Debris flows in the southern Coast Mountains exhibit different dynamic and
sedimentologic characteristics, depending on the lithology of their source areas. Fine-textured
debris flows originating in the Quaternary volcanic complexes are much more mobile than those
originating in the coarse-textured plutonic rocks which form most of this mountain range.
Mobility can be described as the velocity of flow, the distance of travel of debris flows, and the
slope required to sustain flow. The objectives of this study are to examine the effect of different
sediment composition on the mobility of debris flows, and to determine which rheologic models
are most applicable for modeling debris flows in these geologic environments.
About 25 debris flow events in or adjacent to the southern Coast Mountains were
examined, ranging in volume from 10² m³ to over 10⁷ m³. Field methods included sampling of
grain-size distribution, measurement of the deposit and channel dimensions, and observation of
the stratigraphy of debris flow fans. Shear strength, permeability, and consolidation tests were
performed on samples of reconstituted debris, representative of typical fine-textured and coarsetextured
debris flows. These samples were also used to model debris flows in a flume.
The coarse-textured, plutonic-source, debris flows typically had a distinct, inverselygraded,
clast-supported, surface layer of cobbles and boulders. Their deposits tended to be
irregular in thickness, with lobes and levees of coarse material. The fine-textured, volcanicsource,
debris flows had no such surface layer, and their deposits were generally uniform in
thickness and surface morphology. These observations, and corroborating evidence from the
flume results, suggest that fine-textured debris flows behave according to the Bingham flow
model, while coarse-textured debris flows can be better described by a granular, or dilatant, flow
model. A clay content of about 4% in the matrix (sub-4 mm material) is a useful measure to
distinguish the two populations. Several debris flow events of intermediate behaviour and
sediment composition were also examined. The permeability of the debris, and hence its rate of
consolidation, is an important factor controlling mobility. The volume of debris flow events was
found to be the most significant factor controlling runout distance.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/8796 |
| Date | 05 1900 |
| Creators | Jordan, Robert Peter |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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