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TitleUse of digital photogrammetry to establish lichenometric dating controls in the Selwyn Mountains, NWT
AuthorMcCarthy, D P; Demuth, M N; Zdanowicz, C M
SourceCanadian Quaternary Association (CANQUA) annual congress, Program with abstracts; 2007, 1 pages
Alt SeriesEarth Sciences Sector, Contribution Series 20090142
MeetingCanadian Quaternary Association (CANQUA) annual congress; Ottawa; CA; June 4-8, 2007
ProvinceNorthwest Territories
AreaRagged Ranges; Nahanni National Park; Selwyn Mountains
Subjectssurficial geology/geomorphology; geochronology; glaciers; ice; ice conditions; vegetation; remote sensing; photogrammetric surveys; moraines; glacial deposits; glacial landforms; lichen
AbstractA recent glacier inventory and field work at glaciers in the Ragged Ranges near Nahanni National Park has found that many moraine complexes in the area support lichen growth, but are far above timberline and are unlikely to have buried logs or datable organics. Thus lichenometry may be the only dating control that can be used to establish ages for the moraines. Accordingly, an attempt was made to calibrate a lichen "growth curve" using repeated measurements of annual growth. Initially we attempted to use calipers and painted reference points to directly measure the annual radial growth of a few dozen Rhizocarpon geographicum agg. over the last year. This was unsuccessful in part because growth at the calibration points either did not occur or was too slight to be accurately measured using calipers. Slight slippage and/or imprecise placement of the calipers on the varnished cross-hairs made it very hard to ensure that all measurements were accurate to within 0.02 mm. A solution was found using repeated macrophotography and new tools in Adobe® Photoshop® CS2 software. Highly accurate measurements were obtained by carefully overlaying transparent image pairs from 2005 and 2006 and precisely aligning rock crystals and crosshairs. This approach will allow us to monitor recruitment, growth and mortality in lichen populations. Measurements are now being done using a tedious manual approach, but the image pairs will soon be analysed using GIS software. This will permit the development of indices other than diameter as a way to assign lichenometric ages to moraines in this region. This new digital approach to lichen measurement will also provide a statistical base that gives a robust estimate of within and between thallus variability in growth and facilitates statistical testing of data sets developed in other regions.