Résumés
Abstract
Cores retrieved from two slump blocks at the west end of Elkwater Lake, Alberta were used to determine which of two mass wasting events was responsible for impounding the lake and to establish a maximum age of lake formation. A high resolution Digital Elevation Model of the study area was used to estimate the volume of material involved in each mass wasting event, recreate pre-slump topographic conditions, determine the probable extent and elevation of the lake at different periods in time, and evaluate the viability of alternative outlets. Results suggest that the lake formed no more than 9440 BP as a result of impoundment by the eastern slump block. The lake rose to its highest mid-Holocene elevation prior to 7245 BP, establishing an outlet through Feleski Creek 3.5 km northeast of the present shoreline. Lake levels then dropped during the comparatively dry Altithermal, concurrent with a period of rapid sediment influx and the development of the alluvial fan on which the Stampede site is located. As water levels rose during the late Holocene, and with the former outlet cut off by progradation of the alluvial fan, Elkwater Lake established its present outlet though Ross Creek.
Résumé
Les carottages effectués dans les zones des deux glissements de terrain survenus à l’extrémité ouest de l’Elkwater Lake ont servi à déterminer lequel des deux était responsable de l’endiguement des eaux afin d’évaluer l’âge de la formation du lac. Une modélisation numérique à haute résolution des altitudes dans la région à l’étude a permis de déterminer le volume de matériel déplacé au cours de chacun des glissements, de recréer la topographie préalable des lieux, de déterminer l’étendue et le niveau probables du lac à différentes périodes et d’évaluer l’existence éventuelle d’autres exutoires. Les résultats indiquent que le lac s’est formé avant 9440 BP par suite de l’endiguement créé par le glissement situé le plus à l’est. Le lac aurait alors atteint son plus haut niveau avant 7245 BP à l’Holocène moyen, créant un exutoire au droit du Feleski Creek, à 3,5 km au nord-est du rivage actuel. Le niveau du lac s’est peu à peu abaissé au cours de l’Altithermal, une période relativement sèche au cours de laquelle il y eut apport rapide de sédiments, puis formation du delta alluvial aujourd’hui occupé par le site Stampede. Avec l’élévation du niveau lacustre à l’Holocène supérieur et l’alluvionnement de l’ancien exutoire, le Ross Creek est devenu le nouvel exutoire de l’Elkwater Lake.
Resumen
El examen de bloques de roca obtenidos en las zonas de dos deslizamientos de terreno ocurridos en el extremo oeste del Elkwater Lake en Alberta fue empleado para determinar cual de los dos eventos fue el responsable de la retención del agua y también para establecer una edad máxima para la formación del lago. Una modelización numérica de alta resolución de la elevación del área de estudio fue empleada para calcular el volumen del material involucrado en cada deslizamiento de terreno, reconstituir las condiciones topográficas anteriores, determinar la dimensión y la elevación probables del lago durante diferentes periodos en el tiempo e igualmente, evaluar la viabilidad de canales alternativos. Los resultados obtenidos sugieren que el lago se formó hace unos 9400 años como resultado de la contención de agua debido a un deslizamiento de terreno en la zona este. El lago alcanzó su elevación máxima en el Holoceno medio hace unos 7245 años, estableciendo una salida a través de Feleski Creek a unos 3.5 km al noreste de la ribera actual. Más tarde durante un periodo de calentamiento seco el nivel lacustre fue disminuyendo coincidiendo con una afluencia rápida de sedimentos y con la formación de un cono aluvial en la zona que ocupa actualmente el sitio Stampede. Durante el Holoceno superior, a medida que el nivel de agua iba aumentando, el cono aluvial bloqueó por progradación el canal inicial de salida y el Elkwater Lake estableció el actual canal de evacuación a través de Ross Creek.
Parties annexes
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10.7202/032646ar