What are these mysterious holes?

I live in the Hunter Valley in New South Wales, and my house sits on the edge of the river/flood plain. Yes, the soil is a rich alluvial soil great for gardens and crops.

The bedrock is sandstone and sits about nine feet below the surface.

The reason I know this is that in the past year holes have begun appearing in my yard. The first one began as a depression in the lawn. Upon closer inspection, I discovered in was very soft and in fact, my foot sunk into the ground.

Being the curious person I am, I decided to dig a little to see if there was anything to see.

Below the top soil was a gap of about six inches. The ground had sunk. This depression/hole was about a metre wide.

My first thought was it was an old well as where I live before water supplies were made available everyone had a well. We thought maybe it was a failed well as that was always a possibility. But digging some of the hole out, I didn’t find anything that suggested it was a filled in the hole as I’d expected to find rubble of some sort inside it.

My neighbour and I decided to try a few tests to see if it was still sinking. So, we did a home-made compression test, and after a week we couldn’t see any further sinkage. So, we filled it in with rocks and what we could find.

Since then I have noticed the hole is still sinking, ever so slightly and so I am topping it up with soil in the hope it settles.

Added to that I have discovered other much smaller sinkages. These I discover mowing the lawn as every so often my foot goes down in a soft spot…. I recently discovered three such spots, dug them out and filled them in, hoping I had solved the problem.

Now I have consulted with the Water Board, and it has nothing to do with the sewer line. I’ve also been to my local council, and they assure me there are no drains under my place. To the best of my knowledge, there are no mines under there either, so mine subsidence has been ruled out.

The only explanation so far has been that below the surface it is likely there is water flowing through the sandstone. Over time and with an increase in rainfall weathering occurs in the rock and forms pockets which fill by the earth above sinking into the gaps created. Hence in my yard, these sinkages are occurring. It’s interesting that these sinkages have only begun appearing since the huge rainfall in April 2015.

I don’t think I can argue any sort of natural wonder was occurring and my back yard has the potential to become a tourist mecca. Rather I think there is more chance of me or a grandchild disappearing down one if we are not careful. Though I have no plans for that just at this moment. Though I’m sure my kids see it as a cheap way to bury dad should a hole conveniently appear around the time I pass on.

Needless to say, it never ceases to be a topic of conversation around my place.

In the centre of the photo, the round dirt bit is the hole I first discovered. Beyond that are the spots I have since discovered.

If you have any thoughts on this problem, please feel free to share with me before I disap…..

What are your thoughts on Michael’s problem? Leave them in the comments down below. We’ll try to send them down the hole to him.

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