Effects of Talus Deposits on Umtanum Creek Geomorphology Christopher Levy Project Mentor(s): Lisa Ely, PhD
Umtanum Creek is a tributary to the Yakima River south of Ellensburg, Washington. The creek flows through a narrow valley along the base of two geologic features that are a part of the Yakima fold and thrust belt region. To the north of the creek is a talus slope of large basalt boulders and to the south an alluvial fan. The purpose of this study is to determine whether or not the flow of Umtanum Creek is capable of transporting talus boulders of various sizes that fall into the creek channel. The results could indicate how the talus boulders affect the position of the creek channel and morphology. I created eight sites where 40 boulders were measured in the creek along their long and short axes to determine size, shape, and distance from the talus slope. The measurements were graphed to show the depositional distribution of boulders of different angularity and size to determine if they were closer to the talus slope or the alluvial fan. I found that the largest boulders in the channel are closer to the talus slope. These results indicate that the talus is not being transported by the creek under normal flow rates and remains in the creek for extended periods. The influx of talus thus could cause the creek to adjust its path, which might be a characteristic of similar streams adjacent to basalt hillslopes in our region. Presentation Type: Poster Presentation (May 21, 9:30am–3:00pm) Keywords: Talus, Geomorphology, deposition, creek SOURCE Form ID: 130 Did the CRBs Cross the Cascades? Geochemical Characterization of the Mafic Basalt Inclusions in the Devils Horns Rhyolite, Goat Rocks Volcanic Cluster, WA Jess Maynard 1 , Julie Wake 1 , Hannah Shamloo 1 , Kellie Wall 2 1 Central Washington University, Ellensburg, WA; 2 Oregon Department of Geology and Mineral Industries, Portland, OR Project Mentor(s): Hannah Shamloo, PhD 1 The Goat Rocks Volcanic Cluster (GRVC) is an extinct volcanic center of the central Cascades of Washington State. Although extinct, the GRVC records the life cycle of a Cascade volcano from its earliest eruptive deposits ~3.2 Ma to its death ~100 ka. The GRVC provides a unique opportunity to study the development and evolution of a Cascade system, furthering the understanding of volcanic hazards of the Cascades subduction zone. The earliest eruptive unit of Goat Rocks includes the 3.2 Ma Devils Horns Rhyolite, resulting from an explosive caldera-forming eruption which includes mafic lithics. The origin of the mafic inclusions is unknown but is indicative of the substrate the Devils Horns eruption interacted with. To contribute to this understanding, this study characterizes the mafic inclusions, sample GR23-02, found in the Devils Horn Rhyolite of Goat Rocks Volcanic Cluster using bulk rock trace element geochemistry obtained through x-ray fluorescence (XRF) and laser-ablation inductively-coupled-plasma mass-spectrometer (LA-ICP-MS) analysis. Geochemical analysis indicates sample GR23-02 did not originate from nearby Eocene-aged volcanic sources. Instead, the geochemistry of the inclusions agrees closely with compositional signatures of Columbia River Basalt flows, particularly Grouse Creek and Ortley members of the Grande Ronde flow, which occurred between 15.6 and 16.0 Ma, significantly predating Goat Rocks eruptions. The presence of mafic basalt inclusions in significantly younger rhyolite tuff of Devils Horns, Goat Rocks has important implications regarding the extent of Columbia River Basalt flows, timing of major Cascade Range uplift, and mechanisms of transport between the two. Presentation Type: Poster Presentation (May 21, 9:30am–3:00pm) Keywords: Geology, Volcanology, Geochemistry, Petrology SOURCE Form ID: 102
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