Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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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 Effect of permafrost thaw on methane and carbon dioxide exchange in two western Alaska peatlands(Montana State University - Bozeman, College of Agriculture, 2013) Johnston, Carmel Eliise; Chairperson, Graduate Committee: Stephanie A. Ewing; Stephanie A. Ewing, Jennifer W. Harden, Paul C. Stoy, Ruth K. Varner, Kimberly P. Wickland, Joshua Koch, Christopher Fuller and Mark T. Jorgenson were co-authors of the article, '2.0 effect of permafrost thaw on CO 2 and CH 4 exchange in a western Alaska peatland chronosequence' submitted to the journal 'Environmental research letters' which is contained within this thesis.; Stephanie A. Ewing, Merritt R. Turetsky, Jennifer W. Harden, A. David McGuire and Miriam Jones were co-authors of the article, '3.0 effect of recent permafrost thaw on the spatial distribution of CO 2 and CH 4 exchange in a western Alaska peatland' submitted to the journal 'Environmental research letters' which is contained within this thesis.Methane (CH 4) causes about 20% of greenhouse gas radiative forcing despite its relatively short lifetime (~10 y) and low concentration (1800 ppb) in the atmosphere. Wetlands are the largest natural source of CH 4, amounting to 22% of CH 4 production globally, with emission of CH 4-C by both diffusion and ebullition pathways. Permafrost peatlands store about 10% of permafrost C and 5% of global belowground C; hence CH 4- C emission with peatland permafrost thaw is of concern. We quantified temporal and spatial aspects of CH 4 and CO 2 emissions from northern peatlands using two approaches: (1) a ~1000 y thaw chronosequence in remote western Alaska (Innoko Flats Wildlife Refuge; May-September, 2011), and (2) lateral transects in intermediate age (~20-500 y) collapse-scar bog features at a well-instrumented site near Fairbanks, Alaska (Alaska Peatland Experiment (APEX)/Bonanza Creek Long Term Experimental Research site; June-September, 2012). At Innoko Flats, peak CH 4 production was observed in features aged 30-590 y since thaw, which had warmer soils than younger sites and shallower water tables than older sites. Average surface flux at these 30-590 y sites (+2.52 ± 0.98 mg CH 4-C m -2 hr -1) was greater than estimated ebullition flux (0.13 ± 0.05 mg CH 4-C m -2 hr -1) based on an observed rate of 0.78 ± 0.33 mL m -2 hr -1. Net ecosystem exchange of CO 2-C (NEE) did not differ among chronosequence features, and offset CH 4-C emissions by a factor of 2 to 400 when considered as 100-y global warming potential. At APEX, bogs reflecting <100 y since most recent thaw showed high variability in CH 4 exchange, but rates were generally consistent with levels at the Innoko 30-590 y sites (mean of 5.42 ± 1.16 mg CH 4-C m -2 hr -1). APEX bogs showed greater balance between CH 4-C efflux and CO 2-C influx, with CH 4-C fluxes offsetting 80-140% of NEE during the growing season when considered as 100-y global warming potential. We argue that CH 4 contributes most significantly to post-thaw C loss over timescales of decades to centuries in these northern peatlands.Item The effects of snow compaction on water release & sediment yield(Montana State University - Bozeman, College of Letters & Science, 1982) Grady, Thomas R.Item Experimental investigation of the thermal effects of frost susceptible soils(Montana State University - Bozeman, College of Engineering, 2005) Newell, Zachary Allen; Chairperson, Graduate Committee: Robert Mokwa.Damages to engineering structures attributed to frost action of subgrade soils amounts to millions of dollars annually. Theoretical research has been conducted to examine the details of the frost action phenomenon since the 1940's. However, a reliable and practical approach for evaluating the frost susceptibility of soils is nonetheless a goal that has eluded engineers and scientists alike. The research presented herein focuses on the procedures necessary to obtain a numerical model capable of predicting the thermal response of frost susceptible soils. A field facility was designed and constructed with the purpose of measuring and comparing in-situ frost heave characteristics with laboratory-scale test results. A laboratory-testing device was also designed, constructed, and instrumented in order to measure the thermal response of various soil types in a controlled freezing environment. Geotechnical index testing was conducted on the soil types used in the freezing experiments to fully characterize the soils and examine potential correlations between common soil index properties and frost action behavior. The results of the first season of experimentation provided the framework for a testing protocol necessary for the development of a predictive numerical model. The data obtained from the laboratory tests was used to calculate a new engineering parameter called the segregation potential (SP), which was used as an input into the numerical model developed throughout this research. The model simulated the freezing and thawing characteristics of the soil type found at the field facility. The simulated results were then compared to the in-situ frost action behavior observed at the facility. An improved testing protocol is necessary to obtain more accurate and consistent results. As this research progresses and laboratory testing proceeds, a more extensive database will be acquired and used to build empirical correlations between the thermal and geotechnical index properties of frost susceptible soils. Furthermore, continued research will allow for the advancement of a predictive numerical model that design engineers could use to simulate and predict the freezing and thawing effects of frost susceptible soils incorporated into common engineering structures.