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TitleDebris flow hazard in the Canadian Rocky Mountains: observations on the geomorphology of montane fans and a methodology for the identification of debris flow hazard on fans in geologically similar northern upland areas
AuthorJackson, L E, Jr
SourceGeological Survey of Canada, Paper 86-11, 1987, 20 pages,
MapsPublication contains 3 maps
Map Info.surficial geology, sample sites, 1:126,720
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia; Alberta
NTS82J/10; 82J/11; 82G/14; 82G/15; 82K/07; 82K/08
AreaRocky Mountains
Lat/Long WENS-115.3833 -115.0000 51.0000 50.6833
Lat/Long WENS-114.7000 -114.7000 49.7500 49.3333
Lat/Long WENS-116.1667 -116.1667 51.5167 51.2500
Subjectsgeochronology; sedimentology; surficial geology/geomorphology; stratigraphy; debris flows; landslides; debris flow deposits; morphology; basins; basin geometry; fans; climate; holocene; alluvial fans; debris fans; erosion; deposition; glaciers; glaciation; radiocarbon dating; dendrochronology; bedrock geology; stratigraphic analyses; drainage systems; textures; sorting; fluvial deposits; sediments; tephrochronology; Precambrian; Paleozoic; Mesozoic
Released1987 09 01; 2013 05 29
AbstractValley margins in the Rocky Mountains are locally prone to periodic inundation by debris flows. Alluvial fans and landforms and related features may be constructed by and are loci for debris flow deposition. A total of 103 fans within three areas of the Rocky Mountain Front Ranges and Main Ranges were studied in order to establish the occurrence and past frequency of debris flows. These three areas are characteristic of a wide range of physiographic settings found in the Rocky and Mackenzie mountains.
Alluvial fans and landforms, at least partly constructed by debris flows, generally have slope angles of 4° or greater whereas strictly fluvially constructed fans have angles less than 4°. Drainage basins in which debris flows reach fans at the basin mouth are predominantly smaller than 10-12 km 2 and have an internal relief of more than 500 m. Basins smaller than 1 km 2 may produce debris flows but avalanche activity is the dominant erosional, transportational, and depositions! process operating in these basins. Indications of past debris flow activity include debris flow levees, bouldery terrac'es marking former debris flow margins, and large isolated boulders on the fan surface. Debris flow deposits in fans can be identified visually by their matrix-supported structure and texturally by the anomalous association of large components of both pebble and cobble size clasts (>2 mm .-<64 mm) and clay size ( < 2 1.1 m) particles.
Debris flow hazard is best evaluated by.establishing the past frequency of debris flow events.
Events can be assigned maximum and minimum ages by combinations of 14C dating, dendrochronology, and tephrochronology. Some of the debris flow fans studied were predominantly deposited shortly after deglaciation and have been largely inactive during the past 6600 years. Water courses crossing these fans are usually deeply incised. These inactive fans provide low hazard sites for development along otherwise high hazard valley margins.