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The hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer 总被引：1，自引：0，他引：1
Rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface. For a given cover level, rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation. Compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface. For the same cover level, rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer. The effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage. Micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by Poesen (1986): i.e. runoff generated as rock flow or as Horton overland flow can (partly) infiltrate into the unsealed soil surface under the rock fragments, provided that they are not completely embedded in the top layer. Hence, rock fragment position, beside other rock fragment properties, should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers. A simple model, based on the proportions of bare soil surface, soil surface occupied by embedded rock fragments, and soil surface covered with rock fragments resting on the soil surface, describes the runoff coefficient data relatively well. 相似文献
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In this paper, the authors present the results of both macroscopic and microscopic investigations on structure development created by repeated ice lensing in various loamy experiments. Experimental data are compared with observations performed on active forms in High Arctic and Alpine Mountain environments. Those observations are also compared with phenomena observed in fossil periglacial formations of Western Europe. Platy and short prismatic structure formation is bonded to the hydraulic and thermal conditions during ice segregation. When a long series of alternating freezing and thawing affects platy structures, the fabric evolves, also being influenced by slope and drainage conditions: cryoturbations, frostcreep, and gelifluction can appear. They are characterized by specific microfabrics which are better developed with an increasing number of cycles: this is clear in experiments where hydraulic and thermal parameters are better controlled. Vesicles are also a prominent characteristic of the surface horizon in experiments and arctic soils. The genesis of vesicles is discussed on the basis of new observations and is related to the mechanical collapse of frost-created aggregates under the mechanical work of soil air escape during soil saturation by water at thaw. 相似文献
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During its storage or ascent, basaltic magma inevitably interacts with the surrounding rocks. In this study, schist xenoliths incorporated within ascending basalt are examined. Heating of the xenoliths combined with decompression effect of rapid magma uprise led to dehydration melting of hydrous minerals producing hercynitic spinel, melt, sillimanite and FeTi oxides. The melt is rhyolitic, strongly peraluminous (1.77 < A/CNK < 2.35) and corundum normative. It may contain up to 8 wt%FeOt. It occurs between the foliation planes and in the intragranular environment. Dehydration melting of micas in the schist is probably related to combined effects of heating by basaltic magma and decompression due to the rapid rise. Melting of xenoliths was a progressive process at low pressure. To cite this article: H. Bayhan et al., C. R. Geoscience 338 (2006). 相似文献
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Morphometric analysis of magmatic enclaves: a tool for understanding magma vesiculation and ascent 总被引：3，自引：0，他引：3
The extent of deformation of magmatic enclaves that occur in different portions of the Khaggiar endogenous lava dome (Island of Pantelleria, Italy) has been quantified using two morphometric techniques: thin-plate splines and fractals. Deformation of enclaves decreases from the outer portions of the dome to the more internal portions, defining two exponential trends. The amount and distribution of vesicles have also been quantified using image analysis of digital images obtained by a scanning electron microscope. The variation of deformation of enclaves correlates with the variation of their vesicle content, suggesting that deformation and vesiculation are related. We envisaged a continuous feedback system between vesiculation of enclaves and radial forces exerted by the surrounding host magma during the growth of the dome. These relationships are used as dynamic markers to infer the eruptive style of the endogenous dome. In particular, it is suggested that the variation of vesicularity of enclaves is related to the pressure exerted by magma on the extrusion vent. This resulted in enclaves being more vesicular and more deformed in the outer portions of the dome that emplaced first and at lower pressure, and less vesicular and less deformed in the more internal portions that emplaced later and at higher pressure. We interpret the occurrence of the two trends in the variation of deformation and porosity as related to two main eruptive pulses of dome growth. 相似文献
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