2018. The scheme chosen here provides much more aggressive and realistic compensation. It applies 20% compensation for loads less than 200 m and increases to 50% compensation for the portion of the load between 200 m and 500 m. For the portion of load in excess of 500 m, 80% compensation is applied. Moreover, symmetrical compensation is implemented for the negative loads produced by material removed by bedrock erosion. Note that the compensation is instantaneous and that the fraction of compensation increases with increasing sediment load height. The assumption that the compensation is instantaneous would, at first, seem difficult to justify, even as an approximation. However, when one takes into account the extreme reduction in rock strength throughout the mantle caused by the stress weakening mechanism associated with runaway lithospheric slabs and mantle plumes, it becomes more plausible. Dynamical calculations show that the weakening, which starts in the vicinity of a slab or plume that is entering the runaway regime, quickly spreads to encompass the entire mantle. The reduction in rock strength throughout the mantle then approaches a factor of a billion. This reduction in rock strength also affects the lithosphere. It implies that a rapid response of the continental lithosphere to surface loading during the Flood while the mantle is in its weakened state is likely. To describe the water flow over the earth in a quantitative way, the numerical model makes use of what is known as the shallow water approximation. This approximation requires that the water depth everywhere be small compared with the horizontal scales of interest. The depth of the ocean basins today—and presumably also during the Flood—is about four kilometers. By contrast, the horizontal grid point spacing of the computation grid for the case described in this paper is about 60 km, half that of the 2018 studies. The expected water depths over the continental regions, where our main interest lies, are yet much smaller than those of the ocean basins. Hence the shallow water approximation is entirely appropriate for this problem. That approximation allows the water flow over the surface of the globe to be described in terms of a single layer of water with laterally varying thickness. What otherwise would be an expensive three-dimensional problem now becomes a much more tractable two-dimensional one. Appendix G in Baumgardner (2018a) outlines the mathematical approach for solving the shallow water equations for the water velocity and water height over the surface of the earth as a function of time. These equations express the conservation of mass and the conservation of linear momentum. They are solved in a discrete manner using what is known as a semi-Lagrangian approach on a mesh constructed from the regular icosahedron as shown in Fig. 1 of Baumgardner (2018a). In this numerical treatment, a separate spherical coordinate system is defined at each grid point in the mesh such that the equator of the coordinate system passes through the grid point and the local longitude and latitude axes are aligned with the global east and north directions. The semi-Lagrangian approach, because of its low levels of numerical diffusion (Staniforth and Cote 1991), is also used for horizontal sediment transport. Over the continents seven layers of fixed thickness are used to resolve the sediment concentration in the vertical direction, with thinner layers at the bottom and thicker layers at the top of the column. This semi-Lagrangian method in the framework of the icosahedral mesh using local spherical coordinates has been applied and validated in one of the world’s foremost numerical weather forecast models, a model known originally as GME and now ICON (for icosahedral non-hydrostatic), developed by the German Weather Service in the late 1990s (Majewski et al. 2002). The code that incorporates these many numerical features specifically for modeling the hydrological aspects of the Genesis Flood has been named ‘MABBUL.’ That word, of course, is the one used exclusively for the Flood in the Hebrew Old Testament. B. Accounting for continent motion history The original study (Baumgardner 2013) as well as a subsequent one (Baumgardner 2018a) utilized a single static continent. The study reported at the previous ICC (Baumgardner 2018b) added a displacement history for the various continental blocks spanning, in terms of geological nomenclature, the Paleozoic, Mesozoic, and Cenozoic eras, that is, the portion of the geological record formed during the Flood. It is to be noted that, while the reconstruction of continent motions since the early Mesozoic has relatively small uncertainty because of the abundance of constraints from the present-day ocean floor, the motions during the Paleozoic typically have much more uncertainty because of the lack of surviving Paleozoic seafloor. The primary observational data for recovering the Paleozoic continent motions therefore are from paleomagnetism. Magnetic minerals in igneous rocks, provided that the rocks have not been significantly reheated since they crystalized, can record the orientation of the earth’s magnetic field when the rocks crystallized. By measuring the magnetic declination and inclination in suitable igneous rocks from many points through the geological record for a given continent, one can construct a paleolatitude history for the continent. This procedure unfortunately provides no information on paleolongitude. Paleomagnetic determinations were first undertaken in the late 1940s. By the early 1950s paleomagnetic ‘polar wander paths’ for Europe and North America were being published showing that both continents, relative to today’s North Pole, had seemingly migrated northward dramatically since the mid-Paleozoic—by many tens of degrees. At the time this created quite a stir in the earth science community. In the decade of the 1960s, these paleomagnetic determinations helped convince many in the community that plates and plate mobility are indeed genuine realities. In subsequent decades more detailed and comprehensive paleomagnetic studies continued to reveal that same large amount of northward motion of Europe and North America relative to today’s North Pole. The current estimated amount of northward motion is about 110°. From the vast number of paleomagnetic determinations now available from all the continents, secular geoscientists have been able to reconstruct the history of continental motion during the Paleozoic to what they believe to be a reasonable level of confidence despite the lack of strong longitude constraints in the paleomagnetic measurements. Several secular authors (e.g., Scotese 2021; Blakey 2008) have now published continent motion histories that span the neo-Proterozoic to present. The work described in this present paper draws upon global paleogeography maps by both Scotese (2021) and Blakey (2008) as guides to that continent motion history. Fig. 3(a) is Blakey’s map BAUMGARDNER AND NAVARRO Large tsunamis and Flood sediment record 2023 ICC 368
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