There is no documented instance of a cornfield transforming into a volcano. This scenario is purely fictional and likely inspired by the unusual and surprising events that nature can sometimes bring.

Here's why this is unlikely:

* Volcano formation: Volcanoes are formed by geological processes deep within the Earth. They occur when molten rock (magma) rises to the surface, usually along tectonic plate boundaries or hotspots.

* Cornfield formation: Cornfields are created by human intervention, planting corn seeds in cultivated land.

It's possible you're thinking of a story or legend, or perhaps there's a misunderstanding. If you can provide more context or details, I might be able to help further!