Magnitude–frequency relationships of debris flows — A case study based on field surveys and tree-ring records

Based on observational meteorological data since A.D. 1864 and tree-ring records of debris-flow activity, this paper assesses changes in rainfall characteristics and their impact on the triggering of geomorphic events in a high-elevation watershed of the Swiss Alps since the end of the Little Ice Age. No trends are visible in the frequency of heavy rainfall events, but we observe a reduced number of heavy, shortlived rainfalls in summer and a concentration of advective storms is recorded in late summer and early fall since the late 1980s. These changes in triggering meteorological conditions resulted in a cluster of debris flows in the early decades of the twentieth century and a lowering of debris-flow activity since the mid 1990s, and may be mirroring the observed changes in persistent high-pressure systems over the Alps. We also observe intra-seasonal differences in debris-flow system response reflecting the state of the permafrost body in the source area of debris flows, allowing for very small debris flows to be released by limited rainfall inputs (<20 mm) in June and July. The same quantities of rain will not trigger debris flows in August or September, when a thick active layer of the permafrost body is capable of absorbing water. With the projected amplitude of climatic change, seasonality, return intervals and volumes of debris flows are likely to be altered. RCM projections based on the IPCC A2 scenario suggest a decrease in heavy summer rainfalls which will most likely result in a (further) reduction of the overall frequency of debris flows, leaving more time for sediment to accumulate in the channel. Such an increase of channel accumulation rates along with the projected destabilization of the steep rock-glacier body is likely, M. Stoffel (B) · M. Bollschweiler · M. Beniston

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“…For the last 300 year (i.e. 1706-2005), results suggest a mean annual frequency of 0.33 events (Stoffel and Beniston 2006;Stoffel 2010).…”

Section: Study Sitementioning

confidence: 98%

Rainfall characteristics for periglacial debris flows in the Swiss Alps: past incidences–potential future evolutions

2011

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“…This technique has successfully been applied to the spatio-temporal analysis of debris-flow activity (Bollschweiler et al, 2007;Pelfini and Santilli, 2008;Šilhán and Pánek, 2010;Stoffel, 2010), snow avalanches (Butler and Sawyer, 2008;Casteller et al, 2008), landslides (Fantucci and Sorriso-Valvo, 1999;Stefanini, 2004;Lopez-Saez et al, 2012a, b;Šilhán et al, 2013) and gully erosion (Corona et al, 2011;Stoffel et al, 2012). The great advantage of dendrogeomorphic methods is that they allow rapid acquisition of data, which is otherwise accessible only by means of long-term field monitoring.…”

Section: Introductionmentioning

confidence: 99%

Implications of spatial distribution of rockfall reconstructed by dendrogeomorphological methods

Šilhán

Pánek

Hrádecký

2013

Nat. Hazards Earth Syst. Sci.

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Rockfall is a dangerous geomorphological process. The prediction of potentially threatened areas requires thorough reconstruction of spatial rockfall activity. Dendrogeomorphic methods allow precise determination of both temporal and spatial occurrences of rockfall without the necessity of long-term monitoring. At the case-study site of Taraktash, located among southern slopes of the Crimean Mountains, 114 Crimean pine trees (Pinus nigra ssp. pallasiana) were sampled on a talus slope located under a 150 m high rockwall. Based on their age, the trees were divided into two distinct groups (young and old trees). Considerable disturbance in the age structure of the trees on the talus was probably caused by a series of strong earthquakes. Major differences were identified in the ability of young and old trees to record a rockfall event. We found that in the first decades of their growth, the ability of the studied P. nigra to record rockfall events gradually increased. The trees showed the highest sensitivity at the age of 80 to 90 yr; after that age their sensitivity gradually decreases. Two indicators were selected for the spatial reconstruction of rockfall events (the number of rockfall events per tree and recurrence interval). The highest activity was identified on the talus using selected indicators

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“…In general, lahar and debris-flow magnitude is inversely related to frequency (for example, Scott and others, 1995;van Steijn, 1996;Stoffel, 2010). Typically on large composite volcano, like Mount Rainier, most smaller, more-frequent lahars are glacier or precipitation related, and volcanic eruptions control the frequency of larger lahars.…”

Section: N F or K B A Il Ey Cr Eek S F O R K B A Il E Y C R Ee K mentioning

confidence: 99%

Magnitude–frequency relationships of debris flows — A case study based on field surveys and tree-ring records

Cited by 153 publications

References 61 publications

Rainfall characteristics for periglacial debris flows in the Swiss Alps: past incidences–potential future evolutions

Rainfall characteristics for periglacial debris flows in the Swiss Alps: past incidences–potential future evolutions

Implications of spatial distribution of rockfall reconstructed by dendrogeomorphological methods

Lahar hazard zones for eruption-generated lahars in the Lassen Volcanic Center, California

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