**Rock fall** Alum Pot

[undergroundHP]

Hi Ian
I did the North west SRT route on Friday 3rd and did not notice anything out of place at the top of the pot by the trees and ledges on the way down.
I have noticed a few wobbly rocks on the traverse around to the bridge /greasy slab area over the years .
Glad you came to no harm.

 

[paul]

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.

Also during the EuroSpeleo event in the Dales in 2016, I just touched a large boulder, again about microwave size coincidentally, in the rift on the surface approaching Little Gully route in Jingling Pot as I was looking for the next bolt nearby and it suddenly fell to the ledge below. See https://ukcaving.com/board/index.php?threads/jingling-pot-caution.20437/ .

 

[Pegasus]

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.

The link to removing the water tank - a fine day 😁

 

[braveduck]

The only British Earthquake on Sunday the 5th was at St Austal in Cornwall , so that was not the cause !

 

[Ian Ball]

Almost reported you to yourself there Pegasus Thought the report button was a link to the water tank removal report.

 

[Ian P]

*Update*

I descended the NW route this afternoon.
Approaching the “Traverse path” to the top of “The Bridge” I could see evidence of rockfall on the path.
After some aerial acrobatics to swing over and climb onto the ledge, I had a good look around.
I have written a bit of a “summary” below.

“There has been a small rockfall from the face of rocks just above the traverse path that leads to the top of “The Bridge”.
The area affected is between the 1st and 2nd anchor of the traverse.
This rock fall has impacted the “path” and compromised the solidity of it, leaving it in a crumbled state in parts.
Users of the traverse path need to exercise extreme caution, both for any further rockfall and also for the extremely likelihood of knocking stones down the open pot onto the route below. Keeping on the “inside” of the traverse line, whilst a bit more inconvenient, would help mitigate any potential problems.

Anyone venturing deeper into Alum Pot needs to exercise caution regarding the potential of rocks from above.”

End of “official” report.

Some aspects of the rockfall were a bit hard to understand, particularly the large flat area (shown in pictures with a stop for scale).
As Tim mentioned in an earlier post, when you start looking around it is quite sobering the “condition” of the rock in places. There are definitely some areas that look “suspect” above the path. The area above the rockfall also appears to be the route of a stream from a bedding plane above.

I think some “gardening” maybe beneficial and I am happy to put it on my “to do” list. Any advice gladly appreciated.

Some photos below and more on the link (inc some interesting videos). https://drive.google.com/drive/folders/13CwK7vymWwuvdhyPota8qDuVwO_6hc80


Take care.

Ian

 

[PeteHall]

Some aspects of the rockfall were a bit hard to understand, particularly the large flat area (shown in pictures with a stop for scale).

From your pictures, the large flat area looks like a slab has been there for some considerable time and has now disappeared. Is that too obvious an observation?

How to explain it? Someone deliberately moved it? Down the shaft, presumably...

 

[Flotsam]

The Greasy Slab is a rockfall of course.

Speaking of rockfalls, apologies for drift. I did some very early trips down King Pot, East Kingsdale. King Henry's Hall was the scene of a lot of very recent (at the time) rockfalls. How is it doing there these days?

 

[Ian P]

From your pictures, the large flat area looks like a slab has been there for some considerable time and has now disappeared. Is that too obvious an observation?

How to explain it? Someone deliberately moved it? Down the shaft, presumably...

That was definitely my initial thought but in the end I have gone with a “natural” occurrence (although that “slab” missing is a mystery).
Numerous other factors point to a natural event, but yes that slab is a question I cannot answer.

 

[ChrisB]

From the pictures, my guess is that the rock dropped out of the wall above and landed on the ledge, shattering the slab (which had previously delaminated from the ledge). Some bits of the slab would have been scattered and forced off the ledge by the impact, and the rest of the debris may have been tidied up by somebody before your re-visit.

 

[Russell Myers]

That was definitely my initial thought but in the end I have gone with a “natural” occurrence (although that “slab” missing is a mystery).
Numerous other factors point to a natural event, but yes that slab is a question I cannot answer.

The open shaft of Alum makes it prone to freezing up in winter so the freeze/thaw effect may have come into play with the pebble you encountered when it decided just at that moment to let go but it clearly didn't have your name on it!
From observations of winters past, after about 9-10 days of continuous freezing temperatures, the surface waterfall freezes solid and a huge ice boss builds together with other spectacular ice formations. I was down in the bottom photographing back up the waterfall when the frozen sheet of ice wall below the "Greasy Slab" peeled off and a few tons of ice crashed down! Freeze/thaw in action.
Since I'm writing this, you can assume I survived.

 

[alanw]

I'm not sure if this will be of any use, perhaps I was standing a little bit too far forward, but here is a photo of the ledge from 2008

 

[cseal]

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 too can attest to the acoustics of Alum Pot. Many years back (late 80's/early 90's), I was descending the SE route. I was abseling down and was just in the process of rigging the rebelay when there was an almighty crashing sound. It was very loud and the whole chasm seemed to reverberate for some time. I tucked in as much as I could to the cliff edge, expecting a major rock collapse. It quietened and I was looking around trying to work out what had happened. Then it happened again but this time I was looking upward and saw the second RAF fighter jet fly at very low level straight over the trees!!

Chris