Author Topic: Top Hole  (Read 467 times)

Offline tim.rose2

  • Tim R
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Top Hole
« on: May 21, 2021, 10:56:41 pm »
Thursday 20th May...

Sometime ago myself and Richard set to on a mission to re-find a number of caves on Portland previously explored and recorded, but since 'lost' due to paths vanishing and entrances getting grown over.  We ticked off most of these which were listed in the Portland book a few years ago but a few short caves remained which we'd not visited.  Yesterday, following lockdown and then some 'knee recovery time' myself and Richard met for the first time in many months and decided to go looking for Top Hole, one such cave still on our to do list.  I'd previously hunted around most of the easily accessible parts of King Barrow Quarries with out success and had come to the conclusion the cave was either lost or now hidden in the undergrowth.  It took a couple of hours and some 'speculative gardening' but eventually we found the entrance amongst the bushes and brambles. 

Despite being only 15 m in length the cave is a reasonable size for Portland, consisting of a low entrance area and two rift chambers joined by crawls through boulders.  The rift chambers contain some nice orange flowstone.  It's situated in an island of freestone left behind by the former quarrymen measuring approximately 50 m x 30 m completely surrounded in quarry.  The end of the cave is obviously within this 'island' and is clearly just a mud / rock choke in the continuing passage.  Obviously the prospects here are small but a 50 m through trip is certainly plausible.  The other side of the 'island' is equally inaccessible but will in time be searched for a potential opening.  The other hope is that the cave goes down.  The quarrying in this area has only removed the upper freestone with the lower cherty series intact.  Elsewhere on Portland the rifts span the height of the limestone existing in both the freestone and cherty series and so this is a distinct possibility.  As a result we decided to have a couple hours attacking the end and have established a reasonable draft emanating from some small gaps in the mud / rock infill.  We're intending at least one more session here in the coming weeks.  I'm guessing most wouldn't bother but we're mad, the digging is easy and on Portland every metre counts! 

The cave had clearly in the past been used as a 'den' containing all sort of detritus.  Richard did a fantastic job of clearing all this whilst I'd popped back to the car for a prodding stick.

Some photo's...

The pre-caving gardening & the classic Richard arse shot:


The entrance at floor level:


The low entrance area:


Rift Chamber 1:


Rift Chamber 2:


The end of the cave as we found it:


OK so it's a bit claggy!!!  Richard doing the hard work here:


Second Rift chamber with it's new slightly raised floor:





Offline tim.rose2

  • Tim R
  • obsessive maniac
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Re: Top Hole
« Reply #1 on: June 04, 2021, 09:55:20 pm »
Today marked the return to Top Hole for pokey pokey no.2.  Firstly we wanted to see if there was any evidence of the continuation of the rift on the other side of the quarry.  Unfortunately despite appearing to be solid rock, upon closer inspection the opposite wall consists entirely of stacked blocks.  We gardened our way along the appropriate section and poked around in some 'gaps in boulders' but failed to find any solid rock so gave up with that effort.  Back in top hole a few mins poking and a hole with a view into open space appeared.  It then took a good hour of shifting muck and rock but eventually we had our 'breakthrough'.  In the process of doing so, Richard received a dose of rocks which he declared 'had looked solid'.  Fortunately no harm done.  So what did we find... well bugger all really, closed down almost immediately so in total I'd say we gained 1.5 m of cave!  Our break though was nothing more than a void in the choke.  Interestingly we did find a fair few white snails and a number of bones in the mix.  God knows where they've come from.  They certainly didn't get there the way we did.  It's possible they've come from above as our choke contained a lot of wet mud however I'd estimate we're a good 5 or 6 m below the surface.  It doesn't look like they came from ahead as the passage is again completely choked but fortunately free of mud and still emanating a draft.  We gave up at this point and did a quick survey.  Whether we'll return is uncertain.  Any further progress is going to require some stabilisation work and shifting a hell of a lot of rubble which in all reality probably isn't worth it for this site. 

A couple of photo's:

The new end of the cave


Our mucky dig


The survey showing the island of rock in which the cave is contained.  The survey makes the project look reasonably worthwhile, but unfortunately inside the cave less so.  For record the total cave length is 18 m.


We did wander around the 'island' after we came out the hole but most of it is hidden behind vegetation obscuring the view of anything which might be hiding around the far side.     We did note that floor level was higher on the far side but it wasn't clear whether this was due to less quarrying or backfilling.  Either way, my gut feeling it that anything significant will require going down.

 

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