Pertes de Thémines

Useful Information

Location:	Southern side of Thémines. (44.738654, 1.829566)
Open:	no restrictions. [2023]
Fee:	free. [2023]
Classification:	Losing Stream
Light:	bring torch.
Dimension:	L=18 km, A=290 m asl.
Guided tours:	self guided
Photography:	allowed
Accessibility:	no
Bibliography:	David Viennet, Guillaume Lorette, David Labat, Matthieu Fournier, Mathieu Sebilo, Olivier Araspin, Pierre Crançon (2023): Mobile Sources Mixing Model Implementation for a Better Quantification of Hydrochemical Origins in Allogenic Karst Outlets: Application on the Ouysse Karst System, Water 15, no. 3: 397. online DOI
Address:	Pertes de Thémines.
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then. Please check rates and details directly with the companies in question if you need more recent info.

History

1979	first exploration by local cavers.
1980	sinks at the end of the cave explored by cave divers.

Description

The Pertes de Thémines (Sinks of Thémines) are a series of swallow holes where the river Ouysse vanishes underground. The sinks are quite spectacular, a riverbed which cuts into the ground forming a gorge, which then ends like a cul-de-sac. The river vanishes completely, no matter how much water flows. In times of high water flow, after heavy rains or during snow melt, the river flows to the end of the gorge, the swallow hole are filled with water. During summer, when the flow is low the water vanishes completely when it reaches the first sinks, and the rest of the gorge has a dry riverbed.

The bigger sinks actually have names. The first two are called Moulin Raffi, the third trou des écrevisses, the sixth de la mouline or du lavoir, the seventh de l'arche, and the eighth and last one terminale or aval. The dry part of the river bed is mostly covered by alluvial sediments through which the water vanishes, but there is also a cave entrance, the eighth sink, which is also called Perte de Thémines. Cavers have explored the cave system behind, which has mostly sections which are most of the time water-filled. There are huge scallops, dolly tubs, cave lakes, and vertical shafts. But there are also dry side passages, where speleothems can be found. The water filled branch is called rivière Vieussens, the dry galerie de l'Aga, both end in sinks. The cave is only for cavers, and actually the exploration is rather dangerous. It is important to have an eye on the weather, as rainfall would cause a rise of the water, creating a deadly trap.

A problem for the inhabitants of Thémines is, when the swallow holes get blocked. During floods the river brings dead wood, even timbers,with it, which get stuck in the cave entrance. Smaller material stick between the wood and finally ther is a plug of wood, leaves, and clay, and the water cannot flow freely. The result is a flooding of the nearby village Thémines. To avoid this they placed iron bars in the opening, which works like a sieve. So it is possible to remove the bigger pieces of wood and thus destroy the plug.

The Ouysse is a rather small river, but the karst related sights along the river are quite spectacular. The 45 km long tributary of the Dordogne flows above ground when the ground is impermeable, and vanishes underground when the ground is karstified. In total the river is most of its course actually underground. It is impossible to tell it actual length as most of the underground parts are water filled and unexplored.

The official spring of the Ouysse is in the southern foothills of the Massif Central at the village Anglars. But there are numerous tributaries and other springs in this area. It flows 9 km to the sink. Until the Cenozoic, the river actually flowed above ground deepening a valley into the limestone of the Causse de Gramat, but when the drainage went underground it became a dry valley. Some former tributaries, like the Alzou, seasonally reactivate the valley. During dry seasons they also flow completely underground.