It’s ridiculously easy. Come on. Volcanoes literally spit hot flows of lava (two types of which are called ‘ā’a and pāhoehoe), and pyroclastics (“fire fragments”, hot gases and tephra) that reach hundreds of degrees and hundreds of kilometers per hour that, according to UGGS.gov, “will destroy nearly everything in its path”. Volcanoes helped to kill over 90% of the Earth at one point. They’re rife with mythology and metaphor, and ingrained in our idioms. What else do you need?
You can talk about igneous rocks and various volcanic ejecta, like tough-sounding but actually soft tuff and the porous-looking but actually abrasive pumice. Get poetic with lava fountains, obsidian and other forms of volcanic glass, like Pele’s hair or Pele’s tears. Pumice rafts, basalt columns, lava lakes, domes, tubes and all sorts of structures can be explored. The distinction between magma and lava may be worth mentioning (though most trivialists might consider it common knowledge and thus an affront to their intelligence). Calderas and other features of the volcano are very rhymable. Very very.
And perhaps throw in some origin stories. Hot spots. Convergent and divergent boundaries. Rising magma and building pressure. The whole shebang. Maybe the different types of volcano, too: shield, cone, compound, dormant, active, extinct, and so on. The impact of supervolcanic or even just large-scale eruptions is awesome (semiarchaic meaning of “awe-inspiring” used here) and mind-bogglingly (1964 colloquialism) devastating – gorgeous sunsets, years without summer, and the always cheerful mass extinction are very suitable subjects for being compressed into the form of a short three-and-a-half minute song delivered rhythmically through the faculty of speech.
Seriously, you have so much to work with.
Legitimate rappers do not want to do this, yes, but semi-decent amateur aficionados that happen to be middle-school science teachers might! Many science teachers would love to be “relatable to the teens”, and many of them have made song renditions of common topics. People will cringe (rightly) at the puns and the badness, but you’re educating people about earth sciences, dammit. I have not yet found a single “volcano rap” song on YouTube that fully utilizes the sheer potential this topic possesses.
Someone get on this.