• ndhold

Activity in Grolsch Passage and Iles Inlet

By Martin - 13h30m - 40 - Martin, John, Arthur, Tom Foord, Alan Brady

Digging time: 8 hours (6 hours at Grolsch, 2 hours at Iles)
Grolsch progress: 2m
Iles progress: dropped floor at Iles by 0.5m
Grolsch prospects: the view ahead looks really good - bigger airspace. Air is worse though.
Iles prospects: the wall appears to be curving, sand strata look good

The weekend didn't start well at all when I left my wallet at home. I only realised this when I was crossing the Severn Bridge and then had the humiliation of being escorted back onto the England-bound carriageway in order to find some money. This whole escapade added about 40 minutes to the journey time.

Everyone looked well ready when I arrived at a packed Whitewalls (there was a large group from Nottingham Uni staying at the hut). I thus entered into a completely manic packing and dressing mode, desperately trying not to forget anything that would be required for either this coming trip or next weekend's trip. We were able to leave Whitewalls at about 10:40 following this mess that I had created.

We seemed to have a leisurely trip down to Severn Beach arriving in a little under 3 hours. It was good to be back there with a large team (that turned out to not be quite large enough in the end). After some lunch, John moved the tape in Severn Beach to allow us to increase the size of the spoilheap and crawled off to the digface.

Digging seemed to progress well to start with though there were obviously problems with dragging the spoil back. Initially we had Alan at the alcove and Tom in the passage above that. This avoided any issues with the dragtray snagging on the sides of the passage but meant that Alan had to continually ferry himself backwards and forwards to the digface to also act as John's digging mate. This was a situation that couldn't be sustained so Alan moved forward to be just the digger's mate. Once Alan and Tom had moved forward, the last drag out became a pain (with the tray continually snagging on the passage sides). We never really seemed to get any momentum up which was a shame. We think we can sort out the snagging by taking some scaffolding in in order to guide the trays on their way up Grolsch. We know of several scaffolding stashes down at that end of the cave!

After about 2 hours we adjourned for a break. No-one was really expecting the good news that John had for everyone: the passage was apparently opening up nicely ahead of us. The airspace was apparently reaching the 1 foot or greater level. At this stage it looked like we would soon be crawling forwards.

Alan was the next man at the digface. He had a fairly torrid time what with diminishing air quality and the fall of a loose block from the roof (the roof is now in better condition hopefully: can't have been that bad as Alan did not complain vociferously). This must have been all the more disheartening given the obviously good prospects ahead. Tom then had a go at the dig face but was having a similarly torrid time. I then got about 5 trays out from the digface spurred on by the obviously good prospects ahead, but by this stage interest was waning and the drag was becoming harder as Alan had made an early exit and we were now down to a 4 man team. Air quality was not exactly good either by this stage.

We had a break at Severn Beach and decided to move operations for the day back down to Iles Inlet. On the way to Iles Inlet, we noticed that there was a definite draught from Severn Beach to Glevum Hall (we could smell the candle smoke in the passage). We also noticed a draught from Birthday Surprise into Severn Beach. This draught was a little odd: there was a definite outwards draught in the depths of Aggy, but there was a howling inwards draught in the entrance series. How does this work?

Tom, John and I set to work on the first pit in Iles Inlet (Arthur joined us once he had sorted out his light). This had been dug a little bit by a previous team, but there is now no doubt that it is being dug. We set to work on the floor of the pit with the crowbar and started removing spoil by chucking it into my black dragbag and depositing it back down the passage towards Priory Road. We swapped over every 15 minutes or so making steady progress in a step wise fashion. We dropped the floor by a couple of feet and had some very encouraging signs that we were digging under a phreatic arch:

  • the side wall is starting to overhang (as though it might at some stage form an undercut or a dip through to another passage like in the Hard Rock Extensions / OyDC),
  • there is a layer of sand in the pit that we had dug that dips significantly towards the right wall. There are similar sand strata under a phreatic arch in the passages towards Maytime
  • at the end we kicked the crowbar into the sand by the right wall at a 45 degree angle and it pushed in a significant way (indeed the sediment by the right wall seems to be less well compacted than elsewhere)
  • there is a ponding line around Iles Inlet that is similar to a ponding line under a phreatic arch in Maytime.
  • scallops on the wall at Iles Inlet suggest that there was rapid flow of water at Iles Inlet and that Iles Inlet is actually an outlet (is it older than the extension of Priory Road towards Glevum Hall? Why would the water be so up for going down Iles Inlet if there was open passage towards Glevum Hall which there clearly is). There is also coarse grained sand in this vicinity which suggests a fast flow of water.

We dug Iles Inlet for one to two hours before setting off out. We made a reasonably fast exit to be greeted by a howling gale through the Aggy entrance series and a snowy Llangatock escarpment (maybe a couple of inches of snow). We followed a single set of footprints back to a warm Whitewalls (Tom had exited an hour earlier) in pretty cold conditions to be met by Tom and the Nottingham University crowd relaxing by the warm radiators (the Nottingham Uni cavers seemed to have done 3 excellent trips amongst them: Outer Circle, Grand Circle and Antlers / Man in the Roof).

The prospects in Grolsch look really good from a physical perspective. We can see larger passage ahead. We feel that we are approaching the fault: this would be the source of the water that is causing the gloopy mud (does the passage sump in very wet weather?). Once we reach the fault then we will hopefully hit some cave development along the line of the fault (hopefully back towards Dweebland). John also feels that we are close to the low point in Grolsch and we should start rising soon (this will be good from an air perspective). We are going to need to move some of the scaffolding from the Iles Inlet region to Grolsch in order to facilitate the drag. In order to make substantial progress on a long digging trip, we are going to need a team of at least 5 diggers and are going to need to get serious with wafting. The other approach would be to chip away at the problem with smaller teams on shorter trips and shuttle the trays back up the passage (tiring, but feasible for a couple of hours). There is clearly everything to play for at Grolsch. The prospects are just too alluring.

The prospects at Iles Inlet also look good. At the moment, the task is simply to remove as much of the floor in this area as possible. Once a large amount of mud and sand have been removed, we should then be in a good position to look for the phreatic arch. At the moment, this is easy digging that can be done with a small team (of two people). It would help to have a bolt in the roof, a bucket and a pulley for the purposes of removing spoil from the pit floor.

Martin Beale, Bristol, January 2005 » 

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