How deep is OFD?

[Martin Laverty]

"OFD is Britain's third longest cave and at 308 m deep is its deepest." - so says the SWCC website, and numerous derivatives.

Yet, in looking at some figures in the course of reviewing the content of the Cambrian Cave Registry, I find that the resurgence is at an altitude of around 184m and sink at Pwll Byfre is at just less than 480m. I don't know of any passage in OFD being claimed to be above the level of Pwll Byffre (although it could be as the surface goes up to 538m in the vicinity), so the maximum possible depth (excluding any very deep sumps) would appear to be 296m. Looking at survey elevations, the actual vertical range appears to be more like 275m - still the deepest in the UK.

As newly enrolled Registrar, I would appreciate any comments on the Cambrian Cave Registry [ http://www.cambriancavingcouncil.org.uk/cave_registry.html ] - its content, presentation, and future direction...

 

[Duncan Price]

Add 17 m for the maximum depth at the elbow of Gothic Passage Sump which ends at a boulder choke close to the resurgence.

 

[robjones]

308m is almost exactly 1,000ft. Is it possible that n round figure estimate of depth in Imperial units has been converted to a misleadingly exact figure in Metric units?

 

[graham]

Hi Martin

I am currently engaged in editing a revised version of the archaeological "cave burial" gazetteers that used to be hosted on Sheffield Uni's website under the CAPRA online journal. Andrew Chamberlain has updated them all and UBSS will be hosting them. I'll put up a link when it's in usable form, hopefully in the next week or so. For the Welsh sites, we have included a direct link to the entry on the CCR where one exists. The data sets are complementary rather than duplicating much & both user groups will find useful additional references.

WRT your question about content, presentation, and future direction... it would be good to see a map search facility, as many people find that easier to visualise than grid references etc.

WRT the one about OFD, that figure has been around since the original survey was done. I remember talking to Paddy about how they did that & have had doubts about its accuracy ever since although it was always extremely good for navigating your way around the cave. Hasn't there been a resurvey in progress for a while now?

 

[Tony_B]

Hasn't there been a resurvey in progress for a while now?

Yes, there has. Some of it has already been published but the whole thing is, as far as I know, very close to completion. The main protagonists have just been away in France but I'll see if I can get a definitive answer for the depth of Ogof Ffynnon Ddu.

 

[Rhys]

This issue has been discussed here before:
http://ukcaving.com/board/index.php?topic=11036.0
http://ukcaving.com/board/index.php?topic=10846.0
http://ukcaving.com/board/index.php?topic=5595.75

Those threads suggest that the re-survey gives the vertical range as some 30m less that the earlier claimed 308m. So around 278m. If Tony could get a definitive answer though, that would be great!

 

[dudley bug]

Brian Clipstone has recently put together a useful online resource, including the OFD survex data.

This can be found on the following link http://www.clipstone1.plus.com/survey1.htm

The data supports the post Rhys made.

 

[Rhys]

Brian Clipstone has recently put together a useful online resource...

I'd forgotten about that. Thanks for the reminder!

 

[Tony_B]

From the horse's mouth. This sent by surveyor-in-chief Brian Clipstone, still sunning himself in France:

"The highest point in the cave is above the Columns at 459m and the lowest is Gothic sump near the resurgence at 184m. Which makes the total depth 275m."

 

[Rob]

Only a 2-3 meters deeper than Peak Speedwell then (once Rowter connects)!

 

[graham]

From the horse's mouth. This sent by surveyor-in-chief Brian Clipstone, still sunning himself in France:

"The highest point in the cave is above the Columns at 459m and the lowest is Gothic sump near the resurgence at 184m. Which makes the total depth 275m."

Only a 2-3 meters deeper than Peak Speedwell then (once Rowter connects)!

The depth potential of Cheddar is also about 280 m All very similar except that the OFD area, according to the model linked to above, does have potential, still, to go over 300 m.

 

[Rob]

...
The depth potential of Cheddar is also about 280 m All very similar except that the OFD area, according to the model linked to above, does have potential, still, to go over 300 m.

Ok, I've looked at the figures and I get this:

...The deepest potential [in Peak] is somewhere under the Mountbatten Pot area, where if you were unfortunate enough to get to the water table and then swim to a point equal to the depth of Main Rising (I'm so glad this is theoretical) you would have 309m of the best bit of limestone in the UK above your head......

 

[Martin Laverty]

Thanks to all of you who have responded in such an exemplary manner. I'm sure we would all like to thank Brian Clipstone for his answer and, of course, for all his and his assistants' work leading to the release of the spaghetti-like model of SWCC's wonderful cave.

I like the idea of 308m being just a metrification of a nice round 1000ft, although checking that it seems to show they added a 1% exaggeration first!

It will be interesting to see how long it takes for the revision to work its way through the numerous sources of (mis)information we have nowadays - Wikipedia, deepest cave lists, ...

 

[graham]

Thanks to all of you who have responded in such an exemplary manner. I'm sure we would all like to thank Brian Clipstone for his answer and, of course, for all his and his assistants' work leading to the release of the spaghetti-like model of SWCC's wonderful cave.

Indeed, if only all surveyors were so generous.

I like the idea of 308m being just a metrification of a nice round 1000ft, although checking that it seems to show they added a 1% exaggeration first!

Do you think it's like the story that Everest was declared to be 29,002 ft high 'cos they reckoned nobody would accept the measured 29,000 ft as having been done with any real degree of precision?

It will be interesting to see how long it takes for the revision to work its way through the numerous sources of (mis)information we have nowadays - Wikipedia, deepest cave lists, ...

Aeons.

 

[Pitlamp]

A classic example of such misinformation is all the varied depths quoted for Gaping Gill up here in the Dales. "360 feet" is a common one - I reckon this stems from as early as Martel's days when he published his elevation showing the depth (from moor level) as 110 m. However, if you look at this drawing it's clear that the depth of Main Shaft itself is shown as 100m. This demonstrates the value of going back to the original source and not just churning out misquotes from secondary literature.

When we measured it directly a few years ago we obtained an exact depth of 98.10 metres, although variations in the level of the sediments on the floor (caused by flooding) have been well documented over the years. So old Edouard's data, from the Victorian period, were obviously pretty good.

Going back to others' posts above about potential depths outside Wales (and purely for completeness) the Malham Cove Rising system has a potential depth of about 312m (or greater, if the sump goes any deeper before it surfaces).

 

[graham]

Interesting post John, thanks.

What you now need to is place a robust depth measure up the side of GG main chamber, linked to a couple of securely surveyed points, so that our successors over the next few centuries can see how the thickness of the sediment floor will vary over time.

 

[Fulk]

For what it's worth ? many years ago I descended GG Main Shaft by the simple expedient of tying a rope to a big rock, lobbing it over the edge of the shaft, and abbing down (with a rope protector over the edge). I left the rope for a wander round Main Chamber and when I got back to the rope tied a knot at the point at which it touched the floor. When I had prusiked out I tied another knot where the rope went over the edge, and subsequently measured the distance between knots as 94 metres.

 

[Mrs Trellis]

Only a 2-3 meters deeper than Peak Speedwell then (once Rowter connects)!

then when Maskhill 458m OD connects via New Oxlow & Crusader , then when Eldon 470m OD connects.

 

[Pitlamp]

Interesting post John, thanks.

What you now need to is place a robust depth measure up the side of GG main chamber, linked to a couple of securely surveyed points, so that our successors over the next few centuries can see how the thickness of the sediment floor will vary over time.

That's a very good point Graham; setting up a permanent datum in there would potentially be of value.

Fulk's rope measuring comments above are also of value. Mind you, the 98.10 m measurement we obtained was done with two professional quality 50 metre non stretch surveying tapes, connected accurately together.

Both of us have published our observations, yet that darned "360 feet" still gets perpetuated from time to time in trivial writings by self appointed "experts". C'est la vie.

(I do apologise to Welsh cavers; we seem to have drifted some way from the question the O P asked.)