Study of Rare Corrosion Forms Found in a Karst Syphon

P. Boudinet

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The aim of this article is to describe two-dimensional scallops (scallops guided inside ribs) found in a syphon, to compare them to the ordinary three-dimensional corrosion forms frequently found in karst systems (scallops and flutes). We also raise a certain number of questions regarding analogical and numerical modeling. The syphon is named “Combe du Creux” (department of the Doubs, France, EU). We have been exploring this flooded cave since 2003. Since 2015, we are studying its morphology and especially its scallops. When diving underwater underground (cave diving), observation work is more difficult. Therefore, photographs of the forms, of the tools used to measure them, have been made in order to be processed afterwards. The ordinary scallops found at four locations inside the cave have been documented, as well as two-dimensional scallops found at a fifth location. Very likely, these particular scallops have formed inside pre-existing ribs. They seem, from a qualitative point of view, to behave like ordinary scallops: they have qualitatively the same profile and obey the Curl relationship. However, regarding details, differences appear and lead to new questions about the formation and evolution of scallops: what is the influence of the material (kinetic and diffusion coefficients)? Of the flow rate? Of the boundary conditions? Ultimately, we insist on the fact that studying scallops in caves or modeling them is still an open field.