Recently, I've been trying to work with a volcano in a flat glacier; just now I've perfected an obsidian farm that works without any pumps as long as you have both; all that's necessary is walls, bridges, levers, and of course, some miners.

For those who are asking "why no pumps?": I just happen not to like them. I find it annoying to have to get pipes so often, since they have to be made from non-replenishable resources.

Top level:
OOOOO
O_BBD
d_BBO
O_BBD
OOOOO

The right side should be connected to some lava, which can be obtained from the volcano.

Bottom level:
OOOII
OoIII
OoIII
OoIII
OOOII
Legend:
O = wall
D = mechanical door
d = dwarf-open door
_ = blank space; place to dig a channel
o = place to be filled with obsidian. May or may not be filled with ice at any time.
I = ice
B = Bridge (aligned vertically and raisable); should have a floor beneath them.

To operate:

Leave the right bridge down, keep the right doors and left bridge up. Open the right doors, and fill the area above the right bridge with lava (3/7 is best). Close those doors. Then let the left bridge down. The lava will spread out approximately evenly. This will melt the ice in the center of the bottom, letting water spread to the leftmost squares (as they will be empty after operation). Lava will then spread further, mixing with the ice and leaving obsidian at the bottom of the left. Close the middle bridge and right bridges to clear the lava, wait for the melted water to ice up again, and channel out the newly formed obsidian. Rinse, repeat.

This can be remade on a grand scale, which is my next project.
=Uncool-