems, characterized by different rock properties. Phase distribution, fluid composition, and the related signals depend on the nature and properties of the rock sequence through which the fluids propagate. Results show that the distribution of porosity and permeability affects all the observable parameters, controlling the timing and the amplitude of their changes through space and time. Preferential pathways for fluid ascent favor a faster evolution, with larger changes near permeable channels. Slower changes over wider areas characterize less permeable systems. These results imply that monitoring signals do not simply reflect the evolution of the magmatic system: intervening rocks leave a marked signature that should be taken into account when monitoring data are used to infer system conditions at depth.

Kosmotoga arenicorallina sp. nov. a thermophilic and obligately anaerobic heterotroph isolated from a shallow hydrothermal system occurring within a coral reef, southern part of the Yaeyama Archipelago, Japan, reclassification of Thermococcoides shengliensis as Kosmotoga shengliensis comb. nov., and emended description of the genus Kosmotoga

A novel thermophilic and sulfur-reducing bacterium, strain S304(T), was isolated from the Taketomi submarine hot spring shallow hydrothermal field located at southern part of the Yaeyama Archipelago, Japan. The cells were non-motile short thick rods or oval cocci 1.1-2.7 μm in length and 1.1-1.9 μm in width. Strain S304(T) was an obligately anaerobic heterotroph and sulfur reduction stimulates growth. Growth was observed between 50-65°C (optimum 60°C), pH 6.2-8.0 (optimum pH 7.1), 1.0-6.0% NaCl concentration (optimum 3.0%). The fatty acid composition was C(16:0) (71.4%), C(18:0) (20.9%) and C(18:1) (7.7%). The G + C content of genomic DNA was 40.8 mol%. The 16S rRNA gene sequence analysis indicated that strain S304(T) belonged to the genus Kosmotoga. Based on physiological and phylogenetic features of a new isolate, we propose new species in the genus Kosmotoga: the type strain of Kosmotoga arenicorallina sp. nov is S304(T) (=JCM 15790(T) = DSM22549(T)). Thermococcoides shengliensis 2SM-2(T) is phylogenetically associated with Kosmotoga olearia 14.5.1(T). Based on the phylogenetic relationship between Thermococcoides shengliensis 2SM-2(T) and Kosmotoga olearia 14.5.1(T), we propose the reclassification of Thermococcoides shengliensis as Kosmotoga shengliensis comb. nov. (type strain 2SM-2(T)). In addition, an emended description of the genus Kosmotoga is proposed.

Shallow hydrothermal vents in the southern Tyrrhenian Sea

Shallow hydrothermal systems represent particularly suitable fields for studying the interactions between fluids and microorganisms inhabiting extreme environments. Coastal zones of the southern Tyrrhenian Sea are home to shallow hydrothermal systems, related to both active and extinct volcanism, located in the Flegrean area, at Cape Palinuro and around the Eolian Islands. A great diversity of Archaea and Bacteria has been reported at shallow hydrothermal vents, where they are key elements in ecosystem functioning. When compared with deep-sea locations, photosynthetic microorganisms appear to be the main characteristic of shallow hydrothermal vents, where both light and hydrothermal energy support a complex microbial community displaying primary productivity (phototrophic and chemotrophic) of mixed origin. Viriobenthos abundances are low compared with other shallow marine systems, suggesting that viruses are less tolerant than prokaryotes of high temperatures and consequently are believed to have a low impact on prokaryotic abundance and biodiversity. Microorganisms from shallow hydrothermal vents represent an almost unexploited resource for thermostable enzymes and biomolecules potentially valuable in biotechnology.

Depth determinations of shallow hydrothermal systems by self-potential and multi-scale wavelet tomography

In hydrothermal studies, the depth of the hydrothermal system is always required, but rarely known via traditional geophysical exploration techniques. While previous studies have shown that continuous wavelet transform algorithms applied to self-potential data can theoretically determine the depth of the hydrothermal fluids, this study uses multi-scale wavelet tomography with multiple wavelets, field measurements and geophysical models to accurately determine this depth. On Stromboli, Waita and Masaya volcanoes, multi-scale wavelet tomography of field measurements gives reproducible depth results, supported by independent geophysical measurements and models, and accurately locates the main water flow paths at shallow depths. Unlike other traditional geophysical methods, multi-scale wavelet tomography using self-potential data is a low cost tool to rapidly determine depths of the shallowest hydrothermal structures. This approach has the potential to significantly enhance our ability to locate geothermal systems and monitor active volcanoes.

Leudugeria thermalis sp. nov. (Bacillariophyta): a new centric diatom from shallow hydrothermal venting systems in Saba, Dutch Antilles

Leudugeria thermalis is a new diatom species that was collected in abundance from inter-tidal shallow hydrothermal venting systems in the Caribbean island of Saba, Dutch Antilles. Frustules of freshly collected individuals were examined in light and scanning electron microscopy and their ultrastructural morphology compared to other members of the semi-circular biddulphioid diatoms, as well as to the closely related species Leudugeria janischii. Gross valve morphology and areola pattern are characters shared by both Leudugeria species, whereas smaller frustules, shorter pseudoseptum, unique cingulum structure, complete hyaline valvocopula, unusual occluded pseudocellus, and remarkable valve granulation are the characters specific to L. thermalis. The distribution and ecology of L. thermalis are discussed, particularly in relation to its occurrence in extreme environments such as hydrothermal vents.

Hydrothermal instability and ground displacement at the Campi Flegrei caldera

Abstract Ground deformation is commonly observed at active volcanoes, where it represents a reliable sign of unrest and a potential precursor of eruptive activity. The source of deformation, however, is not always unequivocally constrained. Magma ascent and differentiation are generally involved, but hydrothermal fluids may play a role, due to thermal expansion and pore pressure acting on rocks. The identification of mechanisms driving ground displacement bears important consequences for hazard evaluation. The aim of this work is to evaluate mechanical effects associated with pressurization and heating of hydrothermal fluids. We first simulate the heat and fluid flow driven by the arrival of magmatic fluids from greater depth. Then, we calculate the rock deformation arising from simulated pressure and temperature changes within a shallow hydrothermal system. We employ a mathematical model, based on the linear theory of thermo-poro-elasticity and on a system of distributed equivalent forces. Results show that stronger degassing of a magmatic source may cause several centimeters of uplift.

Structures involved in the vertical deformation at Lake Taupo (New Zealand) between 1979 and 2007: New insights from numerical modelling

Since 1979, repeat levelling measurements have been conducted on the lake filling the caldera of the dormant Taupo rhyolitic volcano in the North Island of New Zealand. Interpretation of these data through numerical modelling provides information on the structures involved in the relative vertical crustal movement throughout the southern end of the Taupo Volcanic Zone (TVZ), an area of active back-arc extension. The best-defined feature is a long term global subsidence of the northern part of the lake (7 mm yr − 1 ) due to the cumulative effect of the crust stretching and a deep deflation source. This long term subsidence is occasionally disturbed by strong short-term uplifts linked with overpressure sources located below the northern part of the lake, near active geothermal fields. Episodes of uplift can be attributed to various combinations of the following two processes taking place beneath the geothermal field (1) Movement or formation of rhyolitic magma (deepest sources) (2) Pressurization of the shallow hydrothermal fluid reservoir that traps volatiles exsolved from a crystallizing rhyolitic magma (shallowest sources). The pressurization of the shallow hydrothermal system gives rise to tensional stresses in the upper crust, resulting in seismic and aseismic fault ruptures. Slow slip motion of the Kaiapo fault decouples on a short-term time scale the ground deformation pattern on both sides of the fault. Our results, discriminating what parts of the deformation are due to the regional setting, the hydrothermal circulations and the seismic activity, reveal that each seismic swarm is preceded by 1 to 3 years of inflation of the eastern part of the lake. This systematic behaviour may allow us in the future to better predict the occurrence of the seismic swarms below the lake.

Bacterial and archaeal populations at two shallow hydrothermal vents off Panarea Island (Eolian Islands, Italy)

The aim of this study was to investigate the microbial community thriving at two shallow hydrothermal vents off Panarea Island (Italy). Physico-chemical characteristics of thermal waters were examined in order to establish the effect of the vents on biodiversity of both Bacteria and Archaea. Water and adjacent sediment samples were collected at different times from two vents, characterised by different depth and temperature, and analysed to evaluate total microbial abundances, sulphur-oxidising and thermophilic aerobic bacteria. Total microbial abundances were on average of the order of 10(5) cells ml(-1), expressed as picoplanktonic size fraction. Picophytoplanktonic cells accounted for 0.77-3.83% of the total picoplanktonic cells. The contribution of bacterial and archaeal taxa to prokaryotic community diversity was investigated by PCR-DGGE fingerprinting method. The number of bands derived from bacterial DNA was highest in the DGGE profiles of water sample from the warmest and deepest site (site 2). In contrast, archaeal richness was highest in the water of the coldest and shallowest site (site 1). Sulphur-oxidising bacteria were detected by both culture-dependent and -independent methods. The primary production at the shallow hydrothermal system of Panarea is supported by a complex microbial community composed by phototrophs and chemolithotrophs.

Ground deformation induced by geothermal processes: A model for La Fossa Crater (Vulcano Island, Italy)

Since the last eruption in 1888–1890, volcanic activity at Vulcano Island (Aeolian Archipelago, Italy) has been limited to fumarolic degassing, concentrated near the active cone of “La Fossa” crater in the northern sector of the island. During the period 1990–1996, EDM and leveling data indicate a deflation and contraction focused on the La Fossa Cone. We jointly inverted these data sets using for volume change both a spherical Mogi (1958) source and an ellipsoid as defined by Davis (1986). The best fitting source for the 1990–1996 deflation is a shallow subvertical prolate ellipsoid positioned roughly under the crater. Our model is consistent with increased activity in a shallow hydrothermal system, supported by observations of water evaporation testified by the increase of steam emission and temperature at crater fumaroles. The fluid loss from a shallow geothermal reservoir is the most likely cause of the subsidence recorded at La Fossa Cone during the same period. This clear linkage between the deformation signals and hydrothermal activity, has important implications in the hazard assessment and monitoring of the Vulcano activity.

Extreme spatial and temporal variability of hydrothermal microbial mat communities along the Mariana Island Arc and southern Mariana back‐arc system

Twenty‐five microbial communities were sampled from 18 different hydrothermal systems located at seven different sites along the Mariana Island Arc and at a single site from the southern Mariana Spreading Center over a 3‐year period. Terminal restriction fragment length polymorphism (T‐RFLP) analysis of the small subunit rRNA gene revealed that the microbial community diversity is much greater along the Mariana Arc/back‐arc than at either hot spot volcanoes or mid‐ocean ridges along the same spatial scale. Cluster analysis of T‐RFLP fingerprints reveals the microbial communities formed three distinct clusters designated Mariana clusters I, II, and III. Microbial communities in Mariana Cluster I are all associated with iron‐rich microbial mats and are dominated by members of the ζ‐Proteobacteria and by unique phylotypes clustering deeply in the δ‐Proteobacteria and within the Nitrospira division. Mariana Cluster II communities are all from shallow hydrothermal systems and mostly from colder sediments or microbial mats that are dominated by putative heterotrophic phylotypes usually associated with seawater and sediments not generally associated with hydrothermal fluid inputs. Mariana Cluster III is generally from much hotter vent sites and is dominated by sulfur‐oxidizing ɛ‐Proteobacteria. Quantitative‐polymerase chain reaction (Q‐PCR) of Archaeal abundance reveal that all of the microbial communities are dominated by members of the Bacterial domain. Sampling of microbial mats from Iceberg Vent at NW Rota‐1 in 2004 and again in 2006 reveal the community has shown a transition from Caminibacter group ɛ‐Proteobacteria phylotypes to a mixed population of Caminibacter, Sulfurovum, and Sulfurimonas group ɛ‐Proteobacteria.

Culture-Dependent and -Independent Characterization of Microbial Communities Associated with a Shallow Submarine Hydrothermal System Occurring within a Coral Reef off Taketomi Island, Japan

Microbial communities in a shallow submarine hydrothermal system near Taketomi Island, Japan, were investigated using cultivation-based and molecular techniques. The main hydrothermal activity occurred in a craterlike basin (depth, approximately 23 m) on the coral reef seafloor. The vent fluid (maximum temperature, >52 degrees C) contained 175 microM H2S and gas bubbles mainly composed of CH4 (69%) and N2 (29%). A liquid serial dilution cultivation technique targeting a variety of metabolism types quantified each population in the vent fluid and in a white microbial mat located near the vent. The most abundant microorganisms cultivated from both the fluid and the mat were autotrophic sulfur oxidizers, including mesophilic Thiomicrospira spp. and thermophilic Sulfurivirga caldicuralii. Methane oxidizers were the second most abundant organisms in the fluid; one novel type I methanotroph exhibited optimum growth at 37 degrees C, and another novel type I methanotroph exhibited optimum growth at 45 degrees C. The number of hydrogen oxidizers cultivated only from the mat was less than the number of sulfur and methane oxidizers, although a novel mesophilic hydrogen-oxidizing member of the Epsilonproteobacteria was isolated. Various mesophilic to hyperthermophilic heterotrophs, including sulfate-reducing Desulfovibrio spp., iron-reducing Deferribacter sp., and sulfur-reducing Thermococcus spp., were also cultivated. Culture-independent 16S rRNA gene clone analysis of the vent fluid and mat revealed highly diverse archaeal communities. In the bacterial community, S. caldicuralii was identified as the predominant phylotype in the fluid (clonal frequency, 25%). Both bacterial clone libraries indicated that there were bacterial communities involved in sulfur, hydrogen, and methane oxidation and sulfate reduction. Our results indicate that there are unique microbial communities that are sustained by active chemosynthetic primary production rather than by photosynthetic production in a shallow hydrothermal system where sunlight is abundant.

Geophysical and hydrogeological experiments from a shallow hydrothermal system at Solfatara Volcano, Campi Flegrei, Italy: Response to caldera unrest

Integration of high‐resolution geophysical and hydrogeological investigations at Solfatara Volcano, Campi Flegrei, Italy, allowed us to (1) image the shallow and intermediate subsurface to the crater, (2) elucidate patterns in the shallow subsurface degassing, and (3) refine and upgrade volcano‐monitoring strategies for this dynamic area. Our results show that the subsurface to the crater can be divided roughly into two zones: a dry, outcropping layer overlying a horizon saturated by hydrothermal fluids. Within this saturated zone, intersections of dominant NW‐ and ENE‐striking structural lineaments act as preferential escape conduits for the fluids which generate high microseismic noise amplitudes in the southeastern part of the crater. Hydrogeological data suggest an uprising of the isotherms below Solfatara crater, and a marked increment of fluid degassing, over the last 40 years. Sudden variations of both seismic noise level and noise cycling are positively correlated with early stages of ground inflation during the AD 2000 uplift. We believe therefore that monitoring of seismic noise can be used for upgrading early warning strategies in this sector of the Campi Flegrei volcanic system.

Concentrations, distributions, and energy yields of dissolved neutral aldoses in a shallow hydrothermal vent system of Vulcano, Italy

Large numbers of heterotrophic microorganisms inhabit hydrothermal systems, but few organic geochemistry studies have been carried out on these environments. This study presents the first data on total dissolved neutral aldose (TDNA) composition in a shallow hydrothermal system on the Island of Vulcano, Italy. Samples were collected from geothermal wells, sediment seeps, and shallow submarine vents. Temperatures and geochemical conditions varied between sample locations. Concentrations of TDNA were 56–55,128 nM, a larger range than those reported for non-hydrothermal systems. TDNA yields ranged from 0.47% to 16.54%. The highest yields were observed in sediment seeps and these yields are higher than any reported for non-hydrothermal systems. Similar to other marine environments, glucose and galactose had the highest mole fractions in most samples. Mole fractions of the deoxysugars fucose and rhamnose were low, indicating that algal material is not a likely source for TDNA. High TDNA concentrations correlated with high amino acid (AA) concentrations, indicating that the source and sink processes for AA and TDNA may be similar. High concentrations of both TDNA and AA occurred in samples with low pH and high temperature, but only pH showed a significant correlation with organic parameters. At the in situ geochemical conditions and per mole of aldose reacted, fermentation yields 220–420 kJ, anaerobic respiration yields 500–2400 kJ, and aerobic respiration yields ∼2750 kJ. The generally high aldose yields indicate a large fraction of biologically labile material, and energy calculations show that aldose respiration is more exergonic than chemolithotrophic reactions within the system.

Variability of volcanic gas emissions during a crater lake heating cycle at Ruapehu Volcano, New Zealand

We present the first routine measurements of emissions (CO 2, SO 2, and H 2S) from Ruapehu volcano, New Zealand during a crater lake heating cycle. Emissions were generally at a low level consistent with quiescent degassing of the volcano and the presence of a crater lake. Maximum concentrations (∼ 3–4 km downwind) during the highest measurement in May, 2004 were 14 ppm, 0.37 ppm, and 7 ppb for CO 2, SO 2 and H 2S, respectively. CO 2 emissions varied between not detectable to 900 t d − 1 over periods of months. SO 2 was not detectable until February, but gradually increased to 35 t d − 1 . Emissions of H 2S were detected in April and May, although were < 1 t d − 1 . The CO 2/SO 2 ratio in the plume was ∼ 37 by weight for each measurement during the peak of the cycle suggesting that significant scrubbing of SO 2 occurs through the crater lake, and that a common source exists for both gases. Magma volumes estimated from CO 2 emissions (0.001–0.004 km 3) are consistent with eruptive volumes given repose periods of 20–30 years. Delays between peaks in crater-lake heating and degassing suggests that volcanic emissions do not primarily reside in the shallow hydrothermal system directly beneath the crater. Further data is needed to adequately model the system, but first indications of the travel time associated with the degassing cycle suggests that the gas resides at minimally 300 m depth beneath the crater lake. Depths greater than 300 m are consistent with the top of the single-phase steam zone in heat pipe models (200–700 m depth) or perhaps even below the plastic–brittle transition zone above the cooling magmas (> 1 km deep).

Carbon dioxide emissions from vegetation-kill zones around the resurgent dome of Long Valley caldera, eastern California, USA

A survey of diffuse CO 2 efflux, soil temperature and soil-gas chemistry over areas of localized vegetation-kill on and around the resurgent dome of Long Valley caldera California was performed to evaluate the premise that gaseous and thermal anomalies are related to renewed intrusion of magma. Some kill sites are long-lived features and others have developed in the past few years. Total anomalous CO 2 emissions from the thirteen areas average around 8.7 t per day; but the majority of the emissions come from four sites west of the Casa Diablo geothermal power plant. Geochemical analyses of the soil-gases from locations west and east of the plant revealed the presence of isobutane related to plant operations. The δ 13C values of diffuse CO 2 range from − 5.7‰ to − 3.4‰, similar to values previously reported for CO 2 from hot springs and thermal wells around Long Valley. At many of the vegetation-kill sites soil temperatures reach boiling at depths ≤ 20 cm. Soil temperature/depth profiles at two of the high-emissions areas indicate that the conductive thermal gradient in the center of the areas is around 320 °C m − 1 . We estimate total heat loss from the two areas to be about 6.1 and 2.3 MW. Given current thinking on the rate of hydrothermal fluid flow across the caldera and using the CO 2 concentration in the thermal fluids, the heat and CO 2 loss from the kill areas is easily provided by the shallow hydrothermal system, which is sourced to the west of the resurgent dome. We find no evidence that the development of new areas of vegetation kill across the resurgent dome are related to new input of magma or magmatic fluids from beneath the resurgent dome. Our findings indicate that the areas have developed as a response to changes in the shallow hydrologic system. Some of the changes are likely related to fluid production at the power plant, but at distal sites the changes are more likely related to seismicity and uplift of the dome.

Modeling hydrothermal fluid circulation and gravity signals at the Phlegraean Fields caldera

Abstract The Phlegraean Fields caldera is an active volcanic system where episodes of ground deformation are accompanied by significant changes in geochemical and geophysical parameters monitored at the surface. These changes derive from a complex interaction between magmatic system and hydrothermal fluid circulation. We calculate the gravity changes associated with the variable density of hydrothermal fluids. We simulate the multi-phase and multi-component fluid circulation triggered by a pulsating magma degassing, periodically increasing the discharge of CO 2 -enriched fluids into the shallow hydrothermal system. The simulated evolution of the hydrothermal system successfully reproduces the observed composition of gas discharged at the surface. At the same time, results indicate that changes in average fluid density generate a detectable gravity signal that is of the same order of magnitude of the observed changes. This contribution to gravity changes can explain the peculiar behavior of gravity data collected at Solfatara, where surface hydrothermal phenomena are present. Simultaneous fitting of two independent sets of monitoring data (gas composition and gravity changes) confirms the conceptual model proposed for the hydrothermal system at Solfatara, and it provides new insights for the interpretation of gravity data.

Concentration and distribution of dissolved amino acids in a shallow hydrothermal system, Vulcano Island (Italy)

Hydrothermal systems are known to harbor a large number of microorganisms, but the organic chemical composition of the solution that comprises their potential substrate is largely unknown. Concentrations and distributions of dissolved free amino acids (DFAA) and dissolved combined amino acids (DCAA) were determined in fluids from the moderate-temperature (42–89 °C), shallow hydrothermal system on the volcanically active island of Vulcano, Italy. The seven samples represent three different geological settings on the island; shallow (∼1 m) submarine vents, geothermal wells, and seeps in heated beach sediments, in addition to ambient local seawater from the bay, Baia di Levante. All hydrothermal sites, with one exception, had TDAA concentrations that were 3–114 times higher than local seawater in Baia di Levante. There were large similarities in amino acid concentration and composition among samples from the same geological setting. The highest amino acid concentrations were found at sites with acidic and reducing conditions, which also had the largest freshwater component. An unusually high fraction of the TDAA pool was represented by DFAA (33–87%), possibly due to in situ acid hydrolysis of DCAA to DFAA. Both DFAA and DCAA concentrations were correlated to DOC, indicating similar source and sink functions for these pools. The yield of TDAA (TDAA-carbon as fraction of organic carbon) ranged from 2% to 25%, which is high compared with non-hydrothermal settings, and indicates high biological lability. The mole fraction of β-alanine plus γ-aminobutyric acid (%BALA + GABA) was 2–2.7% of TDAA, also indicating high biological lability. Owing to the high over-all amino acid concentrations, the high fraction of DFAAs, and the high biological lability of the organic matter, organic matter in general and amino acids specifically could represent significant carbon and energy sources for archaea and bacteria in this hydrothermal system. The clear delineation of three different groups of sites with distinct AA composition and concentrations indicates that the different geological settings within this system have the potential for harboring different microbial communities.

Massive collapse of volcano edifices triggered by hydrothermal pressurization

Catastrophic collapse of steep volcano flanks threatens lives at stratovolcanoes around the world. Although destabilizing shallow intrusion of magma into the edifice accompanies some collapses (e.g., Mount St. Helens), others have occurred without eruption of juvenile magmatic materials (e.g., Bandai). These latter collapses can be difficult to anticipate. Historic collapses without magmatic eruption are associated with shallow hydrothermal groundwater systems at the time of collapse. Through the use of numerical models of heat and groundwater flow, I evaluate the efficacy of hydrothermally driven collapse. Heating from remote magma intrusion at depth can generate temporarily elevated pore-fluid pressures that propagate upward into an edifice. Effective-stress deformation modeling shows that these pressures are capable of destabilizing the core of an edifice, resulting in massive, deep-seated collapse. Far-field pressurization only occurs with specific rock hydraulic properties; however, data from numerous hydrothermal systems illustrate that this process can transpire in realistic settings.

A fluorescein tracer release experiment in the hydrothermally active crater of Vailulu'u volcano, Samoa

On 3 April 2001, a 20 kg point source of fluorescein dye was released 30 m above the bottom of the active summit caldera of Vailulu'u submarine volcano, Samoa. Vailulu'u crater is 2000 m wide and at water depths of 600–1000 m, with the bottom 200 m completely enclosed; it thus provides an ideal site to study the hydrodynamics of an active hydrothermal system. The magmatically driven hydrothermal system in the crater is currently exporting massive amounts of particulates, manganese, and helium. The dispersal of the dye was tracked for 4 days with a fluorimeter in tow‐yo mode from the U.S. Coast Guard icebreaker Polar Sea. Lateral dispersion of the dye ranged from 80 to 500 m d−1; vertical dispersion had two components: a diapycnal diffusivity component averaging 21 cm2 s−1, and an advective component averaging 0.025 cm s−1. These measurements constrain the mass export of water from the crater during this period to be 8−1.3+4.6 × 107 m3 d−1, which leads to a “turnover” time for water in the crater of ∼3.2 days. Coupled with temperature data from CTD profiles and Mn analyses of water samples, the power output from the crater is 610−100+350 MW, and the manganese export flux is ∼240 kg d−1. The Mn/Heat ratio of 4.7 ng J−1 is significantly lower than ratios characteristic of hot smokers and diffuse hydrothermal flows on mid‐ocean ridges and points to phase separation processes in this relatively shallow hydrothermal system.