An official website of the United States government
Abstract Explosive volcanic eruptions radiate seismic waves as a consequence of pressure and shear traction changes within the conduit/chamber system. Kinematic source inversions utilize these waves to determine equivalent seismic force and moment tensor sources, but relation to eruptive processes is often ambiguous and nonunique. In this work, we provide an alternative, forward modeling approach to calculate moment tensor and force equivalents of a model of eruptive conduit flow and chamber depressurization. We explain the equivalence of two seismic force descriptions, the first in terms of traction changes on conduit/chamber walls, and the second in terms of changes in magma momentum, weight, and momentum transfer to the atmosphere. Eruption onset is marked by a downward seismic force, associated with loss of restraining shear tractions from fragmentation. This is followed by a much larger upward seismic force from upward drag of ascending magma and reduction of magma weight remaining in the conduit/chamber system. The static force is upward, arising from weight reduction. We calculate synthetic seismograms to examine the expression of eruptive processes at different receiver distances. Filtering these synthetics to the frequency band typically resolved by broadband seismometers produces waveforms similar to very long period seismic events observed in strombolian and vulcanian eruptions. However, filtering heavily distorts waveforms, accentuating processes in early, unsteady parts of eruptions and eliminating information about longer (ultra long period time scale depressurization and weight changes that dominate unfiltered seismograms. Our workflow can be utilized to directly and quantitatively connect eruption models with seismic observations.
more »
« less
This content will become publicly available on April 1, 2026
Inferring Eruption Dynamics From Seismometer Tilt: A Case Study of Erebus and Augustine Volcanoes
Abstract Broadband seismometers are sensitive to tilt as a consequence of their design. We used broadband data from Erebus volcano on Ross Island, Antarctica, and Augustine volcano in Lower Cook Inlet, Alaska, to make tilt measurements associated with individual volcanic explosions and investigate the near‐terminal magmatic system configuration of each volcano. At Erebus volcano we found no evidence of tilt associated with the classic Strombolian eruptions from the lava lake. Tilt has been observed preceding Strombolian eruptions at volcanoes. The lack of tilt at Erebus is evidence that its conduit system lacks sufficient viscous plugging or mechanical restrictions to generate slug‐transport or explosion‐related forces large enough to produce measurable tilt. At Augustine volcano we measured tilt changes associated with 13 events during the explosive phase of its 2006 eruption. We used the tilt changes to invert for a dual deformation source model of a depressurizing open conduit above a depressurizing prolate spheroid. This deflation source geometry is in agreement with an existing magmatic system model developed from petrologic, seismic, and Global Positioning System data. This further supports this model while highlighting the capabilities of seismometer ground tilt measurements as independent model constraints.
more »
« less
- Award ID(s):
- 1916978
- PAR ID:
- 10596972
- Publisher / Repository:
- AGU
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 130
- Issue:
- 4
- ISSN:
- 2169-9313
- Subject(s) / Keyword(s):
- Eruption Seismology Tilt Erebus Augustine
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Erebus volcano, Antarctica, with its persistent phonolite lava lake, is a classic example of an evolved, CO 2 -rich rift volcano. Seismic studies provide limited images of the magmatic system. Here we show using magnetotelluric data that a steep, melt-related conduit of low electrical resistivity originating in the upper mantle undergoes pronounced lateral re-orientation in the deep crust before reaching shallower magmatic storage and the summit lava lake. The lateral turn represents a structural fault-valve controlling episodic flow of magma and CO 2 vapour, which replenish and heat the high level phonolite differentiation zone. This magmatic valve lies within an inferred, east-west structural trend forming part of an accommodation zone across the southern termination of the Terror Rift, providing a dilatant magma pathway. Unlike H 2 O-rich subduction arc volcanoes, CO 2 -dominated Erebus geophysically shows continuous magmatic structure to shallow crustal depths of < 1 km, as the melt does not experience decompression-related volatile supersaturation and viscous stalling.more » « less
-
The intensity of explosive volcanic eruptions is correlated with the amplitude of eruption tremor, a ubiquitously observed seismic signal during eruptions. Here we expand upon a recently introduced theoretical model that attributes eruption tremor to particle impacts and dynamic pressure changes in the turbulent flow above fragmentation (Gestrich et al., 2020). We replace their point source model with Rayleigh wave Green's functions with full Green's functions and account for depth variation of input fields using conduit flow models. The latter self-consistently capture covariation of input fields like particle velocity, particle volume fraction, and density. Body wave contributions become significant above 2-3 Hz, bringing the power spectral density (PSD) closer to observations. Conditions at the vent are not representative of flow throughout the tremor source region and using these values overestimates tremor amplitude. Particle size and its depth distribution alter the PSD and where dominant source contributions arise within the conduit. Solutions with decreasing mass eruption rate, representing a waning eruption, reveal a shift in the dominant tremor contribution from turbulence to particle impacts. Our work demonstrates the ability to integrate conduit flow modeling with volcano seismology studies of eruption tremor, providing an opportunity to link observations to eruptive processes.more » « less
-
Abstract At Stromboli Volcano, Italy, very long period (VLP) seismic signals and Strombolian eruptions have been attributed to the unsteady flow of gas slugs through the shallow plumbing system followed by explosive slug bursting at a free surface. In data from a 2018 seismo‐acoustic deployment, ∼92% of events in two main VLP multiplets do not coincide in time with impulsive infrasonic signals (the expected signal of explosive slug bursting); we term these “silent VLPs.” The lack of infrasonically detected explosions relative to repeating VLPs does not support the commonly invoked “gas slug” model. We propose that VLPs may be generated when gas bubbles move into a weak semi‐solid plug in the uppermost portion of the conduit. The plug then acts as a mechanical filter in which pathways vary and guide or trap ascending gas slugs, allowing for passive (silent) gas release and explosive escape mechanisms decoupled in time from VLPs.more » « less
-
Abstract Volcanic summit craters are typically noted to form by roof collapse into a depressurized magma chamber or by explosive excavation. Recent examples of effusive activity (e.g., Kilauea Volcano, Hawai'i) allowed specifically for quantification of the collapse process. However, small spatiotemporal morphologic change related to background mass wasting and low‐level explosive activity has not been well quantified in volcanic craters. Telica volcano, Nicaragua, is a persistently restless basaltic‐andesite stratovolcano. Telica's persistent restlessness is caused by a long‐lived magmatic‐hydrothermal system with high‐temperature crater fumaroles and low‐frequency seismicity, punctuated by subdecadal, low‐explosivity (VEI 1–2) phreatic eruptions. We use photographic observations (1994 to 2017) and structure‐from‐motion point cloud construction and differencing (2011 to 2017) to analyze changes at Telica in the context of summit crater formation and eruptive precursors. Crater wall retreat (up to 40 m) spatially correlates with long‐lived high‐temperature fumaroles in the crater walls, whereas eruptions eject material (>5 m) from the crater floor through vent formation and/or clearing. These processes sustain a morphology similar to that of pit craters but without a shallow depressurized magma chamber. Our observations indicate system‐wide sealing prior to eruption by viscous magma in the conduit and eruption of a dome in 2017 and hydrothermal mineralization, not from vent covering talus; though, vent covering talus can redirect the shallow conduit. This study shows promise for photogrammetric techniques in correlating morphologic change with summit crater formation and volcanic activity and the power of long‐term visual observations in understanding active volcanic processes.more » « less
