The effects of rock uplift and rock resistance on river morphology in a subduction zone forearc, Oregon, USA

Abstract

Relationships between riverbed morphology, concavity, rock type and rock uplift rate are examined to independently unravel the contribution of along-strike variations in lithology and rates of vertical deformation to the topographic relief of the Oregon coastal mountains. Lithologic control on river profile form is reflected by convexities and knickpoints in a number of longitudinal profiles and by general trends of concavity as a function of lithology. Volcanic and sedimentary rocks are the principal rock types underlying the northern Oregon Coast Ranges (between 46°30′ ′ ′ − − − −1 , to subsidence (< < < < <0 mm a − − − − −1 ). These observations are consistent with models of transient river response to a decrease in uplift rate. Conversely, the rivers between 44° and 43°N have similar concavities and flow on the same mapped bedrock unit as the central region, but have bedrock channels and irregular longitudinal profiles, suggesting the river profiles reflect a transient response to an increase in uplift rate. If changes in rock uplift rate explain the differences in river profile form and morphology, it is unlikely that rock uplift and erosion are in steady state in the Oregon coastal mountains. sediment supply effects on fluvial erosion can exert controls on longitudinal profiles as well (Sklar and Dietrich, 2001). Moreover, longitudinal profiles not only respond to climate by modulating the hydrologic and erosional conditions, but also show effects driven by orographic precipitation (Roe et al., 2002). Longitudinal profile development is also complicated by variable rock strength. Gilbert (1877) first suggested that lithology was of fundamental importance in river erosion and longitudinal profile form. Stock and Montgomery (1999) argued that lithologic controls produce large variability in river long-profile development. Duvall et al. (2004) showed that lithology is important in determining the concavity of river profiles. Although long-profiles are the consequence of complex interactions between a range of variables, they are markers for understanding crustal processes in the topographic landscape.The aim of this study is to distinguish between rock resistance and rock uplift influences on river profile and topographic form in the terrestrial forearc of an active subduction zone. A simple approach is taken here to assess the relationship between river morphology, rock resistance and tectonic rock uplift in the coastal mountains of Oregon between 42° and 46°N. Forty-one rivers flowing generally from the drainage divide westward to the Pacific Ocean on the windward, western flank of the range were selected to minimize orographic effects. To a first order, therefore, the variables controlling river profile form, and hence the topographic relief of the range, are rock uplift rate and lithologic variation, all of which vary systematically along-strike. Two uplift rate datasets exist for the west flank of the Coast Range. We invoke established slope-area analyses (Hurtrez et al., 1999;Snyder et al., 2000;Kirby an...

Scale Dependence of Lithological Control on Topography: Bedrock Channel Geometry and Catchment Morphometry in Western Scotland

“…Other examples of lithology influencing channel concavity (and steepness) are documented for streams draining the Santa Ynez Mountains, California (Duvall et al 2004), and the Oregon coastal mountains ( VanLaningham et al 2006), andMiller (1958) demonstrates an important role for lithology in channel slope and morphology in the Sangre de Cristo Range, New Mexico. On the other hand, Brookfield (1998) argues for absence of lithological control of regional-scale river slopes fringing the Himalayas in favor of discontinuities being the product of differential rock uplift or river capture.…”

“…Measures of concavity (C i and v) vary widely in the study catchments and are not systematically scaled with drainage area or substrate erodibility. If concavity is influenced by lithological controls, as suggested by VanLaningham et al (2006) for the Oregon coastal mountains, such effects are restricted to the subcatchment scale in western Scotland.…”

Geomorphic evidence of unrecognized Balapur fault segment in the southwest Kashmir basin of northwest Himalayas

“…The morphology of longitudinal profiles are the consequence of complex interactions between a range of variables (e.g., lithological contrasts, structural features, tectonic episodes, climate, landslides, stream power, and anthropogenic interferences) (Seeber and Gornitz, 1983;Merritts and Vincent, 1989;Moglen and Bras, 1995;Sklar and Dietrich, 1998;Hurtrez et al, 1999;Stock and Montgomery, 1999;Whipple and Tucker, 1999;Snyder et al, 2000;Kirby and Whipple, 2001;Duvall et al, 2004;Whipple, 2004;VanLaningham et al, 2005;Korup, 2006;Ouimet et al, 2007). In the present study, we used the longitudinal river profile and SL to identify morphotectonic anomalies and their correlation with controlling factors, i.e., lithology and tectonics; however, other factors affecting the stream gradient are not addressed in the present study.…”

Morphometric Analyses of Danxia Landforms in Relation to Bedrock Geology: A Case of Mt. Danxia, Guangdong Province, China

“…Our results agree with Duvall et al [7] who indicated streams flowing from resistant to less resistant bedrock exhibit highly concave profiles and increased gradients along their lower reaches. In addition, VanLaningham et al [43] noted that rivers on more resistant rocks have lower longitudinal concavity.…”