Updated October 29th 2002; 1st November 2009; 8th October 2010; 5th October 2011; 25th April, 25th September, 6th October 2012; 15th September 2013; 22nd April, 15th October 2016
The resurgence for water flowing west in Cueva de Riaño (105).
The large window into the water to the side of the sump [water's edge at 30T 451329 4800890] has
been dived to where it becomes too narrow. This is the Pozo Negro and is site 4445. The underwater investigation was repeated at April 2016 and the route forward appeared to be blocked with vegetation.
This was first investigated by Fred Winstanley in August 1985. He reported the way on as "muy estrecho".
In 2011, an incompletely explored, 2m deep chimney was noted above the resurgence dropping into the pool from which daylight can be seen. There was no obvious draught. At Easter 2012, the water was seen resurging up through holes in the floor between rocks.
The breakthrough came when John Taylor and Dan Hibberts dived in August 2012. Over 8 days, the pair pushed upstream in poor visibility, first dropping to -14m then rising to between -2 and -3m. The dive continued about 207m from base.
In August 2013, Colin Hayward and Jim Lister investigated the entrance, noting a possible new and more straightforward dive entrance under boulders.
Over the Easter 2016 period, Jim Lister carried out a number of dives, often thwarted by poor visibility, probably from run-off over ground recently cleared of eucalyptus trees. The route soon meets a large, above water cross rift (9m high, 2m wide and 15m long) with stal. The diver noted possible crawls going off at roof level. From the left hand end of the rift, the underwater passage continues low but very wide with a mud floor. The passage changes to a 3 x 2m passage floor and exploration continued after a "gentle right hand bend" to a V-shaped trench in a mud/silt floor. Then within about 60m of the downstream sump in Cueva Riaño, 162m was added to the length of the 2012 dive. The exploration was surveyed but passage detail could not be recorded because of the poor visibility.
The link into the downstream Cueva de Riaño passage was dived through by Jim Lister in mid-July, 2016. On the first dive, he surfaced in a 7m-wide canal where the thick mud floor "did not make crawling in full dive kit easy". The line (88m long) was tied off just before the next sump. The following day, laying 19m of line, the diver surfaced up a steep gravel slope into large stream passage - the downstream end of Cueva Riaño.
Although there is no doubt that the upstream sump joins with the downstream passage at the ends of each survey, the centre line surveys have a considerable overlap. The 4 Valleys System area line survey shows this. There has been no attempt to join the two end points - yet. Most of the error is likely to be on the underwater surveys. The present horizontal error is 60m, the vertical 12m. The underwater survey of site 575 has been drawn up without any adjustments.
References: anon., 1985b (logbook); Corrin J, 1986; anon.,
2002b (summer logbook); anon., 2011d (summer logbook); anon., 2012b (Easter logbook); anon., 2012d (summer logbook); Corrin Juan, 2013a; anon., 2013d (summer logbook); anon., 2016b (Easter logbook); anon., 2016c (summer logbook)
Entrance pictures : yes : Easter 2012 : summer 2012 : Easter 2016 : summer 2016
Underground picture: yes
Video : Dive problems (summer 2012) (YouTube) : Dives April 2016 (YouTube)
summer 2016 connection including almost real time downstream exit dive (YouTube)
Detailed Survey : summer 2012 : centre line addition, Easter 2016 : completed survey, July 2016, after link with Cueva Riaño
Line Survey :
On area survey :
Survex file : dives with some surface survey, summer 2016 (Amended magnetic declination December 2013 to align with Eur79 grid and coordinates altered to fit ETRS89 datum, April 2014.)
on Four Valleys file