Jiří Bruthans

Quantitative study of a rapidly weathering overhang developed in an artificially wetted sandstone cliff

Those factors controlling the weathering and erosion of sandstone on the field scale are still not well understood. In this study, a specific sandstone overhang (and its surroundings) with artificially induced and extremely high erosion rates was subjected to a complex investigation. Contrast between the erosion rate of the wet and dry portions of the same cliff enabled isolation of the factors responsible for rapid sandstone retreat. Erosion rates, moisture, and salt content, as well as suction were monitored in the field. Mineral phases and water chemistry were analyzed. The measurement of tensile strength, laboratory frost weathering tests, and numerical modeling of stress were performed. The acquired data show that an increase of moisture content in pores in the area of the studied overhang decreased tensile strength of the sandstone to 14 % of its dry value, and increases the sandstone weathering and erosion rate, by nearly 4 orders of magnitude, compared to the same sandstone under natural moisture condition outside on the cliff area. Consequently, frost weathering, in combination with wetting weakening was found to play a major role in weathering/erosion of the sandstone cliff and overhang. Frost weathering rate in both the laboratory and field increases up to 15 times with decreasing gravity-induced stress. The results also indicate that sandstone landforms in temperate climates may potentially develop very rapidly if the pore space is nearly saturated with water, and will later remain relatively stable when the moisture content decreases. As a general implication, it is suggested that overhangs in Central Europe (and elsewhere) might be the result of rapid frost weathering of nearly saturated sandstone during the Last Glacial. This article is protected by copyright. All rights reserved.

Jahani Salt Diapir, Iran: hydrogeology, karst features and effect on surroundings environment

The Jahani Salt Diapir (JSD), with an area of 54 km(2), is an active diapir in the Simply Folded Belt of the Zagros Orogeny, in the south of Iran. Most of the available studies on this diapir are f ...

The Bohemian Karst: A Condensed Record of Landscape and Living Nature Evolution

Rich in historical heritage and natural beauties and located close to Prague , the Bohemian Karst has attracted visitors and scholars for centuries. Lower Paleozoic strata, folded and faulted during the Variscan Orogeny , have yielded thousands of fossil species . Well-exposed sedimentary rocks enabled definition of five international stratotype and/or parastratotype sections of geological boundaries. Most of the karst forms are inactive and largely sediment-filled (paleokarst ). The area is poor in karren fields, doline s and underground active streams, but rich in complex maze caves , locally with small but deep cave lakes. Morphological evolution of the present-day landscape was initiated after Cretaceous and Paleogene planation, when the area started to be entrenched by low-gradient Oligocene and Miocene rivers. In the Middle and Late Pleistocene, the entrenchment of river valleys was accelerated, forming steep-walled rocky canyons combined with a system of river terraces. Following earlier thermal water karstification , river floodwater injection was the main speleogenetic process during the Neogene and Quaternary. Archaeological finds and human bones up to ca. 150,000 years old have been discovered in the area. Historical sites, like the former Slavic fortified settlement at Tetin, majestic Gothic Karlstejn Castle, the Baroque monastery and church at Svatý Jan pod Skalou, and the hiking and educational trails annually attract approximately half a million visitors.