"It does, I've seen some."

"Excellent. Did you know obsidian is very similar to glass?"

"Yes. It's possible to transmute either to the other."

"That makes a lot of sense. Does your transmutation alter atoms, or just rearrange them?"

"I wouldn't know how to tell!"

"Could you turn gold into silver, for example?"

"Sure."

"Then you do alter atoms! I should take some radioactive tracer dye and turn myself into a bird with sorcery at some point," she muses. "But first, shall we see if there was a magma pocket here before it first erupted?"

"You don't want to turn yourself into a bird, you won't be able to do sorcery as a bird. I can do it for you."

"Oh, that's good to know, turning back into myself with the transmogrifier when that's not how I turned into the other thing always leaves my teeth feeling weird. What about being a bird interferes with doing sorcery?"

"It's built into the spell but I don't know exactly how - it's what fairies do to each other by way of long term incapacitation."

"Hmm! That suggests it would be possible to develop a variation that doesn't have that problem." Everything she learns always leads to more things to learn, it's so excellent.

"Maybe."

"Well, for now let's go back in time a few more weeks and see how this volcano became a volcano."

It transpires there was a lava pocket there!

There are so many fun things to do in a magma pocket. They can map its extent with sonar! They can do some math about how, if it's infinitely deep, this affects the process of it building up enough pressure to erupt! They can measure the pressure in a couple places and speculate about whether it really is infinitely deep or not! They can go to a point where the lava meets the crust above and check if heat diffusion is working normally!

Promise is glad Corundum is having fun.

Corundum understands that not everyone likes fluid dynamics; she'll keep it brief, at least by by immortal standards.

"So! Where would you like to go next?"

"I don't know."

"Well then," she says, pulling some levers, "why don't we let the Bus decide? She's sure to find us something exciting."