Possibilities and Limitations of Dendrogeomorphic Time-Series Reconstructions on Sites Influenced by Debris Flows and Frequent Snow Avalanche Activity

Abstract

Past debris-flow and snow avalanche activity was assessed for the Reiselehnrinne (Tyrol, Austria) using growth disturbances in growth-ring series of 372 Norway spruce (Picea abies (L.) Karst.) trees. Determination of events was performed by analyzing (a) the number and (b) intensity of growth disturbances within tree-ring series and (c) the spatial distribution of affected trees. Differentiation of debris flow from snow avalanche events was based on the intra-annual position of scars, callus tissues or tangential rows of traumatic resin ducts, and on the spatial distribution of trees with simultaneous reactions in the tree-ring series. We introduce a weighting factor to substantiate the dating of past process activity in a comprehensive way and to compare individual events as to their intensity and total number of tree-ring responses. The accuracy of the dendrogeomorphic assessment was then evaluated by comparing the reconstructed event frequency with chronologies available for the Reiselehnrinne. Comparison of tree-ring with historical data demonstrated clearly that the reconstructed event frequency contains the majority of past debris flow and snow avalanche events in the Reiselehnrinne, but that dating of events is not always possible, especially if they are clustered in time or have a limited spread on the cone.

Modeling debris-flow runout patterns on two alpine fans with different dynamic simulation models

“…The source area of the catchment is dominated by gneiss and mica schists. The middle, channelized part of the watershed consists of debrisoverlaying bedrock, whereas coarse debris-flow material comprises the fan (Kogelnig-Mayer et al, 2011). Data from a rain gauge located in Plangeross (1620 m a.s.l.)…”

“…show that annual rainfall varies between 600 and 1150 mm. Detailed information on the long-term event history of this site can be found in Kogelnig-Mayer et al (2011), who reconstructed several debris-flows and snow avalanches during the last century using dendro-geomorphic methods. The best documented debris-flow event occurred in August 2009 and deposited around 20 000-25 000 m 3 of material on the orographic right side of the fan and ran out onto the provincial road, which was subsequently blocked for several hours.…”

Debris-flow activity in five adjacent gullies in a limestone mountain range

“…Within this study, the analysis of growth disturbances focused primarily on the presence of (i) tangential rows of traumatic resin ducts (TRD) as a sign of mechanical impacts Schneuwly et al, 2009aSchneuwly et al, , 2009b, (ii) compression wood reflecting unilateral pressure and tilting of stems (Kogelnig- Mayer et al, 2011;Lopez-Saez et al, 2012), (iii) sudden growth suppression following decapitation, loss of branch material, exposure of roots or deposition of material at the stem base KogelnigMayer et al, 2013), and (iv) the presence of growth releases in tree-ring records caused by stem burial (Strunk, 1997;Mayer et al, 2010).…”

“…The dating of past events was based on the number of trees showing a growth disturbance within the same year, the intensity of the tree-ring signal and the position of the disturbed trees, following the approach initially proposed by Shroder et al (1978) and adapted by Kogelnig-Mayer et al (2011) and Schneuwly-Bollschweiler et al (2013).…”

“…In his work in calcareous environments, Strunk (1997) reported limitations in dating accuracy in case events were defined with CW, GS and GR alone, as these GD may appear with some delay (up to three years) after the occurrence of a debris-flow in the growth rings of trees Kogelnig-Mayer et al, 2011). The inclusion of TRD considerably helps in this respect as resin is produced in the days following impact and as ducts are being formed in the weeks after the event, thus allowing dating of debris-flows with annual and sometimes seasonal accuracy.…”