ABSTRACT: The use and resolution of dendrochronology as a dating tool on landslides.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Landslides are a serious hazard in coastal British Columbia. Sound management practices of forest lands in British Columbia require significant understanding of attributes contributing to landlsides. Two of those attributes are precipitation and seismic activity. Relating the occurrence of a landslide to either of these attributes requires knowledge of the timeing of that event. Dendrochronology is a mthod whereby the age of a tree is determined by counting that tree's annual growth rings. When the tree is growing on or near a geomorphic feature, those rings may also be used to determine the age of the feature. Dendrochronology was employed as a dating tool on 18 landslide sites, resulting in 28 events in the Tsitika and Schmidt Creek watersheds on northern Vancouver Island. Maximum resolution of the dating was one year. Minimum age cores, release growth in intact timber and tree scars were recorded where possible on the 18 sites. Dates were calibrated against air photographs or archival information, provided it was available. Results indicate that the best minimum age core dates were typically 1-3 years too youg compared to the actual timing of the event. Release growth measured on the periphery often followed a lag time of slightly reduced ring width prior to growth, also typically 1-3 years. Tree scars were usually accurate to within a year. Coupled with air photograph and archival information, Dendrochronology was used with moderate success to relate years of landslide occurrence, with years of extreme precipitation or seismic activity. Resolution of the dates increased (for dendrochronology alone)with increased sample size. However, where minimum age cores are used exclusively, it is unlikely to achieve better resolution than 1-3 years.

Bibliography of Canadian Geomorphology