...I forgot magma doesn't pressurize like water does.
When clearing a hill next to my wagon I found a nearly perfect 4x5 block of obsidian running down through multiple layers was randomly left behind as my miners happened to dig around it, so I kept it and began smoothing/engraving it. Ended up digging down a good ways into the fort, about 10 z levels top to bottom, but it made things unbalanced, so I dfhacked another column of obsidian to repeat it with on the other side, but THAT one had revealed interior blocks by default so I used up/down stairs to clear it and get the engraving done.
Then I thought... hmmm, I accidentally flooded part of my fort through a well with something like this on a much smaller scale... *liquids, m(agma), range 2x3x9* pow, engraved columns filled with magma, ready to go. Got the release tunnels set up, opened it for a test firing... wah-wah-wah-waaaahhhhh. It just sinks to the lowest level it can reach. T.T
Not to be deterred, I whipped up a magma-safe pumpstack, reloaded everything and hooked up a four-wheel perpetual motion machine in the basement, opened it up, giggled with glee at the magma starting to pour out all around my magma safe statues and constructions... and then realized I just started a brush fire in a fairly hot dry biome with heavy trees... it eventually made it around the entire map before there was nothing left to burn.
I thought it would be amazing as an elf caravan popped up just as it neared their side of the map but they happened to stumble into a natural firebreak, so I lured them closer with unforbidden doors, slammed them shut to break their pathing AI, and laughed as they stood there and melted while I started another forest fire...