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Geologic Framework of Large Historic Landslides in Thompson River Valley, British Columbia
Abstract and Figures
At least eight large landslides occurred in Thompson River valley south of Ashcroft, British Columbia, between 1880 and 1982. The landslides were slow-moving translational slides and slumps, and sudden-onset, rapid flowslides. Some of the landslides disrupted trans-continental rail traffic and blocked Thompson River, creating short-lived upstream reservoirs. Most of the landslides occurred in a 10-km reach of Thompson valley, within a thick Quaternary valley fill dominated by glaciolacustrine sediments. Failure occurred on the steep walls of an inner valley that formed during the Holocene when Quaternary sediments filling the broader Thompson River valley were incised. The valley fill sequence consists dominantly of permeable sediments, the exception being a unit of rhythmically bedded silt and clay near the base of the Pleistocene sequence. Large landslides are restricted to areas where this silt-clay unit is present. Failure occurred within, or at the top of, this unit. The landslides may have been triggered by irrigation of benchlands above the river. Irrigation commenced in the 1860s, shortly before the first known large landslide occurred. Early irrigation added large volumes of water to the normally dry Quaternary sediment fill, possibly elevating pore pressures at the top of the rhythmically bedded silt-clay unit. Large landslides may occur in the future in the study area if irrigation is not carefully controlled or if climate becomes wetter for periods of years or decades. Such landslides would probably involve reactivation of nineteenth- and twentieth-century landslide deposits.
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... The North Slide is an ancient landslide that reactivated as a sudden onset, rapid retrogressive flow-slide around 9 pm on October 14, 1880 (Stanton 1898;Evans 1984;Clague and Evans 2003;Fig. 2a). ...
... Valley-bottom benchlands around 350 m elevation have been incised by Thompson River since the last glaciation, forming an inner gorge with steep slopes up to 125 m high (Fig. 2a). Thick (50 m to 150 m) Pleistocene valley-bottom fill is exposed along post-glacial terrace scarps of Thompson River and its tributaries (Ryder 1976;Clague and Evans 2003;Johnsen and Brennand 2004). These sediments include multiple glaciolacustrine units, separated by till and outwash recording at least three glaciations: the last (Late Wisconsinan) glaciation, the penultimate glaciation (Early Wisconsinan), and an earlier glaciation (Ryder et al. 1991;Clague and Evans 2003). ...
... Thick (50 m to 150 m) Pleistocene valley-bottom fill is exposed along post-glacial terrace scarps of Thompson River and its tributaries (Ryder 1976;Clague and Evans 2003;Johnsen and Brennand 2004). These sediments include multiple glaciolacustrine units, separated by till and outwash recording at least three glaciations: the last (Late Wisconsinan) glaciation, the penultimate glaciation (Early Wisconsinan), and an earlier glaciation (Ryder et al. 1991;Clague and Evans 2003). The upper part of the sediment sequence was deposited during deglaciation when repeated glacial lake stages occupied the valley (Fulton 1969;Ryder 1976;Johnsen and Brennand 2004), and shortly after deglaciation when the valley bottom was choked by paraglacial sedimentation (Church and Ryder 1972). ...
Our study focuses on a slow-moving landslide in the Thompson River valley, south-central British Columbia, Canada, that has posed a hazard to the national railway transportation corridor since 1880. Real-time kinematic global navigation satellite systems, unoccupied aerial vehicles, and satellite synthetic aperture radar interferometry time-series show significant displacement encroaching on railway infrastructure. In this paper, geospatial relationships between landslide distribution and specific terrain features, and the environmental conditions triggering instability are determined from field-based geological observations. We describe how earth material stratigraphy, textures, and penetrative planar structures are important controls on sub-surface drainage, and how these factors influence the style, timing, and rate of slope displacement. West of the railway tracks, slide scarps extend across the toe slope, corresponding to narrow zones of high displacement, presence of perennial springs and seepage, and cutbank erosion along the river channel. Fluvial incision exposes weak, failure-prone units at the base of the fill sequence, and with ongoing channel migration promotes instability by altering landslide toe geometry. Currently, the zone of potential displacement does not extend upslope into the inactive (1880) main slide body, east of the tracks. Seasonal variations in hydrogeological conditions influence the spatial and temporal patterns of surface water and groundwater flow, in turn controlling the distribution of translational-rotational displacement of slide blocks, and rates of movement on reactivated shear surfaces that extend under Thompson River. Slope failure occurs along weak, sub-horizontal shear zones within poorly drained glaciolacustrine clay and silt units, overlain by rapidly drained glaciofluvial outwash gravel, and imperfectly drained till diamicton. River levels exert a complex control on landslide stability, influencing hydraulic gradients within the basal glaciolacustrine unit, particularly along rupture surfaces within it. Ground displacement occurs while river levels are at their lowest between February and March, before peak flows in June, or after July until December while storm-fed river levels progressively lower to the next winter minimum. Groundwater levels remain elevated in the slide body throughout the year, contained in porous gravel and sand beds, and along brittle fractures and sub-horizonal shear zones in silt-clay varve beds. Geospatial and temporal change-detection monitoring of active landslides and at-risk infrastructure, when benchmarked with terrain and hydrogeological observations, is a cost-effective hazard management practice that provides important geoscience information to help develop appropriate early warning, mitigation, adaptation, and risk reduction measures.
... The stratigraphy of the ground in this area has been extensively studied by previous researchers, providing valuable insights into the geological layers and formations. (Journault et al. 2018, Clague et al. 2003, Huntley et al. 2014. The landslides along this valley, was formed during postglacial period gradually, by Southward Thompson river's erosion which down-cut up to 150 m of deposited sediments (Journault et al. 2018, Porter et al. 2002. ...
... The landslides along this valley, was formed during postglacial period gradually, by Southward Thompson river's erosion which down-cut up to 150 m of deposited sediments (Journault et al. 2018, Porter et al. 2002. The presence of a weak silt and clay layer were confirmed as the responsible factor for the instability of landslides in this area in other investigations (Journault et al. 2018, Clague et al. 2003). Previous investigations have utilized back analyses to determine that a pre-sheared surface in this layer exhibits residual strengths characterized by no cohesion and friction angles ranging between 9 to 16 degrees. ...
... Sectors closer to the river exhibit more horizontal movement, indicating the presence of a weak clay layer, as suggested in previous research on landslides in the Thompson River valley. (Journault et al. 2018, Clague et al. 2003). ...
Landslide events are one of most common phenomena which can cause catastrophic consequences and damages for the area that hosts these events. Monitoring both natural and man-made slopes is one of the most effective and common methods to mitigate the negative effect of the possible slope failure. Monitoring slopes can help engineers to prevent those events or to plan for any repair schedule for infrastructures. Early warning of landslide events also could be alert risk management teams to decrease damages and avoid possible fatalities. Remote sensing is one of the most effective methods for monitoring, specially in remote areas and can be employed to monitor slope's activity in different infrastructures such as open mines, dams, roads, and railways to have accurate estimation of ground movement. InSAR technology, as a remote sensing method can be used to estimate ground movement with high accuracy (mm/year) to monitor and have early warning of unordinary movements. In this research, InSAR data helps to update understanding of landslides' movement along the Thompson River valley, BC, Canada. This corridor hosts several relatively active landslides. The real movement of landslides along the valley is estimated using two different orbits of Sentinel-1 Satellite in this research, and the result is verified using the existed GPS data for Ripley landslide which is the fastest landslide along the valley. Then the kinematics of landslides is updated using the results of defined method as well as previous results at the same area. RÉSUMÉ La télédétection est l'un des méthodes les plus efficaces pour surveiller l'activité des pentes, en particulier dans les zones éloignées. Elle peut être utilisée pour surveiller l'activité des pentes dans différentes infrastructures telles que les mines à ciel ouvert, les barrages, les routes et les chemins de fer afin d'avoir une estimation précise du mouvement du sol. La technologie InSAR, en tant que méthode de télédétection, peut être utilisée pour estimer le mouvement du sol avec une grande précision (mm/an) afin de surveiller et d'avoir une alerte précoce des mouvements inhabituels. Les données InSAR permettent de mettre à jour la compréhension du mouvement des glissements de terrain le long de la vallée de la rivière Thompson. La vallée de la rivière Thompson, traversée par les chemins de fer CPR et CNR héberge plusieurs glissements de terrain relativement actifs. Le mouvement réel des glissements de terrain le long de la vallée a estimé à l'aide de deux orbites différentes du satellite Sentinel-1, et le résultat est vérifié à l'aide des données GPS existantes pour le glissement de terrain de Ripley, qui est le plus rapide le long de la vallée. Ensuite, la cinématique des glissements de terrain est mise à jour en utilisant les résultats de la méthode définie ainsi que les résultats précédents dans la même région.
... In the late nineteenth century, terraces were intensively irrigated for agricultural land use and toe slopes were incised and over-steepened during railway construction (Stanton 1898;Evans 1984;Clague and Evans 2003). Prehistoric mass movements were consequently reactivated as sudden Fig. 1 Physiography, geology, and permafrost zones of Canada, showing extent of national railway network, major ports, population centres, and location of study area (after Bostock 2014) onset, rapid retrogressive flow-slides during the fall and winter months. ...
... Elsewhere, drift cover is thicker and surficial materials have a greater influence on slope instability. Large retrogressive rotational-translational earth-debris slides were initially triggered by deep incision of Pleistocene fill in the Thompson River valley during the early Holocene (Clague and Evans 2003). ...
... Regional and local groundwater conditions contribute to high pore pressures and slope instability along the transportation corridor. Since clay impedes groundwater flow, pore pressure increases along the surface of clay layers, resulting in reduced material strength and decreased slope stability (Porter et al. 2002;Clague and Evans 2003). Piezometers on active landslides record upward hydraulic gradients and elevated pore pressures, confirming toe slopes are in a discharge zone of a regional groundwater flow system (Eshraghian et al. 2008;Hendry et al. 2015). ...
The Open Access book series of the International Consortium on Landslides (ICL) aims to be the common platform for the publication of recent progress in landslide research and technology for practical applications and the benefit of society contributing to the Kyoto Landslide Commitment 2020, which is expected to continue up to 2030 and even beyond for the global promotion of understanding and reducing landslide disaster risk as well as the 2030 Agenda Sustainable Development Goals. The contributions include original and review articles, case studies, activity reports and teaching tools for the promotion of understanding
and reducing landslide disaster risks.
... The surficial geology of this valley comprises Quaternary deposits formed by a series of glaciation events separated by episodes of incision and erosion in the Pleistocene sequence. Clague and Evans (2003) identified eight formations overlying andesitic bedrock; four of these units are reported to be present at unstable slopes with Units 6 and 8 found close to uplands ( Fig. 3) (Hendry et al. 2015;Clague and Evans 2003). A weak, highly plastic clay seam at the residual state with friction angles of 9-16 • within Unit 2 accommodates the sub-horizontal basal shear surface of the landslides within the Thompson River valley. ...
... The surficial geology of this valley comprises Quaternary deposits formed by a series of glaciation events separated by episodes of incision and erosion in the Pleistocene sequence. Clague and Evans (2003) identified eight formations overlying andesitic bedrock; four of these units are reported to be present at unstable slopes with Units 6 and 8 found close to uplands ( Fig. 3) (Hendry et al. 2015;Clague and Evans 2003). A weak, highly plastic clay seam at the residual state with friction angles of 9-16 • within Unit 2 accommodates the sub-horizontal basal shear surface of the landslides within the Thompson River valley. ...
Interferometric synthetic aperture radar (InSAR) has gained considerable attention as a landslide monitoring strategy owing to its high accuracy, large coverage, and relatively low associated costs. A crucial drawback of InSAR, however, has limited its further incorporation: one-dimensional estimations along the sensor’s line-of-sight (LOS). This leads to an ambiguity in results and a less intuitive understanding of landslide kinematics. A frequently exercised approach to address this issue has been taking inspiration from the topography to establish compatibility assumptions between velocity components, yet little insight exists on the performance of these methods. The objective of this paper is to investigate the performance of four renowned topography-based methods—Surface Parallel Flow Model (SPFM), SPFM coupled with least-squares method (SPF-LSM), Aspect Parallel Flow Model (APFM), and Steepest Terrain Following Model (STFM)—in evaluating the magnitude and geometry of total velocity vectors. To this end, the analysis is performed on 202 Radarsat-2 and 243 Sentinel-1 scenes acquired over a section of the Thompson River valley, a critical railway corridor in Western Canada traversing 14 landslides. The results indicate that the APFM provides estimations with the lowest magnitude error (15–19 mm/yr or 18.75–23.75% of in situ measurements) compared to the other approaches. SPFM and SPF-LSM are highly sensitive to LOS variance and tend to bias the interpreted vectors toward the north orientation. However, APFM and STFM reflect more realistic aspect angles, with the former inclined to steeper travel angles and the latter suffering from erratic upward travel angles due to local topographies.
... Landslides along a ten-kilometre stretch of the Thompson River valley between Ashcroft and Spences Bridge (Fig. 1b) have negatively impacted critical railway infrastructure, arable land, fisheries, and other natural resources since the 1880s (Fig. 1b). In the late nineteenth century, prehistoric mass movements reactivated as sudden onset, rapid retrogressive flow-slides during the fall and winter months at a time when terraces were intensively irrigated for agricultural land use, and toe slopes were incised and over-steepened during railway construction (Stanton 1898;Clague and Evans 2003). ...
... This standardized process was time-consuming and data-intensive, requiring weeks to months of desktop processing to yield meaningful outputs. Historical activity of slow-moving landslides of the Thompson with potential to negatively impact national railway infrastructure, operational services, the environment, local communities, and national economy (after Clague and Evans 2003). c Landslides of concern determined from InSAR results for the Thompson River valley, showing CN and CP tracks (solid black lines); RADARSAT-2 average linear displacement rate rastered at 3 cm year −1 , with purple polygons delimiting 4-sigma confidence levels (modified from Huntley et al. 2021c). ...
This International Programme on Landslide (IPL) Project 202 paper presents a scalable remote piloted aircraft system (RPAS) platform that streamlines unoccupied aerial vehicle (UAV) flight operations for data capture, cloud processing and image rendering to inventory and monitor slow-moving landslides along the national railway transportation corridor in southwestern British Columbia, Canada. Merging UAV photogrammetry, ground-based real-time kinematic global navigation satellite system (RTK-GNSS) measurements, and satellite synthetic aperture radar interferometry (InSAR) datasets best characterizes the distribution, morphology and activity of landslides over time. Our study shows that epochal UAV photogrammetry, benchmarked with periodic ground-based RTK-GNSS measurements and satellite InSAR platforms with repeat visit times of weeks (e.g., RADARSAT-2 and SENTINEL-1) to days (e.g. RADARSAT Constellation Mission) provides rapid landslide monitoring capability with cm-scale precision and accuracy.
... Irrigation-induced landslides have also been documented in California due to the irrigation of avocado fields (Knott 2008). Historical slides, like an ancient landslide in British Columbia, have also been attributed to the effects of irrigation (Clague and Evans 2003). ...
Water table rise near a cliff may trigger a landslide due to the associated increase pore pressure and decrease in frictional resistance. One main cause of water table rise is intense irrigation for agriculture in arid and semi-arid regions. One such case is in Majes, southern Peru, where a landslide has evolved near an intensively irrigated agricultural area. Mitigation strategies for landslides exist, such as physical strengthening of the cliff, but can be expensive. We describe a groundwater management approach to reduce the pore pressure in the vicinity of the cliff to either slow the propagation of an existing landslide or prevent the initiation of a new landslide. A 3D numerical groundwater flow model was built for the Majes area which employs the limited data existing on the local hydrogeology. Simulations were run to understand the connection between the hydraulic properties and the water table level change due to irrigation and pumping. Results show that through a series of pumping wells near the cliff edge, the pore pressure can be decreased effectively. Moreover, decreasing the water table via pumping can be accomplished in 25–35% of the time it took to elevate the water table level by irrigation. In addition, the pumping can capture water that could be reused for irrigation. Thus, based on our analysis, we conclude that wells could provide a groundwater management approach that keeps the pore pressure at low levels to mitigate landslide processes and simultaneously supplies water for irrigation existing and future irrigation-heavy agriculture in semi-arid environments.
... In addition to these sudden catastrophic landslides, the reactivation and destabilization of large-scale ancient landslides can also pose significant hazards (Clague 2003;Iverson et al. 2015;Macciotta et al. 2016;Guo et al. 2020). Landslide reactivation can be induced by many complex factors, such as active tectonics, rainfall, river erosion, and human engineering activities (Brideau et al. 2009;Burda et al. 2013;Carlini et al. 2016). ...
The ancient Woda landslide, located in the upper Jinsha River, China, is a reactivated landslide that poses a potential risk of further instability and river blockage. In this study, we evaluated and modeled the reactivation characteristics, potential instability, dynamic runout, and resulting dam stability of the Woda landslide. Our results show that the landslide is currently experiencing creep, although accelerated deformation is occurring locally. The presence of two sliding zones suggests the potential reactivation of the landslide through a progressive failure mechanism along either a shallow or deep sliding zone. Under these two scenarios, the Woda landslide would form a dam and block the Jinsha River, with maximum modeled runout distances of approximately 1800 and 2110 m, and dam heights of approximately 25 and 62 m, respectively. The resulting backwater areas would reach upstream distances of approximately 13 and 30 km, and the maximum modeled peak flood discharge following a breach scenario would be 2772 and 5102 m³/s, respectively. These results provide an important reference for predicting and managing large geological disaster chains in the upper Jinsha River Basin.
In this paper, we evaluate the effectiveness of four land-deformation measurement techniques for monitoring slow-moving landslides along a high-risk section of the national railway corridor traversing the Thompson River valley, British Columbia, Canada. The geomorphically active North Slide acts as an ideal field laboratory for testing and evaluating novel monitoring techniques and methods. We compare differential processing of Structure from Motion (SfM) products such as point-cloud elevation models and orthophotos derived from Remotely Piloted Aircraft Systems (RPAS), along with satellite based Interferometric Synthetic Aperture Radar (InSAR) deformation measurements derived from RADARSAT Constellation Mission (RCM). These results are ground-truthed with periodic real-time kinematic (RTK) global navigation satellite system (GNSS) measurements. We evaluate point-cloud comparison techniques, including the multi-scale model-to-model cloud comparison (M3C2) algorithm and digital ortho image correlation techniques. Multi-temporal RCM InSAR deformation measurements are processed using a semi-automated processing system for interferogram generation and unwrapping. Manual processing of small baseline subsets (SBAS) leads to the recovery of 1-dimensional line-of-sight (LoS) and 2-dimensional deformation measurements. Lastly, we discuss the strengths and limitations of these techniques, considerations for interpreting their outputs, and considerations for direct comparisons between InSAR, RPAS and RTK-GNSS deformation measurements.
Water erosion is a much-studied and long-continued phenomenon. This chapter includes data on long-term rates of erosion and sedimentation, and examines the many factors that lead to increasing rates of erosion, including deforestation and other land use changes, harvesting, land levelling, tillage, grazing by domestic stock, irrigation, fire, and urbanisation and construction. One consequence of erosion is the formation of gully systems. Soil conservation measures have been introduced to reduce the erosion menace. Humans have also destabilised slopes and have accelerated the occurrence of various types of mass movement.
Thick Quaternary sediments at Quesnel, British Columbia, provide a record of the late Quaternary history of an area near the centre of the former Cordilieran Ice Sheet. These sediments, in part, fill stream valleys that were cut sometime prior to the Late Wisconsinan Fraser Glaciation. Of special note are (1) fluvial or glaciofluvial sand and gravel deposited by aggrading streams, perhaps in part during early Fraser time; (2) thick glaciolacustrine mud, sand, and diamicton laid down later as glaciers advanced across central British Columbia; and (3) glaciolacustrine sediments similar to (2), but deposited in an ice-dammed lake at the end of the Fraser Glaciation. The stratigraphy is punctuated by colluvial deposits that are products of landslides from valley walls at various times during the late Quaternary; this process continues to the present. During the Fraser Glaciation, glaciers from the Coast and Cariboo Mountains coalesced and flowed north over central British Columbia. Fraser Glaciation advance sediments and older Pleistocene deposits were partially removed by this ice sheet and the eroded remnants mantled with till. At the end of this glaciation, the Cordilieran Ice Sheet downwasted and receded southward along an irregular front across the study area. Large amounts of sediment were deposited in glacial lakes dammed by the southward-retreating ice. With complete déglaciation of the interior, glacial lakes drained and the present drainage system was established. At first, valleys were partially aggraded with sand and gravel, but later, streams dissected valley fills to produce a series of terraces at successively lower levels.
Several large landslides are located along Thompson River valley between the towns of Ashcroft and Spences Bridge, British Columbia. Initiation and landslide activity was attributed to irrigation practices by early observers. Recent investigations conducted for the Canadian National and Canadian Pacific Railways have identified at least four other factors controlling stability and ongoing landslide activity: the presence of thick, high plastic glaciolacustrine clays underlying younger glacial tills and glaciolacustrine silts; ongoing bank erosion and channel degradation of Thompson River; artesian groundwater pressures, possibly influenced by increasing precipitation levels; and a delayed pore pressure response to falling river levels in late summer and early fall.
Glaciation is schematically considered as a perturbation of "normal" fluvial conditions. Drift is unstable in a proglacial or postglacial fluvial environment, resulting in heightened sediment movement that continues as long as drift material remains easily accessible for fluvial erosion and transportation. Sediment yield bears no relation to concurrent primary production of weathered debris. Examples of such "paraglacial" denudation and sedimentation are reported from two contrasting areas. Postglacial valley alluvial deposits are widespread in central Baffin Island where rapid sedimentation continues today; estimated denudation rates are an order of magnitude higher than in comparable unperturbed areas. In south-central British Columbia, rapid sedimentation during the paraglacial period contrasts sharply with present-day conditions.
Slope stability analyses carried out in terms of effective stress require an understanding of the distribution of pore-water pressures in a slope. This understanding must be based on a knowledge of the groundwater flow system, which is in turn dependent on the regional geologic environment and the configuration of hydraulic conductivity contrasts. This paper presents several computer simulations of flow systems in a variety of hypothetical slopes. Results show that the presence of low-conductivity units at the surface or at depth can be extremely detrimental to stability, particularly if they confine units of higher conductivity. The contrast in conductivity need not be more than two orders of magnitude. Such situations are common in thrust blocks, interbedded sedimentary rocks, weathering profiles, and deformed metamorphic rocks. Groundwater conditions critical to stability arise in anisotropic formations, where the axis of maximum conductivity is parallel to the dip of the slope. Fluctuations in regional flow systems can be critical to the stability of unconsolidated, terraced sediments.
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