Nettle Pot - Alan Brentnall
I missed last week's trip as I was away on the Isle of Skye. Apparently four cavers braved some quite wintry conditions and gave Raven Mine a good exploring. Unfortunately there wasn't a trip planned for this week when I landed back from Skye, but John and I decided that an SRT venue would be nice, and opted for a blast down Nettle to the foot of Elizabeth and back. John agreed to bring rope for the Narrows and Bottle, while I got the rigging together to cover the Gulley pitch and Elizabeth Shaft. In the end, four of us turned up at the roadside at Oxlow Farm; the fifth, John, could be seen in the distance plodding up the steep hillside with a yellow Lyon bag full of rope. Quickly changing, we followed him to the entrance, and, as I had the next bag, I slid down the rope to the second re-belay.
Here's where it suddenly got a wee bit complex, as John had got to the end of his first rope some 10 metres above the sentry box. He was in the Narrows, just below me, swapping from stop to jammers, and trying to get back to my ledge. Fortunately there was no need to struggle as I could easily lower my foot loop to him, and he could then get the next rope back up to my re-belay, where I could tie it on. So things went smoothly for a bit, until (pretty predictably, I thought) John ran out of rope again about 10 metres above the foot of the bottom of Bottle. However luck was, for once, on our side as this coincided with a fairly large ledge which allowed John to get his weight off the rope so that I could abseil down and tie on the next rope. Eventually we all arrived at the boulder jumble which forms the false floor at the foot of the Gulley Pitch, and just above Elizabeth's P-bolts. Here we chatted and decided that it was pointless abseiling down the top half of Elizabeth just to do a change-over, so we decided to turn back, with me de-rigging. And we all got out into a pleasant, starry evening, surfacing at just after 10pm.
During all the shenanigans, I had been noting down oxygen levels, as Nettle is known to have a CO2 problem on occasions. Against a surface reading of 20.9%, I got 20.9% at the re-belay above the Narrows, 19.7% at the foot of the Bottle Pitch and 19.0% at the head of Elizabeth - so between 1% and 2% CO2. Not really noticeable as far as we went, but it would probably have been higher at lower levels (foot of Elizabeth, bottom of Beza or in Red River) and it is at these levels where people really notice the problem as they are exerting themselves more, especially when prussicking back out - although Hell itself has been known to be quite fresh while other parts of the system are stuffy.
The issue with rope lengths needs addressing. John is going to measure his ropes, and if they are what he thinks they are, then we will need to review the lengths in the rigging guide. This review is long overdue, and my other club, who produce the guide, would be very grateful for any input.