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Gullies in volcanic deposits are among the first signs of erosion that can be observed during or immediately after the volcanic activity and reflective of unstable conditions of newly formed deposits. Gully formation and erosion pulses may well continue to occur long after the initial landform was created, mostly as a result of torrential rainfall and/or land‐use changes. Yet, proper understanding of erosion dynamics and its relations with environmental drivers remains challenging as long‐term observations are, especially in volcanic terrain. Here we applied dendrogeomorphic approaches to (i) analyse both microscopic and macroscopic disturbances in tree roots exposed by gully erosion in a young volcanic landform of central Mexico and to (ii) quantify the evolution of erosion in the volcanic deposits of Paricutin Volcano. To this end we analysed 154 cross‐sections of 30 living, exposed roots of Pinus pseudoestrobus Lindl., of which 25 were used for anatomical and 129 for macroscopic analysis. Wood anatomical – or microscopic – disturbances were mostly in the form of strong growth reductions (~50%) in lumen area of earlywood tracheids, substantial increases in ring widths (mostly stemming from eccentric growth) and the increased formation of latewood cells. We observe major erosion pulses in 2010, 2012, 2015, 2016, 2017 and 2018, triggered primarily by torrential rainfall (with >100 mm 24 h−1 for the maximum intensity event: standard precipitation index values ≥ 2). Along the gully, the lower sector formed between 2009 and 2017, whereas the central sector exhibited important phases of exposure from 2012 to 2018. In the upper, most recent sector of the gully, erosion started only in 2017. Erosion rates in the lower and upper sectors are smaller with a channel widening rate of 6 to 16 cm yr−1. Around the main knickpoint found in the central part of the gully, retreat rates are up to 60 cm yr−1 and gully incision is 30 cm yr−1. The methods applied in this research are novel and can be applied to other volcanic environments with intense gully erosion, so as to provide baseline data for land‐use and environmental management plans. [ABSTRACT FROM AUTHOR]

The purpose of dendrogeomorphic analyses is to amplify the signal related to the geomorphic process under investigation, and to minimize the noise induced by other signals in the tree-ring series. Yet, to date, no study accounts specifically for interferences induced by climate conditions or exogenous disturbances and which can, potentially, affect the quality of tree-ring based process reconstructions. In this paper, we develop a specific procedure allowing evaluation of the quality of reconstructions in five avalanche paths at Oberwald (Swiss Alps). The study is based on possible interferences between snow avalanches, climatic conditions and ecological signals in the tree-ring series. Analysis of past events was based on tree-ring series from 564 heavily affected, multi-centennial European larch trees ( Larix decidua Mill.) growing near or next to the avalanche paths. A total of 2389 growth disturbances, such as scars, tangential rows of traumatic resin ducts, compression wood as well as abrupt growth suppressions or releases, were identified in the samples, indicating 43 destructive snow avalanches since AD 1780. At the same time, 31 potential events, which were detected with the conventional Shroder index value, were rejected from the final reconstruction due to potentially strong interferences between the different signals. This high rejection rate underlines the necessity to systematically–and carefully–discriminate ecological and climatic noise from avalanche-related disturbances. This discrimination is even more so crucial as a significant proportion of dendrogeomorphic studies in the Alps are based on L. decidua trees which are cyclically affected by larch budmoth outbreaks. [ABSTRACT FROM AUTHOR]

Floods represent a common process in Tatra Mountain streams and may cause flood risk in the valleys of the Tatra foreland. Dealing with the hazards and risks caused by floods requires a detailed analysis of the frequency and magnitude of past and recent events. However, the Polish Tatra region is characterized by a scarcity of data on past floods in general and on systematic peak discharge in particular. In this study, we performed a paleohydrological analyses in four high-gradient mountain streams using scarred trees as paleostage indicators. We couple two-dimensional hydraulic modelling in a highly-resolved topographic environment (LiDAR data) with an important spatiotemporal data set of scars on trees to investigate (i) the magnitude of unrecorded major floods of the twentieth century, (ii) the effect of variability in geomorphic tree positions on the peak discharge reconstruction, and (iii) the impact of reconstructed events on the results of flood frequency analyses. The data set is based on a total of 55 scarred trees and allows peak discharge reconstruction of 16 major floods covering the last 113 years. Results suggest that trees growing in straight stream reaches or in the inner side of channel bends would be better candidates for peak discharge reconstructions than trees located on the outer side of channel bends or growing in overbank sections with dense vegetation cover. The largest reconstructed flood is dated to 1903 with an estimated peak discharge of 115.9 ± 59.2 m 3 s − 1 , and larger-than-today floods are found to have occurred at Strążyska and Łysa Polana in the first half of the twentieth century. The inclusion of our results into the flood frequency analyses suggests that flood hazards might have been underestimated by up to 25.5% in the case of a 100-year flood in Strążyski Stream. In that sense, our findings will be useful for the design of future strategies dealing with flood risks in the foreland of the Polish Tatra Mountains. [ABSTRACT FROM AUTHOR]

Trees impacted by the forces of natural processes such as flash floods, snow avalanches, landslides, rockfalls or earthquakes, record these events and exhibit growth disturbances in their growth-ring series. As a consequence, these disturbances provide an excellent signal for the spatio-temporal reconstruction of past natural hazard activity and a means to date and document past disasters. In the context of the Indian Himalayas Climate Change Adaptation Programme (IHCAP; http://www.ihcap.in/), a field trip was carried out in May 2014 to define suitable sites for dendrogeomorphic research in Kullu valley, Himachal Pradesh. Several tree species and sites where recent and past process activity can be reconstructed were inventoried, namely flash floods in the Beas and Sainj rivers as well as snow avalanches in Solang valley. Through this exploratory analysis, we ascertain that tree-ring techniques have wide applicability in the analysis of natural hazards, not only in the Kullu region but also in other geographical contexts of the Himalayas. [ABSTRACT FROM AUTHOR]