Radar facies and architecture of alluvial fans and related sediments in high-energy alpine environments, British Columbia

It is widely recognized that the dominant depositional processes on alluvial fans include rock falls, rock slides, rock avalanches, debris flows, sheetfloods and incised-channel floods. A fundamental question addressed in this thesis is: Can ground penetrating radar (GPR) differentiate between the sediments associated with these processes? Do these individual deposits have characteristic radar reflection signatures?; The dissertation is divided into two parts. In part one, a calibration exercise conducted in southern British Columbia, it was demonstrated that GPR was able to obtain good penetration and resolution in rock fall, rock slide, fluvial and alluvial fan sediments, and that a characteristic radar reflection pattern (or radar facies) can be assigned to these deposits.; Bedrock reflection pattern is characterised by a discontinuous radar signal and by stacked diffractions. The radar facies for rock slide and rock avalanche sediments, where boulders constitute the predominant clast size, is characterized by discontinuous, high amplitude, macro-scale, hyperbolic reflections that are different from diffractions generated by bedrock. Alluvial fans dominated by debris flow processes produce a chaotic and discontinuous radar pattern; diffractions in these patterns are attributed to boulders. Alluvial fans dominated by sheetflood processes are likely to produce surface-parallel, gently dipping, more or less continuous radar patterns.; Large-scale meandering-river radar-patterns are characterized by high amplitude, continuous, dipping clinoforms. Braided-river radar facies, based on data collected on the Kicking Horse braidplain, are characterized by predominantly horizontally continuous reflections with few identifiable features. Based solely on GPR data, it was possible to distinguish between sediments of meandering and braided rivers.; Analysis of over 95 km GPR data suggests that alluvial fan radar-reflection patterns are distinctly different from those observed in other environments, including those from gravel-bed rivers. None of the radar patterns observed in river channel environments were found on any of the alluvial fans surveyed.; The objective of the second part of the thesis is the analysis of the large-scale, three dimensional internal architecture and depositional history of Cheekye Fan in southwestern British Columbia. The fan receives sediments from debris flows which represent a hazard for transportation and residential development on its surface.; GPR proved to be an efficient technique for analysing the large-scale internal architecture of Cheekye Fan. Fan sediments overlie till and undulating bedrock in the northern and eastern fan sector. Two architectural components were defined: subaqueously-deposited fan-delta sediments and subaerial alluvial-fan sediments. Fan sediments were tentatively further divided into: (a) matrix-rich diamicton that appears predominant at the core of the fan and at lower stratigraphic horizons, suggesting bouldery rock-slide or debris flow origin, and (b) horizontally-bedded sheetflood sand and gravel dominating the upper 20--25 m of the stratigraphic column.; Based on GPR data, radiocarbon dating and test-pit information, the post-glacial depositional history and evolution of Cheekye Fan is as follows. It is estimated that 90% of fan volume was deposited prior to 6000 years BP. Sediment availability declined after ca. 6000 yr. BP and fan growth slowed towards equilibrium. Although the last major debris flow which reached lower Cheekye Fan surface occurred at about 1300 yr. BP, Cheekye Fan is essentially a paraglacial fan, largely a product of the geological past. This fact should be taken into consideration when making future hazard estimates. Based on subsurface information there is little similarity between the early and late Holocene rates of deposition.