Looks like they dug it out in the end... It probably was the result of a broken or collapsed drainage tile. Normally when one breaks or collapses, it will bubble up and can cause acouple of acres to turn into a large sink hole.
My father owns/operates a 2500 acre cash crop farm in central NY as well as does custom installation of drainage tile.
It looks like one of the combines may have gotten stuck first, then the tractor, and then another combine. In a situation like that, you really can't tell if there'* a sink hole in front of you when you're picking corn.
When my dad used to plow, we sunk our 8640 articulating tractor so far down that you had to step up from the top of the fuel tanks... Here'* a pic of an 8640:
We unhooked the 9 bottom plow and drug it out with our combine, then drug the tractor out reverse of how it went in with the combine. That wasn't as messy as what those guys have gotten themselves into...