Volcano-tectonic Interactions Research Articles

Geospatial analysis of volcano-tectonic interactions: implications for spatiotemporal variations in water quality and quantity at Lake Beseka, East Africa, Ethiopia

ABSTRACT Water quality deterioration in the Main Ethiopian Rift Lakes is a problem affecting the area’s public health and socioeconomic development. The present study aimed to assess the water level rise in Lake Beseka using Landsat images from 1975 to 2023 and dilution trends at the pumping site from 2004 to 2022. In addition, the spatial water quality parameters, including pH, EC, TDS, and water surface temperature, for the years 2007, 2018, 2021, and 2023 were determined. The water level increased dramatically from 3 km2 in the 1960s to 27.5 km2 in 1980 following the construction of the Koka dam and the beginning of irrigation activity (sugarcane plantation) for the Metehara sugar estate factory. The water level reached a maximum (50 km2 in the dry season) in the mid of 1910s and become decreased and fluctuated after 2015. The observed pH, EC, and TDS were higher in the central portion of the lake, grouped under brackish water, and lower in the southwest, south, and northeast shores. The EC and TDS were higher in 2007, decreased in 2018, and fluctuated. The geothermal anomaly of the area varies from 23.1 to 47.9°C with the highest anomaly occurring at the northern side of the lake at a recent volcanic area that interlinked with geological structures. However, the observed and estimated water temperatures of the lake decreased from west to east due to hot spring discharge from the southwest shore of the lake. The series of hot springs in the southwest and west shores of the lake with high discharge rates indicate the presence of structural connectivity that leads to the emission of heat from a deep-seated source and heated groundwater of the area recharged from irrigation activity. Overall, spatiotemporal lake water quality variations were due to anthropogenic and geogenic factors, including hot springs and groundwater discharge to the lake, water level rise and bathymetric depth variation, evaporation, and irrigation activity. This study is significant in continuously estimating water level fluctuations and providing early warnings and preparedness to maintain the region's socioeconomic development.

Submarine morphology of Pantelleria volcano: The interplay between volcanic and erosive-depositional processes modulated by sea-level fluctuations.

High-resolution multibeam data integrated with seismic reflection profiles are used to identify and characterize the main primary volcanic and erosive-depositional features along the submarine part (about the 80%) of the active Pantelleria volcano located in the Sicily Channel. Volcanic features include lava flows, cones and elongated ridges. Lava flows are mainly recognized over the insular shelf, while volcanic cones and ridges are mostly concentrated along the steep submarine flanks, especially along the wider SE and NW ones. A strong volcano-tectonic interaction is envisaged for their formation, as indicated by their preferential elongation or alignment along the (main) SE-NW and (secondary) SW-NE directions that have controlled the evolution of the whole volcanic edifice. Erosive-depositional features mainly include small-scale landslide scars and narrow gullies affecting the edge of the insular shelf and overlying submarine depositional terraces. Gullies sometimes merge downslope in larger channels, whose formation is primarily controlled by the distribution of volcanic features and/or shelf sectors characterized by different age or lithologies. Based on the marked morphological differences between the different flanks of the Pantelleria volcano, we infer an overall migration of the volcanic activity from SE to NW over time. This migration is apparently in contrast with the presence of a much wider but shallower NW insular shelf with respect to the SE one. This anomaly can be explained through a two-stage model, with the formation, in the NW sector, of a polygenic shelf rejuvenated by volcanic progradation during the last eustatic hemicycle. The different depths of the insular shelf edge around the island also provide insights on vertical deformations that affected the Pantelleria volcano during the Late-Quaternary.

Magma storage and transfer in the Villarrica volcanic chain, South Chile: MT insights into volcano-tectonic interactions

The active volcanic arc of the Andes is controlled by subduction of the Nazca and Antarctic Plates beneath the South American Plate. The Southern Volcanic Zone is the segment with the most active volcanoes in the Andes and the one where volcano-tectonic interactions are more evident. Magmatic fluids are there channeled through the brittle crust by faults and fractures, becoming an important region for understanding the mechanisms associated with melt migration and storage in subduction zones. The Liquiñe–Ofqui Fault System and Andean Transverse Faults, control the overall architecture of the volcanic arc and play an important role on magmatic transport and compositional partitioning. Evidence of this is the oblique chain composed of Villarrica, Quetrupillán and Lanín stratovolcanoes and a number of minor eruptive centers, where a wide range of magma compositions have been erupted with basalts and basaltic andesites dominating the suite. We used long–period and broad–band magnetotelluric stations deployed surrounding of Villarrica volcano to investigate the implications of crustal faulting and volcanism and their consequence on crustal reservoirs. Inversion of the data was used to generate three–dimensional electrical resistivity models. The resistivity distribution shows the upper crust as highly resistive, but below and east of Villarrica volcano, the model suggests the presence of a magmatic reservoir at shallow crustal levels (between 1.5 and 3 km b.s.l.), possibly corresponding to a transient magma storage. Meanwhile, the middle crust contains several intermediate to low conductive features interpreted as fluid pathways and/or melt storage regions, respectively, revealing the important role of fault systems. The lower crust also contains low resistivity zones indicating the presence of partial melt and/or fluids, associated with deep reservoirs (8–20 km), with a significant proportion of them likely non eruptible parts. This would suggest that melt is accumulated as highly crystallized mush or disconnected melt pockets and highlight the complex vertical extent of the structurally-controlled plumbing systems even in thin crust settings.

The 2013–2020 seismic activity at Sabancaya Volcano (Peru): Long lasting unrest and eruption

Sabancaya volcano is the youngest and second most active volcano in Peru. It is part of the Ampato-Sabancaya volcanic complex which sits to the south of the ancient Hualca Hualca volcano and several frequently active faults, thus resulting in complex volcano-tectonic interactions. After 15 years of repose, in 2013, a series of 4 earthquakes with magnitude >4.5 occurred within 24 h, marking the beginning of a new episode of unrest. Several additional swarms of earthquakes occurred in the following years until magmatic eruptive activity started on 6 November 2016. This activity is ongoing as of this writing, with an average of 50 explosions per day. In this study, we present results of multiparametric monitoring of Sabancaya's activity observed during 2013–2020. Seismic data are used to create a one-dimensional seismic velocity model, to catalog, locate, and characterize earthquakes, to detect repeating earthquake families, and to monitor seismic velocity variations by ambient noise cross-correlation. These analyses are complemented by visual and remote sensing observations and ground deformation measurements. All monitored parameters showed significant changes on 6 November 2016, the day of eruption onset, thus dividing the eruptive activity into pre-eruptive and eruptive stages.The unrest is characterized by high levels of seismic activity with hundreds of events detected per day. Volcano-tectonic (VT) earthquakes were dominant during the pre-eruptive period while long-period (LP) events and explosions have been most numerous since the eruption onset. Earthquake locations highlight long-lasting seismogenic zones along multiple previously active regional faults, as well as along newly identified faults. This VT seismicity is mainly distributed in a sector from the northwest to the east of the volcanic complex at distances of up to 30 km from the crater. We focus our analysis on two eruptive episodes: the eruption onset and subsequent crater migration from south to north, and the increase of lava dome extrusion rate in 2019. Both episodes are accompanied by seismic velocity decreases of up to 0.2% and are preceded by a few weeks by bursts of distal VT activity, including numerous repeating earthquakes. These repeated events were located on several remote tectonic faults (5–25 km from the vent). We suggest that these phenomena could be due to the injection of a batch of magma in the deep reservoir and/or conduit, which would generate 1) a pressure wave propagating in the hydrothermal system, triggering the bursts of seismic activity and 2) slow rising of magma by melting old material filling the conduit that eventually produced the eruptive and dome growth acceleration events.

Volcano-tectonic interactions at the southern margin of the Okataina Volcanic Centre, Taupō Volcanic Zone, New Zealand

The c. 15 km-long Ngapouri-Rotomahana Fault (NRF) is a major splay of the Paeroa Fault at the eastern margin of the modern Taupō Rift, the active tectonic structure embedded within the Taupō Volcanic Zone of North Island, New Zealand. The NRF and Paeroa Fault extend to the southern margin of the Okataina Volcanic Centre (OVC) and lie southwest of the Tarawera vent lineation, which is the source of approximately half of the eruptions of the OVC in the past 25 cal. ka BP. Here, we explore volcano-tectonic relationships between the OVC and the NRF and Paeroa Fault. Collective evidence used in our analysis includes: volcanic processes interpreted as occurring during the historic 1886 Tarawera (basalt) and the prehistoric 1314 ± 12 CE Kaharoa (basalt triggered rhyolite) eruptions, both on the Tarawera vent lineation; exposures in five trenches excavated across the NRF and seven trenches across the Paeroa Fault; data on a series of explosion craters formed to the southwest of the volcano associated with the ~1314 CE Kaharoa eruption and the Rotoma rhyolite (~9.4 cal. ka BP) eruption from the OVC; and mafic dykes that primed several of the OVC eruptions. Data from the twelve trenches on the two faults reveal eight surface fault ruptures since 15.6 cal. ka BP, with most closely coinciding with volcanic eruptions, providing a first-order indication of probable causality. Three principal modes of interaction are identified. Firstly, large displacement events on the Paeroa fault, arguably immediately prior to the Mamaku and Rotoma rhyolite eruptions (~7.9 and ~9.4. cal. ka BP, respectively) and on the NRF immediately prior to the ~1314 CE Kaharoa eruption are candidates for earthquake static or dynamic stress triggers for those explosive eruptive events. Secondly, basalt dyke intrusion was also involved in the initiation of the Kaharoa eruption, so the spatial and temporal relationships between dyke intrusion, smaller displacement fault ruptures and initiation of the Kaharoa eruption appear closely connected. Thirdly, faulting events that are interpreted as co- or post-eruption may be the result of stress triggers associated with magma chamber deflation.

Large‐Volume and Shallow Magma Intrusions in the Blackfoot Reservoir Volcanic Field (Idaho, USA)

AbstractThe Blackfoot Reservoir volcanic field (BRVF), Idaho, USA, is a bimodal volcanic field that has hosted silicic eruptions during at least two episodes, as recently as 58 ka. Using newly collected ground and boat‐based gravity data, two large negative anomalies ( mGal) are modeled as shallow ( km) intrusions beneath a NE‐trending alignment of BRVF rhyolite domes and tuff rings. Given the trade‐off between density contrast and model volume, best‐fit gravity inversion models yield a total intrusion volume of ; a density contrast of kg results in two intrusions, each km km and about 0.5 km thick, with cumulative volume of 100 . A network of trending faults lies directly above and on the margins of the mapped gravity anomalies. Most of these faults have m throw; one has throw up to m. We suggest that the emplacement of shallow sill‐like intrusions produced this fault zone and also created a ENE‐trending fault set, indicating widespread ground deformation during intrusion emplacement. The intrusions and silicic domes are located km E of a regional, 20 mGal step in gravity. We interpret this step in gravity as thickening of the Upper Precambrian to lowermost Cambrian quartzites in the Meade thrust sheet, part of the Idaho‐Wyoming Thrust Belt. Silicic volcanism in the BRVF is a classic example of volcanotectonic interaction, influenced by regional structure and creating widespread deformation. We suggest volcanic hazard assessments should consider the possibility of large‐volume silicic eruptions in the future.

Evolution of Seismicity During a Stalled Episode of Reawakening at Cayambe Volcano, Ecuador

Cayambe Volcano is an ice-capped, 5,790 m high, andesitic-dacitic volcanic complex, located on the equator in the Eastern Cordillera of the Ecuadorian Andes. An eruption at Cayambe would pose considerable hazards to surrounding communities and a nationally significant agricultural industry. Although the only historically documented eruption was in 1785, it remains persistently restless and long-period (LP) seismicity has been consistently observed at the volcano for over 10 years. However, the sparse monitoring network, and complex interactions between the magmatic, hydrothermal, glacial, and tectonic systems, make unrest at Cayambe challenging to interpret. In June 2016 a seismic “crisis” began at Cayambe, as rates of high frequency volcano-tectonic (VT) earthquakes increased to hundreds of events per day, leading to speculation about the possibility of a forthcoming eruption. The crisis began 2 months after the Mw7.8 Pedernales earthquake, which occurred on the coast, 200 km from Cayambe. Here we show that the 2016 seismicity at Cayambe resulted from four distinct source processes. Cross correlation, template matching, and spectral analysis isolate two source regions for VT earthquakes–tectonic events from a regional fault system and more varied VTs from beneath the volcanic cone. The temporal evolution of the LP seismicity, and mean Q value of 9.9, indicate that these events are most likely generated by flow of hydrothermal fluids. These observations are consistent with a model where a new pulse of magma ascent initially stresses regional tectonic faults, and subsequently drives elevated VT seismicity in the edifice. We draw comparisons from models of volcano-tectonic interactions, and speculate that static stress changes from the Pedernales earthquake put Cayambe volcano in an area of dilation, providing a mechanism for magma ascent. Our findings provide a better understanding of “background” seismicity at Cayambe allowing faster characterization of future crises, and a benchmark to measure changes driven by rapid glacial retreat.

Volcanotectonic interactions between inclined sheets, dykes, and faults at the Santorini Volcano, Greece

Dykes and inclined sheets are known occasionally to exploit faults as parts of their paths, but the conditions that allow this to happen are still not fully understood. In this paper, we report field observations from a swarm composed of 91 segments of dykes and inclined sheets, the swarm being particularly well-exposed in the mechanically layered caldera walls of the Santorini volcano, Greece. Here the focus is on dykes and sheets in the swarm that are seen deflected into faults and the mechanical conditions that encourage such deflections. In particular, we present new analytical and numerical models to explain the mechanical principles of dyke/sheet deflections into faults. The numerical models are applied to a normal-fault dipping 65° with a damage zone composed of parallel layers or zones of progressively stiffer rocks with increasing distance from the fault rupture plane. We model a sheet-intrusion, dipping from 0° to 90° and with an overpressure of alternatively 1 MPa and 5 MPa, approaching the fault. We further tested the effects of changing (1) the thickness of the sheet-intrusion, (2) the fault-zone thickness, (3) the fault-zone dip-dimension (height), and (4) the loading by, alternatively, regional tension and compression. We find that the stiffness of the fault core, where a compliant core characterises recently active fault zones, has pronounced effects on the orientation and magnitudes of the local stresses and, thereby, on the likelihood of dyke/sheet deflection into the fault zone. Similarly, the analytical models, focusing on the fault-zone tensile strength and energy conditions for dyke/sheet deflection, indicate that dykes/sheets are most likely to be deflected into and use steeply dipping recently active (zero tensile-strength) normal faults as parts of their paths.

Volcanic seismicity beneath Chuginadak Island, Alaska (Cleveland and Tana volcanoes): Implications for magma dynamics and eruption forecasting

Cleveland and Tana are remote volcanoes located in the central Aleutian volcanic arc on the eastern end of the Islands of Four Mountains (IFM). The persistently active Mount Cleveland volcano, on the western side of Chuginadak Island, is surrounded by several closely spaced Quaternary volcanic centers including Carlisle, Herbert, Kagamil, Tana, and Uliaga, and numerous small satellite vents on Chiginadak between Cleveland and Tana. The Alaska Volcano Observatory (AVO) installed two permanent broadband seismometers on Chuginadak Island in 2014, and we operated a temporary broadband network focused on the western side of the island in 2015–2016. Collectively, these stations provided the first seismic observations of this frequently active volcano and the surrounding Holocene-aged volcanic vents. During the study period (July 2014–January 2019), eruptive activity at Cleveland was characterized by small explosions separated by periods of lava effusion that formed small domes in the volcano's summit crater. We characterize seismicity beneath Chuginadak Island through automated analysis of event waveform frequency content, development of a one-dimensional P-wave velocity model, calculation of earthquake hypocenters, magnitudes, focal mechanisms, and identification of earthquake families. This analysis reveals the full range of seismic event types expected in a highly active volcanic environment and includes Volcano-Tectonic (VT) earthquakes, Long-Period (LP) events, and explosion signals. LP events appear to cluster at shallow depth beneath the active crater of Mount Cleveland and almost all of the explosions occur without identifiable short-term (hours to days) seismic precursors. VT earthquakes beneath Mount Cleveland occur at depths of 2 to 8 km below sea level (BSL) and range in magnitude from −0.2 to 1.8. VT focal mechanisms have horizontal P-axes that align with the regional axis of maximum stress. These observations, and a relatively slow one-dimensional seismic velocity model, are consistent with a shallow body of magma that is fed through a deeper conduit system. The time-history of VT earthquakes and shallow LP events suggest their occurrence may track the transfer of magma and fluids from the mid-crust to the shallow portions of the conduit system and may provide a means to anticipate future explosions and periods of dome growth. VT hypocenters also extend ~7 km northeast of Cleveland's summit at depths of 5 to 10 km BSL, under a group of Holocene-aged vents between Mount Cleveland and Tana. These earthquakes have vertically-oriented P-axes and a greater percentage occur in families. These observations, combined with observations of vent orientation and morphology and gas flux, suggest the area between Cleveland and Tana represents a zone of complicated volcano-tectonic interaction, similar to calderas elsewhere in the Aleutian arc. The presence of a larger volcanic system in the eastern IFM could influence magmatism and account for the multiple closely spaced volcanic centers in this region.

The control of preexisting faults on the distribution, morphology, and volume of monogenetic volcanism in the Michoacán-Guanajuato Volcanic Field

AbstractInteractions between volcanic and tectonic processes affect the distribution, morphology, and volume of eruptive products in space and time. The Queréndaro area in the eastern Michoacán-Guanajuato Volcanic Field affords an exceptional opportunity to understand these relationships. Here, a Pleistocene lava plateau and 20 monogenetic volcanoes are vented from an active ENE-striking segment of the Morelia-Acambay fault system. Thirteen scoria cones are aligned along this structure, vented from an extensional gap in between two rotated hanging wall blocks of a listric fault. A new geological map, volcanic stratigraphy, and 40Ar/39Ar dating indicate that this lava plateau and volcanic cluster were emplaced from 0.81 to 0.25 Ma by 11 intermittent eruptive epochs separated by ca. 0.05 Ma, emplacing a total magma volume of 5 km3. Petrography and chemistry of rocks suggest that all volcanic structures were fed by three different magma batches but vented from independent feeder dikes. Our results indicate that preexisting faults exert a strong influence on volcanic spatial and temporal distribution, volcanic morphology, magma volume, and eruptive dynamics in this area. ENE-breached and ENE-elongated scoria cones indicate parallel subsurface fissure and feeder dikes. Additionally, points of maximum fault dilation at depth related to a transtensive state of stress coincide with less fragmented deposits and larger magma volumes. Furthermore, this study raises important questions on the geodynamics of volcano-tectonic interactions possible in similar monogenetic volcanic alignments worldwide.

Eruptive chronology of monogenetic volcanoes northwestern of Morelia – Insights into volcano-tectonic interactions in the central-eastern Michoacán-Guanajuato Volcanic Field, México

Twelve monogenetic volcanoes formed during the last 7 Ma within the Tarímbaro graben, northwest of the city of Morelia, in the central-eastern part of the Michoacán-Guanajuato volcanic field (México). These include four scoria cones (Pelón, Tetillas, Jamanal, and Parastaco), four lava domes (La Cruz, Divisadero, Estadio, and Tetillas), two small shield volcanoes (Quinceo and Tetillas) and two lava flows (Cuto and Cerritos). Based on a detailed geological map and stratigraphy aided by new 40Ar/39Ar and 14C radiometric dates, and whole-rock chemical analyses, we established the eruptive chronology of these monogenetic volcanoes. These volcanoes were built upon four early Miocene successions of regional volcanism named Cuitzeo lavas (18.7 Ma), Cuitzeo ignimbrite (17.4 Ma), Atécuaro ignimbrite (16.8 Ma), and Punhuato lavas (16.3 Ma). Late Miocene to Pliocene activity consisted of the La Cruz, Divisadero, and Estadio domes and the Cuto lava flow (6.7–3.1 Ma). Pleistocene activity included the Cuitzeo fallout pyroclastic sequence (1.48 Ma), the Quinceo small shield volcano (1.36 Ma), the Pelón scoria cone (0.84 Ma), the Tetillas small shield volcano, two lava domes and a scoria cone (0.56–0.34 Ma), the Jamanal and Parastaco scoria cones and the Cerritos lava flow (0.11 Ma). Magma volumes from these volcanoes vary from <0.1 to 4 km3. We ascribe their variety of magma volumes, morphology, volcanic styles, and spatio-temporal distribution to tectonic changes and evolution of the ENE Tarímbaro graben, whose faults belong to the Tarímbaro-Álvaro Obregón fault segment in the central part of the Morelia-Acambay Fault System. Quinceo (2 km3) and Tetillas (4 km3) small shield volcanoes are by far the most voluminous centers dominating the landscape of the city of Morelia. All rock samples have compositions varying from 49.3 to 61.6 wt % in silica with medium-K contents (0.43–1.83 wt %).

Understanding multi-vent Plinian eruptions at Mt. Tongariro Volcanic Complex, New Zealand

The andesitic Tongariro Volcanic Complex in the Central North Island of New Zealand comprises tens of vents along an actively extending graben. Past work has hypothesised that multiple vents may operate during a single explosive eruption episode, providing an unprecedented hazard challenge for this region. The stratigraphic record suggests an irregular clustering of eruption episodes over time, including an unusual ≤ 200-year-long period from ~11.3–11.1 ka when several large explosive eruptions occurred. We carried out new field mapping, stratigraphy, and sedimentology of the resulting pyroclastic deposits to identify seven episodes during this period, locating the vent sites and calculating their climactic dynamic properties. Five of the episodes involved two or more vent locations that produced separate sub-Plinian/Plinian eruption columns. Eruption columns ranged between 16 and 24 km high and erupted volumes of 0.05 to 0.76 km3, indicating magnitudes of 4 to 5. Each of these episodes show north-to-south “unzipping” of the Tongariro Graben, with episodes beginning in northerly vents, before being joined by vents south of these. This included two scenarios; northern edifice vents followed by central edifice ones or central edifice vents followed by southern ones. In both cases, the northerly vents generally display the greatest peak eruption magnitudes and the steadiest eruptions. By contrast, the southernmost vents formed along a fault-controlled fissure-like system. These produced unsteady plumes and pyroclastic density currents. The northward widening tectonic graben structure thus influences the pattern and style of these Plinian-style eruptions. This study highlights a real possibility for an extreme hazard scenario involving successive large-scale eruptions at volcanic systems in slowly rifting environments and sheds new light on the volcano-tectonic interaction in such settings.

The structural architecture of the Los Humeros volcanic complex and geothermal field

The Los Humeros Volcanic Complex (LHVC) is a large silicic caldera complex in the Trans-Mexican Volcanic Belt (TMVB), hosting a geothermal field currently in exploitation by the Comisión Federal de Electricidad (CFE) of Mexico, with an installed capacity of ca. 95 MW of electric power. Understanding the structural architecture of LHVC is important to get insights into the interplay between the volcano-tectonic setting and the characteristics of the geothermal resources in the area. The analysis of volcanotectonic interplay in LHVC benefits from the availability of subsurface data obtained during the exploration of the geothermal reservoir that allows the achievement of a 3D structural view of the volcano system. The LHVC thus represents an important natural laboratory for the development of general models of volcano-tectonic interaction in calderas. In this study, we discuss a structural model of LHVC based on morphostructural and field analysis, integrated with well logs, focal mechanism solutions and magnetotelluric imaging. The structural analysis suggests that inherited regional tectonic structures recognized in the basement played an important role in the evolution of the magma feeding system, caldera collapses and post-caldera deformations. These inherited weak planes have been reactivated by resurgence faults and post-caldera magma-driven hydrofractures under a local radial stress field generated by the shallow LHVC magmatic/hydrothermal system. The local stress field induced caldera resurgence and volcanotectonic faulting. The results of this study are important to better constrain the structural architecture of large caldera complexes. Also, our study is useful to understand the structure of the Los Humeros geothermal field and support the exploration of deeper Super-Hot Geothermal Systems (SHGSs) and engineering of Enhanced Geothermal Systems (EGSs) for electric power production in the LHVC and other active resurgent calderas.

Imbabura volcano (Ecuador): The influence of dipping-substrata on the structural development of composite volcanoes during strike-slip faulting

The geology and long-term structural development of Imbabura volcano (Ecuador) have been discerned from field surveys, as well as petrographical and geochemical studies. The volcano is composed of an ancient edifice (Imbabura I), which has experienced one major volcanic landslide directed N 330–340°. After the emplacement of that debris-avalanche deposit, the petrographically and geochemically different edifices Imbabura II-1 and Imbabura II-2 developed on the N and NE flank of Imbabura I, as well as in its summit zone. Finally the smaller Imbabura II-3 edifice, a dome-complex locally known as Huarmi Imbabura, was emplaced in the SSW flank of Imbabura I. The relatively complex structure of the edifice (i.e. flank collapse direction and spatial distribution of the major stratigraphical units) cannot be explained solely by volcano-tectonic interactions with the regional left-lateral Río Ambi strike-slip fault, which traverses the edifice from NNE to SSW. Instead, the fact that the whole Imbabura edifice stands on a substratum dipping to the NW (i.e. the NW flank of the neighbor Cubilche volcano) is proposed to be the main factor influencing the departure of Imbabura structure from previously known models of volcanic edifices interacting with strike-slip faults. This hypothesis was tested with scaled experiments, during which the dip-direction of the substratum was systematically changed with respect to the strike of the fault. The structures developed by the experimental prototypes are highly coherent with those observed at Imbabura volcano.

Correlated Changes Between Volcanic Structures and Magma Composition in the Faial Volcanic System, Azores

The interaction between magmatic and tectonic processes in ocean intraplate volcanism yields insights into the ascent and transport of magmas. Many oceanic intraplate studies lack a temporal component and do not consider changes in tectonic regime and/or magmatic processes during the evolution of magmatic systems. The eastern part of the Azores archipelago formed under the influence of both an intraplate melting anomaly and a system of ultraslow spreading rift axes. The majority of recent submarine and subaerial eruptions in the Azores occur along volcanic rift zones and thus melt transport and volcanic processes are largely controlled by tectonic processes, and are therefore ideally suited to study volcano-tectonic interactions. Here, we investigate how variable the magmatic and tectonic processes are in space and time and how they interact. We present new bathymetric, geophysical, geochemical and Sr-Nd-Pb isotope data from Faial Island and the surrounding seafloor, providing insights into the interaction between the asthenospheric melting anomaly and extensional lithospheric stresses. The bathymetry reveals large submarine volcanic rift zones on the western flank of Faial, including that of the 1957-1958 Capelinhos eruption. Based on absolute ages and seismic imagery, we develop a relative chronology of the magmatic evolution of the submarine rift zones. Their preferred WNW-ESE orientation implies that the stress field has not changed within the last ~1 Ma. We can however show that melt productivity progressively decreased with time. Compositionally different magma batches fed distinct volcanic rift zones and edifices, suggesting that changes in the melting regime occur on a small spatial scale and that the distribution of compositionally similar lavas is tectonically controlled. As melt supply decreases, the tectonic influence on volcanism increases with a stronger localisation of melts along tectonically controlled lineaments. The youngest mafic and intermediate melts (<10 ka) on Faial are exclusively erupted along single rift zones and cover a smaller area, whereas the older volcanism was more widespread.

Crustal extension in the Tongariro graben, New Zealand: Insights into volcano-tectonic interactions and active deformation in a young continental rift

Crustal extension in the Tongariro graben, New Zealand: Insights into volcano-tectonic interactions and active deformation in a young continental rift

Mineral fabrics in high-level intrusions recording crustal strain and volcano–tectonic interactions: the Shellenbarger pluton, Sierra Nevada, California

The Minarets caldera is a volcano–plutonic complex in the Sierra Nevada, California, that exemplifies complex interactions between volcanism and tectonic deformation in continental-margin arcs. Caldera evolution commenced with emplacement of pre-collapse rhyolitic ash-flow tuff, followed by collapse and deposition of volcanic breccia and rhyodacitic ash-flow tuff. Subsequently, the volcanic rocks were deformed along the regional Bench Canyon shear zone. The caldera centre was then intruded by the resurgent c. 100 Ma steep-sided Shellenbarger granite pluton, which steepened the shear zone foliation. The pluton was overprinted by syn- to post-magmatic ∼NNE–SSW horizontal shortening; the same shortening was documented in several other Late Cretaceous syntectonic plutons in the Sierra Nevada and interpreted to record dextral transpression during convergence of the Farallon and North American plates. To explain the unusual tectonic fabric in the shallow-level Shellenbarger pluton, we develop a general model for strain partitioning in syntectonic magma bodies emplaced at various crustal levels. We propose that shallow intrusions, isolated within stiff crust, may tend to accommodate minor pure shear strain whereas simple shear dominates along weak faults and shear zones. By contrast, a rheological reversal is crossed deeper in the crust and magma bodies become the weakest, simple shear-dominated parts of the system. Supplementary material: Analytical methods and anisotropy of magnetic susceptibility and U–Th–Pb isotopic data are available at https://doi.org/10.6084/m9.figshare.c.3582749

Tectonic Geomorphology and Volcano-Tectonic Interaction in the Eastern Boundary of the Southern Cascades (Hat Creek Graben Region), California, USA

The eastern boundary of the Southern Cascades (Hat Creek Graben region), California, USA, is an extensively faulted volcanic corridor between the Cascade Range and Modoc Plateau. The east-west extending region is in the transition zone between the convergence and subduction of the Gorda Plate underneath the North American Plate; north-south shortening within the Klamath Mountain region; and transcurrent movement in the Walker Lane. We describe the geomorphological and tectonic features, their alignment and distribution, in order to understand the tectonic geomorphology and volcano-tectonic relationships. One outcome of the work is a more refined morpho-structural description that will affect future hazard assessment in the area. A database of volcanic centers and structures was created from interpretations of topographic models generated from satellite images. Volcanic centers in the region were classified by morphological type into cones, sub-cones, shields and massifs. A second classification by height separated the bigger and smaller edifices and revealed an evolutionary trend. Poisson Nearest Neighbor analysis shows that bigger volcanoes are spatially dispersed while smaller ones are clustered. Using volcano centroid locations, about 90 lineaments consisting of at least three centers within 6km of one another were found, revealing that preferential north-northwest directed pathways control the transport of magma from the source to the surface, consistent with the strikes of the major fault systems. Most of the volcano crater openings are perpendicular to the maximum horizontal stress, expected for extensional environments with dominant normal regional faults. These results imply that the extension of the Hat Creek Graben region and impingement of the Walker Lane is accommodated mostly by extensional faults and partly by the intrusions that formed the volcanoes. Early in the history of a volcano or volcano cluster, melt produced at depth in the region propagates to the surface using the easiest and most efficient pathway, mostly controlled by these pre-existing extensional faults and near-surface stress fields. Continued volcano growth is less closely dependent on the regional structures, suggesting control by the development of the volcanic edifice itself.

Volcano–tectonic interactions as triggers of volcanic eruptions

Surface displacements and edifice deformations at active volcanoes can occur when magma reservoirs begin to inflate as new magma enters them. Volcanoes are also subjected to a variety of external lithospheric stresses that are thought to be responsible for triggering volcanic unrest or modifying ongoing activity. However, despite many observations, it is uncertain whether these phenomena can actually interfere with magma chamber dynamics since it is not clear why some volcanoes are more subjected to these interactions than others. In order to determine whether external stresses interfere with volcanic activity, a viscoelastic 3D Finite Element Mogi-based model of Kīlauea volcano's magma chamber was implemented. First, the model was used to replicate an inflation cycle without external stresses. Its results were then compared with the ones obtained if the same model was subjected to tidal stress modulation and a strong (Mw=7.7) tectonic earthquake. The model showed that tidally-induced pressurization is not sufficiently large to modify the pressure in a 5km deep volcanic magma chamber, but it suggested how the magma chamber pressure build-up rate can be influenced by tidal pressurization and thus why some volcanoes seem to experience tidal interferences more than others. Furthermore, the model's results suggested why magma chambers are about the same size as calderas both on the Earth and on other Solar System silicate planets. System. Finally, it was used to propose an explanation of why a short-lived eruption at Kīlauea volcano, Hawai’i, began 30min after the 1975 magnitude 7.7 (Mw) Kalapana earthquake.

The geological and structural evolution of the Cerro Tuzgle Quaternary stratovolcano in the back‐arc region of the Central Andes, Argentina

The aim of our paper is to contribute to a better knowledge of the volcanism in the back-arc region of the Central Andes and its relationships with the basement geology, the stress field and the tectonic evolution, by studying in detail the stratigraphy and the structure of the Quaternary Cerro Tuzgle stratovolcano in the Puna Plateau. Field mapping and remote sensing analysis reveal the stratigraphic architecture, the geological evolution and the volcanotectonic interactions in the Cerro Tuzgle area. For the first time in a volcano of the Puna Plateau, synthemic units bounded by unconformity surfaces have been defined, unrevealing the temporal and spatial relationships between constructive and destructive phases of the volcano history. Our study indicates that after the emplacement of a small ignimbrite deposit and of few scattered lava domes, the central Cerro Tuzgle volcano built up throughout three distinct phases of edifice construction. The first of these constructive phases ended with a previously unreported destructive event, consisting of ≈0.5km3, catastrophic sector collapse of the volcanic edifice, whose stratigraphic position and main characteristics have been identified. The study suggests that the regional stress regime and the topography of the substrata are the main non-magmatic factors controlling the constructive and destructive phases of the volcano, including the directions of magmatic intrusions, faulting and gravitational sector failure of the volcano. The integration of synthemic stratigraphy and volcanotectonic analysis in the study of volcanic edifices showed to be an effective methodological approach for the understanding of the magmatic and tectonic evolution of the Puna Plateau.