Tour Isabelle, Natural arch in Plateau-des-Petites-Roches, France
Tour Isabelle is a limestone arch in the Aulp du Seuil cirque of the Chartreuse mountains, located at about 1790 meters elevation. The formation displays two stacked openings that define this section of the eastern mountainside.
This limestone arch went undocumented in official mountain guides until 2006, when Pascal Sombardier published comprehensive information about the formation. His documentation brought the location into wider public knowledge for hikers and geographers.
The natural arch takes its name from Isabelle de France, connecting the geological landmark to French historical figures and regional nomenclature traditions.
The arch is accessible via a marked trail from Col de Marcieu in Saint-Bernard, following the Grand Sangle de l'Aulp du Seuil loop route. Visitors should expect rocky terrain and mountain conditions, bringing sturdy footwear and a map for orientation.
What sets this formation apart is its double-arch structure with two stacked openings, the lower passage spanning around 30 meters wide. This scale ranks it among the largest natural arches found in the Alps.
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