The Mount Meager volcanic complex in southern British Columbia is snow and ice covered and has steep glaciated and unstable slopes of hydrothermally altered volcanic deposits. Three large-volume (>108 m3) volcanic debris flow deposits derived from the Mount Meager volcanic complex have been identified. The volcanic debris flows travelled at least 30 km downstream from the volcanic complex and inundated now populated areas of Pemberton Valley. Clay content and mineralogy of the deposits indicate that the volcanic debris flows were clay-rich (5%–7% clay in the matrix) and derived from hydrothermally altered volcanic material. The youngest volcanic debris flow deposit is interpreted to be associated with the last known volcanic eruption, ~2360 calendar (cal) years BP. The other two debris flows may not have been directly associated with eruptions. Volcanic debris flow hazard inundation maps have been produced using the Geographic Information System (GIS)-based modelling program, LAHARZ. The maps provide estimates of the areas that would be inundated by future moderate to large-magnitude events. Given the available data, the probability of a volcanic debris flow reaching populated areas in Pemberton Valley is ~1 in 2400 years. Additional mapping in the source regions is necessary to determine if sufficient material remains on the volcanic edifice to generate future large-magnitude, clay-rich volcanic debris flows.
Surficial geology mapping at a scale of 1:50 000, cosmogenic dating, and detailed stratigraphic and sedimentological logging of 86 cliff-bank exposures and more than 3000 roadcuts and hand-driven auger borings have resolved the century-old controversy as to the
number and timing of continental glaciations in the Rocky Mountain Foothills of southwestern Alberta.
The stratigraphy shows a consistent succession repeated throughout much of the area: one to several montane tills are always topped by either one continental till or a complex of continental tills, or a gravel unit containing Canadian Shield lithologies where a continental till has been eroded.
Exceptions only occur along the Rocky Mountain Front, at the mouths of major valleys where no continental till is present.
There is no evidence of subaerial erosion or soil-forming processes that would represent long hiatuses between glacial advances responsible for continental till deposition. The same holds true for montane tills, with the exception of those found in the subsurface of Cloudy Ridge and the sediments
capping Mokowan Butte. The drift units underlying paleosols at these two sites clearly predate the last interglaciation. The upper elevation limits of glacial erratics from the Canadian Shield and their abrupt western limit indicate that montane glaciers prevented penetration of continental glacial
ice up major Rocky Mountain Foothills valleys, hence continental and montane glaciers coalesced during the culmination of the maximum continental ice advance.
Paleomagnetic sampling of the oldest tills infilling buried valley systems shows that all deposition occurred during the Brunhes chron (<0.78 Ma). Cosmogenic 36Cl exposure dating of the foothills erratics train and the former limits of the continental ice-sheet cover constrains the single
continental glaciation to the Late Wisconsinan. The area was deglaciated by ca. 11 200 radiocarbon years before present.
Investigation of stream-gravel lithology, distribution of erratics and high terraces, and natural exposures of terrace gravels along Stewart River have generally corroborated the all-time limits of glaciation mapped by H.S. Bostock in the Stewart River basin of
the Stewart River map area. Stream gravels beyond these limits completely lack lithologies associated with the Selwyn Basin. Placer deposits beyond these glacial limits formed from fluvial con- centration of gold sources occurring in those basins. The upper reaches of streams spanning glacial limits
may contain undisturbed placers, whereas lower reaches may contain placers formed following glaciation, and buried placers. Bostock's unpublished notes have proven to be a valuable aid in mapping the surficial geology of the area.
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