Photos of the lake in Pridhamsleigh

Neil

New member
Hi

We are looking for a good (well lit) photo of the Pridhamsleigh lake for an article my partner is writing about caving for 'Active Dartmoor' magazine. Your photo would of course be credited to you. We need it this week to meet the deadline!

Thanks
Neil
 

The Old Ruminator

Well-known member
Any help.

prid.jpg


Do what you like with it. My photo.
 

gus horsley

New member
How deep is the lake?  Someone told me it's 100ft+.  I've done a lot of trips into Prid but I've never seen any real fluctuation in water level so I'm assuming it's an inactive phreatic feature.
 

Les W

Active member
There is a survey on the wall at Crest Hill (DSS Hut). I thought it was deeper than 100ft though. I seem to remember it being nearer to 200 ft but of course I could be wrong.  :-\
 

mike barnes

New member
I did many dives in there in the 90's. Some narrow rifts were found around the edge of the submerged chamber which, according to the old type of depth gauge I was wearing, showed a max depth of 36m. However, after getting a computer gauge, this always read about 2.5m deeper than the analogue gauge. The computer was confirmed as accurate by being used alongside several digital gauges over the years. So the deepest part I ever dived was probably 38.5m.
 

graham

New member
gus horsley said:
Thanks Mike, so have you any theories as to the formation of the lake?  I'm interested in geomorphology.

At a guess it's a solution void caused by slow moving phreatic water.
 

The Old Ruminator

Well-known member
Of course as Peter Glanvill will tell you the lake itself is only part of the feature. The line in the photo takes you through an archway part way down the vertical pitch that is The Lake. This then rises to an airspace in a huge flooded chamber. Measurements have been taken with a sonar device to ascertain the size of this flooded chamber.No doubt Peter has details and I expect its written up somewhere.
 

The Old Ruminator

Well-known member
Good old Wiki.

Pridhamsleigh Cavern is a cave on the outskirts of Ashburton, Devon, England. It is approximately 1.1 kilometres in length with a total depth of just over 50 m including Prid II.

Pridhamsleigh is a good site for novice cavers although it is quite muddy. It has a large variety of passages which lends itself to longer explorations. Due to the nature of the connecting and non connecting overlapping passages in the cave, surveys (maps) of the cave are hard to interpret. The cave contains 'The Lake', a large elongated pool, which has been dived to discover a second chamber, with no passages leading off it. This chamber is the biggest in Devon and is named Gerry's Chamber after its discoverer, the late Gerry Pritchard.

An accurate, hand-drawn, plan of the cave is held in the reference section of Plymouth Library. Although not requiring any great skill, the cave is quite complex, there being three distinct routes from 'Bishop's Chamber' to the lake. First-timers should note their route carefully as it is possible to get lost.

The cave is the type locality for the cave shrimp endemic to the south-west of England, Niphargus glenniei.

Vertical range: 53m

The cave is a complex multilevel maze. The entrance is large and there are series of passages on either side of the main route in - a low stoop. The cave is extremely muddy but caver erosion over the last half century has resulted in many low crawls becoming of walking size as well as a cave diving site, The Deep Well, now becoming choked with mud.

At the far end of the system is the Lake. Water levels here fluctuate considerably - more so since the construction of the A38 dual carriageway outside the cave. The Lake is over 30 metres deep and in the early 1970s divers from the Devon Spelaeological Society passed an underwater arch to enter the void of Pridhamsleigh Two. Pridhamsleigh Two is a partially water filled chamber approximately 40 metres long 20 metres wide with a total height of 45 metres. Above water there is a high level ledge and the chamber is well decorated with a wide range of speleothems. A stout series of shot lines enable dives to be made safely between Pridhamsleigh One and Two.

A full description and survey were published in Cave Science in the 1960s by the late John Hooper.
 

mrodoc

Well-known member
I have sent Neil a PM. Remember that depth gauges are usually set for seawater which is denser than freshwater so Prid lake is best measured with a string or sonar! Of course they are fine to dive with because it is pressure a diver is concerned with not depth.
 

mike barnes

New member
Hi Pete,

It's been such a long time since diving in the sea, I'd forgotten about that. If I remember, a diver is 2.5 to 3% deeper in fresh water than the gauge shows, unless calibrated for fresh water? So the above mentioned dive is about 1m deeper, 39.5m. Sooo glad I didn't know that at the time. I'd seen a fairly snug rift leading off from the bottom and descended in absolute zero vis before it felt like it pinched in, so turned back. Once in better vis, everything seemed a lot darker. On the deco, realised a double dive torch had come off my helmet in the low passage.

The following week, I went back. Just before the mud rolled in near the dropped reel, saw the torches, and even better, a larger passage leading off at the bottom. Being young and foolish, I picked up the reel and rushed into it without putting on a belay. Within 7/8 m, it closed down, but above me was a big, crystal clear void. I started to swim up into this, with the intention of rejoining the line around the base of the chamber. But I quickly realised I might not be able to find the line, and would have to return along the low passage with even less air. Dropping the reel in an absolute blackout, within a few m's the line went into a 3 cm slot, and it felt tight all around. Thinking 'sod this', I went back to the reel intending to exit via the big clear space, hopefully. However, the blackness was now all prevailing and all I could find was solid rock. At this point, I felt close to panic, and my breathing rate went right up. Decided it would be better to find the way out, so returned to the 3 cm slot to try and find that passage. I have never felt such a surge of relief as when I put my hand on the last lead block belay. And despite mild hypothermia from 30mins of deco due to tables, and a wetsuit with too many holes, I just couldn't stop smiling.

I've included the above story to dispel the myth that Prid is a 'safe' dive. Staying on the mainline, with a max depth of 24m and clean overhead rock it's fairly straightforward. It was afterall my first cave dive. But if you leave the rope line and venture more into the chamber, the silt rains down on you from above, the floor is deep incredibly fine silt, and the water is deep enough to narc you. I almost panicked when I re picked up the reel and could only find rock. Luckily, I was able to focus on what had to be done, and survived. So, a great dive, yes, often sensational vis. But a 'safe' dive, I think not.

Gus, I've often wondered about the chamber and how it formed. There appear to be very few boulders on the floor. Though the silt could be concealing much, like the big river passage that leads out to the sea at Berry Head!
 

mrodoc

Well-known member
Yes, it's a lonely place on the bottom of the lake! I have had my own embarassing time in there. On one occasion I had this cunning plan to lay a line right round the wall held in place by fishing weights. My buddy Jim was to swim behind me looping on the weights as I swam round the wall. Most of the way round I turned to see Jim behind me and a line running out across the chamber - we had dragged the line and weights with us. Having run out of air we had to return to base and another group had to clear up the line. Andy Stewart has now done a much better job I believe although it has resulted in a number of line junctions in Prid 2 now. I cannot repeat Mike's advice enough - never leave the line cos that 30m vis will go to 0m as soon as you touch the walls or floor.
 

gus horsley

New member
mike barnes said:
There appear to be very few boulders on the floor. Though the silt could be concealing much, like the big river passage that leads out to the sea at Berry Head!

Surely that's just wishful thinking!  Now I'm wondering if the cave shows multiple phases of phreatic development or if there's only one phase which extends over a large vertical range.  Is it possible it once connected to the caves on the other side of the valley and that they comprised one system which has been bisected and shared a common resurgence at one time.  Maybe I'm off in fantasy land now.
 

gus horsley

New member
graham said:
mrodoc said:
I have heard it suggested it might have a hydrothermal origin.
Intrigued. Where did you hear that?

Hydrothermal?  I find that hard to believe but I'm also intrigued.  Are we talking about late-stage Variscan Orogeny (cross-course) hydrothermals?  If so that would make Prid about 270 million years old.
 
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