Deformation and seismic precursors to dome-collapse and fountain-collapse nuées ardentes at Merapi Volcano, Java, Indonesia, 1994–1998     

B. Voight  K. D. Young  D. Hidayat  Subandrio  M. A. Purbawinata  A. Ratdomopurbo  Suharna  Panut  D. S. Sayudi  R. LaHusen  J. Marso  T. L. Murray  M. Dejean  M. Iguchi  K. Ishihara 《Journal of Volcanology and Geothermal Research》2000,100(1-4)

Following the eruption of January 1992, episodes of lava dome growth accompanied by generation of dome-collapse nuées ardentes occurred in 1994–1998. In addition, nuées ardentes were generated by fountain-collapse in January 1997, and the 1998 events also suggest an explosive component. Significant tilt and seismic precursors on varying time scales preceded these events. Deformation about the summit has been detected by electronic tiltmeters since November 1992, with inflation corresponding generally to lava dome growth, and deflation (or decreased inflation) corresponding to loss of dome mass. Strong short-term (days to weeks) accelerations in tilt rate and seismicity occurred prior to the major nuées ardentes episodes, apart from those of 22 November 1994 which were preceded by steadily increasing tilt for over 200 days but lacked short-term precursors. Because of the combination of populated hazardous areas and the lack of an issued warning, about 100 casualties occurred in 1994. In contrast, the strong precursors in 1997 and 1998 provided advance warning to observatory scientists, enabled the stepped raising of alert levels, and aided hazard management. As a result of these factors, but also the fortunate fact that the large nuées ardentes did not quite descend into populated areas, no casualties occurred. The nuée ardente episode of 1994 is interpreted as purely due to gravitational collapse, whereas those of 1997 and 1998 were influenced by gas-pressurization of the lava dome.  相似文献   

Watershed and ocean controls of salt marsh extent and resilience     

Fateme Yousefi Lalimi  Marco Marani  James Brendan Heffernan  Andrea D'Alpaos  A. Brad Murray 《地球表面变化过程与地形》2020,45(6):1456-1468

The formation and evolution of tidal platforms are controlled by the feedbacks between hydrodynamics, geomorphology, vegetation, and sediment transport. Previous work mainly addresses dynamics at the scale of individual marsh platforms. Here, we develop a process-based model to investigate salt marsh depositional/erosional dynamics and resilience to environmental change at the scale of tidal basins. We evaluate how inputs of water and sediment from river and ocean sources interact, how losses of sediment to the ocean depend on this interaction, and how erosional/depositional dynamics are coupled to these exchanges. Model experiments consider a wide range of watershed, basin, and oceanic characteristics, represented by river discharge and suspended sediment concentration, basin dimensions, tidal range, and ocean sediment concentration. In some scenarios, the vertical accretion of a tidal flat can be greater than the rate of sea level rise. Under these conditions, vertical depositional dynamics can lead to transitions between tidal flat and salt marsh equilibrium states. This type of transition occurs much more rapidly than transitions occurring through horizontal marsh expansion or retreat. In addition, our analyses reveal that river inputs can affect the existence and extent of marsh/tidal flat equilibria by both directly providing suspended sediment (favoring marshes) and by modulating water exchanges with the ocean, thereby indirectly affecting the ocean sediment input to the system (favoring either marshes or tidal flats depending on the ratio of the river and ocean water inputs and their sediment concentrations). The model proposed has the goal of clarifying the roles of the main dynamic processes at play, rather than of predicting the evolution of a particular tidal system. Our model results most directly reflect micro- and meso-tidal environments but also have implications for macro-tidal settings. The model-based analyses presented extend our theoretical understanding of marsh dynamics to a greater range of intertidal environments. © 2020 John Wiley & Sons, Ltd.  相似文献   

Testing the utility of structure‐from‐motion photogrammetry reconstructions using small unmanned aerial vehicles and ground photography to estimate the extent of upland soil erosion   总被引：1，自引：0，他引：1       下载免费PDF全文

Miriam Glendell  Gareth McShane  Luke Farrow  Mike R. James  John Quinton  Karen Anderson  Martin Evans  Pia Benaud  Barry Rawlins  David Morgan  Lee Jones  Matthew Kirkham  Leon DeBell  Timothy A. Quine  Murray Lark  Jane Rickson  Richard E. Brazier 《地球表面变化过程与地形》2017,42(12):1860-1871

Quantifying the extent of soil erosion at a fine spatial resolution can be time consuming and costly; however, proximal remote sensing approaches to collect topographic data present an emerging alternative for quantifying soil volumes lost via erosion. Herein we compare terrestrial laser scanning (TLS), and both unmanned aerial vehicle (UAV) and ground photography (GP) structure‐from‐motion (SfM) derived topography. We compare the cost‐effectiveness and accuracy of both SfM techniques to TLS for erosion gully surveying in upland landscapes, treating TLS as a benchmark. Further, we quantify volumetric soil loss estimates from upland gullies using digital surface models derived by each technique and subtracted from an interpolated pre‐erosion surface. Soil loss estimates from UAV and GP SfM reconstructions were comparable to those from TLS, whereby the slopes of the relationship between all three techniques were not significantly different from 1:1 line. Only for the TLS to GP comparison was the intercept significantly different from zero, showing that GP is more capable of measuring the volumes of very small erosion features. In terms of cost‐effectiveness in data collection and processing time, both UAV and GP were comparable with the TLS on a per‐site basis (13.4 and 8.2 person‐hours versus 13.4 for TLS); however, GP was less suitable for surveying larger areas (127 person‐hours per ha^?1 versus 4.5 for UAV and 3.9 for TLS). Annual repeat surveys using GP were capable of detecting mean vertical erosion change on peaty soils. These first published estimates of whole gully erosion rates (0.077 m a^?1) suggest that combined erosion rates on gully floors and walls are around three times the value of previous estimates, which largely characterize wind and rainsplash erosion of gully walls. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Spatial optimization for land acquisition problems: A review of models,solution methods,and GIS support   总被引：1，自引：0，他引：1  

Ningchuan Xiao  Alan T. Murray 《Transactions in GIS》2019,23(4):645-671

This article reviews the interdisciplinary research field of spatial optimization for land acquisition problems. We start with a theoretical framework to identify three categories of spatial optimization models: problems with aspatial constraints, location models, and problems with topological constraints. Exact, heuristic, and metaheuristic approaches to solving these problems are critically discussed. Tools that are available in commercial and open‐source GIS packages are reviewed from four aspects. We first survey the off‐the‐shelf support and then the development environments in these packages. A case study of the one‐center problem is used to illustrate the computational performance of different solution methods. Finally the advantages and disadvantages of current GIS data models are discussed. The article concludes with challenges and future directions for solving spatial optimization problems for land acquisition.  相似文献   

Challenges in applying capacitated covering models     

Jing Xu  Alan Murray  Zifan Wang  Richard Church 《Transactions in GIS》2020,24(2):268-290

Service system planning has long been supported by location‐covering models designed to address access and accessibility issues. An important aspect of many systems is limits on service, often conceptualized as facility capacities. Much research can be found that proposes modeling approaches and solution techniques to account for capacitated covering problems, and commercial GIS software exists that is capable of structuring and applying facility service limits. This article reviews issues and challenges associated with the application of capacitated covering models, including critical evaluation of allocation approaches and GIS capabilities. Case studies involving service provision in two cities in California—San Jose and Santa Barbara—are provided to highlight associated issues faced in practice. While user‐friendly commercial software makes it easy to access capacitated cover models, there remain challenges for addressing underlying considerations and assumptions in practice.  相似文献   

Obstacle‐limited service coverage: A new geospatial approach     

Insu Hong  Alan T. Murray 《Transactions in GIS》2020,24(1):213-229

Service coverage is a crucial component of spatial decision‐making involving facility siting. Determining coverage requires knowledge about travel behavior and accessibility across a region, as well as supporting methods of measurement and derivation when actual travel cannot necessarily be observed. When service is provided using vehicles that move freely without the restriction posed by roads (e.g., airplanes, helicopters, unmanned aerial vehicles/drones, boats, ships, and submarines), straight‐line travel is regularly assumed. However, this common assumption is often violated by geographical obstructions, resulting in overestimated service coverage. To date, no methods have been developed capable of accounting for obstacle‐limited service coverage. Existing methods either completely ignore obstructions or crudely estimate impacts on travel. In this research, we develop a novel method, ESP‐Cover, capable of deriving accurate obstacle‐limited coverage without introducing representation errors. A location siting problem involving drone‐based package delivery is presented to highlight the necessity of explicitly accounting for obstacles in system design. The assessment results demonstrate the importance of accurate derivation of the obstacle‐limited coverage for spatial decision‐making and the accuracy of the ESP‐Cover method in coverage derivation.  相似文献   

Spectro-Imaging Polarimetry of the Local Corona During Solar Eclipse     

Z. Q. Qu  G. T. Dun  L. Chang  G. Murray  X. M. Cheng  X. Y. Zhang  L. H. Deng 《Solar physics》2017,292(2):37

Results are presented from spectro-imaging polarimetry of radiation from the local solar corona during the 2013 total solar eclipse in Gabon. This polarimetric observation was performed from 516.3 nm to 532.6 nm using a prototype Fiber Arrayed Solar Optical Telescope (FASOT). A polarimetric noise level on the order of \(10^{-3}\) results from a reduced polarimetric optical switching demodulation (RPOSD) procedure for data reduction. It is revealed that the modality of fractional linear polarization profiles of the green coronal line shows a diversity, which may indicate complex mechanisms. The polarization degree can approach 3.2 % above the continuum polarization level on a scale of 1500 km, and the nonuniform spatial distribution in amplitude and polarization direction is found even within a small field of view of 7500 km. All of this implies that the coronal polarization is highly structured and complex even on a small scale.  相似文献   

Neutral aldoses as source indicators for marine snow   总被引：2，自引：0，他引：2  

Annelie Skoog  Alice Alldredge  Uta Passow  John Dunne  James Murray 《Marine Chemistry》2008,108(3-4):195-206

The chemical characteristics of aggregating material in the marine environment are largely unknown. We investigated neutral aldose (NA) abundance and composition in aggregation of marine snow and other organic matter (OM) size fractions in the field. Four sample sets were fractionated using membrane filtration and ultrafiltration into the following size fractions: particulate material, high-molecular-weight (HMW) material, and low-molecular-weight (LMW) material. We also collected three sample sets of marine-snow aggregates. Each sample set contained small, medium, and large aggregate size fractions and each size fraction consisted of 25–50 aggregates. For 7 marine-snow samples and for each water-sample size fraction, we determined monomeric and polymeric NA concentration, NA yield (amount of NA-C normalized to organic carbon), and composition; total organic carbon (TOC) concentration; transparent exopolymer particles (TEP) concentration, and TEP propensity (TEP concentration after inducing TEP formation in filtered samples). This is the first study to include compound-specific NA determinations on these four marine OM size fractions.The mass balances of organic carbon and NA indicated that there were no serious contamination or loss problems. Concentrations, yields, and NA mol fractions in water samples were similar to results from other studies. Glucose and galactose had the highest relative abundance in all size fractions. The NA yield increased with increasing molecular weight or particle size for all fractions except marine snow. The NA yield increased in the order: LMW< marine snow< HMW< particles. Marine snow had a higher average NA yield than the LMW fraction, but lower than particle and HMW-fractions. This indicates that OM in marine snow could have been diagenetically derived from particulate and HMW-fractions, that is, marine snow may include material from the particulate and the colloidal phase.TEP concentration or TEP propensity was positively correlated with concentrations of all individual NAs as well as the sum NA concentrations, indicating that TEP contains neutral sugars in addition to the acidic polysaccharides stained in the determination of TEP concentrations.Despite the relatively low NA yield in marine snow, marine snow was enriched in NA when compared with seawater, with enrichment factors of 34–225 (average 125). By combining data from this study with data from other studies, we estimate that < 10% of carbohydrates in marine snow comprise NAs.There was no clear correlation between marine-snow aggregate size and NA yield, that is, there appears to be no general age difference between small and large marine-snow aggregates. NA composition was similar among different marine-snow size fracions collected during the same day, indicating that aggregation/disaggregation reactions resulted in homogenizing NA composition in marine-snow aggregates of all sizes. The NA composition of marine snow was different from that of other OM size fractions, indicating either that bacterial degradation has modified the composition of marine snow to a larger extent than other OM size fractions or that marine snow is formed through the aggregation of selected subcomponents of OM.  相似文献   

Optical dating of loessic hillslope sediments constrains timing of prehistoric rockfalls,Christchurch, New Zealand          下载免费PDF全文

Reza Sohbati  Josh Borella  Andrew Murray  Mark Quigley  Jan‐Pieter Buylaert 《第四纪科学杂志》2016,31(7):678-690

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Mapping Medusae Fossae Formation materials in the southern highlands of Mars     

S.K. Harrison  M.R. Balme  J.B. Murray 《Icarus》2010,209(2):405-415

The Medusae Fossae Formation (MFF) is an extensive deposit (2.2 × 10⁶ km², Bradley, B.A., Sakimoto, S.E.H., Frey, H., Zimbelman, J.R. [2002]. J. Geophys. Res. 107, 5058) of wind-eroded material of widely debated origin, which unconformably overlies a considerable area of the crustal dichotomy boundary on Mars. The MFF shows a variety of layering patterns, erosional styles and channel-like forms and has been mapped into five main outcrops and three geological members according to exposure and stratigraphy (Scott, D.H., Tanaka, K.L., 1986. USGS Map I-1802-A; Greeley, R., Guest, J.E., 1987. Map I-1802-B; Zimbelman, J.R., Crown, D., Jenson, D., 1996. Lunar Planet. Sci. XXVII. Abstract #1748.). Away from the three main lobes are numerous outliers of MFF materials. These have mainly been reported in the northern lowlands regions (Keszthelyi, L., Jaeger, W.L., and HiRISE team, 2008. Lunar Planet. Sci. XXXIX. Abstract #2420.) but few studies have examined the possibility of MFF outliers on high ground south of the dichotomy boundary. We have searched Mars Orbiter Camera Narrow Angle (MOC NA) images for outliers in this region. Our observations show that there are many MFF outliers on the southern highlands. The characteristics of the outliers indicate materials which overlie the underlying terrain for they appear widely in dips, craters and topographic lows. The surfaces are typified by yardang fields and have a similar patchy and discontinuous nature to materials of the upper member of the MFF. Most have consistent lineation orientations across the wider area which match the dominant orientation of yardangs in the main MFF outcrops. Furthermore, elevation data shows that the maximum, minimum and mean elevations of these newly discovered outliers are closest to those of the upper member of the MFF. We therefore conclude that these deposits are MFF outliers and that they probably represent remnant upper member material. We suggest that there might be two possible explanations for these outliers: (1) the MFF had a much greater pre-erosional extent than previously estimated, or (2) materials from the main outcrops were eroded and then blown south to accrue in the highland areas, where they were subsequently reworked. We suggest that the topography of the region favors the first option. We outline an “overflowing” layer-cake deposition model, in which layers of sediment stacked up against the dichotomy boundary until they reached the topographic level of the highlands. Further materials (that went onto become upper-member MFF material and outliers) were then deposited across a wider area, including south of the dichotomy boundary. Severe erosion subsequently removed much of this material.  相似文献