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Surface Energy Balance And Melt Thresholds Over 11 Years At Taylor Glacier, Antarctica, Matthew James Hoffman, Andrew G. Fountain, Glen E. Liston

Geography Faculty Publications and Presentations

In the McMurdo Dry Valleys, Victoria Land, Antarctica, melting of glacial ice is the primary source of water to streams, lakes, and associated ecosystems. To understand geochemical fluxes and ecological responses to past and future climates requires a physically based energy balance model. We applied a one-dimensional model to one site on Taylor Glacier using 11 years of daily meteorological data and seasonal ablation measurements. Inclusion of transmission of solar radiation into the ice was necessary to accurately model summer ablation and ice temperatures. Results showed good correspondence between calculated and measured ablation and ice temperatures over the 11 years. …

Economics Of Soil Conservation Adoption In High-Rainfall Areas Of The Ethiopian Highlands, Menale Kassie, Stein Holden, Gunnar Köhlin, Randall Bluffstone

Economics Faculty Publications and Presentations

This study measures the impact of fanya juu bunds (an important soil and water conservation technology and the most popular type of contour bund in east Africa) on the value of crop production in a high-rainfall area in the Ethiopian highlands using cross-sectional multiple plot observations. We applied switching regression, stochastic dominance analysis (SDA), and decomposition and propensity score matching methods to ensure robustness. The switching regression, SDA, and decomposition analyses relied on matched observations, which was important because regression and SDA often do not ensure that comparable plots with conservation technology (conserved) and plots without (unconserved) actually exist in …

Temporal Variations In Physical And Chemical Features Of Cryoconite Holes On Canada Glacier, Mcmurdo Dry Valleys, Antarctica, Andrew G. Fountain, Thomas H. Nylen, Martyn Tranter, Elizabeth A. Bagshaw

Geography Faculty Publications and Presentations

Cryoconite holes in the McMurdo Dry Valleys are ice-lidded, thus isolating the pools of water from the atmosphere and from potential surface melt. Hourly measurements of ice and water temperature and water electrical conductivity (EC) were recorded to broadly characterize the physical and chemical changes on daily to seasonal timescales. Overall, subsurface ice/water temperatures were typically several degrees warmer than air temperatures, underscoring the importance of subsurface solar heating. At no time was surface melt observed and the holes melted from within. Detailed differences in the timing and magnitude of both temperature and EC variations during melt-out and freezeup existed …

Introduction To Special Section On Microcosms In Ice: The Biogeochemistry Of Cryoconite Holes, Andrew G. Fountain, Martyn Tranter

Geology Faculty Publications and Presentations

Cryoconite holes are small, water filled, cylindrical melt-holes on glacial ice surface. Cryoconite, 'cold dust,' refers to the thin layer of sediment at the hole bottom. The holes form from surficial sediment patches that absorbs more solar radiation than the surrounding ice and which preferentially melt into the glacier forming a cylindrical water-filled hole. These holes form on the ice-covered, as opposed to snow covered, parts of glaciers world-wide, wherever there is sufficient energy for melting. Biogeochemically, cryoconite holes are interesting because the sediment is inncoculated with biologic material, a fraction of which thrives in the cryoconite environment of near-freezing …

Hydrologic Response To Extreme Warm And Cold Summers In The Mcmurdo Dry Valleys, East Antarctica, Peter T. Doran, Christopher P. Mckay, Andrew G. Fountain, Thomas H. Nylen, Diane M. Mcknight, Chris Jaros, John E. Barrett

Geography Faculty Publications and Presentations

The meteorological characteristics and hydrological response of an extreme warm, and cold summer in the McMurdo Dry Valleys are compared. The driver behind the warmer summer conditions was the occurrence of down-valley winds, which were not present during the colder summer. Occurrence of the summer down-valley winds coincided with lower than typical mean sea level pressure in the Ross Sea region. There was no significant difference in the amount of solar radiation received during the two summers. Compared to the cold summer, glaciological and hydrological response to the warm summer in Taylor Valley included significant glacier mass loss, and 3- …

Quantifying Twentieth Century Glacier Change In The Sierra Nevada, California, Hassan J. Basagic

Dissertations and Theses

Numerous small alpine glaciers occupy the high elevation regions of the central and southern Siena Nevada, California. These glaciers change size in response to variations in climate and are therefore important indicators of climate change. An inventory based on USGS topographic maps (l :24,000) revealed 1719 glaciers and perennial snow and ice features for a total area of 39.l5 ±7.52 km². The number of 'true' glaciers, versus non-moving ice, is estimated to be 118, covering 15.87 ± 1.69 Km². All glaciers were located on north to northeast aspects, at elevations >3000 m. Historical photographs, geologic evidence, …

Plagioclase Populations And Zoning In Dacite Of The 2004–2005 Mount St. Helens Eruption: Constraints For Magma Origin And Dynamics, Martin J. Streck, Cindy A. Broderick, Carl R. Thornber, Michael A. Clynne, John S. Pallister

Geology Faculty Publications and Presentations

We investigated plagioclase phenocrysts in dacite of the 2004–5 eruption of Mount St. Helens to gain insights into the magmatic processes of the current eruption, which is char­acterized by prolonged, nearly solid-state extrusion, low gas emission, and shallow seismicity. In addition, we investigated plagioclase of 1980–86 dacite.

Light and Nomarski microscopy were used to texturally characterize plagioclase crystals. Electron microprobe analy­ses measured their compositions. We systematically mapped and categorized all plagioclase phenocrysts in a preselected area according to the following criteria: (1) occurrence of zones of acicular orthopyroxene inclusions, (2) presence of dissolution surface(s), and (3) spatial association of 1 …