River of Change: a Model for the Development of Terraces Along the Bow River, Alberta

Abstract

Researchers working in the Bow River valley have identified a minimum of four alluvial terraces, the upper two of which have been designated as paired terraces. Over the past 35 years, they have attempted to correlate these alluvial landforms and to generate models for the development of the terraces along the section of the Bow River between Calgary and the Rocky Mountains. In this study, Mazama ash and an early Holocene paleosol are used to correlate the terrace suites examined by previous researchers and to generate a model which accounts for the development of the upper two sets of paired terraces. These paired terraces reflect major episodes of aggradation and degradation that result from changes in independent variables such as climate and uplift. The initial episode of aggradation, dating from the late Pleistocene, is the result of paraglacial processes in a sparsely vegetated, yet saturated environment. Following a brief episode of degradation at the end of the Younger Dryas, the second episode of aggradation, dating from 9000 to 5000 BP, is caused by increased sediment load and lowered stream power during the Hypsithermal.Les chercheurs travaillant dans la vallée de la rivière Bow ont identifié au moins quatre terrasses alluviales, dont les deux supérieures ont été identifiées comme étant appariées. Au cours des 35 dernières années, ils ont essayé de corréler entre elles ces formes alluviales et d’élaborer des modèles appropriés à la formation des terrasses le long de la Bow River, entre Calgary et les Rocheuses. Dans la présente étude, les cendres de Mazama et un paléosol de l’Holocène inférieur ont servi à faire la corrélation entre les ensembles de terrasses étudiés précédemment et à élaborer un modèle pouvant expliquer la formation des deux ensembles supérieurs de terrasses appariées. Ces dernières résultent d’épisodes importants d’alluvionnement et de déblaiement qu’ont entraînées des modifications apportées à des phénomènes agissant de façon indépendante, comme le climat et le relèvement isostasique. Le premier épisode d’alluvionnement, survenu au Pléistocène supérieur, est le résultat de processus paraglaciaux agissant dans un milieu présentant une végétation clairsemée, bien que saturé. Après un court épisode de déblaiement à la fin du Dryas inférieur, le deuxième épisode d’alluvionnement (9000-5000 BP) est provoqué par une augmentation de la charge solide dans un cours d’eau de faible compétence, à l’Hypsithermal.Los estudios hechos en el valle del Bow River identifican por lo menos 4 terrazas fluviales, las dos terrazas superiores son consideradas terrazas apareadas. Durante los últimos 35 años se ha intentado relacionar estos relieves fluviales y generar modelos que permitan explicar la formación de terrazas a lo largo de la sección del Bow River entre Calgary y las Rocosas. En este estudio, las cenizas de Mazama y análisis de paleosuelos datando del Holoceno temprano han sido empleados para establecer una correlación de la serie de terrazas examinadas con anterioridad y así generar un modelo ...

Post-glacial fluvial response and landform development in the upper Muskegon River valley in North-Central Lower Michigan, U.S.A.

“…Circumstantial evidence suggests that this period of downcutting occurred at the Pleistocene/Holocene transition when the climate began to warm and stream discharge decreased. This form of channel response at the Pleistocene/Holocene transition has been documented in the glacial and periglacial parts of Europe (e.g., Starkel, 1991;Walker, 1995;Tebbens et al, 1999;Howard et al, 2004), along the Bow River in Alberta, Canada (Otelelaar, 2002), and along the upper Susquehanna River in New York (Scully and Arnold, 1981). A variety of evidence (e.g., Webb et al, 1983;Krishnamurthy et al, 1995;Bartlein et al, 1998;Kutzbach et al, 1998;Davis et al, 2000;Booth et al, 2002) indicate that this climate transition occurred at about 10 ka in the Great Lakes region.…”

“…Another observation is that many streams began downcutting at the Pleistocene/Holocene transition because of reduced sediment load, resulting in distinct, paired terraces. This type of channel adjustment has been reported in Europe (Starkel, 1991;Walker, 1995;Tebbens et al, 1999;Howard et al, 2004), the western Canadian prairies (Rains and Welch, 1988;Campbell and Campbell, 1997;Otelelaar, 2002), and the state of New York in the eastern U.S. (Scully and Arnold, 1981).…”

“…Along the upper Susquehanna River in the state of New York, 2 terraces and the floodplain have formed since deglaciation due to climate changes. A series of alluvial terraces has also been recognized in Alberta, Canada that formed since the ice retreated (Otelelaar, 2002;Evans et al, 2004).…”

Quaternary fluvial archives and landscape evolution: a global synthesis

“…The high plains of Canada, which show clear evidence of post-glacial fluvial incision in the form of canyons and terrace systems (Jackson et al, 1982;Rains and Welch, 1988;Rains et al, 1994;Evans et al, 2004), are on post-cratonic Precambrian crust, which explains the occurrence of such evidence, which has sometimes been attributed to glacioisostatic effects (Bryan et al, 1987;Campbell, 1997;Oetelaar, 2002), but disqualifies the area as a direct analogue for Britain. A similar observation can be made with regard to Michigan, where post-glacial incision below terraces representing MIS 2 deglaciation have been observed on Proterozoic crust flanking the Laurentian craton (Arbogast et al, 2008).…”

Constraints on Pleistocene glaciofluvial terrace age and related soil chronosequence features from vertical 10Be profiles in the Ariège River catchment (Pyrenees, France)

“…Ryder (1972, 1989), however, have shown that deglacial episodes generate a major sediment slug during which bedrock denudation rates and flushing of glacigenic sediments off slopes and out of catchments reach an all-time peak. Glaciofluvial aggradation also occurs in such circumstances (Jackson et al, 1982;Owen and Sharma, 1998;Oetelaar, 2002;Barnard et al, 2004Barnard et al, , 2006. Numerical modeling has suggested that the duration and intensity of paraglacial episodes depends (i) on the mass of glacigenic sediments initially present at the ice margin, (ii) on the intensity of hillslope processes, and (iii) on a wide range of environmental parameters that control denudation efficiency such as postglacial climate, revegetation, and catchment size, topography and geology (Church and Slaymaker, 1989;Harbor and Warburton, 1993;Ballantyne, 2002Ballantyne, , 2003.…”