Date of Award
Master of Arts (MA)
At Mt. Rainier, Washington, the intersection of climatic, glacial and volcanic processes conspire to create an extremely active landscape with the potential to respond dramatically to recent warming. In particular, perturbations to the frequency of the debris flows and floods that continually move mass from the mountain’s flanks to downstream settings present a hazard to both the visitors and infrastructure of Mount Rainier National Park and downstream communities.
This work focuses on Tahoma Creek, a 40 km2 basin on the southwest flank of Mt. Rainier. In the first chapter, we investigate fluvial transport processes occurring in the lower reaches of Tahoma Creek, below the influence of debris flows. Three aerial LiDAR datasets are used to create morphologic budgets that document channel change throughout the basin. We translate that change into estimates of bed load transport, and then present a method for interpolating a sediment rating curve for daily transport from this data. We confirm that our ability to predict sediment loads in steep streams is generally meager. Importantly, we show that, while equations generally over-predict transport at low to moderate flows, they significantly under-predict transport during very high flows, with large potential impacts on estimates for net sediment transport when considered over decadal to centennial scales. In the second chapter, we focus on the recent and historical sediment fluxes within Tahoma Creek in the context of geomorphic change. We first document channel change in response to recent debris flows, using LiDAR and dendrogeomorphic methods. We then use a suite of historic records to assess if any long-term trends in the morphology of Tahoma Creek are present that may reflect changes in regional climate. Finally, we construct a chronology of debris flows and floods within the basin since c. 1500 using tree core records from valley-floor conifers. We examine trends in debris flow frequency, and assess which climatic or glacial processes may control that frequency. We show that debris flows occur predominately during the onset of glacial retreat, though whether this reflects changes in sediment availability or changes in outburst flood frequency is unclear.
Anderson, Scott Wallace, "Sediment fluxes in a changing climate: Tahoma Creek over daily to centennial time-scales" (2013). Geography Graduate Theses & Dissertations. 46.