which reminded me of something I've read: after a whole bunch of eruptions/disasters in various places, one of the things you read is some variation of "The locals didn't know the mountain was a volcano." Little or no record keeping other than verbal, and that apparently not touching on nastiness like "The last time the hill over there caught fire".
Which caused me to look for some more volcano stuff at the library, which led to a dvd about Mount Nyiragongo. Which the locals damn well DO know is an active volcano, but which doesn't prevent a bunch of them from starting to rebuild homes on top of the lava from the eruption the ran like hell from not long before. Even after they were warned that there is the possibility of very fast-moving lava rising up from crevices that run underneath the freaking town.
Which brings me to the reason for this whole mess: carbon dioxide. The stuff seeps up from lava degassing in many volcanoes; sometimes it seeps into a lake and, when things get disturbed, surges up out of solution, flows downhill and kills things. Nyiragongo is doing the same charging to Lake Kivu(right next to a big city, of course), but the stuff is also seeping up over large areas of the countryside and gathering in low spots. And killing people.
Ma Nature; she's got lots and lots of ways of turning you into fertilizer.