The geomorphology at Adršpach-Teplice, Czech Republic is dominated by vertical-walled, fracture-controlled features including slot canyons, gorges and pillars. Surfaces of canyon walls in Adršpach are case-hardened and more resistant to erosion than the bulk of the sandstone, which appears to be fundamental to the formation and preservation of canyons. Core and whole rock samples from Adršpach-Teplice were analyzed in thin section, including SEM analysis with cathodo luminescence. XRF and XRD analyses indicated that silica case-hardened surfaces are chemically and mineralogically similar to the rock interior, while iron case-hardened surfaces have an increase in iron present at the surface as the mineral goethite. Permeability analysis indicates a decrease in porosity in case-hardened surfaces. The rock at Adršpach-Teplice is poorly cemented yet has the strength to maintain vertical faces because of a locked sand structure, which was formed by pressure solution. Fracture faces contain disaggregation and cataclastic bands that reduce porosity and increase strength. Case-hardening exists on fracture faces and other surfaces as either silica or iron. Silica case-hardening is ubiquitous in the area and consists of a slight increase in abundance of silica overgrowths and sometimes an increase in clay content. It can form on fresh surfaces in as little as five years, creating what is essentially a self-repairing material. Iron case-hardening is composed of goethite, is much less prevalent than silica case-hardening, and does not appear to be actively depositing. Lichens, fungi, and other biological material are present on case-hardened surfaces and may add to the strength of the material. The internal structure of the rock lends the strength to form and maintain the features seen at Adršpach-Teplice, while case-hardening helps to protect them from erosion.



College and Department

Physical and Mathematical Sciences; Geological Sciences



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Case-hardening, Adršpach-Teplice, locked sand, pressure solution, sandstone, vertical-walled, rock city

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Geology Commons