Is it possible for a planet to have an area saturated with lava but at the same time is still habitable to humans and other lifeforms?

Question

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?

Answer 1

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.

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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.

Answer 2

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.