Efforts to map the lithology and geometry of sand and gravel channel-belts and valley-fills are limited by an inability to easily obtain information about the shallow subsurface. Until recently, boreholes were the only method available to obtain this information; however, borehole programmes are costly, time consuming and always leave in doubt the stratigraphic connection between and beyond the boreholes. Although standard shallow geophysical techniques such as ground-penetrating radar (GPR) and shallow seismic can rapidly obtain subsurface data with high horizontal resolution, they only function well under select conditions. Electrical resistivity ground imaging (ERGI) is a recently developed shallow geophysical technique that rapidly produces highresolution profiles of the shallow subsurface under most field conditions. ERGI uses measurements of the ground's resistance to an electrical current to develop a two-dimensional model of the shallow subsurface (<200 m) called an ERGI profile. ERGI measurements work equally well in resistive sediments (ÔcleanÕ sand and gravel) and in conductive sediments (silt and clay). This paper tests the effectiveness of ERGI in mapping the lithology and geometry of buried fluvial deposits. ERGI surveys are presented from two channel-fills and two valley-fills. ERGI profiles are compared with lithostratigraphic profiles from borehole logs, sediment cores, wireline logs or GPR. Depth, width and lithology of sand and gravel channel-fills and adjacent sediments can be accurately detected and delineated from the ERGI profiles, even when buried beneath 1-20 m of silt/clay.
Landslide hazards in the Thompson River valley, British Columbia adversely impact vital national railway infrastructure and operations, the environment, cultural heritage features, communities, public safety and the economy. Field investigations and monitoring of
the very slow-moving Ripley Landslide, 7 km south of Ashcroft, indicates movement across the main body, with the greater displacement at the south end of the slide near a lock-block retaining wall separating Canadian National (CN) and Canadian Pacific (CPR) rail tracks. Knowledge of the internal
composition and structure of the landslide as interpreted through surficial geology mapping and geophysical surveys provide contextual baseline data for interpreting monitoring results and understanding mass-wasting processes in the Thompson River transportation corridor. Bathymetry measurements,
electrical resistivity tomography, frequency-domain electromagnetic terrain conductivity, ground penetrating radar, seismic refraction, multi-spectral surface wave analyses, and borehole logging of natural gamma, conductivity and magnetic susceptibility all suggest a moderately high relief bedrock
sub-surface overlain by a &gt;20 m thick package of clay, silt, till diamicton and gravel. Planar physical sub-surface features revealed in field observations, geophysical profiles and borehole logs include tabular bedding and terrain unit contacts, in addition to curvilinear-rectilinear
features interpreted as sub-horizontal rotational-translational slide surfaces in clay-rich beds beneath the rail ballast and retaining wall at depths between 5 m and 15 m below the surface of the main landslide body. Geophysical data presented support field observations and borehole logs that show
sub-surface glaciolacustrine unit boundaries are gradational rather than sharply defined. Geophysical profiles show that clay-rich glacial deposits are the units most likely to contain failure planes. The landslide toe extends under the Thompson River where clay-rich sediments are confined to a
&gt;20 m deep bedrock basin. The upper clay beds are armoured from erosion by a lag deposit of modern fluvial boulders except along the west river bank where a deep trough has been carved by strong currents. Waterborne conductivity measurements indicate groundwater discharge at three zones
across the submerged landslide toe. Fluvial incision of the submerged toe slope at the south end of the landslide is observed &lt;50 m west of where critical railway infrastructure is at risk. Integrating data from surficial geology mapping and an array of geophysical techniques provided
significantly more information than any one method on its own.
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