Deep Well - Pridhamsleigh

[mrodoc]

You do see stal underwater at times. The Navy guys reported it at depth in the 50's in the first lake but it's always pretty murky there. I am sure divers reading this will look around. The stal in the film is fairly modern although I can't say for certain as I don't know what the water levels were like when the film was made. When I first visited the cave in the late 60's water levels were generally a lot lower. It changed after they built the dual carriageway.

 

[Pitlamp]

Do you know if any of this "modern" stal been dated Mrodoc?

By the way, I'll be sending a PM to pick your brains about something else shortly.

 

[mrodoc]

Nobody has done any dating in Prid as far as I know.

 

[Pitlamp]

Thanks - OK then, if I learn of an opportunity to get a date done (which sometimes crops up from time to time) I'll get in touch.

 

[D.Send]

The road works lowered the water table by about four feet at Prid, as trench cutting uncapped a small fissure spring just downstream of the entrance. (There was also a recorded perched water-table above prid).
As for underwater stals, there is a video recording of a dive through to Prid 2 which clearly shows them deep down.
Remember that the weir at Buckfastleigh has raised the profile of the Dart upstream of it. Dart river cave should really be well above river level. Tony Sutcliffe did some work on river dart downcutting and terraces.
During the road works, shaky cabe dried out completely due to ditch deepening.
Devon was only slightly affected by small glaciers on northern dartmoor and exmoor. But it is well known that the Devon 'rias' were much deeper during glacial maxima, and have back-filed since. For example, the Tamar flowed through a deep gorge as far as the Eddystone!
We also tend to forget that during interglacials, sea-levels flooded many devon caves...explaining the dissolution of many stal formations...hence the 'starlight' reflections of stal when untouched by human muddy hands.

 

[Pitlamp]

Thank you.

Do you have any suggestions where I might be able to see that video?

 

[D.Send]

Hi,
See DIVING PRIDHAMSLEIGH CAVERN on youtube, about 3 mins into the video.
On second viewing, it is not evident at which depth underwater the stals are found at.
During the roadworks, it appeared that the limestone was downfaulted after the spring mentioned previously. This might explain why Prid 2 sump goes down so deep? The rock walls of the deep sump certainly appear to be very shaly, rather than solid rock as in the prid 1 series. Perhaps roadwork geologists made observations at the time.
Good caving folks!

 

[D.Send]

Hi again,
Upon a second full viewing, it would appear that the stals may in fact only be some four feet under water surface. There is a second prid dive video on youtube, which adds nothing to the debate.
So as mentioned by somebody in a previous post, Prid may not have been affected by pleistocene river reprofiling.
The famous Grotte Cosquer near Marseille has underwater stal, as its entrance is well below the current level of the medittereanen sea. The stal on the survey goes down some 5 to 10 metres below water level. (Sea wikipedia).
I will try to get more accurate data as soon as possible, as the 'survey' is rather sketchy.
The Plymouth limestones go down some 700 feet at stonehouse, so one would expect that stal should exist quite deep, but no known caves go anywhere near as deep, except perhips the millbay 'conger pit' resurgence, which remained unexplored in the mid-seventies when I was last caving in Devon...

 

[Pitlamp]

Ah - yes, I'd thought it might be that video which shows stals not too far below surface. Two people who have been regular users of this forum and who have dived there often have separately told me they've seen stals a metre or two below surface but they've never seen the deep stals (-12 m) alluded to in an article (despite specifically looking). Those were reported by a military diver who wasn't (I don't think) a caver - so he may have been mistaken. Also, the article isn't a first hand account (so possibly less reliable than a direct description).

You're right about many coastal caves around the world having submerged stal. (The Bahaman Blue Holes are a well known example). But my area of interest is more in caves becoming submerged for reasons other than sea level rises. The substantial flowstones at -9 m in the Kingsdale phreas, for example, were submerged because of glacially derived sediments accumulating. Devon has been far less affected by glaciation than the Dales, so if the existence of deep stal in Prid is confirmed, this would form an interesting comparison.

Thanks very much for taking the time to add the above as it's a useful part of the overall picture.

 

[mrodoc]

D. Send refers to the Millbay resurgence at Plymouth. I have researched this and it seems to be an apocryphyal tale. Police divers are supposed to have explored a tunnel at depth many years ago but I spoke to police divers from the area and they had no knowledge of anything like that but did mention a sewage outfall in that area :yucky:. However they did direct me to Brixham where we did find some submerged caves. I took the late Rob Palmer and Rob Parker to the site in Plymouth as there is a large section of underwater cliff going to depths of 40 metres or more but no caves were found. However further upstream at Devil's Point there are some caves at depth but not that extensive.

 

[Cartwright26]

except perhips the millbay 'conger pit' resurgence, which remained unexplored in the mid-seventies when I was last caving in Devon...

not heard of this one where abouts is it? is it a diving site?

 

[D.Send]

Hi,
The 'Conger Pit' is a deep hole in Plymouth Sound off Millbay which reportedly emits fresh water, visible at low tide. Local anglers know the spot very well, as it is the best conger site around. But remember, I left England in the mid-seventies, when PCG divers had not been to the location, which, by the way has VERY strong tidal currents.
The sewage outfall was situated off the tinside seapoool, but Plymouth sewage is now treated. (You could easily see the place because of the seagulls it attracted!) . It is perhaps worth enquiring with the Navy if they have mapped the site, as approaches to the dockyard are well documented. Also at the Plymouth Sea Angling Club.
By the way, has the entire Prid 2 (Gerry's Chamber), been fully explored at Depth?

 

[mrodoc]

As I mentioned before the Millbay site hasn't yielded any cave and I made intensive enquiries about the rumours. I have dived on the wall there and I know people who have been to the bottom but no cave seen. Regarding Prid I explored round the walls at the bottom in the 80's and there was nothing very obvious. Since then other divers have been in and explored the walls higher up finding some loop passages and potential ways on. Work continues. Diving on the bottom means swimming ahead of a blinding silt cloud and a return in nil vis!

 

[Grump Gnome]

If anyone needs a hand shifting gear in for diving I can help, if I'm not up to something else. Give me a shout.

 

[D.Send]

Hi,
I have just made some enquiries by telephone about the conger pit. It lies a good way off devils point ( rather than within mill bay). Anglers report that its site can be seen from shore at low tide as it causes a large eddy that also affects engine noise when boats pass through! This is therefore situated right in the deep channel...
The big question is : Where would such a large upwelling of water originate? There are very few known sinks along the Plymouth limestone outcrop, unless there is a submarine freshwater connection with the Plym? (Unlikely in the tidal zone!).
Good luck with Prid Diving...
D.Send.

 

[Joe90]

Coming from prid?

 

[Joe90]

Hi,

Just wondering if there was any further discussion on this (off the thread). Or if anybody was keen for any specific footage from the lake. I was going to go down on Wednesday so can have a go at getting it for you.

Cheers all.

Sent from my HUAWEI TIT-AL00 using Tapatalk

 

[mrodoc]

The Conger Pit story is interesting as the deep area on the admiralty chart is down at Millbay. There are caves on the cliff at Devil's Point explored a few years ago by the guys from Divers Down at Babbacombe. The whole Millbay thing started back around 76/77 with a report in the DKRP Journal that police divers had penetrated a cave for 100 feet but been repelled by the current. If there is truly a water upwelling then it could well be explained purely by tidal flow as coastal limestone caves are tidal. We know from historic reports that some way back from Firestone Bay there is a cave system (now concealed) that had tidal sumps in it. The report can be seen in an old PCG publication.

 

[maxf]

The University of Plymouth often conducts field work for various marine based degrees in the Devils Point/ Mill Bay area, if there was a quantity of freshwater discharge from subsea caves then it is likely that they would have detected it during the work they do using various instruments: CTD, SVP, water sampling, ADCP and likely to be the most obvious if uncorrected for in a swathe bathymetry dataset.

(No mention was made whilst I was there 2004-2007).

If there was strong outflow then there should be sign of this in the bottom sediment which once down at the bottom is quite soft, there was a Hydrographic conference in Plymouth sound in 2005 and again in 2015 and an RN school so it is a well surveyed patch of water.

Students often base their dissertation on various phenomenon of this area such as the mid water gyres which occur nearby.

I chose to base mine upon some subsea fresh water springs in Torbay.

I'll see if I can dig out any of the data for the area.