Rules for lava / magma

[Blue Ghost]

Are there rules in GURPS for effects of lava and/or magma? Specifically how much heat damage do they deal to a normal PC standing nearby? Are there also rules for just Volcanic activity in general and sulfur dioxide?

Thanks much for any reply.

[A Ladder]

Per Dungeon Fantasy 2 (p. 19) falling into lava does 8d+2 burning (average 30 points). Which is enough damage to immediately light most things on fire (see Making Things Burn and Flame in Campaigns p. 433).

I would also probably make my PCs roll against choking on the toxic gases of a lava pit (see Hazardous Atmospheres in Campaigns p. 429 and take a look at the Lethal Gases and Suffocating).

If the PCs are just standing near lava I would divide burning damage by 3 for every yard away they are from it (So 8d+2 burn if they fall in, 3d burn if they're standing right next to it, and 1d-1 burn for two yards out). Then make sure that things taking too much burning damage catch fire (per the pages mentioned above).

[Celjabba]

This thread http://forums.sjgames.com/showthread.php?t=85770
have some info too.

[Blue Ghost]

Many profuse thank yous to both of you for your replies.

Much appreciated.

[clu2415]

Remember that pudding and the Dead Sea are about 1.24 g/cm^3 while magma varies from 2.2 to 2.8 g/cm^3. It would be a challenge to sink into it.

[Bruno]

Originally Posted by clu2415

Remember that pudding and the Dead Sea are about 1.24 g/cm^3 while magma varies from 2.2 to 2.8 g/cm^3. It would be a challenge to sink into it.

However very few people gently wade out into lava. You can DIVE and FALL into it. Doing a belly flop would be horrible though.

For comparison, there are videos of people throwing bags of garbage into volcanos with open lava caulderas. The garbage is camp waste, mostly food scraps, and dropping a decent distance had the bag of garbage vanish under the surface. And then all the liquid vaporized and lava started fountaining everywhere quite spectacularly :D

So what happens when you fall into lava? You die! But it's awesome looking.

The trickier situation is when improbably durable people fall into lava.

[Johnny1A.2]

Originally Posted by Bruno

However very few people gently wade out into lava. You can DIVE and FALL into it.

Sometimes, the outer layer of a lava flow solidifies enough that people can walk on it, while hot liquid lava continues to run within the shell, just inches below. (Rock is actually a decent insulator.)

People will sometimes walk on this lava crust, but my attitude is 'better them than me'.

[Bruno]

Originally Posted by Johnny1A.2

Sometimes, the outer layer of a lava flow solidifies enough that people can walk on it, while hot liquid lava continues to run within the shell, just inches below. (Rock is actually a decent insulator.)

People will sometimes walk on this lava crust, but my attitude is 'better them than me'.

I still wouldn't want to swan dive onto it. Ice that can hold you walking gingerly is not necessarily ice that can hold you jumping up and down on it. Stone and ice are annoyingly similar in the brittleness department (admitedly barely-solidfied stone is probably doing better in plasticity but if you step on the "crust" and it's like mud, you have a big problem)

[Dalin]

Originally Posted by clu2415

Remember that pudding and the Dead Sea are about 1.24 g/cm^3 while magma varies from 2.2 to 2.8 g/cm^3. It would be a challenge to sink into it.

If an otherwise normal human (i.e., standard density) could resist the heat somehow, how would they interact with the magma? Could you swim through it? Roll across the surface? Stand up? (My conception of how buoyancy operates is limited to whether a rock will float.) Is the viscosity of the fluid important?

[Bruno]

Originally Posted by Dalin

If an otherwise normal human (i.e., standard density) could resist the heat somehow, how would they interact with the magma? Could you swim through it? Roll across the surface? Stand up? (My conception of how buoyancy operates is limited to whether a rock will float.) Is the viscosity of the fluid important?

Magma/lava are pretty much more viscous than water. Some is only modestly more viscous (like in Hawaii which has famously runny lava), a lot of it is a LOT more viscous. Viscosity matters in that it dictates how fast the liquid can "move out of your way" when you step or fall into it, as well as when you push against it to "swim", walk, burrow, whatever.

A substance with high viscosity and low density than you would have you *smack* into it like a nigh-solid surface and then sloooooooowly sink into it all the way to the bottom. The opposite, a substance with low viscosity ("goo-y-ness") and more density than you (e.g. water - air in your lungs tends to make you less dense) will have you splash into it (potentially all the way to the bottom and bashing yourself painfully on said bottom), then bob up to the top.

Consider Honey, a substance you're probably much more familiar with than magma and lava. It is both denser than water (to the tune of about 50%) and obviously much more viscous. Magma and lava are ~ 2 to 3 times as dense as honey, but it's still a good mental model.

You can "drop" a wooden spoon into a jar of honey from right above the surface of the honey (also known as "gently placing") and it doesn't really "sink". It kinda sticks on top. It will fall over, though. It's not stable on the narrow end.
If you drop it from a few feet up it does go in a bit - it's a narrow-ish shape and that helps combined with the extra energy from falling makes it cut through the honey just like diving helps you cut through water (Compare a belly flop). But it doesn't go very far in a large jar because the honey is so gooey that it doesn't have the energy to shove itself all the way down. Then you have to wait veeeery patiently, and the spoon will rise up to the surface of the honey and "bob" there sideways.

If you gently place a metal spoon into a jar of honey, it will start sinking. A lot slower than water - the steel spoon is much more dense than the honey, but honey is still sticky-gooey.

If you drop that spoon, it will pierce the honey and *chunk* hit the bottom of the jar (do this with a plastic jar) but still not super duper fast compared to water. It doesn't rise up again, because it's denser than the honey.

PCs are significantly less dense than lava, even with say metal armor and a 60-lb backpack of junk, but when you step onto lava, it's a very small cross-section of you that concentrates that weight - your feet are just a very small cross sectional area. You'll start sinking in, just like you sink into snow without snowshoes. You'll also be unstable, and you'll fall over into a much more stable but death-y position of lying on top of the lava. If you had "lava shoes" you could slog around on top, except that lava is super way more sticky and heavy than snow so you'd still probably become unstable and fall over. Walking on lava without the hard, dry, non-sticky crust requires not getting stuck to the lava and big wide feet, or magic. I prefer magic.

If you fall in from a height, e.g. a bridge over lava, rim of the volcano, etc (more "normal" scenarios than randomly wading into the stuff IME, but if you're immune to heat/fire i guess you might just walk out ), you can splat into the lava, to a depth determined by your cross-sectional area and velocity on impact as well as your density. Because you're pretty low density compared to lava and it's viscous, you probably won't go every deep even if you jump from 40-50 feet, but "a couple of meters" is super problematic even if you can't be cooked, carbonized, or suffocated. It's heavy and sticky and while you'll eventually rise to the surface you'll still have it all over you and getting out will be like struggling your way out of a vat of honey.