History
The source called the "Gargouillère" of Lignat is located in the town of Saint Georges sur Loire.
This source is intermittent due to an artificial well, existing in Roman times. This spring flows at the bottom of a small lost valley. Until the 1970s, the site was not finished, the well was simply covered with a sandstone wheel and the water gushed through the centre hole of the wheel for 1 minute at 10-20 cm in height every 10 minutes. The attendance and trampling of the site have deteriorated it. Water and gas was leaking laterally; spurts became less frequent, less tall and less abundant. Work was undertaken to restore and seal the well and briefly develop its immediate surroundings. In December 2011, the mill was surrounded by a plank floor in a kind of masonry square which could be accessed by a few steps. The source gushed and gurgled for about 1 minute at 30-50 cm high every 3 to 4 minutes.
Geological aspect
It may be sources operating on the same principle as conventional geysers, geysers spewing boiling water. Remember that CO2 is more soluble in water at high pressure than at low pressure.
Let us consider a very fractured rock with a water-filled open fractures network and imagine a CO2 supply at the base of the system. Water depth under high hydrostatic pressure will load in dissolved CO2 and will eventually be saturated with carbon dioxide: any additional consideration involves degassing. A CO2 bubble will form, rise into the fissure by driving in his rise CO2 saturated water, a that on its way up decreases its pressure and lowers the CO2 solubility, this water will then release a bubble gas, which will push the overlying water which CO2 solubility will decrease until the spouting of the gas bubble into the surface and a water mixed with gas. The continuous supply of CO2 to the base of the system resupplies the water and the cycle repeats. In some cases, it can also be a trap operation type if the geometry of fractures and other cavities is the appropriate to.
Gushing source - How does it works?
A permanent arrival of CO2 increases the volume and pressure in a pocket. Between the stage (1) and step (4), the pressure goes from atmospheric pressure “Patm” to “Patm + ρgh” where h is the height difference between the water in the gas pocket and the water in the conduit, ρ the density of water and g the gravity. In step (4) of the device here imagined, the level of the gas reaches the lower elbow of the siphon, and the gas bubbles rise along the vertical duct. Going up, they will chase out the water off the conduit. Less water in the conduit means less hydrostatic pressure. The pressure in the pocket will exceed the one exerted by the water column, which will be powered up and gush to the surface. The gas pocket empties. When the water level reaches the upper elbow of the siphon, the phenomenon stops until the next refill.
At the indicated coordinates, you can't find an infoboard, to validate your log, please send me the answers to the following questions. You can log without waiting for my reply, if a problem occurs we will try to find a solution together.
Log this cache as a "found it" and send me your answers via my profile or via message on geocaching.com, and I will contact you in case of problem.
1-.In order to create a chart, the day of your visit, tell me the time you visited the source and its height.
2-.If the source does not exceed the height of 1m, choose a reason why from the list the below:
a) The pocket is not big enough to store the gas.
b) The soil is very porous and does not give enough time to fill with gas and that's why she gushes every 10-20 min
c) There are not enough CO2 in the water so therefore less pressure.
3-.How many steps do you need to go down to get to the source and how many benches are around it?