Can we distinguish meteorological conditions associated with rockfall activity using dendrochronological analysis? - An example from the Tatra Mountains (Southern Poland).

Rockfall leads to visible changes in mountain areas and as high-magnitude event has geohazard potential and should be monitored. On forested slopes, active rockfall could be identified with high precision from visible anatomical changes in tree-rings. To discern possible rockfall events in the Tatra Mountains, dendrogeomorphologic methods were applied and correlated with meteorological conditions. Field research was carried out on Norway Spruce (Picea abies L. Karst) in the Kościeliska Valley. Rockfall signals (RSs) were obtained from both qualitative (scars and traumatic resin ducts) data and quantitative (growth release and suppression) data. Multiple regression and ANOVA analysis were employed to recognize the meteorological conditions, which cause rockfall activity. Different periods of rockfall activity were observed during the years 1950-2014. The weakest activity was observed during 1950-1970 while after 1970 a continuous increase in rockfall activity was observed in our study. There was a clear peak in the number of RSs recorded per year in 1985. Cumulative precipitation and temperatures for January, March, May, June, July, August, September and October are statistically significant as the periods of the year in which rockfall is activated in the Tatra Mountains. In terms of activity, three different Levels of Rockfall Activity (LoRAs) were recognized and show significant correlation with the meteorological data. Distinguished meteorological control factors determining rockfall explains 53% of the total parameters determining rockfall activity. The complexity of the rockfall process means that a better understanding of local conditions and the possible uncertainties associated with the dendrogeomorphologic method and the quality of the meteorological data is needed.