Establishing a record of extreme debris flow events in a high Alpine catchment since the end of the Little Ice Age using lichenometric dating

ABSTRACT

Establishing a record of large debris flow events in high Alpine areas prior to the availability of high resolution remote sensing data can be very challenging. In this study, we investigate the debris flow activity in two tributary valleys of the Horlachtal catchment in Tyrol, Austria between the end of the Little Ice Age at about 1850 and the first available area wide aerial images from 1947. To accomplish this, we calculated a local lichenometric calibration curve using the long axis diameters of the five largest Rhizocarpon lichen thalli at 51 different reference locations. Because of the interval-censored dating of most of the reference sites, we established a bootstrapping approach within the calibration curve calculation process. With the help of the lichenometric calibration data, we were able to date 47 old debris flow deposits in the study area. The results indicate no increasing or decreasing trends in frequencies of extreme debris flow events. In addition, the results point to a very local character of debris flow triggering precipitation events, as we can detect major differences in neighbouring valleys. Lichenometric derived datings also provide temporal informations about the end of debris flow activity at some sites in the study area and thus can contribute to a better understanding of debris flow systems.

KEYWORDS:

• Debris flows
• lichenometry
• central Alps
• Horlachtal
• extreme events

Acknowledgements

This study is part of the SEHAG research group (SEnsitivity of High Alpine Geosystems to climate change since 1850). We would like to thank the Federal Office of Meteorology and Surveying (BEV) as well as the Province of Tyrol (Land Tirol) for providing the historical aerial images. Furthermore, we would like to thank the Bezirkshauptmannschaft Imst and especially Mag. Eva Loidhold and Mag. Gudrun Hofmann, the municipality of Umhausen with Mayor Mag. Jakob Wolf as well as Mag. Johannes Kostenzer, Dr. Werner Schwarz, Mag. Kathrin Herzer and all residents of Niederthai and Umhausen for supporting the research in Horlachtal. In addition, we want to thank Anja Sauer and Christian Sender who supported us with the fieldwork. Special thanks to the reviewers Maciej Dąbski and Danny McCarroll as well as the Associate Editor Tom Bradwell for their help to improve our article.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – project number 394200609 and by the Austrian Sciene Fund.

Notes on contributors

Jakob Rom

Jakob Rom is Research Associate at the Catholic University of Eichstätt-Ingolstadt with research interests in geomorphologic process dynamics, gravitational mass movements and alpine natural hazards.

Florian Haas

Florian Haas is Research Associate at the Catholic University of Eichstätt-Ingolstadt and has a research focus on alpine process dynamics in the field of geomorphology, soil erosion and natural hazards.

Tobias Heckmann

Tobias Heckmann is Research Associate at the Catholic University of Eichstätt-Ingolstadt with focus on geomorphology in the Alps, hydrological processes as well as statistical analyses.

Fabian Dremel

Fabian Dremel is Research Associate at the Paris Lodron University of Salzburg. He is researching on landscape evolution modelling, geomorphologic processes and their geological background.

Fabian Fleischer

Fabian Fleischer is Research Associate at the Catholic University of Eichstätt-Ingolstadt. His research interests are in geomorphologic alpine processes, permafrost landforms and natural hazards.

Moritz Altmann

Moritz Altmann is Research Associate at the Catholic University of Eichstätt-Ingolstadt and has a research focus on fluvial dynamics in high alpine environments, soil erosion and natural hazards.

Manuel Stark

Manuel Stark is Research Associate at the Catholic University of Eichstätt-Ingolstadt. He is specialist in the acquisition, processing and evaluation of remote sensing data, especially for alpine environments.

Michael Becht

Michael Becht is Professor for Physical Geography at the University of Eichstätt-Ingolstadt. His focus lies on climate impact research on high alpine geomorphologic systems, slope processes and mass movements, catchment hydrology and natural hazards.