The changing morphology of an open lava channel on Mt. Etna     

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   

The morphological characteristics of diamonds from the Ekati property, Northwest Territories, Canada     

John J. Gurney  Peter R. Hildebrand  Jon A. Carlson  Yana Fedortchouk  Darren R. Dyck 《Lithos》2004,77(1-4):21-38

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MORPHOLOGY AND GROWTH PATTERNS OF THE USRI RIVER POINT BARS, BIHAR, INDIA     

《国际泥沙研究》2000,(4)

1 INTRODUCTIONThe exact mechanism of accumulation of sediments in point bars is not clearly known. Many scientistsinvestigated the problem. In the river Klaralven, Sundborg (1956) observed the development of sometransverse bars in the initial stage of the point bar formation. These transverse bars tend to becomelongitudinal as they extend close to the stream bed. Martvall and Nilsson (1972) investigated the problemof point bar formation experimentally in a laboratory flume. The flume st…  相似文献   

Modelling the effect of water on the surface structure and stability of forsterite   总被引：1，自引：0，他引：1  

N. H. de Leeuw  S. C. Parker  C. R. A. Catlow  G. D. Price 《Physics and Chemistry of Minerals》2000,27(5):332-341

 We describe the application of atomistic simulation techniques to investigate the effect of associative and dissociative adsorption of water on the structures and stabilities of the low-index surfaces of forsterite. All surfaces are amenable to associative adsorption of water, while dissociative adsorption is energetically favourable on all but the non-dipolar {1 0 0} surface. Often, otherwise unstable (dipolar) surfaces are stabilised to a large extent by hydration, e.g. the dipolar {0 1 0} surface. However, on thermodynamic grounds we do not expect associatively adsorbed water to dissociate on all surfaces, as the energies released for dissociative adsorption of water on the non-dipolar {0 1 0} and {1 0 0} surfaces are less than those released for associative adsorption. As such, there is no energetic incentive for the associatively adsorbed water molecules to dissociate. The stabilities of the two terminations of the {0 1 0} surface, the main cleavage plane of forsterite, are reversed when hydroxylated, indicating that some dissolution of the magnesium ions may occur upon hydration, which is shown to be an exothermic process for both surface terminations. The equilibrium morphology was calculated as a way of assessing the change in surface energies. The experimental morphology of forsterite is adequately reproduced, suggesting that the relative stabilities of the surfaces, both unhydrated and hydroxylated, are calculated correctly. Received: 4 August 1999 / Revised, accepted: 11 October 1999  相似文献   

Évolution récente et actuelle de la côte basque française (analyse et perspectives)     

Antonin Genna  Jean-Pierre Capdeville  Jacques Dubreuilh  Cyril Mallet 《Comptes Rendus Geoscience》2005,337(16):1474

A recent multidisciplinary study, comprising existing data analysis and geomorphological and geological fieldwork, has helped clarify marine erosion processes of Pyrenean formations along the Basque Coast. An important discovery was made during our study of an alterite of regional extent, which calls into question recent and present evolution of the Basque Coast and the processes leading to coastline retreat. Modelling these factors has made it possible to propose a predictive scenario for future coastal evolution. To cite this article: A. Genna et al., C. R. Geoscience 337 (2005).  相似文献   

The Morphological and Optical Properties of Volcanic Glass: A Tool to Assess Density-induced Vertical Migration of Tephra in Sediment Cores     

Mihaela D. Enache  Brian F. Cumming 《Journal of Paleolimnology》2006,35(3):661-667

Volcanic ash layers in sediment cores are valuable geochronological markers in paleolimnological research. The composition of volcanic glass is related to identifiable, chronologically distinctive volcanic eruptions. Consequently, tephra layers provide time horizons allowing regional-scale correlations for lake sediments. Volcanic glass is often present in samples routinely prepared by paleolimnologists such as diatom slides and thin sections. Knowledge of the morphological and optical properties of volcanic glass allows for its identification. This is essential for the identification of ash layers that are not macroscopically visible or to track their vertical migration in soft organic sediments. The purposes of this note are to: (1) describe how the morphological (i.e., shape, vesicularity) and optical (i.e., refractive index and birefringence) properties can be used to identify volcanic glass in preparations from lake sediments; and (2) show how the quantification of volcanic glass from diatom slides is used to quantify the density-induced displacement of a 4.5 cm-thick Mazama ash-layer through organic sediments and to approximate its timing of initial deposition.  相似文献   

烟台第一海水浴场沙源匮乏型海滩地貌和表层沉积物粒度特征     

解燕  ;王张华  ;金秉福 《山东地质》2008,(5):37-40

在烟台第一海水浴场,利用经纬仪进行2条海滩横剖面形态测量,并在不同地貌单元采集沉积物样品进行粒度分析。测量显示,该海滩仅有小规模沙坝和沟槽体系。后滨上有风成沉积,但滩肩和海岸沙丘发育均不明显。粒度分析结果表明,海滩沉积物以中砂、粗砂为主,杂以砾或细砂,比山东半岛其他海滩沉积物明显要粗。由陆向海沉积物呈带状分布,平均高潮线附近和沙坝迎水坡侵蚀作用均显著。因此认为缺乏沙源供应的基岩岬湾式海岸是导致沙滩地貌发育不典型、海滩侵蚀作用显著的主要原因。  相似文献   

Unique Aeolian Bedforms of Mars: Transverse Aeolian Ridges     

Zhibao Dong  Lü Ping  Chao Li  Guangyin Hu 《地球科学进展》1986,35(7):661-677

Transverse Aeolian Ridges (TARs) are among the unique aeolian bedforms of Mars, which witnessed a series of investigation for the last two decades thanks to the high-resolution remote sensing data. This paper summarized the understanding with respect to distribution, morphology, sedimentology, formation hypotheses and formation time of TARs. It is suggested that TARs are a kind of aeolian bedforms with meter-scale height and decameter-scale wavelength. TARs are primarily distributed in the equator and low-latitude regions, being rare in high and mid-latitude regions, and more popular in the south hemisphere than in the north hemisphere. Higher albedo and symmetric cross-sections are the most outstanding features of TARs, being analogous to the megaripples and reversing dunes on the Earth. The grain-size distribution of TARs’ sediments is generally bimodal, with granule cover and low thermal inertia. Three formation hypotheses were proposed for TARs: Megaripple hypothesis, reversing dune hypothesis and dust induration hypothesis, with more evidences supporting the megaripple hypothesis. Similar to dunes, TARs are geologically recent morphology on Mars, but generally predate dunes, formed in the last few million years so that most TARs are indurated or lithified and are immobile. However, contemporary mobileTARs are also developed in some regions. The unique features of TARs make them the mostenigmatic aeolian bedforms of Mars. It is proposed that high-resolution information on TARs sedimentology and integrated regional surveying should be listed in the priorities of future Mars exploration with respect to TARs study.  相似文献   

Some observations concerning the morphology and sedimentology of a protalus rampart,Okstindan, Norway     

Charles Harris 《地球表面变化过程与地形》1986,11(6):673-676

A protaius rampart up to 4.75 m high and consisting largely of angular clasts up to boulder size is described. Bulk samples contained up to 35 per cent fines by weight, compared with up to 68 per cent fines in adjacent till. Although the rampart material was clast dominated, fines filled much of the void space, in contrast with most other protalus ramparts described in the literature.  相似文献   

鱼类血栓细胞免疫功能的研究现状     

高迎莉  韩高尚  姚海静  陈香凝  周谦青 《海洋科学》2021,45(1):120-128

血细胞研究是鱼类基础研究的重中之重.鱼类血细胞的前期研究主要聚焦于淋巴细胞、巨噬细胞和嗜中性粒细胞等细胞的功能特性,而忽略了血栓细胞.血栓细胞是低等脊椎动物具有的类似于哺乳动物血小板的一类细胞,该细胞的经典功能是参与凝血和血栓形成.近年来的研究表明,血栓细胞是一类特殊的免疫细胞,在鱼体免疫应答中发挥重要作用.作者将对鱼...  相似文献