OUCC Proceedings 13 (1991)

Scientific work in the Picos de Europa

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This is an outline of the hydrological work carried out by O.U.C.C. expeditions in the years '87 to '90. For a summary of previous work carried out in the area see references [1] and [4].


Two caves were explored: 1/4 to its conclusion, and 2/7. Neither cave (in the passages explored at that time) contained large streams, but dye traces were attempted in both cases. Approximately 500g of Lissamine FF was placed into the very small trickle of water present at the top of the second pitch in 1/4 and a similar quantity of Rhodamine B was added to the small stream in the shaft series of 2/7. Detectors (consisting of small bags of activated charcoal) had been placed in a number of the resurgences in the area, including Culiembro, Puente Bolin, El Hoya la Madre, and the Rio Cares at Cain and at Carmamena.

The detectors were changed prior to dye being added to the caves and again at the end of the expedition. Any adsorbed dye was eluted with ethanol/KOH solution and the samples analysed using a spectrofluorimeter. The results (Table 1) were a positive trace from 1/4 to Culiembro resurgence (Lissamine identified by its absorption and emission maxima), but a negative for 2/7 to any of the detectors.


Exploration concentrated on 2/7 and the large main stream was discovered. Two dye traces were attempted in 2/7. Approximately 100-200g of Rhodamine B was placed in the stream in the pitch series prior to the '87 limit and 1.5kg of Rhodamine was placed in the main stream. Dye detectors were placed and changed as in '87. The results (Table 1) were that a visible positive trace was seen after 1.5hrs from the '87 limit to a small inlet on the big ledge in Just Awesome and a positive trace was detected at Culiembro.

Table 1

Date         Cave              Resurgence             Throughput Time  

July 87      1/4               Culiembro              -                

July 88      2/7 '87 limit     Inlet on big ledge in  1.5 hr           
                               Just Awesome                            

July 88      2/7 (main         Culiembro              -                

July 89      2/7 (main         1) Culiembro           <52hr            

                               2) Upstream of         <7 days          


It was decided to repeat this trace and to determine a throughput time by changing the detectors regularly. Detectors were placed at Culiembro resurgence, at the upstream sump in Culiembro cave, at the Trea resurgence and 150m upstream from the Culiembro resurgence. The results (Table 2) were that dye (Lissamine FF) emerged at Culiembro resurgence in under 52hrs (but more than 6 hrs) Although the initial throughput time was short, dye continued to be detected until the end of the expedition. The detectors upstream of Culiembro were also strongly positive.

From this we can conclude that, due to the short throughput time, there is still a lot of open passage still to be found between the '89 limit in 2/7 and the resurgence. Additionally the strong positive upstream of Culiembro suggests that 2/7 may also resurge at springs upstream of Culiembro. Searches for other resurgences in this area on previous expeditions have, however, not been successful. For further details of the hydrological work carried out on the '89 expedition see [5].

Table 2

Dye placed in 2/7 stream at 6am GMT 21/7/89

Location of       Date changed      Fluorescence      Fluoresces in UV   
detector          (GMT)             (Arbitrary        light              

Culiembro         12am 21/7/89      0                 -                  

Culiembro         10am 23/7/89      151               +++                

Culiembro         27/7/89           45                +                  

Culiembro         29/7/89           105               ++                 

Culiembro         14/8/89           108               -                  

Culiembro cave,   in 24/7/89        76                ++                 
upstream sump     out 27/7/89                                            

Upstream from     27/7/89           152               ++                 

,,                29/7/89           120               ++                 

,,                14/8/89           0                 -                  

Trea resurgence   18/8/89           0                 -                  

The size of the main 2/7 streamway was estimated at 0.25 cumecs (m3s-1) by measuring water speed at a convenient location (time taken for a floating object to travel a measured distance, average of several readings) and measuring the area occupied by the stream at this point. This compares with 0.7 cumecs, the estimated flow rate of Culiembro resurgence [2]. Other known or postulated feeders of the Culiembro resurgence are Sistema Xitu [1], [3] (flow estimated at 0.05 cumecs); 1/4 (flow negligeable); and Cabeza Muxa (flow estimated at approx. 0.15-0.2 cumecs).

This provides a total of 0.45-0.5 cumecs contribution to the flow at Culiembro resurgence. Therefore, especially if some of the 2/7 water resurges upstream from Culiembro, there are more large feeders to Culiembro still to be found. However care should be taken in considering these calculations, because whilst the flow rates of 2/7 and Cabeza Muxa were measured or estimated in the same year, the flow rate for Culiembro resurgence was measured in 1983. More accurate results would be obtained if all the measurements were made in the same year at similar times, as we have experienced very variable flow rates in the caves from year to year. For example 1990 was a dry summer with very low permanent snow levels and the flow rate measured in 2/7 was less than half the '89 rate (see later).


The dye trace and flow rate measurements for 2/7 were repeated, but a more accurate value for the throughput time was determined by using an automatic water sampler set up at Culiembro resurgence by members of the Diving Expedition (Northern Pennine Club). In the event this was not needed as the 2kg of Fluorescein placed at the Primula Point (see survey) in 2/7 emerged as a visible trace in the Cares Gorge 60hrs later. Dye was also visible in the upstream sumps of Culiembro cave reducing the diver's visibility from 20+m to less than 3m. Measurements of the flow rate within the cave (carried out as in 1989) gave a value of 0.1 cumecs: less than half last year's value. This was due to the low rainfall and the much lower levels of permanent snow in 1990. Calculations suggest that the throughput time for the '89 trace was mid-way between the limits set in '89 (6) No dye was seen emerging upstream of the Culiembro resurgence indicating either i) the '89 trace was in error due to contamination of the detectors placed upstream or ii) the route to the possible upstream resurgence is a flood overflow and was not flowing in the much lower water levels experienced this year.


[1] Gale, S. (1984) Water tracing in the Western Picos Proc. Oxford Univ. Cave Club 11 33-35.

[2] Gale, S. (1984) Some measurements of discharge in the los Lagos Rio Cares area. Proc. Oxford Univ. Cave Club 11 36-38.

[3] Willis, R.G. (1981) Pozu del Xitu - 1981 Dye Tests. Proc. Oxford Univ. Cave Club 10 49-50.

[4] Winchester, H. (1986) Scientific Work 1984-85. Proc. Oxford Univ. Cave Club 12 33.

[5] Horsley, D., Roberts, S. G., Arthur, J. and Taylor R. (Eds.) (1989) Oxford University Cave Club Juracao Expedition Final Report.

[6] Lowe, G. (Ed.) (1991) OUCC Jultayu Expedition Final Report.

Dave Horsley

Some Thoughts on the Hydrology of the Ario Area

The region around the Ario Refugio contains many deep caves [1,2] including Pozu del Xitu which is over 1000m deep. However the hydrology of the region remains unclear.

The area is bounded on one side by the Cares Gorge, to which it is likely most, if not all, the caves resurge. The Cares Gorge contains only one major resurgence on its west bank - Culiembro Resurgence - which emits about 0.7cumecs under normal conditions, though this can be much reduced in dry periods (eg. summer 1990) and up to 8cumecs in flood conditions. It is likely that this is the resurgence for most of the caves in the Ario area. To date only three caves have been positively dye traced to Culiembro: Pozu del Xitu (-1135m, alt. 1652m), Pozu del Ojo de la Bruja (2/7, -810m, alt. 1860m) and Cueva de la Roca Naranja (-162m) (see above).

The resurgence is at river level and no passage can be entered. Above is an abandoned resurgence, Cueva Culiembro. This was first explored by the Swiss in the 1970s. The cave is a complex phreatic network of generally large passages which after some distance reaches a large fast flowing streamway, which emerges from a clear sump pool. This sump was dived by NPC expeditions in 1986-87 and 1990 and a large amount of new passage was found [3,4] (see survey inside back cover).

The entrance of Cueva Culiembro is believed to be at 420m with the actual resurgence at 340m. The NPC survey showed the upstream sump to be only 2m higher than the entrance, i.e. at 422m. Whether the streamway carries all the water which flows to the resurgence is not known, but the 1990 dye trace showed that the upstream sumps contain the 2/7 flow.

Pozu del Xitu is the deepest cave in the western massif at -1135m and contains two separate streams. The first sumps at -362m in the Trench Series and the second continues to the terminal sump at -1135m. The destination of the Trench series stream is not known, though it seems probable that it resurges at Culiembro, whilst the second streamway was dye tested to the Culiembro resurgence. The amount of water observed in Xitu is small and can account for only a small fraction of the Culiembro water. The rest of the Culiembro stream must be from other cave systems.

To the north of Xitu is Cabeza Muxa (alt. 1504m). This cave was explored by the SIE in 1978-84 (ref. [1] p41 and [2] pp265-267) and was finally bottomed at -906m. A large streamway is met at a depth of 600m. This extends upstream to a boulder choke and downstream to a sump which was dived by Rick Stanton in 1988 [5]. Initially the passage is at -4m for approximately 40m where a shaft drops to -24m. from here a tall rift passage was followed for a further 40m descending to a depth of -27m. At this point two ways on were possible: a small rift ascended to a blind chamber at -9m; or a steeply descending tube in the floor of the pasage which rapidly dropped to -33m and was seen to continue deeper for at least a further 15m. From the amount of water in the cave and the altitude of the final sump it seems probable that Cabeza Muxa resurges at Culiembro, though no dye trace was attempted by either NPC or the SIE. The source of the Cabexa Muxa stream is thought to be Pozu los Cuerries explored in 1986 by SIE to -575m [1] where a large streamway was met which sumped in a short distance both upstream and downstream. The source of this water is unknown, but at least some of it appears to come from Pozu los Texos (-218m) which has a streamway at the bottom.

Cabeza Muxa accounts for approx 30% of the Culiembro water whilst Pozu del Ojo de la Bruja accounts for a further 35%. The remaining 35% has not been accounted for, suggesting that a number of major cave systems remained to be discovered.

The feeders for Pozu del Ojo de la Bruja are not known, but some possibilities can be suggested.

1) Area 9 which contains La Jayada and the 306m shaft Tras La Jayada. This is a large catchment area, with (as yet) no major horizontal cave development. Also La Jayada in particular contains a very large snow plug which could account for some of the 2/7 stream. It is hoped to test this possiblity in 1991 by dye tracing.

2) The caves around the peaks near Punta Gregoriana (the Top Camp caves). OUCC have explored three major systems in the area: Sistema Conjurtao (-655m, alt. 1982m), Sistema Jorcada Blanca (-594m, alt. 1940m) and Pozu del Redondo (-582m, alt. 1937m) [6]. Close by are two caves explored by the Speleo-Klub Gliwicze, Sima del Porru de la Capilla (-863m, alt. 2200m) and Pozu de la Torre de los Traviesos (-416m, alt. 2180m) [1]. Sima del Porru Cappilla sumps reasonbly close to Sistema Conjurtao and it is possible that the large inlet which enters from a small aven near the sump in Sistema Conjurtao is the water from Capilla. The caves near Punta Gregoriana have been dye tested on a number of occassions. One possible positive trace was seen from Sistema Jorcada Blanca to the resurgence at El Hoya La Madre, but this was discounted as a second detector downstream from the main resurgence was not positive. Dye traces from the other caves have been negative even after 3-4 weeks. Therefore, considering the short throughput times from 2/7 to Culiembro it seems unlikely that the Top Camp caves supply the 2/7 water unless there is some large complicated phreatic network connecting them to retard dye flow.

A summary of the postulated hydrology of the area is shown in Fig. 1. Most of these links are awaiting confirmation by dye tracing. The confirmation of the Texos-Cueres-Muxa-Culiembro system and the determination of the source of the 2/7 stream seem to me to be particularly glaring omissions.


[1] Puch, C. (1987) Atlas de las Grandes Cavidades Espanolas. Exploraciones 11 Espeleo Club de Garcia.

[2] Courbon, P., Chabert, C., Bosted, P. and Lindsley, K. (1989) Atlas Great Caves of the World. Cave Books, St. Louis, USA.

[3] Danilewicz, C. (1987) Spain 1986 - the return trip. NPC Journal 4 5-58.

[4] CDG Newsletter 82 (1987) 2-22.

[5] CDG Newsletter 92 (1989) 25-26.

[6] Roberts, S. G. and Collie, U. (Eds) (1986) Proc. Oxford Univ. Cave Club 12.

Dave Horsley