Major rail routes through the southern Cordillera of British Columbia (BCR – BC Rail; CPR – Canadian Pacific Railway; CN – Canadian National railways); with location of Ripley Slide south of Ashcroft. 

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Context 1

... geoscience information is presented that will help reduce the economic, environmental, health and public safety risks that landslides pose to the national railways operating through part of Canada’s western Cordillera. Knowledge of the nature and stratigraphic relationships of surficial earth materials leads to a better understanding of some controls on mass wasting near Ashcroft, British Columbia, and in particular at the Ripley Slide: an active, slow-moving translational failure situated along a critical section of the national transportation corridor. This work compliments and will help guide other aspects of a multi-year international investigation of this landslide. Keywords : Ripley Slide, Canadian National Railway, Canadian Pacific Railway, British Columbia, geohazards, slope stability, landslide, surficial geology, mapping, ground motion monitoring, GPS, InSAR corner reflectors, fibre optic sensing, shallow geophysical survey, risk management, As Canada’s economy continues to grow, there will be an increasing demand for safe and secure transportation of natural resources, agricultural products, manufactured goods, people and other cargo using the national network of railways. Landslides in the Cordillera of southern British Columbia ( Figure 1 ) are costly geological hazards that have challenged railroads in the mountains of western Canada since the late 19 th Century. Pronounced economic and environmental repercussions occur when railways are severed and infrastructure is damaged by landslide activity. In southern British Columbia, both Canadian National (CN) and Canadian Pacific (CPR) railways run along the lower valley slopes of Thompson and Fraser rivers. Up to 80 trains per day, some with lengths up to 4 km, run through these valleys. Landslides in this transportation corridor have the potential to stop the flow of exports and imports to, and from the Port of Vancouver and thus the rest of Canada, resulting in economic losses that grow exponentially with the duration of service interruption (Bunce and Chadwick, 2012). In addition, both Thompson and Fraser rivers are highly sensitive aquatic ecosystems subject to contamination and long-term environmental damage by train derailment. Domestic passenger services and international tourism would also have the potential to be adversely impacted by outages due to landslides along this section of the CN-CPR ...

Context 2

... Canada's economy continues to grow, there will be an increasing demand for safe and secure transportation of natural resources, agricultural products, manufactured goods, people and other cargo using the national network of railways. Landslides in the Cordillera of southern British Columbia (Figure 1) are costly geological hazards that have challenged railroads in the mountains of western Canada since the late 19 th Century. Pronounced economic and environmental repercussions occur when railways are severed and infrastructure is damaged by landslide activity. ...

Context 3

... till and retreat phase glaciolacustrine units are overlain by a massive to crudely stratified boulder and sand-rich gravel (Unit 6). This unit forms a prominent terrace at 340 m to 350 m elevation (Figures 4 and 10a, b). Gravel is porous, rapidly drained and prone to gully erosion (Figure 10c). ...

Context 4

... unit forms a prominent terrace at 340 m to 350 m elevation (Figures 4 and 10a, b). Gravel is porous, rapidly drained and prone to gully erosion (Figure 10c). Unit 6 records the transition from glacial to proglacial conditions, and is interpreted to be deposited following catastrophic drainage of the ice, sediment and landslide-dammed lake confined to the Thompson River valley, ca. 13 ka to 11 ka (glacial lakes Thompson-Deadman;Fulton, 1969;Ryder et al., 1991;Johnsen and Brennand, 2004). ...

Context 5

... ka to 10 ka. Unit 7 is graded to successively lower elevations reflecting falling post- glacial regional base-levels (Figure 11a; cf. Fulton, 1969;Clague and Evans, 2003;Ryder et al., 1991;Johnsen and Brennand, 2004). ...

Context 6

... 1969;Clague and Evans, 2003;Ryder et al., 1991;Johnsen and Brennand, 2004). Alluvial fans (with surface slopes from 3 o to 8 o ) and cones (slopes >8 o and <12 o ) drape bedrock, till and late-glacial flood deposits (Figure 11b). Observation pits expose diamicton and gravels fining upward to sand then silt, with this sequence generally less than a metre in thickness (Figure 11c). ...

Context 7

... fans (with surface slopes from 3 o to 8 o ) and cones (slopes >8 o and <12 o ) drape bedrock, till and late-glacial flood deposits (Figure 11b). Observation pits expose diamicton and gravels fining upward to sand then silt, with this sequence generally less than a metre in thickness (Figure 11c). As sediment sources diminished and regional base-levels fell after 10 ka, the post-glacial drainage system deeply incised unconsolidated glacial deposits and bedrock, forming the distinctive benchland terraces, gullies and canyons of the modern Thompson River valley (Figures 4 and 11a). ...

Context 8

... pits expose diamicton and gravels fining upward to sand then silt, with this sequence generally less than a metre in thickness (Figure 11c). As sediment sources diminished and regional base-levels fell after 10 ka, the post-glacial drainage system deeply incised unconsolidated glacial deposits and bedrock, forming the distinctive benchland terraces, gullies and canyons of the modern Thompson River valley (Figures 4 and 11a). ...

Context 9

... ka to present) unconformably overlying valley fill on over-steepened slopes. On steep bedrock slopes, gelifraction is focused along slope-parallel fractures, and in places, the resulting detritus is transported down slope through rock fall and debris fall, to accumulate as talus and scattered colluviated blocks (Figure 12a). On moderately steep unconsolidated slopes exposed by the down-cutting Thompson River, glacial sediments are remobilized by debris fall, debris flows, slides, avalanches, soil creep, solifluction, gully erosion and surface runoff; and deposited as stratified, clast-supported gravels and sand-rich diamicton on the colluvial mid-slope (Figure 12b) and toe slope of the valley (Figure 12c). ...

Context 10

... steep bedrock slopes, gelifraction is focused along slope-parallel fractures, and in places, the resulting detritus is transported down slope through rock fall and debris fall, to accumulate as talus and scattered colluviated blocks (Figure 12a). On moderately steep unconsolidated slopes exposed by the down-cutting Thompson River, glacial sediments are remobilized by debris fall, debris flows, slides, avalanches, soil creep, solifluction, gully erosion and surface runoff; and deposited as stratified, clast-supported gravels and sand-rich diamicton on the colluvial mid-slope (Figure 12b) and toe slope of the valley (Figure 12c). Unit 9: Alluvial floodplain sediments (late post-glacial) Unit 9 includes alluvial deposits of Thompson River below 265 m elevation (high bench-level of the active floodplain). ...

Context 11

... steep bedrock slopes, gelifraction is focused along slope-parallel fractures, and in places, the resulting detritus is transported down slope through rock fall and debris fall, to accumulate as talus and scattered colluviated blocks (Figure 12a). On moderately steep unconsolidated slopes exposed by the down-cutting Thompson River, glacial sediments are remobilized by debris fall, debris flows, slides, avalanches, soil creep, solifluction, gully erosion and surface runoff; and deposited as stratified, clast-supported gravels and sand-rich diamicton on the colluvial mid-slope (Figure 12b) and toe slope of the valley (Figure 12c). Unit 9: Alluvial floodplain sediments (late post-glacial) Unit 9 includes alluvial deposits of Thompson River below 265 m elevation (high bench-level of the active floodplain). ...

Context 12

... modern river channel is laterally eroding bedrock, till, glaciolacustrine and colluvial deposits; a scour pool beyond the inferred southwest limit of the landslide indicates the river is locally incising the channel bed. Floodplain deposits are predominantly boulder and cobble-rich rich, reflecting the fast-flowing conditions of Thompson River during spring and summer runoff (Figure 13a). Sand is deposited as a matrix within the framework of cobbles and boulders during low-flow conditions in autumn through winter (Figures 4 and 13b). ...

Context 13

... deposits are predominantly boulder and cobble-rich rich, reflecting the fast-flowing conditions of Thompson River during spring and summer runoff (Figure 13a). Sand is deposited as a matrix within the framework of cobbles and boulders during low-flow conditions in autumn through winter (Figures 4 and 13b). The presence of horsetails (Equisitales sp.) between ca. ...

Context 14

... CN and CPR tracks are positioned on a linear, low grade railway corridor along the eastern valley floor of Thompson River (Figure 14a). To accommodate this vital infrastructure, a 50 m to 100 m wide segment of toe slope was excavated in colluvium, alluvial sediments, till and underlying glaciolacustrine deposits. ...

Context 15

... accommodate this vital infrastructure, a 50 m to 100 m wide segment of toe slope was excavated in colluvium, alluvial sediments, till and underlying glaciolacustrine deposits. This corridor was infilled to varying depths (<20 m) with a base of weathered granodiorite boulders, overlain by cobble-sized ballast (Figure 14b) consisting of fine-to medium crystalline igneous and metamorphic rocks (e.g., granodiorite, rhyolite, amphibolite, phyllite). CN and CPR tracks are separated by a 3 m high retaining wall along the southern flank of the Ripley Slide, near GPS3 (Figures 4 and 14c). ...

Context 16

... corridor was infilled to varying depths (<20 m) with a base of weathered granodiorite boulders, overlain by cobble-sized ballast (Figure 14b) consisting of fine-to medium crystalline igneous and metamorphic rocks (e.g., granodiorite, rhyolite, amphibolite, phyllite). CN and CPR tracks are separated by a 3 m high retaining wall along the southern flank of the Ripley Slide, near GPS3 (Figures 4 and 14c). Unit 10 is the youngest surficial earth material, spanning construction of the railways in the late 1880s to the yearly addition of ballast to accommodate movement on the Ripley Slide as part of track maintenance. ...

Context 17

... interpretative cross sections across the map area (A-A', B-B' and C-C') were generated using the CANVEC DEM files and Global Mapper TM software (Figures 4 and 15). The distribution of Pleistocene units in cross-section is hypothetical, but based in part on observed stratigraphic relationships and knowledge of the internal structure of other landslides in the Thompson River valley (Porter et al., 2002;Clague and Evans, 2003;Bishop et al., 2008;Eshraghian et al., 2007;Bunce and Chadwick, 2012). ...

Context 18

... distribution of Pleistocene units in cross-section is hypothetical, but based in part on observed stratigraphic relationships and knowledge of the internal structure of other landslides in the Thompson River valley (Porter et al., 2002;Clague and Evans, 2003;Bishop et al., 2008;Eshraghian et al., 2007;Bunce and Chadwick, 2012). Sediments logged in geotechnical drill hole DH05-26 have also been interpreted in the context of the stratigraphy described above (Figure 15). however, movement could also be accommodated along rectilinear planes (dashed black lines); materials removed for railway right-of-way (dotted black lines). ...

Context 19

... movement could also be accommodated along rectilinear planes (dashed black lines); materials removed for railway right-of-way (dotted black lines). For locations of GPS stations (GPS1-3); InSAR corner reflectors (GSC1-9); and observation well (DH05-26) also see Figure 4. (Figure 15). Eroded remnants of units 2 and 3 are inferred to lie beneath the modern river channel bed. ...

Context 20

... landslides in the Thompson River valley fail along planar to listric scarp planes that intersect sub-horizontal bedding (Porter et al., 2002;Clague and Evans, 2003;Bishop et al., 2008;Eshraghian et al., 2007;. Two end-member interpretations of the internal architecture of the Ripley Slide are depicted: listric failure planes are shown in red; rectilinear failure planes are shown as dashed black lines (Figure 15). The objective of geophysical surveys will be to employ seismic reflection, ground penetrating radar, direct electrical current resistivity tomography and electromagnetic techniques to test the validity of the landslide architecture depicted in the cross-sections (Figure 15). ...

Context 21

... end-member interpretations of the internal architecture of the Ripley Slide are depicted: listric failure planes are shown in red; rectilinear failure planes are shown as dashed black lines (Figure 15). The objective of geophysical surveys will be to employ seismic reflection, ground penetrating radar, direct electrical current resistivity tomography and electromagnetic techniques to test the validity of the landslide architecture depicted in the cross-sections (Figure 15). ...

Context 22

... units 4 to 7 likely host an unconfined aquifer, recharged by infiltrating precipitation and surface runoff on the slopes above the Ripley Slide. Groundwater flows laterally and downward through porous till and glaciofluvial units (4 and 6); and through vertically fractured glaciolacustrine units (3 and 5) until it encounters fractured, non-porous bedrock (Unit 1) or sub-horizontal sub-shear zones in Unit 3. As with other landslides in the area, units 3 and 5 function as aquitards but also accommodate landslide movement along shear zones approximately corresponding to stratigraphic boundaries (Figure 15). Artesian conditions at the landslide toe suggest the presence of an aquifer in Unit 1 bedrock and Unit 2 diamicton, confined by Unit 3 clay and silt. ...

Context 23

... extensive suite of monitoring technology is now being applied at the Ripley Slide that ranges from: 1) traditional applications including permanent monitoring using survey benchmarks, GPS stations and piezometers; 2) subsurface investigations involving drilling and shallow geophysical surveys; 3) novel technologies such as linear fibre optic sensing and vertical subsurface ShapeAccelArray (SAA) inclinometry for down-hole monitoring; 4) InSAR corner reflectors for satellite (RADARSAT-2) interferometry have been installed across the landslide and adjacent stable terrain ( Figure 16); and 5) round-based SAR and LiDAR have also been deployed for ongoing comparative work ( Bobrowsky et al., 2014). ...

Context 24

... geology mapping, borehole instrumentation and interferometric techniques reveal limited information on the subsurface nature of the Ripley Slide (Figures 4 and 15). Knowledge of the internal structure and composition of the landslide (to at least a depth of 50 m) as revealed by geophysical surveys will be of critical importance for interpreting the results gleaned from other monitoring applications. ...