"Also worrisome is Lake Kivu, a lake over 1,000 times larger than Nyos and in a much more populous area."

I stayed on the Rwandan side of Lake Kivu and had a great relaxing time. Met many peace core volunteers.

Lake Kivu is a major source of methane gas, which powers much of Rwanda. I am assuming they are very aware of the dangers. If something like that would happen at the scale of Lake Kivu, it would be a major catastrophe. That said, I encountered nothing regarding the potential of disaster. Nothing like tsunami/flood zone warnings. Rwanda tends to be a bit more western (aka not chaotic African) in its safety precautions. The DRC on the other side would definitely be more lax.