Search

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. [ABSTRACT FROM AUTHOR]

Accelerator radiocarbon dating of 147 charcoal samples recovered from colluvial and alluvial fan deposits at 29 sites was used to reconstruct the Holocene fire history of an inland temperate rainforest watershed in east-central British Columbia (BC), Canada. Radiocarbon dates ranged from 182 to 9558 cal. yr BP, with prominent peaks in the probability distribution of calibrated dates at c. 7100, 3900, 2300, 1600 and 250–1000 cal. yr BP. The inferred median fire return interval (FRI) was 800–1200 cal. yr, depending on the extent of inbuilt age errors resulting from charring of wood pre-dating actual fire ages. This FRI is likely an overestimate, as less severe events may not have created sufficient erosion and slope instability to preserve a record of charcoal in buried soils and slope deposits. Median time since fire was 467 cal. yr based on ages of the uppermost charcoal found at each site, but the severity of heart-rots in the dominant redcedars (Thuja plicata Donn ex D. Don) prevented independent confirmation of stand ages by dendrochronology. Sites with multiple charcoal-containing layers having similar radiocarbon ages can be explained with reference to contemporary post-fire mass-wasting processes. Peaks in fire-related sedimentation probability coincided broadly with periods of higher fire frequency c. 600–1000, 1300–2400 and 3500–4500 cal. yr BP inferred from sedimentary charcoal records at subalpine sites in southwestern BC. Correspondence with fire records from more distant sites in northwestern North America was less clear. [ABSTRACT FROM AUTHOR]

Abstract: At least thirty-eight, large, catastrophic landslides, each either larger than 0.5 M m3 or longer than 1 km, have occurred in northern British Columbia in the last three decades. The landslides include low-gradient flowslides in cohesive sediments, long-runout rock slides (rock avalanches), and complex rock slide-flows. The flowslides have occurred in a variety of sediments, including glaciolacustrine silt, clay-rich till, and clay-rich colluvium. The rock failures have happened in weak shale overlain by sandstone and volcanic rocks. The frequency of large landslides in northern British Columbia appears to be increasing, suggesting a link to climate change. [Copyright &y& Elsevier]

Abstract: In early July 2002, a large rockslide–debris avalanche occurred on the west slope of the Pink Mountain anticline in northeastern British Columbia (57°04′N; 122°52′W). The slopes have been subjected to previous deformation and landsliding. Pre- and post-slide digital elevation models (DEMs) were created from aerial photography. Approximately 1.04 M m3 of sandstone and shale travelled nearly 2 km from an elevation of 1460 m to 1010 m. The landslide has a fahrböschung of 11.6° and covered 43 ha. The rock debris entrained a certain amount of fine-textured till and colluvium increasing its volume by 15%. This entrainment caused partial liquefaction of the underlying soil thereby enhancing the mobility of the landslide. We used a Bingham rheological model to dynamically model the landslide with excellent correspondence between the analysis of the actual observed behaviour of the landslide. [Copyright &y& Elsevier]

Abstract: A landslide of 2.5 million m3 of sensitive glaciomarine sediments, predominantly silty clays, occurred at Mink Creek near Terrace, British Columbia (54°27′N, 128°37′W) some time between 1 December 1993 and 9 January 1994. We divide the landslide deposit into seven zones, distinguished on the basis of morphological characteristics. We interpret processes of flowing, spreading and sliding, often in succession, as the landslide retrogressed. The landslide is similar to other movements involving sensitive marine sediments, but is unique in that both flowing and spreading occurred, involving multiple rupture surfaces. Thus the landslide may be classified as a composite earth flow–spread. A decade of warm and wet climate preceded the landslide event. Since most global circulation models predict a warmer and wetter future for Terrace, more of these landslides may be expected. [Copyright &y& Elsevier]

• A landslide inventory is made using the Landsat Archive (1985–2017). • Cumulative difference of NDVI and a harmonic fit is used to detect landslide timing. • Timing of respectively 80% and 85% of the landslides was determined using CDNDVI and dCDNDVI. • Mean dating errors decreased after detrending CDNDVI. • The Landsat archive can be used for detecting and dating Landslides in remote areas. We manually detected and mapped 66 landslides from Landsat imagery over a 33-year period from 1985 to 2017 in the Buckinghorse River region, British Columbia, Canada. We semi-automatically determined landslide timing using the cumulative difference (CD) between the normalized difference vegetation index (NDVI) and a fitted harmonic sinusoidal curve (CDNDVI). The semi-automated dating method was capable of determining the timing of 80% of the landslides using CDNDVI and 85% of the landslides after detrending CDNDVI (dCDNDVI). The CDNDVI method generally detects landslides too early and the dCDNDVI method is generally too late. Mean absolute errors (in days) are lower for the dCDNDVI (208 and 188) than the CDNDVI (227 and 267), respectively. This study, however, has many examples of extreme outliers with very large errors (>1000 days). Our method is portable to other remote regions as long as vegetation anomalies can be used as an indicator for landslide activity. We conclude that the timeseries of images available in the Landsat Archive are useful for landslide mapping, but the pixel size limits the size of the landslides that can be mapped. [ABSTRACT FROM AUTHOR]