Matienzo Caves 2015

About 50 cavers took part in the 2015 Matienzo expedition mainly at Easter and summer but some work took place at other times throughout the year. About 10km of cave was surveyed of which some 5.5km were in new discoveries with open leads left for 2016. In addition 128 new caves and sites were found and located and many were explored Full information on all the work of expedition is on our website

Nearly 4.5km of resurvey work was carried out in the major systems in our area, as we need modern digital surveys in order to tie in different finds and distribute any errors – most of the original surveys that need updating are from the 1970s and 1980s.

As part of the hydrological work agreed at the SEDEC conference at Ramales del la Vitoria in 2014 a major water test was carried out at Cueva Valline (733). This test showed that the water flowed to the main upstream sump in Cueva-Cubio de la Reñada (48) in Matienzo and then directly to the resurgence at Cueva del Comellantes (40). Detectors in the passage that had been connected to Comellantes by diving were negative, showing that this is a separate flow and that the main stream by-passes this area. The resurgence at Cueva del Molino (791) in Bustablado was negative. With the proven link between the Vallina and South Vega systems it shows that there is the potential for another 100km system in the Alto Ason area.

2015 highlights

Cueva-Cubio de la Reñada, Ghost Lake (Peter Eagan)

Cueva-Cubio de la Reñada, Ghost Lake (Peter Eagan)

In Cueva Valline (733) a major water tracing exercise (as described above) showed that there is a link to Cubio de la Ren?ada (48) and work was started to prepare for a major diving exercise at Easter 2016, with the first 5 sumps re-lined (old line had broken) and diving gear taken in and stored for the work next year. A new passage was found and surveyed going off from about 100m prior to sump 1. This parallels the sumps and is formed on a series of joints and runs for about 700m to near the end of sump 5. This series of passages were surveyed to 842m and left with a number of open leads including two pitches at the far end. Each needs gear to both descend and reach continuations of the far side. These passages are phreatic in origin and must have been formed by slow moving water as there are many sharp delicate flakes dividing the rift type passage in places. Details and surveys of this system can be found on:

Diane Arthurs in one of the tight pitches in Not Too Bad a Pot (Fleur Loveridge)

Diane Arthurs in one of the tight pitches in Not Too Bad a Pot (Fleur Loveridge)

Cubio de la Reñada (48) Work continued to re-survey part of the system, including the now linked Cueva del Comellantes (40), that was found and surveyed in the 1970s. Over 3km was surveyed in 2015 of which just over 1km was new passage found at various points. Work on this re-survey and pushing the system will continue in 2016.

Not Too Bad Pot (2964) is a site that sits on the north side of the ridge to the east of Cruz Uzano. This 65m deep narrow shaft was capped open during Easter 2015. Over 3 trips 7 pitch heads had to be capped out to make progress. This involved drilling over 100 holes and using around 400 caps. The cave now reaches a depth of 196m. Down the final 11m pitch the cave continues into a tight meandering passage, with a lump of rock in the floor preventing entry. Removal of this was attempted but needs more work in 2016. There is a small draught and it takes some water in wet weather.

Testing is needed to see if this water flows to the Matienzo side (e.g. to Cueva del Risco (25) or to the Ogarrio side via the Cueva de Humo system (734). The survey can be downloaded from the Matienzo Caves Project website at:


The Four Valleys System

Rob Smallshire in Carcavuezo, Afternoon Stroll, Southern Passage junction (Paul "Footleg" Fretwell)

Rob Smallshire in Carcavuezo, Afternoon Stroll, Southern Passage junction (Paul “Footleg” Fretwell)

Cueva de Carcavuezo (81) – following extensive flooding over the winter, work was carried out to both check the line of the cave near where the water normally sinks and also a surface survey to check the line of the river. This is needed as the current map shows it in the wrong place (due to tree cover hiding it in the aerial photographs. A radio location system was used to locate key passages and a comprehensive survey was produced. In the cave a 100m extension was found going towards the surface, this was also radio located. Work continued for the update and resurvey work of the Four Valleys System.

Torca la Vaca (2889) The exploration at Easter was hampered by finding that the connection crawl from the dry entrance BigMat Calf Hole (3916) had partly collapsed due to the flooding and wet weather over the winter. The blockage was cleared out over two days and temporary wooden shoring put in place. In August strong tubes were placed in this crawl, after they had been cut into a “kit” form so they could be lowered down the entrance tube. Using the BigMat Calf Hole entrance the area south of the system was pushed and in total over 2km of new passages in the far SE of the system, a 200m inlet to half way toward the passage was found and surveyed. The main finds were new along “Suit Wrecker Inlet” and a second 600m extended this major inlet to a choke, which is about 500m from Cueva de Collada (0394) in the adjacent valley of La Gatuna.

A new nearby site Cueva del Ciervo (4117) was found and seemed to be developed as part of a maze cave. It is at the same horizon as the more extensive maze cave Cueva de los Urros (2927) which is about 300m to the south, and may be Cueva del Ciervo of a similar origin. The Cave is heavily calcited and contans a number of bear bones and a number of bear pits. The cave was linked to The Langdales (3034) which gives an easier entrance.

The details of the 20k Vaca system can be found at

Text: Philip Papard

Download: Summary Report | Full Expedition Report


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