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[vanatteveldt]

I got an interesting start with a vulcano that isn't actually a mountain, just a flat coastal area with a caldera in it (I edited world gen settings to get vulcanos so that is probably why these kind of things happened)

2 levels below the magma surface is an aquifier. I read the topic on breaching aquifiers with the 'double slit' method and the 4x4 corner pumps method, but I also read that it should be easy (and imho very dwarfy) to just use the magma to create an obsidian "caisson" to breach the aquifier.

I fiddled around with it and in general did something like this:

(1) dig out the aquifier, channel magma to a floodgate

#     X~~~~~~~~
AWWWWWA
AAAAAAA


A = aquifier
W = water from the aquifier
#= wall
X = floodgate
~ = magma

2) Open the floodgate, turn water into obsidian, cut away center, channel aquifier one lower


#     X~~~~~~~~
AO   OA
AAWWWAA


3) Repeat


I have two questions:

1) I can't think of a way to create a "shaft" instead of an inverted pyramid, e.g. what I do now is start with a 5x5 hole, then the outer obsidian wall is left alone to keep the water out, and the next level down is 3x3, etc. Is there a way to avoid having to start with an ugly 15x15 hole for a 7 level aquifier?

2) It takes me very long to do each level. If I let in a bit too much magma I need to wait for the for the magma to slowly evaporate. I can throw in "pond" water from above, but that takes a lot of time as well, especially since I have to start a big hole initially to get down deep enough, so I need to throw in 7x7 buckets or worse to reach the middle of the hole.

What do people normally do? just ignore the magma and start pumping?

[AutomataKittay]

I've not done any magma caissoning, but every projects I've seen that involves obsidian shaft involves building it layer by layer then dropping it. Casted obsidians don't deconstructs when they falls, unlike constructed materials.

A possible way to do it might be to cave in each 'pancake' as you digs in and out, if your miners are fast enough to dig out a few aquifier tiles each time, eventually building up an obsidian shaft, though it seems to be rather brute force approach.

On bright side you'll get a lot of obsidian rock to craft and sell?

( Personally I'd just use the pumps, obsidian casting takes too much effort, though it'd be cool late fortress project or for someone used to above-ground dwelling )

[ManaUser]

Is there any chance you can simply dig through the natural obsidian around the lava?

[vanatteveldt]

In my case, this was only one tile thick, and the wiki suggests that this is normally the case. It is not advised to dig through that layer ;-)


Actually, my embark site also has a mountain, and it seems that the stone under the mountain is solid, so if needed I can breach the aquifier from below. The added z-levels of the mountain mean that I haven't actually needed to dig down deep yet although I will need to go find metals soon. The embark site has no wood whatsoever, so that gives a nice extra challenge... happily playing around with magma smelters and glass makers.

Another question if I may: I pumped water into the caldera to make a nice little island to use as an entrance to my fortress. The obsidian was mostly flat but contained a couple obsidian "walls" above the obsidian floor, which I started digging out... but this resulted in cave-ins killing one miner and injuring another. Any idea what went wrong there?

As far as I can tell, the side crossection looks like this:


#####    O  O  /#####
    O   OOOOOOOO
    O~~~~~~~~~~O


And I ordered the miner to 'mine' the two loose O's above, which are listed as "rough hewn obsidian walls".

[Kaos]

maybe using retractable bridges?

1) channel a 3x3 hole on the first aquafier level (I think this is what you mean by a "shaft", a 3x3 with the center tile being stairs
2) build a retractable bridge to cover the 3x3 hole, and link it to a lever
3) allow magma  to flow and cover the bridge.
4) pull the lever, the magma falls on the water casting a 3x3 obsidian block
5) dig the center tile stairs....

ahhhh... I see... to dig the next 3x3 lower level you have to dig a 5x5 above it, and a 7x7 above it and a 9x9 above it and so on.... the best you can do to have a continuous 3x3 shaft, is refill with obsidian after you are done... so basically you end up with an inverted obsidian stepped pyramid with the shaft in the center...

[GreatWyrmGold]

There was an obsidian "floor" above the walls. I made that mistake once. Tossed the miner right into the volcano! Now I use up-ramps to do that stuff.

[vanatteveldt]

So you build a ramp, channel the floor, and deconstruct the ramp?

[GreatWyrmGold]

No, I use d-r.

[vanatteveldt]

Sorry for being a newb here... So what you do is turn the wall into an upward ramp, and then use d-z to deconstruct the upward ramp?

[GreatWyrmGold]

That's what I do. No cave-ins.

[vanatteveldt]

Thanks, will try. It's a shame my best miner will not be available to do the actual trying, though...

[Hans Lemurson]

How does falling water interact with falling magma?  Do they create a block of obsidian in mid-air, or does this interaction only take place in the presence of a floor?

If you channeled 2 layers into an aquifer, so that water from Z-1 is falling down into Z-2, if you then pour magma in directly above the channeled area, will obsidian form at Z-1 or Z-2?

If there's even a small chance that magma can make it into Z-2, then I believe a constant-diameter aquifer bore could be possible using an obsidian Caisson.  If the Magma always gets intercepted at the upper levels though, then you're going to be stuck with the inverted pyramid.

Alternately, you could cheat, and use other constant-diameter aquifer piercing techniques and then fill the hole thus created with obsidian.