Is a complete global flood physically possible on Earth?

Question

Genesis 7:11-20 presents an account of an event which, in 40 days, submerges the entire surface of the earth:

[On] the seventeenth day of the second month — on that day all the springs of the great deep burst forth, and the floodgates of the heavens were opened…

For forty days the flood kept coming on the earth… all the high mountains under the entire heavens were covered. The waters rose and covered the mountains to a depth of more than fifteen cubits [6.86 m].

Based on this account, my questions are:

1. Given the amount of water on Earth (including all the water as liquid, solid, and gas, in all possible places: the atmosphere, the surface, and underground), is there enough water to flood the whole earth until ‘all the high mountains… were covered’?

2. What is the estimated rainfall intensity based on this description, and how intense is it in comparison with today’s rainfall intensity in tropical areas?

Regardless of the veracity or otherwise of the account, this makes for an interesting thought experiment.

Answer 1

Just to add some further discussion to @Pont and @fre0n excellent answers.

The problem of the water needed to submerge the world during the Genesis flood have been discussed for centuries. The narrative could seem legit as traces of marine condition can be seen even in high mountains. The Biblical flood was the most logic explanation for marine fossils and wave patterns far away from any coast. Moreover, at the time when the Bible was written in the Levant, there might still have been a collective memory of sudden sea level rise from the possible opening of Bosporus and flooding of the Black Sea. Other experiences, as tsunamis formed in the tectonic active Eastern Mediterranean would also add to the idea of flooding as a divine respond to human actions.

Early scientists that described and compared features in the nature, e.g. Ibn-Sinaa, could also see that some rocks was formed by water. They added the superposition principle, that younger rocks are situated above older rocks and that the processes that formed the rocks continues today and must have taken long time. What they could see, describe and test was a continuation of the earlier ideas of flooding, but they used reason instead of dogma. Modern disciplines of science, as radiometric dating and taxonomy, have further refined our understanding of time and the relation between water and dry ground, but we are still building on the traditions of earlier scholars as Ibn-Sinaa. Sometimes we prove them wrong, just like future scientists will (hopefully) prove us wrong, but the human wish to understand the nature around us can easily be traced back to Old Testament and before.

Sea levels are constantly changing during the history of Earth. There is a number of parameters that controls the global sea level, some are slow but have a large impact. E.g. during Ordovician, the sea level might have been 3-400m higher than today. Not enough to reach the foot of modern Mt Ararat, but the planet was certainly more blue when the first fishes appeared. Also during Cretaceous, the sea level was 2-300m higher than today and more recent, in early Holocene, the sea level was 120m lower than today. Our ancestors could walk (and maybe a short swim or paddle) from Asia to Alaska, from Java to Australia, and across the Black Sea.

So where did the water go? At colder conditions water can be be trapped in ice shields, glaciers. Antarctica and Greenland holds a rather large fraction of the global fresh water. But most water are in the oceans, and larger sea level changes must be caused by changes of the oceans.

The oceanic crust is, relatively to the continental crust, thin and soft, but get harder and chemically heavier with age. The oceanic crust press down the asthenosphere and this results in more space for water, and the sea level sinks (in relation to the geoid). Mid-ocean volcanism on the other hand lifts the seafloor and forces the sea level to rise. Temperature of water is also a factor to consider. Warm water is has less density and occupies larger volume.

The total change in sea level in the past 500 million years have been estimated to about 500m, this is impressive, but far more than the 3,896m of Mt Ararat, that was supposed to be covered in the Genesis flood narrative. As mentioned, there might be more water trapped in the mantle transition zone, but it's hard to see how it could have slipped out to form liquid water, and even more difficult, how it could get back to the mantle, against gravity, after the flood.

However, as a homage to the Biblical believes, there could be an interesting link between sea level changes and mass extinction. Changing sea levels, especially when it happens rapidly, results in new conditions that species might not have time to adapt to. The connection is discussed in this article by Hallam and Wignall, 1999 (Mass extinctions and sea-level changes). The article is also a good example of scientific methods and reason. The language in a scientific article might not be so colorful as in Genesis, but it can open a world far more complex and wonderful than any dogma.

Finally, a reading tip: One solution is proposed in Umberto Eco's The Island of the Day Before, maybe the water was borrowed from another day, as the Earth contains two days, separated by the date line.

Answer 2

there is not enough existing water inside this geosystem IMO for such a thing to occur. Let's see these figures here:

One estimate of global water distribution

Oceans, Seas, & Bays 1,338,000,000 -- 96.54% of all water

this figure means that most of the existing water at the global scale is seawater. Sea floor is quite irregular, with some abyss like pits (ex: Mariana trench), up to low water in shallow sea near continents and islands (See figure). A variable topography overall

This mean that considering the current volume of existing sea water, at say an average of 3 km depth (hypothetical, but it doesn't change the overall reasoning), and removing the continents, you would have to double, and probably more than double the current volume of sea water to raise the oceanic water level of 1 km, 2 km etc... or ~5 km if we consider MT Ararat.

Here is some hypothetically (rough) calculation to illustrate. Let's say the Earth have a surface area of 510 million km² (Wikipedia) and the overall global water (USGS link in my post) amount to 1386 million km². Dividing the volume by the surface provides the height, as shown by this dimensional analysis :$\frac {L^3}{L^2}=L$, which would amount to 2.71 km in height in this case. But let's not forget that this figure imply

a) the impermeability of the surface

b) the surface flatness.

Multiple problems further arise when considering how such an amount of hypothetical water could be suspended at once - there is a interesting debunking explaining implications here:

Talk Origins - 5. the Flood itself

I think @Pont nicely answered the subquestion about the precipitation rate

Answer 3

The "precipitation rate" part is easy to answer, at least to a first approximation. We have 40 days and nights (960 hours) in which to raise sea level above the peak of Mount Everest (let's round up and call it 9000m). Thus, we need a precipitation rate of around 9000/960 =~ 9.4 metres per hour. For comparison, the largest rainfall ever recorded over an hour is 305mm. So a Noachian flood would require a precipitation rate over 30 times greater than the highest-ever recorded one-hour rate at a single site, sustained continuously over every point on the globe for the entire 40 days and nights.

Answer 4

1.Given the amount of water on Earth (including all the water as liquid, solid, and gas, in all possible places: the atmosphere, the surface, and underground), is there enough water to flood the whole earth until ‘all the high mountains… were covered’?

Yes. According to Massive 'ocean' discovered towards Earth's core

A reservoir of water three times the volume of all the oceans has been discovered deep beneath the Earth's surface.

Considering that the average depth of the ocean is 2.3 miles and the Earth is 71% water, three times this amount would be about the amount needed to reach the top of the highest mountains.

2.What is the estimated rainfall intensity based on this description, and how intense is it in comparison with today’s rainfall intensity in tropical areas?

There is no way to estimate rain fall from the description, because Genesis makes clear water came from "the deep" as well as from above. For example the passage qouted in the OP says "springs of the great deep burst forth" and Genesis 8:2 says "the fountains also of the deep and the windows of heaven were stopped, and the rain from heaven was restrained. "

Answer 5

Without requiring any rainfall, if you accept a theoretical scenario of a "dead Earth", meaning with no more active tectonics, no flux of heat from the mantle/core and given a long-enough time to almost completely erode mountains, then yes, a complete global flood may be possible. Just imagine to displace all the rocks that today are above the average sea level into the oceanic basins, then let them to compact (reducing porosity) and to reach isostatic equilibrium, pushing water above the sediments by density difference.

The thought experiment may then continue, calculating the average altitude of sediments and the average height of the water column above the surface in that case. A rough estimation should be in the order of a couple thousands meters of water above the global seafloor.

However I do not suppose that this may happen in 40 days, or anytime soon.

Answer 6

If you'll accept a much slower rain it could happen. Consider: As others have shown there is not enough water on Earth to do this. Since there's no feasible mechanism to get all the water on Earth into rain in the first place this isn't all that important anyway.

Instead, lets look elsewhere for the source of our rain: A large comet. It's captured by the Earth with the assistance of the Moon but it's in an orbit with a very low perigee. Comet stuff is shed, hits the atmosphere and comes down. Since it's mostly gas and ice you get rain, rain and more rain.

This can't happen in 40 days, though--there has to be enough time for it to cool. If that much water comes down in 40 days it's going to make Venus look positively arctic by comparison.

Thus it's possible for the Earth to become a waterworld like in the movie but not like in Genesis.

Answer 7

The primary source for the water that generated the flood was neither the upper mantle nor the atmosphere as rainfall, nor cometary bombardment or grazing, but earth's existing ocean water itself. Some water is liberated from the mantle in volcanoes and undersea vents, but these amounts are negligible except over very long periods of time. Planet earth has a large amount of radioactive elements in its core and lower mantle. Radioactive element decay sequences, if they occur synchronized, could generate significant and rapid changes in the volume occupied by the elements, therefore, could rapidly change Earth's volume, same as a star can change volume in a collapse towards its core or in red giant phase but by a different process. If earth were to have shrunk, it would have displaced earths oceans to overwhelm the continents in wave after wave of tsunamis. If as the decay sequence continues, earths volume again increased, the water would have been displaced off the continents back into the ocean basins. No extra mystery water is needed to generate the flood, and no mystery as to where all the extra water went after the flood. This radioactive decay would have generated massive heat, which would have shut off earth's protective electromagnetic field generating dynamo; however, an expanding earth would also create large rifts, and expose earth's mantle to the oceans, generating mass extinctions in the oceans, massive rainfall in equatorial regions, and massive blizzards at the poles; ergo, the ice ages; extreme cloud cover would have protected earth's life from cosmic rays till the dynamo turned back on; when the EMF turned back on centuries later, with rapid fluctuations, it seems to have generated a memory scrambling effect, recorded as The Tower of Babel event as the scrambling of languages.