2649: Mareserection Hole
Riaño 30T 452118 4800695 (Datum: ETRS89. Accuracy code: G) Altitude 270m
Length 159m Depth 12m
Area position

Updated 11th October, 18th December 2007; 7th May 2009; 16th January 2010

A draughting, excavated hole to a 3m drop into a rift passage. Upstream quickly closes down, but downstream the passage gains height, passing an inlet on the right which has not been pushed to a conclusion. Continuing downstream the passage narrows forcing a traverse until it breaks out into a chamber with a 3m deep hole in the floor and a large slab boulder in the middle. There is a potential dig at the right hand end of the chamber. The main way on is straight across the chamber over the back of the slab, heading downstream in a muddy walking passage until a T junction is reached at a roof fall. To the right it is possible to climb over a boulder followed by a flat out crawl at floor level under a huge delicately supported boulder. This leads into a small chamber where the roof appears to be peeling off in huge slabs which are largely unsupported (care!). It may be possible to squeeze up next to the right hand wall to get on top of the roof slabs, but if they fell the way out would be permanently sealed off, so this has not been pushed.

In the summer, 2007, a few boulders were removed from the roof fall at the T junction and a hands-and-knees crawl entered (unsurveyed). This heads left from the T junction for about 30 metres to a right hand bend. Straight on at the bend is a too tight rift which appears to be wider below, but requires some work shifting boulders and fill to gain entry. The main passage right continues as a crawl for around 50 metres to a squeeze, beyond which it narrows to very awkward going. This appears to be heading upstream and does not look promising. Back at the T junction with the roof fall, a clean washed stream bed can be seen down a hole under the boulders, and this is potentially the best lead in the cave. It looks possible to squeeze down into a potential downstream continuation here with a little excavation of mud and small boulders (if you can ignore the unstable rock around you!). The end of the cave is located about 70 metres above the large rift complex discovered in 2007 at the most northerly part of Cueva Riano (site 105).

At Easter 2009, the cave was extended a short distance to where it became too tight.

Reference: anon., 2007b (Easter logbook); anon., 2007d (summer logbook); Corrin Juan, 2007a; anon., 2009a (Easter logbook)
Entrance pictures : yes
Underground pictures : yes
Video :
Detailed Survey : 1:500 pdf Easter 2009
On Paul Fretwell's latest version of the Fours Valleys survey
Line Survey :
On area survey :
Survex file : yes (Amended magnetic declination December 2013 to align with Eur79 grid and coordinates altered to fit ETRS89 datum, April 2014.)

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