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Articles 121 - 150 of 346
Full-Text Articles in Geophysics and Seismology
Pervasive Changes In Stream Intermittency Across The United States, Kendra E. Kaiser
Pervasive Changes In Stream Intermittency Across The United States, Kendra E. Kaiser
Geosciences Faculty Publications and Presentations
Non-perennial streams are widespread, critical to ecosystems and society, and the subject of ongoing policy debate. Prior large-scale research on stream intermittency has been based on long-term averages, generally using annually aggregated data to characterize a highly variable process. As a result, it is not well understood if, how, or why the hydrology of non-perennial streams is changing. Here, we investigate trends and drivers of three intermittency signatures that describe the duration, timing, and dry-down period of stream intermittency across the continental United States (CONUS). Half of gages exhibited a significant trend through time in at least one of the …
Kinematics Of The Exceptionally-Short Surge Cycles Of Sít’ Kusá (Turner Glacier), Alaska, From 1983 To 2013, Andrew Nolan, William Kochtitzky, Ellyn M. Enderlin, Robert Mcnabb, Karl J. Kreutz
Kinematics Of The Exceptionally-Short Surge Cycles Of Sít’ Kusá (Turner Glacier), Alaska, From 1983 To 2013, Andrew Nolan, William Kochtitzky, Ellyn M. Enderlin, Robert Mcnabb, Karl J. Kreutz
Geosciences Faculty Publications and Presentations
Glacier surges are periodic episodes of mass redistribution characterized by dramatic increases in ice flow velocity and, sometimes, terminus advance. We use optical satellite imagery to document five previously unexamined surge events of Sít’ Kusá (Turner Glacier) in the St. Elias Mountains of Alaska from 1983 to 2013. Surge events had an average recurrence interval of ~5 years, making it the shortest known regular recurrence interval in the world. Surge events appear to initiate in the winter, with speeds reaching up to ~25 m d−1. The surges propagate down-glacier over ~2 years, resulting in maximum thinning of ~100 …
Silicate Melt Inclusions In The New Millennium: A Review Of Recommended Practices For Preparation, Analysis, And Data Presentation, D. Schwartz
Geosciences Faculty Publications and Presentations
Mineral-hosted melt inclusions have become an important source of information on magmatic processes. As the number of melt inclusion studies increases, so does the need to establish recommended practice guidelines for collecting and reporting melt inclusion data. These guidelines are intended to ensure certain quality criteria are met and to achieve consistency among published melt inclusion data in order to maximize their utility in the future. Indeed, with the improvement of analytical techniques, new processes affecting melt inclusions are identified. It is thus critical to be able to reprocess any previously published data, such that reporting the raw data is …
Beyond Streamflow: Call For A National Data Repository Of Streamflow Presence For Streams And Rivers In The United States, Kendra E. Kaiser
Beyond Streamflow: Call For A National Data Repository Of Streamflow Presence For Streams And Rivers In The United States, Kendra E. Kaiser
Geosciences Faculty Publications and Presentations
Observations of the presence or absence of surface water in streams are useful for characterizing streamflow permanence, which includes the frequency, duration, and spatial extent of surface flow in streams and rivers. Such data are particularly valuable for headwater streams, which comprise the vast majority of channel length in stream networks, are often non-perennial, and are frequently the most data deficient. Datasets of surface water presence exist across multiple data collection groups in the United States but are not well aligned for easy integration. Given the value of these data, a unified approach for organizing information on surface water presence …
Backarc Lithospheric Thickness And Serpentine Stability Control Slab-Mantle Coupling Depths In Subduction Zones, Buchanan C. Kerswell, Matthew J. Kohn, Taras V. Gerya
Backarc Lithospheric Thickness And Serpentine Stability Control Slab-Mantle Coupling Depths In Subduction Zones, Buchanan C. Kerswell, Matthew J. Kohn, Taras V. Gerya
Geosciences Faculty Publications and Presentations
A key feature of subduction zone geodynamics and thermal structure is the point at which the slab and mantle mechanically couple. This point defines the depth at which traction between slab and mantle begins to drive mantle wedge circulation and also corresponds with a rapid increase in temperature along the slab-mantle interface. Here, we consider the effects of the backarc thermal structure and slab thermal parameter on coupling depth using two-dimensional thermomechanical models of oceanic-continental convergent margins. Coupling depth is strongly correlated with backarc lithospheric thickness, and weakly correlated with slab thermal parameter. Slab-mantle coupling becomes significant where weak, hydrous …
Atmospheric Blocking Drives Recent Albedo Change Across The Western Greenland Ice Sheet Percolation Zone, Hans Peter Marshall, Tate Meehan
Atmospheric Blocking Drives Recent Albedo Change Across The Western Greenland Ice Sheet Percolation Zone, Hans Peter Marshall, Tate Meehan
Geosciences Faculty Publications and Presentations
Greenland Ice Sheet (GrIS) albedo has decreased over recent decades, contributing to enhanced surface melt and mass loss. However, it remains unclear whether GrIS darkening is due to snow grain size increases, higher concentrations of light-absorbing impurities (LAIs), or a combination. Here, we assess albedo controls in the western GrIS percolation zone using in situ albedo, LAI, and grain size measurements. We find a significant correlation between albedo and snow grain size (p < 0.01), but not with LAIs. Modeling corroborates that LAI concentrations are too low to significantly reduce albedo, but larger grain sizes could reduce albedo by at least ∼3%. Strong atmospheric blocking increases grain sizes and reduces albedo through increased surface temperature, fewer storms, and higher incoming shortwave radiation. These findings clarify the mechanisms by which anomalously strong blocking contributed to recent GrIS albedo decline and mass loss, highlighting the importance of improving projections of future blocking.
Tree Canopy And Snow Depth Relationships At Fine Scales With Terrestrial Laser Scanning, Ahmed Hojatimalekshah, Zachary Uhlmann, Nancy F. Glenn, Jake D. Graham, Hans-Peter Marshall, James P. Mcnamara, Josh Enterkine
Tree Canopy And Snow Depth Relationships At Fine Scales With Terrestrial Laser Scanning, Ahmed Hojatimalekshah, Zachary Uhlmann, Nancy F. Glenn, Jake D. Graham, Hans-Peter Marshall, James P. Mcnamara, Josh Enterkine
Geosciences Faculty Publications and Presentations
Understanding the impact of tree structure on snow depth and extent is important in order to make predictions of snow amounts and how changes in forest cover may affect future water resources. In this work, we investigate snow depth under tree canopies and in open areas to quantify the role of tree structure in controlling snow depth, as well as the controls from wind and topography. We use fine-scale terrestrial laser scanning (TLS) data collected across Grand Mesa, Colorado, USA (winter 2016–2017), to measure the snow depth and extract horizontal and vertical tree descriptors (metrics) at six sites. We utilize …
The Influence Of The Permian-Triassic Magmatism In The Tunguska Basin, Siberia On The Regional Floristic Biota Of The Permian-Triassic Transition In The Region, V. I. Davydov, E. V. Karasev
The Influence Of The Permian-Triassic Magmatism In The Tunguska Basin, Siberia On The Regional Floristic Biota Of The Permian-Triassic Transition In The Region, V. I. Davydov, E. V. Karasev
Geosciences Faculty Publications and Presentations
The end-Permian extinction event (EPEE) considered to have been caused by the eruption of the Siberian Large Igneous Province (SLIP), the age of which is critical for extinction-SLIP model evaluation. The Tunguska Basin flora during this time, in accordance with the EPEE model, supposed to have been killed by the massive injection into the atmosphere of poisonous substances such as methane, sulfates, mercury and massive combastion of coals. In addition, supposed numerous fires presumably devastated the regional flora. However, the diversity of the Tunguska Basin flora drasticly increased at the beginning of Induan or slightly earlier and become diverse at …
Nasa's Surface Biology And Geology Designated Observable: A Perspective On Surface Imaging Algorithms, Nancy F. Glenn
Nasa's Surface Biology And Geology Designated Observable: A Perspective On Surface Imaging Algorithms, Nancy F. Glenn
Geosciences Faculty Publications and Presentations
The 2017–2027 National Academies' Decadal Survey, Thriving on Our Changing Planet, recommended Surface Biology and Geology (SBG) as a “Designated Targeted Observable” (DO). The SBG DO is based on the need for capabilities to acquire global, high spatial resolution, visible to shortwave infrared (VSWIR; 380–2500 nm; ~30 m pixel resolution) hyperspectral (imaging spectroscopy) and multispectral midwave and thermal infrared (MWIR: 3–5 μm; TIR: 8–12 μm; ~60 m pixel resolution) measurements with sub-monthly temporal revisits over terrestrial, freshwater, and coastal marine habitats. To address the various mission design needs, an SBG Algorithms Working Group of multidisciplinary researchers has been formed …
Co-Evolution Of Xylem Water And Soil Water Stable Isotopic Composition In A Northern Mixed Forest Biome, Jenna R. Snelgrove, James M. Buttle, Matthew J. Kohn, Dörthe Tetzlaff
Co-Evolution Of Xylem Water And Soil Water Stable Isotopic Composition In A Northern Mixed Forest Biome, Jenna R. Snelgrove, James M. Buttle, Matthew J. Kohn, Dörthe Tetzlaff
Geosciences Faculty Publications and Presentations
Plant–soil water isotopic dynamics in northern forests have been understudied relative to other forest types; nevertheless, such information can provide insight into how such forests may respond to hydroclimatic change. This study examines the co-evolution of xylem water and soil water stable isotopic compositions in a northern mixed forest in Ontario, Canada. Gross precipitation, bulk soil water and xylem water were sampled from pre-leaf out to post-senescence in 2016 for eastern white cedar, eastern hemlock, red oak and eastern white pine. Near-bole soil water contents and mobile soil water isotopic compositions were measured for the last three species. Mobile soil …
Reconstruction Of Historical Surface Mass Balance, 1984–2017 From Greentraacs Multi-Offset Ground-Penetrating Radar, Tate G. Meehan, H.P. Marshall
Reconstruction Of Historical Surface Mass Balance, 1984–2017 From Greentraacs Multi-Offset Ground-Penetrating Radar, Tate G. Meehan, H.P. Marshall
Geosciences Faculty Publications and Presentations
We present continuous estimates of snow and firn density, layer depth and accumulation from a multi-channel, multi-offset, ground-penetrating radar traverse. Our method uses the electromagnetic velocity, estimated from waveform travel-times measured at common-midpoints between sources and receivers. Previously, common-midpoint radar experiments on ice sheets have been limited to point observations. We completed radar velocity analysis in the upper ∼2 m to estimate the surface and average snow density of the Greenland Ice Sheet. We parameterized the Herron and Langway (1980) firn density and age model using the radar-derived snow density, radar-derived surface mass balance (2015–2017) and reanalysis-derived temperature data. We …
Timescales Of Partial Melting And Melt Crystallization In The Eastern Himalayan Orogen: Insights From Zircon Petrochronology, Huxia Ding, Zeming Zhang, Matthew J. Kohn, Zhenbin Gou
Timescales Of Partial Melting And Melt Crystallization In The Eastern Himalayan Orogen: Insights From Zircon Petrochronology, Huxia Ding, Zeming Zhang, Matthew J. Kohn, Zhenbin Gou
Geosciences Faculty Publications and Presentations
Revealing the timescales of metamorphic and anatectic processes is central to our understanding of tectonic evolution of collisional orogens. High‐temperature migmatites and leucogranites are well exposed in the Himalayan orogenic core, making it an ideal region to study the timing and duration of partial melting and melt crystallization of the orogen. Here, we report an integrated and comprehensive data set of petrography, U‐Pb age, and trace element data for zircon from a pelitic granulite and associated leucosomes of the Greater Himalayan Sequence (GHS) in the Yadong area, eastern Himalaya. Zircon grains with complex internal structure retain variable ages ranging from …
Autocorrelation Infrasound Interferometry, Hugo D. Ortiz, Robin S. Matoza, Jeffrey B. Johnson, Stephen Hernandez, Juan C. Anzieta, Mario C. Ruiz
Autocorrelation Infrasound Interferometry, Hugo D. Ortiz, Robin S. Matoza, Jeffrey B. Johnson, Stephen Hernandez, Juan C. Anzieta, Mario C. Ruiz
Geosciences Faculty Publications and Presentations
Seismic and infrasound multistation ambient‐noise interferometry has been widely used to infer ground and atmospheric properties, and single‐station and autocorrelation seismic interferometry has also shown potential for characterizing Earth structure at multiple scales. We extend autocorrelation seismic interferometry to ambient atmospheric infrasound recordings that contain persistent local noise from waterfalls and rivers. Across a range of geographic settings, we retrieve relative sound‐speed changes that exhibit clear diurnal oscillations consistent with temperature and wind variations. We estimate ambient air temperatures from variations in relative sound speeds. The frequency band from 1 to 2 Hz appears most suitable to retrieve weather parameters …
The Miocene: The Future Of The Past, M. J. Kohn
The Miocene: The Future Of The Past, M. J. Kohn
Geosciences Faculty Publications and Presentations
The Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned toward modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval—the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO2, and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO2 (∼400–600 ppm), the MCO has been suggested as …
A Broad, Distributed Active Fault Zone Lies Beneath Salt Lake City, Utah, Lee M. Liberty, James St. Clair, Adam P. Mckean
A Broad, Distributed Active Fault Zone Lies Beneath Salt Lake City, Utah, Lee M. Liberty, James St. Clair, Adam P. Mckean
Geosciences Faculty Publications and Presentations
Although the Wasatch fault is currently known to have a high‐seismic hazard from motion along range‐bounding faults, new seismic data reveal faulted and folded 13,000–30,000‐yr‐old Lake Bonneville strata beneath Salt Lake City (SLC). Coupled with previous excavation trench, borehole, and other geologic and geophysical observations, we conclude that a zone of latest Pleistocene and/or Holocene faulting and folding kinematically links the East Bench and Warm Springs faults through a 3 km wide relay structure and transfer zone. We characterize faults beneath downtown SLC as active, and these faults may displace or deform the ground surface during an earthquake. Through offset …
Understanding The Effect Of Fire On Vegetation Composition And Gross Primary Production In A Semi-Arid Shrubland Ecosystem Using The Ecosystem Demography (Edv2.2) Model, Karun Pandit, Hamid Dashti, Andrew T. Hudak, Nancy F. Glenn, Alejandro N. Flores, Douglas J. Shinneman
Understanding The Effect Of Fire On Vegetation Composition And Gross Primary Production In A Semi-Arid Shrubland Ecosystem Using The Ecosystem Demography (Edv2.2) Model, Karun Pandit, Hamid Dashti, Andrew T. Hudak, Nancy F. Glenn, Alejandro N. Flores, Douglas J. Shinneman
Geosciences Faculty Publications and Presentations
Wildfires in sagebrush (Artemisia spp.)-dominated semi-arid ecosystems in the western United States have increased dramatically in frequency and severity in the last few decades. Severe wildfires often lead to the loss of native sagebrush communities and change the biogeochemical conditions which make it difficult for sagebrush to regenerate. Invasion of cheatgrass (Bromus tectorum) accentuates the problem by making the ecosystem more susceptible to frequent burns. Managers have implemented several techniques to cope with the cheatgrass–fire cycle, ranging from controlling undesirable fire effects by removing fuel loads either mechanically or via prescribed burns to seeding the fire-affected areas …
Snow Avalanche Detection And Source Constraints Made Using A Networked Array Of Infrasound Sensors, J. B. Johnson, J. F. Anderson, H. P. Marshall, S. Havens, L. M. Watson
Snow Avalanche Detection And Source Constraints Made Using A Networked Array Of Infrasound Sensors, J. B. Johnson, J. F. Anderson, H. P. Marshall, S. Havens, L. M. Watson
Geosciences Faculty Publications and Presentations
We studied a triggered snow avalanche (∼60 s in duration and with ∼1,100 m run-out) using a network of infrasound arrays and time-synced video, with the objective of understanding the relationship between infrasound generation and flow dynamics. Using standard array processing techniques, we compared the infrasound source back azimuths with the avalanche flow path identified by frame-differenced, geo-referenced video. Results show that infrasound records begin with direct arrivals followed by echoes from the avalanche-triggering explosions and these decay within 35 s of the detonations. Subsequent infrasound, which lasts 20–30 s, could then be attributed exclusively to the avalanche. These infrasound …
The 31 March 2020 MW 6.5 Stanley, Idaho, Earthquake: Seismotectonics And Preliminary Aftershock Analysis, Lee M. Liberty, Zachary M. Lifton, T. Dylan Mikesell
The 31 March 2020 MW 6.5 Stanley, Idaho, Earthquake: Seismotectonics And Preliminary Aftershock Analysis, Lee M. Liberty, Zachary M. Lifton, T. Dylan Mikesell
Geosciences Faculty Publications and Presentations
We report on the tectonic framework, seismicity, and aftershock monitoring efforts related to the 31 March 2020 Mw 6.5 Stanley, Idaho, earthquake. The earthquake sequence has produced both strike-slip and dip-slip motion, with minimal surface displacement or damage. The earthquake occurred at the northern limits of the Sawtooth normal fault. This fault separates the Centennial tectonic belt, a zone of active seismicity within the Basin and Range Province, from the Idaho batholith to the west and Challis volcanic belt to the north and east. We show evidence for a potential kinematic link between the northeast-dipping Sawtooth fault and the …
Snow Ensemble Uncertainty Project (Seup): Quantification Of Snow Water Equivalent Uncertainty Across North America Via Ensemble Land Surface Modeling, Hans-Peter Marshall
Snow Ensemble Uncertainty Project (Seup): Quantification Of Snow Water Equivalent Uncertainty Across North America Via Ensemble Land Surface Modeling, Hans-Peter Marshall
Geosciences Faculty Publications and Presentations
The Snow Ensemble Uncertainty Project (SEUP) is an effort to establish a baseline characterization of snow water equivalent (SWE) uncertainty across North America with the goal of informing global snow observational needs. An ensemble-based modeling approach, encompassing a suite of current operational models is used to assess the uncertainty in SWE and total snow storage (SWS) estimation over North America during the 2009–2017 period. The highest modeled SWE uncertainty is observed in mountainous regions, likely due to the relatively deep snow, forcing uncertainties, and variability between the different models in resolving the snow processes over complex terrain. This highlights a …
Diatoms In Hyporheic Sediments Trace Organic Matter Retention And Processing In The Mcmurdo Dry Valleys, Antarctica, Anna J. Bergstrom
Diatoms In Hyporheic Sediments Trace Organic Matter Retention And Processing In The Mcmurdo Dry Valleys, Antarctica, Anna J. Bergstrom
Geosciences Faculty Publications and Presentations
In low‐nutrient streams in cold and arid ecosystems, the spiraling of autochthonous particulate organic matter (POM) may provide important nutrient subsidies downstream. Because of its lability and the spatial heterogeneity of processing in hyporheic sediments, the downstream transport and fate of autochthonous POM can be difficult to trace. In Antarctic McMurdo Dry Valley (MDV) streams, any POM retained in the hyporheic zone is expected to be derived from surface microbial mats that contain diatoms with long‐lasting silica frustules. We tested whether diatom frustules can be used to trace the retention of autochthonous POM in the hyporheic zone and whether certain …
Resonant Frequency Derived From The Rayleigh‐Wave Dispersion Image: The High‐Impedance Boundary Problem, Lee M. Liberty, James St. Clair, T. Dylan Mikesell, William D. Schermerhorn
Resonant Frequency Derived From The Rayleigh‐Wave Dispersion Image: The High‐Impedance Boundary Problem, Lee M. Liberty, James St. Clair, T. Dylan Mikesell, William D. Schermerhorn
Geosciences Faculty Publications and Presentations
We present a simple and automated approach to estimate primary site‐response resonance, layer thickness, and shear‐wave velocity directly from a dispersion image for a layer over half‐space problem. We demonstrate this for high‐impedance boundary conditions that lie in the upper tens of meters. Our approach eliminates the need for time‐consuming dispersion curve picking and 1D shear‐wave velocity inversion for large data volumes that can capture velocity structure in profile. We highlight important relationships between dispersion characteristics and resonance parameters through synthetic modeling and field data acquired over Atlantic Coastal Plain sediments. In this environment, shallow soil conditions are critical to …
Stick-Slip Tremor Beneath An Alpine Glacier, J. Umlauft, F. Lindner, P. Roux, T. D. Mikesell, M. M. Haney, M. Korn, F. T. Walter
Stick-Slip Tremor Beneath An Alpine Glacier, J. Umlauft, F. Lindner, P. Roux, T. D. Mikesell, M. M. Haney, M. Korn, F. T. Walter
Geosciences Faculty Publications and Presentations
Sliding of glacial ice over its base is typically described by a frictionless or slowly deforming bed. This view is challenged by recent seismic observations of stick-slip motion at the icebed interface. We revisit a high-frequency (20–35 Hz) harmonic tremor recorded on Gornergletscher, Switzerland. In contrast to previous interpretation in terms of glaciohydraulic tremor, we present evidence for superimposed stick-slip episodes as tremor sources: we locate the tremor source with matched field processing polarity optimization, which allows for azimuthal polarity patterns associated with nonisotropic moment tensors and yields a tremor source clustering near the glacier bed. Our analysis confirms an …
Spatial Patterns And Drivers Of Nonperennial Flow Regimes In The Contiguous United States, Kendra Kaiser
Spatial Patterns And Drivers Of Nonperennial Flow Regimes In The Contiguous United States, Kendra Kaiser
Geosciences Faculty Publications and Presentations
Over half of global rivers and streams lack perennial flow, and understanding the distribution and drivers of their flow regimes is critical for understanding their hydrologic, biogeochemical, and ecological functions. We analyzed nonperennial flow regimes using 540 U.S. Geological Survey watersheds across the contiguous United States from 1979 to 2018. Multivariate analyses revealed regional differences in no-flow fraction, date of first no flow, and duration of the dry-down period, with further divergence between natural and human-altered watersheds. Aridity was a primary driver of no-flow metrics at the continental scale, while unique combinations of climatic, physiographic and anthropogenic drivers emerged at …
The Impact Of Initial Snow Conditions On The Numerical Weather Simulation Of A Northern Rockies Atmospheric River, William Rudisill, Alejandro Flores, James Mcnamara
The Impact Of Initial Snow Conditions On The Numerical Weather Simulation Of A Northern Rockies Atmospheric River, William Rudisill, Alejandro Flores, James Mcnamara
Geosciences Faculty Publications and Presentations
Snow’s thermal and radiative properties strongly impact the land surface energy balance and thus the atmosphere above it. Land surface snow information is poorly known in mountainous regions. Few studies have examined the impact of initial land surface snow conditions in high-resolution, convection-permitting numerical weather prediction models during the midlatitude cool season. The extent to which land surface snow influences atmospheric energy transport and subsequent surface meteorological states is tested using a high-resolution (1 km) configuration of the Weather Research and Forecasting (WRF) Model, for both calm conditions and weather characteristic of a warm late March atmospheric river. A set …
Stable Isotopes Of Water Reveal Differences In Plant – Soil Water Relationships Across Northern Environments, Matthew J. Kohn, James P. Mcnamara
Stable Isotopes Of Water Reveal Differences In Plant – Soil Water Relationships Across Northern Environments, Matthew J. Kohn, James P. Mcnamara
Geosciences Faculty Publications and Presentations
We compared stable isotopes of water in plant stem (xylem) water and soil collected over a complete growing season from five well‐known long‐term study sites in northern/cold regions. These spanned a decreasing temperature gradient from Bruntland Burn (Scotland), Dorset (Canadian Shield), Dry Creek (USA), Krycklan (Sweden), to Wolf Creek (northern Canada). Xylem water was isotopically depleted compared to soil waters, most notably for deuterium. The degree to which potential soil water sources could explain the isotopic composition of xylem water was assessed quantitatively using overlapping polygons to enclose respective data sets when plotted in dual isotope space. At most sites …
Extreme Heterogeneity In Mid-Ocean Ridge Mantle Revealed In Lavas From The 8°20′N Near-Axis Seamount Chain, Molly Anderson, V. Dorsey Wanless, Michael Perfit, Ethan Conrad, Patricia Gregg, Daniel Fornari, W. Ian Ridley
Extreme Heterogeneity In Mid-Ocean Ridge Mantle Revealed In Lavas From The 8°20′N Near-Axis Seamount Chain, Molly Anderson, V. Dorsey Wanless, Michael Perfit, Ethan Conrad, Patricia Gregg, Daniel Fornari, W. Ian Ridley
Geosciences Faculty Publications and Presentations
Lavas that have erupted at near‐axis seamounts provide windows into mid‐ocean ridge mantle heterogeneity and melting systematics which are not easily observed on‐axis at fast‐spreading centers. Beneath ridges, most heterogeneity is obscured as magmas aggregate toward the ridge, where they efficiently mix and homogenize during transit and within shallow magma chambers prior to eruption. To understand the deeper magmatic processes contributing to oceanic crustal formation, we examine the compositions of lavas erupted along a chain of near‐axis seamounts and volcanic ridges perpendicular to the East Pacific Rise. We assess the chemistry of near‐ridge mantle using a ∼200 km‐long chain at …
Age And Paleoenvironmental Significance Of The Frazer Beach Member: A New Lithostratigraphic Unit Overlying The End-Permian Extinction Horizon In The Sydney Basin, Australia, James L. Crowley
Geosciences Faculty Publications and Presentations
The newly defined Frazer Beach Member of the Moon Island Beach Formation is identified widely across the Sydney Basin in both outcrop and exploration wells. This thin unit was deposited immediately after extinction of the Glossopteris flora (defining the terrestrial end-Permian extinction event). The unit rests conformably on the uppermost Permian coal seam in most places. A distinctive granule-microbreccia bed is locally represented at the base of the member. The unit otherwise consists of dark gray to black siltstone, shale, mudstone and, locally, thin lenses of fine-grained sandstone and tuff. The member represents the topmost unit of the Newcastle Coal …
Thermometry And Microstructural Analysis Imply Protracted Extensional Exhumation Of The Tso Morari Uhp Nappe, Northwestern Himalaya: Implications For Models Of Uhp Exhumation, Sean P. Long, Matthew J. Kohn, Buchanan C. Kerswell, Jesslyn K. Starnes, Kyle P. Larson, Nolan R. Blackford, Emmanuel Soignard
Thermometry And Microstructural Analysis Imply Protracted Extensional Exhumation Of The Tso Morari Uhp Nappe, Northwestern Himalaya: Implications For Models Of Uhp Exhumation, Sean P. Long, Matthew J. Kohn, Buchanan C. Kerswell, Jesslyn K. Starnes, Kyle P. Larson, Nolan R. Blackford, Emmanuel Soignard
Geosciences Faculty Publications and Presentations
Documenting the processes that facilitate exhumation of ultrahigh‐pressure (UHP) rocks at convergent margins is critical for understanding orogen dynamics. Here, we present structural and temperature data from the Himalayan UHP Tso Morari nappe (TMN) and overlying nappes, which we integrate with published pressure‐temperature‐time constraints to refine interpretations for their structural evolution and exhumation history. Our data indicate that the 5.5‐km‐thick TMN is the upper portion of a penetratively deformed ductile slab, which was extruded via distributed, pure shear‐dominated, top‐down‐to‐east shearing. Strain in the TMN is recorded by high‐strength quartz fabrics (density norms between 1.74 and 2.86) and finite strain data …
Sharp Contrasts In Observed And Modeled Crevasse Patterns At Greenland’S Marine Terminating Glaciers, Ellyn M. Enderlin, Timothy C. Bartholomaus
Sharp Contrasts In Observed And Modeled Crevasse Patterns At Greenland’S Marine Terminating Glaciers, Ellyn M. Enderlin, Timothy C. Bartholomaus
Geosciences Faculty Publications and Presentations
Crevasses are affected by and affect both the stresses and the surface mass balance of glaciers. These effects are brought on through potentially important controls on meltwater routing, glacier viscosity, and iceberg calving, yet there are few direct observations of crevasse sizes and locations to inform our understanding of these interactions. Here we extract depth estimates for the visible portion of crevasses from high-resolution surface elevation observations for 52 644 crevasses from 19 Greenland glaciers. We then compare our observed depths with those calculated using two popular models that assume crevasse depths are functions of local stresses: the Nye and …
Changes In Crater Geometry Revealed By Inversion Of Harmonic Infrasound Observations: 24 December 2018 Eruption Of Mount Etna, Italy, Leighton M. Watson, Jeffrey B. Johnson, Mariangela Sciotto, Andrea Cannata
Changes In Crater Geometry Revealed By Inversion Of Harmonic Infrasound Observations: 24 December 2018 Eruption Of Mount Etna, Italy, Leighton M. Watson, Jeffrey B. Johnson, Mariangela Sciotto, Andrea Cannata
Geosciences Faculty Publications and Presentations
In December 2018, Mount Etna (Italy) experienced a period of increased eruptive activity that culminated in a fissure eruption on the southeast flank. After the onset of the flank eruption, the peak frequency of the summit infrasound signals decreased while resonance increased. We invert infrasound observations for crater geometry and show that crater depth and radius increased during the eruption, which suggests that the flank eruption drained magma from the summit and that eruptive activity led to erosion of the crater wall. By inverting the entire infrasound amplitude spectra rather than just the peak frequency, we are able to place …