Numerical Modeling of Long Waves from Atypical Sources: Atmospheric Disturbances and Volcanic Origin

Doğan Bingöl, Gözde Güney
Earthquakes are the main cause mechanisms of tsunamis and large tsunamigenic earthquakes, especially in the subduction zones, occur on relatively much shorter timescales, but destructive tsunamis are also produced by volcanic eruptions, which have been threatening the coastal communities throughout history. Furthermore, while earthquake-generated tsunamis have been studied immensely, there is less focus on research related to tsunamis induced by atmospheric disturbances (meteotsunamis). Consequently, this study focuses on numerical modeling of long waves (tsunamis and meteotsunamis) sourcing from those atypical origins, volcanic activities and atmospheric disturbances and investigates the complex mechanisms behind them. Initially, scenario-based research for the numerical modeling of the December 2018 Gunung Anak Krakatau tsunami was conducted to investigate the possible source mechanisms and their contribution to explaining the observed sea level disturbances. A flank collapse (partial destabilization of the volcano) scenario was suggested appearing capable of generating the observed tsunami along the coast of the affected area, Sunda Strait. Coupling of a two-layer landslide model and a hydrodynamic model was performed to test the ability of such an implementation to reproduce a recent and large-scale volcanic eruption induced tsunami via post-tsunami field survey observations and tide gauge record comparisons. Secondly, the long wave generation and amplification induced by spatial and temporal changes of the atmospheric pressure disturbance is numerically solved by introducing pressure and wind field terms to the nonlinear shallow water equations. Several numerical tests are conducted to compare against a new analytical solution for meteotsunami generation in water channels of quasi-parabolic shape (including triangular cross-section) and satisfactory results with less than 1% error are achieved. Furthermore, the possible wave amplification factors, oceanographic and hydrodynamic, are investigated via more than 500 simulations based on different basin configurations and pressure field characteristics, prepared with the “isolation of parameter” principle in mind. The influence of the wind field characteristics, which is the other contributing forcing mechanism in meteotsunami generation but lacks sufficient coverage in literature, on the wave response is also discussed based on several numerical tests. The relationships between the parameters and the possible wave amplification mechanisms are discussed based on the empirical curves derived from the simulation results. Finally, the propagation of the air pressure waves induced by the January 2022 Hunga Tonga-Hunga Ha’apai volcanic explosion and the consequent sea waves are modeled globally. Two different modeling approaches are proposed to solve the air pressure propagation: i) development of a synthetic pressure model based on barometric measurements and ii) implementation of the nonlinear shallow-water theory using an initial disturbance at the volcano. Then, the hydrodynamic model was forced with the produced pressure fields to compute the resulting tsunami waves in the Pacific Ocean, the Caribbean and the Mediterranean. The modeling results are presented with discussions on the possible sea level amplification mechanisms. Fairly well agreement between the computed and measured air pressure waves and sea levels at several locations around the globe is promising for explaining the far reach and long duration of the tsunami generated by the Hunga Tonga-Hunga Ha'apai eruption. The suggested novel approaches can be alternative modeling applications for such phenomena with the efficient utilization of global data available for such an event for the first time.


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Citation Formats
G. G. Doğan Bingöl, “Numerical Modeling of Long Waves from Atypical Sources: Atmospheric Disturbances and Volcanic Origin,” Ph.D. - Doctoral Program, Middle East Technical University, 2022.