Sinks in GG main chamber

[Speleotron]

A few weeks back I was in GG and it was fairly lively, I noticed that aswell as the usual flow of water to the left (as you stand facing the waterfalls) to that sink below the mud bank, some was flowing to the right to sink behind a boulder a shorter distance away, near a small corner. I was just curious about this sink and wondered if it was known about? ALso did the ground-probing radar show that the cobbles were the same depth everywhere or could the real floor of the chamber be close to the surface in some spots?

 

[braveduck]

The sinks change a lot ,in the last few years there have been big changes.
But when anything new turns up it can never be followed for any distance before it chokes.
Pitlamp will probably answer question about the depth of fill.

 

[Pitlamp]

H'm, sorry Braveduck - I've not got a definitive answer to hand - but I've seen it online somewhere recently. (From memory, no, I don't think the fill is shallow anywhere - the real floor of the chamber is a long way down all over.)

In case it helps, a caver called Bill Spencer who died a few years ago made a lifelong study of the floor of the chamber and how the sinks and sediments are different between flood events. I'm pretty sure Bill's interest in this stemmed from his involvement in recovering the body in 1947. In the latter part of his life he wrote an article in a CPC publication entirely devoted to changes in the sediment floor of the chamber which is somewhere in a CPC publication (probably "Record" rather than "Journal"). I'm a bit too pre-occupied with another job to look this up for you as I type but there are various indexes available to CPC stuff (at least one online) - or someone else might kindly post here where this can be found.

(If you are absolutely desperate to have the definitive answer on the GPR work then PM me and I might be able to put you in touch with someone who was directly involved.)

 

[dunc]

Caves & Karst Science 32/1 has information and images on GPR of GG Main Chamber.

 

[gus horsley]

The fill in the chamber could be very deep.  In about 1970 a rift opened up against the north wall which had solid rock on one side and rubble everywhere else.  It was about 70ft deep and so unstable that it had closed again a couple of weeks later.  Over a period of about 25 years I observed the water sinking in about ten different places in the Main Chamber which would support the idea that the water just finds the most convenient route down through the boulders. 

 

[Speleotron]

Thanks for the info and the reference to that paper. I was just wondering how much was known about the floor of the chamber, and how the water sinks and about whether we would get lucky one day and find a sink that could be followed, but it sounds unlikely now.


How did that rift open up by the way? Did anyone get a photo?

 

[gus horsley]

Thanks for the info and the reference to that paper. I was just wondering how much was known about the floor of the chamber, and how the water sinks and about whether we would get lucky one day and find a sink that could be followed, but it sounds unlikely now.
How did that rift open up by the way? Did anyone get a photo?

The rift opened up after several days of intense rain.  We did a trip down Bar and could hear the water in the Main Chamber near SE Pot, with a gale-force wind blowing through the crawls.  When we got to the Main Chamber the floor was covered in a lake and there were 11 waterfalls entering through the roof.  It was the most impressive thing I've ever seen underground.  We did another trip the following weekend and found that the water was sinking in several places, mostly under the east boulder slope and it appeared that one of the biggest boulders had slumped by several feet.  The floor of the chamber was completely different.  The rift was also open under the north wall.  We didn't get a photo because it wasn't the sort of place anyone wanted to hang around in because it was essentially where the chamber floor had peeled away from the wall and was extremely unstable, with water entering from every direction, a bit like descending a vertical colander. Somebody might correct me on this but I was under the impression that the water from the Main Chamber is next seen at the bottom of SE Pot and then reappears in Far Country.

 

[dunc]

I was just wondering how much was known about the floor of the chamber, and how the water sinks and about whether we would get lucky one day and find a sink that could be followed, but it sounds unlikely now.

I'm no expert but I read somewhere that the depth of fill was around 30m, which I would imagine put the base of the main chamber somewhere around the level of the ('dry') bottom of places such as SE Pot, it could well descend further like them (into flooded shafts) and this would mean any passage to follow would probably be underwater. (I could of course be wrong)

 

[Pitlamp]

I think you're absolutely right Dunc.

The Main Chamber water has been linked to the deep sump in South East Pot by a fairly comprehensive dye test. (In between it's probably encountered fairly soon in the Mud Pot sump and slightly further on in deep unattainable sumps which rocks can be dropped into through the boulder floor of an extension we found by climbing over the head of the last pitch of Stream Passage Pot - i.e. the pitch below Stream Chamber / Mud Pot. Note also that flood water emerges upwards through the choked floor of Sand Cavern on occasions. There is also evidence of flooding to a high level above the Lost River Chamber extensions sumps next to South East Pot.) All these sumps are probably at the same level as the Deep Well sump in Far Country which is itself probably at the level of Terminal Lake in Ingleborough Cave. It is likely that the GG water reappears through huge floor chokes (related to the Hurnell Moss Fault) within Sump 4 in the Terminal Lake Sumps - i.e. just upstream of Radagast's Revenge.

Main Chamber water probably falls down through various sinks in the massively choked Main Chamber floor to enter a deep rift sump straight away. The first part of this deep rift sump is probably also similarly choked. This deep sump conveys the GG water directly to Terminal Lake in normal conditions.

The above is supported by two important hydrological observations:

1. In low water dye takes a long time to get from GG to Ingleborough Cave (i.e. it travels very slowly through a long phreas).

2. When a flood pulse hits GG the water at Ingleborough Cave responds very quickly; obviously the pulse at the GG end is displacing water in the long U-tube which pours out of the downstream end - i.e. Terminal Lake - virtually straight away.

I've spent many years pondering on those various sinks in Main Chamber but have never really spent any time digging any because I don't think the effort would be justified by the likely reward (for the reasons suggested above).

By the way - further information about the above is all readily available in a variety of existing caving publications.

Hope this helps.

 

[braveduck]

If someone really wants to dig in GG Main Chamber,you might like to consider this.
South East passage sits on the Porcelanus band,you see it on the floor at the start of the passage.
To enter South East passage you have to climb up about 15ft off the Main Chamber floor.
Instead of climbing up,move left until a gap between boulders is seen,up and over a boulder drops you into a narrow rift between huge blocks.You can then move forward 15ft or so before been stopped by large detached blocks.But in this area there is a powerfull draft coming towards you from under South East passage!
In the first part of S.E. passage at least there are no holes in the floor or any signs of an obvious connection with anything underneath.Never managed to get anyone intrested in this so far.
So I comend it to the house!

 

[gus horsley]

What's the vertical difference between the floor of the Main Chamber and the water level in SE Pot?  That should be about the distance you'd have to dig in order to get to a massively boulder-choked sump.

 

[braveduck]

The draft is not coming up it is coming from ahead.
I am wondering if there is a blocked passage under S.E. passage.
We are talking horizontal here ,not vertical.

 

[Pitlamp]

Extremely interesting, Brave Duck. What occurs to me is that the porcellanous band is not always a single bed - in some areas it splits into two with a lens of normal limestone in between. (I think this is seen in various of Hensler's crawls here and there.) I wonder if there's summat developed in between two porcellanous bands where your draught is? H'm - interesting!