In the 3rd picture, most of the participants in the trip to L’Ariège by ICHN Bages in the intermittent wellspring of Fontestorbes (Belesta), in 18.06.2017.
Realize the difference in water flow between the 1st and 2nd images that are separated by just 15 minutes. From October to mid-June, in rainy season, a high and constant water flow comes from Fontestorbes. However, from mid-June to September the flow rate out of Fontestorbes fluctuates regularly in a period between 45 and 90 minutes.
The phenomena must be caused by a large reservoir into the mountain with two exit channels: a main one with its first stretch in slope up that drains the reservoir and a second beneath with the mouth slightly above from main one that can work as a air intake. The channels join before Fontestorbes. There is a delicate balance of pressure between them. When in dry season the flow rate to the inner reservoir decreases to be smaller than the output flow in Fontestorbes, the level of water in the reservoir goes down to suddenly open the mouth of the channel beneath. The intake of air reduces the water flow in the spring in Fontestorbes and through the main channel. This significant reduction of water flow allows the reservoir to fill in to cover again the mouth of the channel beneath and to stop the air intake. At this moment, the high water flow rate recovers. The cycle repeats until the start of rainy season when the flow of water into the reservoir takes over the average output in Fontestorbes; then the water flow remains high and steady in Fontestorbes. Isn’t it nice?
[photos Jordi Badia]
Further information in Notícies de la ICHN nr.133.