Wednesday, September 1, 2021

SearchResearch Challenge (9/1/21): Floods, floods, and history?

 As you might have noticed, I'm fascinated by floods. 

Flooding in Texas, 2021.  P/C NSF

We've investigated floods before in this blog.  See SRS in 2016 when we asked "what's common between these floods?"  or this SRS from 2020 when we discussed flood and debris basins near Los Angeles.  

There are certainly a LOT of floods this year (Tennessee, Louisiana, North Carolina, Belgium, China, etc.) and perhaps that's why floods are on my mind this week.  

But, as always, I'm interested in even BIGGER floods that have reshaped the land at large.  

I've heard about such things:  Epic floods that created canyons and seas, changing the very shape of the countryside, but I don't know the details of when and where such floods have taken place.  Can you find out? 

So this week's Challenge is about really big floods... 

1. Can you find the 3 largest floods of all time?  What are they?  We're not counting life or property loss here, we're just interested in size--especially total water movement. Hint: they all have to do with geology rather than human-made causes.  

2. What causes these gigantic floods?  That is, how would such things occur?  What's the underlying root causes? 

3. Where are the biggest risks of giant floods today?  Sure, every dam in the world can cause flooding, but are there other places that might have a giant flood today?  Where?  And how bad are the risks?  

I love these kinds of SRS Challenges because they make me look for information in resources that I don't normally visit.  They make me think on time-scales and sizes that are much larger than myself.  I hope you enjoy these Challenges for the same reason.  I hope they pique your curiosity and inspire further research on your part.  

Speaking of "further research," my plan for the next two weeks is to visit Bonaire on a scuba diving trip with a few good friends.  I HOPE I'll be able to post an answer next week, but if I'm not able to do so, you'll know why.  Not to worry--I'll return shortly.  

With any luck, I'll come back with more SRS Challenges having to do with marine biology, cultural anthropology, or geopolitics.  In any case, I'll be indulging my curiosity with a bit of field investigation.  

Search on! 


  1. 1) I started with "Largest floods in history" but this was talking about human / recorded history and I felt sure that the list at was not what was wanted. (If so, then the the 3 deadliest floods all took place in China - but the question said "largest" not "deadliest" or "largest loss of life"). So I tried "largest floods ever" and got "The largest known meteorological flood—one caused by rainfall, as in the current Mississippi River flood—happened in 1953, when the Amazon River overflowed." Also not what I wanted. My memory is that one hypothesis was that Noah's flood was caused by the Black Sea being formed as the sea broke through to the previous lake. So I added in this and searched for "largest floods ever black sea opening" which turned up several clues and terms such as megaflood and outburst flood. The Wikipedia article on this mentions something called the Zanclean Flood that may have occured over 5m years ago that essentially created the Mediterranean by flooding a dried or partially dried basis as the Straits of Gibraltar opened. (See: This article mentions two other catastrophic floods of this sort - the Black Sea deluge (as I started with) that may have occurred 7500 years ago. (
    However although the Zanclean wins number 1, I'm not sure of 2nd or 3rd position. Perhaps the Black sea but also it could be the Altai Flood which had a different cause, from the failure of a glacial damn around 10-12,000 years ago. - This flood may have been the greatest discharge of freshwater on Earth, since its magnitude has been estimated similar to that of the Missoula flood which is another contender for the largest flood - also at the end of the last ice age for similar reasons. Searching for Zanclean, Altai and Missoula also gave the Bonneville flood - Wikipedia says this may have been the 2nd largest flood in known geologic history.

    So I then searched for "Largest flood in geologic history" and this turned up gold in the form of "The world's largest floods, past and present". -
    This suggests the Zanclean flood was largest followed by the Black Sea basin filling followed by the Altai and Missoula floods.

    2) The article above gives reasons as a breach of a tectonically closed basin, allowing sea water to fill the basin, followed by the failure of ice damns (as with Altai and Missoula).

    3) Climate change seems to be the biggest risk for massive floods today. For example—-Like-California-Did-With-Wildfire-Prevention-—-May-Spell-Disaster,-Experts-Say says "Scientists expect flooding to get worse because weather extremes are growing as the climate crisis worsens globally, said Daniel Swain, a UCLA Climate Scientist and California Climate Fellow at The Nature Conservancy." (Found using "megaflood risk" and similar searches). The focus of this is flooding in California, but shows the risks globally if the sea level rises - as does

    1. I started my search with : 3 largest geological floods and The World's Largest Floods, Past and Present was at the top . A great site for this search

    2. Both of you found the USGS pub on "largest floods." Nice work. Are there any USGS publications on this topic? How about from other countries?

  2. [Biggest floods without man causes]

    History: The World’s Most Catastrophic Floods, in Photos

    This I'm reading. It has links to explain many things about floods

    With [Biggest floods geological causes]

    Need to read USGS ( mentioned by Arthur) and NatGeo.

    With [mayores inundaciones de la historia]

    The Ice Age Flood
    The Altai Flood
    The Alaska Volcanic Flood

    1. I think Dr. Russell and hopefully many of you will like (because of the tool and data, not because the actual events) these too:

      California droughts ;

      Fires and floods

    2. I was reading this story about Michelangelo and made me remember previous SRS Challenges. It's amazing how fast time flies and how much I have learned and discovered with Dr. Russell. Thank you!

      Have a fantastic trip to Bonaire.

  3. Replies
    1. The Bonneville Flood is epic, but not quite as large as others.

      I DO love the Wikipedia lists... who knew they'd have a list like this ("World's Deadliest Floods") or the one I point to in my post ("World's Largest Floods")?

  4. I would suggest the number 1 contender is the Flood Noah was floating on--its was of biblical proportions. This might have been, say, 1k over the entire planet.

  5. Another contender is the Washington state Scablands flood as clearly explained by my geologic guru Nick Zenter, Try this:

  6. yet another is the one that followed the last ice age when the now Britain was attached to Europe. The wavy ripples from thousands of years ago are clearly seen in the "English" Channel even today. LIke this search: [The megaflood that made Britain an island]

  7. This is a timely topic for me. Having strong ties to the Gulf Coast, I have been following Ida and just yesterday was reading about the Galveston Storm. I started brainstorming and came up with more questions than answers about floods - at first I thought this might be a Fermi estimation problem. I did become fascinated by how even “minor” floods have reshaped the geography of our planet.

    I vote for the Bonneville flood as the second largest flood ever:

    These largest floods seemed to be one-off catastrophic events that could happen anywhere, anytime triggered by some geologic event over which we have no control.
    Regarding the future threats, I found an article describing the danger for the Central Valley of California to be flooded, more likely to be sooner due to increased precipitation caused by climate change, so stock up on almonds, broccoli, and artichokes while you can:

    The consensus of scientific opinion seems to support the notion that climate change is likely to be a major contributor to future flooding (though that is partly of human origin). I would add destruction/loss of wetlands to that:

  8. This comment has been removed by the author.

    1. Might be your post is too big. There is a size limitation but I do not know what it is. I just make mine smaller.

    2. Thanks Jon, but that wasn't it. When I tried the first post, I was not subscribed, so I resubscribed, reposted, and got a message that blogspot was blocking my message. Same for the second post. But they obviously weren't being blocked. All's well that ends well.

  9. An interesting report that may be relevant The Largest floods Past and Present their Causes and Magnitudes

  10. I used the search terms: largest geological floods and found the document: In the document on page 2 in chart 3, there was a list of the largest floods caused by ice-dam failure in the Late Pleistocene period. They were in descending order: Kuray,
    Missoula, and Darkhat Lakes. These were in Russia, USA and Mongolia.

  11. not trying to put a damper on the scuba-ing, but I'm curious how you pick some of your images…
    fwiw: Dan, the photo caption seems misleading…? (not TX…)
    used bing to track the source photo (ShutterStock/Roschetzky Photography/Bryan Roschetzky)
    5 rows down, on the right…
    verifying text and/or images is slippery stuff
    captions can change the whole visual context — and then it just perpetuates… saw a Thai story that used the image/different geo attribution…
    his Instagram
    like saying this is Dubuque…
    or this… is Fruita
    or this is San Fran…
    nice view, foolish action…imho… that's how SaR find skeletons… maybe

    1. Great catch, Remmij. The place I got it from mislabelled it! Sigh.

  12. Have a safe trip, Dan. Give our best to the Phoenicopterus ruber.

    1. Of course! I'm going to try and get some better photos this time around.

    2. Not too good pictures, please. The other Russell tells me that envy is the most unfortunate of human characteristics.

      In the meantime, I am excited about this challenge. It turns out I have history with one of these giant floods. I was hiking with a biologist friend today and telling him about the Mediterranean drying up and refilling and he was asking me questions I could not answer. Onward!

    3. Yes, thank you, it was Lord Russell. I misremembered that Oscar Wilde had said that about envy but know that with this bunch I have to triple-check everything.

      I recommend all of remmij’s resources about the Zanclean Flood, especially the videos.

      So, the second question of the challenge was what caused these giant floods. First, the Zanclean Flood would not have happened if it had not been preceded by the initial desiccation, the Messinian Salinity Crisis. What caused that? According to PBS (one of my trusted sources)

      there have been numerous hypotheses, but the most accepted today is that Gibraltar closed all those years ago due to a combination of repeated changes in the Earth’s crust, repeated erosions, and climate cycles. Then it opened again due to tectonic shifts and erosion. This and other sources warn that it is likely to happen again.

      Next, I wondered what was the effect on the animals who lived in that area of the world at that time. According to Wikipedia

      many African species migrated into the empty basin. There was no citation for this and other references were not helpful.

      The PBS video discussed this and explained concepts such as insular dwarfism and insular gigantism to explain the existence of now-extinct dwarf elephants and giant rabbits. This flood and the MSC changed more than the topography of the area.

      Now I’m wondering why the beach at Nice is so rocky while those near Athens and Tel Aviv are so sandy. (Rivers have brought the pebbles from the mountains to the French coast.) It also turns out that the Mediterranean is one of the saltiest seas in the world (from the MSC), and water in the eastern part is saltier than that in the western part.

    4. The Black Sea flood is a whole other story... worth checking into, if you've got the time!

  13. Dan the angler, the photographer, the scuba-meister, the searcher…
    seems he has already seen a Spotlight Parrot fish/wrasses, a much more rare
    Natural Buffet Scaridae and an almost extinct Chlorurus Phoenicopterus ruber-beakus…
    a true wrasses wrangler – above and below the water… already a successful outing…
    I'm sure it was a catch and release situation for the young Gutu (not fully feathered yet…)
    somewhere near Bonaire…
    you have to love a good mucus cocoon…
    kinda like the movie - mucus didn't test well with the early audiences…

  14. periscoping flamingo… (water is apparently the cause of most floods)
    disembodied periscope

    1. Stunning mirror image, perfectly symmetric except for the lighting.

  15. I have been exploring what life would have been like in the Mediterranean Basin between the Messinian Salinity Crisis and the Zanclean Flood, or Deluge we could call it. There would have been no humans at the time, but animals moved in there. I found a sort of guided lesson on air pressure which I wrote early in this millennium and here is one (not completely historically accurate) question I asked:

    “About 5.5 million years ago the Strait of Gibraltar closed and the Mediterranean Sea dried up, forming a vast desert. If its maximum depth was 3.17 miles, what was the air pressure at this desert’s lowest point?”

    At a depth of 3.17 miles the air pressure would have been a phenomenal 28.5 pounds per square inch, almost double the 14.7 we enjoy at sea level. At half of that depth, the air pressure would have been 20.5 psi, or 39% higher than sea level.

    For comparison, at the lowest point on land today, air pressure is 15.5 psi or about 6% higher than that at sea level. Even that small increase is noticeable and refreshing.

    What effect would this high air pressure have had on wind patterns? And on the movement of water when it started flowing in again?

    Information is endlessly available to us; where shall wisdom be found?

    1. from somewhere above seal level —
      human caused depth
      below sea level
      elusive sea level
      speaking of Utah - one perspective on wisdom
      "Wisdom can be defined as the ability to grasp human nature, which is paradoxical, contradictory, and subject to continual change. These two constructs hold potential for highlighting positive and adaptive features of development in the later years."
      …wisdom seems available for varying amounts from Amazon, but alas, seems to be out of stock at the moment…

    2. Thanks for all the quantitative data. It will keep me entertained for days. There seems to be some dispute as to whether Jericho or Baku is the city at the lowest elevation.
      The Fundamentals of Caring is on Netflix.

    3. speaking Baku…
      HOK - flames

      "Among the most startling additions to the modern skyline are the Flame Towers, a trio of sky-high structures that resemble tongues of fire reaching high over the Caspian Sea. Designed by US architecture firm HOK, and with Tower 1 standing at182 meters, they're the tallest buildings in Azerbaijan."
      …so at the top of the towers, you are above sea level…
      "Baku/Elevation - 91.9′"

      the three
      large firm, large projects
      HOK home

      Maiden Tower - at least it wasn't made out of iron…

    4. I hadn't thought about the air pressure connection--that's really interesting! Thanks.

      Equally interesting, but I didn't cover it in my post, is the formation of the salt deposits in the bottom the Mediterranean basin. The deposits under the Med are REALLY big--0.9 miles (1.5 km) thick! Check out: