Physical Sciences and Mathematics | Open Access Articles

Spatial And Temporal Melt Variability At Helheim Glacier, East Greenland, And Its Effect On Ice Dynamics, M. L. Andersen, T. B. Larsen, M. Nettles, P. Elosegui, D. Van As, Gordon S. Hamilton, Leigh A. Stearns, J. L. Davis, A. P. Ahlstrøm, J. De Juan, G. Ekström, L. Stenseng, S. A. Khan, R. Forsberg, D. Dahl-Jensen

Earth Science Faculty Scholarship

Understanding the behavior of large outlet glaciers draining the Greenland Ice Sheet is critical for assessing the impact of climate change on sea level rise. The flow of marine-terminating outlet glaciers is partly governed by calving-related processes taking place at the terminus but is also influenced by the drainage of surface runoff to the bed through moulins, cracks, and other pathways. To investigate the extent of the latter effect, we develop a distributed surface-energy-balance model for Helheim Glacier, East Greenland, to calculate surface melt and thereby estimate runoff. The model is driven by data from an automatic weather station operated …

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Discovery Of A Nanodiamond-Rich Layer In The Greenland Ice Sheet, Andrei V. Kurbatov, Paul Andrew Mayewski, Jorgen P. Steffensen, Allen West, Douglas J. Kennett, James P. Kennett, Ted E. Bunch, Mike Handley, Douglas S. Introne, Shane S. Que Hee, Christopher Mercer, Marilee Sellers, Feng Shen, Sharon B. Sneed, James C. Weaver, James H. Wittke, Thomas W. Stafford, John J. Donovan, Sujing Xie, Joshua J. Razink, Adrienne Stich, Charles R. Kinzie, Wendy S. Wolbach

Earth Science Faculty Scholarship

We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5!106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or …

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Softening The Lower Crust: Modes Of Syn-Transport Transposition Around And Adjacent To A Deep Crustal Granulite Nappe, Parry Sound Domain, Grenville Province, Ontario, Canada, Nicholas Culshaw, Christopher Gerbi, Jeff Marsh

Earth Science Faculty Scholarship

The Parry Sound domain is a granulite nappe-stack transported cratonward during reactivation of the ductile lower and middle crust in the late convergence of the Mesoproterozoic Grenville orogeny. Field observations suggest the following with respect to the ductile sheath: (1) Formation of a carapace of transposed amphibolite facies gneiss derived from and enveloping the western extremity of the Parry Sound domain and separating it from high-strain gneiss of adjacent allochthons. This ductile sheath formed dynamically around the moving granulite nappe through the development of systems of progressively linked shear zones. (2) Transposition initiated by hydration (amphibolization) of granulite facies gneiss …

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Three-Dimensional Mechanics Of Yakutat Convergence In The Southern Alaskan Plate Corner, Peter O. Koons, B. P. Hooks, T. Pavlis, P. Upton, A. D. Barker

Earth Science Faculty Scholarship

Three-dimensional numerical models are used to investigate the mechanical evolution of the southern Alaskan plate corner where the Yakutat and the Pacific plates converge on the North American plate. The evolving model plate boundary consists of Convergent, Lateral, and Subduction subboundaries with flow separation of incoming material into upward or downward trajectories forming dual, nonlinear advective thermal/mechanical anomalies that fix the position of major subaerial mountain belts. The model convergent subboundary evolves into two teleconnected orogens: Inlet and Outlet orogens form at locations that correspond with the St. Elias and the Central Alaska Range, respectively, linked to the East by …

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Sudden Increase In Tidal Response Linked To Calving And Acceleration At A Large Greenland Outlet Glacier, Julia De Juan, Pedro Elósegui, Meredith Nettles, Tine B. Larsen, James L. Davis, Gordon S. Hamilton, Leigh A. Stearns, Morten L. Andersen, Göran Ekström, Andreas P. Ahlstrøm, Lars Stenseng, S. Abbas Khan, Rene Forsberg

Earth Science Faculty Scholarship

Large calving events at Greenland's largest outlet glaciers are associated with glacial earthquakes and near instantaneous increases in glacier flow speed. At some glaciers and ice streams, flow is also modulated in a regular way by ocean tidal forcing at the terminus. At Helheim Glacier, analysis of geodetic data shows decimeter-level periodic position variations in response to tidal forcing. However, we also observe transient increases of more than 100% in the glacier's responsiveness to such tidal forcing following glacial-earthquake calving events. The timing and amplitude of the changes correlate strongly with the step-like increases in glacier speed and longitudinal strain …

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A New Technique For Firn Grain-Size Measurement Using Sem Image Analysis, N. E. Spaulding, D. A. Meese, I. Baker, Paul Andrew Mayewski Dr., Gordon S. Hamilton

Earth Science Faculty Scholarship

Firn microstructure is accurately characterized using images obtained from scanning electron microscopy (SEM). Visibly etched grain boundaries within images are used to create a skeleton outline of the microstructure. A pixel-counting utility is applied to the outline to determine grain area. Firn grain sizes calculated using the technique described here are compared to those calculated using the techniques of Cow (1969) and Gay and Weiss (1999) on samples of the same material, and are found to be substantially smaller. The differences in grain size between the techniques are attributed to sampling deficiencies (e.g. the inclusion of pore filler in the …

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Ice Layers As An Indicator Of Summer Warmth And Atmospheric Blocking In Alaska, Eric P. Kelsey, Cameron P. Wake, Karl J. Kreutz, Erich Osterberg

Earth Science Faculty Scholarship

Samples were collected from a snow pit and shallow urn core near Kahiltna Pass (2970 m a.s.l.), Denali National Park, Alaska, USA, in May 2008. The record spans autumn 2003 to spring 2008 and reveals clusters of ice layers interpreted as summertime intervals of above-freezing temperatures. High correlation coefficients (0.75-1.00) between annual ice-layer thickness and regional summertime station temperatures for 4 years (n=4) indicate ice-layer thickness is a good proxy for mean and extreme summertime temperatures across Alaska, at least over the short period of record. A Rex-block (aka high-over-low) pattern, a downstream trough over Hudson Bay, Canada, and an …

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Subcritical Propagation And Coalescence Of Oil-Filled Cracks: Getting The Oil Out Of Low-Permeability Source Rocks, Z.-H. Jin, Scott E. Johnson, Z. Q. Fan

Earth Science Faculty Scholarship

We use a fracture mechanics model to study subcritical propagation and coalescence of single and collinear oil-filled cracks during conversion of kerogen to oil. The subcritical propagation distance, propagation duration, crack coalescence and excess oil pressure in the crack are determined using the fracture mechanics model together with the kinetics of kerogen-oil transformation. The propagation duration for the single crack is governed by the transformation kinetics whereas the propagation duration for the multiple collinear cracks may vary by two orders of magnitude depending on initial crack spacing. A large amount of kerogen (>90%) remains unconverted when the collinear cracks …

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Earth Science Faculty Scholarship

Earth Science Faculty Scholarship

Softening The Lower Crust: Modes Of Syn-Transport Transposition Around And Adjacent To A Deep Crustal Granulite Nappe, Parry Sound Domain, Grenville Province, Ontario, Canada, Nicholas Culshaw, Christopher Gerbi, Jeff Marsh

Earth Science Faculty Scholarship

Three-Dimensional Mechanics Of Yakutat Convergence In The Southern Alaskan Plate Corner, Peter O. Koons, B. P. Hooks, T. Pavlis, P. Upton, A. D. Barker

Earth Science Faculty Scholarship

Earth Science Faculty Scholarship

A New Technique For Firn Grain-Size Measurement Using Sem Image Analysis, N. E. Spaulding, D. A. Meese, I. Baker, Paul Andrew Mayewski Dr., Gordon S. Hamilton

Earth Science Faculty Scholarship

Ice Layers As An Indicator Of Summer Warmth And Atmospheric Blocking In Alaska, Eric P. Kelsey, Cameron P. Wake, Karl J. Kreutz, Erich Osterberg

Earth Science Faculty Scholarship

Subcritical Propagation And Coalescence Of Oil-Filled Cracks: Getting The Oil Out Of Low-Permeability Source Rocks, Z.-H. Jin, Scott E. Johnson, Z. Q. Fan

Earth Science Faculty Scholarship