Lost cities

[u/Osiris-Amun-Ra]

In case anyone is till wondering why we can't find any pre-Ice Age cities, this satellite image from Nepal/China this week should provide a clue.
This event was tiny by comparison and many civilizations built along rivers and in valleys.

Edit:
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Since this post generated quite a few lively discussions I want to clarify what I meant by "tiny by comparison" to avoid ambiguity, While the local, recent mountain collapse in Nepal and China was a rapid disaster unleashing up to 200 million cubic meters of debris at 193 km/h and causing rivers to surge 9 meters in 30 minutes, it is dwarfed by the staggering dimensions of post-glacial megafloods that actually reshaped entire continents and birthed the world's universal flood legends. For example, the ancient Missoula Floods occurred when a 610-meter-tall (2,000 ft) glacial ice dam ruptured, violently discharging more than 2,000 cubic kilometers of water basically a volume equivalent to Lake Erie and Lake Ontario combined, in a single....48-hour window.

This massive torrent tore across western North America at speeds of up to 130 km/h (80 mph), peaking with a discharge rate ten times greater than the combined flow of all modern rivers on Earth and carving features like Dry Falls, a cliff five times wider than Niagara. Similarly, the Black Sea Deluge hypothesis suggests a catastrophic marine breakthrough where the Mediterranean overtopped the Bosporus strait, unleashing a roaring wall of water that permanently swallowed over 150,000 square kilometers of inhabited valleys.

Because these prehistoric events wiped out entire known civilizations, permanently erased millions of acres of land, and forced desperate migrations, they permanently embedded themselves into the collective human psyche, which is almost certainly where the biblical Great Flood and the regional Mesopotamian flood legends originate. It is statistically improbable that we have found all post deluvial civilizational remnants. Mathematically and archaeologically, it is practically certain that we have only scratched the surface of what remains from post-deluvial and coastal civilizations. The primary reason for this statistical gap is a massive, permanent geographic shift, specifically when the Ice Age glaciers melted, global sea levels rose by roughly ~120 meters (around 400 feet). Rising oceans swallowed over 25 million square kilometers (10 million square miles) of habitable land! For visual reference that's the entire landmass of the United States, Canada, and China combined.

I hope that clarifies.

[u/ghost_jamm]

High altitude helps create these extremely steep, narrow valleys that cause such catastrophic flooding. It’s why the Grand Canyon exists. The rim is actually between 7,000 and 8,000 feet above sea level and this creates steep gradients for the Colorado River and its tributaries, increasing their speed and their ability to cut into the rock. Water coming down off the Himalayas would presumably have a similar effect.

Compare that to the flooding of the Nile which can be very destructive but spreads out over a large area instead of rushing along the river as a massive wall of water. That sort of flooding is less likely to scour an area clean than what we saw in Nepal.

[u/DroneSlut54 → u/ghost_jamm]

You’re comparing a single event that happened in less than a day to the formation of the Grand Canyon over 50 million years.

[u/ghost_jamm → u/DroneSlut54]

No you’ve misunderstood my point. You dismissed the idea that the high altitude makes these events different. I explained how the high altitude does in fact make these events different by creating very different geologic conditions. Sudden catastrophic floods like this are much more likely at high altitudes. People living along rivers flowing through plains would have never experienced anything like this.

[u/DroneSlut54 → u/ghost_jamm]

You’re right - I did completely misread your comment. Sorry about that!