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Journal by khallow
I just drove through what is presently the largest known terrestrial landslide, the Heart Mountain slide. It happened a vast 48-50 million years ago, but you can still see some traces of it today in dark colored mountain peaks in the area.
Geologists found the landslide when they discovered this mountain with a peak that was almost 300 million years older than the rest of the mountain. It happens to be a short distance from the far better known Yellowstone hot spot, which generated (in addition to over a hundred other major eruptions) one of the largest known volcanic eruptions of the past 26 million years.
Apparently, the volume of the landslide was about 2000 cubic km which is similar in volume to that eruption. It's interesting to see how many categories of disasters have prehistorical evidence for disasters far bigger than anything we've seen in human history.
Geologists found the landslide when they discovered this mountain with a peak that was almost 300 million years older than the rest of the mountain. It happens to be a short distance from the far better known Yellowstone hot spot, which generated (in addition to over a hundred other major eruptions) one of the largest known volcanic eruptions of the past 26 million years.
Apparently, the volume of the landslide was about 2000 cubic km which is similar in volume to that eruption. It's interesting to see how many categories of disasters have prehistorical evidence for disasters far bigger than anything we've seen in human history.
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
Kirk to Enterprise -- beam down yeoman Rand and a six-pack.
(Score: 1) by khallow on Sunday March 07 2021, @07:00AM (7 children)
(Score: 2) by Arik on Sunday March 07 2021, @08:24AM (6 children)
If laughter is the best medicine, who are the best doctors?
(Score: 2, Interesting) by khallow on Sunday March 07 2021, @03:39PM (5 children)
(Score: 2) by Arik on Sunday March 07 2021, @04:52PM (4 children)
People, then as now, tended to concentrate on the coastlines and in the valleys along rivers. The carnage must have been incredible. Some people think this is the event that gave rise to many similar flood legends around the world.
If laughter is the best medicine, who are the best doctors?
(Score: 1) by khallow on Sunday March 07 2021, @06:24PM (3 children)
Probably not. The landslides would have happened shortly after the glaciers retreated. There wouldn't be much food for anything except a few hardy plants so not much reason for anything, including people to be in harms way. And the sea level rise was so slow (~120 meter rise mostly over 10k years with some pulses of fast sea level that would have been 5 or more cm per year) that the carnage from sea level rise was probably little different than the carnage without sea level rise. I think there's one or two big flooding events, Black Sea [wikipedia.org] and perhaps some parts of the Doggerland (which eventually became completely submerged in the southern part of the North Sea), due to the relative weirdness of European/Mediterranean geography. But even then, the casualties from direct flooding was probably pretty light. I heard, for example, that the Black Sea flood was slow, taking about a year to fill to its current dimensions. If you weren't near the inlet when it started to fill (which probably was pretty catastrophic since it's apparently now , then you probably could have easily walked out of the flood zone.
The hypothesized Black Sea flood is notable for being a possible cause of the Indo-European migrations, which might have included a bit of carnage, depending how peaceful they were. That might have been a source of flood legends.
Bottom line is that most of these disasters would either occur away from most human occupied land or be slow enough that you could walk out of the area of effect. Thus, I don't think they directly killed many humans. The accompanying human migration might be a different story.
(Score: 2) by Arik on Sunday March 07 2021, @07:17PM (2 children)
Well, by human scales, even the glaciers retreat would have been slow, as you correctly worked out. Leaving plenty of time for flora and fauna of all kinds to move in as it was still in progress.
At the same time, once a landslide starts, it happens frightfully fast, even by human scale. So I see more than enough opportunity for carnage here.
"And the sea level rise was so slow"
Except that's not really so slow, when you realize that's a global average and local values behave very differently. Some spots would see very quick rises and falls. Also just a 5cm change is enough to turn a beach paradise complete with numerous easily caught sources of food into a salt marsh full of mosquitos and crocodiles.
Yes, it would have been slow enough that /most/ people could escape the worst effects, one way or another, but everyone would have been affected and many would have died prematurely, one way or another.
"and perhaps some parts of the Doggerland"
*Perhaps some parts*? Really?
Just how do you suppose *any* of it winds up beneath the north sea without being catastrophically flooded at some point?
That and the Black Sea are good examples of cases where we *know* this happened, and both were (by the standards of the day and region, at least) heavily populated areas. Even before agriculture, fertile lowlands draw larger populations, because they can support larger populations, and because hunters go where the game is.
How many actually drowned on Dogger Bank? I would suspect relatively few, there would have been a lot of time to flee from the water *in most cases* but when people retreat from water they tend to go towards the high points, and that wouldn't necessarily have been a safe direction long term. The Dogger Hills would have been filled with people and other animals retreating from the water, creating overpopulation and leading to food shortage; and eventually even those hills sink beneath it.
Did they know how to make canoes? Probably, there's a surviving example from the area that's old enough, it's a pine dugout. But did that last generation even have any pine trees left when they realized they had to leave? And even if they did have the trees, and made the canoes, by that point they would have been quite some ways from the coast. The North Sea probably was no more gentle then than now. Perhaps an intrepid traveler showed up with a boat from somewhere else, where they still had trees, and wanted to rescue them. Perhaps some told him no, they would die where their ancestors were buried instead of risking the journey. We'll never know exactly what happened, but that's likely the character of it.
"then you probably could have easily walked out of the flood zone."
If you were near the other end of the plain, and somehow *knew* that you needed to leave, then yes, doubtless.
But how would you know? At the moment the water is breaking through hundreds of miles away, there's certainly nothing to tell you this. How close does the water come before people of the time would have known to start running?
If laughter is the best medicine, who are the best doctors?
(Score: 1) by khallow on Sunday March 07 2021, @09:02PM (1 child)
By it being flooded slowly.
And that's pretty much that.
I doubt there would be any such local effects unless a basin like the Black Sea were being filled in. Past that you're getting into effects like ocean currents and land subsidence/rebound which would be on the order of millimeters per year (or less!), similar to today.
Well, how close would it need to come before they say "Hey! That's a lot of water!"
(Score: 2) by Arik on Sunday March 07 2021, @09:36PM
I would think that it doesn't really matter how slowly it floods, if it's an island that becomes a sea mount, it undergoes catastrophic flooding.
"And that's pretty much that."
Not really. Just because someone in the area could make a canoe, doesn't mean anyone on the disappearing island could do so; and remember we're talking about a small, crude, dugout canoe at best. In open water, very very cold open water.
"I doubt there would be any such local effects unless a basin like the Black Sea were being filled in."
NOAA gives a 40cm spread for local effects currently. https://oceanservice.noaa.gov/facts/globalsl.html (the graphic at top)
Granted, the negative measures seem to be concentrated in deep sea areas. Why? I'm not sure, so I'll assume that this is inherent and not accidental so as to very careful not to overestimate; giving more like a 20cm variance in shorelines. That's still considerably more than your 5cm/year estimate. Notice that red hotspot in the Baltic Sea? That's where glacier fed rivers feed into the sea. The Black Sea is also fed by snowcapped mountains and also shows a nice red spot.
Lots of yellow and red near the poles, where glacier meltoff is entering the ocean. A huge red patch centered around Indonesia, the Philippines, Papua, Micronesia, Melanesia - areas with heavy rainfall. The shoreline varies up to 20cm higher than the global average sea level as a result of these sorts of inputs currently.
At the height of the meltoff the local differences would not have been any /less/ dramatic than they are now. They would develop quickly, and then fade slowly as the global average increased more slowly.
If laughter is the best medicine, who are the best doctors?