How do you even go about filling in something like that?
Rough calcs;
100m deep
~20m diameter
So that's about 31,500 cubic meters, or about 47 thousand tonnes of earth. Now, because I work in the mines I've actually seen 47,000t (and much more) with my own eyes and let me say that it is a metric FUCKLOAD of dirt.
Even if they have an endless stream of 150t jumbo trailer trucks feeding 20t bucket 996 loaders, it'd take weeks to even make a dent in the thing. God knows how balsy/incredibly stupid you'd have to be to drive heavy equipment around something so unstable though.