Author Topic: Rockfall in GB  (Read 1576 times)

Offline PeteHall

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Rockfall in GB
« on: February 02, 2021, 12:03:13 am »
There has been a fairly significant rock fall in GB.

In the region of 5-10 tons of sand, gravel and rock has slipped out of the left hand wall, just below the waterfall. There is a significant amount that has been undercut, but is still hanging high above the climb down. This appears to be very recent, given that the sand has not washed away yet and there was a pretty decent flow.

No photo as I didn't have a camera with me.

I would strongly recommend that people avoid climbing the waterfall until this area has settled down (the other route is nicer anyway  :)  ).

CSCC and CCC have been informed.
« Last Edit: February 02, 2021, 12:13:29 am by PeteHall »

Offline Tomferry

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Re: Rockfall in GB
« Reply #1 on: February 02, 2021, 06:38:05 am »
I visited 1st November and their was a very large undercut section at the top of the waterfall  around 5 tone literally floating their , if climbing It would have been a few meters back at the very top to the right it did look unstable then .
« Last Edit: February 02, 2021, 06:56:43 am by Down and beyond »

Offline PeteHall

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Re: Rockfall in GB
« Reply #2 on: February 02, 2021, 08:01:11 am »
There are a few undercut sections. Mostly cemented together with calcite on top, so hopefully fairly solid. The best obviously being 'The Bridge'

Offline PeteHall

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Re: Rockfall in GB
« Reply #3 on: February 08, 2021, 01:31:57 pm »
Update from the Charterhouse Caving Company:

Quote
Dear All

The site of the reported rockfall in GB near the waterfall climb in Main Chamber has been checked. There has been a recent fall of mud, gravel and smallish boulders on the left (when viewed facing downstream) of the waterfall climb, near the bottom. The wall above the last part of the climb (the big steps) appears as it did before, but should be considered loose due to the recent fall. The top part is calcited but might be subject to further falls, although it is equally possible that it might not change for a long time. However, as assessing such future possibilities is not an exact science, care should be taken here, and everyone should conduct their own risk assessments whenever they approach this area from any direction. There are still loose rocks almost covering the steps and when inspected it was not possible to pass the steps without using the unconsolidated debris. The floor below the climb is currently covered with unconsolidated debris and the boulders here will move underfoot when stepped on, so care should also be taken here.

This waterfall has been formed on a major vertical structural fault (see Ford, D.C., 1964. On the Geomorphic History of G.B. Cave, Charterhouse-on-Mendip, Somerset. UBSS Proceedings, 10(2) , pp 149-188 available from http://www.ubss.org.uk/resources/proceedings/vol10/UBSS_Proc_10_2_149-188.pdf), which states that there is much fault breccia to be found and so events of this nature are likely to occur from time to time.

Graham Mullan

Secretary

Charterhouse Caving Company Ltd

Offline mrodoc

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Re: Rockfall in GB
« Reply #4 on: February 08, 2021, 05:35:23 pm »
There are a few undercut sections. Mostly cemented together with calcite on top, so hopefully fairly solid. The best obviously being 'The Bridge'

There have been collapses under the Bridge in the past apparently and it was mooted that it should be collapsed for safety reasons.  That was more than half a century ago but very recent in geological terms so still needs to be regarded with caution.

Offline Keris82

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Re: Rockfall in GB
« Reply #5 on: April 08, 2021, 08:27:43 pm »
CSCC has released the following statement:

“There has been a recent fall of mud, gravel and smallish boulders on the left (when viewed facing downstream) of the waterfall climb, near the bottom of Main Chamber. The wall above the last part of the climb (the big steps) appears as it did before, but should be considered loose due to the recent fall. The top part is calcited but might be subject to further falls, although it is equally possible that it might not change for a long time. However, as assessing such future possibilities is not an exact science, care should be taken here, and everyone should conduct their own risk assessments whenever they approach this area from any direction. There are still loose rocks almost covering the steps and when inspected it was not possible to pass the steps without using the unconsolidated debris. The floor below the climb is currently covered with unconsolidated debris and the boulders here will move underfoot when stepped on, so care should also be taken here.”

A further inspection trip was scheduled for 6 April, following the relaxation of covid restrictions. On 5th April, a report was received of a further fall. The inspection trip comprised myself, Dave King and Graham Price (plus two others). We found that a large area of the side of the passage above the big steps on the left hand side (when travelling into the cave, heading downstream) has come away, resulting in a massive, unstable talus cone of boulders, large rocks, smaller shattered rocks and mud that now completely covers the steps almost to the base of the ledge in the middle of the climb. Boulders and large rocks are spread over a wide area in the passage below the climb.

There is still a ridge of loosely calcited unstable rock high up on the wall above this area, so further falls cannot be ruled out. In addition, there has been some mud slumping on the right hand side of the passage when going downstream and this area might also be subject to some movement.

A thorough inspection was carried out. As a result, warning tape has been placed across the passage above and below the climb, stating: “WARNING, LOOSE BOULDERS, DO NOT USE WATERFALL CLIMB, USE WHITE PASSAGE/LOOP ROUTE INSTEAD, CCC Ltd 6.4.21” These signs are laminated and attached to the tape with cable ties. A sign was also placed at the Bridge and one has been hung from the bar in the entrance. Please DO NOT cross these tapes to look at the fall.

As there is an alternative route to reach the lower part of the cave and Bat Passage, it was not felt necessary to close the cave as the area around the Waterfall climb can be bypassed in entirety, and the taping below the climb was placed some distance outside the furthest extent of the boulder fall. It will need several years of winter water conditions to even start to stabilise this area, so this part of the cave will need to remain off limits for the foreseeable future. The situation will be monitored. An attempt was made at fixed point photography so we have a baseline for the monitoring. As an aside, one of our original fixed photography points at the base of the lower ‘big step’ for SSSI monitoring is now completely covered by the talus cone. This is certainly the most dramatic change to the cave in the time I have been conducting the monitoring! Previously to this, the only change in the photos was the door falling off one of the cars at the very top of the Gorge.

A further news report with photographs will be put together and published.

Would all club reps please circulate this warning as widely as possible in your clubs and ensure that key issuing procedures include this warning. Also please ask all parties to report any broken tape or missing warning signs so that we can replace them. For information there is one sign in the blockhouse, one at the Bridge and three hanging from each section of tape.

If anyone has any queries, please let me know.

Linda Wilson
CCC Ltd Conservation Officer
lindawilson@coly.org.uk

Offline Tomferry

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Re: Rockfall in GB
« Reply #6 on: April 09, 2021, 06:41:57 am »
Thanks for passing the message on i did plan to re visit here  :thumbsup:
« Last Edit: April 09, 2021, 06:52:25 am by Down and beyond »

Offline Keris82

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Re: Rockfall in GB
« Reply #7 on: April 09, 2021, 08:04:58 am »
You're welcome   :)

Offline PeteHall

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Re: Rockfall in GB
« Reply #8 on: April 09, 2021, 09:50:24 am »
Thanks for passing the message on i did plan to re visit here  :thumbsup:

99% of the cave is still accessible, you just get to do White Passage twice now  :)

Offline Tomferry

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Re: Rockfall in GB
« Reply #9 on: April 09, 2021, 10:10:16 am »
Thanks for passing the message on i did plan to re visit here  :thumbsup:

99% of the cave is still accessible, you just get to do White Passage twice now  :)

White passage is this the name for the passage when you cross the bridge go all the way up and it leads you to the bottom of the waterfall near the sump ?

Online mikem

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Re: Rockfall in GB
« Reply #10 on: April 09, 2021, 10:36:27 am »
If you go all the way up you'll miss the turning that takes you through the Oxbow  ;)

Offline PeteHall

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Re: Rockfall in GB
« Reply #11 on: April 09, 2021, 10:40:33 am »

Offline Tomferry

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Re: Rockfall in GB
« Reply #12 on: April 09, 2021, 11:44:10 am »
Thankyou very much ! I think I missed way to much on my trip here ! Right in need of a return visit !

 

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