if i were to channel out a moat and fill it with lava, from the top, would the rate of refill balance out the fill of the moat?
Probably not. The drain of the moat filling will likely eclipse the refill of the volcano by a large margin, and if your workshops are on the top level, they will lose magma and switch off.
When I build my magma forge area, I excavate a chamber on level -1 (to hold the magma), and a chamber on level 0 (to hold the workshops). Then I pump the reservoir full, then puncture the floor once pumping stops. You never need to worry about magma dropping mid-mood this way. (You can ruin a mood and lose a dwarf if magma workshops de-power due to magma loss!)
When I create the reservoir, I'm pumping magma out of the volcano into a fixed reservoir. Three bags of sand, three logs = Magma Safe Pump for 12 Embark points. (...and only three points, if you can cut wood on site to make charcoal.) The input tile of the pump has a ramp up to the level of the pump, and is directly adjacent to the magma-tube wall. Dwarf on level -1 smooths/carves, then walks immediately up the ramp and out of danger. A magma safe grate is placed over the ramp (keeps dodgers out of the lava, and magma critters out of the fort, magma doesn't flood up unless pumped), and the pump is manually operated to fill the reservoir from there.
i think i get the idea, but i have another question. a murky pool was generated right on the lip of my volcano. so much so that it's craterward side collapsed immediately on embark, and the water spilled into the crater, creating a bit of obsidian. not an amazing amount, perhaps slightly less than 1/16th of the total crater area. now, if i remember what i've read, 1 tile water + 1 tile magma = 1 tile of obsidian wall, right? so, if i were to dig it from the side (or channel down from the top?) i would be left with 1 tile obsidian floor, correct? and if i leave the border tiles intact (including those pesky corner tiles) i will have a little room inside the top z of lava, right?
taking the idea a step further, i could obsidianize the top of the crater, and piece by piece remove floor tiles and use pit/ponds to then obsidianize the level below and then channel down. then i could refloor each z level, leafinf a hole in the middle, surrounded by wall, and a ceiling on the top level i want to actually inhabit (but still under at least 1 z from the top of the tube) and then, through floodgates, open up that hollow middle bit to allow the lava to restore itself to the top of the crater, submerging all my rooms i've built.
then, as the moat draws from the top z, my magma workshops on my lowest in-crater floor would never have to worry about power.
or am i missing something glaring?
