The Proceedings of the Eighth International Conference on Creationism (2018)

measurements, this locking and episodic unlocking and slip of the overriding plate takes place even as the subducting plate is moving continuously downward into the mantle below. Relative motion between the subducting plate and overriding plate occurs only during these extremely brief episodes as the two plates suddenly unlock and slide rapidly past each other. In almost all cases today the episode of slip produces an earthquake and often also a tsunami. In the context of the Flood, when the plates were moving approximately a billion times faster than they are at present, a crucial issue is the nature of the subduction zone mechanics. Currently, no one has yet undertaken a careful numerical investigation of the dynamics in these zones under such conditions. Despite the consequent uncertainties, the approach taken in this study is to assume that subduction zone behavior during the Flood resembled that of today. That assumption is likely to be valid if during the Flood the plates remained cool enough to behave elastically and therefore stored substantial elastic energy as they do today. To me that is plausible. Studies of plate motions during the Flood yield plate speeds on the order of 2 m/s (Baumgardner 1994; Baumgardner 2003). Using that horizontal speed for the subducting plate and assuming a subduction angle of 45° implies that the ocean bottom in the subduction zone is being pulled downward at a speed of 2 m/s sin (45°) = 1.4 m/s. If the locking persists for 96 minutes (5,760 s), the sea bottom is depressed by more than 8,000 m. Sudden unlocking and slip between the overriding plate and the subducting plate will cause the sea bottom to rise by that height, unleashing a huge tsunami. Globally during the Flood, it is likely that subduction zones were comparable in linear extent as today, on the order of 50,000 km. If, as shall be assumed, at any given time there are only 16 active subduction zone segments, each 1,500 km in length, for a total active length of 24,000 km, and if each of these segments locked and slipped every 96 minutes, this would imply 10 mega- tsunamis unleashed each hour, 240 each day, and 36,000 over the course of five months in the world’s ocean basins. These are the tsunami parameters assumed for the calculation reported in the results section below. However, the length of the zones that unlock and slip in today’s world typically is much less than 1,500 km. If, in reality, during the Flood it was only 750 km on average, then keeping the locking time the same would increase the total number of events to 480 each day and 72,000 over a span of five months. The erosive power of these waves as they strike the continental margins and then race largely unhindered across the continental surface is difficult for the human mind to imagine. The turbulence where the water is relatively shallow over the continental surface is strong enough to maintain many tens of m of sediment in suspension. Turbulence is the physical mechanism that enables the suspension and makes possible the long-distance transport of the sediment. Subsequent discussion of the numerical results reveals that these processes are readily adequate to account for major aspects of the Flood sediment record. 1. Mathematical framework Prominent features of the sediment record suggest that sheets of turbulent water sweeping over the continent surface must have played a key role. Such water motion is in the general category of turbulent boundary layer flow, which is one of great practical interest and one that has been studied experimentally for many years. In the hydrologic engineering community, this type of water flow is referred to as open channel flow. Examples of open channel flows include rivers, tidal currents, irrigation canals, and sheets of water running across the ground surface after a rain. The equations commonly used to model such flows are anchored in experimental measurements and decades of validation in many diverse applications. It is the turbulence of the flowing water in such flows that keeps the sediment particles in suspension. The Journal of Hydraulic Engineering is but one of several journals that has published a wealth of papers on turbulent open channel flow and sediment transport over the past many decades. Appendix A in Baumgardner (2016) summarizes the observations, experiments, and efforts to formulate a mathematical description of fluid turbulence over the past two centuries. A description of turbulent fluid flow provided almost a century ago by the British scientist L. F. Richardson (1920) is still valid today. His description is a flowwhose motions are characterized by a hierarchy of vortices, or eddies, from large to tiny. These eddies, including the large ones, are unstable. The shear that their rotation exerts on the surrounding fluid generates smaller new eddies. The kinetic energy of the large eddies is thereby passed to the smaller eddies that arise from them. These smaller eddies in turn undergo the same process, giving rise to even smaller eddies that inherit the energy of their predecessors, and so on. In this way, the energy is passed down from the large scales of motion to smaller and smaller scales until reaching a length scale sufficiently small that the molecular viscosity of the fluid transforms the kinetic energy of these tiniest eddies into heat. When a fluid is moving relative to a fixed surface, the speed of the fluid, beginning from zero at the boundary, increases—first rapidly, and then less rapidly—as distance from the surface increases. The region adjacent to the surface in which the average speed of the flow parallel to the surface is still changing, at least modestly, as one moves away from the surface is known as the boundary layer. When the speed of the fluid over the surface is sufficiently high, the boundary layer becomes turbulent and becomes filled with eddies that can span a broad range of spatial scales. Appendix B in Baumgardner (2016) summarizes some of the prominent features of turbulent boundary layers, including the discovery that the mean velocity profile within the turbulent boundary layer is very close to a logarithmic function of distance from the boundary. Remarkably, the parameters specifying the profile can be determined merely from the thickness of the layer and its mean flow speed. The theory of open channel flow applies this mathematical representation of a turbulent boundary layer to describe sediment suspension, transport, and deposition by turbulent water flow for cases where the width of the flow is much greater than the water depth. Appendix C in Baumgardner (2016) provides the derivation of a mathematical expression for the sediment carrying capacity of a layer of turbulent water as a function of sediment particle size. This expression is utilized in the numerical treatment to quantify the sediment suspension of the water flow. The expression requires the particle settling speed for each of the particle sizes that is assumed in the model. Appendix D in Baumgardner (2016) describes how these settling speeds may be obtained via empirical fits to experimental data. Obviously, a prominent issue in the formation of the earth’s sediment record is the origin of the sediment. From the rock record it is clear that there were pre-Flood continental sediments. However, for sake of simplicity, these sediments are ignored in the current version of the model. Instead, it is assumed that all the sediment deposited is derived from erosion of continental bedrock. In terms of erosional processes, I restrict the scope to the mechanism of cavitation, Baumgardner ◀ Large tsunamis and the Flood sediment record ▶ 2018 ICC 290