OUCC Proceedings 12 (1986)
Scientific Work 1985
|OUCC Proceedings 12 contents|
by Hilary Winchester
Precipitation measurements, together with some measurement of pressure and temperature, were taken in 1984 and 1985 in order to gain data for high-altitude stations, which are scarce because of the inaccessibility of such areas. Measurements were taken at three sites at 1100m, 1600m and 1800m, in order to provide a more complete record of rainfall variation with altitude. In 1984, the measurements were taken over a period of 32 days, and in 1985, 29 days. The data are at present being analysed in association with sea-level data obtained from the Meteorological Office.
Preliminary analysis of the results and the synoptic charts indicate that summer precipitation in the Picos de Cornion may be categorised into three types. First, the presence of cloud and mist at this altitude provides a small but significant proportion of measurable precipitation. Secondly, periods of steady rainfall are associated with northerly airstreams bringing moist air from the Bay of Biscay. Thirdly, the dramatic intense rainfall events are associated with the passage of frontal systems, augmented by orographic effects. However, the relationship of precipitation to altitude is by no means straightforward as it is heavily influenced by the type of precipitation, as well as by topography and turbulence effects. Further analysis of these data will enable us to understand more fully the complex nature of summer precipitation in high-altitude areas.
S.J. Gale and H.P.M. Winchester, Mountain Rainfall in the Picos de Europa, Weather, forthcoming (1986).
Dye-tracing experiments were again undertaken in 1985 in order to establish the routes taken by water flowing through the caves of and in the gorges bounding the Massif del Cornion. Control measurements of fluorescence were taken before dye was placed in the cave systems. Fluorescein was used in F20, a major high-level cave, and in the low-altitude cave of Cueva del Viento. Charcoal tracers were set up in the gorges of the Cares, the Dobra and at El Hoya la Madre, and at Rio Pomperu and Vega la Cueva; in other words, at all the major resurgences and surface streams of the area.
The charcoal was tested by eluting the samples and by testing for fluorescence using a photospectrometer. Unfortunately, no positive traces were found. This could be due to a variety of reasons. It is rather disappointing, as the hydrological development of this area is still poorly-known, and these experiments took a number of man-days to establish. It will be necessary to continue this work next year, probably using a greater range of dyes, and allowing a greater time-lag between the insertion of the dye and the collection of the tracer. Our understanding of the hydrological development of this area would be greatly improved if some positive results could be achieved in future years.
The aim of the surface survey is to provide an accurate map of the topography and location of cave entrances in the area of the Pena Blanca Basin, approx. 1100m x 750m, which ranges in height from 1800m to peaks of over 2100m. This area is highly significant as it contains two entrances to one of the major cave systems of the Picos de Cornion, Pozu Jorcada Blanca and Pozu las Perdices. The ridge and basin also contain two major cave systems still undergoing exploration, and 26 smaller caves logged by OUCC.
Initial surveying work was carried out in 1984, and the height of Top Camp established by a number of altimeter runs. The survey was carried out by establishing a triangulation base with five cairns. Cave entrances and major peaks along the ridge were then surveyed with reference to two or more of the cairns.
In 1985 this work was extended, and the number of survey points more than doubled. New cave entrances were surveyed to an extended triangulation network. The bulk of the work concentrated on surveying significant ridges and depressions within the basin, in order to establish a more accurate contour map of the area. The contours on the map shown were produced from the raw survey data by a computer program.