write about what would happen if Yellowstone erupts and why

sticking more to the “why” side of the topic regarding why might it erupt, what evidence is present, geology of the plume, etc. If you want to cover what might happen if it erupts, focusing on the geologic events would be suitable. The difficulty with focusing on what would happen if it erupts dips into the modeling side of things, which is super interesting, but may be difficult to cover in the scope of this paper.