**Rock fall** Alum Pot

[Ian P]

Sunday 5th May

We had just got to the bottom of Diccan Pot when we heard a rock “boom” from the direction of the open shaft. Time: 12.55.
We headed up towards the bottom of the last pitch of Alum Pot to look at the view.
Literally as we looked up at the daylight a rock (we both estimated to be the size of a microwave) came down and smashed into the floor and disintegrated and sent debris in our direction, my caving partner felt some small bits hit him. The air smelled of impacting rock. Time 13.05

We made a swift retreat and headed out.

A detailed look around the inside top of the enclosure showed no evidence of movement, I also abseiled down to the rebelay of the NW route and saw no evidence of any rockfall.

Take care.

Ian Patrick

Best guess of location

The view we were looking at.

 

[paul]

Could it have been thrown down or knocked down on purpose? I suppose a rock the size of a microwave would be very heavy.

 

[Ian P]

Could it have been thrown down or knocked down on purpose? I suppose a rock the size of a microwave would be very heavy.

A response from a post I put FB.

“Hi Ian, my group and I walked past the uphill side of the wall at that time and I can confirm that nothing was chucked over the wall or disturbed by anything other than footfall.

Glad you’re ok 👍”

My response:
“Thanks for that information. We did consider it could be rocks thrown, however the size of the rock and the fact we only heard a single impact and not multiple impacts led us to believe it was not “malicious” (hopefully)
Cheers
Ian”

 

[ChrisB]

Just measured my microwave - 50cm x 30cm x 30cm, at 2400kg/m3 that's 180kg

 

[Pitlamp]

One is reminded of the Mabel Binks accident here.

It'll be interesting to see if any earthquakes were logged at that time, when the BGS earthquake site next updates.

 

[Pitlamp]

P·S. glad you're OK Ian!

 

[Ian P]

Just measured my microwave - 50cm x 30cm x 30cm, at 2400kg/m3 that's 180kg

We both “independently” thought it was about that size, it definitely wasn’t a “cobble”. Hopefully things will become clearer in the coming days, unfortunately I am committed elsewhere, otherwise I would get down there for a look.

 

[Ian P]

P·S. glad you're OK Ian!

Thanks, just needed to wash my undersuit on a higher temperature 😂

 

[Pegasus]

I keep thinking of the noise it must have made, blimey! 😲
So glad you are all safe xx

 

[ChrisB]

I keep thinking of the noise it must have made

Some more physics, then - the energy in a 180kg rock falling 100m is the same as a typical car travelling at about 30mph.

 

[Boy Engineer]

I keep thinking of the noise it must have made, blimey! 😲
So glad you are all safe xx

Presumably a ‘ping’?

 

[Fulk]

Morning Ian, that sounds scary, and I'm glad you weren't injured. Out of curiosity, can I ask you a question?
Some time ago I set up a picture of someone climbing the waterfall in GB Cave, with me at the bottom with a camera and my daughter with a flash-gun, while somebody else was supposed to fire a second flash down the pitch. However, this somebody else unfortunately kicked a rock that Charlotte and I estimated to be the size and shape of a rugby ball down the waterfall. It shattered and sent 'shrapnel' flying in all directions, resulting in Charlotte's receiving a minor injury.
The odd thing is, that to both of us it seemed to descend at a very slow pace, rather than come wizzing down. So – the question – did you experience the same sensation?
John

 

[ChrisB]

it seemed to descend at a very slow pace, rather than come wizzing down

I've seen this with rockfall on a climb, and also on a motorway when a car had a blowout and slewed across two lanes into our path. It only happens when you perceive a threat to your own safety, adrenalin etc kick in instantly and speed up your brain so that you can react - and since your brain has speeded up, everything appears to happen slowly.

 

[Badlad]

In my youth we set off an air bomb repeater firework at the bottom of Alum. Wow oh wow was it loud. We thought it was going to bring the place down and end the world, but it never did. Alum has amazing acoustics.

On a different note, more recently, when we removed the old water tank from near the sump, we hauled it up the shaft on various technical cross hauls and rigs. This led me to examine the walls of the shaft in places you don't normally go, for fear of dislodging rock. There is a lot of stuff that just appears to be 'hanging on', especially in the area between the bridge and the main hang. I guess it is inevitable that over time rocks will fall.

Very glad you weren't underneath it.

 

[Fulk]

In my youth we set off an air bomb repeater firework at the bottom of Alum. Wow oh wow was it loud. We thought it was going to bring the place down and end the world, but it never did. Alum has amazing acoustics.

I once did something similar in GG Main Chamber, with a similar result – scared the shit out of us!

 

[Ian P]

*Snip*
The odd thing is, that to both of us it seemed to descend at a very slow pace, rather than come wizzing down. So – the question – did you experience the same sensation?
John

Hi John

Absolutely!! Im really glad you mentioned this, it has been ticking over in my mind.

We were just looking up at the daylight “shaft” when the rock came down into view, it did absolutely appear to be traveling slowly, I think this is why we were both sure about the “microwave size”, at this point I “froze” and just watched the rock coming down and then impacted and sent shrapnel towards us again in slow motion, I was still “frozen” at this point, then everything seemed to “speed up” and at this moment I turned and started moving away as quickly as possible. The whole incident certainly had a “surreal” feeling about it for sure.

Hope to catch up in person at some point 👍

Ian

 

[Ian P]

In my youth we set off an air bomb repeater firework at the bottom of Alum. Wow oh wow was it loud. We thought it was going to bring the place down and end the world, but it never did. Alum has amazing acoustics.

On a different note, more recently, when we removed the old water tank from near the sump, we hauled it up the shaft on various technical cross hauls and rigs. This led me to examine the walls of the shaft in places you don't normally go, for fear of dislodging rock. There is a lot of stuff that just appears to be 'hanging on', especially in the area between the bridge and the main hang. I guess it is inevitable that over time rocks will fall.

Very glad you weren't underneath it.

Thanks Tim.

The sobering part is that as one of the most popular caves in the country I (and countless other people) have been stood in that exact spot numerous times.

I suspect you are right regarding the location.

Unless reports come back before from someone else, I intend to descend the NW route tomorrow afternoon and have a good look around.
As you say, rocks do fall.

 

[Ian P]

Heart rate monitor from yesterday. First spike is from the “brisk” walk up, the second spike is exactly the time of the rockfall 😱

 

[skippy]

During Euro Speleo, we were sent into Juniper to deal with the mobile rock at the top of the big pitch.
Armed with crowbars and hammers, all it took was slight fingertip pressure to send it on its way..now this slab was 4ftx2ftx8 inches...the boom was mighty impressive..however the shock wave up the shaft even more so. It was later reported(by Ian P I think) that there wasn't a single piece of shrapnel bigger than a large pebble at the bottom.

 

[Loki]

Many moons ago I went down alum via the bridge on a cold day and we marvelled at the large icefall going over the top from the stream. To make this tale concise - I was derigging the final pitch with a mate when the whole shebang detached and exploded all around the 3-4 people waiting and ascending the pitch near the stream below. A warm front had come in while we were down there and destabilised it. Suffice to say they were a little‘surprised’ but miraculously unharmed by the near death experience! Learning point - don’t stupidly go caving down shafts full of icicles of doom! 🤦