Oxford University Cave Club

Science

Hydrology

This year it was decided to repeat last years successful dye trace (from 2/7 to Culiembro resurgence); by changing the detectors regularly we aimed to determine a throughput time. Detectors were placed at Culiembro resurgence, the upstream sump in Culiembro cave, Trea Resurgence and 150m upstream from the Culiembro resurgence. (See map).

1kg of lissamine FF dye was placed into the 2/7 main streamway just upstream of Choke Drusilla on 21st July. The charcoal detectors at the Culiembro resurgence were changed regularly and retained for analysis in Britain. Any adsorbed dye was eluted with ethanol/KOH mixture and detected both by its visual fluorescence in UV light, and by using a spectrofluorimeter.

In 1988 the dye used for water tracing was 1.5 kg of Rhodamine B which gave a weak positive trace from 2/7 to Culiembro. This year 1kg of Lissamine FF gave a much stronger positive trace. The probable reason for this is that Rhodamine B is strongly absorbed by sediments whilst Lissamine is not (Smart and Laidlaw 1977). The Lissamine, therefore, is much more suitable for water tracing, its main disadvantage being its high cost.

The results are shown in Table 1. Dye emerged at Culiembro in under 52hrs, but there was a long tail after the peak with some dye still emerging at the end of the expedition. Additionally the detectors 150m upstream of Culiembro were strongly positive.

Table 1 Results of the dye tracing experiments.

Location of detector	Date Removed	Fluorescence (Arbitrary units)	Fluoresces in UV light.
Culiembro	21/7/89	0	-
	23/7/89	151	+++
	27/7/89	45	+
	29/7/89	105	++
	14/8/89	108	-
Culiembro cave, in upstream sump 24/7/89	27/7/89	76	++
Upstream from Culiembro	27/7/89	152	++
	29/7/89	120	++
	14/8/89	0	-
Trea resurgence	18/8/89	0	-

From this we can conclude that, due to the short throughput time, a large amount of open passage still remains to be discovered between the '89 limit in 2/7 and the resurgence. There is approx. 2km horizontally and 650m vertically between the two. Additionally the strong positive trace upstream of Culiembro suggests that 2/7 may also resurge at springs upstream of Culiembro. However searches for other resurgences in this area on previous expeditions were not successful (P. Brennan, pers. comm.).

The next expedition will continue this project. Temperature readings of the Rio Cares will be taken to locate any cooler cave water emerging in the river bed.

The size of the main 2/7 streamway was estimated at 0.25 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 m3s-1, the estimated flow rate of Culiembro resurgence (Gale 1984b). Other known or postulated feeders of the Culiembro resurgence are Sistema Xitu (Gale 1984a, Willis 1981) (flow 0.05 m3s-1, Pozu de la Roca Naranja (1/4) (OUCC to be published) (flow negligible) and Cabeza Muxa (flow estimated at approx. 0.15 to 0.2 m3s-1 (W. Stead pers. com.)).

This provides a total of 0.45 to 0.5 m3s-1 contribution to the flow at Culiembro resurgence. Therefore, especially if some of the 2/7 water resurges upstream from Culiembro, there are very probably more large feeders to Culiembro still to be found.

References

Gale, S. J. 1984a, Water tracing in the Western Picos. Proc. O. U.Cave Club 11, 33-35.
Gale S. J. 1984b, Some measurements of discharge in the Los Lagos Rio Cares area. Proc. O. U. Cave Club 11, 36-38.
Willis, R. G. 1981, Pozu del Xitu: The 1981 dye tests. Proc. O. U. Cave Club 10, 49-50.
Smart P. L. and Laidlaw I. M. J. 1977, An evaluation of some fluorescent dyes for water tracing. Water Resources Research 13 15-33.

Analysis of Sediments.

Samples of sediments were collected from a number of locations in the cave and these, combined with rock samples both from in the cave and on the surface, are presently being analysed by a variety of techniques, including Scanning Electron Microscopy. By comparing the quartz crystals extracted from the sediments with those from the rock samples we will find out from which (if any) of the surface rock types the crystals came. The surface wear on the quartz crystals will provide information on the historical flow rates in the different regions of the cave and enable us to reconstruct the paleo-environment (environmental and climatical conditions) at the time of sediment deposition.

A piece of a speleothem was removed from the campsite in Mr. Jones. Uranium series dating of this will give a minimum age for this section of the cave. The results of these experiments will be published in the scientific press.

Samples of sediments from a number of caves in the Picos de Cornion were collected for dating during the '84, '85, and '86 expeditions. The work was carried out by S.J.Gale, P.L.Smart, C.O.Hunt and J.N.Andrews. Below is a summary of the results.

Cueva del Osu: A stalagmite from the main streamway was dated by 230Th : 234U methods. Two samples from the top of deposit have yielded ages of around 3000 years (upper sample) and 16000 years (lower sample). The base of the stalagmite has not yet been dated, but the entire speleothem promises to provide a record of events from the present back through the last cold stage.

Cueva Culiembro: Several speleothems were collected from the main passage and the higher phreatic loops of the cave. One of the samples yielded an age of approx. 130 000 years. This is indicative of a maximum rate of entrenchment along the Rio Cares of 0.7m per thousand years. This figure is comparable with the maximum rates of fluvial entrenchment which have been derived by Smart (1986) for the Rio Urdon in the Macizo de Andara.

Pozu de la Cistra: Analysis of some samples of laminated, indurated silts from the roof of chaos chamber revealed the prescence of the pollen of pine, oak and cypress. This is suggestive of a lowland flora of Plio-Pliestoceine age. If this age is confirmed it could have major impications for the interpration of the geomorphic and tectonic history of the massif and the Picos de Europa as a whole. A sample of reworked speleothem from physically lower, but stratigraphically higher in the same sequence has not yet been properly dated, but preliminary results suggest an age of less than about 1.5 million years for the sample.

Reference

Smart, P. L. 1986, Origin and development of glacio-karst closed depressions in the Picos de Europa, Spain. Zeitschrift fur Geomorphologie N. F. 30, 423-443.