After leaving the gours, we arrive at the Grand Couloir (Grand Corridor) and we can notice that the roof is higher. On the right, the light touches stalagmite streams producing great effect. On the roof, fistulous stalactites, also called ‘macaroni’, appear. They are formed around drops of water rich in calcium carbonate that leave tiny crystalline circles at the bottom of the tubes and make them grow rapidly.
We can notice growing ‘living’ fistulous by their almost transparent tube. Fistulous that are not fed any more have a muddy aspect.A twisted stalactite and an associated stalagmite try to meet – unique view that experts always observe with pleasure.
What explains the movement of the concretion is the draught. The dried out drop of water pushed by the draught carries off the course of the growth of the stalactite. It is very strange to see that the course of fistulous stalactites are not carried off by the draught; there is no water flowing and the effect of the wind is not sufficient to deform the drops of water since they are inserted into their glass tube. So, the direction of the growth is not changed.
The Grand Couloir finishes by splendid pendants enhanced by special lighting. The various facets of the calcite monocrystals gleam like diamonds during the periods of drought.