>literally use an excavator to

That might be understating the issue. The excavators we use to dig coal have been, and are monstrous. Thousand ton beasts requiring a fleet of support vehicles around them and the ever increasing depth of overburden.

Also the fly ash leftovers tend to get piled up and occasionally break lose in human and ecological disasters at massive scales.

https://en.wikipedia.org/wiki/Bagger_288

This is the same kind of scale as those fictional "Spice Harvesters" in Dune. Look around for a photo where there's a person or a familiar object you know the size of in the same frame as the Bagger 288