Tontini
F. Caratori
Tontini
F. Caratori
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PreprintInterpretation of gravity and magnetic anomalies at Lake Rotomahana: geological and hydrothermal implications( 2015-03) Tontini, F. Caratori ; de Ronde, Cornel E. J. ; Scott, Bradley J. ; Soengkono, Supri ; Stagpoole, Vaughan ; Timm, Christian ; Tivey, Maurice A.We investigate the geological and hydrothermal setting at Lake Rotomahana, using recently collected potential-field data, integrated with pre-existing regional gravity and aeromagnetic compilations. The lake is located on the southwest margin of the Okataina Volcanic Center (Haroharo caldera) and had well-known, pre-1886 Tarawera eruption hydrothermal manifestations (the famous Pink and White Terraces). Its present physiography was set by the caldera collapse during the 1886 eruption, together with the appearance of surface activities at the Waimangu Valley. Gravity models suggest subsidence associated with the Haroharo caldera is wider than the previously mapped extent of the caldera margins. Magnetic anomalies closely correlate with heat-flux data and surface hydrothermal manifestations and indicate that the west and northwestern shore of Lake Rotomahana are characterized by a large, well-developed hydrothermal field. The field extends beyond the lake area with deep connections to the Waimangu area to the south. On the south, the contact between hydrothermally demagnetized and magnetized rocks strikes along a structural lineament with high heat-flux and bubble plumes which suggest hydrothermal activity occurring west of Patiti Island. The absence of a well-defined demagnetization anomaly at this location suggests a very young age for the underlying geothermal system which was likely generated by the 1886 Tarawera eruption. Locally confined intense magnetic anomalies on the north shore of Lake Rotomahana are interpreted as basalts dikes with high magnetization. Some appear to have been emplaced before the 1886 Tarawera eruption. A dike located in proximity of the southwest lake shore may be related to the structural lineament controlling the development of the Patiti geothermal system, and could have been originated from the 1886 Tarawera eruption.
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ArticleCrustal magnetization and the subseafloor structure of the ASHES vent field, Axial Seamount, Juan de Fuca Ridge : implications for the investigation of hydrothermal sites(John Wiley & Sons, 2016-06-24) Tontini, F. Caratori ; Crone, Timothy J. ; de Ronde, Cornel E. J. ; Fornari, Daniel J. ; Kinsey, James C. ; Mittelstaedt, Eric ; Tivey, Maurice A.High-resolution geophysical data have been collected using the Autonomous Underwater Vehicle (AUV) Sentry over the ASHES (Axial Seamount Hydrothermal Emission Study) high-temperature (~348°C) vent field at Axial Seamount, on the Juan de Fuca Ridge. Multiple surveys were performed on a 3-D grid at different altitudes above the seafloor, providing an unprecedented view of magnetic data resolution as a function of altitude above the seafloor. Magnetic data derived near the seafloor show that the ASHES field is characterized by a zone of low magnetization, which can be explained by hydrothermal alteration of the host volcanic rocks. Surface manifestations of hydrothermal activity at the ASHES vent field are likely controlled by a combination of local faults and fractures and different lava morphologies near the seafloor. Three-dimensional inversion of the magnetic data provides evidence of a vertical, pipe-like upflow zone of the hydrothermal fluids with a vertical extent of ~100 m.
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ArticleGeophysical modeling of collapse-prone zones at Rumble III seamount, southern Pacific Ocean, New Zealand(John Wiley & Sons, 2013-10-18) Tontini, F. Caratori ; de Ronde, Cornel E. J. ; Kinsey, James C. ; Soule, Samuel A. ; Yoerger, Dana R. ; Cocchi, L.Catastrophic collapses of submarine volcanoes have the potential to generate major tsunami, threatening many coastal populations. Recognizing the difficulties surrounding anticipations of these events, quantitative assessment of collapse-prone regions based on detailed morphological, geological, and geophysical mapping can still provide important information about the hazards associated with these collapses. Rumble III is one of the shallowest, and largest, submarine volcanoes found along the Kermadec arc, and is both volcanically and hydrothermally active. Previous surveys have delineated major collapse features at Rumble III; based on time-lapse bathymetry, dramatic changes in the volcano morphology have been shown to have occurred over the interval 2007–2009. Furthermore, this volcano is located just ∼300 km from the east coast of the North Island of New Zealand. Here, we present a geophysical model for Rumble III that provides the locations and sizes of potential weak regions of this volcano. Shipborne and near-seafloor geological and geophysical data collected by the AUV Sentry are used to determine the subsurface distribution of weak and unstable volcanic rocks. The resulting model provides evidence for potentially unstable areas located in the Southeastern flank of this volcano which should be included in future hazard predictions.
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ArticleHeat flow and near-seafloor magnetic anomalies highlight hydrothermal circulation at Brothers volcano caldera, southern Kermadec arc, New Zealand(American Geophysical Union, 2019-07-18) Tontini, F. Caratori ; Tivey, Maurice A. ; de Ronde, Cornel E. J. ; Humphris, Susan E.Brothers volcano is the most hydrothermally active volcano along the Kermadec arc, with distinct hydrothermal fields located on the caldera walls and on the postcollapse volcanic cones. These sites display very different styles of hydrothermal activity in terms of temperature, gas content, fluid chemistry, and associated mineralization. Here we show the results of a systematic heat flow survey integrated with near‐seafloor magnetic data acquired using remotely operated vehicles and autonomous underwater vehicles. Large‐scale circulation is structurally controlled, with a deep (~1‐ to 2‐km depth) central recharge through the caldera floor and lateral discharge along the caldera walls and at the summits of the postcollapse cones. Shallow (~ 0.1‐0.2 km depth) circulation is characterized by small‐scale recharge zones located at a distance of ~ 0.1–0.2 km from the active vent sites.
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Article3-D focused inversion of near-seafloor magnetic data with application to the Brothers volcano hydrothermal system, Southern Pacific Ocean, New Zealand(American Geophysical Union, 2012-10-11) Tontini, F. Caratori ; de Ronde, Cornel E. J. ; Yoerger, Dana R. ; Kinsey, James C. ; Tivey, Maurice A.We describe and apply a new inversion method for 3-D modeling of magnetic anomalies designed for general application but which is particularly useful for the interpretation of near-seafloor magnetic anomalies. The crust subsurface is modeled by a set of prismatic cells, each with uniform magnetization, that together reproduce the observed magnetic field. This problem is linear with respect to the magnetization, and the number of cells is normally greater than the amount of available data. Thus, the solution is obtained by solving an under-determined linear problem. A focused solution, exhibiting sharp boundaries between different magnetization domains, is obtained by allowing the amplitudes of magnetization to vary between a pre-determined range and by minimizing the region of the 3-D space where the source shows large variations, i.e., large gradients. A regularization functional based on a depth-weighting function is also introduced in order to counter-act the natural decay of the magnetic field intensity with depth. The inversion method has been used to explore the characteristics of the submarine hydrothermal system of Brothers volcano in the Kermadec arc, by inverting near-bottom magnetic data acquired by Autonomous Underwater Vehicles (AUVs). Different surface expressions of the hydrothermal vent fields show specific vertical structures in their underlying demagnetization regions that we interpret to represent hydrothermal upflow zones. For example, at focused vent sites the demagnetized conduits are vertical, pipe-like structures extending to depths of ~1000 m below the seafloor, whereas at diffuse vent sites the demagnetization regions are characterized by thin and inclined conduits.
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ArticleComplex subsurface hydrothermal fluid mixing at a submarine arc volcano supports distinct and highly diverse microbial communities(National Academy of Sciences, 2020-12-04) Reysenbach, Anna-Louise ; St. John, Emily ; Meneghin, Jennifer ; Flores, Gilberto ; Podar, Mircea ; Dombrowski, Nina ; Spang, Anja ; L’Haridon, Stephane ; Humphris, Susan E. ; de Ronde, Cornel E. J. ; Tontini, F. Caratori ; Tivey, Maurice A. ; Stucker, Valerie ; Stewart, Lucy C. ; Diehl, Alexander ; Bach, WolfgangHydrothermally active submarine volcanoes are mineral-rich biological oases contributing significantly to chemical fluxes in the deep sea, yet little is known about the microbial communities inhabiting these systems. Here we investigate the diversity of microbial life in hydrothermal deposits and their metagenomics-inferred physiology in light of the geological history and resulting hydrothermal fluid paths in the subsurface of Brothers submarine volcano north of New Zealand on the southern Kermadec arc. From metagenome-assembled genomes we identified over 90 putative bacterial and archaeal genomic families and nearly 300 previously unknown genera, many potentially endemic to this submarine volcanic environment. While magmatically influenced hydrothermal systems on the volcanic resurgent cones of Brothers volcano harbor communities of thermoacidophiles and diverse members of the superphylum “DPANN,” two distinct communities are associated with the caldera wall, likely shaped by two different types of hydrothermal circulation. The communities whose phylogenetic diversity primarily aligns with that of the cone sites and magmatically influenced hydrothermal systems elsewhere are characterized predominately by anaerobic metabolisms. These populations are probably maintained by fluids with greater magmatic inputs that have interacted with different (deeper) previously altered mineral assemblages. However, proximal (a few meters distant) communities with gene-inferred aerobic, microaerophilic, and anaerobic metabolisms are likely supported by shallower seawater-dominated circulation. Furthermore, mixing of fluids from these two distinct hydrothermal circulation systems may have an underlying imprint on the high microbial phylogenomic diversity. Collectively our results highlight the importance of considering geologic evolution and history of subsurface processes in studying microbial colonization and community dynamics in volcanic environments.