I spent two dwarf years carving out a set of spiral impulse ramps up from the magma sea, and another year figuring out the dumping station at the top and how to get the cart to keep moving through the magma at the bottom. With the addition of a perpetual motion plant, I now have a minecart based magma elevator! Sadly though, it lifts magma at a very, very slow rate. And murders children and dogs. Some design modifications later, and the tracks are sealed from all dwarves! Safety ensues. But the magma is coming in so slowly that it's evaporating faster than I can get it up from the sea. A system for adding more carts in without endangering dwarves is added, taking about 3 months to implement. Finally, 5 years after the building started, I have magma forges, smelters, glass furnaces and kilns, a mere 10 layers below the soil.
The device was finally deactivated.
Later, in an attempt to get rid of the 5s and 6s dancing around in the magma trench, and replace them with glorious 7s, I kept the device running, until it overflowed and melted all my non-magma safe track stops and rollers -_- now the 6 iron carts keep going round and round, and the safeguard I put in in case of this sort of emergency, a floodgate to block the water in the power plant at the bottom, isn't working because some fool of a dwarf dropped his Armok-damned socks into it. So now the whole pipe to the surface is slowly filling up with magma, and I can't disable it because the carts just pummel to death anyone who walks on the tracks.