For a strip 1 m in width, we find that the amount of sediment per second required to be entering the left boundary is (106 m) x (1 m) x (1.4x10-4 m/s) = 140 m3/s. If this sediment is being transported by water moving to the right at a speed of 20 m/s, the water column on the left edge must be transporting a vertical equivalent of 7 m of suspended sediment. At a distance of 500 km from the left edge the water column must be transporting 3.5 m vertical equivalent of suspended sediment. The amount drops to zero at the right edge. The percentage of sediment that a moving water column can maintain in suspension is typically 5-10% or less (Pierson 2005). Let us choose a value of 7%. This implies that at the left edge in this thought experiment the water column must be on the order of 7 m/0.07 =100 m (330 ft) high. Note that the deposition rate 1.4x10-4 m/s used above was the time average over the entire 150-day ‘prevailing’ stage of the cataclysm and spatially averaged over the entire continental portion of the earth’s surface. When the likelihood of significant time variation is taken into account, the peak sediment and water column heights are substantially higher. When the mechanism involves episodic tsunamis, the water column heights of necessity become much larger. Approximating each tsunami as a step function pulse one-fourth the duration of the interval between tsunamis means that the height of the water column during the pulse is four times the average value. Such estimates are difficult for the human mind even to conceive. It is not easy to imagine pulses of water 400 m (1300 ft) high, carrying some 28 m of sediment in suspension, moving at 20 m/s (45 mph) across the continental surface of the earth, depositing on average 12 m (39 feet) of new sediment each day for a time span of 150 days. Yet that is the sort of water process the fossil-bearing sedimentary record we observe on the continents today constrained by the time scale of the Genesis text seems to demand! This is the glaring challenge that this research effort is endeavoring to resolve. This challenge prompted the first author about twelve years ago to pursue a numerical modeling strategy as a beginning attempt to address the issue. Two previous papers (Baumgardner 2013; Baumgardner 2018a) documented the mathematical underpinnings and numerical methods in moderate detail. In brief, the approach has been to solve for the water flow across the earth’s surface utilizing what are known as the shallow water equations (Vreugdenhil 1994) that enforce conservation of mass and a balance of forces on each cell in the computational grid. The shallow water equations are a version of the standard Navier-Stokes equations for fluid flow under the simplifying assumption that fluid depth is small compared with the horizontal scales of interest. The shallow water equations allow one to treat the water as a single layer with laterally varying surface height above a laterally varying bottom topography. In addition, over continental regions, where the water depths are much smaller relative to the deep ocean and where turbulence can be expected to arise because of high water velocities, the equations of open channel flow are added to track the suspension, transport, and deposition of any sediment present. Erosion is treated assuming that cavitation was the dominant mechanism under the conditions that prevailed during the Flood. B. A crucial question: What drove the water flow? Among the important issues for understanding the Flood is that of the process responsible for producing and maintaining the required water flow. In the investigations leading to the Baumgardner (2013) paper, several possibilities were explored, including bolide impacts in the ocean, torque from a close approach of a planetary body, and the tidal effects of such a close encounter. Of these three possibilities, it was found that only the third could conceivably drive the water flow strongly enough and over a large enough fraction of the earth’s surface to generate sufficient sediment and distribute it over the land surface in any sort of pattern that might bear some resemblance to the actual sediment record. Even in that case it was necessary to postulate multiple near approaches, presumably by the same extraterrestrial body, during the brief time span of the Flood. It was hence deemed a less than satisfying proposition, even though it did provide a means for testing and validating the other aspects of the numerical machinery. Following the 2013 ICC presentation, a colleague inquired if tsunamis generated by catastrophic plate tectonics during the Flood had been seriously considered as a candidate mechanism. Although I (Baumgardner) had briefly considered this possibility, I had dismissed it because I had thought the tsunami amplitude would be too small. However, prompted by my colleague’s inquiry, I reexamined the idea and realized that if the locking interval of the subducting plate with the overriding plate were on the order of merely an hour, then a tsunami of staggering amplitude would be unleashed when the plates unlocked and slipped. To illustrate, a subducting plate moving at 2 m/s at a steep angle into the mantle and dragging the overriding plate locked to it downward over an interval of an hour (3,600 s) creates a V-shaped trench exceeding 6 km in depth. When the fault between plates no longer can sustain the accumulated stress, the plates unlock and the overriding plate rebounds elastically to its undeformed shape. The seawater that had filled the V-shaped trench is quickly heaved upward, and a huge tsunami is launched, one capable of traversing a continent! How many such giant tsunamis might have occurred during the Flood? In today’s oceans active subduction zones total some 62,000 km in length (Bird 2003). If during the Flood the total length of active subduction zone were 50,000 km, the average subduction segment length were 1,000 km, and the average locking interval were one hour, this would imply (50,000 km/1,000 km) = 50 events per hour, or an event somewhere on earth every 72 seconds. This is equivalent to 1,200 mega-tsunamis per day or 180,000 in a span of 150 days. This is a direct logical implication of catastrophic plate tectonics. I realized that this process indeed represented a potent mechanism for driving high velocity water motion during the Flood. Implementing this new feature in the numerical model was not difficult. Results from this tsunami forcing mechanism were reported in Baumgardner (2018a) for the case of two continental configurations that were fixed in time and in Baumgardner (2018b) which included the realism of a dynamic continent motion history. Both studies found that the erosion of bedrock by the cavitation mechanism on continent margins by repetitive large tsunamis arising from rapid plate tectonics was sufficient to supply most of the currently observed sediment inventory on the continents. These studies also BAUMGARDNER AND NAVARRO Large tsunamis and Flood sediment record 2023 ICC 365
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