The Moon: An Archive of Small Body Migration in the Solar System     

Katherine H. Joy  Ian A. Crawford  Natalie M. Curran  Michael Zolensky  Amy F. Fagan  David A. Kring 《Earth, Moon, and Planets》2016,118(2-3):133-158

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Flooding duration and volume more important than peak discharge in explaining 18 years of gravel–cobble river change     

Arielle A. Gervasi  Gregory B. Pasternack  Amy E. East 《地球表面变化过程与地形》2021,46(15):3194-3212

Floods play a critical role in geomorphic change, but whether peak magnitude, duration, volume, or frequency determines the resulting magnitude of erosion and deposition is a question often proposed in geomorphic effectiveness studies. This study investigated that question using digital elevation model differencing to compare and contrast three hydrologically distinct epochs of topographic change spanning 18 years in the 37-km gravel–cobble lower Yuba River in northern California, USA. Scour and fill were analysed by volume at segment and geomorphic reach scales. Each epoch's hydrology was characterized using 15-min and daily averaged flow to obtain distinct peak and recurrence, duration, and volume metrics. Epochs 1 (1999–2008) and 3 (2014–2017) were wetter than average with large floods reaching 3206 and 2466 m³/s, respectively, though of different flood durations. Epoch 2 (2008–2014) was a drought period with only four brief moderate floods (peak of 1245 m³/s). Total volumetric changes showed that major geomorphic response occurred primarily during large flood events; however, total scour and net export of sediment varied greatly, with 20 times more export in epoch 3 compared to epoch 1. The key finding was that greater peak discharge was not correlated with greater net and total erosion; differences were better explained by duration and volume above floodway-filling stage. This finding highlights the importance of considering flood duration and volume, along with peak, to assess flood magnitude in the context of flood management, frequency analysis, and resulting geomorphic changes.  相似文献   

An experimental study of Ti and Zr partitioning among zircon, rutile, and granitic melt     

Amy E. Hofmann  Michael B. Baker  John M. Eiler 《Contributions to Mineralogy and Petrology》2013,166(1):235-253

In order to evaluate the effect of trace and minor elements (e.g., P, Y, and the REEs) on the high-temperature solubility of Ti in zircon (zrc), we conducted 31 experiments on a series of synthetic and natural granitic compositions [enriched in TiO₂ and ZrO₂; Al/(Na + K) molar ~1.2] at a pressure of 10 kbar and temperatures of ~1,400 to 1,200 °C. Thirty of the experiments produced zircon-saturated glasses, of which 22 are also saturated in rutile (rt). In seven experiments, quenched glasses coexist with quartz (qtz). SiO₂ contents of the quenched liquids range from 68.5 to 82.3 wt% (volatile free), and water concentrations are 0.4–7.0 wt%. TiO₂ contents of the rutile-saturated quenched melts are positively correlated with run temperature. Glass ZrO₂ concentrations (0.2–1.2 wt%; volatile free) also show a broad positive correlation with run temperature and, at a given T, are strongly correlated with the parameter (Na + K + 2Ca)/(Si·Al) (all in cation fractions). Mole fraction of ZrO₂ in rutile $ \left( {\mathop X\nolimits_{{{\text{ZrO}}_{ 2} }}^{\text{rt}} } \right) $ in the quartz-saturated runs coupled with other 10-kbar qtz-saturated experimental data from the literature (total temperature range of ~1,400 to 675 °C) yields the following temperature-dependent expression: $ {\text{ln}}\left( {\mathop X\nolimits_{{{\text{ZrO}}_{ 2} }}^{\text{rt}} } \right) + {\text{ln}}\left( {a_{{{\text{SiO}}_{2} }} } \right) = 2.638(149) - 9969(190)/T({\text{K}}) $ , where silica activity $ a_{{{\text{SiO}}_{2} }} $ in either the coexisting silica polymorph or a silica-undersaturated melt is referenced to α-quartz at the P and T of each experiment and the best-fit coefficients and their uncertainties (values in parentheses) reflect uncertainties in T and $ \mathop X\nolimits_{{{\text{ZrO}}_{2} }}^{\text{rt}} $ . NanoSIMS measurements of Ti in zircon overgrowths in the experiments yield values of ~100 to 800 ppm; Ti concentrations in zircon are positively correlated with temperature. Coupled with values for $ a_{{{\text{SiO}}_{2} }} $ and $ a_{{{\text{TiO}}_{2} }} $ for each experiment, zircon Ti concentrations (ppm) can be related to temperature over the range of ~1,400 to 1,200 °C by the expression: $ \ln \left( {\text{Ti ppm}} \right)^{\text{zrc}} + \ln \left( {a_{{{\text{SiO}}_{2} }} } \right) - \ln \left( {a_{{{\text{TiO}}_{2} }} } \right) = 13.84\left( {71} \right) - 12590\left( {1124} \right)/T\left( {\text{K}} \right) $ . After accounting for differences in $ a_{{{\text{SiO}}_{2} }} $ and $ a_{{{\text{TiO}}_{2} }} $ , Ti contents of zircon from experiments run with bulk compositions based on the natural granite overlap with the concentrations measured on zircon from experiments using the synthetic bulk compositions. Coupled with data from the literature, this suggests that at T ≥ 1,100 °C, natural levels of minor and trace elements in “granitic” melts do not appear to influence the solubility of Ti in zircon. Whether this is true at magmatic temperatures of crustal hydrous silica-rich liquids (e.g., 800–700 °C) remains to be demonstrated. Finally, measured $ D_{\text{Ti}}^{{{\text{zrc}}/{\text{melt}}}} $ values (calculated on a weight basis) from the experiments presented here are 0.007–0.01, relatively independent of temperature, and broadly consistent with values determined from natural zircon and silica-rich glass pairs.  相似文献   

Simulating the Effect of Climate Extremes on Groundwater Flow Through a Lakebed   总被引：1，自引：0，他引：1  

Makhan L. Virdi  Terrie M. Lee  Amy Swancar  Richard G. Niswonger 《Ground water》2013,51(2):203-218

Groundwater exchanges with lakes resulting from cyclical wet and dry climate extremes maintain lake levels in the environment in ways that are not well understood, in part because they remain difficult to simulate. To better understand the atypical groundwater interactions with lakes caused by climatic extremes, an original conceptual approach is introduced using MODFLOW‐2005 and a kinematic‐wave approximation to variably saturated flow that allows lake size and position in the basin to change while accurately representing the daily lake volume and three‐dimensional variably saturated groundwater flow responses in the basin. Daily groundwater interactions are simulated for a calibrated lake basin in Florida over a decade that included historic wet and dry departures from the average rainfall. The divergent climate extremes subjected nearly 70% of the maximum lakebed area and 75% of the maximum shoreline perimeter to both groundwater inflow and lake leakage. About half of the lakebed area subject to flow reversals also went dry. A flow‐through pattern present for 73% of the decade caused net leakage from the lake 80% of the time. Runoff from the saturated lake margin offset the groundwater deficit only about half of that time. A centripetal flow pattern present for 6% of the decade was important for maintaining the lake stage and generated 30% of all net groundwater inflow. Pumping effects superimposed on dry climate extremes induced the least frequent but most cautionary flow pattern with leakage from over 90% of the actual lakebed area.  相似文献   

Sub-micron-scale trace-element distributions in natural zircons of known provenance: implications for Ti-in-zircon thermometry     

Amy?E.?HofmannEmail author  Michael?B.?Baker  John?M.?Eiler 《Contributions to Mineralogy and Petrology》2014,168(3):1057

NanoSIMS measurements of Ti, P, Y, Ce, and Hf in zircon separates from the Youngest Toba Tuff, the Bishop Tuff, the Quottoon Igneous Complex, the Sierra Nevada batholith, and an Adirondack migmatite show that micron-scale oscillatory zoning of Ti is common. The zircons we have studied typically display banded concentration gradients, having between 1 and 7 peaks in Ti abundance over length scales of 10–20 μm—the beam diameter commonly used for SIMS trace-element zircon analyses—with amplitudes of up to 4.5 ppm Ti (baseline values are ~1–4 ppm) and widths (measured at half-height) of between ~0.2 and 4 μm. Spatial correlations between concentrations of Ti and other trace elements (P, Y, and Ce) are also common, but variable in character, ranging from oscillatory co-variation of Ti, P, Y, and Ce to cases where only a subset of peaks for a given element is spatially correlated with peaks in Ti. There are also longer length-scale, generally positive correlations among concentrations of Ti, P, Y, and Ce (i.e., gradients on which narrower peaks are superimposed). In contrast, Hf concentrations are either uncorrelated or inversely correlated with these longer length-scale variations in Ti concentrations. The wide range in Ti concentrations over distances of less than 1 μm and the various correlations between Ti concentrations and those of the other analyzed elements suggest that on the micron scale and at temperatures between ~700 and 800 °C, zircon-liquid Ti partitioning is not controlled by bulk or lattice equilibrium. Treating our NanoSIMS Ti ion maps as though they were conventional SIMS analyses (i.e., generating an average Ti concentration for each map), we evaluate the hypothesis that while micron-scale variations in Ti concentrations might be kinetically controlled, when averaged over 100–400 μm², such variations capture the thermal state of the growing zircon. Using these average Ti concentrations, independent petrologic pressure and temperature constraints, estimates of silica and titania activities based on phase assemblages as well as calculations using rhyolite-MELTS, we show that crystallization temperatures predicted by Ti-in-zircon geothermometry generally do not agree with the independently constrained temperatures for the samples.  相似文献   

Electromagnetic properties of natural expansive soils under one-dimensional deformation   总被引：1，自引：1，他引：0  

Botao Lin  Amy B. Cerato 《Acta Geotechnica》2013,8(4):381-393

Macroscopic behavior of expansive soil is governed by surface forces rather than gravitational forces. These physicochemical surface forces can be investigated through two electromagnetic properties in response to an applied electromagnetic field as real (relative) permittivity, κ′, and effective (electrical) conductivity, σ. This paper presents the results of dielectric measurements on four natural expansive soils using 1–100 MHz electromagnetic waves in two different test setups. The equipment setup, calibration process and measurement limitations are evaluated, and the dielectric spectra, in terms of the dispersion of real permittivity/effective conductivity with frequency, are presented. A procedure is presented to quantify the thickness of a fully developed diffuse double layer (DDL). The influence of salt concentration on DDL, as well as the dielectric responses, is assessed. Two parameters of special physical meaning are defined in the article: ${\upkappa} _{{{\text{inf}}}}^{\prime }$ , representative of the dielectric response by sample mineralogy, microstructure and saturation ratio, and σ_dc, combining the roles assumed by both surface conduction and pore fluid conduction. Evaluation is attempted on their magnitudes at the optimum compaction state and evolutions at different one-dimensional deforming stages. Extensive analysis is performed on the roles of ${\upkappa} _{{{\text{inf}}}}^{\prime }$ and σ_dc on the hydration status and structural anisotropy of an oedometer sample.  相似文献   

How Reliable are Citizen‐Derived Scientific Data? Assessing the Quality of Contrail Observations Made by the General Public     

Amy Fowler  J. Duncan Whyatt  Gemma Davies  Rebecca Ellis 《Transactions in GIS》2013,17(4):488-506

Citizen science projects encourage the general public to participate in scientific research. Participants can contribute large volumes of data over broad spatial and temporal frames; however, the challenge is to generate data of sufficient quality to be useable in scientific research. Most observations made by citizen‐scientists can be independently verified by “experts”. However, verification is more problematic when the phenomena being recorded are short‐lived. This article uses a GIS methodology to verify the quality of contrail observations made by the general public as part of the OPAL Climate Survey. We verify observations using datasets derived from a variety of different sources (experts, models and amateur enthusiasts) with different spatial and temporal properties which reflect the complex 3D nature of the atmosphere. Our results suggest that ～70% of citizen observations are plausible, based on favorable atmospheric conditions and the presence or absence of aircraft; a finding which is in keeping with other, more conventional citizen science projects. However, questions remain as to why the quality of the citizen‐based observations was so high. Given the lack of supporting data on observers, it is impossible to determine whether the dataset was generated by the activities of many participants or a small but dedicated number of individual observers.  相似文献   

The Use of Environmental Features on Tactile Maps by Navigators Who Are Blind     

Amy Lobben  Megan Lawrence 《The Professional geographer》2013,65(1):95-108

Maps designed for and used by sighted audiences benefit from map symbol standardization and convention but, with very limited exception (most notably two European projects), neither standardization nor convention guides the design and use of symbols for tactile maps. In this project, we developed and field tested symbolization for and use of tactile street maps. The development process included consultation with the literature as well as with field experts (orientation and mobility teachers, Braillists, and teachers working with students who are blind or have low vision). Following development, we undertook a three-year field testing and validation phase, in which we conducted pilot testing and formal testing with travelers who are blind or have low vision. Research results reveal not only a discriminable and useful tactile symbol set but also environmental feature use by travelers who are blind or have low vision.  相似文献   

Estimating traveler populations at airport and cruise terminals for population distribution and dynamics     

Warren C. Jochem  Kelly Sims  Edward A. Bright  Marie L. Urban  Amy N. Rose  Phillip R. Coleman  Budhendra L. Bhaduri 《Natural Hazards》2013,68(3):1325-1342

In recent years, uses of high-resolution population distribution databases are increasing steadily for environmental, socioeconomic, public health, and disaster-related research and operations. With the development of daytime population distribution, temporal resolution of such databases has been improved. However, the lack of incorporation of transitional population, namely business and leisure travelers, leaves a significant population unaccounted for within the critical infrastructure networks, such as at transportation hubs. This paper presents two general methodologies for estimating passenger populations in airport and cruise port terminals at a high temporal resolution which can be incorporated into existing population distribution models. The methodologies are geographically scalable and are based on, and demonstrate how, two different transportation hubs with disparate temporal population dynamics can be modeled utilizing publicly available databases including novel data sources of flight activity from the Internet which are updated in near-real time. The airport population estimation model shows great potential for rapid implementation for a large collection of airports on a national scale, and the results suggest reasonable accuracy in the estimated passenger traffic. By incorporating population dynamics at high temporal resolutions into population distribution models, we hope to improve the estimates of populations exposed to or at risk to disasters, thereby improving emergency planning and response, and leading to more informed policy decisions.  相似文献   

Social studies of volcanology: knowledge generation and expert advice on active volcanoes   总被引：2，自引：1，他引：1  

Amy Donovan  Clive Oppenheimer  Michael Bravo 《Bulletin of Volcanology》2012,74(3):677-689

This paper examines the philosophy and evolution of volcanological science in recent years, particularly in relation to the growth of volcanic hazard and risk science. It uses the lens of Science and Technology Studies to examine the ways in which knowledge generation is controlled and directed by social forces, particularly during eruptions, which constitute landmarks in the development of new technologies and models. It also presents data from a survey of volcanologists carried out during late 2008 and early 2009. These data concern the felt purpose of the science according to the volcanologists who participated and their impressions of the most important eruptions in historical time. It demonstrates that volcanologists are motivated both by the academic science environment and by a social concern for managing the impact of volcanic hazards on populations. Also discussed are the eruptions that have most influenced the discipline and the role of scientists in policymaking on active volcanoes. Expertise in volcanology can become the primary driver of public policy very suddenly when a volcano erupts, placing immense pressure on volcanologists. In response, the epistemological foundations of volcanology are on the move, with an increasing volume of research into risk assessment and management. This requires new, integrated methodologies for knowledge collection that transcend scientific disciplinary boundaries.  相似文献