Except game, the Excursion de France additionally supplies a possibility to (re)uncover our landscapes and from time to time their geological oddities. The path of the seventeenth level, on July 23, between Chambéry in Savoy and Voiron in Isère, takes the runners during the towers of Saint-Jacques, within the Bauges massif, in Haute-Savoie. A neighborhood geological interest with an strange legend to mention the least.
For its seventeenth level, on July 23, the riders of the Excursion de France will input the massif of Bauges (Haute-Savoie) via an opening: the Cherand Valley.
Mountain landscapes ceaselessly evoke feelings with their easy aesthetics. When their working out additionally bears witness to a unprecedented and atypical phenomenon, the beauty will increase tenfold.
At Cluse de Bange, within the early morning hours, consideration is interested in the “towers” emerging from the southern flank of the Semnoz massif. Pierre Reneau, Equipped through the creator
The towers of Saint-Jacques are any such puts: at the southwest facet of the Semnoz massif in Bauges, overlooking the village of Alleves (Haute-Savoie), those rocky peaks named after the chapel of the outdated monastery draw in consideration. As soon as known as the “Needles of Racheroche”, those 3 limestone monoliths, the most important of which measures 70 meters prime and culminates at an altitude of 991 meters above sea degree, are intriguing. From a distance, they resemble the ruins of historic towers.
The tale of the eagle, the wolf and the lamb
Like many strange puts, those magnificent needles have their very own native legend.
A detailed-up view of some of the tops of the towers of Saint-Jacques. Torsade de Pointes, CC BI
It’s stated that someday an eagle carried off a lamb threatened through a wolf to reserve it from being wolfed. The lamb, a little bit giant and a little bit too heavy for the chook to hold a long way, could be put on some of the 3 peaks, out of succeed in of the wolf. Years later, a mountaineer came upon a ram there. The Alevi folks, amazed through this surprising gesture, would see it as a divine signal.
Then the eagle and the lamb turned into symbols of peace and coverage of town. The towers thus introduced, from this tale, their identification to Alleves.
Herbal sculptures
The towers of Saint-Jacques were moved over the years, however have retained a lot in their construction. Christian Giusti, Equipped through the creator
The geological phenomenon of “packed packing”, wherein rocks slide downstream and not using a whole lack of construction, is obviously visual during the towers of Saint-Jacques.
Actually, such reliefs are identified within the Alps in more than a few puts and are normally known as “fairy chimneys”. Essentially the most well-known are the “young lady’s coiffures” from Pontis, east of Lake Ser-Ponson (Alpe-de-Haute-Provence). Those reliefs are the results of differential erosion that gets rid of cushy sediments (marl, sandy clay, ash, and many others.) from below a cap of extra resistant rock (limestone block, volcanic bomb, and many others.)
Younger girls dressed in hairstyles from Pontis, a commune within the Alps of Haute-Provence positioned close to Lake Ser-Ponson. Wikifrederic/Wikimedia, CC BI-SA
The towers that dominate Alleves are the results of a a lot more complicated procedure. The slope from which those towers upward push bureaucracy the southern flank of the Semnoz massif, the highest of which consists of Cretaceous limestone (Valanginian, from -140 million to -136 million years outdated), referred to as “fontanil limestone” and even “bastard marble”. This massif bureaucracy an arch (anticline) whose slope descends to the southwest.
This thick layer of limestone rests on fairly older marls and marly limestones (Berriasian, from -145 million to -140 million years in the past). Marl, a lot more plastic than limestone, can shape one of those “soap” layer on which blocks indifferent from the cliff above, like icebergs at the face of a glacier, can slide against the Sheran River.
Diagram explaining the formation of the towers of Saint-Jacques. Equipped through the creator
However some unknowns stay.
3 theories at the check
3 proposals are recently being put ahead to give an explanation for the present scenario.
3 chances for the formation of the Saint-Jacques towers: at the left, differential erosion of a non-moving plate; within the middle, the blocks detach and slide down, fairly eroding; at the proper, the plate is disintegrating, blocks of various sizes are eroding, some resisting higher. Equipped through the creator
The primary will be the end result of a easy erosive phenomenon. As we’re at the outcrop of the ledge, the strata are tilted down, against the valley. They’re parallel – or virtually – to the slope. Topic to erosion, portions disappear, however positive blocks withstand higher and slide decrease. They might thus shape witness mounds: the towers of Saint-Jacques.
Some other postulates an enormous landslide. On the face of the limestone slab, the blocks can destroy off, somewhat like icebergs breaking off from an ice sheet. Because the slab is tilted, positive parts resting at the plastic layer (Beriasian marls) start to slide slowly keeping up their vertical place.
A 3rd rationalization makes use of a extra complicated common sense, linking separation and sliding. The limestone slab on the most sensible would get a divorce into a large number of slabs of more than a few sizes. Those parts would start to slide. Some would tilt, others would cave in, they’d be eroded, briefly, some would in the end change into invisible within the topography. Others would withstand a little bit higher, breaking into sub-blocks however proceeding to slip with out collapsing: the present towers of Saint-Jacques.
Some other concept is recently the only appreciated to give an explanation for the starting place of those constructions. It’s also the most efficient documented. The weather would now not tilt through collapsing, however through gently sliding up the slope. Now they’re a number of hundred meters clear of their “home port”, 700 meters for the perfect and 960 meters for the bottom and thinnest.
And above all, they proceed to descend, at a variable price relying at the parts: 2.1 cm/12 months for the tallest, 1.8 cm/12 months for the center block, and as much as 4.6 cm/12 months for the thinnest, lowest, quickest.
