QR Les Martres-de-Veyre 1
The Grand Saladis
A failed venture
The current pool is not natural. It was created on the unsuccessful initiative of Dr Roux, the former owner of the spring, who used explosives in 1882 to try and increase the flow. It was at this time that the popularity of spa treatments led many entrepreneurs to exploit small mineral springs, such as those at Sainte-Marguerite, located 500m to the east on the right bank of the Allier. In 1905, the municipal council of Les Martres-de-Veyre voted in favour of a project to build a spa at Les Saladis, but the project never saw the light of day.
A very long journey
Some of the rainwater percolates very slowly down to a depth of several kilometres, through the cracks and fissures in the different layers of rock it passes through. The water then heats up and fills with carbon dioxide from deep underground. This dual phenomenon then causes the water to slowly rise. As it rises, the hot water dissolves some of the minerals and fills with salts (calcium, magnesium, chlorine, sodium, etc.). They have a concentration of around 8 grams per litre in the Grand Saladis, including around 3g of sodium chloride. Carbon dioxide, which also rises with other gases in small quantities, appears as bubbles or chains of bubbles on the water’s surface. These CO2 emissions have a flow rate of around 3 litres per minute.
A delicate balance
Over the more than 140 years of its existence, the Grand Saladis basin has gradually been transformed until it achieved a new ecological equilibrium. Variations in the water level and the release of gases have shaped the banks, marked by carbonate deposits, where micro-cliffs alternate with small, almost-white beaches. All around, vegetation, adapted to the high salt levels, has flourished. The water in the basin, which is almost 3 metres deep in its southern part, is populated by microscopic algae, diatoms, which are also halophilic. The colour and clarity of the water in the basin change with the seasons according to the air temperature and the strength of the wind.
Halophilous plants
Around the springs, the vegetation has arranged itself according to the level of salinity. The saltier areas are home to rare and protected halophilic species, which are usually found on the coast. These plants, which must limit their loss of water to the salty ground, resemble certain species characteristic of arid environments, with, for example, narrow, fleshy leaves or a thick, even waxy cuticle.
Lysimachia maritima, which grows very close to the water, forms a dense carpet of vegetation, dotted by small white and pink flowers in summer.
Sea plantain grows in clumps or swards of paler green. From May to September, spikes of small yellow flowers emerge from its fine, fleshy leaves, turning brown.
Occasionally combined with glaux or plantain, spergularia media stands out thanks to its beautiful little white five-petal flowers.
Together with other halophytes such as the Puccinellie distante, which is more characteristic of the salt marsh to the east of the site, all these species are of exceptional ecological interest.
Image captions
- Sea plantain
- Spergularia media