The geomorphology of planetary calderas   总被引：1，自引：0，他引：1  

Peter J. Mouginis-Mark  Scott K. Rowland 《Geomorphology》2001,37(3-4)

Satellite-derived observations of the geomorphology of calderas on Earth, Mars and Venus can be used to learn more about shield volcanoes. Examples of terrestrial basaltic volcanoes from the Galapagos Islands, Hawaii, and the Comoro Islands show how these volcanoes contrast with examples found on Mars and Venus. Caldera structure, degree of infilling, and the location of vents on the flanks are used to interpret each volcano's recent history. The geometry of the caldera floor can be used to infer some of the characteristics of the magma storage system, and the orientation of the deep magma conduits. The formation of benches within the caldera and the effects of the caldera on the distribution of flank eruptions are considered, and it is evident that most calderas on the planets are/were dynamic features. Presently, deep calderas, with evidence of overflowing lavas and ponded lavas high in the caldera wall, show that these calderas were once shallow. Similarly, shallow calderas filled with ponded lavas are evidence that they were once deeper. It is probably a mistake, therefore, to place great significance on caldera depth with regard to the position, shape, or size of subsurface plumbing.  相似文献   

Caldera morphology in the western Galápagos and implications for volcano eruptive behavior and mechanisms of caldera formation     

Duncan C. Munro  Scott K. Rowland 《Journal of Volcanology and Geothermal Research》1996,72(1-2)

Caldera morphology on the six historically active shield volcanoes that comprise Isabela and Fernandina islands, the two westernmost islands in the Galapagos archipelago, is linked to the dynamics of magma supply to, and withdrawal from, the magma chamber beneath each volcano. Caldera size (e.g., volumes 2–9 times that of the caldera of Kilauea, Hawai'i), the absence of well-developed rift zones and the inability to sustain prolonged low-volumetric-flow-rate flank eruptions suggest that magma storage occurs predominantly within centrally located chambers (at the expense of storage within the flanks). The calderas play an important role in the formation of distinctive arcuate fissures in the central part of the volcano: repeated inward collapse of the caldera walls along with floor subsidence provide mechanisms for sustaining radially oriented least-compressive stresses that favor the formation of arcuate fissures within 1–2 km outboard of the caldera rim. Variations in caldera shape, depth-to-diameter ratio, intra-caldera bench location and the extent of talus slope development provide insight into the most recent events of caldera modification, which may be modulated by the episodic supply of magma to each volcano. A lack of correlation between the volume of the single historical collapse event and its associated volume of erupted lava precludes a model of caldera formation linked directly to magma withdrawal. Rather, caldera collapse is probably the result of accumulated loss from the central storage system without sufficient recharge and (as has been suggested for Kilauea) may be aided by the downward drag of dense cumulates and intrusives.  相似文献   

The effect of maturation on the configuration of pristane in sediments and petroleum     

R.L. Patience  S.J. Rowland  J.R. Maxwell 《Geochimica et cosmochimica acta》1978,42(12):1871-1875

The absolute stereochemistry of pristane in a sample of contemporary marine Zooplankton, Messel shale (Germany) and Djatibarang (Java) crude has been determined by gas Chromatographic methods. The relative stereochemistry in Irati shale (Brazil), Green River (U.S.) crude, Halibut (Australia) crude has also been determined, and confirmed for a sample of the Green River shale. The stereoisomer distributions indicate a loss of stereospecificity of the phytol-derived 6(R),10(S) pristane with increasing geological maturation. For example, the least mature geological sample, the Eocene Messel shale, contains solely the 6(R),10(S) isomer, whereas a mature sample, Djatibarang crude, contains 50% of the 6(R),10(S) isomer and 25% of each of the 6(R),10(R) and 6(S),10(S) isomers.  相似文献   

In vitro screening for endocrine disruptive activity in selected South African harbours and river mouths     

JC Truter  JH van Wyk  BK Newman 《African Journal of Marine Science》2015,37(4):567-574

Various waterborne anthropogenic contaminants disrupt the endocrine systems of wildlife and humans, targeting reproductive pathways, among others. Very little is known, however, regarding the occurrence of endocrine disruptive activity in South African freshwater ecosystems, and coastal ecosystems have not been studied in this regard. In a first attempt to investigate endocrine disruptive activity in South African coastal waters, surface water samples collected from harbours, river mouths and estuaries in three metropolitan municipalities, eThekwini (which includes Durban), Nelson Mandela (specifically Port Elizabeth Harbour) and City of Cape Town, were screened for (anti) oestrogenicity and (anti)androgenicity using recombinant yeast bioassays. Moreover, levels of the female hormone 17β-(o)estradiol (E2) were determined in all samples, as well as a selection of hydrocarbons in the eThekwini samples. A high proportion of samples collected from eThekwini were oestrogenic, whereas none from Port Elizabeth Harbour and only a single river mouth sampled in the City of Cape Town were oestrogenic. E2 was detected in all the samples tested, but at higher concentrations at the eThekwini and City of Cape Town localities than Port Elizabeth Harbour. In addition, the recombinant yeast assays revealed that anti-androgenicity was widespread, being detected in the majority of samples screened apart from those representing Port Elizabeth Harbour. Conversely, no anti-oestrogenic or androgenic activity was detected. Anti-androgenicity did not associate with hydrocarbon loads, providing evidence that other anti-androgens were responsible for the observed activity. The present data suggest potential reproductive disruption in marine and estuarine fauna inhabiting the eThekwini and City of Cape Town regions.  相似文献   

Density-Stratified Flow Events in Great Salt Lake,Utah, USA: Implications for Mercury and Salinity Cycling     

David L. Naftz  Gregory T. Carling  Cory Angeroth  Michael Freeman  Ryan Rowland  Eddy Pazmiño 《Aquatic Geochemistry》2014,20(6):547-571

Density stratification in saline and hypersaline water bodies from throughout the world can have large impacts on the internal cycling and loading of salinity, nutrients, and trace elements. High temporal resolution hydroacoustic and physical/chemical data were collected at two sites in Great Salt Lake (GSL), a saline lake in the western USA, to understand how density stratification may influence salinity and mercury (Hg) distributions. The first study site was in a causeway breach where saline water from GSL exchanges with less saline water from a flow restricted bay. Near-surface-specific conductance values measured in water at the breach displayed a good relationship with both flow and wind direction. No diurnal variations in the concentration of dissolved (<0.45 μm) methylmercury (MeHg) were observed during the 24-h sampling period; however, the highest proportion of particulate Hg_total and MeHg loadings was observed during periods of elevated salinity. The second study site was located on the bottom of GSL where movement of a high-salinity water layer, referred to as the deep brine layer (DBL), is restricted to a naturally occurring 1.5-km-wide “spillway” structure. During selected time periods in April/May, 2012, wind-induced flow reversals in a railroad causeway breach, separating Gunnison and Gilbert Bays, were coupled with high-velocity flow pulses (up to 55 cm/s) in the DBL at the spillway site. These flow pulses were likely driven by a pressure response of highly saline water from Gunnison Bay flowing into the north basin of Gilbert Bay. Short-term flow reversal events measured at the railroad causeway breach have the ability to move measurable amounts of salt and Hg from Gunnison Bay into the DBL. Future disturbance to the steady state conditions currently imposed by the railroad causeway infrastructure could result in changes to the existing chemical balance between Gunnison and Gilbert Bays. Monitoring instruments were installed at six additional sites in the DBL during October 2012 to assess impacts from any future modifications to the railroad causeway.  相似文献   

From Grain to Floodplain: Evaluating heterogeneity of floodplain hydrostatigraphy using sedimentology,geophysics, and remote sensing     

H.F. Malenda  N.A. Sutfin  G. Guryan  S. Stauffer  J.C. Rowland  K.H. Williams  K. Singha 《地球表面变化过程与地形》2019,44(9):1799-1815

Stratigraphy is a fundamental component of floodplain heterogeneity and hydraulic conductivity and connectivity of alluvial aquifers, which affect hydrologic processes such as groundwater flow and hyporheic exchange. Watershed-scale hydrological models commonly simplify the sedimentology and stratigraphy of floodplains, neglecting natural floodplain heterogeneity and anisotropy. This study, conducted in the upper reach of the East River in the East River Basin, Colorado, USA, combines point-, meander-, and floodplain-scale data to determine key features of alluvial aquifers important for estimating hydrologic processes. We compare stratigraphy of two meanders with disparate geometries to explore floodplain heterogeneity and connectivity controls on flow and transport. Meander shape, orientation, and internal stratigraphy affected residence time estimates of laterally exchanged hyporheic water. Although the two meanders share a sediment source, vegetation, and climate, their divergent river migration histories resulted in contrasting meander hydrofacies. In turn, the extent and orientation of these elements controlled the effective hydraulic conductivity and, ultimately, estimates of groundwater transport and hyporheic residence times. Additionally, the meanders’ orientation relative to the valley gradient impacted the hydraulic gradient across the meanders—a key control of groundwater velocity. Lastly, we combine our field data with remotely sensed data and introduce a potential approach to estimate key hydrostratigraphic packages across floodplains. Prospective applications include contaminant transport studies, hyporheic models, and watershed models. © 2019 John Wiley & Sons, Ltd.  相似文献   

Atypical size selection of captive school prawns,Metapenaeus macleayi,by three recreational fishing gears in south‐eastern Australia     

Matt K. Broadhurst  Russell B. Millar  Damian J. Young  Michael E. L. Wooden  Stuart Rowland 《新西兰海洋与淡水研究杂志》2013,47(5):755-766

Three manipulative experiments were done to estimate the selectivity of conventional and new sizes and configurations of mesh for school prawns, Metapenaeus macleayi, in three south‐eastern Australian recreational fishing gears (haul, push, and scoop nets). The treatment meshes examined were: (1) conventional‐sized, diamond‐shaped mesh used in all gears (20 mm in scoop nets and 30 mm in push and haul nets); (2) 30 mm in scoop nets; and (3) 40‐mm diamond‐ and (4) 23‐mm square‐shaped mesh in all gears. In all experiments, known quantities of school prawns (6–24 mm carapace length (CL)) were placed in purpose‐built enclosures, monitored to ensure no experimental‐induced stress (as measured by changes in L‐lactate in their haemolymph) and the replicate treatments of the various gear configurations deployed. Escapees from the various treatment nets were collected from the enclosures using fine‐meshed nets. Logistic selection curves were derived for all treatment nets and specific comparisons made within and among gears. All nets had 50% retention lengths (L₅₀) comparable to other penaeid‐catching gears with similar mesh sizes, but most had selection ranges (SRs) that were atypically inflated. The large SRs were attributed to a combination of factors that included the mesh geometry and towing speed of the gears and the behaviour of school prawns. The 20‐mm scoop net had the smallest selection parameters, retaining >99% of individuals larger than 13 mm CL. Mesh size in this gear would need to be increased to at least 30 mm to allow some maturing prawns (>18 mm CL) to escape.  相似文献   

Geochemistry and arsenic behaviour in groundwater resources of the Pannonian Basin (Hungary and Romania)   总被引：1，自引：0，他引：1  

Helen A.L. Rowland  Enoma O. OmoregieRomain Millot  Cristina Jimenez  Jasmin Mertens  Calin BaciuStephan J. Hug  Michael Berg 《Applied Geochemistry》2011,26(1):1-17

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Quantifying and relating land-surface and subsurface variability in permafrost environments using LiDAR and surface geophysical datasets   总被引：1，自引：0，他引：1  

S. S. Hubbard  C. Gangodagamage  B. Dafflon  H. Wainwright  J. Peterson  A. Gusmeroli  C. Ulrich  Y. Wu  C. Wilson  J. Rowland  C. Tweedie  S. D. Wullschleger 《Hydrogeology Journal》2013,21(1):149-169

The value of remote sensing and surface geophysical data for characterizing the spatial variability and relationships between land-surface and subsurface properties was explored in an Alaska (USA) coastal plain ecosystem. At this site, a nested suite of measurements was collected within a region where the land surface was dominated by polygons, including: LiDAR data; ground-penetrating radar, electromagnetic, and electrical-resistance tomography data; active-layer depth, soil temperature, soil-moisture content, soil texture, soil carbon and nitrogen content; and pore-fluid cations. LiDAR data were used to extract geomorphic metrics, which potentially indicate drainage potential. Geophysical data were used to characterize active-layer depth, soil-moisture content, and permafrost variability. Cluster analysis of the LiDAR and geophysical attributes revealed the presence of three spatial zones, which had unique distributions of geomorphic, hydrological, thermal, and geochemical properties. The correspondence between the LiDAR-based geomorphic zonation and the geophysics-based active-layer and permafrost zonation highlights the significant linkage between these ecosystem compartments. This study suggests the potential of combining LiDAR and surface geophysical measurements for providing high-resolution information about land-surface and subsurface properties as well as their spatial variations and linkages, all of which are important for quantifying terrestrial-ecosystem evolution and feedbacks to climate.  相似文献   

Editorial     

WL Gates  H Oeschger  JC Duplessy 《Climate Dynamics》1992,7(4):165-165

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