showed that the tsunamis were effective in transporting this sediment into the continent interiors, depositing the sediment in laterally extensive layers on generally smooth intermediate surfaces. Both studies included initial continental topographies that were low along the continent margins and increased smoothly toward the continental centers. The tsunami-driven sedimentation preferentially filled the lowest regions to yield a flatter and flatter continental surface as time into the simulation progressed. Astonishingly, the Baumgardner (2018b) study yielded a global sediment distribution pattern at larger scales remarkably similar to what exists on the earth today. Is there any clear objective physical evidence for such intense tsunami activity in the earth’s past? The answer is yes! If one takes seriously the account provided in the biblical text for the Flood, including its short duration, then guyots, which are submerged oceanic volcanos whose tops have been beveled away by erosion, provide compelling physical evidence for the reality of intense global tsunami activity during the Flood. The larger of two examples shown in Fig. 2 has a surface area of 384 km2 or 148 mi2. To bevel away the top of a basaltic volcano during the short time span of the Flood requires extraordinary erosive intensity. These flat-topped seamounts occur in all the earth’s ocean basins except for the Arctic. Out of a worldwide total of about 300, some 200 occur on the Pacific Ocean floor alone. III. APPROACH This present investigation also assumes that tsunamis, generated by the locking, and subsequent unlocking, and slip of the plate that overrides a rapidly subducting lithospheric slab in oceanic subduction zones, were the primary mechanism for driving water motion during the Flood. In today’s subduction zones, the overriding plate is locked against the adjacent subducting oceanic plate except for extremely brief episodes of rapid unlocking and slip. As documented by GPS measurements (Prawirodirdjo and Bock 2004), this locking and episodic slip of the overriding plate takes place while the subducting plate is moving continuously downward into the mantle below. Relative motion between the subducting plate and overriding plate occurs only during those extremely brief intervals 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. Until recently, no one had undertaken a careful numerical investigation of the dynamics in these zones under such conditions. During the past year preliminary numerical results indicate that lithospheric slabs do behave as assumed in previous modeling, even when the deformation rates are a billion times higher. It is expected that these results will be presented as a poster at this meeting. Studies of plate motions during the Flood yield plate speeds on the order of 2 m/s (Baumgardner 1994; Baumgardner 2003). Using that surface speed for the subducting plate and assuming a subduction angle of 60° implies that the ocean bottom in the subduction zone is being pulled downward at a speed of 2 m/s sin (60°) = 1.73 m/s. If the locking persists for 60 minutes (3,600 s), the sea bottom is depressed by some 6235 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 60,000 km. If, as shall be assumed, there are 40 active subduction zone segments, each about 1,250 km in length, for a total active length of 50,000 km, and if each of these segments were locked and then slipped every 60 minutes, this would imply 40 mega-tsunamis unleashed each hour, 960 each day, and 144,000 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. 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 meters 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. A. 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 Figure 2. Examples of guyots, or tablemounts, which are submerged oceanic volcanos whose tops have been beveled away by erosion. The Gifford guyot and an unnamed one above it in this image are located in the southern Coral Sea, approximately 700 km east of Brisbane, Australia (Nanson et al., 2018). These seamounts have a depth range of approximately 3 km, rising from -3400 m on the abyssal plain to -250 to -350 m across their summits, and are dated to the Middle Miocene (Heap et al., 2009), that is, near the end of the Flood cataclysm. The plateau surface area of the Gifford guyot is 384 km2. BAUMGARDNER AND NAVARRO Large tsunamis and Flood sediment record 2023 ICC 366
RkJQdWJsaXNoZXIy MTM4ODY=