Author Topic: Deep Well - Pridhamsleigh  (Read 16974 times)

Offline Pitlamp

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Re: Deep Well - Pridhamsleigh
« Reply #50 on: March 04, 2014, 09:00:44 pm »
Exactly Graham - what mechanism could account for a water level rise of (at least) 12 m?

Global Warming  8)

More seriously, I do not know the controls on base level in this area, but sea level around the south coast has risen by far more than 12 m since the Last Glacial Maximum about 20,000 years ago.

H'm - I understood that Prid is sufficiently far above (present) sea level for fluctuations not to be a likely factor in this investigation. But I've never had the opportunity to go caving in Devon and I'm just not familiar with its Pleistocene history. We need a sample to get a date on ideally (if these stals are there). Even if the -12 m stals can't be found, there is a more recent reference to stals at -5 m under the Prid 2 air surface in the CDG Newsletter. I've never seen a reference to the Lake surface falling as much as that, so it does seem that the water level is higher than it must have been formerly.

Was there a pitch of at least 5 m down into the Lake before they built that road? If not, should the finger of blame be pointed at some much less recent event?

Wish I lived a bit nearer as I'd do several dives there myself to go and look, as I find this very interesting.

Offline Les W

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Re: Deep Well - Pridhamsleigh
« Reply #51 on: March 04, 2014, 10:25:25 pm »
Base level controls here would be the River Dart, however, as somebody already alluded to here, the construction of the bypass may have changed local drainage routes also.
I doubt the bed of the Dart has risen significantly, much more likely to have down cut, which wouldn't account for higher water levels though in the cave.

The bypass construction is looking like the most likely culprit, assuming there are stals at depth in the cave...

You sure about that, Les. As I say, I don't know the history of the area at all well, but looking at a map, the lower reaches of the Dart, the Teign, Kingsbridge Estuary & the Avon look a lot like they could be rias to me.

You are correct, the estuaries are rias, but the River Dart, at Buckfastleigh is about 30 metres above current sea level. The river contains several weirs, both in the area, and downstream as well, and is quite fast flowing. It is somewhere between a youthful and a mature stage river at this location so erosion ought to be the predominant process here rather than deposition. Although it can't be ruled out it is unlikely that the river has built up its bed and banks, especially in such confining valleys.
I guess the clincher would be to see if the river had bedrock as a bed, rather than alluvium, but I can't see that from here. I will check next time I am there though. There is a particularly good viewpoint to study the river, from the terrace of the Abbey Inn, with Tribute on tap as an added bonus.  :thumbsup:
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Offline graham

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Re: Deep Well - Pridhamsleigh
« Reply #52 on: March 04, 2014, 10:41:37 pm »
I can think of rivers in Portugal that have aggraded quite significantly since the last glacial maximum. You are quite right that hunting for bedrock will help come to a conclusion on the matter, but I certainly wouldn't rule out base level rise in the area until sufficient evidence was in.
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Offline mrodoc

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Re: Deep Well - Pridhamsleigh
« Reply #53 on: March 04, 2014, 11:19:32 pm »
A few comments. The Navy divers weren't as you say cavers and the best account is reproduced in the Cave Science paper on Pridhamsleigh written by John Hooper where the letter is verbatim. I am sure there are copies in the BCRA library! Pitlamps remarks on re-solution are relevant. The walls of Pridhamsleigh lake at depth are quite extraordinary in that they have  a brittle crystalline surface such that one crunches into it when one hits it - does not do much for visibility. I haven't encountered this material in caves anywhere else. The Dart has a limestone bedrock, certainly outside Dart River cave only a mile or so from Pridhamsleigh. Finally the husband of my cousin, who is a civil engineer, told me some years ago that when they were building the bridge pilings for the overpasses to the dual carriageway outside Prid they had to pump large amounts of concrete into the cavities they found. Othere cavities were noted elsewhere on the dual carriageway construction site by Fish when they were working on it. Hope this helps.

Offline Les W

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Re: Deep Well - Pridhamsleigh
« Reply #54 on: March 04, 2014, 11:25:28 pm »
The Dart has a limestone bedrock, certainly outside Dart River cave only a mile or so from Pridhamsleigh.

Dart River Cave is right by the Abbey Inn (where they keep an exceptional pint of Tribute...  :beer2: ). In fact I believe it is accessed from their terrace...

I think some summer study of the river bed there is in order...  :beer2: :thumbsup:
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Offline bograt

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Re: Deep Well - Pridhamsleigh
« Reply #55 on: March 04, 2014, 11:27:41 pm »
Dart River Cave is right by the Abbey Inn (where they keep an exceptional pint of Tribute...  :beer2: ). In fact I believe it is accessed from their terrace...

I think some summer study of the river bed there is in order...  :beer2: :thumbsup:

Are you on commission? ;) ;)

Seriously, I think we may be looking at some inter-glacial developement here, question is Which Glaciatian(?) the only way on is to find it, get a sample and date it.

P.S. Messages crossed ;D
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Offline Les W

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Re: Deep Well - Pridhamsleigh
« Reply #56 on: March 04, 2014, 11:30:23 pm »
Dart River Cave is right by the Abbey Inn (where they keep an exceptional pint of Tribute...  :beer2: ). In fact I believe it is accessed from their terrace...

I think some summer study of the river bed there is in order...  :beer2: :thumbsup:

Are you on commission? ;) ;)

No, but I am partial to a decent pint of premium Cornish Ale...  ;)
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Offline graham

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Re: Deep Well - Pridhamsleigh
« Reply #57 on: March 04, 2014, 11:46:26 pm »
Pete

The nature of the Lake walls is interesting. Maybe you need to get a proper geomorphologist (Joyce?) to dive in there and take a look at them. If there is stal & re-solution then it can only be explained by base-level rise. Someone must surely have done a study of the Pleistocene history of that part of Devon.

But are you absolutely certain that the stream bed is bedrock & not sediment? If the downstream end of the Dart is a ria, as it seems, then it is highly unlikely, in my view that this stretch of the river will be actively downcutting today.

Maybe I need to organise a pint with Les in July.

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Offline Les W

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Re: Deep Well - Pridhamsleigh
« Reply #58 on: March 04, 2014, 11:50:52 pm »
Maybe I need to organise a pint with Les in July.

 :thumbsup:
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Offline graham

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Re: Deep Well - Pridhamsleigh
« Reply #59 on: March 04, 2014, 11:55:27 pm »

Seriously, I think we may be looking at some inter-glacial developement here, question is Which Glaciatian(?) the only way on is to find it, get a sample and date it.


bograt, what you northerners forget is that this part of the world was not not glaciated during the Devensian, so we ain't looking at inter glacial development here, as you cannot be inter two events that didn't happen - I don't remember* whether ice got this far south during MIS6 but I don't think it did.


*I've drunk too much whisky tonight, but sometimes too much is just right.
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Offline graham

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Re: Deep Well - Pridhamsleigh
« Reply #60 on: March 05, 2014, 12:03:08 am »
Pete

One last comment before I collapse for the night, do you know if the navy divers involved with Edgar Reed in Prid were any relation to the navy divers involved with Big Willie in Swildons in 1946?

Just a thought.
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Offline Pitlamp

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Re: Deep Well - Pridhamsleigh
« Reply #61 on: March 05, 2014, 10:03:00 am »
Maybe I need to organise a pint with Les in July.

 :thumbsup:

I'm impressed by your dedication in researching all possible venues for future BCA Conferences Les.  ;)  I wish we had nice pubs outside our Dales cave entrances. It always seems to be icy desolation and freezing cold changes round here.

Graham - I hope you're now over the after effects of your favourite tipple last night. Is Joyce a diver? I never knew that. I've met her - and was involved a bit in writing a paper with her - but I never knew she was a diver.

Pete - your most recent post was particularly helpful; many thanks. (And thanks to other folk for your contributions.)

Offline graham

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Re: Deep Well - Pridhamsleigh
« Reply #62 on: March 05, 2014, 10:04:08 am »
John

I've no idea whether Joyce dives or not, but I wouldn't put it past her.
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Offline mrodoc

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Re: Deep Well - Pridhamsleigh
« Reply #63 on: March 06, 2014, 10:53:27 pm »
She hasn't mentioned diving to me when I have spoken to her - but then I didn't ask her about that. The person who really knows about Devon caves is Chris Proctor. He did his doctorate on halocline systems at Brixham. I remember years ago we discussed (that means I listened) the topic of  whether Prid 2 was of hydrothermal origin (as I believe is the origin of Pen Park Hole). Somewhere i have some correspondence from Pete Cousins about it.

Offline graham

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Re: Deep Well - Pridhamsleigh
« Reply #64 on: March 07, 2014, 08:29:17 am »
Peter

More and more interesting! Chris would certainly be a good person to take a look, does he still dive I wonder?

PPH is undeniably hydrothermal and also has a dived lake at the bottom. I'd be very interested to hear Chris's reasoning about Prid.
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Offline Pitlamp

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Re: Deep Well - Pridhamsleigh
« Reply #65 on: March 07, 2014, 10:04:35 am »
Me too.

Please can I just ask a quick question? What's the difference between "hydrothermal" and "hypogenic"?

Graham's probably the best person to answer that - but please bear in mind I'd need an "answer for dummies" rather than anything too technical.

Mrodoc - thanks for your latest contribution. All this is making me start to think about having an expedition to Devon at some stage with a few tanks.

Offline mrodoc

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Re: Deep Well - Pridhamsleigh
« Reply #66 on: March 07, 2014, 10:18:23 am »
If you come down, let me know and perhaps we can organize some sherpas. My interest is in doing some U/W photography with slave flashes now I  have a decent one. The best one I have got so far is at http://www.darkanddeep.co.uk/images/caving_devon/PRI-049.jpg. This shows the arch between Prid 1 and Prid 2.

Offline mrodoc

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Re: Deep Well - Pridhamsleigh
« Reply #67 on: March 07, 2014, 10:19:33 am »
Perhaps this link will work then go the image http://www.darkanddeep.co.uk/caving_devon.asp

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Re: Deep Well - Pridhamsleigh
« Reply #68 on: March 07, 2014, 10:20:25 am »

Offline mrodoc

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Re: Deep Well - Pridhamsleigh
« Reply #69 on: March 07, 2014, 10:21:37 am »
Should not have put a full stop after first :-[

Offline graham

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Re: Deep Well - Pridhamsleigh
« Reply #70 on: March 07, 2014, 10:50:08 am »
Me too.

Please can I just ask a quick question? What's the difference between "hydrothermal" and "hypogenic"?

Graham's probably the best person to answer that - but please bear in mind I'd need an "answer for dummies" rather than anything too technical.

Hypogenic means 'formed at depth' Hydrothermal means 'hot water'

Hypogenic caves, that is, ones which are formed below the surface without reference to the surface (unlike all that stuff in t'Dales wot is formed by the incessant rain in them parts) are formed by hydrothermal water rising up through the rock. The water will have been heated at depth, but may not be nascent water, actually formed by chemical processes at depth but rather be rain water which has fallen & then circulated deep (very deep) underground. The hot stuff that rises at Bath (& at other places in the Bristol area) is thought to be of the latter type & to have been 10,000 years or more on its journey down from the surface & then back up again. This process & the Bath Springs are one of the things that might well be disrupted by fracking in this area.

Mrodoc - thanks for your latest contribution. All this is making me start to think about having an expedition to Devon at some stage with a few tanks.

Is your passport up to date? ;)
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Offline Pitlamp

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Re: Deep Well - Pridhamsleigh
« Reply #71 on: March 07, 2014, 10:58:29 am »
Thanks Graham - an excellent explanation. So hypogenic caves are generally likely to have been formed by hydrothermal waters and the two terms are closely linked.

There is a possibility that certain caves in the Dales might have had an element of hypogenic formation, which is why I was interested. The natural rifts under Elbolton Hill in Wharfedale  spring to mind as possible contenders.

(I don't need a passport to enter Devon as I can travel from the Dales without passing between Yorkshire & Lancashire if necessary!)   ;)

Offline ccasling

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Re: Deep Well - Pridhamsleigh
« Reply #72 on: March 07, 2014, 04:26:26 pm »
did someone mention Sherpas. if anything big does go down I'm sure I can gather a merry crew of hands

Offline Pitlamp

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Re: Deep Well - Pridhamsleigh
« Reply #73 on: March 07, 2014, 08:12:24 pm »
That's a very generous offer ccasling - much appreciated. I don't know when I'd get chance any time soon but the local CDG members might appreciate a chuck with the gear some time?

That's an excellent picture MROdoc - looks like peculiar limestone though. Out of interest, is the subject a certain Leeds area based Northern Section member who likes making diving gear from unrelated scrap parts?

Offline Cartwright26

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Re: Deep Well - Pridhamsleigh
« Reply #74 on: March 07, 2014, 08:25:44 pm »
I too will happily sherpa and hump gear in!! Just a thought but going back to water flow there is evidence from olden days of flourecene into the well to see if it flows to lake but could we not try that from lake to the well?
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