How fast does tufa grow? Very high-resolution measurement of the tufa growth rate on artificial substrates by the development of a contactless image-based modelling device     

Ivan Marić  Ante Šiljeg  Neven Cukrov  Vlatko Roland  Fran Domazetović 《地球表面变化过程与地形》2020,45(10):2331-2349

Accurate determination of the tufa growth rate (TGR) is required to answer the fundamental geomorphological question of tufa evolution. The TGR has been measured by various direct and indirect methods. One of the most popular direct methods uses modified micro-erosion meter (MEM), which has several drawbacks. Here, we present for the first time a coordinate measuring macro-photogrammetry device (CMD) for monitoring the TGR in a contactless manner. The CMD was applied on 28 limestone plates at 14 locations within the Skradinski buk area, Croatia, and measurements were performed in the laboratory. The TGR was derived from digital tufa high-resolution models (DTHRMs). The accuracy of the device was evaluated using state-of-the-art three-dimensional (3D) scanners and error calculation at checkpoints. Moreover, the precision was evaluated with the split test (n = 5). A total of 74 DTHRMs with a spatial resolution of 0.0236 mm were created. The TGR ranged from 0.327 to 19.302 mm a⁻¹, with an average of 5.771 mm a⁻¹. A higher TGR was observed on the limestone plates near mosses, located in fast and turbulent water rather than in stagnant water. We found that specific micro-environmental factors (e.g. proximity to moss) positively affected tufa growth. Erosion events were observed, as well as the presence of aquatic insect larvae (Simuliidae and Chironomidae), which positively affected tufa growth. The CMD is a precise and accurate device that does not suffer from the drawbacks of the MEM method and has many other advantages. It has a high capability of tufa erosion detection, enables the identification of macroinvertebrates, and multispectral or hyperspectral cameras can be mounted on the device for spectral reflectance analysis of the tufa surface. The CMD can be applied in any study requiring a sub-millimetre data quality and involving the comparison of consecutive 3D models and derivation of various parameters of smaller objects. © 2020 John Wiley & Sons, Ltd.  相似文献   

Contrasting magma types and timing of intrusion in the Permian layered mafic complex of Mont Collon (Western Alps,Valais, Switzerland): evidence from U/Pb zircon and <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar amphibole dating     

Philippe Monjoie  François Bussy  Urs Schaltegger  Andreas Mulch  Henriette Lapierre  Hans-Ruedi Pfeifer 《Swiss Journal of Geoscience》2007,100(1):125-135

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Carbon dioxide dynamics in rivers and coastal waters of the “big island” of Hawaii,USA, during baseline and heavy rain conditions     

François S. Paquay  Fred T. Mackenzie  Alberto V. Borges 《Aquatic Geochemistry》2007,13(1):1-18

The distributions of the partial pressure of carbon dioxide (pCO₂) and total alkalinity (TA) were examined for a 6-month period in the Wailuku and Wailoa rivers and coastal waters of Hilo Bay on the west coast of the Island of Hawaii, USA. Main results for the largest and turbulent Wailuku River show in the watershed an oversaturation in CO₂ with respect to atmospheric equilibrium and a CO₂ undersaturation in the estuary. In the Wailoa river-estuary system, extremely high pCO₂ values ranging from 1500 to 10500 ppm were measured with significant shifts in pCO₂ from drought to flood period. In the two rivers, water residence time, groundwater inputs and occasional flood events are the predominant drivers of the spatial and temporal patterns in the distribution of pCO₂. In Hilo Bay, CO₂ oversaturation dominates and the bay was a source of CO₂ to the atmosphere during the study period. TA is conservative along the salinity gradient, indicating calcification in the bay is not a significant source of CO₂ to the atmosphere.  相似文献   

The December 26th 2004 Tsunami Recorded along the Southeastern Coast of Brazil     

Carlos A. S. França  Afranio R. De Mesquita 《Natural Hazards》2007,40(1):209-222

Sea level measurements along the southeastern Brazilian coast, between 20° S and 30° S, show the effect of the Sumatra Tsunami of December 26, 2004. Two records from stations, one located inside an estuary and other inside a bay, shows oscillations of about 0.20 m range; one additional record from a station facing the open sea shows up to 1.2 m range oscillations. These oscillations have around 45 min period, starting 20–22 h after the Sumatra earthquake in the Indian Ocean (00:59 UTC) and lasting for 2 days. A computer modelling of the event reproduces the time of arrival of long shallow-water tsunami waves at the southeastern Brazilian coast but with slight longer period and amplitudes smaller than observed at the coast, probably due to its coarse resolution (1/4 of a degree). The high amplitudes observed at the coast suggest a mechanism of amplification of these waves over the southeastern Brazilian shelf.  相似文献   

Textural evolution of polyhedral olivine experiencing rapid cooling rates     

François Faure  Pierre Schiano  Gilles Trolliard  Christian Nicollet  Bernard Soulestin 《Contributions to Mineralogy and Petrology》2007,153(4):405-416

Dynamic crystallization experiments in the CaO–MgO–Al₂O₃–SiO₂ (CMAS) system have been used to investigate the change in crystal shape when pre-existing polyhedral olivine crystals are cooled rapidly (1,639–2,182°C/h). Polyhedral olivines are crystallized initially in a first step using a slow cooling rate (2°C/h), then skeletal and dendritic overgrowths develop on the polyhedral crystals during a subsequent fast cooling event. During this second episode small dendritic olivines also nucleate within the liquid phase. Observation of the experimental sample by optical microscopy shows that the polyhedral olivine shape progressively changes to a skeletal and then to a dendritic morphology in the following sequence: polyhedral ⇒ hopper polyhedral ⇒ dendritic polyhedral. This evolutional sequence is discussed in terms of changes in the crystal growth conditions during cooling and a general relation between these olivine dynamic crystallization experiments and the integrated model of crystal growth by Sunagawa (Bull Minér 104:81–87, 1981, Morphology of crystals, Terra Scientific Publishing Company, 1987) is proposed.  相似文献   

Modeling surface roughness degradation of rock joint wall during monotonic and cyclic shearing   总被引：2，自引：0，他引：2  

Tikou Belem  Mountaka Souley  Françoise Homand 《Acta Geotechnica》2007,2(4):227-248

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Impact of coherent eddies on airborne measurements of vertical turbulent fluxes     

Marie Lothon  Fleur Couvreux  Sylvie Donier  Françoise Guichard  Pierre Lacarrère  Donald H. Lenschow  Joël Noilhan  Frédérique Saïd 《Boundary-Layer Meteorology》2007,124(3):425-447

During the Hydrological-Atmospheric Pilot Experiment (HAPEX)-Sahel, which took place in Niger in the transitional period between the wet and dry seasons, two French aircraft probed the Sahelian boundary layer to measure sensible and latent heat fluxes. The measurements over the Niamey area often revealed organised structures of a few km scale that were associated with both thermals and dry intrusions. We study the impact of these coherent structures using a single day’s aircraft-measured fluxes and a numerical simulation of that day with a mesoscale model. The numerical simulation at high horizontal resolution (250 m) contains structures that evolve from streaks in the early morning to cells by noon. This simulation shows distribution, variance and skewness similar to the observations. In particular, the numerical simulation shows dry intrusions that can penetrate deeply into the atmospheric boundary layer (ABL), and even reach the surface in some cases, which is in accordance with the observed highly negatively skewed water vapour fluctuations. Dry intrusions and thermals organised at a few km scale give skewed flux statistics and can introduce large errors in measured fluxes. We use the numerical simulation to: (i) evaluate the contribution of the organised structures to the total flux, and (ii) estimate the impact of the organised structures on the systematic and random errors resulting from the 1D sampling of the aircraft as opposed to the 2D numerical simulation estimate. We find a significant contribution by the organised structures to the total resolved fluxes. When rolls occur, and for a leg length of about 30 times the ABL depth, the 1D sampled flux is shown to be sometimes 20% lower than the corresponding 2D flux when the 1D sampling direction is the same as the main axis of the rolls, whereas the systematic error is much lower when the direction of the leg is transverse to the rolls. In the case of cells, an underestimate of around 10% can still be observed with the 1D approach independent of direction, due to poor sampling of the energy-containing scales.  相似文献   

Sulfur partition coefficient between apatite and rhyolite: the role of bulk S content   总被引：2，自引：1，他引：1  

Fleurice?ParatEmail author  Fran?ois?Holtz 《Contributions to Mineralogy and Petrology》2005,150(6):643-651

Experimental studies have been performed to constrain sulfur behavior during apatite crystallization and to determine sulfur partition coefficient between apatite and melt (Kd_S^apatite/melt) at oxidizing conditions. Crystallization experiments have been conducted with a hydrous rhyolitic melt and different bulk sulfur contents (0.15 to 2 wt.% S) at 900 and 1,000°C, 200 MPa and Δlog =NNO+3.6. The sulfur content in the glass increases with increasing amount of added S. Anhydrite crystallizes for S added = 0.75 wt.% (0.10 and 0.13 wt.% SO₃ in glass at 900 and 1,000°C, respectively). The amount of anhydrite increases and the amount of apatite decreases with increasing amount of added sulfur. The sulfur exchange reaction in apatite is influenced by the bulk composition of the melt (e.g., P content). However, changing melt composition has only little effect on Kd_S^apatite/melt for the investigated rhyolitic composition. The Kd_S^apatite/melt does not depend directly on temperature, decreases from 14.2 to 2.7 with increasing S content in glass from SO₃=0.03 to 0.19 wt.%, respectively, and can be predicted from the following equation: ln Kd = −0.0025×S in melt (in ppm)+2.9178. The combination of experimental data obtained for rhyolitic and andesitic melts reveals that the sulfur partition coefficient tends toward a value of 2 for high-sulfur content in the glass (>0.2 wt.% SO₃). Using S in apatite as proxy for determining S content in melt is promising but additional experimental data are needed to clarify the individual effects of T, , and P and Ca content in the melt on S partitioning.  相似文献   

Fluoride pollution in French rivers and estuaries     

Jean-Marie Martin  François Salvadori 《Estuarine, Coastal and Shelf Science》1983,17(3):231-242

Fluoride concentrations have been determined in major French rivers and estuaries. The unpolluted estuary in the Loire has been compared with the Seine, Gironde and Charente where important discharges occur. Natural dissolved concentration can be multiplied by a factor of 30. Particulate fluorine concentration reach almost 2000 ppm in the Seine estuary. The percentage between free and complexed dissolved fluoride is not affected by the anthropic discharge. The present French rivers discharge of fluoride is 700% higher than the pristine value. At a global scale, dissolved fluoride has probably increased by 25% compared with the natural situation.  相似文献   

A site effect study in the Verchiano valley during the 1997 Umbria-Marche (Central Italy) earthquakes     

Stéphane Gaffet  Giovanna Cultrera  Michel Dietrich  Françoise Courboulex  Fabrizio Marra  Michel Bouchon  Arrigo Caserta  Cécile Cornou  Anne Deschamps  Jean-Paul Glot  Robert Guiguet 《Journal of Seismology》2000,4(4):525-541

Strong site effects were observed during the two M _W 5.7 and M _W 6.0 main shocks of the Colfiorito seismic crisis which occured on September 26, 1997 in Umbria-Marche (Central Italy).The most obvious indications of these effects are the dramatic differences in damage shown by buildings of similar construction in neighboring villages.Such observations were specifically made in the Verchiano valley in the fault area, 15 km south of Colfiorito where the Verchiano village and the Colle and Camino hamlets were heavily damaged (MCS intensity IX-X) since the first main shock of 1997/09/26,while in contrast, the Curasci village located 2 km eastwards remains almost intact.In order to study the anomalous ground motion amplifications in this area, an array of 11, 3-components seismo- and accelero-meters was set up during the 1997/10/20-24 period, extending from the western side of the valley, up to the top of Mount San Salvatore, going accross the Colle and Curasci hamlets.During the experiment, 67 aftershocks enlightened the valley from the Colfiorito (10 km north) and the Sellano (6 km south) active swarms.Seismic refraction experiments were conducted at the same time in the 500 m wide, 1500 m long Verchiano valley in order to determine the thickness and main characteristics of the alluvial infilling.The main results are: (i) compared to the valley side ground motion, and for all the events, recordings in the central part of the valley (piana di Verchiano) show relative amplification of 10 with a clear lengthening of the seismogram duration by a factor of 2 – (ii) broad band relative amplification of 6–8 is also clearly identified at the top of the Mount San Salvatore overhanging the valley – (iii) any of the site effect measurements done explains by itself the strongly contrasted damage observed at Colle and Curasci: i.e. the modification of the near-field radiation pattern by interaction with the free heterogeneous surface may have induced local shadow zones that saved Curasci.  相似文献