UKC

There is massive disruption on the roads through Broadbottom (Glossop) this morning, apparently because of a sinkhole.

I thought sinkholes were limestone features where running water (more quickly if acidic) exploited existing cracks, enlarging them to create a cavern then the roof collapsed in creating the hole.

Given that Broadbottom quarry is gritstone as is everything else in the area, I'm confused. My conclusions are:

1) Sinkholes also happen on gritstone but I've never seen or heard of one before.
2) There must be some limestone under the grit that the grit has fallen into.
3) It isn't actually a sinkhole as reported but a similar feature that has been simplified by the media.

Any geology bods out there want to educate me?

I'm also a teacher at a school in Glossop and loads of the kids are likely to ask me about this today so it would be nice to have an answer for them.

In reply to Somerset swede basher:
Tell them the real truth. Satan is breaking free and is about to release the zombie armies.
Hadfield is a gonner!

In reply to Somerset swede basher:

I think they're talking about a sinkhole in the road construction rather than a sinkhole in the bedrock.

Google 'sinkhole Mancunian Way' for example.

In reply to Somerset swede basher:

I have to admit the Satan explanation sounds more likely, but you also get sinkholes in sandstone areas.

Happens in Dresden every spring, as the valley floor is packed with sand. The sinkholes are then created by water, especially when floodwater saturates the sandy soil. If you then have a means of removing the wet sand, e.g. if the water can force its way into a broken drain, holes can be flushed out rapidly. From the surface these cavities are often visible only as sagging tarmac, but when they dig them out would have been big enough to swallow a bus.

CB

In reply to Somerset swede basher:

Google 'Lud's Church'. Cavities in gritstone can arise quite naturally on a slope like a river valley where a portion of the rock detaches itself and shifts downhill.

In reply to Somerset swede basher:


They can be, but not always - they can just be where underlying soil and sediment gets washed away, causing a collapse on the surface.

A colleague had to move out of their house for months when pipes channeling an underground stream collapsed, and the sand and gravel above them gradually fell in and were washed away. They had large, flooded, hole in their garden, slowly expanding towards their house!

In reply to Andy Morley:

That looks awesome, I had no idea it was there. Will be sure to take a look next time I'm over at the Roaches.

In reply to RyanOsborne:
Do you mean the one in Manchester is in what they've built rather than the rock underneath? Most of the google links are to do with traffic rather than formation.

Or has a pipe broken in Manchester causing the removal of the rock underneath?

In reply to Ghastly Rubberfeet:



Will they notice?

In reply to Hat Dude:


Yes, I was going to say Hadfield is His already.

In reply to Somerset swede basher:


You can walk there from Roach End, or you can park at Wincle/ Danebridge and walk from there, taking advantage of the microbrewery to stock up on ales and eat posh fish and chips at the Ship Inn - pricey but worth it!

In reply to Somerset swede basher:

The grit overlies the limestone (but the collapse of the limestone is not necessarily the cause of the sink hole).

In reply to Somerset swede basher:


I'm not a geologists, but from what I've noticed over the years, Chew Valley, Longdendale etc., the grit sits on top of a layer of rotten shaley sandstone, which is probably easily washed away.

In reply to Lusk:
For info: http://www.bgs.ac.uk/research/engineeringGeology/shallowGeohazardsAndRisks/...
for 'proper' sink holes you really need soluble rocks but in modern parlance it seems any kind of collapse structure is labelled a sink hole
you've also got a few old coal mines round there which could well be the culprit!

In reply to ebdon:

An interesting read, thanks