Axial Seamount is a basaltic hot spot volcano with a summit caldera at a depth of ∼1,500 m below sea level, superimposed on the Juan de Fuca spreading ridge, giving it a robust and continuous magma supply. Axial erupted in 1998, 2011, and 2015, and is monitored by a cabled network of instruments including bottom pressure recorders and seismometers. Since its last eruption, Axial has re‐inflated to 85%–90% of its pre‐eruption level. During that time, we have identified eight discrete, short‐term deflation events of 1–4 cm over 1–3 weeks that occurred quasi‐periodically, about every 4–6 months between August 2016 and May 2019. During each short‐term deflation event, the rate of earthquakes dropped abruptly to low levels, and then did not return to higher levels until reinflation had resumed and returned near its previous high. The long‐term geodetic monitoring record suggests that the rate of magma supply has varied by an order of magnitude over decadal time scales. There was a surge in magma supply between 2011 and 2015, causing those two eruptions to be closely spaced in time and the supply rate has been waning since then. This waning supply has implications for eruption forecasting and the next eruption at Axial still appears to be 4–9 years away. We also show that the number of earthquakes per unit of uplift has increased exponentially with total uplift since the 2015 eruption, a pattern consistent with a mechanical model of cumulative rock damage leading to bulk failure during magma accumulation between eruptions.
We present deformation measurements of the Kirishima volcanic complex from ALOS and ALOS‐2 Interferometric Synthetic Aperture Radar (InSAR) time series during 2006–2019. Shinmoe‐dake deflated ∼6 cm during the 2008–2010 phreatic eruptions and inflated ∼5 cm prior to the 2017 magmatic eruption. Iwo‐yama inflated ∼19 cm within the crater since January 2015 and ∼7 cm around the southern and western vents since 4 months before the 2018 eruption. These deformations can be modeled as ellipsoids at ∼700 m depth beneath Shinmoe‐dake and as a sphere on top of an ellipsoid at ∼130 and ∼340 m depths beneath Iwo‐yama. Combining geodetic, geoelectric, geochemical, and petrological analysis, we interpret the hydrothermal origin of the deflation at Shinmoe‐dake and inflation at Iwo‐yama; the hydrothermal–magmatic transition during the 2011 Shinmoe‐dake eruption; and water‐boiling and bottom‐up pressurization as driving mechanisms of the inflation at Iwo‐yama. The study highlights the imaging potential of InSAR time series on complex hydrothermal systems.
more » « less- NSF-PAR ID:
- 10375049
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 11
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Axial Seamount is an active submarine volcano located at the intersection of the Cobb hot spot and the Juan de Fuca Ridge (45°57′N, 130°01′W). Bottom pressure recorders captured co‐eruption subsidence of 2.4–3.2 m in 1998, 2011, and 2015, and campaign‐style pressure surveys every 1–2 years have provided a long‐term time series of inter‐eruption re‐inflation. The 2015 eruption occurred shortly after the Ocean Observatories Initiative (OOI) Cabled Array came online providing real‐time seismic and deformation observations for the first time. Nooner and Chadwick (2016,
https://doi.org/10.1126/science.aah4666 ) used the available vertical deformation data to model the 2015 eruption deformation source as a steeply dipping prolate‐spheroid, approximating a high‐melt zone or conduit beneath the eastern caldera wall. More recently, Levy et al. (2018,https://doi.org/10.1130/G39978.1 ) used OOI seismic data to estimate dip‐slip motion along a pair of outward‐dipping caldera ring faults. This fault motion complicates the deformation field by contributing up to several centimeters of vertical seafloor motion. In this study, fault‐induced surface deformation was calculated from the slip estimates of Levy et al. (2018,https://doi.org/10.1130/G39978.1 ) then removed from vertical deformation data prior to model inversions. Removing fault motion resulted in an improved model fit with a new best‐fitting deformation source located 2.11 km S64°W of the source of Nooner and Chadwick (2016,https://doi.org/10.1126/science.aah4666 ) with similar geometry. This result shows that ring fault motion can have a significant impact on surface deformation, and future modeling efforts need to consider the contribution of fault motion when estimating the location and geometry of subsurface magma movement at Axial Seamount.
