Abstract
Abstract. Theoretical source models of underwater explosions are often applied in studying tsunami hazards associated with subaqueous volcanism; however, their use in numerical codes based on the shallow water equations can neglect the significant dispersion of the generated wavefield. A non-hydrostatic multilayer method is validated against a laboratory-scale experiment of wave generation from instantaneous disturbances and at field-scale subaqueous explosions at Mono Lake, California, utilising the relevant theoretical models. The numerical method accurately reproduces the range of observed wave characteristics for positive disturbances and suggests a relationship of extended initial troughs for negative disturbances at low-dispersivity and high-non-linearity parameters. Satisfactory amplitudes and phase velocities within the initial wave group are found using underwater explosion models at Mono Lake. The scheme is then applied to modelling tsunamis generated by volcanic explosions at Lake Taupō, New Zealand, for a magnitude representing an ejecta volume of 0.1 km3. Waves reach all shores within 15 min with maximum incident crest amplitudes around 0.2 m at shores near the source. This work shows that the multilayer scheme used is computationally efficient and able to capture a wide range of wave characteristics, including dispersive effects, which is necessary when investigating subaqueous explosions. This research therefore provides the foundation for future studies involving a rigorous probabilistic hazard assessment to quantify the risks and relative significance of this tsunami source mechanism.
Highlights
Subaqueous eruptions are poorly understood volcanic phenomena that can generate hazardous tsunamis
Accompanying models used for validation and comparative purposes include a Navier–Stokes volume-of-fluid (NS/VOF) method in the same framework which solves the two-phase Navier–Stokes equations for interfacial flows, including variable density and surface tension (Popinet, 2009, 2018), a solver for the shallow water or Saint-Venant (SV) equations, and another for the Serre–Green– Naghdi equations (SGN), a Boussinesq higher-order approximation for non-linear and weakly dispersive flows (Popinet, 2015)
The non-hydrostatic multilayer scheme used in this paper has been shown to accurately replicate the collapse of various initial disturbances into a resultant wavefield that exhibits varying degrees of non-linear properties and frequency dispersion
Summary
Subaqueous eruptions are poorly understood volcanic phenomena that can generate hazardous tsunamis. Numerical solutions often either utilise the empirically derived relations without validating their use in a numerical scheme against a suitable explosive physical experiment or test a generation mechanism in the local spatial range only at the cost of neglecting investigation of the generated wave field Often, models such as those based on non-linear shallow water equations are applied to these problems without considering how dispersive the resultant waves may be (Paris and Ulvrová, 2019). Data from one of the last military explosive test series focused on surface wave observations is compared with results produced by implementing the theoretical model’s initial conditions in the numerical method These tests are to establish the fitness of the underlying models, which are applied to a hypothetical explosive subaqueous eruption at Lake Taupo, New Zealand, to provide an example of how these models can be used
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