•Five landslide signal detection procedures from anatomical data were tested.•The anatomical parameter studied was the vessel lumen area from F. sylvatica.•The results were validated by comparison ...with real landslide monitoring data.•The approach using only data from the disturbed tree was the most effective.
Knowledge of past landslide movements is one of the parameters for defining landslide hazard or trigger analysis. Dendrogeomorphology, as one of the most accurate approaches to date landslides, is commonly based on macroscopic analysis of growth disturbances in tree-ring series of disturbed trees. However, the use of anatomical indices for landslide detection has not been properly tested, despite could be more sensitive than macroscopic approaches. This is because the lack of a methodology for extracting anatomical-based landslide signal. Thus, the aim of this study was to define an optimal procedure that will allow a wider use of anatomical analyses in landslide research. For this purpose, 41 disturbed beech (Fagus sylvatica L.) individuals growing on a monitored landslide with a known date of reactivation (May 2010) were sampled. A total of five procedures were designed and tested, based on defining a threshold for signal detection by calculating the mean value of the vessel lumen area (VLA) or its annual percentage change and subtracting the stdev. Of all the procedures tested, the one in which the threshold calculation was based solely on VLA values from the disturbed tree proved to be the most effective. This procedure correctly identified the known landslide year while introducing the least noise (4.0%) into the resulting chronology. A general potential threshold is a natural age-dependent increase in VLA values, however, due to the relatively young age of the trees analyzed, this effect did not show up. Thus, the proposed procedure can only be recommended for younger trees. This study has thus provided a new approach that will allow a wider and more efficient use of anatomical analyses in dendrogeomorphological research on landslides.
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•A regional chronology of landsliding on the banks of the Váh River has been compiled.•Data from 408 tree-ring series allowed to reveal 45 landslide events.•The spatio-temporal ...behaviour of landslides was reconstructed.•Spatial analysis revealed specific relationships between landslide and river.
Landslides on the banks of meander bends of lower rivers pose a potential risk to the navigability of rivers, but also to their potentially dangerous damming. To properly understand the relationship of river action on the stability of adjacent landslides, it is necessary to analyse the historical evolution and spatial extent of landslide activity. In this study, the results of a regional reconstruction of landslide movements on the lower reaches of the Váh River (central Slovakia) are presented, which allows for a more comprehensive disclosure of the river-slide relationship compared to classical case studies. Using data from a 408 tree-ring series of 204 disturbed trees, 43 reactivations of five landslides were dated over the last ca. 45 years. Analysis of the relationship between the spatial extent of landslide activity and distance from the river revealed that in two cases there was a direct relationship where landslide activity gradually decreased with increasing distance from the river (these were the landslides closest to the river). Given the absence of erosional forms on the riverbank, it is likely that the landslides are not being destabilized by lateral river erosion and the relief of their faces, but rather by the loading of their bodies due to rising groundwater during floods. On the other hand, one landslide (furthest from the river) showed increasing landslide activity towards the main scarp. This pattern is consistent with the retrogressive landslide development generally expected for other landslides in the wider region. For the remaining two landslides, no significant relationship between spatial landslide activity and distance from the river was found, which, however, cannot rule it out, but rather suggests that the influences on the initiation of landslide movements in this case are very complex and probably combine both the influence of groundwater level fluctuations and the occurrence of critical rainfall events.
This paper explores the snow-avalanche regime based on tree-ring reconstructions and their triggering weather conditions with classification tree algorithms.
The results show a significant increased ...frequency of avalanche events on Zăvoaie NE slope for the second half of the 20th century by comparison to the Scărița SW slope. The classification tree models highlight the weather conditions leading to avalanche release with three scenarios in each path. The first scenario underlines the wind's effect as a key weather variable on both slope aspects. The second scenario corresponds to a spring regime, while rain and warm temperatures are the main triggers. The third general weather condition favouring snow avalanche activity are persistent low temperatures and important snowfall throughout the winter season. However, this triggering condition was mainly found on the NE avalanche path, probably related to the pattern of snow accumulation, the prevailing winds, but above all the lower solar radiation which favours a slower and later melting of the snow cover. Finally, the return periods and runout distances calculated from tree ring analysis show a high risk for the location of the infrastructure planned for the ski area expansion, showing once again the usefulness of dendrogeomorphology in natural hazard assessment where historical data are lacking.
•Tree-ring based chronologies and statistical analysis of weather conditions were used to assess snow-avalanche regime.•Three weather scenarios leading to avalanche release have been defined.•Return periods and runout distances show a high risk for the planned expansion of the ski area infrastructure.
The 137Cs deposited in soil and exposed tree roots have been widely applied to estimate medium-term soil erosion rates. However, comparative studies between these methods are scarce. For this ...purpose, three hillsides in two Mediterranean dehesas (rangeland with disperse tree cover) were selected. Regarding the 137Cs technique, a reference site close to the study areas and with similar altitude and rainfall was selected. In order to reduce uncertainties related to the use of point soil profiles, all those collected in an area were combined to form a representative composite profile. The total inventory was 2790±50Bq/m2, and the relaxation coefficient indicated it was an undisturbed soil. The radiocaesium inventory in the study areas was 14–23% lower than in the reference area. The erosion rates for 137Cs were in the range 20.9–38.1tha−1y−1. The exposed root technique was applied to holm oak trees (age about 90years), and the erosion rates were in the range 22–34tha−1y−1. The ratio between exposed root and 137Cs techniques was 1.02±0.11 (S.D.) within the range 0.89–1.2. Both methods produced very similar results equally with respect to the mean erosion rate as well as the relative difference between the hillslope sections, i.e. displaying the same spatial variation in the study areas. As the accounting time for these two techniques is different, 50 and 90y for 137Cs and exposed roots respectively, results suggest that no change in mid-term erosion rates was implied for these areas for almost a century. The use of 137Cs and exposed roots methodology for the determination of mean erosion rates can be reproduced in other ecosystems, but a careful selection of the reference site for 137Cs is essential.
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•There are few papers comparing erosion rates 137Cs method with other methods.•Erosion rates: 137Cs (20.9–38.1) tha−1y−1; exposed roots (22–34) tha−1y−1•Ratio exposed roots/137Cs=1.02±0.11 (S.D.)•No change in mid-term erosion rates in the 50–90years period
Approximately 42 % of Mexico is affected by soil denudation resulting from moderate to severe sheet erosion and gullying processes. At Huasca de Ocampo (central Mexico), soil degradation has been ...linked to intense land use dating back to pre-Hispanic times as well as to unfavorable geological, geomorphic, and climatic conditions. Here, we quantify erosion rates with high precision at annual to multi-decadal timescales by combining, for the first time, dendrogeomorphic reconstructions and UAV-based remote sensing. To assess rates of sheet erosion and gullying processes over the longer-term erosion rates (10–60 yrs), we assessed the age and first exposure of 159 roots to determine sheet erosion rates and gullying processes. At shorter timescales (<3 yrs), we employed an Unmanned Aerial Vehicle (UAV) to develop digital surface models (DSMs) for February 2020 and September 2022. Exposed roots provided evidence of sheet erosion ranging between 2.8 and 43.6 mm yr−1 and channel widening ranging between 11 and 270 mm yr−1, with highest erosion rates found along gully slopes. The UAV-based approach pointed to intense gully headcut retreat with rates between 164.8 and 870.4 mm yr−1; within gullies, channel widening rates ranged between 88.7 and 213.6 mm yr−1 and gully incision rates were between 11.8 and 109.8 mm yr−1. The two approaches yielded very comparable results regarding gully erosion and channel widening; this underlines the potential of using exposed roots to quantifying soil degradation processes retrospectively and considerably beyond the period covered by UAV imagery.
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•Combined use of dendrogeomorphology with tree roots and UAV imagery to estimate rates of sheet and gully erosion.•Erosion rates estimated with both methods are very similar but cover different time periods.•Most erosion occurs at the headcut of gullies and on the slopes near the bottom of the channel.
Landslides represent an important and possibly very dangerous natural hazard. Dendrogeomorphic methods can provide unique data on the behaviour of landslides in the past by studying the tree-ring ...series of disturbed trees. Knowledge about past landslide activity in the flysch part of the Outer Western Carpathians is generally very scarce or missing. The past activity of selected landslides (possibly endangering neighbouring settlements) was studied using data from 106 increment cores from 53 disturbed individuals of Picea abies (L.) H. Karst. to assess its past spatiotemporal activity. In total, six certain event years and 13 probable events were detected during the period between 1927 and 2017. Certain events always occurred in groups of the two following events, suggesting the inertia of landslide movements after the initial triggering. The spatiotemporal reconstruction revealed a distinctly increased activity of movements in the zone of the main scarp and particularly in the landslide front, which could possibly endanger human infrastructure during its significant reactivation. However, the reconstruction performed suggests general landslide inactivity since 1997, when the last high-magnitude reactivation occurred.
Determining the age of landslide events is crucial for determining landslide risk, triggers, and also for predicting future landslide occurrence. Currently, the most accurate method for dating ...historical landslide events is dendrogeomorphic analysis. Unfortunately, the standard use of macroscopic growth responses of damaged trees for dating landslide activity suffers from many shortcomings. Thus, the aim of this study is to analyze in detail the growth response of trees to landslide movements at the anatomical level, a completely groundbreaking methodological approach. Ten specimens of European beech (Fagus sylvatica L.) were analyzed at two sampling heights, growing in two morphologically contrasting zones of the landslide area. Detailed anatomical analysis was focused on changes in morphometric parameters of the vessels and in the number of radial rays. The period (2008–2012) with the occurrence of the largest landslide movement (2010) recorded by long-term monitoring was analyzed. The results obtained revealed different anatomical responses in trees growing in different morphological zones of landslide. The tree responses on the ridge corresponded to the manifestations of tension wood formation, which corresponded to the stem tilting due to the landslide block movement. In the case of the trees in the trenches, root damage due to the subsidence of the landslide block blocked the flux of phytohormones, and their accumulation caused a significant reduction in the parameters of vessels and an increase in the number of rays. The study also includes recommendations in the future application of anatomical analyses in landslide research resulting from the obtained results. Thus, the obtained findings will improve the acquisition of chronological data for the purpose of landslide risk assessment.
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•The anatomical responses of F. sylvatica to landslide movements were investigated.•The magnitude of the causal movements was accurately recorded by monitoring.•Changes in vessel size and number of radial rays were found.•Different anatomical responses were found at different sampling heights.•The effect of the studied site on the nature of the response was determined.
Detailed knowledge of the occurrence of debris flows in the past is key to understanding their linkage to changing climatic variables and their occurrence in the future. For a comprehensive ...understanding of the origin of these processes, regional reconstruction is optimal rather than detailed analysis of isolated catchments. This study presents the results of a dendrogeomorphic reconstruction of debris flows across an entire medium-high mountain range in Central Europe covering more than 500 km2. The tree-ring data allowed the reconstruction of 96 debris flow events at 21 sites. The average frequency of events was 6.8 per decade, which is comparable or higher compared to alpine valleys. A detailed analysis of potential precipitation triggers was also performed in the paper, whose magnitude significantly influenced not only the number of debris flows but also their magnitude. Debris flows occur in two forms in the study area, with channelized debris flows showing significantly higher magnitude but lower frequency than fan debris flows. The differences between the two types are probably due to the different source of material that is reactivated during precipitation events of different duration and magnitude.
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•Regional debris flow reconstruction was performed using tree-ring dating.•96 events were reconstructed including their magnitude and frequency.•The specifics of channelized and fan debris flow were studied.•Extreme rainfall events were analysed as triggers of debris flows.
