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Item Construction and modification of debris-flow alluvial fans as captured in the geomorphic and sedimentary record: examples from the western Sangre de Cristo Mountains, south-central Colorado(Montana State University - Bozeman, College of Letters & Science, 2020) Nicovich, Sylvia Rose; Chairperson, Graduate Committee: Mary S. Hubbard; James G. Schmitt (co-chair); James Schmitt was a co-author of the article, 'Deposition and modification of debris-flow alluvial fans, western rangefront of the Sangre de Cristo Mountains, south-central Colorado' submitted to the journal 'Journal of sedimentary research' which is contained within this dissertation.; Jim Schmitt, Ralph Klinger and Shannon Mahan were co-authors of the article, 'Late Pleistocene record of surface-modifying processes on the Pioneer debris-flow alluvial fan, San Luis Valley, Colorado' submitted to the journal 'Geological Society of America bulletin' which is contained within this dissertation.; James Schmitt was a co-author of the article, 'Impact of wind-blown sediment on the Pioneer debris-flow alluvial fan, south-central Colorado: concepts of fan activity' submitted to the journal 'Geosphere' which is contained within this dissertation.Alluvial fans and their deposits in the stratigraphic record are key in unraveling intricacies of landscape, tectonic, and climatic dynamics, though integrative geomorphologic and sedimentologic studies that comprehensively evaluate processes which build and modify fans are lacking. Therefore, a gap within the current body of literature exists concerning the sedimentological signature of depositional and surface-modifying processes on alluvial fans. This dissertation presents the sedimentological characteristics, both surficial and in the sedimentary record, of processes that build and modify alluvial fans while revisiting the contemporary concept of what defines an active surface. Detailed analysis of a suite of Quaternary active debris-flow alluvial fans on the western range front of the Sangre de Cristo Mountains in south-central Colorado was made using integrative sedimentological and geomorphic analysis, facies and soils mapping, along with infrared stimulated luminescence (IRSL) geochronology to document timing of fan construction and modification processes recorded in the alluvial fan deposits. Analysis of surface geomorphology, facies assemblages, and particle-size distributions of matrix from various facies of exposed alluvial fan deposits were also applied. These data show a clear distinction between sedimentary facies that represent processes of the primary depositional lobe surfaces versus those operating during periods of non-primary deposition, dominant on abandoned lobes. Primary processes on depositional lobes are debris flow and hyperconcentrated flow with minimal secondary modifying processes. Overland flow, input of eolian material, pedogenesis, and rock and mineral weathering are the main secondary modifying processes that govern abandoned lobes. Addition of wind-blown material, a secondary modifying process, plays a significant part in the sedimentary processes that operate on alluvial fan surfaces, ultimately influencing fan smoothing by mobilizing material derived from primary processes.Item Landslide morphology and its insight into the timing and causes of slope failure: case study of post-glacial landslides in Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2018) Nicholas, Grace Ellen; Chairperson, Graduate Committee: Jean DixonLandslides are ubiquitous to post-glacial landscapes worldwide. Withdrawal of glacier ice exposes over-steepened landscapes that may be unstable, and consequently susceptible to landsliding. Glacial debuttressing may directly destabilize slopes; however, seismicity and transitions to interglacial climates associated with greater effective moisture and subsequent degradation of permafrost may also play a role. Here, we explore disparate potential mechanisms of slope failure in a set of post-glacial landslides in northwest Yellowstone National Park. We quantify spatial relationships, topographic metrics, and relative age of eight landslides within the north entrance to the park, a system traversed by over 700,000 visitors every year. Analysis of high-resolution topography indicates increasing surface roughness of non-active landslides southward. These roughness values in ancient slides are roughly half those of the active Slide Lake Landslide, and suggest younging ages along the retreat path of the Yellowstone Ice Cap, consistent with glacial debutressing as the likely trigger for these slides. However, roughness values and their application for relative age dating are strongly confounded by topographic biases such as gullying, fluvial erosional contacts, and anthropogenic features (e.g., roads, structures). Once roughness biases are removed, we find roughness differences between landslides decrease, and do not support younging ages along the path of ice retreat. Thus, glacial debuttressing most likely only had a preparatory influence on slope failure, and was not the direct trigger. Analysis of subsurface soils at landslide toes indicate a >17 plasticity index, pointing to highly expansive clays that are sensitive to moisture addition. Stratigraphic relationships between post-glacial terraces and soil analyses suggest a late Pleistocene (~13 - 11.5 ka) timing for slide initiation, a period coincident with high available moisture. Stream power analysis indicates that Holocene incision of the Gardiner River is focused at a knickpoint locally coincident with the toe of the active Slide Lake Landslide, providing a mechanism for modern, local reactivation of the ancient slides. Together, our findings broadly show how quantifying the temporal and spatial patterns of landslides can be diagnostic of the controls on slope failure, and can be used to understand risk. They also highlight the importance of careful site calibrations and bias removals in roughness analysis.Item Morphologic and climatic controls on soil evolution in the Bitterroot and Sapphire Mountains, Montana(Montana State University - Bozeman, College of Letters & Science, 2017) Benjaram, Sarah Sarojini; Chairperson, Graduate Committee: Jean DixonTo what extent is chemical weathering governed by a landscape's topography? Two neighboring mountain ranges in the northern Rockies of western Montana, USA, provide an ideal natural laboratory in which to investigate the relationship between soil chemical weathering, persistence of soil cover, and topography. We also examine the connection between the topography and climate history. The mountain ranges we explore are the previously glaciated Bitterroot Mountains, which consist of steep, rock-dominated hillslopes, and the neighboring unglaciated Sapphire Mountains which display convex, soil-mantled hillslopes. Soil thickness measurements, soil and rock geochemistry, and digital terrain analysis reveal that soils in the rock-dominated Bitterroot Mountains are less thoroughly weathered than those in the Sapphire Mountains. These differences are even greater when we adjust weathering for rock fragments and consider surface weathering intensity at a landscape scale using our newly developed metric, the rock-adjusted chemical depletion fraction (RACDF) and rock-adjusted mass transfer coefficient (RA t). The Bitterroots overall are 30% less weathered than the Sapphires despite higher mean annual precipitation in the former, with an average RACDF of 0.38 in the postglacial Bitterroots catchment and 0.61 in the nonglacial Sapphire catchment, suggesting that 38% of rock mass is lost in the conversion to soil in the Bitterroots, whereas 61% of rock mass is lost in the nonglaciated Sapphires. Though we find little evidence for modern climate influence on weathering, data suggest that precipitation may influence slope thresholds for soil cover. Forested soils persist on slopes that are 5° higher in the Bitterroots than the Sapphires (25° and 20° respectively), based on land cover data. Because the previously glaciated Bitterroots are less weathered despite being wetter, we conclude that the glacial history of this landscape exerts more influence on soil chemical weathering than does modern climate. However, while previous studies have correlated weathering intensity with topographic parameters such as slope gradient, we find little topographic indication of specific controls on weathering in these complex systems.Item Sedimentology of alpine debris-flow and talus deposits in Sacajawea cirque Bridger Range, Montana(Montana State University - Bozeman, College of Letters & Science, 1994) Werner, Amanda VroomanItem Cenozoic geology and geomorphology of the Dry Creek Valley, Gallatin County, Montana(Montana State University - Bozeman, College of Letters & Science, 1980) Hughes, Gary ClaudeItem Quaternary glacial geology and geomorphology of the Teton drainage area, Teton County, Montana(Montana State University - Bozeman, College of Letters & Science, 1968) Chalmers, Ann LeslieItem A spatial comparison of channel morphology between burn, timber and old growth areas within the Yellowstone ecosystem(Montana State University - Bozeman, College of Letters & Science, 1997) Myers, Stephen CharlesItem Geomorphic response of the Madison River to point sediment loading at the Madison Slide, southwest Montana(Montana State University - Bozeman, College of Letters & Science, 1995) Turner, Theodore RoyItem Evaluation of GIS-based topographic attributes and a soil wetness model for assessing landslide potential in the Middle Fork of the Payette River catchment, Idaho(Montana State University - Bozeman, College of Letters & Science, 1998) Lineback, Mandy AliciaItem The use of multispectral digital imagery to map hydrogeomorphic stream units in Soda Butte and Cache Creeks, Montana and Wyoming(Montana State University - Bozeman, College of Letters & Science, 1998) Wright, Andrea