A progression of induration in Medusae Fossae Formation transverse aeolian ridges: evidence for ancient aeolian bedforms and extensive reworking     

Laura Kerber  James W. Head 《地球表面变化过程与地形》2012,37(4):422-433

A progression of induration, erosion, and redeposition of transverse and networked transverse aeolian ridges (TARs) has been documented in the Medusae Fossae Formation (MFF), Mars. Cratered and eroded aeolian bedforms are rarely observed on Mars, indicating that those found in the MFF have been inactive for much longer than those found elsewhere. Indurated TARs are observed to grade into faceted MFF terrain, indicating a genetic relationship between the two. We propose that TAR deposition, induration and erosion have played a larger role in the surface morphology and evolution of the MFF than previously recognized. The deposition, induration, and erosion of TARs indicate that the MFF has undergone multiple cycles of reworking, and that much of its current surface morphology does not reflect the circumstances of its primary emplacement. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Complex dynamics of small-moderate volcanic events: the example of the 2011 rhyolitic Cordón Caulle eruption,Chile     

Marco?PistolesiEmail author  Raffaello?Cioni  Costanza?Bonadonna  Manuela?Elissondo  Valerie?Baumann  Antonella?Bertagnini  Laura?Chiari  Rafael?Gonzales  Mauro?Rosi  Lorella?Francalanci 《Bulletin of Volcanology》2015,77(1):3

After decades of repose, Puyehue-Cordón Caulle Volcano (Chile) erupted in June 2011 following a month of continuously increasing seismic activity. The eruption dispersed a large volume of rhyolitic tephra over a wide area and was characterized by complex dynamics. During the initial climactic phase of the eruption (24–30 h on 4–5 June), 11–14-km-high plumes dispersed most of the erupted tephra eastward towards Argentina, reaching as far as the Atlantic Ocean. This first eruptive phase was followed by activity of lower intensity, leading to the development of a complex stratigraphic sequence, mainly due to rapid shifts in wind direction and eruptive style. The resulting tephra deposits consist of 13 main layers grouped into four units. Each layer was characterized based on its dispersal direction, sedimentological features, and on the main characteristics of the juvenile fraction (texture, density, petrography, chemistry). The lowest part of the eruptive sequence (Unit I), corresponding to the tephra emitted between 4 and 5 June, is composed of alternating lapilli layers with a total estimated volume of ca. 0.75 km³; these layers record the highest intensity phase, during which a bent-over plume dispersed tephra towards the southeast-east, with negligible up-wind sedimentation. Products emitted during 5–6 June (Unit II) signaled an abrupt shift in wind direction towards the north, leading to the deposition of a coarse ash deposit in the northern sector (ca. 0.21 km³ in volume), followed by a resumption of easterly directed winds. A third phase (Unit III) began on 7 June and resulted in tephra deposits in the eastern sector and ballistic bombs around the vent area. A final phase (Unit IV) started after 15 June and was characterized by the emission of fine-grained white tephra from ash-charged plumes during low-level activity and the extrusion of a viscous lava flow. Timing and duration of the first eruptive phases were constrained based on comparison of the dispersal of the main tephra layers with satellite images, showing that most of the tephra was emitted during the first 72 h of the event. The analyzed juvenile material tightly clusters within the rhyolitic field, with negligible chemical variations through the eruptive sequence. Textural observations reveal that changes in eruption intensity (and consequently in magma ascent velocity within the conduit) and complex interactions between gas-rich and gas-depleted magma portions during ascent resulted in vesicular clasts with variable degrees of shear localization, and possibly in the large heterogeneity of the juvenile material.  相似文献   

Geophysical and Hydrologic Studies of Lake Seepage Variability          下载免费PDF全文

Laura Toran  Jonathan Nyquist  Donald Rosenberry  Michael Gagliano  Natasha Mitchell  James Mikochik 《Ground water》2015,53(6):841-850

Variations in lake seepage were studied along a 130 m shoreline of Mirror Lake NH. Seepage was downward from the lake to groundwater; rates measured from 28 seepage meters varied from 0 to ?282 cm/d. Causes of this variation were investigated using electrical resistivity surveys and lakebed sediment characterization. Two‐dimensional (2D) resistivity surveys showed a transition in lakebed sediments from outwash to till that correlated with high‐ and low‐seepage zones, respectively. However, the 2D survey was not able to predict smaller scale variations within these facies. In the outwash, fast seepage was associated with permeability variations in a thin (2 cm) layer of sediments at the top of the lakebed. In the till, where seepage was slower than that in the outwash, a three‐dimensional resistivity survey mapped a point of high seepage associated with heterogeneity (lower resistivity and likely higher permeability). Points of focused flow across the sediment–water interface are difficult to detect and can transmit a large percentage of total exchange. Using a series of electrical resistivity geophysical methods in combination with hydrologic data to locate heterogeneities that affect seepage rates can help guide seepage meter placement. Improving our understanding of the causes and types of heterogeneity in lake seepage will provide better data for lake budgets and prediction of mass transfer of solutes or contaminants between lakes and groundwater.  相似文献   

Floodplain connection buffers seasonal changes in urban stream water quality          下载免费PDF全文

Sarah H. Ledford  Laura K. Lautz 《水文研究》2015,29(6):1002-1016

Urban streams in the Northeastern United States have large road salt inputs during the winter, increased nonpoint sources of inorganic nitrogen and decreased short‐term and permanent storage of nutrients. Restoration activities that re‐establish connection between streams and riparian environments may be effective for improving urban stream water quality. Meadowbrook Creek, a first‐order stream in Syracuse, NY, provides a unique setting to explore impacts of stream–floodplain connection because it flows along a negative urbanization gradient, from channelized and armoured headwaters to a broad, vegetated floodplain with a riparian aquifer. In this study, we investigated how reconnection to groundwater and introduction of riparian vegetation impacted urban surface water chemistry by making biweekly longitudinal surveys of stream water chemistry in the creek from May 2012 until June 2013. We used multiple methods to measure groundwater discharge rates along the creek. Chloride concentrations in the upstream, disconnected reach were influenced by discharge of road salt during snow melt events and ranged from 161.2 to 1440 mg/l. Chloride concentrations in the downstream, connected reach had less temporal variation, ranging from 252.0 to 1049 mg/l, because of buffering by groundwater discharge, as groundwater chloride concentrations ranged from 84.0 to 655.4 mg/l. In the summer, there was little to no nitrate in the disconnected reach because of limited sources and high primary productivity, but concentrations reached over 1 mg N/l in the connected reach because of the presence of riparian vegetation. During the winter, when temperatures fell below freezing, nitrate concentrations in the disconnected reach increased to 0.58 mg N/l but were still lower than the connected reach, which averaged 0.88 mg N/l. Urban stream restoration projects that restore floodplain connection may impact water quality by storing high salinity road run‐off during winter overbank events and discharging that water year‐round, thereby attenuating seasonal fluctuations in chloride. Contrary to prior findings, we observed that floodplain connection and riparian vegetation may alter nitrate sources and sinks such that nitrate concentrations increase longitudinally in connected urban streams. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

A New Integrated Weighted Model in SNOW-V10: Verification of Categorical Variables     

Laura X. Huang  George A. Isaac  Grant Sheng 《Pure and Applied Geophysics》2014,171(1-2):289-302

This paper presents the verification results for nowcasts of seven categorical variables from an integrated weighted model (INTW) and the underlying numerical weather prediction (NWP) models. Nowcasting, or short range forecasting (0–6 h), over complex terrain with sufficient accuracy is highly desirable but a very challenging task. A weighting, evaluation, bias correction and integration system (WEBIS) for generating nowcasts by integrating NWP forecasts and high frequency observations was used during the Vancouver 2010 Olympic and Paralympic Winter Games as part of the Science of Nowcasting Olympic Weather for Vancouver 2010 (SNOW-V10) project. Forecast data from Canadian high-resolution deterministic NWP system with three nested grids (at 15-, 2.5- and 1-km horizontal grid-spacing) were selected as background gridded data for generating the integrated nowcasts. Seven forecast variables of temperature, relative humidity, wind speed, wind gust, visibility, ceiling and precipitation rate are treated as categorical variables for verifying the integrated weighted forecasts. By analyzing the verification of forecasts from INTW and the NWP models among 15 sites, the integrated weighted model was found to produce more accurate forecasts for the 7 selected forecast variables, regardless of location. This is based on the multi-categorical Heidke skill scores for the test period 12 February to 21 March 2010.  相似文献   

Baseflow and Runoff Event Metal Concentrations,Partition and Its Relation with Physicochemical Variables in an Agroforestry Catchment          下载免费PDF全文

Laura Palleiro  María Luz Rodríguez‐Blanco  María Mercedes Taboada‐Castro  María Teresa Taboada‐Castro 《洁净——土壤、空气、水》2014,42(4):462-471

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Transmission Sources of Waterborne Viruses in South Sudan Refugee Camps          下载免费PDF全文

Laura Guerrero‐Latorre  Ayalkibet Hundesa  Rosina Girones 《洁净——土壤、空气、水》2016,44(7):775-780

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Influence of the nonlinear behavior of viscous dampers on the seismic demand hazard of building frames   总被引：1，自引：0，他引：1       下载免费PDF全文

Andrea Dall′Asta  Enrico Tubaldi  Laura Ragni 《地震工程与结构动力学》2016,45(1):149-169

This paper analyzes the influence of damper properties on the probabilistic seismic performance of building frames equipped with viscous dampers. In particular, a probabilistic methodology is employed to evaluate the influence of the damper nonlinearity, measured by the damper exponent, on the performance of structural and nonstructural components of building frames, as described by the response hazard curves of the relevant engineering demand parameters. The performance variations due to changes in the damper nonlinearity level are evaluated and highlighted by considering two realistic design scenarios and by comparing the results of a set of cases involving dampers with different exponents designed to provide the same deterministic performance. By this way, it is possible to evaluate the influence of the nonlinear response and of its dispersion on the demand hazard. It is shown that the damper nonlinearity level strongly affects the seismic performance and different trends are observed for the demand parameters of interest. A comparison with code provisions shows that further investigation is necessary to provide more reliable design formulas accounting for the damping nonlinearity level. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

An integrated approach for investigating geomorphic response to extreme events: methodological framework and application to the October 2011 flood in the Magra River catchment,Italy          下载免费PDF全文

Massimo Rinaldi  William Amponsah  Marco Benvenuti  Marco Borga  Francesco Comiti  Ana Lucía  Lorenzo Marchi  Laura Nardi  Margherita Righini  Nicola Surian 《地球表面变化过程与地形》2016,41(6):835-846

A high‐magnitude flash flood, which took place on 25 October 2011 in the Magra River catchment (1717 km²), central‐northern Italy, is used to illustrate some aspects of the geomorphic response to the flood. An overall methodological framework is described for using interlinked observations and analyses of the geomorphic impacts of an extreme event. The following methods and analyses were carried out: (i) hydrological and hydraulic analysis of the event; (ii) sediment delivery by event landslide mapping; (iii) identification and estimation of wood recruitment, deposition, and budgeting; (iv) interpretation of morphological processes by analysing fluvial deposits; (v) remote sensing and geographic information system (GIS) analysis of channel width changes. In response to the high‐magnitude hydrological event, a large number of landslides occurred, consisting of earth flows, soil slips, and translational slides, and a large quantity of wood was recruited, in most part deriving from floodplain erosion caused by bank retreat and channel widening. The most important impact of the flood event within the valley floor was an impressive widening of the overall channel bed and the reactivation of wide portions of the pre‐event floodplain. Along the investigated (unconfined or partly confined) streams (total investigated length of 93.5 km), the channel width after the flood was up to about 20 times the channel width before the event. The study has shown that a synergic use of different methods and types of evidence provides fundamental information for characterizing and understanding the geomorphic effects of intense flood events. The prediction of geomorphic response to a flood event is still challenging and many limitations exist; however a robust geomorphological analysis can contribute to the identification of the most critical reaches. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Historical trace metal loading to a large river recorded in the sediments of Lake St. Croix,USA   总被引：1，自引：0，他引：1  

Steven J. Balogh  Laura D. Triplett  Daniel R. Engstrom  Yabing H. Nollet 《Journal of Paleolimnology》2010,44(2):517-530

The global cycling of anthropogenic trace metals intensified during the twentieth century, impacting aquatic systems throughout the world. There are, however, few quantitative records showing the history of this contamination in large rivers. Here we present a well-dated sedimentary record of trace metal accumulation in Lake St. Croix, a natural riverine lake on the St. Croix River (Minnesota and Wisconsin, USA), revealing the history of heavy metal inputs to the river over the past 200 years. Concentrations of Hg, Pb, Ag, Cd, Cr and Zn and stable Pb isotopes were measured in eight ²¹⁰Pb-dated sediment cores collected from profundal depositional areas throughout the lake. Time trends of trace metal concentrations and accumulation rates differed greatly between the upper lake (above Valley Creek) and the lower lake, reflecting contrasting sediment sources along the flow axis of the lake. For most of the study period (1800–2000 AD), sediment deposited throughout the lake derived almost exclusively from the suspended sediment load carried by the main-stem river into the lake. From 1910 through 1970, however, large inputs of eroded soils and stream channel sediments from side-valley tributaries resulted in greatly increased sediment and trace metal accumulation in the lower lake. Anthropogenic accumulation rates of Hg, Pb, Cd, Zn, and Ag in the upper lake correlate well with those from Square Lake, a small, relatively undisturbed nearby lake that has received trace metal inputs almost exclusively via atmospheric deposition. The similarity of these records suggests that atmospheric deposition was primarily responsible for trace metal accumulation trends in upper Lake St. Croix. Trace metal accumulation in the lower lake was also strongly influenced by atmospherically derived inputs, but metal contributions from native soils were important, as well, during the period of elevated sediment inputs from side-valley tributaries. Concentrations and accumulation rates of trace metals in both upper and lower lake sediments have decreased substantially since the 1970s due to decreased atmospheric inputs and sediment loadings, but accumulation rates remain well above pre-settlement values. Metal inputs to Lake St. Croix have been far lower than those to nearby Lake Pepin, located on the Mississippi River downstream of the Minneapolis-St. Paul metropolitan area, but there nevertheless remains a clear record of anthropogenic impact on the relatively pristine St. Croix River.  相似文献