How does sediment grain size decrease as rocks are transported within the flowing water of a river?

Keywords: rocks, sediment, mass, silt, river
Abstract Type: Poster Abstract

Abstract

Rocks originate in landscapes and can break down into sediments through groundwater processes or erode downslope and enter river channels. This study focuses on the latter. Finding how sediments erode within a river can provide a better understanding of how it can impact other aspects of a river system. The sediment used in this study is densely welded volcanic tuff from Northern California. The rocks were first separated into four distinct size distributions, and then were placed in a water bath until they weighed 1850g when fully soaked. Before and after each tumble, the rocks were weighed, measured, and photographed. The process was repeated until the set had lost ten percent of its total mass. The post-tumble product of silt, fragments, and rocks were dumped over a grate and into a bucket for the silt to settle. Once the silt has settled, it was placed in an oven to begin the evaporation process and dry out the wear product. Our results show that these rocks generated many fragments, despite the grains not rounding. Additionally, we found that each set of rocks lost roughly the same amount of mass no matter the size distribution class, and that distance traveled is a heavy factor in the amount of mass lost for these rocks.