Oh, I though you accidentally

Oh, I though you accidentally made Flubber!

Not a Sinkhole

Your modeling the wrong part of the country for that. Sinkholes usually occur where there is a lot of limestone. Water seeping into the ground slowly eats away at the limestone and as the water channel gets bigger eventually a sinkhole develops.

My kids on the other hand decided they were going to dig a hole in the backyard to who knows where. Due to pathic work hours I didn't see it for a few weeks. They had managed to dig down over a foot and about 2-3ft by around 4-5ft. I made them fill it back in.

Still ya gotta have fun here. So kids digging the hole to China? Or a treasure hunter? Or maybe it's whatever is going to be digging up the potato patch?

Jack

Aye, my masters thesis was on

Aye, my masters thesis was on karst terrain which we has in southern Indiana around Bloomington's Indiana University.

Jack and Jim, Though I'm not

Jack and Jim,

Though I'm not interested in modelling a sink hole, it is an interesting subject, I'm told the area I’m modelling does get sink holes, but not often. I looked some up and found them happening more so in the last 5 years after heavy rainfalls, but I suspect this had to do with erosion.

One happened near the area I model decades ago and they found a mastodon in it.

Jim. I had to look up who

Jim. I had to look up who Flubber was.

Lava River Cave

Look like the Lava River Cave  Arizona

Aye, my masters thesis was on

Indiana?

Meh.

Kentucky is hollow.

"Indiana?   Meh.   Kentucky

"Indiana?

Meh.

Kentucky is hollow."

Florida has entered the room....

...

It looks good.

I'd leave it.

Or maybe Superman

Is that possible that Superman just landed and hid his space capsule?

I must confess, Benny, it is

I must confess, Benny, it is growing on me.

Watch out!

There's a fungus among us! So be careful, it is also highly contagious!

...

I don't know your local modeling area, but to be honest, the large rock felt geologically out of place.

What you have here is a depression, and anywhere you have underground water moving around, you have underground currents, erosion, caves, and collapses.  This may have been enlarged by an animal den.  Now it's a simple depression...

Mine cave in

Looks like a mine cave in caused by the timbers of an old mine rotted and gave out.  Growing up in western PA, a friend was working picking apples in an orchard and as he got to the truck,the ground opened under him.  An old (+/- 100 years) shaft had less than 2 feet overburden. 

We have had sink holes in California where there was no lime.

It has been caused by deteriorating infrastructure, namely water mains rusting out and not getting fixed until the resulting water washed away all of the dirt under pavement.  Of course when a gas main rusts out, the result is often explosive!

Sink Hole

Set an Out House next to the sink hole with three or four workers with shovels standing around the hole and looking down into it. You could also add a loader or Cat Tractor on the way there 5 to 6 inches away and maybe a dump truck behind them.