Paper No. 39
Presentation Time: 9:00 AM-6:00 PM
EVIDENCE OF A VALLEY GLACIER ANTEDATING THE LLEWELLYN GLACIER, JUNEAU ICEFIELD, CANADA: AN ANALOGUE FOR THE ADIRONDACKS?
General and widespread glacier retreat is exposing glaciated landscapes, which are being used to better understand ancient glacier systems. The recent retreat of the Llewellyn Glacier has exposed a mountain peak (Camp-26 nunatak), which has evidence of an incipient valley glacier. Two ridges with the intervening valley, all oriented approximately southwest-northeast define the study area. 58 small-scale, glacial erosional forms were collected from both ridges and the intervening valley of the Camp-26 nunatak. Because data were collected as undirected features, they were normalized to azimuths from 0-179o and were analyzed using EZ-ROSE 1.0 software (Baas, 2000) for semi-circular, two-dimensional vectorial data and plotted as equal-area rose diagrams. Local glacial geomorphology was mapped (12.8 km2) using photogrammetric techniques; the map was used as an underlay for analysis of the rose diagrams. Rayleigh’s Tests of uniformity revealed two distinct directional patterns: a) a north-south trend (~007-187 degrees) surrounding b) spatially preserved erosional forms in the valley bottom (~097-277 degrees). This 90-degree offset of valley-parallel striations indicates the existence of a small, incipient valley glacier sometime before the south-flowing Llewellyn glacier covered the valley. In order to test the hypothesis that the Juneau Icefield could act as a modern analogue for the Adirondack Mountains (ADKs), 143 undirected, small-scale, glacial erosional forms were measured from the bare summits of eight ADK high peaks. Tentative statistical analyses of these data reveal a uniform distribution, which suggests radial ice flow perpendicular to isohypses (i.e., downhill). Conceivably, by the time the Laurentide Ice Sheet covered the ADKs, horizontal flow was significantly diminished by the rough, mountainous topography, leaving only vertical glacier flow radially down and around the peaks. If these tentative results are correct, the use of the Juneau Icefield as an ADK analogue is going to require careful consideration.