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Petrifying springs with tufa formation and slope fens

Springs or wetlands?

A large part of the rainwater seeps into the soil and circulates inside it until it comes across impermeable material or uneven terrain and then it surfaces.

It can do so en masse to create water sources or natural springs, or it can do so diffusively, soaking the soil and circulating slowly to form slope fens.

Slope fens are very often found next to springs.

Water source or natural spring

Photo: E. Carrillo

Slope fen

Photo: E. Carrillo

The hardness of the water

The hardness or mineralisation of water is due to the presence of salts, especially calcium.

Different plants and mosses can be found depending on the temperature and degree of mineralisation of the water. The vegetation of the petrifying springs with tufa formation and calcareous wetlands is quite different from that found in soft water springs and wetlands. In the high-mountain landscapes distinctive patches of both types of wetlands can sometimes be found in the same place.

Travertine or tufa

The precipitation of calcium carbonate in the very mineralised waters onto the vegetation that lives in little waterfalls, springs and trickles makes a crust that covers it and, over time, grows there. Moss, algae and even some grasses are transformed into porous rock this way.

Rock that is formed over a period of years

Photo: E. Carrillo

Moss on which travertine forms

Photo: T. Llobet

The natural value of some springs

On a European scale, the springs of carbonated water that form travertine and the wetlands that are rich in calcium are especially interesting. Their value lies in the richness of the species that grow there and in the rareness of these habitats, which in the Pyrenees occupy very small land areas.

Two good examples of carbonated springs in the Catalan Pyrenees are the ones found in Montsent de Pallars in the Fosca valley (left) and Estanyeres de Son in Vall d’Àneu (right), both in the Aigüestortes i Estany de Sant Maurici National Park.

Photo: E. Carrillo

Main species

Petrifying springs with tufa formation


  • Palustriella falcata
  • Palustriella commutata
  • Philonotis calcarea
  • Philonotis seriata


  • Saxifraga aizoides
  • Saxifraga stellaris
  • Epilobium alsinifolium
  • Cochlearia pyrenaica
  • Caltha palustris

Slope fens


  • Carex davalliana
  • Carex lepidocarpa
  • Scirpus cespitosus
  • Primula farinosa
  • Pinguicula grandiflora
  • Parnassia palustris
  • Bartsia alpina
  • ofieldia calyculata

Petrifying springs

Cochlearia pyrenaica

Despite its name, this plant is rare in the Pyrenees and in Catalonia it is only found in Val d’Aran and Estanyeres de Son.

It likes cold, carbonated water and it blooms from when the snow melts until well into July.

Saxifraga aizoides

This plant is very different from most of the other saxifrages, both in terms of the environment in which it grows and the colour of its flowers.

The creeping growth of the stems allows it to make dark green carpets from which small groups of spectacular yellow flowers stand out in the middle of the summer.

Caltha palustris

In spring, its large, dazzling, yellow flowers are a sign that the fine weather has arrived. This plant is unmistakeable with its large, shiny kidney-shaped leaves. Although it is not only found in carbonated springs, it does tend to grow on the banks of cold, running water.

Molleres carbonatades

Primula farinosa

The pink flowers of this small plant draw attention in springtime when the wetlands are starting to turn green and it is commonly found in carbonated water.

Parnassia palustris

The bog star has delicate, heart-shaped leaves that make a small rose.

In the middle of summer, the wetlands are full of these spectacular, white flowers.

Pinguicula grandiflora

This plant, which only lives in wetlands, blooms in spring and is very spectacular with its large, dark purple coloured flowers.

Its bright green leaves are quite singular in that they trap small insects, which they digest with the help of a system of epidermic glands.