The desire to see volcanoes active and the land flooded with magma has lead my dwarves to fix both problems with the use of dwarven mechanics.
If, using a normal stack of pumps, you've tried to flood the map with magma before you'll be aware that it spreads too slowly and dries too quickly to coat the whole map.
The problem is that while the pumps are fast enough they never receive a constant supply of 7/7 magma. This is because magma spreads slowly and often when you breach the magma pipe the source tile for the pump stack is only being fed by three tiles.
The solution to this problem is to submerge a stack of magma safe pumps in the magma pipe allowing them an almost constant supply of magma from all sides. Having the top few levels of the pump stack out of the magma and plugging the pipe one level down helps the magma spread on the surface.
The designOne level down a plug has been established to stop already pumped magma from falling back down the pipe. Bridges should also be used to allow it to refill. Powering from bellow is possible but it would have disrupted the flow slightly in my working example.
The result:384 pumps, 4 on each of 94 levels, 4000+ power. The above image shows the map after only 20 of the 94 levels of magma pipe have been emptied. It achieves this level of coverage after surprisingly little time.
This is just a working concept; I plan to rig one of these up to a water clock and have it erupt on it's own every now and again in a future fort. Building smaller reservoirs of magma with submerged pumps would allow for the fast delivery of magma in more limited traps.
A detailed explanation of it's workings.
A map from which the above image was created.