Contention between supply of hydrothermal fluid and conduit obstruction: inferences from numerical simulations

Abstract

We investigate a volcanic hydrothermal system using numerical simulations, focusing on change in crater temperature. Both increases and decreases in crater temperature have been observed before phreatic eruptions. We follow the system's response for up to a decade after hydrothermal fluid flux from the deep part of the system is increased and permeability is reduced at a certain depth in a conduit. Our numerical simulations demonstrate that: (1) changes in crater temperature are controlled by the magnitude of the increase in hydrothermal fluid flux and the degree of permeability reduction; (2) significant increases in hydrothermal flux with decreases in permeability induce substantial pressure changes in shallow depths in the edifice and decreases in crater temperature; (3) the location of maximum pressure change differs between the mechanisms. The results of this study imply that it is difficult to predict eruptions by crater temperature change alone. One should be as wary of large eruptions when crater temperature decreases as when crater temperature increases. It is possible to clarify the implications of changes in crater temperature with simultaneous observation of ground deformation.

Influence of permeability on the hydrothermal system at Vulcano Island (Italy): inferences from numerical simulations

“…In recent decades, a number of efforts have been made to improve the comprehension of the interplay between fluid flow and mechanical rock response (Chiodini et al 2016;Ingebritsen et al 2010;Rinaldi et al 2010;Tanaka et al 2018;Troiano et al 2011). Thermo-poro-elastic approaches, coupling fluid flow and rock strain, have been explored in several volcano geothermal areas, which have demonstrated the important role of elastic and transport properties in leading to changes in geochemical and geophysical observables at the surface related to hydrothermal activity (Chiodini et al 2016;Peiffer et al 2018;Rinaldi et al 2010;Tanaka et al 2018). Vulcano Island, whose hydrothermal activity has been characterized by different unrest phases since 1890, when the last eruption occurred (Paonita et al 2013;Selva et al 2020), may well be considered a representative case.…”

Observing Posteruptive Deflation of Hydrothermal System Using InSAR Time Series Analysis: An Application of ALOS‐2/PALSAR‐2 Data on the 2015 Phreatic Eruption of Hakone Volcano, Japan

“…Additionally, A and b are empirically derived parameters that express the rheological properties of the compacting layer: A is a scalar associated with the magnitude of creep compaction, and b is related to the apparent viscosity of the system (Todesco et al., 2014). The initial thickness h 0 was set to 500 m, considering the structure beneath the bell‐shaped conductor where the posteruptive deflation source is located (Seki et al., 2021; Figure 4), and the porosity ϕ 0 was set to 0.1 as a typical value used for simulations of hydrothermal systems (e.g., Tanaka et al., 2018). The other parameters were estimated by fitting, assuming that the LOS displacements were entirely in the vertical direction.…”

Special issue “Towards forecasting phreatic eruptions: examples from Hakone volcano and some global equivalents”

“…Simulations can examine the influence of a simple key mechanism on the subsequent complex behavior of the volcanic system. In this special issue, two contributions document simple-but-insightful simulation experiments (Noguchi et al 2018;Tanaka et al 2018). Noguchi et al (2018) focused on rootless eruptions caused by lava flows entering inland water or water-rich sediment.…”

“…Their unique analogue experiment using cooking ingredients such as syrup and baking powder shows a non-linear relationship between reaction efficiency and baking soda/poured heated syrup (= water/lava) proportion which may stem from a Rayleigh-Taylor instability occurring between lava and substrate water or sediment. Tanaka et al (2018) implemented a numerical simulation of a conduit system, through which hydrothermal fluid reaches the surface, and monitored crater temperature and pressure distribution of the edifice interior after changing the permeability of the conduit. The simulation showed how crater temperature can decrease before a phreatic eruption.…”