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We present a comparative study of large wood (LW) mobility in two steep channels (0.06

Headwater catchments are frequently prone to debris flows/floods. Dendrogeomorphic methods allow for the accurate dating of the frequencies and spatial patterns of these events. Nevertheless, a combined approach based on the sampling of increment cores from tree stems and the extraction of cross-sections of scarred roots has been rarely used together at one site to determine the headwater dynamics. Such sampling strategy was performed in the Rudohorský potok catchment (the Hrubý Jeseník Mountains, Eastern Sudetes, Czech Republic) to compile the debris flow/flood chronology and to describe the detailed spatial patterns in the studied sub-catchments. In total, 44 events of increased hydrogeomorphic activity during the last 110 years were identified based on the analysis of 860 growth disturbances from 322 trees and 85 roots. The largest events (debris flows) occurred in 1921, 1951, 1965, 1975, 1991, 1997, 2001 and 2010. Higher dynamics of hydrogeomorphic processes were investigated in the sub-catchment affected by deep-seated rockslides. The inclusion of root analyses facilitated the completion of the event chronology mainly during the last 20 years. With respect to the decreasing sensitivity of tree stems with increasing age to the recording of geomorphic disturbances, the root analysis helped to better illustrate the spatial imprint of recent debris flow events (especially the most recent one in 2010). [ABSTRACT FROM AUTHOR]

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Hydrogeomorphic processes (HP) are dangerous natural hazards, particularly in areas with increasing settlement. The Mediterranean region is a highly endangered area, particularly due to its high sensitivity to environmental changes. Chronological information about past events occurrence is crucial for modelling its development in the future. This study aims at building the chronology of past HP in two ungauged gorges along the southern coast of Crete using dendrogeomorphic methods. In total, 188 wounded trees revealed information about 13 events in nine various years over the past 80 years. Dendrogeomorphic records were obtained from Italian cypress ( Cupressus sempervirens L.) – a tree species that has never before been used for palaeoflood analysis. Limitations of this species are presented and discussed. Moreover, the analysis of the growth responses of Italian cypress to HP events at the anatomical level resulted in important findings regarding its possible use for dating in the future. The reconstructed chronology of events expresses the number of HP events over past decades. The spatiotemporal patterns of affected trees suggest various characters of the process during individual events. Moreover, the type/character of the process is most likely changed even in the longitudinal profile of the gorges during the same event. [ABSTRACT FROM AUTHOR]

Dendrogeomorphology is an established discipline that is commonly used to date natural hazards, including landslides, debris flows, rockfalls, snow avalanches, and flash floods, by examining tree-ring records. Anthropogenic impacts frequently alter the present landscape, resulting in changing frequencies or increased spatial extents of geomorphic processes, such as subsidence-induced landslides or rockfalls caused by mining activities. In such cases, dendrogeomorphic records from afforested sites may provide information where ground movement monitoring is lacking. Additionally, the temporal occurrence of subsidence can vary greatly, ranging from gradual to abrupt movements. While radar interferometry can currently measure subsidence rates, such data typically covers short time periods and are less precise in forested areas. Comparing tree-ringbased data with in situ monitoring may clarify the sensitivity and reliability of dating methods in these particular conditions of continuous ground movement. We conducted dendrogeomorphic analyses at various sites in the Czech Republic with geomorphic activity caused by past or current underground mining of black coal or ore. We discovered over 20 rockfall events in three stopes that emerged after medieval ore mining, with increased rockfall activity in the Eastern Sudetes since the 1980s. Furthermore, we obtained the years of exposures from ten roots, revealing ground subsidence and the opening of tension cracks, and even the lateral retreat of the flanks of minor depressions. We also employed dendrogeomorphic techniques to detect subsidence-induced surface displacements in the Upper Silesian Coal Basin, which has been affected by underground coal mining. Chronological data were compared with in-situ monitoring and among various sites with lower and higher subsidence rates. Most events occurred in the 1930s, 1970s, 1990s, and late 2000s, with a peak of activity in 1973 and other notable events in 1986, 1995-1997, and 2005-2011. Moreover, not only the timing of mining operations, but also site-specific factors such as soil, morphology, and precipitation events, are essential for characterizing surface displacements in the forested post-mining landscape. [ABSTRACT FROM AUTHOR]

Gully erosion is a worldwide issue that is often caused or accelerated by inappropriate land management. This study comprehensively evaluates accelerated gully erosion in fluvioglacial sediments left by a Pleistocene ice sheet in northeastern Czechia. Geomorphic mapping of an area of approximately 2 km² revealed gullies up to 3.5 m wide and deep, with their heads starting at the boundaries of fields and pastures. One of the causes of accelerated gully erosion are considered to be anthropogenic interventions, mainly melioration measures, or natural piping that cause concentrated subsurface runoff. Dendrogeomorphic methods were used to determine the development of the gully system. Trees respond to erosion processes by changing the anatomy of the cells in the newly grown root rings. When we determine the time of anatomical change onset, we are able to identify the year of erosion processes. Microscopic analysis and dating of 102 cross-sections from 28 exposed tree roots revealed 18 years of gully incision since 1985, with increased activity from 2007 to 2014. The mean incision rates ranged between 1–20 cm/year but could reach 1 m during individual events. To determine predispositions of gully erosion a geophysical survey with the use of Ground Penetrating Radar (GPR) was carried out. A total of 17 GPR profiles were conducted in the agriculture field above the gully systems. The geophysical survey confirmed the presence of subsurface structures (possibly the melioration measures in the area) and their possible connectivity to the gully systems. The combination of concentrated subsurface and surface runoff is considered to have a significant effect on the expansion of gullies in the present. [ABSTRACT FROM AUTHOR]