\nFor centuries there has been an \u201cupper\u201d Orbe and a \u201clower\u201d Orbe. Intuitively the inhabitants of this part of the Jura felt there had to be an underground connection between the Vall\u00e9e de Joux and Vallorbe. The \u201cupper Orbe\u201d rises in France from the Lac des Rousses and then winds lazily (\u201corb\u201d = curve, circle, orbit) before running into the Lac de Joux. The Vall\u00e9e de Joux is in fact one of the most perfect \u201cclosed\u201d catchment basins one can find in Central Europe. The depression which forms it was created by the folds of the Jura when the chain of the Risoux and the Mont Tendre were formed.<\/p>\n
At the end of the Vall\u00e9e de Joux (Le Pont) another major geological feature intervenes. A huge North-South fault (or fall) placed a whole mountain (the Dent de Vaulion) across the Valley, in effect creating a natural dam. We can easily understand how the lakes, or glaciers (during the Ice Ages) were formed and survived. We can imagine how the waters would have filled the whole valley before flowing over the little pass of Pierre \u00e0 Punex between le Pont and Vallorbe were it not for the deeply fissured and porous limestone rocks which border the Lac de Joux and the Lac Brenet and which can channel vast quantities of water into their depths. Thus many \u201cswallow holes\u201d or leakages (Bonport, Rocheray, Moulin etc) fulfilled this function, before any human intervention.
\nThen about 100 years ago it was decided to excavate an artificial outlet in the direction of Vallorbe, to achieve better control of water levels. Later this fall of water was used to generate electricity (the Power Station of La Dernier). The \u201cswallow holes\u201d or dolines were also \u201cimproved\u201d in order to control leakages. Today the basic rate of flow of the Lower Orbe which breaks forth at the source is maintained by underground drainage in relation to much greater surface areas (the slopes of the Mont Tendre and the Risoux etc.
\nThe flow of this truly underground water, which is the direct product of the train and snow falling on the flanks of those massifs, following approximately the same course as the surface waters, but several hundred meters lower! Thus in effect two Orbes \u2013 one above the other – coexist in the region of the Vall\u00e9e de Joux. One can imagine the underground Orbe running \u2013 probably violently \u2013 through the vast galleries evolving beneath the Lac de Joux.<\/p>\n
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GOING THROUGH THE CAVES<\/h4>\n
Frequently \u2013 and erroneously \u2013 characterised as a \u201cVauclusian eruption\u201d the source of the Orbe and its first \u201csump\u201d or submerged gallery are in fact caused by a simple build-up of moraines (from glaciers) and of scree or rubble accumulated at the base of the valley and thus blocked the lower part of the gallery, forcing the water to rise; \u2013 nothing to do with the famous Vaucluse Fountain, the waters of which rise from a submerged \u201ckarst\u201d formed at a depth of 300 meters.<\/p>\n
Today\u2019s visitor, who may not wish to follow this submerged route to the cave, can use an artificial tunnel which leads directly to the \u201cLac du Cairn\u201d. From here the re-discovered river Orbe falls a dozen metres or more. Underwater lighting shows that this large submerged cavity is particularly calm.
\nThe contrast is very striking when one considers the turbulence of the water before and after this sump. The flow is about two cubic metres per second low water, but can rise to eighty cubic metres per second in periods of full flood (February 1990). The water temperature varies according to the conditions of the lakes on the surface, and can vary from four to thirteen degrees (C). The air temperature in the caves is around ten degrees C throughout the year, and the humidity approaches 100%. The carbon dioxide content of the air is around 0.3% or about 10% higher than the outside atmosphere. This presents absolutely no risk or discomfort to the visitor.<\/p>\n
<\/h4>\nFROM CASCADES TO BUILD-UP<\/h4>\n
Upstream from the first sump the river runs freely, as it does on the outside, through enormous blocks of stone which have fallen from the vault. Going more than 200 metres back up the flow the cavers were able to discover a new working sump: the \u201cSiphon des Marmites\u201d (Marmite = \u201ccooking pot\u201d) (cf map). This passage is only passable when the flow of the river is low because the \u201cGallery of the Half-drowned\u201d is very narrow in places.<\/p>\n
Before arriving at the \u201cSiphon des Marmites\u201d one sees an enormous redundant gallery running six hundred metres in the direction of Vallorbe. This great branch tunnel is an ancient course of the Orbe, from when the river emerged much higher, near to the shooting range (!). This section of the caves is richly concretised, especially in the \u201cSalle des Aiguilles\u201d (= \u201cThe Chamber of Needles\u201c) where thousands of stalactites hang in serried ranks.<\/p>\n
Access to sections upstream from the main caves,Access to sections upstream from the main caves, towards the Vall\u00e9e de Joux, requires leaving the developed section and going back up the \u201cGrande Salle\u201d (The Great Chamber). The imposing size of this chamber has been formed by falls of great blocks of stone from the walls and roof.This place was blessed when a major fracture or rift created this underground Cathedral.<\/p>\n
As for the internal decorations, nothing is missing; Imposing stalactites on the left hang from the roof while on the right ripples an immense flow of calcite and \u201cmoon milk\u201d, followed by a \u201crain\u201d of translucent threads while a regiment of \u201cplate pile\u201d stalagmites rise from the floor. At the far end of the \u201cGrande Salle\u201d a superb accumulation of disc-shaped stones are spread over the floor making a natural \u201cRoman Road\u201d.<\/p>\n
Here we are at one of the great cross-roads of the caves. By following the direction of the Grand Salle we can rejoin the Orbe as it runs between the \u201cSiphon des Marmites\u201d and the \u201cSiphon de la Baignoire\u201d (the Bathtub Sump). To the right, after scaling a fifteen-metre slope, one reaches the start of a large, partly accessible gallery which is the key to further exploration.<\/p>\n
It is to be observed that at times of very high water this gallery fills up completely and that a significant waterfall flows into the Grand Salle. The rest of the caves are rather more austere since \u2013 apart from the Fossil Gallery, which enables the Sump of Block No. 1 to be avoided, and ends at the Sump of Block No 2 \u2013 the going is fairly uniform and only partly concretised.<\/p>\n
As we pick up the tour route at the beginning of the developed section, leaving the \u201cSalle du Cairn\u201d you will be able to see a multitude of very varied mineral formations which Nature has created in this \u201cfossil\u201d (i.e. through which the river no longer runs) level. (See the diagram on page 15). Roofs, walls and the floor are ornamented and decorated with all sorts of concretions. Among the best known are the famous \u201cStalactites\u201d (\u201ctite = fall) and Stalagmites (\u201cmite\u201d = rise) which are the most frequently found types of underground concretions.<\/p>\n As well as the classic forms, resembling candles or pendants, there is an infinite variety of shapes, depending on the strength of the calcite solution and the caprice of the ground through which it flows. Alongside the first flight of stairs the concretion has even taken the form of a \u201cstalagmitic flow\u201d. The first fistulae (or \u201cmacaroni\u201d) appear in the same area; little tubes of 4 \u2013 5 mm diameter, growing at about two to four centimetres per century, formed by crystalline deposits on the periphery of small drops of water \u201csweating\u201d from the roof. At the top of the spiral stair beautiful drapes or curtains decorate the roof and the walls.<\/p>\n Leaving the \u201cSalle Blanche\u201d (the White Chamber) the visitor crosses the \u201cLac du Mouton\u201d (Sheep Lake), which ought really to be called \u201cSheep Sump\u201d as it has been drained to allow dry-shod access. Here, and further on, underwater concretions can be found, such as excrescences in the shapes of cauliflowers or bunches of grapes.<\/p>\n Many gours (also called \u201crimstones\u201d) and micro-gours have also formed in this part of the grotto, after the \u201cGrande Colonne\u201d (the Great Column). A stair on the right leads to the \u201cSalle de La M\u00e9duse\u201d (the Medusa Chamber) also rich with concretions. the \u201cGrande Colonne\u201d (the Great Column) at eight metres high is one of the largest concretions in the caves. Very often visitors perceive objects or entities from the outside world in this huge collection of mineral formations.<\/p>\n In such places these descriptions are, of course, the products of visitors\u2019 own imagination, whether triggered by a desire for security or from fright. The stone \u201cBison\u201d protruding on the right is certainly the best example in the whole cave system of such a visual resemblance and bring to mind the live bison which frolic about, some 250M above, in the fields of the Mont d\u2019Orzeires.<\/p>\n Descending again towards the river there are still more formations to be seen including the longest fistula in Switzerland \u2013 around four metres.<\/p>\n Also to be seen in the caves of the Orbe are the \u201ceccentric concretions\u201d which can grow in filaments or in fine droplets, defying the laws of gravity or \u2013 again \u2013 the famous \u201cpiles of plates\u201d which are caused by drops of water splashing after falling from a great height.![](\"https:\/\/grottesdevallorbe.ch\/wp-content\/uploads\/2016\/11\/grottes-vallorbe-51.jpg\")
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\nThe Water destroys, the Water builds:<\/strong><\/p>\n\n
CRYSTALLINE ECHOS<\/h4>\n
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