An official website of the United States government
Abstract Extensive vertical deformation (>4.5 m) observed at Sierra Negra volcano Galápagos, Ecuador, between 1992 and the 2005 eruption led scientists to hypothesize that repeated faulting events relieved magma chamber overpressure and prevented eruption. To better understand the catalyst of the 2005 eruption, thermomechanical models are used to track the stress state and stability of the magma storage system during the 1992–2005 inflation events. Numerical experiments indicate that the host rock surrounding the Sierra Negra reservoir remained in compression with minimal changes in overpressure (~10 MPa) leading up to the 2005 eruption. The lack of tensile failure and minimal overpressure accumulation likely inhibited dike initiation and accommodated the significant inflation without the need for pressure relief through shallow trapdoor faulting events. The models indicate that static stress transfer due to the Mw5.4 earthquake 3 hr prior to the eruption most likely triggered tensile failure and catalyzed the 2005 eruption.
more »
« less
How Accurately Can We Model Magma Reservoir Failure With Uncertainties in Host Rock Rheology?
Abstract Forecasting the onset of a volcanic eruption from a closed system requires understanding its stress state and failure potential, which can be investigated through numerical modeling. However, the lack of constraints on model parameters, especially rheology, may substantially impair the accuracy of failure forecasts. Therefore, it is essential to know whether large variations and uncertainties in rock properties will preclude the ability of models to predict reservoir failure. A series of two‐dimensional, axisymmetric models are used to investigate sensitivities of brittle failure initiation to assumed rock properties. The numerical experiments indicate that the deformation and overpressure at failure onset simulated by elastic models will be much lower than the viscoelastic models, when the timescale of pressurization exceeds the viscoelastic relaxation time of the host rock. Poisson's ratio and internal friction angle have much less effect on failure forecasts than Young's modulus. Variations in Young's modulus significantly affect the prediction of surface deformation before failure onset when Young's modulus is < 40 GPa. Longer precursory volcano‐tectonic events may occur in weak host rock (E< 40 GPa) due to well‐developed Coulomb failure prior to dike propagation. Thus, combining surface deformation with seismicity may enhance the accuracy of eruption forecast in these situations. Compared to large and oblate magma systems, small and prolate systems create far less surface uplift prior to failure initiation, suggesting that more frequent measurements are necessary.
more »
« less
- PAR ID:
- 10375035
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 124
- Issue:
- 8
- ISSN:
- 2169-9313
- Page Range / eLocation ID:
- p. 8030-8042
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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.more » « less
-
null (Ed.)Ensemble based data assimilation approaches, such as the Ensemble Kalman Filter (EnKF), have been widely and successfully implemented to combine observations with dynamic forecast models. In this study the EnKF is adapted to assimilate ground deformation observations from interferometric synthetic-aperture radar (InSAR) and GPS into thermomechanical finite element models (FEM) to evaluate volcanic unrest. Two eruption hindcasts are investigated: the 2008 eruption of Okmok volcano, Alaska and the 2018 eruption of Sierra Negra volcano, Galápagos, Ecuador. At Okmok, EnKF forecasts tensile failure and the lateral movement of the magma from a central pressure source in the lead up to its 2008 eruption indicating potential for diking. Alternatively, at Sierra Negra, the EnKF forecasts significant shear failure coincident with a Mw 5.4 earthquake that preceded the 2018 eruption. These successful hindcasts highlight the flexibility and potential of the volcano EnKF approach for near real time monitoring and hazard assessment at active volcanoes worldwide.more » « less
-
This article presents a study of seismically-induced failure of massive steep rock slopes. A dynamic implementation of the bonded particle model (BPM) for rock is used to simulate the dynamic response and initiation of fracture in the slopes. Observation of forces that develop within the model in response to wave transmission and dynamic excitation provides insight into the fundamental mechanisms at work in seismically induced rock slope failure. Five distinct mechanisms of failure initiation are identified using non-destructive simulations and confirmed with destructive simulations. Three distinct modes of rock mass movement enabled by the failure mechanisms are identified. The predominant co-seismic failure mode was a shallow, highly-disrupted cliff collapse. Cliff collapse is initiated by relatively low levels of shaking. Shallow failures are also triggered at higher levels of shaking prior to the initiation of deeper, more coherent failures in the same seismic event. The results of the numerical study agree with qualitative historical surveys of seismically-induced rock slope failure trends and provide insight into the mechanisms behind observed co-seismic rock slope behavior. The frequently observed shallow failures are triggered by high compression stresses near the cliff toe combined with shallow subhorizontal ruptures behind the cliff face. These mechanisms are not well-captured by simplified analysis methods which may lead to underprediction of shallow co-seismic events. Deeper failure surfaces from stronger shaking create a base-isolation effect, slowing further disruption in the failure mass. Slope dynamic response and damage accumulation were shown to be interdependent and complex, emphasizing the importance of further research into the interaction between rock mass strength, slope geometry, structure, and ground motion characteristics.more » « less
-
Fabricating micro and nanosized structures to induce hemiwicking on a heated surface has risen in popularity due to the higher heat flux the surface can experience. Recent studies have focused on the effects on the pillar geometry and spacing on the wicking velocity and the critical heat flux. As a result, a majority of the models that have been derived focus on the fluid properties and the wicking structure geometry and spacing. This study presents changes to the wicking performance when the stiffness of a soft material is taken into effect. Multiple similar wicking structures were fabricated using a negative mold method utilizing an in-house stamping apparatus. Using the mold, multiple polydimethylsiloxane (PDMS) samples were created, where the stiffness of the samples was varied by altering the mixing ratio and the curing time. The wicking velocity of ethanol, isopropyl alcohol, and isooctane did not vary for the samples that had a Young's Modulus greater than 1 MPa, but a notable decrease in the wicking velocity for all three fluids were observed for samples with a Young's Modulus less than 1 MPa. This study provides insight to the importance of the stiffness of the material is for hemiwicking on soft materials and that deformation effects have to be taken into account for Young's Moduli less than 1 MPa.more » « less
