Sink holes

The Southern sinkhole

I live near Brighton and use the UK’s worse train service, Southern, to commute to work during the week.

For Southern, cancellations and delays are just business as usual.  They recently amended their timetable, removing around 300 services, just so they wouldn’t have to cancel them every day!  Genius solution huh?

However Southern always feel the need to try and blame their delays on external factors, in the hope that their passengers won’t blame their extreme incompetence.  And they clearly put a lot of creative effort into this, often with elaborate backstories of downstream delays, signaling issues, track maintenance, ambient temperature and gremlin uprisings.

So when I heard last week that trains were cancelled due to the emergence of a Sink Hole between London Bridge and East Croydon, I initially thought this was just a wild fantasy their line controller had concocted to conceal some other screw up.

But it turns out that there was, indeed, a genuine sink hole!

Okay, so maybe there is a genuine reason for delays this time!  Apparently the sinkhole was 4 meters deep, and was caused by a sewer under the track which had collapsed.  So sounds like not only is it a sinkhole, its also a sh*thole!

Still, I’m glad it’s not me cleaning it up!

Sinkholes worldwide

So this got me thinking, what other interesting sinkholes have appeared around the world?

A youtube channel has put together a 14 minute compilation of big sinkholes emerging over the last 5 years with live-action footage, including another railway example at 4:20 in video.  These are all much bigger and nastier than our Southern Rail friend.

However the footage I found that had the best combination of being deeply shocking while also slapstick hilarious (which I feel guilty about!) is the following.  The video is from a public bus’s CCTV camera in South Korea.  A couple steps off the bus onto the pavement, and then are swallowed up by the ground beneath them.  Initially I thought this must be a hoax, but the video I link to below is from accredited news service AFP, and googling it funds numerous serious news websites (BBC, etc) covering the story.

The Zombie Apocalypse?

I was talking to my mum about this.  She’s a traditional kind of gal, and she doesn’t have a lot of time for “geology” and “science”.  For her, sinkholes are about the end-of-times and are possibly connected with an impending zombie apocalypse. It’s an interesting perspective, but probably not the main driver here.

What causes sinkholes?

Okay, time for the educational bit.  What causes sinkholes?

I’m not a geologist, but some quick research suggests that:

  • Sinkholes generally occur where water seeps through the surface and slowly dissolves soluble bedrock like limestone or chalk.
  • As small chunks of rock dissolve, naturally occurring fissures expand and create cavities.
  • The surface layer can hold firm while deep-lying holes continue to expand.
  • But eventually it does “pop”, and the surface layer collapses into the cavity created.

That’s the case for naturally forming ones.  When you have a sewage pipe that collapses, that’s a whole other kettle of cr*p!