Abstract
Abstract. The application of the principles of dendrogeomorphology for the dating of high-magnitude snow avalanches is well established in the natural hazards literature. A variety of methodologies are employed by different authors, however, and no standardization currently exists for appropriate sample sizes, the issue of "weighting" certain tree-ring responses as more important than others, or the minimum number of responding trees required in order to infer an avalanche event. We review the literature of dendrogeomorphology as it applies to snow avalanches, and examine the questions of sample size, type of ring reactions dated and weighted, and minimum responses. We present tree-ring data from two avalanche paths in the Rocky Mountains of Montana, USA, from trees uprooted by major snow avalanches in the winter of 2002. These data provide distinct chronologies of past avalanche events, and also illustrate how the critical choice of a minimum Index Number can affect the number of avalanche events in a final chronology based on tree-ring analysis.
Highlights
Snow avalanches in mountains around the world descend from alpine and subalpine reaches into lower elevations where they are a hazard to human activity
Varying numbers of sampled trees are employed in constructing chronologies of past avalanches, the question of how many sampled trees need to illustrate distinct tree-ring responses is open to question, and the type of dated tree-ring responses varies among studies
Use of a 40% value further reduces the record to only 1971, 1976, and 1979, even though strong historical corroboration exists for both 1982 and 1991. It is clear from our preceding examples that selection of an Index Number value for specific sites must be tempered with knowledge of the historical record as well as assessment of the nature of the tree-ring responses and the site-specific geomorphology
Summary
Because the nature of shrub and low-tree growth on avalanche paths provides only a general estimate of time since avalanching, rather than a year-specific indication, the use of damage to tree rings in trees within and along the margins of avalanche paths has become well established in the natural hazards literature using principles of dendrogeomorphology elucidated by Alestalo (1971) and Shroder (1980). Varying numbers of sampled trees are employed in constructing chronologies of past avalanches, the question of how many sampled trees need to illustrate distinct tree-ring responses is open to question, and the type of dated tree-ring responses varies among studies. It is the purpose of this paper to: 1. Examine the type of tree-ring responses most typically employed in construction of high-magnitude snow. The first three objectives are accomplished through a literature review, and the fourth objective is completed by examining tree ring samples collected in a mountain region of northwest Montana, USA, where well-developed historical chronologies of past highmagnitude snow avalanching, based on archival and dendrochronological data, exist
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