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An area of my planet is very saturated with lava. Being quite similar to the Siberian Lava Traps, it is essentially a lava sea. This lava “sea” area isn’t necessarily all lava however, as there are actually some rocky islands dotted about the sea.

Life, always finding a way, has seeded themselves on these islands. They’ve even achieved sentience. Being incredibly heatproof however, costed them their looks, the other sentient races labeling them “demons”. They’re quite nice though, just misunderstood.

For some reason, the lava doesn’t emit any greenhouse gases nor does it emit gases not conducive to life. That’s why the rest of the planet is very Earth-like. Only being near to that area would you start to feel the heat.

Is there any rock or metal that this molten sea should be composed out of, so that it won’t emit greenhouse and poisonous gases?

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  • $\begingroup$ ? This is how the typical landscape in the Siberian Traps area looks like. No need for exotic life forms. Lava cools down, wind brings soil and seeds, in a few centuries you have a spectacular landscape teeming with life. Or do you mean that the massive eruption is still going on? $\endgroup$
    – AlexP
    Apr 6, 2020 at 7:50
  • $\begingroup$ @AlexP the planet releases the special lava every now and then to replenish the lava seas. $\endgroup$ Apr 6, 2020 at 8:12
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    $\begingroup$ You're making a fundamental error here, by supposing that basaltic lava flows were (and still are) a short-term phenomenon. They're not: they're something that happen over at least hundreds of thousands of years. If you visit for instance Craters of the Moon National Monument nps.gov/crmo/index.htm you'll be standing in just such a lava flow. "The time between eruptive periods in the Craters of the Moon Lava Field averages 2,000 years..." $\endgroup$
    – jamesqf
    Apr 6, 2020 at 17:31
  • $\begingroup$ If you want sizeable lakes of molten lava, you need to move to someplace like Jupiter's moon Io: space.com/36788-lava-waves-jupiter-volcanic-moon-io.html $\endgroup$
    – jamesqf
    Apr 7, 2020 at 4:48

2 Answers 2

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tl;dr

Pick one, not two:

  1. Small ephemeral lava flows, and no persistent wide lava "seas". Habitable planet.
  2. Large persistent lava seas. Inhabitable planet.

Lava, by definition, is molten rock at the surface. Taking that limited definition, there is no problem being around lava, more than being around molten chocolate is more dangerous compared to solid chocolate. People stand just next to Hawaiian lava flows all the time.

The problem is that it's very hot. You obviously don't want to touch the lava, or stand too close.

Lava does not necessarily have toxic gases. The most abundant volcanic gas is H2O, which is dangerous when at several hundreds of degrees, but rather nice when liquid. Some lavas contain gases like carbon dioxide, hydrogen sulfide or sulfur dioxide, but not all. Another interesting fact is that once on the surface, the gas bubbles away very rapidly. So you can imagine a volcano erupting lava flows, and by the time the flows reach the bottom, several hundreds of metres away, they have already degassed and quite safe to stand next to.

Your problem is not the necessarily the toxic gas. It's keeping the lava liquid. Lava tends to solidify very fast. It quickly forms a solid crust on the top where in contact with the much colder atmosphere, and then lava flows underneath in lava tubes. The top of the lava tubes is usually very hot and brittle, not a place suitable for life. And once the lava reaches its destination, it again solidifies in a matter of hours to days. It can remain too hot to the touch for days to weeks, though.

You suggest that you can just keep erupting more and more lava ("replenish the lava seas"), but that lava has to go somewhere. It will just fill up the lower areas, then solidify, then form more and more layers on top, burying whatever is there.

If you want your lavas to stay liquid for very long (years? decades?), they need to erupt into an environment which is hot. Think something like the surface of Venus. Your planet as a whole needs to be very hot, and it gets very hard to sustain life as we know it on a planet like this.

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Well lets look at what normal lava is made of. Here it says it has silicon, oxygen, aluminum, iron, magnesium, calcium, sodium, potassium, phosphorus, and titanium. Hereit says some gases it emits that are dangerous include CO2, SO2, H2S and Hydrogen halides. So let's make your lava sulfurless and have a lower concentration of hydrogen and halogens. That's all you need to do to make the lava not give off poison.

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