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Longevity of dams from landslides with sub-channel rupture surfaces, Peace River region, Canada

Longevity of dams from landslides with sub-channel rupture surfaces, Peace River region, Canada Background: We examined seven landslide dams and their changes over time in the Peace River region of Canada. These landslides had subchannel rupture surfaces in glacial and glaciolacustrine sediments. We assessed the stability of the dams using 6 separate, morphometric-based stability indices (with a total of 10 stability thresholds). Results: The landslides caused the streambeds to be elevated from 4 to 30 m forming the dams. The landslide lakes diminished in size over one to several years through stream incision into the dams and sediment infilling. The longest-lived dam persisted for up to 20 years. For two dams, incision into the dams lowered the lake levels by about half of the total depth, while the remainder of the water in the basins was displaced by sediment infilling. After the lakes drain, the sediment accumulations behind the dams can persist for decades. The stability analyses overpredicted unstable conditions which is inconsistent with the observed longterm persistence of the dams. Conclusions: The landslide dams in our study were relatively stable. Their lakes persisted for up to 2 decades and diminished over time through a combination of slow incision and basin infilling. The stability indices we assessed overpredicted unstable conditions and thus would require modification for these particular types of dams in this regional setting. Keywords: Landslide, Dam, Stability, Peace River, Quaternary, Sediment Background Fletcher et al. 2002) and the Halfway River dam Large landslides in Quaternary sediments are common- (Bobrowsky and Smith 1992) lasted for a few hours). place in the Peace River regions of Alberta and British Here we examine seven landslide dams on small tribu- Columbia (Geertsema et al. 2006; Miller and Cruden taries of the Peace River, including: the Eureka River 2008), and many of the landslides create dams which dam (Miller 2000; Miller and Cruden 2001, 2002, 2008, disrupt streamflow, damage timber, and threaten infra- 2014), the Fox Creek dam (Kim et al. 2010), the Hines structure both downstream and upstream. Creek dam (Lu et al. 1998; Miller and Cruden 2001, On smaller streams, with narrow valleys, large land- 2008), the Montagneuse River dam (Cruden et al. 1997; slides tend to fully obstruct the valleys, creating lakes Miller and Cruden 2008), the Pouce Coupe River dam that can persist for decades (Lu et al. 1998; Miller and (British Columbia 2014), the Saddle River dam (Cruden Cruden 2001, 2002, 2008, 2014; Geertsema and Clague et al. 1993; Alberta 1997; Miller and Cruden 2001, 2008, 2006, 2008). In contrast, regional dams on the larger 2014), and the Spirit River dam (Miller 2000; Miller and systems are generally short-lived (for example, the Cruden 2001, 2008, 2014) (Fig. 1). Attachie dam on the Peace River (Evans et al. 1996, We classified landslides according to Cruden and Varnes (1996) and landslide dams according to Costa and Schuster (1988), where six dam types are described: I) Partial, II) * Correspondence: brendan.miller@gov.bc.ca Complete, III) Divergent, IV) Convergent, V) Multi-lobed, British Columbia Ministry of Forests, Lands, Natural Resource Operations and and VI) Uplifted (from Cruden and Van Dine 2013). The Rural Development, 499 George Street, Prince George, BC V2L 1R5, Canada landslide dams we describe are all Type VI. Type VI dams Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 2 of 14 Fig. 1 Locations of the landslide dams. The regional topography was generated using digital topographic data from Natural Resources Canada (licenced under the Open Government Licence – Canada). The Peace River region is a broad, gently sloping plain which is deeply dissected by Holocene streams. The inset map shows the general study location (green box) in relation to the boundaries of the provinces of Alberta and British Columbia, Canada form when a landslide’s rupture surface extends under a (Atkinson and Paulen 2010, Morgan et al. 2012, and stream channel, and emerges on the opposite valley side references therein, Fig. 2). from the landslide, causing the channel to be displaced up- The five major LTAs, from highest (youngest) to lowest wards and the stream flow to be impeded (Costa and (oldest), can be summarized as follows: Schuster 1988). We have assessed dam stability using 6 separate in-  LTA5 retreat phase glaciolacustrine sediment; dices (with a total of 10 stability thresholds) based on  LTA4 glacial sediment (including till); watershed and dam morphometric attributes (from:  LTA3 advance phase glaciolacustrine sediment; Canuti et al. 1998; Casagli and Ermini 1999; Ermini  LTA2 massive sands (with bone dates of 25.1 ka BP); and Casagli 2003; Korup 2004; Tacconi Stefanelli et al. and 2015, 2016, 2017). This assessment tests the applic-  LTA1 preglacial sands and gravels (with wood dates ability of these indices and thresholds on these dams, between 43.5 and 27.4 ka BP). in our regional setting. The aims of this paper are to describe the landslide This stratigraphy records the up-valley advance of the dams, the evolution of the dams and their lakes over Laurentide Ice Sheet and subsequent down-valley ice front time, and to test various dam stability indices. retreat, and the preceding non-glacial intervals (Hartman and Clague 2008). These events filled the pre-glacial top- Setting and stratigraphy ography with up to 200 m of Quaternary sediment. General description Our Peace River study area is situated on a flat to rolling Stratigraphy, erosion, and landslides dissected plain, located east of the Rocky Mountains, in The distribution of deep-seated landslides correlates northeastern British Columbia and northwestern Alberta with the location of buried pre-glacial valleys of the an- (Fig. 1). The Peace River and its tributaries dissect glacial cestral Peace River and its tributaries. The ice- advance- and non-glacial sediments as well as shale and sandstone phase glaciolacustrine (LTA3, Fig. 3) sediment has been bedrock (Holland 1976; Morgan et al. 2012). The area has recognized as a prominent décollement plane for several a continental climate, characterized by warm, wet sum- deep-seated failures (Cruden et al. 1993, 1997; Miller mers and cold, dry winters (Foord 2016). 2000; Miller and Cruden 2001, 2002; Geertsema et al. Previous work in the region has determined the 2006; Kim et al. 2010; Morgan et al. 2012). Quaternary stratigraphy of the Peace River and its Figure 2 plots variable valley slopes (normal to valley tributaries (Bayrock 1969; Fenton 1984; Liverman et al. axis) against the regional stratigraphy for segments of 1989; Catto et al. 1996; Hartman and Clague 2008), Clear and Eureka rivers, and the Saddle and Spirit rivers. with recent studies generalizing the sedimentary suc- The top of the plots represent the valley slope angles asso- cession into five major lithotype assemblages (LTAs) ciated with stream incision into the uppermost Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 3 of 14 Fig. 2 Generalized stratigraphy found within buried preglacial valleys in the Peace River lowlands (right; modified after Morgan et al. 2012), and (left) average valley slopes of the lower Clear River (to the Eureka River) and the Eureka River (blue), and the lower Saddle River (to the Spirit River) and the Spirit River (red). Five of the landslides described appear be associated with ice-advance -phase glaciolacustrine sediment (LTA3), and two with the lower portion of the glacial sediments (LTA4). The valley slopes appear to reflect the stratigraphy. The slopes are lowest where the rivers are incising through LTA3 or LTA5, and steepen where the river incises into LTA4. Note that thickness of LTA4 has been exaggerated in this diagram, as the diamict is not topography constrained and will impact the valley slope response to incision over a longer distance than the unit thickness would otherwise suggest Fig. 3 Upthrust advance phase glacial lacustrine sediment (LTA3) at the toe of the Eureka River landslide. The reorientation of the lacustrine rhythmites to near vertical, was likely caused by the landslide. Note the scattering of boulders and cobbles at discrete locations. This material likely originated in the pre-landslide channel and was introduced into the post-landslide channel by bank erosion. Also note the small landslide into the channel in the distance. (Source: BGN Miller, September 28, 2007) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 4 of 14 sedimentary unit, at the upper reaches of the streams; Eureka River landslide dam whereas, the bottom of the plots represent slope angles The Eureka River landslide (Fig. 5) was an enlarged trans- from stream incision through the entire sedimentary se- lational earth slide with an estimated volume of 50Mm quences. Postglacial stream incision through the strati- (Miller 2000; Miller and Cruden 2002). The landslide oc- graphic sequence in Fig. 2 may have progressed as follows: curred sometime between 28 October 1989 and 28 March 1990, based on bracketing Landsat 5 Thematic Mapper Initial incision through the uppermost glaciolacustrine images. The landslide’s rupture surface, in advance phase sediments (LTA5), resulting in slope angles from 5 to glaciolacustrine sediment (LTA3), extended beneath the 10 degrees. streambed causing it to be elevated by approximately Subsequent incision into the more stable glacial 20 m, creating a Type VI landslide dam. sediment (LTA4), resulting in slope angles of up to The old channel was abandoned and a new channel 18-degrees. formed around the toe of the landslide. Initially, coarse Further incision into the advance-phase glaciolacustrine alluvium was generally absent in the new channel, allow- sediment (LTA3), where slopes decrease to as low as 6 ing for rapid stream incision to occur - up to 20 m in a degrees. decade near the centre of the landslide. This rapid inci- Final incision into the lower fluvial units (LTA1 and 2) sion promoted extensive instability from both banks, and into bedrock, where slopes increase to near 10 and reintroduced coarse alluvium (cobbles and boulders) degrees. from the pre-slide channel into the new channel (Fig. 3). This coarse material however, had a short residence time in the channel and was quickly mobilized downstream, Methods leaving the channel base unprotected. We described the landslides and landslide dams using in- Following an initial lake length of about 7 km (1990), formation predominently from previous studies and gov- the lake began to get progressively smaller as a result of ernment reports. We used aerial and satellite imagery, slow dam incision (Table 2). Incision was slowed when the coupled with field observations, to measure and post landslide channel encountered the uplifted pre- characterize the changes in the landslide dams and lakes landslide channel, near the upstream edge of the landslide over time. We analysed lidar data in a Geographic Infor- dam. After about 20 years the lake ceased to exist from a mation System (GIS) to determine the amount of stream combination of sedimentary infilling and dam incision. A incision into the dams and the depths of basin sediment lidar-generated longitudinal profile of Eureka River shows infilling. For the dam stability analyses, we used indices approximately 8 m of sediment accumulation occurred drawn from literature and compared the results to the ob- within the landslide lake basin (Fig. 6). As the landslide served behaviours. We derived morphometric attribute dam height was estimated to be 20 m, incision into the values for the stability analyses from Natural Resource dam lowered the lake by approximately 12 m, whereas Canada digital elevation data and LiDAR data in a GIS. sediment infilling of the basin amounted to 8 m. Results Fox Creek landslide dam Peace River regional landslide dams The May 5, 2007 Fox Creek landslide was a rapid transla- The following provides a description of seven landslide tional block slide involving about 47Mm of Quaternary dams and their development over time (Tables 1 and 2, sediments (Kim et al. 2010; Fig. 7). The basal rupture sur- Fig. 4). face of the landslide, in advance-phase glaciolacustrine Table 1 Landslide and landslide dam attributes Landslide year Landslide Volume (Mm ) Dam Height (m) Dam Width (m) Lake Duration (years) Eureka River 1989–90 50 20 1000 <20 Fox Creek 2007 47 19 1700 >10 Hines Creek 1990 X 25 120–150 <7 Hines Creek Pre-1952 48 X 1000 X Montagneuse River 1939 78 30 X X Pouce Coupe River 2013 1–3 4 170 <1 Saddle River 1990 39 24 800 <17 Spirit River 1995 20 9 X >18 Notes: X = No Data Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 5 of 14 Table 2 Changes in the landslide lakes lengths over time with data sources and approximate ground resolution indicated Date Lake Length (km) Source Data Resolution (m) Eureka River Sep 29, 1990 7 Landsat 5 Thematic Mapper 30 Oct 6, 1992 6 Alberta Air Photo AS4892, 148 1 Sep 1, 1997 2.9 Alberta Air Photo AS4892, 148 1 Aug 1999 1.7 Field Survey NA Aug 25, 2006 0.7 Alberta Air Photo AS5379B, 15 1 May 28, 2009 0.1 RapidEye 3–5 Jun 7, 2009 0 RapidEye 3–5 Fox Creek 28 Aug, 2007 1.6 Landsat 7 Enhanced Thematic Mapper 30 Jun 17, 2010 1.1 RapidEye 3–5 May 15, 2011 1 RapidEye 3–5 Sep 17 2012 1 Digital Globe 0.5 Sep 19, 2013 0.8 Digital Globe 0.5 Jul 4, 2014 0.6 RapidEye 3–5 Jun 3, 2015 0.6 RapidEye 3–5 May 23, 2016 0.1 RapidEye 3–5 Jun 10, 2017 0.1 RapidEye 3–5 Hines Creek Jun 25, 1991 1.7 Landsat 5 Thematic Mapper 30 Jun 14, 1992 1.5 Landsat 5 Thematic Mapper 30 Aug 17, 1992 1.4 Alberta Air Photo AS4314–251 1 Jun 26, 1993 1.5 Landsat 5 Thematic Mapper 30 Jun 20, 1994 1.2 Landsat 5 Thematic Mapper 30 Jun 16, 1995 1.0 Landsat 5 Thematic Mapper 30 Jun 25, 1996 0.9 Landsat 5 Thematic Mapper 30 Oct 8, 1996 0.7 Landsat 5 Thematic Mapper 30 Apr 18, 1997 0 Landsat 5 Thematic Mapper 30 Pouce Coupe River Aug 23, 2013 2.0 RapidEye 3–5 Sep 3, 2013 2.0 Landsat 8 Operational Land Imager 30 Sep 12, 2013 2.0 Landsat 8 Operational Land Imager 30 Oct 13, 2013 2.0 Landsat 7 Enhanced Thematic Mapper 30 Apr 8, 2014 0 Landsat 8 Operational Land Imager 30 Saddle River Mar 30, 1991 5.7 Landsat 5 Thematic Mapper 30 Sep 19, 1995 2.8 Alberta air photo AS4680–33 1 Sep 17, 2001 1.0 Alberta air photoAS5194B-40 1 May 2, 2005 0.5 Landsat 7 Enhanced Thematic Mapper 30 Aug 13, 2006 0 Alberta air photo TRSG0602–1536 1 Spirit River Sep 19, 1995 2.1 Alberta Air Photo AS4680–32 1 Jul 1999 0.7 Field Survey NA Sep 19, 2013 0.3 Digital Globe 0.5 Notes: 1 – objects on the ground of less than 1 m can be recognized using film-based air photos Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 6 of 14 Eureka Saddle Hines Spirit Pouce Coupe Fox 0 5 10 15 20 25 Years Since Dam Formation Fig. 4 Changes in the lengths of 6 landslide lakes over time, since the formation of the landslide dams. The data used to derive these curves forms Table 2. The lake lengths go to unity through a combination of incision into the landslide dams and sediment infilling of the basins sediment (LTA3), extended beneath Fox Creek, causing sediment (LTA4). The landslide formed a Type VI land- the stream bed to be elevated and creating a Type VI land- slide dam, with an estimated height of 25 m dam, and a slide dam (Kim et al. 2010). The abandoned, pre-landslide lake length of 1.5 to 1.7 km (Lu et al. 1998). stream bed was evident at the toe of the slope. The 1990 Hines Creek landslide occurred on the oppos- The landslide dam was a maximum of 19 m in height, ite valley wall of a much larger landslide. This larger land- with a width of 1.7 km (Kim et al. 2010). The largest of slide predates the earliest provincial aerial photographic the resultant lakes extended upstream beyond the east coverage of the site, in 1952. Lu et al. (1998) speculate that flank of the landslide for approximately 1.5 km. Two the pre-1952 landslide was a major contributing factor to smaller lakes formed atop the landslide debris. An ana- the occurrence of the 1990 landslide, as it directed the lysis of 2 m Alberta lidar data, collected on October 22, stream into the opposite valley wall, causing undercutting 2013, shows the stream’s longitudinal profile having not of the slope. They estimated the volume of the pre-1952 substantially recovered from the landslide event (Fig. 8). landslide to be 48Mm . An extensive sedimentary deposit formed upriver of the pre-1952 landslide, which persisted Hines Creek landslide dam until at least 1988 (Alberta air photo AS3729–88). The Hines Creek landslide occurred between June 9th and June 25th, 1990 (based on Landsat 5 Thematic Montagneuse River landslide dam Mapper bracketing dates) and was a reactivated, retro- The April 1939 Montagneuse River landslide was a reacti- gressive earth slide, with a rupture surface in glacial vated, retrogressive earth slide that moved in translation Fig. 5 Oblique perspective of the Eureka River landslide and dam, using a Digital Elevation Model derived from lidar data (dated September 26, 2013; source: Government of Alberta, reproduced with permission), at 2-times vertical exaggeration. The lidar data was collected approximately 4 years after the landslide lake had drained. The red polygon delineates the landslide colluvium, and the black hatched line delineates the landslide’s main scarp. The yellow polygon delineates an area of thick lacustrine sediment accumulation (up to 8 m), deposited within the landslide lake basin. The blue line traces the post-landslide dam Eureka River. The scale bar is accurate at the downstream (proximal) edge of the landslide colluvium Lake Length (km) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 7 of 14 Fig. 6 Plan view and channel longitudinal profile of the lower Eureka River, generated from lidar data (dated September 26, 2013; source: Government of Alberta, reproduced with permission). The red line (cross-section) roughly follows the longitudinal profile of the lower Eureka River (below the landslide). The grey area situated above red line indicates areas of lacustrine and deltaic sedimentation upstream of the landslide dam (Cruden et al. 1997). The landslide’s rupture surface, in ad- Pouce Coupe River landslide dam vance phase glaciolacustrine sediment (LTA3), extended ThePouce Coupe River wasdammedbyalandslide under the channel creating a Type VI landslide dam on August 21, 2013. The landslide originated from (Cruden et al. 1997, Fig. 9). The estimated height of the the east bank of the river, approximately 210 m dam was 30 m. Anecdotal information indicates that the downstream from theLandryBridge(Fig. 10).The dam stopped the flow in the river for about 2 weeks, caus- landslide caused the river bed to be elevated by ap- ing a 4 km lake to form. proximately 3.8 m, forming a Type VI landslide dam By June 15, 1945, the lake had drained (Canada air photo (Fig. 11). An Environment Canada water monitoring A8108, 23–25). Cruden et al. (1997) mapped lacustrine de- station, located immediately downstream from the posits extending about 1.5 km upstream of the landslide Landry Bridge, recordedthe backingupofthe river dam using 1952 aerial photographs. They noted that by over a 2.5 day period (British Columbia 2014). Fol- 1988, the sedimentary deposit had been eroded away. lowing the landslide, a new channel formed across a Fig. 7 Oblique air photo of the 2007 Fox Creek landslide, dam and lake, looking upstream. Note that much of the timber atop the landslide remained upright. (Source: Alberta Geological Survey, 2009; reproduced with permission) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 8 of 14 Fig. 8 Plan view and channel longitudinal profile of Fox Creek, generated from 2 m lidar (dated October, 22, 2013; source: Government of Alberta, reproduced with permission). The black hatched line traces the landslide’s main scarp. A continued, pronounced effect of the landslide dam on the longitudinal profile of the stream is evident point bar attached to the opposite stream bank. A encountered the pre-landslide channel alluvium (Cruden British Columbia, Ministry of Transportation and In- et al. 1993). The alluvium was later bypassed when the frastructure field investigation of the dam on August channel widened (Hansen 1994). Continued incision into 22, 2013 determined that there was no imminent the dam was accompanied by progressive shortening of threat to the bridge or road infrastructure, and no the lake (Table 2, Figs. 12, 13). By August 13, 2006, the mitigative action was taken. lake had fully drained. A longitudinal profile of the Saddle River, derived from Saddle River landslide dam the 2 m lidar data (dated October 22, 2013, Fig. 14), re- The June 1990 Saddle River landslide (Fig. 12) was a vealed approximately 14 m of sediment accumulation reactivated, retrogressive earth slide (Cruden et al. 1993). within the landslide lake basin. Therefore, incision into The landslide rupture surface, in advance phase glaciola- the dam amounted to 10.5 m. A bathymetric survey of the custrine sediment (LTA3), extended under the Saddle basin, which ceased 7.25 years after the landslide in River, causing the streambed to be displaced southwards September 1997, recorded a final water depth of 14.8 m by 60 m and upwards by approximately 24.5 m, creating (Alberta 1997, Fig. 13). Beyond this time, very little further a Type VI landslide dam (Cruden et al. 1993; Alberta incision into the dam occurred despite the basin 1997). The volume of water retained behind the dam remaining flooded for up to another 9 years (August was estimated at approximately 4Mm (McClung and 2006; Table 2). Weimer 1990). Overtopping of the dam began during the annual spring Spirit River landslide dam freshet of 1991 (Hanson 1994; Fig. 13), when a new chan- The July 1995 Spirit River landslide was a reactivated and nel formed at the toe of the landslide. Incision was slowed retrogressive earth slide that moved southwards by transla- near the upstream edge of the dam, where the stream tion (Miller 2000). The emerging rupture surface at the toe Fig. 9 Cross-section of the Montagneuse River landslide and dam. (Modified from Cruden et al. 1997) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 9 of 14 Fig. 10 Oblique aerial image mosaic of drone imagery, from June 2017, draped over a photogrammetrically generated digital elevation model depicting the Pouce Coupe River, and Landry Road and bridge (Source: Government of British Columbia; reproduced with permission). The 2013 landslide and dam are visible in the lower left. The approximate trace of the pre-landslide Pouce Coupe River channel is the blue line. The post-landslide stream channel cut through a point bar attached to the opposite stream bank, abandoning the pre-landslide channel of the landslide was bounded above and below by glacial At its maximum, the large lake was approximately sediment (LTA4); however, as the rupture surface was 2100 m long and 9 m deep (Miller 2000). The lake was trending upwards, it may have extended into underlying impounded behind a pressure ridge that formed at the glaciolacustrine sediment (LTA3). An Alberta aerial photo- toe of the landslide. Our 1999 field survey found coarse graph (Table 2), taken about 2 months after the landslide, alluvium was absent along much of the post-landslide shows a large lake upstream of the landslide and three channel, with the exception being just downstream of smaller lakes along the length of the landslide. Our field the large landslide lake, where the post-landslide channel survey in July 1999 found that the 3 smaller lakes had encountered the coarse alluvium of the pre-landslide drained; thus, these lakes lasted for less than 48 months. channel. This alluvium appears to be slowing drainage of Fig. 11 The 2013 Pouce Coupe River landslide and dam, captured at the Landry Road bridge, looking downstream. The yellow polygons delineate uplifted channel alluvium. (Source: British Columbia Ministry of Transportation and Infrastructure, August 22, 2013; reproduced with permission) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 10 of 14 Fig. 12 The Saddle River landslide and dam. a. Digital Elevation Model derived using 2 m lidar data (dated October 22, 2013; source: Government of Alberta, reproduced with permission) showing the 1990 landslide colluvium (outlined in red) and mainscarp (black). b. The landslide lake in July 1999. Note the drowned timber within the landslide dam basin. (source: BGN Miller, July 1999.) c – e. Time series of aerial photographs showing the landslide dam lake in September 1995 and 2001, and the drained basin in August 2006 (air photos AS4680–33, AS5194B-40, and TRSG0602–1536 respectively; source: Alberta Environment and Parks, Air Photo Distribution, Copyright Government of Alberta, reproduced with permission). The white dot in d indicates the photograph location of b the lake. Digital Globe imagery, dated September 19, A landslide dam is considered unstable when it “has 2013, shows the lake continues to persist. undergone erosion or collapse leading to a catastrophic breach, with the subsequent release of the impounded lake Stability analysis waters” (Ermini and Casagli 2003; p.32). Landslide dams Here, we test the ability of landslide dam stability indices are considered stable when they have not undergone a from the literature to predict the observed behavior of catastrophic breach and upstream lakes or infilled basins our studied Type VI landslide dams. The stability indices remain in place (e.g. Costa and Schuster 1988; Ermini and we used are based on morphometric parameters (Canuti Casagli 2003; Korup 2004; Tacconi Stefanelli et al. 2016). et al. 1998; Casagli and Ermini 1999; Ermini and Casagli We consider dams to be stable when the hazard of a cata- 2003; Korup 2004; Tacconi Stefanelli et al. 2016). Table 3 strophic breach is low. lists the indices we assessed. Table 4 provides dam and The calculated stability values for the described land- watershed morphometric parameters for each of the slide dams are presented in Table 5. For these assess- landslide dams. ments, we use a dam volume equaling 10% of the 6 30 5 25 Lake Length 4 20 Depth 3 15 2 10 1 5 0 0 02468 10 12 14 16 18 Years Since Dam Formation Fig. 13 Changes in the length and depth of Saddle River landslide lake since formation in June 1990. The depth data was derived from a bathymetry survey (Alberta 1997). The initial increase in the lake depth records basin flooding prior to the dam being overtopped Lake Length (km) Depth (m) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 11 of 14 Table 3 Landslide dam stability assessment indices assessed against the recorded behaviour of the Peace River regional landslide dams Indices Formula Published Thresholds Reference and Region Applied Unstable Uncertain Stable Blockage B = log(V /A)<4 4–5 > 5 Canuti et al. 1998; Casagli and Ermini 1999 (Italy) I D C Impoundment I = log(V /V ) < 0 > 0 Casagli and Ermini 1999 (Italy) I D L < 1 > 1 Korup 2004 (New Zealand) Dimensionless Blockage DBI = log(A H /V ) > 3.08 2.75–3.08 < 2.75 Ermini and Casagli 2003 (world-wide) C D D >5 3–5 < 3 Korup 2004 (New Zealand) > 3.98 2.43–3.98 < 2.43 Tacconi Stefanelli et al. 2016 (Italy) Backstow I = log(H /V)< −3 −3 - 0 > 0 Korup 2004 (New Zealand) S D L Relief I = log(H /H)< −1> −1 Korup 2004 (New Zealand) R D R Hydromorphologic HDSI = log(V /A S) < 5.74 5.74–7.44 > 7.44 Tacconi Stefanelli et al. 2016 (Italy) D C < 5.26 5.26–8.07 > 8.07 Tacconi Stefanelli et al. 2017 (Peru) landslide volume (V becomes V in Table 3). Based on (2003). Thus the indices are over-predicting unstable D D10 cross-sectional profiles through the described landslides conditions. and dams, we found that only approximately 10% of the landslide volume goes into forming the dams. Figure 9 Discussion provides an example of the typical landslide and dam con- Each of the landslides we described had a basal rupture figuration in the Peace River region. Figure 9 shows that surface within the advance phase glaciolacustrine sedi- only a very small portion of the landslide is involved in the ment (LTA3) or near the base of the glacial sediment stream obstruction, with most of the landslide remaining (LTA4). The rupture surfaces extended under the chan- out of the valley bottom. nels causing the channels to be elevated, forming Type The assessments produced 43 unstable, 19 uncertain, VI landslide dams. Type VI landslide dams appear to be and 5 stable results. As these dams have not breached common in the Peace River region, based on our field catastrophically, but rather continued to impound an observations. In contrast, Type VI dams represent only existing or relict lake, they could not be considered 3% of the dams in Costa and Schuster’s (1988) world- unstable using the definition of Ermini and Casagli wide database of 184 dams. Fig. 14 Plan view and channel longitudinal profile of the Saddle River, generated from 2 m lidar data (dated October 22, 2013; source: Government of Alberta, reproduced with permission). The longitudinal profile extends from near the Peace River to approximately 4 km upstream of the landslide dam. The red line roughly follows the longitudinal profile of the lower Saddle River (below the landslide). The grey area situated above red line indicates areas of sedimentation upstream of the landslide dam Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 12 of 14 Table 4 Morphometric parameters of the Peace River regional landslide dams Attribute Units Symbol Landslide Dam Eureka Fox Hines Montagn. Pouce C. Saddle Spirit Landslide volume Mm V 50 47 48 78 2 39 20 Dam volume Mm V 5.0 4.7 4.8 7.8 0.2 3.9 2.0 D10 Dam height m H 20 19 25 30 4 24 9 Lake volume Mm V 11 1.2 1.2 0.34 4 0.26 Catchment area km A 1200 362 1055 95 2860 889 278 Relief upstream m H 510 213 296 373 478 429 254 Highest elevation in catchment m E 1075 750 910 930 1015 1010 820 max Elevation dam crest m E 526 494 535 510 537 502 520 min Longitudinal channel slope ° S 0.2 0.2 0.2 0.2 0.1 0.2 0.2 The landslide lakes diminish over several years through water was displaced by predominantly deltaic sediment a combination of fluvial incision into the dams and deltaic infilling of the basin. For the 20 m Eureka River landslide and lacustrine sediment infilling of the basins. For the dam, incision brought the lake level down by 12 m, while 24.5 m high Saddle River landslide dam, incision into the basin infilling amounted to 8 m. dam lowered the lake level by 10.5 m, while 14 m of sedi- The rate of incision into the dams is known to be ment infilling into the basin displaced the remaining related to a number of factors including material type. water. At the Saddle River landslide dam, the draw-down The fine textured glaciolacustrine sediments (LTA3) of the lake level due to incision was initially more rapid tend to erode readily, but the incision may be slowed (Fig. 13); however, after 7.25 years, when the last bathy- where the contemporary channel encounters the imbri- metric survey was conducted, almost no further incision cated coarse alluvium of the pre-landslide channel. This into the dam occurred, and most of the remaining lake phenomenon was observed at the Eureka, Saddle and Table 5 Results of the assessment of landslide dam stability indices Index Published Thresholds Landslide Dam Unstable Uncertain Stable Eureka Fox Hines Montag. Pouce Saddle Spirit Blockage <4 4-5 >5 3.62 4.11 3.66 4.91 1.84 3.64 3.86 Impoundment <0 >0 -0.34 0.59 0.60 No Data -0.23 -0.01 0.89 <1 >1 -0.34 0.59 0.60 No Data -0.23 -0.01 0.89 Dimensionless >3.08 2.75-3.08 <2.75 3.68 3.17 3.74 2.56 4.76 3.74 3.10 Blockage >5 3-5 <3 3.68 3.17 3.74 2.56 4.76 3.74 3.10 4.76 >3.98 2.43-3.98 <2.43 3.68 3.17 3.74 2.56 3.74 3.10 Backstow <-3 -3-0 >0 -3.14 -2.24 -1.89 No Data -3.73 -2.46 -2.55 -2.08 Relief <-1 >-1 -1.41 -1.05 -1.07 -1.09 -1.25 -1.45 Hydromorph. <5.74 5.74-7.44 >7.44 4.32 4.81 4.36 5.61 2.84 4.34 4.56 <5.26 5.26-8.07 >8.07 4.32 4.81 4.36 5.61 2.84 4.34 4.56 Red background indicates “unstable”, blue indicates “stable”, and white indicates "uncertain" stability Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 13 of 14 Spirit River dams. The coarse alluvium was less effective Acknowledgements We thank Tai Hoon Kim for providing data for the Fox Creek landslide and at slowing incision once the clast imbrication had been dam. Hans-Balder Havenith and a second anonymous reviewer provided upset (for example, the pre-landslide channel gravels insightful comments, which significantly improved the manuscript. The that slid into the new Eureka channel were rapidly mobi- Government of Alberta provided access to and permission to reproduce the lidar images and air photos. Funding for this research was provided by the lized out of the reach as bedload (Miller and Cruden British Columbia Ministry of Forests, Lands, Natural Resource Operations and 2001, 2002)). Rural Development, Alberta Geological Survey, and the Natural Sciences and The long-lasting effects of the landslide dams on the Engineering Research Council of Canada. tributary streams are evident in the persistent sediment Availability of data and materials accumulations upstream of the Montagneuse River and N/A. Hines Creek (pre 1952) landslide dam sites. These exam- Authors’ contributions ples suggest that the sediment wedges observed behind BM - Contributed to all sections. AD - Contributed to Stability Analysis and the the Eureka River, Fox Creek, and Saddle River dams Discussion sections. MG - Contributed to all sections except Stability Analysis, (Figs. 6, 8, and 14) could take several decades to be fully provided lidar and imagery. NA - Contributed to Regional Stratigraphy section, and provided lidar. HE - Analysed Pouce Coupe landslide and acquired data. DC mobilized, before the pre-landslide longitudinal profiles - Contributed to Landslide Dams section. All authors read and approved the are re-established. final manuscript. We found that the morphometric indices over- predicted dam instability (Table 5), using a realistic dam Funding British Columbia Ministry of Forests, Lands, Natural Resource Operations and volume of 10% of the landslide volume. These indices Rural Development, Alberta Geological Survey, Natural Sciences and also overestimated instability in the Halden Creek water- Engineering Research Council of Canada. shed, approximately 250 km northwest of our study area Ethics approval and consent to participate (Geertsema and Clague 2006). The databases that these Not Applicable. empirical indices are derived from include a wide range of landslide types (from slow, smaller soil slides to large, Consent for publication rapid rock avalanches), and the determined thresholds Not Applicable. might not be appropriate for the Peace River region’s Competing interests dams. Regional differences have already been noted by The authors declare that they have no competing interests. Korup (2004) and Tacconi Stefanelli et al. (2017). A larger dataset of Type VI landslide dams which are com- Publisher’sNote posed of glacial and glaciolacustrine sediments would Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. facilitate the statistical evaluation of the significance of the various input parameters, and appropriate stability Author details thresholds for these particular types of landslide dams British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development, 499 George Street, Prince George, BC V2L 1R5, Canada. might then be determined. Engineering Geology and Hydrogeology, RWTH-Aachen University, Aachen, Germany. Alberta Geological Survey, Twin Atria Building Suite 402, 4999 - 98 Conclusions Avenue, Edmonton, Alberta T6B 2X3, Canada. BC Ministry of Transportation and Infrastructure, Suite 213, 1011 4th Ave, Prince George, BC V2L 3H9, Our main findings for Peace River area landslide dams Canada. University of Alberta, Civil and Environmental Engineering, are as follows: Edmonton T6H 1G9, Alberta, Canada. Received: 28 August 2017 Accepted: 6 December 2017 The landslide rupture surfaces, in advance phase glaciolacustrine sediment or glacial sediment, extend under the channel causing the channel to be References elevated and forming Type VI dam. Alberta. 1997. Saddle River landslide reservoir summary. Alberta Environment unpublished report. Grande Prairie. The dams range in height from 4 to 30 m. Atkinson, N., and R.C. Paulen. 2010. Surficial geology and quaternary history of The post-landslide streams form new channels the Cleardale area, northwestern Alberta (NTS 84D/SW). Energy Resources around the toes of the landslides. Conservation Board, ERCB/AGS Open File Report: 2010, 27 p–2011. Bayrock, L. 1969. Incomplete continental glacial record of Alberta, Canada. In The landslide lakes can persist for up to 2 decades Quaternary geology and climate, volume 16 of the proceedings of the VII and diminish through a combination of dam incision congress of the International Association for Quaternary Research, H.E. Wright, and basin infilling. Jr,99–103. Washington, D.C.: National Academy of Sciences. Bobrowsky, P.T., and C.P. Smith. 1992. Quaternary studies in the Peace River Incision into the dams is slowed when the post- district, 1990: Stratigraphy, mass movements and glaciation limits (94P), landslide stream encounters the pre-landslide channel. geological fieldwork 1991. British Columbia Geological Survey Branch, Ministry More broad-based landslide dam stability indices, of Energy, Mines and Petroleum Resources, Paper 1992-1: 363–374. British Columbia. 2014. Landry slide. British Columbia Ministry of Transportation developed for other regions, poorly characterize the and Infrastructure unpublished report. Dawson Creek. observed performance of the Type VI dams in our Canuti, P., N. Casagli, and L. Ermini. 1998. Inventory of landslide dams in the study. northern Apennine as a model for induced flood hazard forecasting. In: Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 14 of 14 Managing hydro-geological disasters in a Vulnerate environment, ed. K. Andah, Miller, B.G.N., and D.M. Cruden. 2002. The Eureka River landslide and dam. 189–202. Perugia: CNR-GNDCI publication 1900. CNR-GNDCI-UNESCO (IHP). Canadian Geotechnical Journal 39: 863–878. Casagli, N., and L. Ermini. 1999. Geomorphic analysis of landslide dams in the Miller, B.G.N., and D.M. Cruden. 2008. Landslide dams, Peace River lowlands, northern Apennines. Transactions of the Japanese Geomorphological Union 20: Alberta. 61st Canadian geotechnical conference, Canadian Geotechnical Society. 219–249. Edmonton, Alberta. Catto, N.R., D.G.E. Liverman, P.T. Bobrowsky, and N. Rutter. 1996. Laurentide, Miller, B.G.N., and D.M. Cruden. 2014. Landslide dams, Peace River lowlands, Cordilleran, and montane glaciation in the western Peace River – Grande Alberta. Geological Society of America Conference, Vancouver, British Columbia. Prairie region, Alberta and British Columbia, Canada. Quaternary International Morgan A.J., R.C. Paulen, S.R. Slattery, and C.R. Froese. 2012. Geological setting 32: 21–32. for large landslides at the town of Peace River Alberta (NTS 84C). Energy Resources Conservation Board / Alberta Geological Survey, Open File Report Costa, J.E., and R.L. Schuster. 1988. The formation and failure of natural dams. 2012–04. Geological Society of America Bulletin 100: 1054–1068. Tacconi Stefanelli, C., F. Catani, and N. Casagli. 2015. Geomorphological Cruden, D.M., T.R. Keegan, and S. Thomson. 1993. The landslide dam on the investigations on landslide dams. Geoenvironmental Disasters 2: 21. Saddle River near Rycroft, Alberta. Canadian Geotechnical Journal 30: Tacconi Stefanelli, C., S. Segoni, N. Casagli, and F. Catani. 2016. Geomorphic 1003–1015. indexing of landslide dam evolution. Engineering Geology 208: 1–10. Cruden D.M., and D. Van Dine. 2013. Classification, description, causes and Tacconi Stefanelli C, V. Vilímek, A. Emmer, and F. Catani. 2017. Morphological indirect effects - Canadian technical guidelines and best practices related to analysis and features of the landslide dams in the Cordillera Blanca, Peru. landslides. Geological Survey of Canada, Open File 7359, 22 pages. Landslides, https://doi.org/10.1007/s10346-017-0888-6. Cruden, D.M., and D.J. Varnes. 1996. Landslide types and processes. In: Landslides: Investigation and Mitigation, Transportation Research Board, special report 247. Washington, D.C., USA: National Academy of Science. Cruden, D.M., Z. Lu, and S. Thomson. 1997. The 1939 Montagneuse River landslide, Alberta. Canadian Geotechnical Journal 34: 799–810. Ermini, L., and N. Casagli. 2003. Prediction of the behaviour of landslide dams using a geomorphological dimensionless index. Earth Surface Processes and Landforms 28 (1): 31–47. Evans S.G., X.Q. Hu, and E.G. Enegren. 1996. The 1973 Attachie slide, Peace River valley, near Fort St. John, B.C., Canada: A landslide with a high-velocity flow th slide component in Pleistocene sediment, 7 International Symposium on Landslides, Balkema, Trondheim, Norway, 2: 715–720. Fenton, M.M. 1984. Quaternary stratigraphy, Canadian prairies. In Quaternary stratigraphy of Canada, Geological Survey of Canada, Paper 84-10: 57–68. Fletcher, L., O. Hungr, and S.G. Evans. 2002. Contrasting failure behaviour of two large landslides in clay and silt. Canadian Geotechnical Journal 39: 46–62. Foord, V.N. 2016. Climate patterns, trends, and projections for the Omineca, Skeena, and Northeast, Natural Resource Regions, British Columbia. B.C. tech rep. 097. www.for.gov.bc.ca/hfd/pubs/Docs/Tr/Tr097.htm , 17 pp. Geertsema, M., and J.J. Clague. 2006. 1000-year record of landslide dams at Halden Creek, northeastern British Columbia. Landslides 3: 217–227. Geertsema M., and J.J. Clague. 2008. Natural dams, temporary lakes, and outburst floods in western Canada. Proceedings of the 1st World Landslide Forum, Tokyo Japan. 211-214. Geertsema, M., J.J. Clague, J.W. Schwab, and S.G. Evans. 2006. An overview of recent large landslides in northern British Columbia, Canada. Engineering Geology 83: 120–143. Hanson, R. 1994. Saddle River landslide. Alberta Environment unpublished report. Grande Prairie. Hartman, G.M.D., and J.J. Clague. 2008. Quaternary stratigraphy and glacial history of the Peace River valley, northeast British Columbia. Canadian J Earth Sciences 45: 549–564. Holland, S.S. 1976. Landforms of British Columbia. A physiographic outline. British Columbia Department of Mines and PetroleumResources Bulletin 48. Kim, T.H., D.M. Cruden, and C.D. Martin. 2010. The 2007 Fox Creek landslide, Peace River lowland, Alberta, Canada. Landslides 7 (1): 89–98. Korup, O. 2004. Geomorphic characteristics of New Zealand landslide dams. Engineering Geology 73: 3–35. Liverman, D.G.E., N.R. Catto, and N.W. Rutter. 1989. Laurentide glaciation in west- central Alberta: A single (late Wisconsin) event. Canadian Journal of Earth Sciences 26: 266–274. Lu, Z.Y., D.M. Cruden, and S. Thomson. 1998. Landslides and preglacial channels st in the western Peace River lowland, Alberta. 51 Canadian geotechnical conference. Canadian Geotechnical Society, Edmonton, Alberta 1: 267–274. McClung JE, and N. Weimer. 1990. Rycroft landslide geotechnical report. Geotechnical Branch, Development and Operations Division, Alberta Environment. Grande Prairie, file 8040–5-1. Miller, B.G.N. 2000. Two landslides and their dams, Peace River Lowlands, Alberta. Master of Science Thesis, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta. Miller, B.G.N., and D.M. Cruden. 2001. Landslides, landslide dams and the th geomorphology of tributaries in the Peace River lowlands, Alberta. 54 Canadian geotechnical conference. Canadian Geotechnical Society. Calgary, Alberta. 1: 363–370. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoenvironmental Disasters Springer Journals

Longevity of dams from landslides with sub-channel rupture surfaces, Peace River region, Canada

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Copyright © 2018 by The Author(s).
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Environment; Environment, general; Earth Sciences, general; Geography, general; Geoecology/Natural Processes; Natural Hazards; Environmental Science and Engineering
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Abstract

Background: We examined seven landslide dams and their changes over time in the Peace River region of Canada. These landslides had subchannel rupture surfaces in glacial and glaciolacustrine sediments. We assessed the stability of the dams using 6 separate, morphometric-based stability indices (with a total of 10 stability thresholds). Results: The landslides caused the streambeds to be elevated from 4 to 30 m forming the dams. The landslide lakes diminished in size over one to several years through stream incision into the dams and sediment infilling. The longest-lived dam persisted for up to 20 years. For two dams, incision into the dams lowered the lake levels by about half of the total depth, while the remainder of the water in the basins was displaced by sediment infilling. After the lakes drain, the sediment accumulations behind the dams can persist for decades. The stability analyses overpredicted unstable conditions which is inconsistent with the observed longterm persistence of the dams. Conclusions: The landslide dams in our study were relatively stable. Their lakes persisted for up to 2 decades and diminished over time through a combination of slow incision and basin infilling. The stability indices we assessed overpredicted unstable conditions and thus would require modification for these particular types of dams in this regional setting. Keywords: Landslide, Dam, Stability, Peace River, Quaternary, Sediment Background Fletcher et al. 2002) and the Halfway River dam Large landslides in Quaternary sediments are common- (Bobrowsky and Smith 1992) lasted for a few hours). place in the Peace River regions of Alberta and British Here we examine seven landslide dams on small tribu- Columbia (Geertsema et al. 2006; Miller and Cruden taries of the Peace River, including: the Eureka River 2008), and many of the landslides create dams which dam (Miller 2000; Miller and Cruden 2001, 2002, 2008, disrupt streamflow, damage timber, and threaten infra- 2014), the Fox Creek dam (Kim et al. 2010), the Hines structure both downstream and upstream. Creek dam (Lu et al. 1998; Miller and Cruden 2001, On smaller streams, with narrow valleys, large land- 2008), the Montagneuse River dam (Cruden et al. 1997; slides tend to fully obstruct the valleys, creating lakes Miller and Cruden 2008), the Pouce Coupe River dam that can persist for decades (Lu et al. 1998; Miller and (British Columbia 2014), the Saddle River dam (Cruden Cruden 2001, 2002, 2008, 2014; Geertsema and Clague et al. 1993; Alberta 1997; Miller and Cruden 2001, 2008, 2006, 2008). In contrast, regional dams on the larger 2014), and the Spirit River dam (Miller 2000; Miller and systems are generally short-lived (for example, the Cruden 2001, 2008, 2014) (Fig. 1). Attachie dam on the Peace River (Evans et al. 1996, We classified landslides according to Cruden and Varnes (1996) and landslide dams according to Costa and Schuster (1988), where six dam types are described: I) Partial, II) * Correspondence: brendan.miller@gov.bc.ca Complete, III) Divergent, IV) Convergent, V) Multi-lobed, British Columbia Ministry of Forests, Lands, Natural Resource Operations and and VI) Uplifted (from Cruden and Van Dine 2013). The Rural Development, 499 George Street, Prince George, BC V2L 1R5, Canada landslide dams we describe are all Type VI. Type VI dams Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 2 of 14 Fig. 1 Locations of the landslide dams. The regional topography was generated using digital topographic data from Natural Resources Canada (licenced under the Open Government Licence – Canada). The Peace River region is a broad, gently sloping plain which is deeply dissected by Holocene streams. The inset map shows the general study location (green box) in relation to the boundaries of the provinces of Alberta and British Columbia, Canada form when a landslide’s rupture surface extends under a (Atkinson and Paulen 2010, Morgan et al. 2012, and stream channel, and emerges on the opposite valley side references therein, Fig. 2). from the landslide, causing the channel to be displaced up- The five major LTAs, from highest (youngest) to lowest wards and the stream flow to be impeded (Costa and (oldest), can be summarized as follows: Schuster 1988). We have assessed dam stability using 6 separate in-  LTA5 retreat phase glaciolacustrine sediment; dices (with a total of 10 stability thresholds) based on  LTA4 glacial sediment (including till); watershed and dam morphometric attributes (from:  LTA3 advance phase glaciolacustrine sediment; Canuti et al. 1998; Casagli and Ermini 1999; Ermini  LTA2 massive sands (with bone dates of 25.1 ka BP); and Casagli 2003; Korup 2004; Tacconi Stefanelli et al. and 2015, 2016, 2017). This assessment tests the applic-  LTA1 preglacial sands and gravels (with wood dates ability of these indices and thresholds on these dams, between 43.5 and 27.4 ka BP). in our regional setting. The aims of this paper are to describe the landslide This stratigraphy records the up-valley advance of the dams, the evolution of the dams and their lakes over Laurentide Ice Sheet and subsequent down-valley ice front time, and to test various dam stability indices. retreat, and the preceding non-glacial intervals (Hartman and Clague 2008). These events filled the pre-glacial top- Setting and stratigraphy ography with up to 200 m of Quaternary sediment. General description Our Peace River study area is situated on a flat to rolling Stratigraphy, erosion, and landslides dissected plain, located east of the Rocky Mountains, in The distribution of deep-seated landslides correlates northeastern British Columbia and northwestern Alberta with the location of buried pre-glacial valleys of the an- (Fig. 1). The Peace River and its tributaries dissect glacial cestral Peace River and its tributaries. The ice- advance- and non-glacial sediments as well as shale and sandstone phase glaciolacustrine (LTA3, Fig. 3) sediment has been bedrock (Holland 1976; Morgan et al. 2012). The area has recognized as a prominent décollement plane for several a continental climate, characterized by warm, wet sum- deep-seated failures (Cruden et al. 1993, 1997; Miller mers and cold, dry winters (Foord 2016). 2000; Miller and Cruden 2001, 2002; Geertsema et al. Previous work in the region has determined the 2006; Kim et al. 2010; Morgan et al. 2012). Quaternary stratigraphy of the Peace River and its Figure 2 plots variable valley slopes (normal to valley tributaries (Bayrock 1969; Fenton 1984; Liverman et al. axis) against the regional stratigraphy for segments of 1989; Catto et al. 1996; Hartman and Clague 2008), Clear and Eureka rivers, and the Saddle and Spirit rivers. with recent studies generalizing the sedimentary suc- The top of the plots represent the valley slope angles asso- cession into five major lithotype assemblages (LTAs) ciated with stream incision into the uppermost Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 3 of 14 Fig. 2 Generalized stratigraphy found within buried preglacial valleys in the Peace River lowlands (right; modified after Morgan et al. 2012), and (left) average valley slopes of the lower Clear River (to the Eureka River) and the Eureka River (blue), and the lower Saddle River (to the Spirit River) and the Spirit River (red). Five of the landslides described appear be associated with ice-advance -phase glaciolacustrine sediment (LTA3), and two with the lower portion of the glacial sediments (LTA4). The valley slopes appear to reflect the stratigraphy. The slopes are lowest where the rivers are incising through LTA3 or LTA5, and steepen where the river incises into LTA4. Note that thickness of LTA4 has been exaggerated in this diagram, as the diamict is not topography constrained and will impact the valley slope response to incision over a longer distance than the unit thickness would otherwise suggest Fig. 3 Upthrust advance phase glacial lacustrine sediment (LTA3) at the toe of the Eureka River landslide. The reorientation of the lacustrine rhythmites to near vertical, was likely caused by the landslide. Note the scattering of boulders and cobbles at discrete locations. This material likely originated in the pre-landslide channel and was introduced into the post-landslide channel by bank erosion. Also note the small landslide into the channel in the distance. (Source: BGN Miller, September 28, 2007) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 4 of 14 sedimentary unit, at the upper reaches of the streams; Eureka River landslide dam whereas, the bottom of the plots represent slope angles The Eureka River landslide (Fig. 5) was an enlarged trans- from stream incision through the entire sedimentary se- lational earth slide with an estimated volume of 50Mm quences. Postglacial stream incision through the strati- (Miller 2000; Miller and Cruden 2002). The landslide oc- graphic sequence in Fig. 2 may have progressed as follows: curred sometime between 28 October 1989 and 28 March 1990, based on bracketing Landsat 5 Thematic Mapper Initial incision through the uppermost glaciolacustrine images. The landslide’s rupture surface, in advance phase sediments (LTA5), resulting in slope angles from 5 to glaciolacustrine sediment (LTA3), extended beneath the 10 degrees. streambed causing it to be elevated by approximately Subsequent incision into the more stable glacial 20 m, creating a Type VI landslide dam. sediment (LTA4), resulting in slope angles of up to The old channel was abandoned and a new channel 18-degrees. formed around the toe of the landslide. Initially, coarse Further incision into the advance-phase glaciolacustrine alluvium was generally absent in the new channel, allow- sediment (LTA3), where slopes decrease to as low as 6 ing for rapid stream incision to occur - up to 20 m in a degrees. decade near the centre of the landslide. This rapid inci- Final incision into the lower fluvial units (LTA1 and 2) sion promoted extensive instability from both banks, and into bedrock, where slopes increase to near 10 and reintroduced coarse alluvium (cobbles and boulders) degrees. from the pre-slide channel into the new channel (Fig. 3). This coarse material however, had a short residence time in the channel and was quickly mobilized downstream, Methods leaving the channel base unprotected. We described the landslides and landslide dams using in- Following an initial lake length of about 7 km (1990), formation predominently from previous studies and gov- the lake began to get progressively smaller as a result of ernment reports. We used aerial and satellite imagery, slow dam incision (Table 2). Incision was slowed when the coupled with field observations, to measure and post landslide channel encountered the uplifted pre- characterize the changes in the landslide dams and lakes landslide channel, near the upstream edge of the landslide over time. We analysed lidar data in a Geographic Infor- dam. After about 20 years the lake ceased to exist from a mation System (GIS) to determine the amount of stream combination of sedimentary infilling and dam incision. A incision into the dams and the depths of basin sediment lidar-generated longitudinal profile of Eureka River shows infilling. For the dam stability analyses, we used indices approximately 8 m of sediment accumulation occurred drawn from literature and compared the results to the ob- within the landslide lake basin (Fig. 6). As the landslide served behaviours. We derived morphometric attribute dam height was estimated to be 20 m, incision into the values for the stability analyses from Natural Resource dam lowered the lake by approximately 12 m, whereas Canada digital elevation data and LiDAR data in a GIS. sediment infilling of the basin amounted to 8 m. Results Fox Creek landslide dam Peace River regional landslide dams The May 5, 2007 Fox Creek landslide was a rapid transla- The following provides a description of seven landslide tional block slide involving about 47Mm of Quaternary dams and their development over time (Tables 1 and 2, sediments (Kim et al. 2010; Fig. 7). The basal rupture sur- Fig. 4). face of the landslide, in advance-phase glaciolacustrine Table 1 Landslide and landslide dam attributes Landslide year Landslide Volume (Mm ) Dam Height (m) Dam Width (m) Lake Duration (years) Eureka River 1989–90 50 20 1000 <20 Fox Creek 2007 47 19 1700 >10 Hines Creek 1990 X 25 120–150 <7 Hines Creek Pre-1952 48 X 1000 X Montagneuse River 1939 78 30 X X Pouce Coupe River 2013 1–3 4 170 <1 Saddle River 1990 39 24 800 <17 Spirit River 1995 20 9 X >18 Notes: X = No Data Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 5 of 14 Table 2 Changes in the landslide lakes lengths over time with data sources and approximate ground resolution indicated Date Lake Length (km) Source Data Resolution (m) Eureka River Sep 29, 1990 7 Landsat 5 Thematic Mapper 30 Oct 6, 1992 6 Alberta Air Photo AS4892, 148 1 Sep 1, 1997 2.9 Alberta Air Photo AS4892, 148 1 Aug 1999 1.7 Field Survey NA Aug 25, 2006 0.7 Alberta Air Photo AS5379B, 15 1 May 28, 2009 0.1 RapidEye 3–5 Jun 7, 2009 0 RapidEye 3–5 Fox Creek 28 Aug, 2007 1.6 Landsat 7 Enhanced Thematic Mapper 30 Jun 17, 2010 1.1 RapidEye 3–5 May 15, 2011 1 RapidEye 3–5 Sep 17 2012 1 Digital Globe 0.5 Sep 19, 2013 0.8 Digital Globe 0.5 Jul 4, 2014 0.6 RapidEye 3–5 Jun 3, 2015 0.6 RapidEye 3–5 May 23, 2016 0.1 RapidEye 3–5 Jun 10, 2017 0.1 RapidEye 3–5 Hines Creek Jun 25, 1991 1.7 Landsat 5 Thematic Mapper 30 Jun 14, 1992 1.5 Landsat 5 Thematic Mapper 30 Aug 17, 1992 1.4 Alberta Air Photo AS4314–251 1 Jun 26, 1993 1.5 Landsat 5 Thematic Mapper 30 Jun 20, 1994 1.2 Landsat 5 Thematic Mapper 30 Jun 16, 1995 1.0 Landsat 5 Thematic Mapper 30 Jun 25, 1996 0.9 Landsat 5 Thematic Mapper 30 Oct 8, 1996 0.7 Landsat 5 Thematic Mapper 30 Apr 18, 1997 0 Landsat 5 Thematic Mapper 30 Pouce Coupe River Aug 23, 2013 2.0 RapidEye 3–5 Sep 3, 2013 2.0 Landsat 8 Operational Land Imager 30 Sep 12, 2013 2.0 Landsat 8 Operational Land Imager 30 Oct 13, 2013 2.0 Landsat 7 Enhanced Thematic Mapper 30 Apr 8, 2014 0 Landsat 8 Operational Land Imager 30 Saddle River Mar 30, 1991 5.7 Landsat 5 Thematic Mapper 30 Sep 19, 1995 2.8 Alberta air photo AS4680–33 1 Sep 17, 2001 1.0 Alberta air photoAS5194B-40 1 May 2, 2005 0.5 Landsat 7 Enhanced Thematic Mapper 30 Aug 13, 2006 0 Alberta air photo TRSG0602–1536 1 Spirit River Sep 19, 1995 2.1 Alberta Air Photo AS4680–32 1 Jul 1999 0.7 Field Survey NA Sep 19, 2013 0.3 Digital Globe 0.5 Notes: 1 – objects on the ground of less than 1 m can be recognized using film-based air photos Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 6 of 14 Eureka Saddle Hines Spirit Pouce Coupe Fox 0 5 10 15 20 25 Years Since Dam Formation Fig. 4 Changes in the lengths of 6 landslide lakes over time, since the formation of the landslide dams. The data used to derive these curves forms Table 2. The lake lengths go to unity through a combination of incision into the landslide dams and sediment infilling of the basins sediment (LTA3), extended beneath Fox Creek, causing sediment (LTA4). The landslide formed a Type VI land- the stream bed to be elevated and creating a Type VI land- slide dam, with an estimated height of 25 m dam, and a slide dam (Kim et al. 2010). The abandoned, pre-landslide lake length of 1.5 to 1.7 km (Lu et al. 1998). stream bed was evident at the toe of the slope. The 1990 Hines Creek landslide occurred on the oppos- The landslide dam was a maximum of 19 m in height, ite valley wall of a much larger landslide. This larger land- with a width of 1.7 km (Kim et al. 2010). The largest of slide predates the earliest provincial aerial photographic the resultant lakes extended upstream beyond the east coverage of the site, in 1952. Lu et al. (1998) speculate that flank of the landslide for approximately 1.5 km. Two the pre-1952 landslide was a major contributing factor to smaller lakes formed atop the landslide debris. An ana- the occurrence of the 1990 landslide, as it directed the lysis of 2 m Alberta lidar data, collected on October 22, stream into the opposite valley wall, causing undercutting 2013, shows the stream’s longitudinal profile having not of the slope. They estimated the volume of the pre-1952 substantially recovered from the landslide event (Fig. 8). landslide to be 48Mm . An extensive sedimentary deposit formed upriver of the pre-1952 landslide, which persisted Hines Creek landslide dam until at least 1988 (Alberta air photo AS3729–88). The Hines Creek landslide occurred between June 9th and June 25th, 1990 (based on Landsat 5 Thematic Montagneuse River landslide dam Mapper bracketing dates) and was a reactivated, retro- The April 1939 Montagneuse River landslide was a reacti- gressive earth slide, with a rupture surface in glacial vated, retrogressive earth slide that moved in translation Fig. 5 Oblique perspective of the Eureka River landslide and dam, using a Digital Elevation Model derived from lidar data (dated September 26, 2013; source: Government of Alberta, reproduced with permission), at 2-times vertical exaggeration. The lidar data was collected approximately 4 years after the landslide lake had drained. The red polygon delineates the landslide colluvium, and the black hatched line delineates the landslide’s main scarp. The yellow polygon delineates an area of thick lacustrine sediment accumulation (up to 8 m), deposited within the landslide lake basin. The blue line traces the post-landslide dam Eureka River. The scale bar is accurate at the downstream (proximal) edge of the landslide colluvium Lake Length (km) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 7 of 14 Fig. 6 Plan view and channel longitudinal profile of the lower Eureka River, generated from lidar data (dated September 26, 2013; source: Government of Alberta, reproduced with permission). The red line (cross-section) roughly follows the longitudinal profile of the lower Eureka River (below the landslide). The grey area situated above red line indicates areas of lacustrine and deltaic sedimentation upstream of the landslide dam (Cruden et al. 1997). The landslide’s rupture surface, in ad- Pouce Coupe River landslide dam vance phase glaciolacustrine sediment (LTA3), extended ThePouce Coupe River wasdammedbyalandslide under the channel creating a Type VI landslide dam on August 21, 2013. The landslide originated from (Cruden et al. 1997, Fig. 9). The estimated height of the the east bank of the river, approximately 210 m dam was 30 m. Anecdotal information indicates that the downstream from theLandryBridge(Fig. 10).The dam stopped the flow in the river for about 2 weeks, caus- landslide caused the river bed to be elevated by ap- ing a 4 km lake to form. proximately 3.8 m, forming a Type VI landslide dam By June 15, 1945, the lake had drained (Canada air photo (Fig. 11). An Environment Canada water monitoring A8108, 23–25). Cruden et al. (1997) mapped lacustrine de- station, located immediately downstream from the posits extending about 1.5 km upstream of the landslide Landry Bridge, recordedthe backingupofthe river dam using 1952 aerial photographs. They noted that by over a 2.5 day period (British Columbia 2014). Fol- 1988, the sedimentary deposit had been eroded away. lowing the landslide, a new channel formed across a Fig. 7 Oblique air photo of the 2007 Fox Creek landslide, dam and lake, looking upstream. Note that much of the timber atop the landslide remained upright. (Source: Alberta Geological Survey, 2009; reproduced with permission) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 8 of 14 Fig. 8 Plan view and channel longitudinal profile of Fox Creek, generated from 2 m lidar (dated October, 22, 2013; source: Government of Alberta, reproduced with permission). The black hatched line traces the landslide’s main scarp. A continued, pronounced effect of the landslide dam on the longitudinal profile of the stream is evident point bar attached to the opposite stream bank. A encountered the pre-landslide channel alluvium (Cruden British Columbia, Ministry of Transportation and In- et al. 1993). The alluvium was later bypassed when the frastructure field investigation of the dam on August channel widened (Hansen 1994). Continued incision into 22, 2013 determined that there was no imminent the dam was accompanied by progressive shortening of threat to the bridge or road infrastructure, and no the lake (Table 2, Figs. 12, 13). By August 13, 2006, the mitigative action was taken. lake had fully drained. A longitudinal profile of the Saddle River, derived from Saddle River landslide dam the 2 m lidar data (dated October 22, 2013, Fig. 14), re- The June 1990 Saddle River landslide (Fig. 12) was a vealed approximately 14 m of sediment accumulation reactivated, retrogressive earth slide (Cruden et al. 1993). within the landslide lake basin. Therefore, incision into The landslide rupture surface, in advance phase glaciola- the dam amounted to 10.5 m. A bathymetric survey of the custrine sediment (LTA3), extended under the Saddle basin, which ceased 7.25 years after the landslide in River, causing the streambed to be displaced southwards September 1997, recorded a final water depth of 14.8 m by 60 m and upwards by approximately 24.5 m, creating (Alberta 1997, Fig. 13). Beyond this time, very little further a Type VI landslide dam (Cruden et al. 1993; Alberta incision into the dam occurred despite the basin 1997). The volume of water retained behind the dam remaining flooded for up to another 9 years (August was estimated at approximately 4Mm (McClung and 2006; Table 2). Weimer 1990). Overtopping of the dam began during the annual spring Spirit River landslide dam freshet of 1991 (Hanson 1994; Fig. 13), when a new chan- The July 1995 Spirit River landslide was a reactivated and nel formed at the toe of the landslide. Incision was slowed retrogressive earth slide that moved southwards by transla- near the upstream edge of the dam, where the stream tion (Miller 2000). The emerging rupture surface at the toe Fig. 9 Cross-section of the Montagneuse River landslide and dam. (Modified from Cruden et al. 1997) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 9 of 14 Fig. 10 Oblique aerial image mosaic of drone imagery, from June 2017, draped over a photogrammetrically generated digital elevation model depicting the Pouce Coupe River, and Landry Road and bridge (Source: Government of British Columbia; reproduced with permission). The 2013 landslide and dam are visible in the lower left. The approximate trace of the pre-landslide Pouce Coupe River channel is the blue line. The post-landslide stream channel cut through a point bar attached to the opposite stream bank, abandoning the pre-landslide channel of the landslide was bounded above and below by glacial At its maximum, the large lake was approximately sediment (LTA4); however, as the rupture surface was 2100 m long and 9 m deep (Miller 2000). The lake was trending upwards, it may have extended into underlying impounded behind a pressure ridge that formed at the glaciolacustrine sediment (LTA3). An Alberta aerial photo- toe of the landslide. Our 1999 field survey found coarse graph (Table 2), taken about 2 months after the landslide, alluvium was absent along much of the post-landslide shows a large lake upstream of the landslide and three channel, with the exception being just downstream of smaller lakes along the length of the landslide. Our field the large landslide lake, where the post-landslide channel survey in July 1999 found that the 3 smaller lakes had encountered the coarse alluvium of the pre-landslide drained; thus, these lakes lasted for less than 48 months. channel. This alluvium appears to be slowing drainage of Fig. 11 The 2013 Pouce Coupe River landslide and dam, captured at the Landry Road bridge, looking downstream. The yellow polygons delineate uplifted channel alluvium. (Source: British Columbia Ministry of Transportation and Infrastructure, August 22, 2013; reproduced with permission) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 10 of 14 Fig. 12 The Saddle River landslide and dam. a. Digital Elevation Model derived using 2 m lidar data (dated October 22, 2013; source: Government of Alberta, reproduced with permission) showing the 1990 landslide colluvium (outlined in red) and mainscarp (black). b. The landslide lake in July 1999. Note the drowned timber within the landslide dam basin. (source: BGN Miller, July 1999.) c – e. Time series of aerial photographs showing the landslide dam lake in September 1995 and 2001, and the drained basin in August 2006 (air photos AS4680–33, AS5194B-40, and TRSG0602–1536 respectively; source: Alberta Environment and Parks, Air Photo Distribution, Copyright Government of Alberta, reproduced with permission). The white dot in d indicates the photograph location of b the lake. Digital Globe imagery, dated September 19, A landslide dam is considered unstable when it “has 2013, shows the lake continues to persist. undergone erosion or collapse leading to a catastrophic breach, with the subsequent release of the impounded lake Stability analysis waters” (Ermini and Casagli 2003; p.32). Landslide dams Here, we test the ability of landslide dam stability indices are considered stable when they have not undergone a from the literature to predict the observed behavior of catastrophic breach and upstream lakes or infilled basins our studied Type VI landslide dams. The stability indices remain in place (e.g. Costa and Schuster 1988; Ermini and we used are based on morphometric parameters (Canuti Casagli 2003; Korup 2004; Tacconi Stefanelli et al. 2016). et al. 1998; Casagli and Ermini 1999; Ermini and Casagli We consider dams to be stable when the hazard of a cata- 2003; Korup 2004; Tacconi Stefanelli et al. 2016). Table 3 strophic breach is low. lists the indices we assessed. Table 4 provides dam and The calculated stability values for the described land- watershed morphometric parameters for each of the slide dams are presented in Table 5. For these assess- landslide dams. ments, we use a dam volume equaling 10% of the 6 30 5 25 Lake Length 4 20 Depth 3 15 2 10 1 5 0 0 02468 10 12 14 16 18 Years Since Dam Formation Fig. 13 Changes in the length and depth of Saddle River landslide lake since formation in June 1990. The depth data was derived from a bathymetry survey (Alberta 1997). The initial increase in the lake depth records basin flooding prior to the dam being overtopped Lake Length (km) Depth (m) Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 11 of 14 Table 3 Landslide dam stability assessment indices assessed against the recorded behaviour of the Peace River regional landslide dams Indices Formula Published Thresholds Reference and Region Applied Unstable Uncertain Stable Blockage B = log(V /A)<4 4–5 > 5 Canuti et al. 1998; Casagli and Ermini 1999 (Italy) I D C Impoundment I = log(V /V ) < 0 > 0 Casagli and Ermini 1999 (Italy) I D L < 1 > 1 Korup 2004 (New Zealand) Dimensionless Blockage DBI = log(A H /V ) > 3.08 2.75–3.08 < 2.75 Ermini and Casagli 2003 (world-wide) C D D >5 3–5 < 3 Korup 2004 (New Zealand) > 3.98 2.43–3.98 < 2.43 Tacconi Stefanelli et al. 2016 (Italy) Backstow I = log(H /V)< −3 −3 - 0 > 0 Korup 2004 (New Zealand) S D L Relief I = log(H /H)< −1> −1 Korup 2004 (New Zealand) R D R Hydromorphologic HDSI = log(V /A S) < 5.74 5.74–7.44 > 7.44 Tacconi Stefanelli et al. 2016 (Italy) D C < 5.26 5.26–8.07 > 8.07 Tacconi Stefanelli et al. 2017 (Peru) landslide volume (V becomes V in Table 3). Based on (2003). Thus the indices are over-predicting unstable D D10 cross-sectional profiles through the described landslides conditions. and dams, we found that only approximately 10% of the landslide volume goes into forming the dams. Figure 9 Discussion provides an example of the typical landslide and dam con- Each of the landslides we described had a basal rupture figuration in the Peace River region. Figure 9 shows that surface within the advance phase glaciolacustrine sedi- only a very small portion of the landslide is involved in the ment (LTA3) or near the base of the glacial sediment stream obstruction, with most of the landslide remaining (LTA4). The rupture surfaces extended under the chan- out of the valley bottom. nels causing the channels to be elevated, forming Type The assessments produced 43 unstable, 19 uncertain, VI landslide dams. Type VI landslide dams appear to be and 5 stable results. As these dams have not breached common in the Peace River region, based on our field catastrophically, but rather continued to impound an observations. In contrast, Type VI dams represent only existing or relict lake, they could not be considered 3% of the dams in Costa and Schuster’s (1988) world- unstable using the definition of Ermini and Casagli wide database of 184 dams. Fig. 14 Plan view and channel longitudinal profile of the Saddle River, generated from 2 m lidar data (dated October 22, 2013; source: Government of Alberta, reproduced with permission). The longitudinal profile extends from near the Peace River to approximately 4 km upstream of the landslide dam. The red line roughly follows the longitudinal profile of the lower Saddle River (below the landslide). The grey area situated above red line indicates areas of sedimentation upstream of the landslide dam Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 12 of 14 Table 4 Morphometric parameters of the Peace River regional landslide dams Attribute Units Symbol Landslide Dam Eureka Fox Hines Montagn. Pouce C. Saddle Spirit Landslide volume Mm V 50 47 48 78 2 39 20 Dam volume Mm V 5.0 4.7 4.8 7.8 0.2 3.9 2.0 D10 Dam height m H 20 19 25 30 4 24 9 Lake volume Mm V 11 1.2 1.2 0.34 4 0.26 Catchment area km A 1200 362 1055 95 2860 889 278 Relief upstream m H 510 213 296 373 478 429 254 Highest elevation in catchment m E 1075 750 910 930 1015 1010 820 max Elevation dam crest m E 526 494 535 510 537 502 520 min Longitudinal channel slope ° S 0.2 0.2 0.2 0.2 0.1 0.2 0.2 The landslide lakes diminish over several years through water was displaced by predominantly deltaic sediment a combination of fluvial incision into the dams and deltaic infilling of the basin. For the 20 m Eureka River landslide and lacustrine sediment infilling of the basins. For the dam, incision brought the lake level down by 12 m, while 24.5 m high Saddle River landslide dam, incision into the basin infilling amounted to 8 m. dam lowered the lake level by 10.5 m, while 14 m of sedi- The rate of incision into the dams is known to be ment infilling into the basin displaced the remaining related to a number of factors including material type. water. At the Saddle River landslide dam, the draw-down The fine textured glaciolacustrine sediments (LTA3) of the lake level due to incision was initially more rapid tend to erode readily, but the incision may be slowed (Fig. 13); however, after 7.25 years, when the last bathy- where the contemporary channel encounters the imbri- metric survey was conducted, almost no further incision cated coarse alluvium of the pre-landslide channel. This into the dam occurred, and most of the remaining lake phenomenon was observed at the Eureka, Saddle and Table 5 Results of the assessment of landslide dam stability indices Index Published Thresholds Landslide Dam Unstable Uncertain Stable Eureka Fox Hines Montag. Pouce Saddle Spirit Blockage <4 4-5 >5 3.62 4.11 3.66 4.91 1.84 3.64 3.86 Impoundment <0 >0 -0.34 0.59 0.60 No Data -0.23 -0.01 0.89 <1 >1 -0.34 0.59 0.60 No Data -0.23 -0.01 0.89 Dimensionless >3.08 2.75-3.08 <2.75 3.68 3.17 3.74 2.56 4.76 3.74 3.10 Blockage >5 3-5 <3 3.68 3.17 3.74 2.56 4.76 3.74 3.10 4.76 >3.98 2.43-3.98 <2.43 3.68 3.17 3.74 2.56 3.74 3.10 Backstow <-3 -3-0 >0 -3.14 -2.24 -1.89 No Data -3.73 -2.46 -2.55 -2.08 Relief <-1 >-1 -1.41 -1.05 -1.07 -1.09 -1.25 -1.45 Hydromorph. <5.74 5.74-7.44 >7.44 4.32 4.81 4.36 5.61 2.84 4.34 4.56 <5.26 5.26-8.07 >8.07 4.32 4.81 4.36 5.61 2.84 4.34 4.56 Red background indicates “unstable”, blue indicates “stable”, and white indicates "uncertain" stability Miller et al. Geoenvironmental Disasters (2018) 5:1 Page 13 of 14 Spirit River dams. The coarse alluvium was less effective Acknowledgements We thank Tai Hoon Kim for providing data for the Fox Creek landslide and at slowing incision once the clast imbrication had been dam. Hans-Balder Havenith and a second anonymous reviewer provided upset (for example, the pre-landslide channel gravels insightful comments, which significantly improved the manuscript. The that slid into the new Eureka channel were rapidly mobi- Government of Alberta provided access to and permission to reproduce the lidar images and air photos. Funding for this research was provided by the lized out of the reach as bedload (Miller and Cruden British Columbia Ministry of Forests, Lands, Natural Resource Operations and 2001, 2002)). Rural Development, Alberta Geological Survey, and the Natural Sciences and The long-lasting effects of the landslide dams on the Engineering Research Council of Canada. tributary streams are evident in the persistent sediment Availability of data and materials accumulations upstream of the Montagneuse River and N/A. Hines Creek (pre 1952) landslide dam sites. These exam- Authors’ contributions ples suggest that the sediment wedges observed behind BM - Contributed to all sections. AD - Contributed to Stability Analysis and the the Eureka River, Fox Creek, and Saddle River dams Discussion sections. MG - Contributed to all sections except Stability Analysis, (Figs. 6, 8, and 14) could take several decades to be fully provided lidar and imagery. NA - Contributed to Regional Stratigraphy section, and provided lidar. HE - Analysed Pouce Coupe landslide and acquired data. DC mobilized, before the pre-landslide longitudinal profiles - Contributed to Landslide Dams section. All authors read and approved the are re-established. final manuscript. We found that the morphometric indices over- predicted dam instability (Table 5), using a realistic dam Funding British Columbia Ministry of Forests, Lands, Natural Resource Operations and volume of 10% of the landslide volume. These indices Rural Development, Alberta Geological Survey, Natural Sciences and also overestimated instability in the Halden Creek water- Engineering Research Council of Canada. shed, approximately 250 km northwest of our study area Ethics approval and consent to participate (Geertsema and Clague 2006). The databases that these Not Applicable. empirical indices are derived from include a wide range of landslide types (from slow, smaller soil slides to large, Consent for publication rapid rock avalanches), and the determined thresholds Not Applicable. might not be appropriate for the Peace River region’s Competing interests dams. Regional differences have already been noted by The authors declare that they have no competing interests. Korup (2004) and Tacconi Stefanelli et al. (2017). A larger dataset of Type VI landslide dams which are com- Publisher’sNote posed of glacial and glaciolacustrine sediments would Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. facilitate the statistical evaluation of the significance of the various input parameters, and appropriate stability Author details thresholds for these particular types of landslide dams British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development, 499 George Street, Prince George, BC V2L 1R5, Canada. might then be determined. Engineering Geology and Hydrogeology, RWTH-Aachen University, Aachen, Germany. Alberta Geological Survey, Twin Atria Building Suite 402, 4999 - 98 Conclusions Avenue, Edmonton, Alberta T6B 2X3, Canada. BC Ministry of Transportation and Infrastructure, Suite 213, 1011 4th Ave, Prince George, BC V2L 3H9, Our main findings for Peace River area landslide dams Canada. University of Alberta, Civil and Environmental Engineering, are as follows: Edmonton T6H 1G9, Alberta, Canada. Received: 28 August 2017 Accepted: 6 December 2017 The landslide rupture surfaces, in advance phase glaciolacustrine sediment or glacial sediment, extend under the channel causing the channel to be References elevated and forming Type VI dam. Alberta. 1997. Saddle River landslide reservoir summary. Alberta Environment unpublished report. Grande Prairie. The dams range in height from 4 to 30 m. Atkinson, N., and R.C. Paulen. 2010. Surficial geology and quaternary history of The post-landslide streams form new channels the Cleardale area, northwestern Alberta (NTS 84D/SW). Energy Resources around the toes of the landslides. Conservation Board, ERCB/AGS Open File Report: 2010, 27 p–2011. Bayrock, L. 1969. 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Geoenvironmental DisastersSpringer Journals

Published: Jan 4, 2018

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