when I got on... around 2 weeks ago (I didnt want to post it on forums at first, but my freind insisted once I told him about it.) at least 100 cave-ins all happened in a row, I could see all the cavern layers... and there were several giant pits leading all the way down to hell.
I decided to call it the armaggedon, but then it got way, way worse- besides the demons flying to the surface at embark, clouds of lava mist was coming out of the rifts, clay all around me was exploding from teh high heat, and the only reason I had even lived this long was because I had dug into the mountain (the part that WASNT exploding.) but the notifications of cave-ins were so common that I had to quit. I went on in adventurer mode... and... well, it was even more crazy. the town I started out in? its most populous part was swallowed whole by a massive fissure. Great clouds of lava Stormed over the surface, burning the citizens alive! the ground- which was clay- literally exploded every two seconds, making the world a minefield. Giant rock pillars appeared and began to move, crushing houses- I called them rock tornadoes, still dont know how they moved.- and I barely made it away with my life (travel mode FTW). when I returned to the edge of the town around 3 minutes later, the entire town was submerged in lava, with swarms of demons flying overhead.
(question, is there unlimited lava in the world? I dont see how multiple lava oceans could get to the surface.)
oh, ps.... I turned off cave-ins to get rid of the messages. and once I did that, the armaggeddons stopped. the holes there were still there, of course, but the lava (slowly) drained back into the earth, and for some unknown reason, the demons topside became less common. Also, no more fissures opened, no more rock tornadoes, and no more exploding earth.