|Department of Geology|
Department of Geology, University of Maryland
Doctorate from Massachusetts Institute of Technology
Probing Earth structure with teleseismic transmitted and reflected waves
September 19, 2014
The U.S. Geological Survey in the 21st Century
Abstract: The U.S. Geological Survey is one of the oldest science bureaus in the federal government. For most of its history, it was organized around the disciplines of geology, hydrology, and topographic mapping. Significant changes in the Survey's disciplinary approach began in the 1990's when it implemented a major national water quality assessment program, added a new discipline in the form of the Biological Resources Division, and downsized its efforts in a number of classical areas of geologic investigation. Over the last 20 years USGS science programs have evolved to meet the needs of modern society for interdisciplinary earth and biological science. During this period the USGS reorganized into a number of interdisciplinary mission areas that cover climate and land use change, natural hazards, ecosystems, energy and minerals, environmental health, and water. The Mid-Atlantic Region is a fertile area for such interdisciplinary investigations, with important ecosystems in the Chesapeake and Delaware Bay regions and the Atlantic coastline. Regulators, resource managers, and planners in the Mid-Atlantic Region and throughout the Nation face many challenges caused by urbanization and population growth, land-use change, climate change, and sea-level rise. The USGS in the 21st Century is striving to generate reliable and objective environmental data and interdisciplinary investigations, which provide important scientific information for wise management of critical natural resources and important ecosystems and for intelligent planning for an uncertain future.
September 26, 2014
Shear Weakening Due to Drainage from Water-Filled Crevasses Along the Margins of Jakobshavn Isbræ
Abstract: Several marine-terminating outlet glaciers on the Greenland Ice Sheet have undergone dynamic thinning, acceleration, and retreat, largely driven by ocean-ice interactions at the glacier terminus. Commensurate with these changes, surface melt rates are also increasing, resulting in enhanced runoff and infiltration known to influence regional ice velocity and mass flux. In particular, Jakobshavn Isbræ has experienced some of the most dramatic changes relative to the other major outlet glaciers largely responsible for Greenland’s contribution to sea level rise. The fast-flowing trunk of Jakobshavn Isbræ is well within the ablation zone and is exposed to significant accumulated runoff and drainage from water-filled crevasses within the shear margins during the summer. The impact of drainage from these structures on Jakobshavn’s response to terminus instability is not well understood. There are seven major water-filled crevasse regions along the margins, with the largest demonstrating potential drainage volume on order of that from large supraglacial lakes. This effort explores the impact of meltwater injection on shear-margin weakening. Meltwater can reduce lateral drag through enhanced sliding due to distributed basal lubrication or reduced ice viscosity due to cryo-hyrologic warming. The finite-element Ice Sheet System Model (ISSM) was used to evaluate the impact of meltwater input into the shear margins on basal sliding and ice stiffness. Ratios of misfit between modeled and measured velocity for inversions of basal friction and ice viscosity show a shift from basal friction-to-viscosity dominated conditions from the winter to the summer, at locations where water-filled crevasses exist.
October 3, 2014
Nonlinear effects of landuse and climate changes on stream channels and networks
October 24, 2014
Ocean Leadership Distinguished Lecture
Old refractory mantle peridotites at mid-ocean ridges
Abstract: Melt supply and crustal thickness can vary along slow-spreading ridges, as suggested by common exposures of serpentinized mantle peridotites on the ocean floor. An unexpected large fraction of these residues of partial melting contains evidence of ancient melt extraction that is unrelated to recent upwelling under the mid-ocean ridges, as well as chemical isolation on a billion year timescale. In this presentation, we will evaluate the geological and geochemical evidence for the widespread distribution of this refractory mantle component, and explore the role that this melting-suppressing material may have during crustal accretion processes at mid-ocean ridges.
October 31, 2014
Revealing the stratigraphy of Martian volcanic deposits using radar
Abstract: Volcanism is one of the key processes that shaped Mars, and huge volcanic provinces such as Tharsis and Elysium produced flows and pyroclastic deposits over hundreds of millions to billions of years. Radar remote sensing has the capability to penetrate through rock and can reveal layers that are hundreds of meters below the surface. Recent ground penetrating radars (GPRs) on the Mars Express and Mars Reconnaissance Orbiter missions have revealed subsurface interfaces associated with lava flows and pyroclastics, and these data provide 3-D stratigraphic profiles, improved limits on unit volumes, and dielectric constant measurements (related to composition and density of the rocks). In the next decade, two rover-based (ExoMars and Mars2020) GPR instruments will provide higher-resolution subsurface profiling. In this talk I will discuss recent results regarding Tharsis and Amazonis Planitia volcanic deposits, show terrestrial analog GPR data, and discuss the future of radars at Mars.
November 7, 2014
Patterns, sources, and impacts of timing variations and trends in seasonal transitions across the coterminous U.S.
November 14, 2014
December 5, 2014
The coordinator for the Colloquium Series is Dr. Sujay Kaushal. You can contact him at skaushal AT umd.edu