Search

In this paper, we examine the influence of the 27 October 2012, Mw7.8 earthquake on landslide occurrence in the southern half of Haida Gwaii (formerly Queen Charlotte Islands), British Columbia, Canada. Our 1350 km2study area is undisturbed, primarily forested terrain that has not experienced road building or timber harvesting. Our inventory of landslide polygons is based on optical airborne and spaceborne images acquired between 2007 and 2018, from which we extracted and mapped 446 individual landslides (an average of 33 landslides per 100 km2). The landslide rate in years without major earthquakes averages 19.4 per year, or 1.4/100 km2/year, and the annual average area covered by non-seismically triggered landslides is 35 ha/year. The number of landslides identified in imagery closely following the 2012 earthquake, and probably triggered by it, is 244 or an average of about 18 landslides per 100 km2. These landslides cover a total area of 461 ha. In the following years—2013–2016 and 2016–2018—the number of landslides fell, respectively, to 26 and 13.5 landslides per year. In non-earthquake years, most landslides happen on south-facing slopes, facing the prevailing winds. In contrast, during or immediately after the earthquake, up to 32% of the landslides occurred on north and northwest-facing slopes. Although we could not find imagery from the day after the earthquake, overview reconnaissance flights 10 and 16 days later showed that most of the landslides were recent, suggesting they were co-seismic.

This study presents the results from field characterisation and runout modelling of debris avalanches from Vancouver Island, British Columbia. Information about the terrain attributes at the initiation, transport and deposition zones of 44 debris avalanches (30 to 9000 m3 in volume) is presented. The slope angle at the initiation point of the debris avalanches was found to be independent of the volume of the failure; the termination slope angle did however show a dependence on the debris avalanche volume. Grain size distribution and soil classification were conducted on till and colluvium samples collected from the initiation zones and the failed material classified as well-graded gravels with a low plasticity fine-grained component. Field measurements of the runout path geometry dimensions for 31 slope failures were used to conduct back-analyses. The dynamic analysis code DAN-W was used to determine rheological input parameters for debris avalanche while the modelled runout distance using the empirical-statistical code UBCDFLOW was compared to field observations. The results of the back-analysed rheological parameters were compared against published values for debris and rock avalanches. Based on the DAN-W results, the debris avalanches from Vancouver Island were found to have higher effective friction angle values than the published back-calculated values for large rock avalanches. UBCDFLOW was able to closely model the runout behaviour of most debris avalanches investigated.

On 28 November 2020, some 18 Mm3 of quartz diorite detached from a steep rock face at the head of Elliot Creek in the southern Coast Mountains of British Columbia. The rock mass fragmented as it descended 1000 m and flowed across a debris-covered glacier. The rock avalanche was recorded on local and distant seismometers, with long-period amplitudes equivalent to a M 4.9 earthquake. Local seismic stations detected several earthquakes of magnitude 2 lake, where it generated a 115 m displacement wave that overtopped the moraine at the far end of the lake. We estimate that some 13.5 Mm3 of water left the lake from the combined impact of the landslide as well as erosion of the dam. The water that left the lake was channelized along Elliot Creek, scouring the valley more than 40 m in some places over a distance of 10 km before depositing debris on a 2 km2 fan in the Southgate River valley. Debris temporarily dammed the river, and turbid water continued down the Southgate River to Bute Inlet, where it produced a 70 km turbidity current and altered turbidity and water chemistry in the inlet for weeks. The landslide followed a century of rapid glacier retreat and thinning that exposed a growing lake basin. The outburst flood extended the damage of the landslide far beyond the limit of the landslide, destroying forest and impacting salmon spawning and rearing habitat. We expect more cascading impacts from landslides in the glacierized mountains of British Columbia as glaciers continue to retreat, exposing water bodies below steep slopes while simultaneously removing buttressing support.

The archipelago of Haida Gwaii, formerly known as the Queen Charlotte Islands, is one of the most dynamic geomorphic environments in Canada. Climatic and geophysical forces have combined to shape the unique landscape of the archipelago. Strong cyclonic storms from the Pacific Ocean are frequent and are accompanied by heavy rainfall. The two strongest earthquakes in Canadian history happened on the Queen Charlotte Fault just west of the archipelago in the Pacific Ocean. Coastal landscapes on the west coast are rugged and rocky, whereas the north and east coasts are formed in thick glacial sediments that are being rapidly eroded by waves. The mountainous spine that runs the length of Haida Gwaii is susceptible to landslides and other mass wasting processes. Slope failures are the primary agent of natural disturbance in these mountains and occur at rates that are among the highest in Canada. They are triggered by heavy rainfall, forestry activities, and earthquakes.

Logging causes increased landslide frequency in British Columbia. In this study, the slope, type, initiation location, aspect, rate, bedrock geology, and size of mass movements located in eight logged tributary valleys of the Chilliwack River Valley are investigated. A landslide inventory was created by digitizing landslides identified on aerial photographs dating from 1941 to 2002. This database was analysed using qualitative observations and simple statistical tests, and a comparison between natural and logging-related landslides was made. Slope tests displayed a significant difference between natural and logging-related events, indicating that, on average, logging-related landslides require lower slope gradients to initiate than natural events. Although aspect, initiation location, and landslide type did not show a significant relationship between natural and logging-related landslides, they do suggest subtle differences. Landslide rate was calculated and compared for natural and logging-related landslides. It was significantly higher for logging-related events, attaining a maximum of 31 times the natural rate in 1978 and an overall average increase of nine times the natural rate. Logging-related landslides were on average smaller than natural landslides but this nevertheless resulted in a 3.1 times increase in area affected by logging-related landslides compared to natural landslides. Geology may influence landslide frequency as well; it appears to be higher over the less resistive sedimentary rocks of the Cultus Formation and Chilliwack Group and lower in granodioritic areas. Finally, roads affected slope stability more than clearcuts in the early decades of the study, but this effect decreased over time, suggesting a correlation with improved road construction.

The channel network on a fluvial fan distributes sediment across the fan surface and determines fan development. We present a method to characterize fan channel networks (FCNs) so that the effect of controls (e.g., sediment supply) on the FCN can be evaluated. We then do a preliminary test of the method using three fans in coastal British Columbia. The method uses a set of three measures: 1) the spatial extent of hydrogeomorphic activity, measured as the percentage of the contemporary fan surface area occupied by active channels; 2) the topologic structure, using node counts to measure channel network complexity; and 3) a sediment budget to indicate the proportion of sediment that is stored on the fan, loosely characterized by comparing the second-largest clast size of sediment at the fan apex or intersection point with the second-largest clast at the toe of the fan. These measures were applied to two fan deltas and one partial fan delta in northern Vancouver Island, British Columbia, using channel surveys conducted in 2006 and 2007. All three fans are located within 30 km of each other, have similar climatic, physiographic, and vegetation settings, and have natural channel networks. Each fan has perennial channel flow at the fan apex. Watershed areas range from 19.5 to 35.6 km2, and contemporary fan areas range from 0.2 to 0.7 km2. The Melton Relative Relief ratio ranges from 0.24 to 0.30 and none of the fans show evidence of debris floods or debris flows. In addition to testing the efficacy of the FCN measures, we use these fans to explore the question of whether fans in similar geomorphic settings and with similar controls develop similar FCNs. Results show the fans have between 4.7–8.5 % of the contemporary fan surface occupied by the active channel network. Topologic node counts indicate that the two fan deltas have a similar level of channel complexity, with 42–54 nodes in total. The partial fan delta channel network is approximately half as complex, with 23 nodes in total. All three fans have boulder-sized sediment (30–50 cm) at the fan apex. On the two fan deltas the largest sediment at the toe of the fan is 10–12 cm, indicating that much of the sediment delivered to the fan apex is stored on the fan. In contrast, the partial fan delta has 18–20 cm sized sediment transported into the axial valley river at the toe of the fan, and a wider and steeper outlet channel, indicating that a greater proportion of sediment is exported from the fan. Although the axial river does not visibly incise into the fan deposits, the lower channel complexity and coarser sediment output indicates that the axial river truncates the toe of the partial fan delta. The two fan deltas have similar FCNs, supporting the idea that fans in similar geomorphic settings develop similar FCNs. The partial fan delta is in a different geomorphic setting that was not identified prior to analysis of the FCNs, and has a different FCN. This study also examines the effects of a large regional storm event that occurred between the 2006 and 2007 surveys. One fan had increased active area, two fans had increased total node counts, and two fans increased output clast size after the flood event, indicating the measures are sensitive and respond to disturbance. Further investigations of FCNs may have utility in hazard assessments, addressing how fans respond to changes in sediment supply or discharge regime, how vegetation type affects FCNs, or the effect of other watershed processes or fan attributes.

Objective To examine the diagnosis of attention-deficit hyperactivity disorder (ADHD) in children with cleft to determine whether language-learning characteristics are taken into account when making this diagnosis. Design Prospective examination of 177 consecutive patients. Objective behavioral ratings, cognitive assessments, and attention/impulsivity testing of 32 of the 177 children with nonsyndromic cleft lip and palate (CLP) who had previously been diagnosed as ADHD and were receiving medication were performed. the prospective 6- to 9-month follow-up examination was examined to determine the accuracy of prior and posttest diagnoses. Setting University hospital-based cleft palate clinic. Main Outcome Measures Pretest/posttest design to determine accuracy of DSM-IV psychiatric diagnosis. Results and Conclusions The results show that the proportion of children originally diagnosed with ADHD (18%) was significantly higher than posttest diagnosis of ADHD (6% p < .001). Also, the frequency of pretest diagnosis of learning disorder (LD; 31%) was significantly different from posttest diagnosis (66% p < .01). The overdiagnosis of ADHD and underdiagnosis of LD in this sample of children with nonsyndromic unilateral cleft lip and palate appears to be due to lack of language-learning assessment.

Analyzed longitudinal behavior ratings (ANOVAs) for 44 children (ages 4-12) with cleft lip and palate and cleft palate only (CLP) and examined the relationship of speech, hearing, and facial disfigurement at age 9 in predicting behavioral characteristics and school achievement (multiple regression). Results indicate increasing levels of social inhibition over age for girls with CLP, but less so for boys. There were also increasing levels of conduct problems for older girls with CLP with variable age fluctuation for boys. Attempts to relate speech, hearing, or facial disfigurement to prediction of behavior or achievement at age 9 were not revealing and further analysis with larger samples is indicated.