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A) Photograph of horizontally bedded, lacustrine silt and sand overlying outburst flood gravel on the west side of Fraser River, 7 km south of the Highway 20 bridge; view to the north-northwest. B) Close-up photograph of the lacustrine sediments, which are up to 11 m thick in this exposure. The location of photograph B is shown in A. The lacustrine sediments indicate that a lake with a surface elevation of about 550 m asl persisted or, alternatively, re-formed after the outburst flood.
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Near the Pleistocene Termination, a glacier-dammed lake in central British Columbia suddenly drained to the south along the Fraser River valley. Floodwater travelled 330 km down the valley to Hope, British Columbia, and from there to the west into the Salish Sea near Vancouver. The flood was caused by the failure of an ice dam formed by the terminu...
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... Because megaflood-derived boulder deposits are imbricated (Figure 1c), their entrainment threshold may be higher than if the same size grains were deposited by a landslide. Additional, the locations of greatest shear stress in an eastern Himalayan megaflood are not confined to the modern channel (Morey et al., 2022), but often occur on hillslopes, making it likely that megafloods also deposit boulders there (e.g., Clague et al., 2021). Boulder deposition on hillslopes could impede soil production, influencing the downslope transport of material (e.g., Glade et al., 2017;Shobe, Turowski, et al., 2021), and blur the line between boulder sources as megaflood-derived boulders make their way into the valley bottom over time. ...
Infrequent, large‐magnitude discharge (>10⁶ m³/s) outburst floods—megafloods—can play a major role in landscape evolution. Prehistoric glacial lake outburst megafloods transported and deposited large boulders (≥4 m), yet few studies consider their potential lasting impact on river processes and form. We use a numerical model, constrained by observed boulder size distributions, to investigate the fluvial response to boulder deposition by megaflooding in the Yarlung‐Siang River, eastern Himalaya. Results show that boulder deposition changes local channel steepness (ksn) up to ∼180% compared to simulations without boulder bars, introducing >100 meter‐scale knickpoints to the channel that can be sustained for >20 kyr. Simulations demonstrate that deposition of boulders in a single megaflood can have a greater influence on ksn than another common source of fluvial boulders: incision‐rate‐dependent delivery of boulders from hillslopes. Through widespread boulder deposition, megafloods leave a lasting legacy of channel disequilibrium that compounds over multiple floods and persists for millennia.
... Although the lakes containing stickleback in BC are not particularly widespread, they are physically separated by land or sea, which likely makes dispersal a challenge for freshwater stickleback. We speculate that evidence for a large flood (∼500 km 3 of water) in the Fraser River valley, dated approximately to the end of the Pleistocene and caused by the failure of a large ice dam (Clague et al. 2021), could provide an explanation. The estimated extent of the flood across the southern Georgia Strait is very similar to the current known distribution of benthic stickleback in BC, raising the tantalizing possibility that it may have been responsible for the spread of the benthic lineage of stickleback from a palaeolake in the Fraser Valley, consistent with previous inference about the evolution of Eastern Pacific freshwater stickleback (Fang et al. 2020). ...
Rapid evolution of similar phenotypes in similar environments, giving rise to in situ parallel adaptation, is an important hallmark of ecological speciation. However, what appears to be in situ adaptation can also arise by dispersal of divergent lineages from elsewhere. We test whether two contrasting phenotypes repeatedly evolved in parallel, or have a single origin, in an archetypal example of ecological adaptive radiation: benthic-limnetic three-spined stickleback (Gasterosteus aculeatus) across species-pair and solitary lakes in British Columbia. We identify two genomic clusters across freshwater populations, which differ in benthic-limnetic divergent phenotypic traits and separate benthic from limnetic individuals in species pair lakes. Phylogenetic reconstruction and niche evolution modelling both suggest a single evolutionary origin for each of these clusters. We detected strong phylogenetic signal in benthic-limnetic divergent traits, suggesting they are ancestrally retained. Accounting for ancestral state retention, we identify local adaptation of body armour due to the presence of an intraguild predator, the sculpin (Cottus asper) and environmental effects of lake depth and pH on body size. Taken together, our results imply a predominant role for retention of ancestral characteristics in driving trait distribution, with further selection imposed on some traits by environmental factors.
... The abrupt absence of till within the Cheakamus Valley (Blaise-Stevens 2008) indicates removal by a post-Fraser glaciation erosional event (i.e., 11 ka: Clague and Ward 2011). One possible explanation is erosion by a major glacial outburst flood event (e.g., Clague et al. 2020) that is suggested by the presence of (i) well-developed, smooth-walled drainage channels and escarpments up to 25 m deep incised into the basalt (Blaise-Stevens 2008), (ii) high-standing, scab-like remnants of BFp lavas (i.e., basalt "eskers"; Mathews 1948Mathews , 1958, (iii) irregular sculpted lava surfaces (Russell et al. 2007), and (iv) the misfit stream, amphitheater-headed canyon at Brandywine Falls ( Fig. 2; Russell et al. 2007) and streamlined, butte-like morphology of Daisy Lake Island. This would suggest that the present-day morphology and distribution of the basalt lavas within the Cheakamus Valley results, in part, from a major flood event during waning of the Fraser glaciation. ...
The Cheakamus basalts are voluminous (1.65 km3) Late Pleistocene, valley-filling lavas erupted from a vent situated near Conflict Lake, in the alpine Callaghan Valley near Whistler, British Columbia. Geochemical and petrographic properties suggest these olivine-plagioclase porphyritic basalts derive from a single magma batch affected by minor sorting of phenocrysts and xenocrystic plagioclase. Thirty-four sites sampled for paleomagnetic direction measurement record a mean pole direction of 345.2 ̊ / 73.0 ̊ (α95 = 1.3°), showing no statistical variation nor drift with stratigraphic position. These data suggest the lavas were emplaced in a single paleomagnetic moment – a period of time significantly less than 2,000 years. 40Ar/39Ar geochronometry on three samples return a weighted mean age estimate of 15.95 ± 7.9 ka (2s) and field evidence, including till-covered, well-glaciated lava flow surfaces, indicate the eruption coincided with the early stages of the Fraser glaciation (~18-20 ka). The lavas preserve features indicative of a landscape hosting diverse and dynamic paleoenvironments. Subaerial eruption of basalt filled an ice-free Callaghan Creek drainage before inundating and damming the paleo-Cheakamus River, creating an upstream rising body of water. Periodic lava-dam overtopping resulted in syn-eruptive intermittent flooding of lava surfaces, expressed by discontinuous interflow sediment lenses. Rare instances of enigmatic cooling columns may also indicate localized ice-contact with glaciers that partially filled the Cheakamus Valley. The displacement of the modern Cheakamus River and the formation of Callaghan and Conflict Lakes via long-term lava-damming remain direct indicators of the impact basaltic eruptions have on the geomorphology of valley systems.
... We informally refer to these sites as the Prince George and Bednesti subaqueous fans, and the Blackwater delta. We use recent analogues together with geomechanical reasoning to infer that these landforms developed as a result of liquefaction flowslides that occurred during the rapid drawdown of glacial Lake Fraser,~11,500 years ago (Clague et al., 2020). ...
... Important controls on the potential for sediment 20-70 m 5 -1 5 k m 2. a. Study sites in central BC and approximate extent of glacial Lake Fraser (blue shading, 736 m a.s.l.), before its southward drainage~11,500 years ago. The glacier dam was located just south of Williams Lake (Clague et al., 2020). This digital elevation model (100-m resolution, processed from 1990s era BC aerial photographs; British Columbia, 2002) is used with permission of the Government of BC. b. ...
... It occupied the central interior and reached a maximum size of~14,500 km 2 . The lake evolved rapidly as the wasting Cordilleran Ice Sheet retreated from the Interior Plateau back towards its source areas in the Coast Mountains to the west and Cariboo Mountains to the east (Clague et al., 2020). ...
Unusual channel-amphitheatre landforms are present in Late Pleistocene–early Holocene, subaqueous fan and
delta deposits in the glacial Lake Fraser basin, central British Columbia. The lake formed during the decay of
the last Cordilleran Ice Sheet and drained ~11,500 years ago during a large outburst flood. The fronts of a delta
and two subaqueous fans consisting of silt to fine sand are marked by branching networks of wide, nearly flat
channels that terminate upstream in digitate, steep-walled amphitheatres. We propose that these channel-amphitheatre landforms formed by liquefaction flowslides that were induced by the rapid drawdown of glacial
Lake Fraser during the outburst flood. Similar geomorphic forms, which we believe also to be associated with
rapid drawdowns of large Late Pleistocene–early Holocene lakes, occur elsewhere in North America. A recent tailings dam failure and an intentional breaching of a 100-year-old hydroelectric dam provide insights into the processes responsible for the landforms. By using geomechanical analysis, we show how rapid lake drawdown can
trigger liquefaction flowslides in deposits of silt to fine sand. The novelty of our approach lies in combining
geomechanical reasoning with geomorphic analogues to understand histories of ancient glacier-dammed lakes
and of the glacial lake outburst floods that are sourced from them
The Texas Creek rock avalanche is a prehistoric deposit in the Fraser River Canyon, 17 km south of Lillooet, southwestern British Columbia, Canada. Original mapping suggested that the debris consisted of two landslides: a 45 Mm ³ event deposited after the Mazama tephra but before about 2 ka ago, and a 7.2 Mm ³ event about 1.1 ka ago. The proposed timing of the younger landslide was correlated with a decline in the First Nations population and was proposed as an agent of cultural collapse driven by its impact on salmon returns vital to the population's sustenance. We provide six surface exposure ages using ¹⁰ Be from boulder tops, with three samples from each surface that were originally posited to be older and younger debris. The six samples yielded similar ages suggesting the landslide deposit represents a single event with an average age of 2.28 ± 0.19 (2σ external error) ka before 1950 AD. Evidently, the landslide played no role in the cultural collapse. Fraser River Holocene incision rates, estimated pre- and post-landslide are between 13 and 24 mm/yr, consistent with previous estimates for the mid-Fraser River region. Landslide timing is coincident with the explosive eruption of Mount Meager, 120 km to the northwest, and with a possible landslide at Mystery Creek 85 km to the west and 65 km south of Mount Meager. The landslide may have been seismically triggered, but attribution is speculative.
The most recent deglaciation of the North American Ice Sheet Complex (NAISC: comprising the Innuitian, Cordilleran, and Laurentide ice sheets) offers a broad perspective from which to analyze the timing and rate of ice retreat, deglacial sea-level rise, and abrupt climate change events. Previous efforts to portray the retreat of the NAISC have been focused largely on minimum-limiting radiocarbon ages and ice margin location(s) tied to deglacial landforms that were not, for the most part, chronologically constrained. Here, we present the first version of North American Deglaciation Isochrones (NADI-1) spanning 25 to 1 ka in calendar years before present. Key new features of this work are (i) the incorporation of cosmogenic nuclide data, which offer a direct constraint on the timing of ice recession; (ii) presentation of all data and time-steps in calendar years; (iii) optimal, minimum, and maximum ice extents for each time-step that are designed to capture uncertainties in the ice margin position, and; (iv) extensive documentation and justification for the placement of each ice margin. Our data compilation includes 2229 measurements of 10Be, 459 measurements of 26Al and 35 measurements of 36Cl from a variety of settings, including boulders, bedrock surfaces, cobbles, pebbles, and sediments. We also updated a previous radiocarbon dataset (n = 4947), assembled luminescence ages (n = 397) and gathered uranium-series data (n = 2). After scrutiny of the geochronological dataset, we consider >90% of data to be reliable or likely reliable. Key findings include (i) a highly asynchronous maximum glacial extent in North America, occurring as early as 27 ka to as late as 17 ka, within and between ice sheets. In most marine realms, extension of the ice margin to the continental shelf break at 25 ka is somewhat speculative because it is based on undated and spatially scattered ice stream and geomorphic evidence; (ii) detachment of the Laurentide and Cordilleran ice sheets took place gradually via southerly and northerly ‘unzipping’ of the ice masses, starting at 17.5 ka and ending around 14 ka; (iii) the final deglaciation of Hudson Bay began at 8.5 ka, with the collapse completed by 8 ka. The maximum extent of ice during the last glaciation occurred at 22 ka and covered 15,470,000 km2. All North American ice sheets merged at 22 ka for the first time in the Quaternary. The highly asynchronous Last Glacial Maximum in North America means that our isochrones (starting at 25 ka) capture ice advance across some areas, which is based on limited evidence and is therefore somewhat speculative. In the Supplementary Data, the complete NADI-1 chronology is available in PDF, GIF and shapefile format, together with additional visualizations and spreadsheets of geochronological data. The NADI-1 shapefiles are also available at https://doi.org/10.5281/zenodo.8161764.
Rapid evolution of similar phenotypes in similar environments, giving rise to in situ parallel adaptation, is an important hallmark of ecological speciation. However, what appears to be in situ adaptation can also arise by dispersal of divergent lineages from elsewhere. We test whether two contrasting phenotypes repeatedly evolved in parallel, or have a single origin, in an archetypal example of ecological adaptive radiation: benthic-limnetic three-spined stickleback ( Gasterosteus aculeatus ) across species-pair and solitary lakes in British Columbia. We identify two genomic clusters across freshwater populations, which differ in benthic-limnetic divergent phenotypic traits and separate benthic from limnetic individuals in species pair lakes. Phylogenetic reconstruction and niche evolution modelling both suggest a single evolutionary origin for each of these clusters. We detected strong phylogenetic signal in benthic-limnetic divergent traits, suggesting they are ancestrally retained. Accounting for ancestral state retention, we identify local adaptation of body armour due to the presence of an intraguild predator, the sculpin ( Cottus asper ) and environmental effects of lake depth and pH on body size. Taken together, our results imply a predominant role for retention of ancestral characteristics in driving trait distribution, with further selection imposed on some traits by environmental factors.
This year marks ten years since the Great East Japan Earthquake in 2011 and the following Fukushima Daiichi nuclear accident. This accident has created a critical need to quantify the seismic response of such critical structures under different levels of seismic hazard. Most seismic-related research studies have been conducted on reinforced concrete walls employed in conventional buildings; however, such walls in nuclear and industrial structures are uniquely designed with very low aspect ratios and relatively large thicknesses. Therefore, several studies have demonstrated that the seismic performance of reinforced concrete walls in nuclear and industrial structures has not been yet adequately quantified to enable robust seismic risk assessment. In this respect, the current study uses a multi-layer shell element in OpenSees to develop a numerical model that can simulate the seismic response of reinforced concrete shear walls with low aspect ratios similar to those used in nuclear and industrial structures. Subsequently, the developed model is validated against the results of several walls tested in previous experimental programs under cyclic loading. The validation results show that the developed model can capture the response of the walls including the initial stiffness, peak load, stiffness degradation, strength deterioration, hysteretic shape, and pinching behaviour at different drift levels.
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Microplastics and their impact on the environment and human health have increasingly become a global issue. Rivers are the main sources of fresh-water for human activities, and the main route for pollution delivery to seas and oceans. Predicting the behavior of microplastics (i.e. plastic particles smaller than 5 mm) in river systems and identifying their accumulation zone is therefore important to understand their environmental impact, risk exposure assessment and mitigation/remediation planning. The presence of microplastics in the Fraser River has been previously shown in different studies through water sampling at different sites along the river. In an attempt to improve understanding of the fate and transport of microplastics within the Fraser River system, an innovative three-dimensional numerical model was used in this study to predict movement of these particles in a highly urbanized and industrialized 35 km stretch of the Fraser River. The modeling system used herein is based on coupling TELEMAC-3D hydrodynamic model with a three-dimensional Particle Tracking Model (PTM) which incorporates physical characteristic of microplastics in calculating their movement in the water. The hydrodynamic model has been calibrated using available data. The model results provide information on behavior and distribution of different types of microplastics within of the modeled stretch, and support identifying their sources and accumulation hotspots.
