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Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

From 19 to 22 June 2013, intense rainfall and concurrent snowmelt led to devastating floods in the Canadian Rockies, foothills and downstream areas of southern Alberta and southeastern British Columbia, Canada. Such an event is typical of late-spring floods in cold-region mountain headwater, combining intense precipitation with rapid melting of late-lying snowpack, and represents a challenge for hydrological forecasting systems. This study investigated the factors governing the ability to predict such an event. Three sources of uncertainty, other than the hydrological model processes and parameters, were considered: (i) the resolution of the atmospheric forcings, (ii) the snow and soil moisture initial conditions (ICs) and (iii) the representation of the soil texture. The Global Environmental Multiscale hydrological modeling platform (GEM-Hydro), running at a 1 km grid spacing, was used to simulate hydrometeorological conditions in the main headwater basins of southern Alberta during this event. The GEM atmospheric model and the Canadian Precipitation Analysis (CaPA) system were combined to generate atmospheric forcing at 10, 2.5 and 1 km over southern Alberta. Gridded estimates of snow water equivalent (SWE) from the Snow Data Assimilation System (SNODAS) were used to replace the model SWE at peak snow accumulation and generate alternative snow and soil moisture ICs before the event. Two global soil texture datasets were also used. Overall 12 simulations of the flooding event were carried out. Results show that the resolution of the atmospheric forcing affected primarily the flood volume and peak flow in all river basins due to a more accurate estimation of intensity and total amount of precipitation during the flooding event provided by CaPA analysis at convection-permitting scales (2.5 and 1 km). Basin-averaged snowmelt also changed with the resolution due to changes in near-surface wind and resulting turbulent fluxes contributing to snowmelt. Snow ICs were the main sources of uncertainty for half of the headwater basins. Finally, the soil texture had less impact and only affected peak flow magnitude and timing for some stations. These results highlight the need to combine atmospheric forcing at convection-permitting scales with high-quality snow ICs to provide accurate streamflow predictions during late-spring floods in cold-region mountain river basins. The predictive improvement by inclusion of high-elevation weather stations in the precipitation analysis and the need for accurate mountain snow information suggest the necessity of integrated observation and prediction systems for forecasting extreme events in mountain river basins. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A ground-based lidar system that has been deployed in Whistler, British Columbia, Canada, since the spring of 2010 provides a means of evaluating vertical aerosol structure in a mountainous environment. This information is used to help to determine when an air chemistry observatory atop Whistler Mountain (2182 m MSL) is within the free troposphere or is influenced by the valley-based planetary boundary layer (PBL). Three case studies are presented in which 1-day time series images of backscatter data from the lidar are analyzed along with concurrent meteorological and air-chemistry datasets from the mountaintop site. The cases were selected to illustrate different scenarios of diurnal PBL evolution that are expected to be common during their respective seasons. The lidar images corroborate assumptions about PBL influence as derived from analysis of diurnal trends in water vapor, condensation nuclei, and ozone. Use of all of these datasets together bolsters efforts to determine which atmospheric layer the site best represents, which is important when evaluating the provenance of air samples. [ABSTRACT FROM AUTHOR]

Major element, trace element and Nd–Sr isotopic data are presented for 82 plutonic rocks from the southern Coast Mountains Batholith (CMB) in British Columbia, Canada, ranging in emplacement age from 210 to 50 Ma. The rocks are part of a large composite magmatic arc batholith, which the major element data show to be of calc-alkaline affinity. The majority of CMB samples lack the depletion in Eu that would be consistent with equilibration of magmas and plagioclase-bearing crystalline residues or fractionates, suggesting that equilibration took place deeper than the pressure limit of plagioclase stability at 35–40 km depth. The CMB samples show a wide variation in the slope of normalized rare earth element (REE) patterns, with chondrite-normalized La/Yb ratios above 10 being mostly confined to periods of high magmatic flux in the arc at 160–140, 120–80, and 60–50 Ma. The clearest relationships between major and trace elements are negative correlations between SiO2 and each of Sc, Y, and the heavier REE Gd to Lu. Nd and Sr isotopes mostly document juvenile origins for the granitoids, but show variations to higher 87Sr/86Sr and lower ϵNd during high-flux periods. The results are interpreted to indicate a deep origin for most CMB magmas, below ∼40 km where mafic to intermediate rock assemblages previously added to the arc crust by mantle melting were transformed to an (amphibole-bearing)-eclogite facies cumulate or restite, such that melting residues consisted mainly of two pyroxenes, garnet and variable proportions of amphibole. Thickened orogenic crust, for which there is clear geological evidence during the period 100–80 Ma, promoted this process. During high-flux periods, larger amounts of older rocks, mostly mafic rocks and some metasediments added to the base of the arc during orogenic shortening, became involved in magma genesis. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The identification and geometric definition of individual cascade and step-pool bedforms are investigated in a steep, coarse-grained, mountain stream, Mosquito Creek, by testing four analytical techniques: visual identification, zero-crossing, bedform differencing, and power spectral analysis. The test is the first use of these techniques in a headwater stream, and the analysis of two bed profiles showed that visual identification was able to (i) identify, (ii) determine the geometry of, and (iii) classify the type of individual bedforms better than the other methods. The other techniques were not able to differentiate step-pools from cascades, and the large range of grain sizes and bedform heights hampered their ability to consistently identify stepped bedforms. The step-pool (pronounced, channel-spanning steps that alternate with channel-spanning pools) and cascade (multi-tiered, partially channel-spanning structures) morphology in Mosquito Creek has formed in the last 20 years as fluvial action has restructured its previously engineered, revetment-lined, planar bed. The channel bed exhibits a morphologic regularity that power spectral analysis captured as periodic fluctuations in the bed profiles, with mean wavelengths slightly greater than those identified by the other methods. Further, the active reorganization of revetment has formed stepped structures with geometries similar (i.e., height to wavelength ratios) to stepped features found in natural mountain streams. Channel slope partially controlled bedform geometry (wavelength and height), and bedform height weakly controlled individual step spacing, but there was no relation between wavelength and grain size (D[sub 90] ).L'identification et la définition géométrique de formes de lits de rivières individuels en cascades et en paliers d'accalmie sont étudiées dans le crique Mosquito, un ruisseau de montagne, abrupte et coulant sur un sol à grain grossier, en mettant à l'essai quatre techniques analytiques : l'identification visuelle, le passage par zéro, la différenciation de la forme du lit et une analyse spectrale de puissance. Ce test constitue la première utilisation de ces techniques dans un ruisseau d'amont et l'analyse de deux profils de lits a démontré que l'identification visuelle pouvait (i) identifier, (ii) déterminer la géométrie et (iii) classifier le type individuel de lit de rivière mieux que les autres méthodes. Les autres techniques ne permettaient pas de différencier entre les paliers d'accalmie et les cascades; de plus, la grande étendue des granulométries et de hauteurs de lits entravaient leur capacité d'identifier avec constance les formes de lits à paliers. Dans le crique Mosquito, la morphologie des paliers d'accalmie (des marches accentuées qui enjambent le chenal alternant avec des bassins calmes qui enjambent le chenal) et des cascades (des structures à plusieurs niveaux qui enjambent partiellement le chenal) s'est formée au cours des 20 dernières années alors que l'action de l'eau a restructuré son ancien lit planaire, artificiel et tapissé. Le lit du chenal montre une régularité morphologique que l'analyse spectrale de puissance a interprétée comme des fluctuations périodiques des profils du lit avec des longueurs d'onde moyennes légèrement supérieures à celles identifiées par les autres méthodes. De plus, la réorganisation active du revêtement a formé des structures en paliers dont les géométries (c.-à-d. les rapports de la hauteur sur la longueur d'onde) sont semblables aux caractéristiques des paliers trouvés dans les ruisseaux de montagne naturels. La pente du chenal a contrôlé en partie la géométrie de la forme du lit (longueur d'onde et hauteur) et la hauteur de la forme du lit a faiblement contrôlé l'espacement des gradins individuels mais il n'y avait aucune relation entre la longueur d'onde et la granulométrie (D[sub 90] ).[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The Quottoon plutonic complex (part of the great tonalite sill) was emplaced into eastern parts of the Coast shear zone along the west flank of the Coast Mountains. U–Pb crystallization ages range from 72.3 to 55.5 Ma. A regional compilation of K–Ar hornblende dates from the tonalite sill indicates a west to east decrease from ~60 Ma to ~54 Ma across the intrusive suite. Paleomagnetic samples were collected at 160 sites ( 8 samples per site) along six transects across the Quottoon complex between the Skeena River and Willard Inlet. Directions of characteristic remanent magnetization (ChRM) were successfully determined by principal component analysis of thermal demagnetization data for about half of the samples collected. Site-mean ChRM directions were determined for 56 sites from the Skeena River, Quottoon Inlet, Steamer Passage, and Wales Island transects, using criteria of 4 sample ChRM directions per site and 95% confidence limit (α[sub 95] ) 25°. For Filmore Island and Willard Inlet, few sites provided adequate determinations of site-mean ChRM directions, but many sample ChRM directions were well determined and consistent. The mean direction from the Skeena River – Quottoon Inlet collection is nearly concordant with the expected Eocene direction. Mean directions from other transects have clockwise-rotated declinations and inclinations that are shallower than the expected direction by up to 23°. Consistent with expectations for east-side-up tilting of crustal panels, sites from the western part of each transect have mean directions farther from the Eocene expected direction than do sites from the eastern part of the transect. The magnitude of east-side-up tilt varies along strike: the Skeena River to Quottoon Inlet segment experienced little or no tilt; Steamer Passage south of Portland Inlet records 15° tilt; north of Portland Inlet, tilts are 40° for Wales Island and 35° for Filmore Island; farther north, tilt decreases to 12° for Willard Inlet. Tilting was driven by Eocene extension of the Coast Mountains, with tilted crustal panels bounded by northwest-striking, east-side-down normal faults and northeast-striking transfer faults or shear zones. The ACCRETE seismic transect imaged east-dipping reflectors down to ~15 km depth, which likely correspond to the east-side-down normal faults. The most significant of the northeast-striking transfer structures must underlie Portland Inlet. Based on a tilting domino model, about 30% extension is required to produce the 40° tilt of crustal blocks at Wales and Filmore islands.Le complexe plutonique Quottoon (une partie du grand filon-couche de tonalite) a été mis en place dans des parties orientales de la zone de cisaillement côtière le long du flanc ouest de la chaîne Côtière. Des âges de cristallisation U–Pb vont de 72,3 à 55,5 Ma. Une compilation régionale de datations K–Ar sur des hornblendes provenant du filon-couche de tonalite indique une décroissance d'ouest en est à travers la suite intrusive de ~60 Ma à ~54 Ma. Des échantillons paléomagnétiques ont été recueillis sur 160 sites ( 8 échantillons par site) le long de six transects à travers le complexe de Quottoon, entre la rivière Skeena et l'inlet Willard. Pour environ la moitié des échantillons recueillis, les directions du magnétisme rémanent caractéristique (ChRM) ont été déterminées avec succès par une analyse des composantes principales de la démagnétisation thermique. Les moyennes des directions ChRM ont été déterminées par site pour 56 sites situés sur les transects de la rivière Skeena, de l'inlet Quottoon, du passage Steamer et de l'île de Wales, utilisant des critères de 4 directions ChRM sur des échantillons par site et une limite de confiance de 95 % (α[sub 95] ) 25º. En ce qui concerne l'île Filmore et l'inlet Willard, peu de déterminations adéquates de directions moyennes ChRM spécifiques au site ont été obtenues; cependant, plusieurs directions ChRM sur les échantillons étaient bien déterminées et cohérentes. La direction moyenne de la collecte provenant de la rivière Skeena – inlet Quottoon concorde presque avec la direction escomptée de l'Éocène. Les directions moyennes d'autres transects ont des déclinaisons et des inclinaisons à rotation de sens horaire qui sont jusqu'à 23º moins profondes que les directions escomptées. Les sites de la portion ouest de chaque transect ont des directions moyennes divergeant plus de la direction escomptée à l'Éocène que les sites de la partie est du transect, ce qui concorde avec les attentes d'un basculement du côté est vers le haut de grands blocs de la croûte. L'amplitude du basculement du côté est vers le haut varie selon la direction : le segment entre la rivière Skeena et l'inlet Quottoon n'a pas ou a peu basculé; le passage Steamer, au sud de Portland Inlet, enregistre 15º de basculement; au nord de l'inlet Portland, le basculement est de 40º pour l'île de Wales, 35º pour l'île Filmore et, plus au nord, l'inclinaison diminue à 12º pour l'inlet Willard. Le basculement provient de l'extension, à l'Éocène, de la chaîne Côtière au moyen de grands blocs inclinés de la croûte limités par des failles normales à direction nord-ouest et le côté est vers le bas et par des failles de transfert ou des zones de cisaillement à direction nord-est. Le transect sismique « ACCRETE » a interprété des réflecteurs à pendage est jusqu'à ~15 km de profond qui correspondent probablement au failles normales à côté est vers le bas. La plus importante des structures de transfert à direction nord-est doit se trouver sous l'inlet Portland. Selon une théorie de basculement de dominos, il faut une extension de 30 % pour basculer de 40º les blocs de la croûte aux îles de Wales et de Filmore.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]