Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item A forest entombed in ice: a unique record of mid-Holocene climate and ecosystem change in the northern Rocky Mountains, USA(Montana State University - Bozeman, College of Letters & Science, 2022) Stahle, Daniel Kent; Chairperson, Graduate Committee: David McWethy; This is a manuscript style paper that includes co-authored chapters.Across the high alpine of the northern Rocky Mountains small vestiges of perennial ice have endured for thousands of years. These ice patches reside hundreds of meters above modern treeline, with some persisting through mid-Holocene warmth and others establishing at the onset of a cooler period that began around 5,000-5,500 years BP. Recent warming-driven melting at the margins of one ice patch high on the Beartooth Plateau of northern Wyoming exposed over 30 intact mature whitebark pine (Pinus albicaulis) tree boles, all > 25 cm in diameter. We extracted cross-sectional samples from the stems of 27 preserved logs, and radiocarbon dated annual growth rings from 11 of these trees, anchoring the chronology to a date range spanning 5,947 to 5,436 years BP + or - 51.3 years. From this fossil wood chronology, we developed estimates of warm-season, annual, and biennial average temperatures for upper-elevation treeline during the mid-Holocene. To identify the predominant climate-growth relationships of the subfossil trees, we sampled live whitebark pine trees growing at an adjacent treeline site approximately 120 m lower in elevation. Temperature was found to be the major driver of variability in tree growth at the modern treeline location, with trees producing narrower (wider) rings during periods of cooler (warmer) growing season temperatures. Using linear and non-linear transfer functions based upon the stable statistical relationship between modern tree growth and temperature, we reconstructed past temperature estimates from the ice patch subfossil ring-width chronology. Our results provide estimates of mid-Holocene warm-season (and biennial) average temperatures ranging from 5.7-6.5 °C (-0.44-0.26 °C) respectively. A multi-century regional cooling trend beginning around 5,650 years BP resulted in average temperatures declining below a warm-season (biennial) critical threshold of ~5.8 °C (-0.34 °C), likely leading to the eventual death of the whitebark pine stand and subsequent formation of the ice-patch. This high-quality paleo-ecological dataset reveals a major shift in the alpine and forest ecotone on the Beartooth Plateau following the mid-Holocene warm period and offers further insight on the thermal limits of whitebark pine trees in the Greater Yellowstone Ecosystem.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 Ice movement and structural characteristics of the Cathedral Glacier system, Atlin Provincial Park, British Columbia(Montana State University - Bozeman, College of Letters & Science, 1983) Johnson, Ronald FrederickItem Regional context, internal structure, and microbiological investigation of the Lone Peak Rock Glacier, Big Sky, Montana(Montana State University - Bozeman, College of Letters & Science, 2011) Florentine, Caitlyn Elizabeth; Chairperson, Graduate Committee: Mark L. Skidmore; Mark Skidmore, Marvin Speece, Curtis Link, William Locke, Christina Carr, and Colin Shaw were co-authors of the article, 'The role of geology in rock-glacier distribution and internal structure: a case study from SW Montana' in the journal 'Journal of geophysical research earth surface' which is contained within this thesis.; Mark Skidmore and Scott Montross were co-authors of the article, 'Rock-glacier ice as a microbial habitat' in the journal 'Journal of glaciology' which is contained within this thesis.This thesis is the first to the author's knowledge to conduct a holistic investigation of the physical, chemical and microbial properties of a rock glacier. The Lone Peak Rock Glacier (LPRG) is located in the Madison Range of southwest Montana on Big Sky Resort property. This thesis focuses on three scales of investigation: regional, landform, and micro. Regional-scale analysis assessed the role of geology and topography as factors in determining rock-glacier distribution in SW Montana above 2000m. Rock glaciers across alpine landscapes in southwest Montana are preferentially distributed according to rock type, with more rock glaciers occurring in intrusive, foliated intrusive and metamorphic catchments relative to the areal proportion of these rock types than in extrusive and sedimentary catchments. This preferential distribution according to catchment geology is likely due to the affect that geology has on topography and provision of talus. Landform-scale analysis focuses on internal structure, flow dynamics and surface topography of the LPRG. The relationship between surface topography and subsurface structure is explained by passive roof duplex faulting. This finding has implications for rock-glacier flow dynamics and the development of transverse ridges, a common surface feature of rock glaciers studied worldwide. Micro-scale analysis characterizes microbiological and geochemical properties of rock-glacier ice and evaluates it as a microbial habitat, exploring potential associations between debris content and microbial activity. Amber ice (containing 0.1% debris by weight) appears to be a more suitable microbial environment than debris-poor ice (containing < 0.01% debris). This finding highlights the importance of debris as a potential nutrient and energy source to enhance microbial viability in rock-glacier ice.