A COMPARISON OF SLOPE-AREA ANALYSIS AND CHI PLOT METHODS IN A GEOMORPHIC ANALYSIS OF THE NORWEGIAN ‘PASSIVE’ MARGIN

Fluvial systems are highly sensitive, and respond in predictable ways, to spatial and temporal changes in climatic or tectonic forcing, making them a useful tool in understanding landscape evolution. River profile analysis, a method that transforms longitudinal profile data obtained from digital elevation models (DEMs) into channel slope and drainage area relationships using a stream power model, allows for the extraction of information regarding climatic history and/or rock uplift rates. Two similar, but distinct, profile analysis methods have been developed with the goal of obtaining information about erosion/incision and/or uplift rates. Slope-area analysis is a linear regression of channel slope versus drainage area that allows the extraction of information about channel steepness (ks), which expresses a direct relationship with uplift. Chi plot analysis, a method developed relatively recently, displays a longitudinal profile of elevation versus a spatial integral of drainage area as the distance. While both methods have successfully been used to obtain information about fluvial systems, slope-area analysis can be subject to noise and uncertainty. The chi-plot method is designed to generate a profile that easily displays a steady state stream versus a non-steady state stream and allows for easier identification of transient knickpoints within a fluvial network.

A comparison of the applicability of these two techniques is the focus of a geomorphic analysis of the Norwegian ‘passive’ margin. The region is incised by recent glaciation providing an excellent study area to test the ease of each method in identifying transient knickpoints. Additionally, the Norwegian ‘passive’ margin displays high elevation and high relief topography that is uncharacteristic of typical ancient rifted margins and it has been proposed that the margin has experienced Cenozoic tectonic rejuvenation. As the processes between glaciation and tectonics are different, we would expect transient knickpoints to be inferred from glacial processes while other knickpoints would be expected from tectonic processes. The focus of this work is to identify and understand the characteristics of glacial and tectonic knickpoints, as well as compare and contrast the identification of knickpoints between the slope-area and chi plot methods.