The Congo Sea

[Chirios]

- The blue circles are the seas
- The black lines are the direction in which they drain
- The orange dot is where the Congo gets blocked.

An idea for a story that I'm working on.

The idea is that the Congo becomes blocked at it's entrance into real world Braazaville, (at the curve before it heads into the Gulf of Guinea), causing a giant inland sea to form. This sea then overflows drains along two routes, one, into modern day Gabon via the Ogooue river, second into lake Chad by joining up with the Chari river. http://www.mapsofworld.com/physical-map/africa.htm#. This, coupled with the effects of the Neolithic subpluvial, causes lake Chad to swell to an enormous size, and then drain out southwards, joining up with the River Niger, and heading out towards the Atlantic ocean.

Both lakes have existed once upon a time, my idea was just a way to make them both permanent, and slightly bigger.

I was thinking that the lakes would act as a giant head sink, and cool the surrounding areas somewhat, increasing rainfall slightly in Central Africa, West Africa and the Sahel. Thus when the Neolithic Subpluvial ends, the effects won't be as bad and the tribes that were resident there might remain in order to develop permanent settlements in the Sahel.

What I was wondering is:

1) If this idea is in any way plausible

2) How might the Congo be blocked?

3) Whether or not there's any way to drain Lake Chad into North Africa, and eventually out into the Mediterranean (that's the option with the coolest after effects).

[Simon_Jester]

I think you're greatly overestimating the ease of forming an inland sea, especially one whose floor is probably hundreds of meters above sea level. You need higher ground on all sides- river basins don't necessarily qualify, as the ground often slopes fairly evenly towards the sea, such that blocking the river channel at one point just causes it to flow around.

The ground to the north, the Sahara, is generally higher than the hypothetical lake basins you describe. This makes it extremely unlikely that water would flow through the desert, even if such a massive inland sea could be formed.

[madd0ct0r]

what time period are we looking at?

becuase from the way you're writing, it seems paelolithic.

(which rather limits the civil engineering available)

when did these lakes exist in the past?

have you included the eroision of the new riverbeds increasing their draining capacity (shrinking the lake)?

is africa plate tilting at all?

[Chirios]

I think you're greatly overestimating the ease of forming an inland sea, especially one whose floor is probably hundreds of meters above sea level. You need higher ground on all sides- river basins don't necessarily qualify, as the ground often slopes fairly evenly towards the sea, such that blocking the river channel at one point just causes it to flow around.

The ground to the north, the Sahara, is generally higher than the hypothetical lake basins you describe. This makes it extremely unlikely that water would flow through the desert, even if such a massive inland sea could be formed.

The ground at the exit through Braasville is lower down than the ground in the Congo basin. The only equivalent area is through the Ogooue, which is actually what happened historically. The Congo lake used to exist, but when the exist through Braasvile (the orange dot) formed due to erosion, the lake decreased in size until it became what you see in the modern day.

And if you look at this map, you see that the land around the Congo river basin is is higher in elevation than the Congo river, and it's main tributaries, except, out through the modern day path; through the Ogooue; and into the Chari river basin, which flows out into Lake Chad. It's harder to see on my one because I've coloured that one in.

@ Maddoctor, Lake Chad definitely used to exist, and was about 400000km in size. It reached it's zenith during the most recent Green Sahara phase, when rainfall in the Sahel was much larger. Lake Congo did exist (or at least there's lots of evidence that suggests that a Congo lake of approximately the same size existed) but I can't remember when.

[Chirios]

what time period are we looking at?

becuase from the way you're writing, it seems paelolithic.

The Event needs to occur while humanity is still in East Africa, or after they've reached the Middle East, so basically either between 200000BC and 100000BC.

[Sea Skimmer]

Old idea; and you think too small! In 1920 German architect Herman Sörgel proposed that the Mediterranean should be damned for hydro power, lowering it level and also allowing for more hydro power from the rivers flowing into it as they now fall into the lower sea. He also wanted a Congo river dam which would fill up to flood Chad and overflow to the Mediterranean. Between the two plans most of the world could have been powered. p





The Gibralter dam isn't likely to work; but a Congo dam most likely could be built in the vaguest sense, if you accepted spending trillions of dollars on it for at least a hundred years doing it, after fighting wars with all the nations it will completely flood. The only plausible means for building a dam that large would be a earth and rock fill gravity dam. You would blow up mountains across the region, bring the largest boulders possible along with endless megatons of rock fill and clay for the waterproof core and just mound it all up for decades. You'd need to pause at times, to allow time for the shear mass to compact itself, constructing too rapidly would risk a land side style collapse.

But even given World UN Conspiracy Level powers and money to let you start work, it is possible that the ground at the site wouldn’t be strong enough and such a massive dam would simply sink into the earths crust and collapse. That’s actually a non trivial concern with the far far smaller Three Gorges Dam. The rock below would need to be very firm because you are literally going to move a major mountain on top of it. Also once the lake begins to fill it would alter the climate, and rainfall might actually diminish as the rain forest is wiped out. Filling the lake would take… I have no idea but a very long time. Luckily filling could begin before the damn is completed.

So plausible… not even remotely. Possible, yeah sure, a world government would help as a believable means to fund construction and wipe out independent nations who are in the way. The biggest problem is... having a giant lake doesn't really change how much hydropower you can generate in a given year, that's still rainfall dependent. Overflowing into the Med is a way to cheat at that but umm... a Gibralter dam would need to be over 3,000ft tall at places. Good luck with that.

Edit: if this can be aliens in the past doing it, then given enough sci tech they could just take an asteroid, carve it to be roughly dam shape, and then lower it down from orbit with anti grav to form a ready made ‘plug’

[Chirios]

Old idea; and you think too small! In 1920 German architect Herman Sörgel proposed that the Mediterranean should be damned for hydro power, lowering it level and also allowing for more hydro power from the rivers flowing into it as they now fall into the lower sea. He also wanted a Congo river dam which would fill up to flood Chad and overflow to the Mediterranean. Between the two plans most of the world could have been powered.

Yeah, I did get the idea from that architect. There's an earthquake prone region pretty much beneath the region I'm talking about. Could an Earthquake block the area sufficiently? Or cause a fissure which results in magma rising, mixing with the water and then blocking the area again?

I don't want to have to use aliens, and I wanted this to affect human development such that you might have city states along the twin seas trading with ancient egypt.

[Simon_Jester]

An individual earthquake- no way; the mass of rock that needs to be moved up (up is harder than down) is too large.

But now that I hear more about this, understand the concept better, it's more interesting... It would require some very strange quirks of geology to make it happen, but as a pretext for writing an alternate-history story it's got some things going for it.

EDIT: The more I think about it, the more I cannot imagine the Gibraltar Dam happening- even if the engineering's possible, the politics aren't.

[Sea Skimmer]

Yeah, I did get the idea from that architect. [img]http://0.tqn.com/d/geology/1/0/6/G/africa.jpg[img] There's an earthquake prone region pretty much beneath the region I'm talking about. Could an Earthquake block the area sufficiently? Or cause a fissure which results in magma rising, mixing with the water and then blocking the area again?

A large enough volcano could block the area, see the Siberian tarps for how big a volcano can get, but it might well destroy the rain forest while it was doing so and change the weather to be much drier. A single earthquake won't work without being able to cause a large landslide or similar 'extra' movement of material; a long series of earthquakes in a compression fault might uplift enough rock to block it... such movements did block Gibraltar after all. But it’d be hard to uplift quickly enough to avoid the Congo River simply carving a new channel through the rising mountain; my state Pennsylvania is full of examples of this like the Delaware Water Gap. Best bet is a moderately large volcano initially blocks the river, and then the land uplifts some as well creating a long lasting barrier. For a fictional story that’s a good enough explanation. A volcano on its own likely could work; life would just have to get lucky that it was not too small, not too big.

If you want to keep things 'balanced' you could even specify that a different volcanic hot spot on earth doesn't exist.. but that's not really necessary for typical story writing.

[madd0ct0r]

accoridng to wikipedia: http://en.wikipedia.org/wiki/African_Plate

the congo itself is a craton - a very stable part of the plate. this logically means the bits around it might be more unstable?

[Chirios]

Okay, so, here's the idea so far:

100000BC: A large earthquake in that region causes a fissure to form in the region near the exit in Braasville.

80000BC: The magma mixing with the water from the river causes the region to become blocked.

60000BC: The entirety of the Congo river basin has filled with fresh water, forming an inland sea. It begins to exit through two regions: the Ogooue basin and into the Chari River. Lake Chad begins to fill.

30000BC: Lake Chad has filled up. The presence of the Chad Sea results in greater rainfall in the South where the sources of Lake Chad are, and in the Sahel, filling the depressions there.

20000 BC: Human tribes from Kenya have now reached all of West Africa. The presence of the Twin Sea's has made it easier for humanity to travel across Northern, Western and Central Africa.

[madd0ct0r]

Well, I think we might be over complicating it.

the story is about the africans, not the geology. Just say the African plate wrinkled slightly differently as it cooled originally. Much simpler (and with less side effects) then having magma punch through a continental plate

[LaCroix]

Well, I think we might be over complicating it.

the story is about the africans, not the geology. Just say the African plate wrinkled slightly differently as it cooled originally. Much simpler (and with less side effects) then having magma punch through a continental plate

This.

You want to have this thing done in prehistoric times for your story, so it always was this way - just write it. If you say that in your world, there is a lake here and there, and it drains there, then that's how it is. If it happened while the continent formed, it was long before any human could have witnessed a dry Congo. You don't have to explain why Hoth is an ice-world or why Naboo has huge oceans - it just is that way.

Just mention it in passing that this happened due to some high mountains next to lake Congo, so the readers have an inkling why it's different than our world, and proceed. They don't need to know that it happened because at some point time, a particular stream of lava burped when it should have farted.

[Serafina]

Quite. There is absolutely no way you can create this inland sea without altering the geology massively anyway. Neither volcanoes nor earthquakes are possible in that region unless you do so.
And since your other options boil down to "aliens did it" and "very specific meteor strike", going with "it just happened that way when the earth was formed, merely by chance" is a very good option.

Unless your story revolves around the lake forming in relatively recent geological times, just make it so and screw the exact origins.

[Chirios]

Quite. There is absolutely no way you can create this inland sea without altering the geology massively anyway. Neither volcanoes nor earthquakes are possible in that region unless you do so.
And since your other options boil down to "aliens did it" and "very specific meteor strike", going with "it just happened that way when the earth was formed, merely by chance" is a very good option.

Unless your story revolves around the lake forming in relatively recent geological times, just make it so and screw the exact origins.

Might just go with "aliens did it". Hey, it worked for the Ring of Fire Verse.

Thanks ppl.

Another option I was thinking of instead was blocking the Upper Zambezi from the Lower Zambezi, thus forcing the Zambezi back into the Makgadikgadi salt pans. But I think that would have fewer storyline options than the Congo Sea.

[Simon_Jester]

If the aliens are unnecessary and you can just say "well, the Earth happened to form that way millions of years ago," it's best not to use the aliens.

[Chirios]

Alright thanks guys. What do you think the effects on the environment would be?

There's going to be greater rainfall across most of Africa, for sure, due to the lower albedo. This might reduce the size of the deserts, which would have quite bad effects on the America's which receive sand grains and nutrients from Africa each year, so the effect might be that Africa becomes slightly more hospitable, while South America desertifies.