Understanding the timeline of the drying up of the Flood waters

Question

After the 40 days of rainfall and 150 of the waters surging, the rest of the Flood period was the time it took the waters to dry up. Rashi (to Gen. 8:3-4,13-14) gives the timeline as follows:

• The Flood waters reached 15 cubits above the highest mountains (ibid. 7:20). They started to recede on the first of Sivan, at the rate of 1/4 of a cubit per day, so it took 60 days for the mountaintops to be revealed. This was on the first of Av.

• Sixty days later, on the first of Tishrei, Noach saw that the water was gone, but the ground was still muddy.

• After another 57 days, on the 27th of Cheshvan, the earth was completely dry.

Ramban (8:4) raises various objections to Rashi's timeline. He has the waters beginning to recede on the 17th of Nissan, then 73 days from then until the mountaintops appeared (on the first of Tammuz), 90 days from then until the water was gone (first of Tishrei), and 57 more days until the earth was dry (27th of Cheshvan).

Now my questions:

1. According to Rashi, how indeed would 60 days have sufficed for the water to recede all the way from the mountaintops to sea level?

2. Even according to Ramban, if it took 73 days for the water to recede 15 cubits, how would the rest of it have disappeared in just 90 days? (It is true that he uses the analogy of a stream, where the rate of its recession accelerates as the water level drops, but this seems all out of proportion to that.)

3. According to both of them, why then did it take so long - almost two months - for the ground itself to dry out?

Answer 1

Wouldn't #3 answer the other two? Proposed answer: part of the miracle of the Mabul was that the ground was able to act as a super sponge when the rain stopped.

(personally, I'm not too comfortable with that, there seems something wrong with it but I can't put my finger on it)

Answer 2

To answer you first two questions.

The Gur Aryeh gives two answers to this question:

1. The water started drying up slowly, and gathered speed as it went along, as the atmosphere dried out. Rashi is not against the idea of much more than 15 cubits of water lost over the first 60 days, he's just saying it couldn't be less than that, since 11 cubits of the Ark was submerged in the water.

2. While all mountains were still submerged, the water receded at a standard pace, since nothing was actually drying out yet (it was all still submerged). Once land started appearing and drying out, this caused the drying out process to speed up.

The Chumash Shai LeMorah also quotes the Mizrachi (I didn't look it up inside) who says that the amount of water started receding at a standard depth every day, but that was only while the land was still covered. Once the mountains started to be uncovered, the same volume of water disappearing per day would mean more depth being uncovered. As more and more land got uncovered, the depth of the water would descend more and more quickly. Also, once the sun started touching more of the land, this would help the evaporation happen quicker.

To perhaps answer your third question:

If you look at the Midrash that Rashi to Bereshit 8:14 is quoting (Bereshit Rabba 33:10), the Midrash says that the ground became so dry that nothing would grow. The ground became arid and it took 57 days to go from wet enough to make other things wet to arid. That is what the Midrash says.

It appears that Rashi agrees that the ground became Arid on the 17th of Cheshvan, but has a different interpretation about the state of the ground on Rosh Hashanah.