The Flood and Tidal Waves

Over at Triablogue Steve Hays has posted an interesting hypothesis regarding the Genesis Flood. He writes:

A staple objection to the global flood interpretation is that it poses a double whammy: where did all the extra water come from, and where did it go?

...Suppose God gradually made the moon pass closer to the earth. Not only would that produce higher tides, but based on the inverse square law, it could generate super-tides. And if, after that peaked, God made the moon recess, that would lower the tides. A single mechanism could account for both rising and lowering sea levels. You'd have the same amount of water throughout, but its distribution would vary depending on which part of the earth was facing the moon at any given time.

In his post, and the comments, various objections to this theory are addressed.

One major problem, which Hays does not consider, is that reducing the Earth-Moon distance would also reduces the length of the lunar month.

The Height of Tidal Waves
Classical orbital mechanics and gravity gradients govern the relationship between the Earth-Moon distance and tidal dynamics. In an idealized model of a planet entirely covered by an ocean, the height of a static tidal bulge is determined by the differential gravitational pull across the planet's diameter. This tidal-generating force (and height) varies with the inverse cube of the distance R of the Moon from Earth.

H ∝ 1/R³

Thus, for example, reducing that distance by a factor of ten multiplies the tidal force and height by a factor of a thousand. Of course, tidal height also depends on the coastline's shape, which giant tidal waves would in turn affect.

The Length of the Month

However, reducing the lunar distance reduces the length of the month. According to Kepler's Third Law, the period T of the Moon's orbit is related to the Earth-Moon distance R by the equation

T ∝ R³ᐟ²

Reducing R by a factor of 10 thus reduces T by a factor of about 32. T is the sidereal period, the time for the Moon to return to its same position relative to the stars. The current T is 27.3 days. The reduced T would thus be less than 1 day. The lunar period concerning the phases of the Moon is determined by the motion of the Moon relative to the Sun. This is called the synodic period (the time between two full moons), which is currently about 29.5 days.

The lunar synodic period S is related to the lunar sidereal period T by the equation

where Y is the sidereal period of the sun (365.26 days). Thus, a lunar sidereal period T of 1 day yields a lunar synodic period S of slightly more than 1 day.

We thus get the following relationship between lunar distance, theoretical open-ocean tidal heights, and the time between full moons (the synodic month):

Earth-Moon Distance (km)	Approximate Distance Scale	Theoretical Tide Height	Length of Lunar Month (Synodic/Phase Cycle)
384,000 km	Current Orbit (1×)	~0.5 metres	29.53 days
192,000 km	Half Distance (1/2)	~4.0 metres	9.92 days
96,000 km	Quarter Distance (1/4)	~32.0 metres	3.45 days
38,400 km	One-Tenth Distance (1/10)	~500.0+ metres	0.87 days (~20.8 hours)

Was the month shorter during the Flood? According to the Bible, the Flood started on day 17 of month 2 (Gen.7:11), and the ark came to rest on Ararat on day 17 of month 7, 150 days later (Gen.8:3-4). Dividing 5 months into 150 days yields a month of 30 days. This indicates that the length of the month did not change significantly during the Flood. In that case, the Earth-Moon distance could not have changed much either, which rules out Hays' suggestion.

Where Did the Water Come From and Go?

As to where the extra water came from, the Bible itself refers to its sources: "all the fountains of the deep burst forth, and the windows of the heavens were opened." (Gen.7:11). The atmosphere would not have provided sufficient rain for a massive global Flood. However, even today there seem to be massive amounts of water inside the Earth. An article in the New Scientist (2014) reports:

A reservoir of water three times the volume of all the oceans has been discovered deep beneath the Earth’s surface. The finding could help explain where Earth’s seas came from.

Where did the Flood water go? Was it swallowed up back into the earth? or did the Flood result in an altered topography, raising mountains and deepening ocean floors to accommodate the extra water? Various such scenarios have been proposed. The most popular of these is the Catastrophic Plate Tectonics (CPT) model (see Jonathan Sarfati, The Genesis Account (2015), pp.531-536 for a discussion of its strengths and problems).

A Caution
A note of caution. D.C. Allen in his book The Legend of Noah (1963) describes how 17th century theologians addressed scientific questions regarding the Flood. Most Roman Catholic theologians met scientific difficulties by declaring that the impossibility of explaining the mechanics of the Flood clearly showed that it was a miracle. But many protestants, anxious to prove that all of the Bible accorded with human reason, tried to work out precise scientific solutions. Their failure to explain the details to the satisfaction of the critics eventually led to the inspired history of Noah being relegated to simply a myth. 

The lesson is that we must always be careful to distinguish the Biblical givens from fallible human models that try to explain these. Our faith in the Bible should not rest on our ability to provide scientific explanations of biblical events. On the contrary, any inability of scientific models to explain biblical events merely reflects the inadequacy of human theorizing. 

References

• Allen, D. C. (1963). The Legend of Noah: Renaissance Essays on Science, Art, and Letters. University of Illinois Press.

• Coghlan, A. (2014). Massive 'ocean' discovered towards Earth's core. New Scientist, June 12, 2014.

• Hays, S. (2013). Genesis Flood. Triablogue, December 16, 2013.

• Sarfati, J. (2015). The Genesis Account: A Theological, Historical, and Scientific Commentary on Genesis 1–11. Creation Book Publishers, pp. 531–536.

• Schmandt, B., Jacobsen, S. D., Biswas, A., Zheng, Z., Kono, Y., & Fei, Y. (2014). Dehydration melting at the top of the lower mantle. Science, 344(6189), 1265–1268.

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