The Control of Igneous Lithology on Step Pools in Alpine Streams: San Juan Mountains, CO

Abstract

Step-pool sequences have long been studied in high-gradient streams for the application in erosion control, ecology, and restoration projects. Step-pool sequences are defined as an alternating series of clasts and pools, which self-form to maximize flow resistance. Many studies have been undertaken to identify the main factors that influence formation, but few have taken lithology into account. This study focuses on igneous rocks in the San Juan Mountains surrounding Ouray, CO, to ascertain if igneous-based step pools adhere to the commonly accepted principles governing formation and characteristics of step pools. Based on the data from this study, no strong evidence was found for a correlation between step wavelength and step height. A large percentage of the data supports a correlation between step wavelength and channel width, but a linear prediction model would be inaccurate. The relationship between clast size and step height appears to have a positive correlation for igneous rock, which coincides with much of the existing literature. Step wavelength and reach slope appear to also have a positive relationship. Step steepness does not appear to be related to slope. The correlation increased dramatically after removing outliers from the dataset, but unfortunately a very small sample size was observed.