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Although Veniaminof Volcano in Alaska experiences frequent eruptions and has eight permanent seismic stations, only two of the past 13 eruptions have had precursory signals that prompted a pre-eruption warning from the Alaska Volcano Observatory (AVO) since 1993. Seismic data from Venianimof indicate that most eruptions from 2000 to 2018 do not coincide with increased seismicity. Additionally, analyses of InSAR data available from 2015 to 2018 which covers the pre-, syn-, and post-eruption periods of the 2018 eruption do not show clear signs of deformation. The systemic lack of systematic precursory signals raises critical questions about why some volcanoes do not exhibit clear unrest prior to eruption. Volcanoes that erupt frequently without precursory signals are often classified as “open” systems with magma migrating through an open network to eruption, rather than pausing at a shallow reservoir. However, the precursory signals, or lack thereof, from a small or deep closed magma system may be difficult to observe, resulting in a stealthy eruption mimicking the behavior of an open system. In this study, we utilize finite element, fluid injection models to investigate a hypothetical closed magma system at Veniaminof and evaluate its ability to erupt with no observable early-warning signals. Specifically, a series of numerical experiments are conducted to determine what model configurations lead to stealthy eruptions – i.e., producing ground deformation below the detection threshold for InSAR (<10 mm) and developing no seismicity, yet resulting in tensile failure which will promote diking and eruption. Model results indicate that the primary control on whether eruption precursors from deformation and seismicity will be present are the rheology of the host rock and the magma flux, followed by the secondary control of the size of the magma chamber, and then its depth and shape. Volcanoes with long-lived thermally mature magma systems with moderate to small magma reservoirs are the most likely to exhibit stealthy behavior, with the smallest systems most likely to fail without producing a deformation signal. This result is likely because small, deep magma systems produce minimal surface deformation and seismicity. For stealthy volcanoes like Veniaminof and others in Alaska (e.g., Cleveland, Shishaldin, Pavlof) and around the world, understanding the underlying magma system dynamics and their potential open vs. closed nature through numerical modeling is critical for providing robust forecasts of future eruptive activity.
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Volcano monitoring and forecasts are crucial to evaluate and mitigate the potential risks and socioeconomic impacts of volcanic activity. Seismicity, ground deformation, and gas emissions are commonly used as precursory signals and play a critical role in providing early warning of volcanic activity and impending eruption (e.g.,
Veniaminof Volcano located in the Aleutian Arc, Alaska.
The goal of this study is to investigate the magmatic processes in closed systems that lead to stealthy eruptive behavior characterized by the absence of seismicity (i.e., shear failure) and observable ground deformation, while still resulting in tensile failure leading to dike initiation and eruption. In other words, we aim to investigate how a closed magma system may behave in a way that mimics open system unrest. We use seismicity and ground deformation observations from Veniaminof in conjunction with finite element method (FEM) modeling (
Mt. Veniaminof is an ice-clad, basalt-to-dacite stratovolcano located on the Alaska Peninsula, ∼750 km southwest of Anchorage (
Since the 1830–1840s, 19 eruptions have been documented (
Changes in seismicity rate can be a precursory signal of imminent eruption. However, Veniaminof eruptions during 2000–2021 either mismatch changes in cumulative seismicity or have no concurrence with rapid increases in seismicity (
Earthquake hypocenters from 2000 to 2021 near Veniaminof Volcano, Alaska.
To observe the spatiotemporal evolution of the ground deformation before and throughout the 2018 Veniaminof eruption (September to December 2018), Persistent Scatter SAR Interferometry (PS-InSAR) (
StaMPS was used to perform time-series analysis of the SAR acquisitions (
To investigate host rock stability in response to the ground deformation caused by inflation of magma chamber, we use a thermomechanical Finite Element Method (FEM) modeling approach. We build upon previous numerical experiments (
The 40 by 16 km two-dimensional model space is constructed with a symmetrical central axis, roller boundary conditions are implemented along the side and bottom, and the ground surface is free boundary including an approximate topography of the edifice and caldera of Veniaminof (
Finite element method (FEM) model set up for Veniaminof. The fluid injection approach of
The time series of observed ground deformation from summer 2015 to 2018 (before and during 2018 eruption) covering the area of volcano edifice of Veniaminof generated by PS-InSAR are provided in
Ground deformation and velocity from InSAR time series from 2015 to 2018.
The primary goal of our numerical experiments is to determine the model configurations needed to produce stealthy eruptions - in other words, magma system states that produce a ground deformation signal that remains below the detection threshold for InSAR and results in little to no seismicity (as calculated by shear failure throughout the model space) while maintaining a minimum flux of magma needed to produce the eruptive volume recorded for the 2018 eruption of Veniaminof Volcano. As with other active systems (e.g., Katla and Grímsvötn in Iceland; subglacial volcanoes in Antarctica; Mount Spurr and Westdahl in Alaska) the center portion of Veniaminof is masked from deformation observations due to summit glacier/snow. As such, modeled deformation results are taken from the caldera rim coinciding with where the InSAR observations are coherent.
The numerical results illustrate how observable ground deformation and the stability of magma system are controlled by the underlying magma reservoir characteristics including size, shape, depth, and magma flux (
Magma chamber depth vs. ground deformation. Depth is to the surface of volcano edifice with summit of ∼2 km, while ground deformation is at the edge of summit caldera (see the edge location in
Magma flux vs. ground deformation. Ground deformation at the edge of summit caldera caused by inflating magma chamber, with a constant depth = −6 km (depth to the surface of volcano edifice with summit of ∼2 km height). Flux = 1e−5, 5e−5, 1e−4, 5e−4, 1e−3, 5e−3, 0.01, 0.05, 0.1 m3/s. Magma chamber size and shape parameters are described in
The parameter space for stealthy eruptions. Plotted results include models that produce <20 mm of surface displacement and little to no shear failure, but exhibit tensile failure surrounding the magma reservoir.
Our study indicates that the key trends apply in both non-temperature dependent and temperature dependent rheological conditions: 1) high flux typically leads to increased displacement and a higher chance of tensile and Mohr-Coulomb failure; 2) shallow depth is associated with high displacement but has very little impact on tensile and Mohr-Coulomb failure; and 3) larger chambers usually exhibit more displacement but are less prone to cause tensile and Coulomb failures.
Temperature-dependent models have a lower calculated displacement and, thus, a lower likelihood of producing tensile and shear failure. Therefore, to reach the same displacement and threshold for failure, temperature-dependent models require a higher magma flux rate ( 1) High flux and large chamber size: high flux combined with a large size tends to produce significant displacement, excluding the likelihood of a stealthy eruption, although Mohr-Coulomb failure may not necessarily be high. This is attributed to the positive association between both high flux and large size with displacement. In temperature-dependent models ( 2) High flux and small chamber size: this combination typically results in high Mohr-Coulomb failure, making seismic signals observable and unambiguous. High flux and small size jointly increase the affected subsurface region of Mohr-Coulomb failure. Yet, this combination contributes to initiate tensile failure, facilitating eruption onset, and displacement may not be significantly high, as the small size counteracts the effect of high flux. This “observable eruption” scenario is illustrated in the unpopulated areas in 3) Low flux and large chamber size: a low flux coupled with a large chamber size typically prevents tensile failure (i.e., reducing likelihood of triggering of eruption) and Mohr-Coulomb failure, as both low flux and large size decrease the probability of such occurrences, although this might result in low displacement due to low flux. In non-temperature-dependent models, a low flux (0.01–0.02 m3/s) combined with a large chamber size remains effective, indicating temperature-dependent wall-rock properties amplify the combined effects of low flux and large size, thereby diminishing the likelihood of tensile failure initiation. 4) Low flux and moderate to small chamber size: in this scenario, tensile failure and Mohr-Coulomb failure are unlikely. Although displacement is below the threshold for detection, the absence of tensile failure suggests that an eruption will not occur. While small size increases the likelihood of tensile failure, the predominant influence is the low flux.
Therefore, the primary determinants on eruption precursors from deformation and seismicity are the rheology of the warm wall rock and the magma flux, followed by secondary parameters of the size of the magma chamber, and then its depth and shape. Essentially, a long-lived system with ample thermal input to warm the rheology has a greater parameter space that will produce stealthy eruptions without precursory signals.
Our models, both temperature dependent and non-temperature dependent, are elastic and do not account for the viscosity of the wall rock. A viscoelastic rheology typically results in greater deformation compared to purely elastic models, as the viscous component allows for more prolonged and extensive deformation under stress before reaching failure (
Distinguishing between transient and long-lived magmatic systems is essential for understanding volcanic behavior and associated hazards. Long-lived magma chambers exhibit sustained activity over protracted periods, often with complex, multi-tiered magma chambers, and extend through the crust and comprise heterogeneously distributed melt, crystals, and exsolved volatiles (
Veniaminof displays some characteristics of a long-lived system, such as sustained activity over millennia, but the behavior of the 2018 eruption also aligns with aspects of a transient system. Veniaminof’s eruption styles vary widely, ranging from effusive to explosive with a history of sustained volcanic activity characteristic of a long-lived system; however, historical eruptions demonstrate simultaneous explosive and effusive activity from separate vents, which could also be indicative of a transient magmatic system (
In long-lived magma systems with substantial heat and material influx, the thermal state of the host rock becomes a critical factor for assessing reservoir stability (
Veniaminof Volcano may exemplify a stealthy eruption scenario, confirming that such eruptions are indeed feasible, an eruption characterized by the absence of observable precursory signals including seismicity and ground deformation, but sufficient tensile stress to initiate an eruption without the observable warnings.
Our models are constructed based on closed volcanic systems and indicate the possibility of two types of eruptions: the “observable” eruption and the “stealthy” eruption. As depicted in
Schematic illustration of eruptive cycle model of two cases:
Ideally, the detection of both earthquakes and ground deformation enables successful forecasts of volcanic eruptions, including detailed predictions of their timing, location, and magnitude. Notable examples include the 1980 eruption of Mount St. Helens, with accurate forecasts of all subsequent eruptions from April 1981 to December 1982 based on seismic and deformation data, leading to precise predictions without false alarms (
In contrast, the stealthy eruption presents a starkly different scenario compared to its observable counterpart, characterized by minimal detectable signals. During the pre-eruptive stage of a stealthy eruption (depicted in
The stealthy eruption cycle often evades early detection due to its subtle manifestations, posing challenges in monitoring and forecasting with current technological capabilities. The magma system can either be long-lived or transient. To produce stealthy eruptions, a lack of seismicity requires a large reservoir size, more oblate shape, and low flux, while low displacement requires a small reservoir size, more prolate shape, low flux, and a deeper chamber. Considering the host rock rheology, long-lived, thermally primed magma systems allow for a wider range of the parameter space to result in feasible scenarios for stealthy eruption as opposed to transient systems (
Many volcanoes that erupt without observed deformation have long been classified as open-system volcanoes (e.g.,
Should Veniaminof be considered stealthy, fed by a closed magmatic system? Some geophysical observations (lack of precursory seismicity and observations of ground deformation) and the frequent eruptions at Veniaminof may point to an open volcanic system. According to the volcanic activity summary by AVO (
The pattern of eruption frequency at Veniaminof does not strictly align with the open system hypothesis. Its historical explosive eruptions including those recent events in 2013, 1983, and 1956 (up to VEI 3,
Recent technological advancements in data collection and analysis have significantly enhanced our capabilities on volcano monitoring and forecasting. Yet, we are still facing complexities in volcano monitoring and forecasting, including the need for approaches that forecast not only the likelihood of an eruption but also its location, magnitude, style, duration, and potential for ash plumes that impact a long distance (
Observable eruptions exhibiting seismicity, deformation, and gas emissions, as depicted in
In scenarios where ground deformation remains undetected by GNSS and InSAR despite sufficient coverage of the volcanic edifice, it is important to recognize these techniques’ inherent limitations, which have been well documented (
In addition to ground-deformation techniques, infrasound monitoring can capture signals of volcanic activity that InSAR or GPS fail to detect, as inaudible low-frequency sound waves are generated by processes such as effusive eruptions and lava lake agitation near volcanic vents (
Enhancing future monitoring and forecasting capabilities for Veniaminof Volcano necessitates overcoming significant challenges posed by the existing technological limitations. The high-elevation, steep-slope terrain and snow-covered landscape of Veniaminof present formidable obstacles to detecting volcanic deformation via InSAR, primarily due to atmospheric noise interference and loss of coherence over the volcano summit. Possible strategies to enhance detection accuracy include enhancing InSAR coherence using long-wavelength SARs with much shorter temporal repeats and employing variogram modeling for precise simulation of residual atmospheric noise (
For stealthy volcanoes like Veniaminof and others in Alaska (e.g.,
Our comprehensive study on Veniaminof Volcano offers pivotal insights into the behavior and characteristics of “stealthy” volcanic eruptions: characterized by the absence of detectable seismic or geodetic precursors, despite the occurrence of an eruption. The numerical modeling results of Veniaminof Volcano, exemplifying stealthy volcanic eruptions within closed magmatic systems, illuminate key factors necessary for such eruptions that occur with minimal ground deformation and seismicity rate changes, based on a series of constraints on various parameter combinations, including magma chamber size, shape, depth, and magma flux rate, under both temperature-dependent and non-temperature-dependent host rock rheology.
Two critical conditions are a low magma flux rate and a warm rheology of the host rock. A reduced magma ascent rate ensures minimal stress on surrounding rock, limiting ground deformation and volcano-tectonic earthquakes. Warm rheology allows gradual magma movement and deformation within detectable thresholds, generating fewer seismic signals.
Veniaminof’s eruptive cycle, including pre-eruptive, co-eruptive, post-eruptive, and repose stages, provides a framework applicable to other volcanic systems globally. Insights from Veniaminof’s stealthy eruption guide future forecasts and highlight the need to integrate multidisciplinary data and numerical modeling for accurate predictions. This enhances risk mitigation strategies, reducing volcanic hazards' impact on communities. This study serves as a model for similar volcanoes and advances future monitoring and forecasting efforts in volcanology.
The original contributions presented in the study are included in the article/
YL: Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Validation, Visualization, Writing – original draft, Writing – review and editing. PG: Conceptualization, Funding acquisition, Methodology, Project administration, Supervision, Writing – original draft, Writing – review and editing. ZL: Conceptualization, Funding acquisition, Writing – original draft, Writing – review and editing. JW: Writing – original draft, Writing – review and editing.
The author(s) declare that financial support was received for the research and/or publication of this article. Investigations of volcanic unrest in the Aleutians is supported by grants from the U.S. National Science Foundation (EAR 1752477, EAR 2122745 – Gregg and Li) and NASA (80-NSSC19K-0357 – Gregg, Wang, and Lu).
The authors thank the anonymous reviewers and V. Acocella whose comments and discussions greatly improved the manuscript. We also thank R. Maguire, M. Loewan, M. Head, and C. Lundstrom for helpful discussions that greatly enhanced this investigation.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The author(s) declare that no Generative AI was used in the creation of this manuscript.
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
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