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[NO-GO]

... at today's worst, a human scratched another human in half with his fingernails...

Looks like there is hope for you yet as a radiation-powered superhero, Meg Griffin!

[Mel_Vixen]

Oo its x-men two all over again.

[Na4SnBe2Si6O18]

So the implication is that you can always dig down far enough to hit magma. Is there a point, far enough down, that you would find nothing but endless magma, like reaching the planet's mantle?

Igneous petrologist here. The mantle is made of white-hot solid peridotite. You only get magma under certain specialized circumstances and even then you never get more than around 10% of it to melt. 

Dwarf fortress generally has excellent geology, probably the best I've ever seen in a game.

[MrWiggles]

So the implication is that you can always dig down far enough to hit magma. Is there a point, far enough down, that you would find nothing but endless magma, like reaching the planet's mantle?

Igneous petrologist here. The mantle is made of white-hot solid peridotite. You only get magma under certain specialized circumstances and even then you never get more than around 10% of it to melt. 

Dwarf fortress generally has excellent geology, probably the best I've ever seen in a game.

I always thought that it was a molten mantel. I know the core is solid due to the pressure. Is the molten model there to help explain the contential shifting?

[Bauglir]

I'd thought the mantle was more similar to really chunky stew or something, m'self. Mostly solid, but with enough fluidity for things to grind past each other. I've not had anything more involved than High School, though, so... Yeah. I'd defer to the expert.

[smjjames]

Its suppoused to be like a really viscous liquid. Theres also the fact that the granite basement rocks of the crust is lighter than the rock of the mantle.

Its not exactly a liquid like we think of water as a liquid, its more of a semisolid.

[madjoe5]

Will arena mode have some sort of copy and paste mechanism? It would make making large numbers of similar creatures much easier.

[smjjames]

Will arena mode have some sort of copy and paste mechanism? It would make making large numbers of similar creatures much easier.

Good idea if that hasn't been implemented already.

[Na4SnBe2Si6O18]

So the implication is that you can always dig down far enough to hit magma. Is there a point, far enough down, that you would find nothing but endless magma, like reaching the planet's mantle?

Igneous petrologist here. The mantle is made of white-hot solid peridotite. You only get magma under certain specialized circumstances and even then you never get more than around 10% of it to melt. 

Dwarf fortress generally has excellent geology, probably the best I've ever seen in a game.

I always thought that it was a molten mantel. I know the core is solid due to the pressure. Is the molten model there to help explain the contential shifting?

Its suppoused to be like a really viscous liquid. Theres also the fact that the granite basement rocks of the crust is lighter than the rock of the mantle.

Its not exactly a liquid like we think of water as a liquid, its more of a semisolid.

In almost all locations the mantle is 100% solid.
It's hot enough that it will deform ductily, similar to how you can bend plastic if you heat it somewhat. It's not flowing as a liquid, it's more crystal-plastic deformation and slip on crystal faces. The "viscosity" is so high that it will only flow anywhere on timescales of tens of thousands of years.
The only places you get partial melting are areas of adiabatic upwelling of the mantle (mid-ocean ridges & hotspots such as Hawaii) or where water is added by subduction of hydrous minerals and sediments (subduction zones such as off the coast of Chile). 
http://www.tulane.edu/~sanelson/images/geothermmelting.gif
Solid black line is the geotherm: the average temperature at a given depth. The grey field is where you get melting. You can shift the grey field to intercept the geotherm by adding water or move material from depth upwards faster than it can lose heat which casues decompression melting. Neither process will generate more than a few weight percent melt e.g. partially melting 1000kg of peridotite at a mid ocean ridge generates < ~100kg of basaltic magma.

[Chandrasekhar]

This is one of the few issues where I'd unequivocally support a departure from realism.  Folks like to have magma, and that means that a lot of people are going to only embark on maps that have magma available.  If magma is only available in a few places across a world map, then there's going to be a lot of tedium involved in finding a fun site.

Realism is a good default goal to strive for, but good game design trumps that, especially since a lot of geological principles are going to be thrown out entirely when DF starts suppoting cosmologies that don't necessarily even have a spherical Earth.

[Na4SnBe2Si6O18]

Oh yeah sure I agree completely here. You need a balance between realism and playability. We're talking about a game with zombie whales so it's entirely possible the worlds of Dwarf Fortress have unusual conditions of extra vigorous convection or whatever mechanism you favor. Could be tidal heating by gravitational kneading as on Io etc.

If you tunneled down into extremely hot rock the walls might start melting due to decompression before they could lose heat to the air of the tunnel. I'll need to think about that some more.

In the South African gold mines (3-4+ Km depth) workers have to worry about "rock burst". the static load on the rocks at that depth is ~1000 bars. When you tunnel through them, you leave a void at 1 bar pressure. The walls will sometimes explode inward with an effect similar to a grenade going off. 

[bombcar]

I like having magma be a bit rare. It's nowhere near as hard to find as it once was, and if it were everywhere as long as you dug deep enough, it would always be used.

As it is, it's hard to get everything you might want in one place, and that makes for more fun. Often you have to choose between magma and flux, for example.

[immibis]

I like having magma be a bit rare. It's nowhere near as hard to find as it once was, and if it were everywhere as long as you dug deep enough, it would always be used.

As it is, it's hard to get everything you might want in one place, and that makes for more fun. Often you have to choose between magma and flux, for example.

Make the magma-at-a-certain-depth controllable from the world generation or embark interface.

[Footkerchief]

I like having magma be a bit rare. It's nowhere near as hard to find as it once was, and if it were everywhere as long as you dug deep enough, it would always be used.

As it is, it's hard to get everything you might want in one place, and that makes for more fun. Often you have to choose between magma and flux, for example.

Make the magma-at-a-certain-depth controllable from the world generation

Already done.  So yeah, people should be able to make it as rare or abundant as they want.

[Neruz]

I like having magma be a bit rare. It's nowhere near as hard to find as it once was, and if it were everywhere as long as you dug deep enough, it would always be used.

As it is, it's hard to get everything you might want in one place, and that makes for more fun. Often you have to choose between magma and flux, for example.

Make the magma-at-a-certain-depth controllable from the world generation or embark interface.

It is, you can choose how deep the layers are and what layers show up and so forth. Also, the magma is real deep down, if you don't want to go for it, you don't have to. Odds are you'll really have to fight for it however.

Also, i disagree with bombcar's assertation that not having everything in one place is more fun. I find it distinctly less fun. Having to fight for resources or making them difficult to find is fine, but flat out saying "you can never have this ever because you got unlucky, har har" is no fun at all for me.


When we get the ability to set up multiple fortresses in the world and trade between them, then magma can become rare and prized again. Until then, having it always available is a huge positive as it means i don't need to hack the iron ores to appear in igneous rock.

--EDIT--

Ninjaed by Footkerchief.