Alternate Geology

There was a post on the Alternate History Online Facebook group earlier this month on a plan nearly a century ago that would have included the damming of the Congo river to create a pair of large lakes in central Africa. That got me thinking back to a novel by Philip José Farmer, Hadon of Ancient Opar. One of the things in that book was a map of the fictional Africa of that story - showing two giant fresh water lakes in the center of the continent.

I sketched my own version of that map using a map of Africa that included contour lines. I never got around to using it in my old GURPS Alternate Earths role-playing game campaign, but I have since scanned the sketch and colored it a bit. Here is is:

This map is upside-down since it was originally going to be for an ancient Africa, about the same time period as the early dynasties of Egypt. That being the case I put south at the top of the map since water flows down and the source of the Nile was in the south.

This opens up an idea of alternate geology being a trigger for an alternate history. Not only can a different outcome of an important event create a divergent timeline, but a few misplaced mountains, slight change in the speed of continental drift, or other geologic events could have an even greater effect on the course of human history.

Right now I'm going through my old notes for the civilizations I was going to put around those lakes. Some of the names and cultural notes need some updates, but I think I can create some very interesting scenarios.

What other major geological changes do you think would be interesting? How do you think they would change our history?