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911.
L. Lodato L. Spampinato A. Harris S. Calvari J. Dehn M. Patrick 《Bulletin of Volcanology》2007,69(6):661-679
The use of a hand-held thermal camera during the 2002–2003 Stromboli effusive eruption proved essential in tracking the development
of flow field structures and in measuring related eruption parameters, such as the number of active vents and flow lengths.
The steep underlying slope on which the flow field was emplaced resulted in a characteristic flow field morphology. This comprised
a proximal shield, where flow stacking and inflation caused piling up of lava on the relatively flat ground of the vent zone,
that fed a medial–distal lava flow field. This zone was characterized by the formation of lava tubes and tumuli forming a
complex network of tumuli and flows linked by tubes. Most of the flow field was emplaced on extremely steep slopes and this
had two effects. It caused flows to slide, as well as flow, and flow fronts to fail frequently, persistent flow front crumbling
resulted in the production of an extensive debris field. Channel-fed flows were also characterized by development of excavated
debris levees in this zone (Calvari et al. 2005). Collapse of lava flow fronts and inflation of the upper proximal lava shield made volume calculation very difficult. Comparison
of the final field volume with that expecta by integrating the lava effusion rates through time suggests a loss of ~70% erupted
lava by flow front crumbling and accumulation as debris flows below sea level. Derived relationships between effusion rate,
flow length, and number of active vents showed systematic and correlated variations with time where spreading of volume between
numerous flows caused an otherwise good correlation between effusion rate, flow length to break down. Observations collected
during this eruption are useful in helping to understand lava flow processes on steep slopes, as well as in interpreting old
lava–debris sequences found in other steep-sided volcanoes subject to effusive activity. 相似文献
912.
Multiple-Point Statistics for Training Image Selection 总被引:2,自引:0,他引:2
Selecting a training image (TI) that is representative of the target spatial phenomenon (reservoir, mineral deposit, soil
type, etc.) is essential for an effective application of multiple-point statistics (MPS) simulation. It is often possible
to narrow potential TIs to a general subset based on the available geological knowledge; however, this is largely subjective.
A method is presented that compares the distribution of runs and the multiple-point density function from available exploration
data and TIs. The difference in the MPS can be used to select the TI that is most representative of the data set. This tool
may be applied to further narrow a suite of TIs for a more realistic model of spatial uncertainty. In addition, significant
differences between the spatial statistics of local conditioning data and a TI may lead to artifacts in MPS. The utilization
of this tool will identify contradictions between conditioning data and TIs. TI selection is demonstrated for a deepwater
reservoir with 32 wells. 相似文献
913.
914.
Tamar Elias A. Jeff Sutton Clive Oppenheimer Keith A. Horton Harold Garbeil Vitchko Tsanev Andrew J. S. McGonigle Glyn Williams-Jones 《Bulletin of Volcanology》2006,68(4):313-322
The correlation spectrometer (COSPEC), the principal tool for remote measurements of volcanic SO2, is rapidly being replaced by low-cost, miniature, ultraviolet (UV) spectrometers. We compared two of these new systems with
a COSPEC by measuring SO2 column amounts at Kīlauea Volcano, Hawaii. The two systems, one calibrated using in-situ SO2 cells, and the other using a calibrated laboratory reference spectrum, employ similar spectrometer hardware, but different
foreoptics and spectral retrieval algorithms. Accuracy, signal-to-noise, retrieval parameters, and precision were investigated
for the two configurations of new miniature spectrometer. Measurements included traverses beneath the plumes from the summit
and east rift zone of Kīlauea, and testing with calibration cells of known SO2 concentration. The results obtained from the different methods were consistent with each other, with <8% difference in estimated
SO2 column amounts up to 800 ppm m. A further comparison between the COSPEC and one of the miniature spectrometer configurations,
the ‘FLYSPEC’, spans an eight month period and showed agreement of measured emission rates to within 10% for SO2 column amounts up to 1,600 ppm m. The topic of measuring high SO2 burdens accurately is addressed for the Kīlauea measurements. In comparing the foreoptics, retrieval methods, and resultant
implications for data quality, we aim to consolidate the various experiences to date, and improve the application and development
of miniature spectrometer systems. 相似文献
915.
Stewart Cohen Denise Neilsen Scott Smith Tina Neale Bill Taylor Mark Barton Wendy Merritt Younes Alila Philippa Shepherd Roger Mcneill James Tansey Jeff Carmichael Stacy Langsdale 《Climatic change》2006,75(3):331-358
The research activity described in this report is a comprehensive regional assessment of the impacts of climate change on
water resources and options for adaptation in the Okanagan Basin. The ultimate goal of the project is to develop integrated
climate change and water resource scenarios to stimulate a multistakeholder discussion on the implications of climate change
for water management in the region.
The paper describes two main objectives: (a) providing a set of research products that will be of relevance to regional interests
in the Okanagan, and (b) establishing a methodology for participatory integrated assessment of regional climate change impacts
and adaptation that could be applied to climate-related concerns in Canada and other countries.
This collaborative study has relied on field research, computer-based models, and dialogue exercises to generate an assessment
of future implications, and to learn about regional views on the prospects for adaptation. Along the way, it has benefited
from strong partnerships with governments, researchers, local water practitioners, and user groups. Building on the scenario-based
study components, and a series of interviews and surveys undertaken for the water management and adaptation case study components,
a set of stakeholder dialogue sessions were organized which focused on identifying preferred adaptation options and processes
for their implementation. Rather than seeking consensus on the “best” option or process, regional interests were asked to
consider a range of available options as part of an adaptation portfolio that could address both supply side and demand side
aspects of water resources management in the Okanagan.
The Canadian Crown reserves the right to retain a non-exclusive, royalty free licence in and to any copyright. 相似文献
916.
Towards quantifying uncertainty in transient climate change 总被引:2,自引:3,他引:2
Matthew Collins Ben B. B. Booth Glen R. Harris James M. Murphy David M. H. Sexton Mark J. Webb 《Climate Dynamics》2006,27(2-3):127-147
Ensembles of coupled atmosphere–ocean global circulation model simulations are required to make probabilistic predictions of future climate change. “Perturbed physics” ensembles provide a new approach in which modelling uncertainties are sampled systematically by perturbing uncertain parameters. The aim is to provide a basis for probabilistic predictions in which the impact of prior assumptions and observational constraints can be clearly distinguished. Here we report on the first perturbed physics coupled atmosphere–ocean model ensemble in which poorly constrained atmosphere, land and sea-ice component parameters are varied in the third version of the Hadley Centre model (the variation of ocean parameters will be the subject of future study). Flux adjustments are employed, both to reduce regional sea surface temperature (SST) and salinity biases and also to admit the use of combinations of model parameter values which give non-zero values for the global radiation balance. This improves the extent to which the ensemble provides a credible basis for the quantification of uncertainties in climate change, especially at a regional level. However, this particular implementation of flux-adjustments leads to a weakening of the Atlantic overturning circulation, resulting in the development of biases in SST and sea ice in the North Atlantic and Arctic Oceans. Nevertheless, model versions are produced which are of similar quality to the unperturbed and un-flux-adjusted version. The ensemble is used to simulate pre-industrial conditions and a simple scenario of a 1% per year compounded increase in CO2. The range of transient climate response (the 20 year averaged global warming at the time of CO2 doubling) is 1.5–2.6°C, similar to that found in multi-model studies. Measures of global and large scale climate change from the coupled models show simple relationships with associated measures computed from atmosphere-mixed-layer-ocean climate change experiments, suggesting that recent advances in computing the probability density function of climate change under equilibrium conditions using the perturbed physics approach may be extended to the transient case. 相似文献
917.
John E. Bailey Andrew J. L. Harris Jonathan Dehn Sonia Calvari Scott K. Rowland 《Bulletin of Volcanology》2006,68(6):497-515
An open channel lava flow on Mt. Etna (Sicily) was observed during May 30–31, 2001. Data collected using a forward looking
infrared (FLIR) thermal camera and a Minolta-Land Cyclops 300 thermal infrared thermometer showed that the bulk volume flux
of lava flowing in the channel varied greatly over time. Cyclic changes in the channel's volumetric flow rate occurred over
several hours, with cycle durations of 113–190 min, and discharges peaking at 0.7 m3 s−1 and waning to 0.1 m3 s−1. Each cycle was characterized by a relatively short, high-volume flux phase during which a pulse of lava, with a well-defined
flow front, would propagate down-channel, followed by a period of waning flow during which volume flux lowered. Pulses involved
lava moving at relatively high velocities (up to 0.29 m s−1) and were related to some change in the flow conditions occurring up-channel, possibly at the vent. They implied either a
change in the dense rock effusion rate at the source vent and/or cyclic-variation in the vesicle content of the lava changing
its bulk volume flux. Pulses would generally overspill the channel to emplace pāhoehoe overflows. During periods of waning
flow, velocities fell to 0.05 m s–1. Blockages forming during such phases caused lava to back up. Occasionally backup resulted in overflows of slow moving ‘a‘ā
that would advance a few tens of meters down the levee flank. Compound levees were thus a symptom of unsteady flow, where
overflow levees were emplaced as relatively fast moving pāhoehoe sheets during pulses, and as slow-moving ‘a‘ā units during
backup. Small, localized fluctuations in channel volume flux also occurred on timescales of minutes. Volumes of lava backed
up behind blockages that formed at constrictions in the channel. Blockage collapse and/or enhanced flow under/around the blockage
would then feed short-lived, wave-like, down-channel surges. Real fluctuations in channel volume flux, due to pulses and surges,
can lead to significant errors in effusion rate calculations.
Editorial responsibility: A. Woods 相似文献
918.
This paper describes and analyses the structure and deposits of a large UK peat slide, located at Hart Hope in the North Pennines, northern England. This particular failure is unusual in that it occurred in the winter (February, 1995) and shows excellent preservation of the sedimentary structures and morphology, both at the failure scar and downstream. The slide was triggered by heavy rain and rapid snowmelt along the line of an active peatland stream flush. Detailed mapping of the slide area and downstream deposits demonstrate that the slide was initiated as a blocky mass that degenerated into a debris flow. The slide pattern was complex, with areas of extending and compressive movement. A wave‐like motion may have been set up in the failure. Within the slide site there was relatively little variability in block size (b axis); however, downstream the block sizes decrease rapidly. Stability analysis suggests the area at the head of the scar is most susceptible to failure. A ‘secondary’ slide area is thought to have only been initiated once the main failure had occurred. Estimates of the velocity of the flowing peat mass as it entered the main stream channel indicate a flow velocity of approximately 10 m s?1, which rapidly decreases downstream. A sediment budget for the peat slide estimates the failed peat mass to be 30 800 t. However, sediment delivery to the stream channel was relatively low. About 37% of the failed mass entered the stream channel and, despite moving initially as debris flow, the amount of deposition along the stream course and on the downstream fan is small (only about 1%). The efficiency of fluvial systems in transporting the eroded peat is therefore high. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
919.
An analysis of mechanisms of ice-wedge casting based on geotechnical centrifuge simulations 总被引:1,自引:1,他引:1
Here we interpret the outcomes of scaled geotechnical centrifuge simulation of ice-wedge casting in terms of the likely significance of Quaternary ice-wedge pseudomorphs observed within different host sediments. Six experiments were completed in which 1/30th scale models of an ice-wedge embedded within frozen host sediments beneath a 25 mm thick unfrozen active layer were thawed from the surface downwards in the geotechnical centrifuge under a 30 times gravity (30×g) acceleration. Host sediment granulometry and/or ice contents were varied in each model, with host materials comprising medium sands, fine sandy silts and silty clays. The model ice-wedge was 50 mm at the top, 150 mm deep, and extended across the full width of the 450 mm wide test box. Centrifuge scaling laws indicate that under an acceleration of 30×g, stress distribution was equivalent to a 13.5 m long section of a 4.5 m high and 1.5 m wide full-scale prototype ice-wedge, covered in an active layer of thickness equivalent to 0.75 m. Thermal regimes, measured pore pressures during thaw, observed thaw consolidation and measured host sediment geotechnical properties are utilised in the interpretation of casting mechanisms. During a single uniform thaw event it is shown that arching of infilling sediment and the formation of a void is likely if negative pore pressures are developed in the host sediment. In fine silt and clays high ice contents are more likely than in sands, thaw consolidation is greater, positive pore pressures encourage complete filling of the ice-wedge void, and soft sediment deformation is likely to cause deformation of the cast and reduce its width and depth. Though natural casting mechanisms are likely to be more complex than those simulated here, modelling experiments highlight the need for care when inferring original ice-wedge geometry from observed shape and size of Quaternary ice-wedge casts. 相似文献
920.
Carbon isotope measurements on diamonds from the Letlhakane kimberlite, and the analyses of their inclusions, permit the examination of km-scale mantle-composition variations by comparing the results with those for the nearby Orapa kimberlite. Diamonds from Letlhakane have a wide range in carbon isotopic composition (−3‰ to −21‰); however, the relative abundance of diamonds depleted in 13C is significantly lower than in the Orapa kimberlite. Most of the 13C-depleted diamonds belong to the eclogictic or websteritic paragenesis. The relative abundance of inclusions in diamonds and their composition indicate that there are significant differences in petrology in the mantle below the two locations. At Letlhakane, peridotitic compositions are more prevalent than at Orapa and the protolith of P-Type inclusions in diamonds may have experienced a higher degree of partial melting at Letlhakane compared to Orapa. P/T estimates for both W- and E-Type diamonds indicate that a region of 13C-depletion may exist beneath the two kimberlites. The relationships between carbon isotopic composition of the host diamond and the Al2O3/Cr2O3 ratios of their websteritic and eclogitic garnet inclusions indicate that the low δ13C regions may represent a primary mantle feature, unrelated to a crustal component. 相似文献