Chronology of the Flood

Exegetical Approaches

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150 Days Which Includes the First 40 Days

The two mentions of 150 days refer to the same time period and encompass the forty days of rain. The ark landed at the conclusion of these 150 days.  This approach subdivides regarding how the commentators understand the chapter's dating:

Months from Creation

All the months mentioned in the verses are calculated according to the yearly calendar, from creation.

Months – These commentators assume that all the months mentioned in the account of the flood are numbered from the beginning of the calendar year.  They disagree, though, regarding whether the first month is Tishrei or Nissan.2
150 and 40 Overlap – This position assumes that the forty days of rain are subsumed in the 150 day period, reading the final verse of Chapter 7 "וַיִּגְבְּרוּ הַמַּיִם עַל הָאָרֶץ חֲמִשִּׁים וּמְאַת יוֹם", as a summary statement of the previously described events rather than a successive event.3
One set of 150 – These sources similarly assume that the statement "וַיַּחְסְרוּ הַמַּיִם מִקְצֵה חֲמִשִּׁים וּמְאַת יוֹם" does not mean that the water receded after a second set of 150 days, but rather that it decreased after (or the reduction was first noticeable at the end of) the 150 days previously mentioned.
"וַיִּגְבְּרוּ הַמַּיִם" and "וַיַּחְסְרוּ הַמַּיִם" – Though all these sources agree that there was but one set of 150 days, they disagree in how they understand the relationship between the periods of increasing and receding waters:4
  • Water first decreased after 150 days ­ - The author of the Qumran Scroll, Yefet the Karaite, Ibn Ezra,5 Ramban, and Sforno all understand the phrase "וַיַּחְסְרוּ הַמַּיִם מִקְצֵה חֲמִשִּׁים וּמְאַת יוֹם" to mean that the water only began to decrease at the end of the 150 days. Until that point the water level was either still rising, or at least, maintaining its height. Sforno suggests that even though the rain stopped after 40 days, the underground sources of water were still open,6 causing continued water pressure during this entire period.7 Ramban, in contrast, seems to maintain that though the waters did not continue to increase after the fortieth day, due to the great humidity8 they retained their height throughout this period.
  • Water decreased after the forty days of rain – Most of the other commentators in this approach9 assume that the water started to recede right after the rain stopped. The phrase " וַיִּגְבְּרוּ הַמַּיִם עַל הָאָרֶץ חֲמִשִּׁים וּמְאַת יוֹם" simply means that the waters were is a state of strength (relative to normal water heights), not that they were increasing, or even maintaining their level.  R"Y Bekhor Shor, R. Hoffmann and U. Cassuto explain the verse "וַיַּחְסְרוּ הַמַּיִם מִקְצֵה חֲמִשִּׁים וּמְאַת יוֹם"   to mean not that the water first began to recede at this point but that the decrease was first noticeable to Noach after this period, when the ark landed.10
Chronology
  • Chronological –Those who maintain that the waters maintained their strength throughout the 150 days, read the verses chronologically, with Chapter 7 describing the rising  flood and the opening  verses of Chapter 8 detailing the decreasing waters at the end of the 150 days.11
  • Achronological – The other commentators, though, assume that verses 8:2-4 (the sending of the wind and closing of the heavenly windows) occurred in the midst of the 150 days that are mentioned in the preceding chapter and that there is an element of achronology in the verses.  Akeidat Yitzchak and Shadal explain that the Torah purposely separated the images of destruction and salvation, detailing the world's collapse in Chapter 7 before describing its rebuilding in Chapter 8.
How do 150 days fit in five months? According to the fixed lunar calendar, months generally alternate between having 29 and 30 days,12 which means that there can be at most 147-149 days in any 5 month period.13  As such, this position must explain how the 150 days fit into the five months between 2/17 when the rain began and 7/17 when the ark rested.   The commentators resolve this issue in different ways:
  • Different calendar – Several sources reject the assumption that the dates in the story are based on the Hebrew lunar calendar:
    • Solar Calendar –  Some commentators14 assert that the months mentioned relate to the solar calendar. According to this reckoning there are 152 days in five months and the 150 day period ended a couple of days before the ark rested.15
    • Persian/Egyptian – Ibn Ezra suggests, in contrast, that Noach was using a calendar like that of the Egyptians or Persians who would intercalate their year by adding 5 days to a certain month. The total days in the five month period can thus equal or surpass 150.16
  • Lunar calendar based on eyewitnesses – Yefet and Anan the Karaites maintain that Noach did use a lunar calendar, but one in which the months were determined by eyewitnesses rather than calculations.17 They assume that if no one can see the moon (as was the case when Noach was in the Ark)18 the default length of a month is thirty days.19  This allows for exactly 150 days between 2/17 and 7/17.20
  • Fixed Hebrew Lunar Calendar – A last group of sources attempt to uphold the idea that the Torah is employing the Rabbinic calendar:
    • Round Numbers - The Rid and U. Cassuto solve the problem by simply suggesting that 150 days is a round number. Though, in reality there were fewer days in the five month period, the Torah rounded up to the the next ten.21
    • Full Leap Year - R. Saadia suggests that one can reach 150 days using a regular fixed lunar calendar if the year was a "full" leap year. In such a year, 4 of the 5 months( Marcheshvan, Kislev, Shevat and Adar I) would all have 30 days. As such 7/17 is the 150th day.22
How did the ark land so soon? These commentators differ in how they understand how the ark managed to land right after the 150 days of strong waters, if the mountain tops were still covered  by fifteen cubits of water:23
  • Receded over 110 days – According to those who say that the water started to decrease already after the 40 days of rain, this is not an issue,24 and is, in fact, one of the factors that motivate them to explain the verses as they do. Shadal even maintains that by this point the higher mountain tops were totally uncovered, and that Bereshit 8:5 describes only the revealing of the shorter mountains.
  • Receded over 2 days – According to those who maintain that the waters retained their strength throughout, but that a solar calendar was used and thus the 150 period ended by the 15th of the seventh month, there was a period of two days in which the water lessened, allowing the ark to land.
  • Miraculous intervention – Ramban, in contrast, is forced to assert that Hashem sent a miraculous wind which decreased the waters substantially on the 150th day itself.25 
Shifting water levels – A simple reading of the verses suggests that the waters decreased at an extremely varied pace:
  • If one posits that the water first decreased after the 150 days, then it went down only 15 cubits in the 2 1/2 months from 7/17 until 10/1 compared to thousands of cubits in the 3 months from then until the land dried on 1/1.26  Ramban explains that there is no reason to think that the water needed to decrease at a steady pace. In addition, according to him, Hashem's intervention on the first day led to a vast decrease in the water, 27 minimizing the difference in the rate of reduction thereafter slightly.28
  • Those who posit that the water began to recede after the rain stopped have an even bigger problem, since according to them, initially the water receded only 15 cubits in over 180 days!29   Shadal minimizes the problem by asserting that by the time the ark landed on 7/17, more than 15 cubits of water had already receded, since Mt. Ararat was not the tallest, but rather one of the shorter mountains.30  There would, nonetheless, still seem to be a significant increase in the rate of water reduction in the last 3 months, assuming that even the shorter mountains were a few thousand cubits high.
"וַיְהִי מִקֵּץ אַרְבָּעִים יוֹם" and the sending of doves
  • From the revealing of the mountain tops – Most of these commentators count the 40 days from the preceding date mentioned in the verses, the first of the tenth month, when the mountain tops were visible. This leaves about a month between the landing of the dove and opening of the ark's cover when the land dried on the first of the first month.31 It is not clear, though, why Noach waited.32
  • From the landing of the ark – The Rid questions the dating of the above approach, wondering why the dove could not find a resting place if the land had already been visible for over a month.33  This prompts him to instead count the forty days from the landing of the ark on the seventeenth of the seventh month.  He assumes that Noach waited for ten days to see how the raven was faring, then sent the first dove 7 days later and the final dove 14 days after that, reaching the first of the tenth month. It was only then, when the mountaintops were finally revealed, that the dove could rest.34

Varied Dating

Some months are counted to creation and some are dated in reference to key points during the flood.

Months – According to Ramban and R. Ashkenazi, the beginning and end of the flood (2/17 and 2/27) are dated to the beginning of the calendar year, but the months mentioned in the middle of the story, the landing of the ark on 7/17 and the revealing of the mountain tops on 10/1, are both dated to the start of the flood, setting them at 8/17 and 11/1 respectively.36 The last date, though, when Noach opens the ark's cover on 1/1, is once again dated to the beginning of the year.  This approach is motivated by a desire to make sense of the various time-frames in the chapter37 but its obvious disadvantage is its inconsistency.38
40 and 150 overlap – Like the above approach, these commentators also view the phrase "וַיִּגְבְּרוּ הַמַּיִם עַל הָאָרֶץ חֲמִשִּׁים וּמְאַת יוֹם", as a summary statement of the previously described events, and assume that the 40 days are included therein.
One set of 150 – Both Ramban and R. Ashkenazi maintain that the verse "וַיַּחְסְרוּ הַמַּיִם מִקְצֵה חֲמִשִּׁים וּמְאַת יוֹם" does not refer to a new period of 150 days, but to the end of the previously mentioned one.
"וַיִּגְבְּרוּ הַמַּיִם" and "וַיַּחְסְרוּ הַמַּיִם" – These commentators assert that the waters maintained their strength throughout the 150 days, and only began to abate afterwards.39
Chronology – This position does not need to assume any achronology in the verses describing the increasing and decreasing waters.
How do 150 days fit in five months? According to this approach there are really six months from the start of the flood until the resting of the ark.40  This easily fits the period of 150 days of increasing waters, even leaving a month over afterwards.
How did the ark land so soon? According to this position, there was a month between the 150 days and the resting of the ark, enough time for the water to recede sufficiently to allow the ark to find a  resting place.
Shifting water levels – As this position reduces the time between the revealing of the mountain tops and the drying of the land to two months,41 it exacerbates the problem of the changing rate of reduction.  It has the waters reducing 15 cubits in about 2.5 months, while they are lowered thousands of cubits in 2 months!
"וַיְהִי מִקֵּץ אַרְבָּעִים יוֹם... וַיְשַׁלַּח אֶת הָעֹרֵב" – R. Ashkenazi dates this from the previously mentioned event, the revealing of the mountain tops, which this position maintains occurred on the first of the eleventh month (the tenth month being counted from the start of the flood).42  As such, the sending of the final dove fell on the first of the first month,43 when the land dried.44 This explains why it was only now, that it did not return.

150 Days Which Do Not Include the First 40 Days

The two mentions of 150 days are one unit of time, while the forty days of rain are a distinct unit.  As such, there was a 190 day period before the waters began to decrease.

Distinct 40 and 150 days – This approach assumes that there is no overlap between the description of the flood and the 150 days of strong waters.  The verses follow sequentially, with the 150 days following the forty days of rain.
One Set of 150 – This position, nonetheless, agrees that there is only one set of 150 days and that the waters receded at the end of the previously mentioned 150 days, and not after a new set.
"וַיִּגְבְּרוּ הַמַּיִם" and "וַיַּחְסְרוּ הַמַּיִם" – Though all these commentators maintain that the water started to abate only after the 150 days (on the first of the ninth month), they differ regarding what happened during the initial period itself:
  • Waters retained strength – According to Seder Olam Rabbah and the Arukh, the water stopped increasing after the forty days of rain, but maintained their level throughout.45 According to this, the phrase "וַיִּגְבְּרוּ הַמַּיִם" does not mean that the waters increased but that they stayed in their strength.
  • Waters increased – According to Ba'alei HaTosafot, in contrast, even after the rain stopped, the water continued to increase throughout the 150 days. He might maintain that the waters continued to emerge from underground.46
How do 190 days fit into 5 months? The verses state that the ark rested on the 17th of the seventh month.   According to this position, though, at this point the waters were still at their height (and would be through the 29th of the eighth month)!47  This forces these commentators to reinterpret this date and to assume that it is dated to an event in the flood narrative rather than the beginning of the calendar year:
  • End of rain – Following Seder Olam Rabbah, most of these commentators48 assert that the 17th of the seventh month is being counted from the month in which the rain stopped.  As such, it is really equivalent to to the 17th of the ninth month,49 which gives ample time for the waters to decrease before the ark landed.50
  • Beginning of rain – The Arukh, Lekach Tov and R. Yitzchak51 get to the same date but through a different calculation. They assert that one needs to count seven full months from the date the rain began. Thus, 2/17 plus 7 months brings one to 9/17.52
"בָּעֲשִׂירִי בְּאֶחָד לַחֹדֶשׁ נִרְאוּ רָאשֵׁי הֶהָרִים" – These sources suggest that this date, too, should not be counted from the beginning of the year and almost unanimously date it to the start of the flood, reaching a date of 11/1.53 This, of course, is inconsistent both with the dates of the start and end of the flood (dated to the beginning of the calendar year), and with the way most of these commentators dated the landing of the ark, which was to the end of the rain, not the beginning.54 They are motivated to do so, though, by their understanding of the verses regarding the sending of the doves - see point below.
"וַיְהִי מִקֵּץ אַרְבָּעִים יוֹם" and the sending of the doves – The verse does not say explicitly from which event the forty days are to be counted.  These commentators offer three different possibilities:
  • From when the waters began to abate – According to Seder Olam Rabbah, Rashbam, and one version of R. Tam55 the 40 days are counted from the first of the ninth month, when the waters began to decrease.  The motivation for their interpretation is the assumption that the first two doves would have found a resting place if the mountaintops had been visible.  Thus, their chronological reconstruction have the third and final dove being sent on the day the mountain tops appear.56  This reading, though, necessitates dating the appearance of the mountains to the first of the eleventh month,57 forcing them to adopt the notion mentioned above that the date mentioned in the verses, the first of tenth month, is really dated to the beginning of the rain (and not the year).58
  • From the revealing of the mountain tops – The Arukh and Rashi,59 in contrast, maintain more simply that the forty days are counted from the last date mentioned in the verses, the revealing of the mountain tops.60 They assume that the final sending of the dove must have coincided with the drying of the land on the first of the first month,61 as only this would explain why it did not return.62 Thus, working backwards from this date (1/1), they, too, need to suggest that the mountain tops appeared on the first of the eleventh month,63 and that the date mentioned in the verses (10/1) is from the beginning of the rain (and not the year).64
  • From the resting of the ark – R. Tam, as brought by R. Chayim Paltiel,65 and R. Eliezer Ashkenazi assert that the forty days began with the landing of the ark, which they date to the seventeenth of the ninth month.66  R. Tam rejects Seder Olam's possibility above, asserting that Noach would have been unaware of the day in which the water started decreasing,67 and so he must have counted the forty days from an event he was cognizant of,68 such as the landing.69 
Shifting water levels – Seder Olam Rabbah, and many of these sources in its wake, assume that the water receded at a steady pace from the first of the ninth month until the mountain tops were seen two months later.  As such they calculate that they receded at a rate of one cubit  every four days.70  This would mean that afterwards, though, there was a drastic change in pace, since in the remaining 3 1/2 months, the water would have to go down the height of an entire mountain!  Chizkuni attempts to suggest that there was lot more volume to the water that was above the mountain tops since there were no land forms intervening.

Two sets of 150 Days Which Include the Second 40 Days

The verses speak of two different sets of 150 days, one in which the waters rose and one in which they receded. The forty days of rain are not included in the first unit, but the forty day wait before the sending of birds is subsumed in the second set.

Two sets of 150 – Radak assumes that the verses speak of two distinct periods of 150 days, one in which the waters rose and one during which they fell.  When the verse says, "וַיַּחְסְרוּ הַמַּיִם מִקְצֵה חֲמִשִּׁים וּמְאַת יוֹם", it is not referring to the previously mentioned days of rising waters described in Chapter 7, but rather a new unit of time depicted in Chapter 8.
40 days of rain – According to Radak, Chapter 7 is sequential and the forty days of rain do not overlap with the first set of 150 days.  Thus, between the two there were 190 days, ending on the first of the ninth month.
40 day wait – Radak assumes that the forty days before the sending of the birds occurred at some point during the 150 days in which the waters decreased.
How do 190 days fit into 5 months – In order to fit the 190 days of rain and rising waters into the period before the landing of the ark, Radak must explain like Seder Olam Rabbah and others above, that the date given for the landing (7/17) is not counted from the beginning of the calendar year but rather from the end of the 40 days of rain.  It is, thus, equivalent to to the 17th of the ninth month, 16 days after the water began to decrease.
"בָּעֲשִׂירִי בְּאֶחָד לַחֹדֶשׁ נִרְאוּ רָאשֵׁי הֶהָרִים" – Radak follows Seder Olam Rabbah in counting the tenth month, when the mountains became visible, to the beginning of the flood.  Thus, according to his reckoning they appeared on the first of the eleventh month.
"וַיְהִי מִקֵּץ אַרְבָּעִים יוֹם" and the sending of the doves – Radak is inconsistent in the way he understand the timing of these events:
  • At the end of the 150 days – In his comments to 8:3, Radak suggests that the 21 days worth of sending of the birds occurred after the second set of 150 days.  He seems to be motivated by a desire to have the times mentioned in the text reach a year: 40+ 150+ 150 + 21=361, or about 12 months of 30 days each.  Such a reckoning, though, is very difficult as it assumes that the birds were sent in the second month of the second year, after Noach had removed the ark's covering and saw that the waters had already dried!71
  • After the ark landed – In his explanation to 8:6, Radak writes that the forty days be counted from when the ark landed (on 9/17),72 assuming that the starting point had to be an event that Noach was aware of.73 This would mean that the first dove was sent after the mountains were already visible,74 making it difficult to understand why it could not find a resting place.75  One of the Ba'alei HaTosafot answers that perhaps "וְלֹא מָצְאָה הַיּוֹנָה מָנוֹחַ" means that she did did not find anything to serve as a sign for Noach and was, thus, not at peace for she did not fulfill her mission.76  
  •  After the mountain tops appeared – A few verses later, Radak suggests that the last dove found a place to land on the first of the first month,77 which would mean that the forty days were counted from the appearance of the mountain tops, two months before.78 This possibility works best with the chronology of the verses.
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