Jan Hradecký’s research while affiliated with University of Ostrava and other places

This study examines the long-term impact of water management and navigation modifications on the hydromorphology of the lower Elbe River in Czechia. The research focuses on gravel-sand bars, which are remnants of the river’s natural morphology. The analysis revealed a significant shift in the hydromorphological quality of the river, evaluated using a morphological quality index and historical data. The study analysed morphological and grain-size parameters of selected gravel-sand bars, as well as daily flow data. The results show a significant reduction in channel width and maximum average daily flows, leading to lower disturbance frequencies of the bars. The analysis suggests that close-to-natural processes affect the development of the bars but are influenced by artificial modifications. The findings indicate the need for restoration measures, which are discussed in this paper.

Quaternary glaciations have repeatedly shaped large tracts of the Andean foreland. Its spectacular large glacial lakes, staircases of moraine ridges, and extensive outwash plains have inspired generations of scientists to reconstruct the processes, magnitude, and timing of ice build-up and decay at the mountain front. Surprisingly few of these studies noticed many dozens of giant (≥10⁸ m³) mass-wasting deposits in the foreland. We report some of the world's largest terrestrial landslides in the eastern piedmont of the Patagonian Ice Sheet (PIS) along the traces of the former Lago Buenos Aires and Lago Puyerredón glacier lobes and lakes. More than 283 large rotational slides and lateral spreads followed by debris slides, earthflows, rotational and translational rockslides, complex slides and few large rock avalanches detached some 164 ± 56 km³ of material from the slopes of volcanic mesetas, lake-bounding moraines, and river-gorge walls. Many of these landslide deposits intersect with well-dated moraine ridges or former glacial-lake shorelines, and offer opportunities for relative dating of slope failure. We estimate that >60% of the landslide volume (∼96 km³) detached after the Last Glacial Maximum (LGM). Giant slope failures cross-cutting shorelines of a large Late Glacial to Early Holocene lake (“glacial lake PIS”) likely occurred during successive lake-level drop between ∼11.5 and 8 ka, and some of them are the largest hitherto documented landslides in moraines. We conclude that 1) large portions of terminal moraines can fail catastrophically several thousand years after emplacement; 2) slopes formed by weak bedrock or unconsolidated glacial deposits bordering glacial lakes can release extremely large landslides; and 3) landslides still occur in the piedmont, particularly along postglacial gorges cut in response to falling lake levels.

Rock-slope failures represent a significant hazard along global coastlines, but their chronology remains poorly documented. Here, we focus on the geomorphology and chronology of giant rockslides affecting the Crimean Mountains along the Black Sea coast. Geomorphic evidence suggests that high (>100 m) limestone cliffs flanking the southern slopes of the Crimean Mountains are scarps of rockslides nested within larger deep-seated gravitational slope deformations (DSGSDs). Such pervasive slope failures originated due to lateral spreading of intensively faulted Late Jurassic carbonate blocks moving atop weak/plastic Late Triassic flysch and tuff layers. By introducing a dating strategy relying on the combination of the uranium-thorium dating (U-Th) of exposed calcareous speleothems covering the landslide scarps with the 36 Cl exposure dating of rock walls, we are able to approximate the time interval between the origin of incipient crevices and the final collapse of limestone blocks that exposed the cliff faces. For the three representative large-scale rockslides between the towns of Foros and Yalta, the initiation of the DSGSDs as evidenced by the widening of crevices and the onset of speleothem accumulation was >300 ka BP, but the recent cliff morphology along the coast is the result of Late Pleistocene/Holocene failures spanning ~20e0.5 ka BP. The exposures of rockslide scarps occurred mostly at ~20e15, ~8, ~5e4 and ~2 e0.5 ka, which substantially coincide with the last major Black Sea transgressions and/or more humid Holocene intervals. Our study suggests that before ultimate fast and/or catastrophic slope failures, the relaxation of rock massifs correlative with karstification, cracks opening, and incipient sliding lasted on the order of 10 4 e10 5 years. Rapid Late Glacial/Holocene transgressions of the Black Sea likely represented the last impulse for the collapse of limestone blocks and the origin of giant rockslides, simultaneously affecting the majority of the SW coast of the Crimean Peninsula.

The rivers draining the Czech part of the Flysch Carpathians have deeply incised their beds over the last 60 years. This paper focuses on the Olše River in the Czech part of the Flysch Carpathians and summarises the results of the increased kinetic energy of flowing water of contemporary channel based on the analyse of hydraulic parameters of channel. The comparison of geodetic measurements from 1960 and 2003 was used together with the assessment of aerial photos from 1950s and present. The average width of the studied reach of the active Olše R. channel narrowed from 35 m in 1955 to 24 m in 2010. In some locations, the original river bed has lowered as much as 2.3 m between the years 1960 and 2003. Morphology of the Olše River channel has accelerated these erosion processes. The main reason for this is an adjustment of water flow dynamics. The unit stream power and hydraulic radius values have increased two to three times from 1960 to 2003 for 5, 20, 50 and 100-recurrence interval discharge. Incision of channel greater than 0.10-0.21m in the studied period may reflect change in cross-sectional geometry and lower than 0.10-0.21m may reflect other factors such as sediment disruption operating in the basin (e.g. with land-use changes, gravel mining etc.). © 2016 Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, Germany.

The area at the confluence of the Morava and Dyje Rivers is one of the biologically most diverse landscapes of Czechia. This paper focuses on its land use/land cover changes, obtained from aerial photographs from 1938, 1953, 1976 and 2009, analyzed by a use of landscape metrics. The most important landscape changes in this period were as follows: (i) an all but complete disappearance of open and structured woodlands; (ii) a transformation of the mosaic of very small agricultural fields into large-scale fields of mostly arable land; (iii) a significant decrease in grasslands; (iv) regulations of water courses; (v) an outstanding increase in logging intensity during the last twenty years. The preservation of the area’s biodiversity demands a start of active conservation management, focused on opening of woodlands, a decrease in forest logging and a suitable selection of logging localities.

Twenty five floodplain sediment profiles from seven rivers in eastern Czech Republic and three in north west England were collected to examine the hypothesis that magnetic enhancement in recent sediments is predominantly of anthropogenic origin and that magnetic parameters can be used as a dating proxy reflecting changes in intensity of industry sources over time. Natural sources of magnetic enhancement were excluded and anthropogenic enhancement was identified as exhibiting elevated values of χlf, ARM, SIRM, SIRM/χ and S-ratios with low values of χfd%. Magnetic spherules, typically formed through fossil fuel combustion processes, were observed by scanning electron microscopy (SEM) in these sediments. To assess the potential of magnetic parameters as a chronometer, the approach was compared with frequently used dating techniques: concentrations of heavy metals and 137Cs.

Central Europe and Czech Lands (recent Czech Republic) itself have recently represented an area with a transitional type between the oceanic and continental types of temperate climate. The climate changed during geological history and various climates played an important role in the evolution of landforms due to changes in type and intensity of weathering and earth surface processes. This chapter describes general trends in climate oscillations during the Tertiary and the Quaternary within the Czech Lands and Central Europe. Climatological and hydrological extremes and fluctuations during the last centuries are along with human activity fundamental drivers of recent changes in the landscape evolution.

The area at the confluence of the Morava and Dyje Rivers is one of the biologically most diverse landscapes of Czechia. This paper focuses on its land use/land cover changes, obtained from aerial photographs from 1938, 1953, 1976 and 2009, analyzed by a use of landscape metrics. The most important landscape changes in this period were as follows: (i) an all but complete disappearance of open and structured woodlands; (ii) a transformation of the mosaic of very small agricultural fields into large-scale fields of mostly arable land; (iii) a significant decrease in grasslands; (iv) regulations of water courses; (v) an outstanding increase in logging intensity during the last twenty years. The preservation of the area's biodiversity demands a start of active conservation management, focused on opening of woodlands, a decrease in forest logging and a suitable selection of logging localities.