Surface Crust Research Articles

Selection for rapid germination and emergence may improve wheat seedling establishment in the presence of soil surface crusts

Semi-arid cropping regions are commonly affected by surface crusting of sodic soils, resulting in reduced seedling emergence and grain yield. Although seedlings of different genotypes potentially differ in their ability to emerge through soil crusts, the underlying reasons for these differences remain unclear. Seedling emergence of 38 genotypes of wheat (Triticum aestivum) was investigated in a crusting sodic soil in the glasshouse. Crusts of differing strength (0.78–2.69 kg/cm2 or 76–263 kPa) and thickness (0.51–2.16 cm) were created using simulated rainfall applied to a representative surface soil with 10% exchangeable Na. Wheat seedling emergence decreased as crust strength and thickness increased. For a strong crust, average emergence was 33%, compared to 87% for a weak crust. However, the rate of emergence differed significantly between the 38 genotypes, and it was found that seedlings that germinated comparatively earlier in non-constrained conditions tended to have a higher emergence through soil surface crusts. The variability in emergence through soil crusts in seedlings of wheat suggests that genotype selection for improved adaptation may be possible. Rapid seed germination and emergence could potentially be used as a pre-selection criterion for genotypes adapted to soil crust.

Rima Marius, the Moon: Formation of lunar sinuous rilles by constructional and erosional processes

Lunar sinuous rilles are large (kilometers long; tens of meters wide) channels commonly found on the lunar maria. Although there is broad consensus that sinuous rilles were generated during lava-flow emplacement, disagreement remains regarding the relative contributions of erosional and constructional processes during rille formation. Careful mapping of portions of Rima Marius (centered at 16.37°N, 49.54°W) using Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) images with resolutions as high as 0.5 m/pixel reveal morphologic evidence for the origin of sinuous rilles. Specifically, shallow (<10 s of meters), narrow (< 500 m wide) rilles (herein called “rillettes”) are observed to anastamose around, and be cross-cut by, the main rille of Rima Marius. We interpret these rillettes to represent the early phases of emplacement of a sheet-like lava flow with a continuous surface crust (similar to terrestrial compound pahoehoe lava flows), in which flowing lava became concentrated into preferred pathways: the rillettes represent those early, and subsequently abandoned, preferred lava pathways. As the eruption continued, lava flow concentrated into a single lava tube (Rima Marius). Observations of active lava tubes at Kilauea volcano, Hawaii, indicate that basaltic lava flowing through an established lava tube can erode the underlying surface, even while the lava is advancing in a laminar fashion, and we infer similar processes occurred at Rima Marius. Thus, the rillettes represent an early, constructional phase of sinuous rille formation, and Rima Marius formed by subsequent downcutting caused by thermal and mechanical erosion.

Impact of soil surface and subsurface properties on soil saturated hydraulic conductivity in the semi-arid Walnut Gulch Experimental Watershed, Arizona, USA

The estimation of saturated hydraulic conductivity (Ks) is of high relevance to correctly reproduce water fluxes, such as infiltration rates or surface runoff in hydrological simulations. Yet, estimation of Ks is challenging especially in semi-arid regions with particular soil surface characteristics like crusting and sealing. This study presents results of a field campaign in the semi-arid Walnut Gulch Experimental Watershed, Arizona (US), where surface and subsurface Ks measurements were undertaken across the watershed. Data of saturated hydraulic conductivity on crust covered and crust-free surfaces was collected and compared to results of commonly used methods to retrieve spatially distributed Ks data. Results reveal that methods typically used for estimating Ks, such as exponential decay functions or pedo-transfer functions (PTFs), can be inadequate in such regions. The analysis shows that in our study area the presence of surface crust is the dominating factor for determining the spatial distribution of Ks. Furthermore, the results reveal that remote sensing data can provide useful information for estimating surface Ks values as it could be successfully applied for the spatial detection of surface crust characteristics.

Surface mineral crusts: a potential strategy for sampling for evidence of life on Mars

AbstractSurface mineral crusts on Earth are highly diverse and usually, contain microbial life. Crusts constitute an attractive target to search for life: they require water for their formation, they efficiently entrap organic matter and are relatively easy to sample and process. They hold a record of life in the form of microbial remains, biomolecules and carbon isotope composition. A miniaturized Raman spectrometer is included in the ExoMars 2020 payload as it is sensitive to a range of photosynthetic pigments. Samples from the Haughton Impact Structure, Canadian High Arctic and others, shows the preservation of pigments in a range of crust types, especially supra-permafrost carbonate crusts and cryptogamic crusts. The Raman spectral signatures of these crusts are shown along with biomarker analysis to showcase these techniques prior to the ExoMars 2020 mission. Carotenoids and other photoprotective microbial pigments are identified in the Haughton surface crusts using Raman spectroscopy. Gas chromatography-mass spectrometry analyses show a distribution of fatty acids which are most likely from a cyanobacterial source. The successful demonstration of these analyses in the Haughton Impact structure shows the biosignature of surface mineral crusts can be easily extracted and provides an excellent target for sampling evidence of life on Mars.

Using the Cone Penetration Test to Divide the Soil Layer and Judge the Aquifer of Ultra-Soft Soil After Vacuum Preloading

No sand cushion vacuum preloading method is widely used in China's coastal areas, as the detection technology of the surface-layer improvement of the ultra-soft soil is not yet mature. In this paper, using the cone penetration test (CPT) to detect the improved ultra-soft soil based on one case in Zhejiang province in China. The result shows that the cone resistance peaks and sleeve friction peaks are formed due to the effect of the surface crust layer and a thin sand layer, which can provide to determine the boundary of soil layer and the soil thickness in combination with drilling. The permittivity can be used to judge the dry zone, the unsaturated zone and the saturated zone of the ultra-soft soil.

Upper crustal anisotropy from local shear-wave splitting and crust-mantle coupling of Yunnan, SE margin of Tibetan Plateau

The upper crustal anisotropy of Yunnan area, SE margin of Tibetan Plateau, is investigated by measuring the shear wave splitting of local earthquakes. The mean value of the measured delay times is 0.054 s and far less than that from Pms splitting analysis, indicating that the crustal anisotropy is contributed mostly from mid-lower crust. The fast polarization directions are mostly sub-parallel to the maximum horizontal compression directions while the stations near fault zones show fault-parallel fast polarization directions, suggesting both stress and geological structure contribute to the upper crust anisotropy. Comparing fast polarization directions from shear wave splitting of local earthquakes and Pms, large angle differences are shown at most stations, implying different anisotropy properties between upper and mid-lower crust. However, in southwestern Yunnan, the fast polarization directions of Pms and S-wave splitting are nearly parallel, and the stress and surface strain rate directions show strong correlation, which may indicate that the surface and deep crust deformations can be explained by the same mechanism and the surface deformation can represent the deformation of the whole crust. Therefore, the high correlation between surface strain and mantle deformation in this area suggests the mechanical coupling between crust and mantle in southwestern Yunnan. In the rest region of Yunnan, the crust-mantle coupling mechanisms are supported by the lack of significant crustal anisotropy with NS fast polarization directions from Pms splitting. Therefore, we conclude that the crust and upper mantle are coupled in Yunnan, SE margin of Tibetan Plateau.

Ammonia emissions from liquid manure storages are affected by anaerobic digestion and solid-liquid separation

The effects of manure management practices on ammonia (NH3) emissions were evaluated using a micrometeorological technique at four contrasting dairy storage facilities: untreated raw manure slurry (RM), solid-liquid separation with storage of separated liquids (SL), anaerobic digestion of manure and off-farm materials (AD), and anaerobic digestion with solid-liquid separation and storage of the liquid fraction (ADL). Annual average NH3 emissions per surface area were lowest for RM (2.7 g m−2 d−1), followed by SL (4.5 g m−2 d−1), AD (10.0 g m−2 d−1), and ADL (15.5 g m−2 d−1). Lower NH3 emissions from the RM storage were partly due to the 30 cm thick surface crust which formed on the storage surface in summer (wood shavings was used as bedding). Greater surface crusting at the AD storage compared to the ADL storage was also likely the reason for higher emissions at the ADL storage. Relationships between NH3 emissions, temperature, and wind-speed were observed at all sites but were strongest at sites with minimal crusting (SL, ADL) and weak at the RM storage with a crust cover. Total NH3 emissions from each storage facility (kg y−1) did not simply track the differences in fluxes; rather, facilities with greater storage (RM, AD, ADL) had higher emissions than the facility with less storage (SL) due to removal of solids and more frequent field application. Overall, bedding material, manure processing, and storage management all have important effects on NH3 emissions from manure storage.

Edaphic characterization and plant zonation in the Qaidam Basin, Tibetan Plateau

This paper presents a study of edaphic characteristics and their relationship with plant distribution in the Qaidam Basin, Tibetan Plateau, and establishes a distribution model for plants in sandy gravel Gobi to dry salt lake areas. All of the communities in the study area were dominated by plants with strong saline-alkaline tolerance. In this area, salts appeared to migrate to the surface; the surface soil was striped, and the salt distribution varied from sandy gravel Gobi to dry salt lake areas. The salt composition mainly consisted of NaCl in the surface crust. In the subsurface layers, the salt composition was dominated by Ca2+, Cl− and SO42−. The type of vegetation at the study site can be divided into two categories: salt-tolerant vegetation and weakly salt-tolerant vegetation. The salt-tolerant vegetation is influenced by Na+, Cl−, and the salinity. The soil of these vegetation communities had a higher salt and Na+ concentration and a lower Ca2+ and K+ concentration. The weakly salt-tolerant vegetation is mainly affected by the Ca2+/Na+ and K+/Na+ ratios. Based on the above results, a vegetation distribution model for saline lakes on the inland plateau was established.

Surface formation, preservation, and history of low-porosity crusts at the WAIS Divide site, West Antarctica

Abstract. Observations at the West Antarctic Ice Sheet (WAIS) Divide site show that near-surface snow is strongly altered by weather-related processes such as strong winds and temperature fluctuations, producing features that are recognizable in the deep ice core. Prominent glazed surface crusts develop frequently at the site during summer seasons. Surface, snow pit, and ice core observations made in this study during summer field seasons from 2008–2009 to 2012–2013, supplemented by automated weather station (AWS) data with short- and longwave radiation sensors, revealed that such crusts formed during relatively low-wind, low-humidity, clear-sky periods with intense daytime sunshine. After formation, such glazed surfaces typically developed cracks in a polygonal pattern likely from thermal contraction at night. Cracking was commonest when several clear days occurred in succession and was generally followed by surface hoar growth; vapor escaping through the cracks during sunny days may have contributed to the high humidity that favored nighttime formation of surface hoar. Temperature and radiation observations show that daytime solar heating often warmed the near-surface snow above the air temperature, contributing to upward mass transfer, favoring crust formation from below, and then surface hoar formation. A simple surface energy calculation supports this observation. Subsequent examination of the WDC06A deep ice core revealed that crusts are preserved through the bubbly ice, and some occur in snow accumulated during winters, although not as commonly as in summertime deposits. Although no one has been on site to observe crust formation during winter, it may be favored by greater wintertime wind packing from stronger peak winds, high temperatures and steep temperature gradients from rapid midwinter warmings reaching as high as −15 °C, and perhaps longer intervals of surface stability. Time variations in crust occurrence in the core may provide paleoclimatic information, although additional studies are required. Discontinuity and cracking of crusts likely explain why crusts do not produce significant anomalies in other paleoclimatic records.

Microbial Diversity in Actively Forming Iron Oxides from Weathered Banded Iron Formation Systems.

The surface crust that caps highly weathered banded iron formations (BIFs) supports a unique ecosystem that is a post-mining restoration priority in iron ore areas. Geochemical evidence indicates that biological processes drive the dissolution of iron oxide minerals and contribute to the ongoing evolution of this duricrust. However, limited information is available on present-day biogeochemical processes in these systems, particularly those that contribute to the precipitation of iron oxides and, thus, the cementation and stabilization of duricrusts. Freshly formed iron precipitates in water bodies perched on cangas in Karijini National Park, Western Australia, were sampled for microscopic and molecular analyses to understand currently active microbial contributions to iron precipitation in these areas. Microscopy revealed sheaths and stalks associated with iron-oxidizing bacteria. The iron-oxidizing lineages Sphaerotilus, Sideroxydans, and Pedomicrobium were identified in various samples and Leptothrix was common in four out of five samples. The iron-reducing bacteria Anaeromyxobacter dehalogens and Geobacter lovleyi were identified in the same four samples, with various heterotrophs and diverse cyanobacteria. Given this arid, deeply weathered environment, the driver of contemporary iron cycling in Karijini National Park appears to be iron-reducing bacteria, which may exist in anaerobic niches through associations with aerobic heterotrophs. Overall oxidizing conditions and Leptothrix iron-oxidizers contribute to net iron oxide precipitation in our sampes, rather than a closed biogeochemical cycle, which would result in net iron oxide dissolution as has been suggested for canga caves in Brazil. Enhancements in microbial iron oxide dissolution and subsequent reprecipitation have potential as a surface-crust-ecosystem remediation strategy at mine sites.

Heterogeneity of Microbial Communities on Deep-Sea Ferromanganese Crusts in the Takuyo-Daigo Seamount.

Rock outcrops of aged deep-sea seamounts are generally covered with Fe and Mn oxides, known as ferromanganese (Fe–Mn) crusts. Although the presence of microorganisms in Fe–Mn crusts has been reported, limited information is currently available on intra- and inter-variations in crust microbial communities. Therefore, we collected several Fe–Mn crusts in bathyal and abyssal zones (water depths of 1,150–5,520 m) in the Takuyo-Daigo Seamount in the northwestern Pacific, and examined microbial communities on the crusts using culture-independent molecular and microscopic analyses. Quantitative PCR showed that microbial cells were abundant (106–108 cells g−1) on Fe–Mn crust surfaces through the water depths. A comparative 16S rRNA gene analysis revealed community differences among Fe–Mn crusts through the water depths, which may have been caused by changes in dissolved oxygen concentrations. Moreover, community differences were observed among positions within each Fe–Mn crust, and potentially depended on the availability of sinking particulate organic matter. Microscopic and elemental analyses of thin Fe–Mn crust sections revealed the accumulation of microbial cells accompanied by the depletion of Mn in valleys of bumpy crust surfaces. Our results suggest that heterogeneous and abundant microbial communities play a role in the biogeochemical cycling of Mn, in addition to C and N, on crusts and contribute to the extremely slow growth of Fe–Mn crusts.

Control of world Albedo by massive salt leaching using the ancient purpose engineered Qanat-Kariz-Falaj technology to control fractional coverage of crystalline white salt precipitation over vast areas of existing endorheic basins.

Huge desert endorheic basins with very substantial areas of flat evaporation pans were once in operation specifically for the precipitation of white crystalline sodium chloride. Maintaining a thin white crust layer of salt during critical hot seasons of the year over these huge areas would increase the world albedo to enable precise control of the total short/long wave reflection, in addition to the high albedo of the polar regions. The surface crust of an inland Sabkha basin typically is made up of layers of salts that have re-crystallized and settled or precipitated during the evaporation process of controlled Qanat system flood waters. Leached Salts dissolve quickly in a desert endorheic basin, and over a short intensely hot period, the process of re-crystallizing the salts can produce purer and more concentrated, layered playa cakes. The dissolved salts leached out of the underlying layers in the vast desert basin flats, are intermittently precipitated back on to the basin surface, predominantly sodium chloride crystals, one after the other leaving the familiar brilliant white salar playa. The original ancient engineered design of the Qanat and its multiple aligned bore-holes was to control desert endorheic basin flooding without destroying the salt mirror playa or causing erosion of the flat evaporation fields. The Qanat was primarily needed to extract salt, rather than for simple irrigation. Additionally considerable quantities of subsoil brines existing in such basin water tables would ensure brine supplies, as is demonstrated by the new potash plants in the Tarim basin using the ancient Qanat technology. The grain size of white sodium chloride crystals may be controlled in a similar way to the fine Polar snow crystals which also provide an improved albedo index. By adding 2-Naphtol green accelerator to the brine, the accepted procedure in the salt industry, analternative switch could reduce the albedo and thus increase warming instead of cooling.

Conditions for the effective chilling of fish using a nano-sized ice slurry

Parameters for chilling fish using nano-sized ice crystals (NI) made from 3.6% salt water were investigated. Flake ice mixed with salt water (CS) was utilized for comparative purposes. The effect of ice : fish ratio (2:1, 1.5:1, 1:1) on chilling rates and on time, at, or below threshold temperatures (lowest achievable, 0 °C, and 4 °C) were investigated. Meltwater handling techniques were also investigated: initially drained (INIT), continuously drained (CONT), or non-drained (NODR). Ice : fish ratio did not significantly affect fish chilling time (p > .05). Increasing ice : fish ratio doubled time at or below 0 °C (11 → 24 → 41 hr) and increased it 1.5-fold for 4 °C (23 → 34 → 48 hr). Both NI INIT and CONT performed similarly as fish cooled to 0 °C. However, lowest internal fish temperature (–.81 °C) was achieved and fish were chilled for longer times at or below 0 °C and 4 °C with NI INIT. Practical applications Chilling and storage of fish in slurries of ice and seawater are common postharvest handling practices for fishing vessels. Chilling with a slurry ice is advantageous to solid ice because it more effectively interacts with the product surface to absorb heat. Limitations of slurry ice include the tendency of the ice to float to the container surface and form hard ice crusts. The resultant ice crusts have to be physically broken (usually with a shovel) by employees and this action often damages product. The nano-sized ice crystals in the slurry investigated does not create damaging ice crusts. It is also gel-like in texture and therefore less abrasive. Finally, it is created directly from salt water thereby negating the need for fishermen to buy their ice. The smaller ice crystal size, however, may result in more rapid melting and less effective chilling than more traditional slurry ice. The project demonstrated, that despite the small size of the ice crystals, this type of slurry ice is just as effective in chilling fish and keeping fish below temperature thresholds as currently commercially available ice slurries.

Impact of NaCl on drying shrinkage behavior of low-plasticity soil in earthen heritages

Cracking of wall surface crusts on salt-laden earthen remains at the site of Yar City, northwest China, is a serious concern. This widespread pathology is closely related to the drying shrinkage behavior of soil and the fundamental mechanisms should be investigated to better interpret the deterioration of these precious heritages. In this paper, tests were conducted on specimens that were initially slurries with NaCl contents of 0%, 2%, and 5%. The soil shrinkage characteristic curve (SSCC) was measured using the fluid displacement method during a slow air-drying process. The drying branch of the soil-water retention curve was also established by combining three common techniques (pressure plate, vapor equilibrium, and filter paper). The microstructure of specimens with varying water and NaCl contents was characterized through mercury intrusion porosimetry (MIP) testing. Results show that NaCl had negligible impact on the SSCC, which was composed of three shrinkage zones. With increasing NaCl content, matric suction was hardly influenced while the total suction increased significantly due to the pore fluid osmotic suction. The analysis indicated that drying shrinkage was actually a process of consolidation governed predominantly by matric suction. MIP test results were consistent with the macroscale observations for specimens that were initially slurries: that the total volume of pores decreased upon drying. In addition, pore-size distribution was unimodal and no significant difference was observed among specimens with different NaCl contents.

Growth of soil algae and cyanobacteria on gold mine tailings material

&#x0D; &#x0D; &#x0D; The goal of revegetation of gold mine tailings storage facilities is to reduce aeolian pollution, nutrient leaching and erosion caused by exposure to wind and water. The establishment of biological soil crusts may prove to be a more cost-effective way to reach the same goal and the aim of this study was therefore to determine if it is possible to establish algae and cyanobacteria on gold mine tailings. Different treatments of Chlamydomonas, Microcoleus and Nostoc were inoculated on gold mine tailings in controlled conditions and algal growth was measured on all of the treatments after 6 weeks. Nostoc treatments had the highest chlorophyll-a concentrations and produced a surface crust, while Chlamydomonas treatments penetrated the tailings material and provided the strongest crust. The results were promising but more research is necessary to determine the best organism, or combination of organisms, to colonise mine tailings and to eventually produce biological crusts.&#x0D; &#x0D; &#x0D; &#x0D; &#x0D; Significance: &#x0D; &#x0D; &#x0D; &#x0D; Determination of the best organisms to colonise mine tailings and to produce biological crusts for the revegetation of gold mine tailings storage facilities.&#x0D; &#x0D; &#x0D; &#x0D;

Ongoing oversanding induces biological soil crust layering – A new approach for biological soil crust structure elucidation determined from high resolution penetration resistance data

The aim of this study was to determine the in-situ strength and microscopic characteristics of bio-physical micro-horizons in the top 40mm of oversanded sand soils detected by depth dependent penetration resistance (PR). These micro-horizons result from the burial of biological soils crust (BSC) surfaces and contribute to soil stability. They are also important as the biotic source for seeding new surficial crusts. Ex-situ polarised optical micrograph was employed to determine the bio-physical structures associated with the fossil BSC horizons. An automated electronic micro penetrometer (EMP) determining in-situ depth dependent soil PR was used for the quantitative detection of surface and buried micro-horizons. PR data was modelled using a multi-component/soil and micro-horizon multilayer plastic shear stress model. This enabled determination of soil and sediment structure, the contribution of buried ‘fossil’ BSCs to soil strength and structural mapping. We also employed proxy (synthetic) layered soil systems to determine the effect of EMP shaft and probe tip shape upon the PR profile. This methodology represents a significant improvement over penetrometer methods that only use single-value surface breaking point information. We find that buried BSC structures can contribute over 80% of the soil strength even at ca. 20mm depth and that the strength of a buried crust, at least in the medium term, can exceed that of (developing) surficial ones. Typical soil strengths of BSCs in the Negev desert, Israel lie between 1.5 and 3.6MPa. Finally we discuss the effects and potential importance that buried BSC horizons may have upon heat, and the percolation and diffusion of moisture and gas through structured bio-physical, BSC capped sand soil systems.

Visibility-consistent thin surface reconstruction using multi-scale kernels

One of the key properties of many surface reconstruction techniques is that they represent the volume in front of and behind the surface, e.g., using a variant of signed distance functions. This creates significant problems when reconstructing thin areas of an object since the backside interferes with the reconstruction of the front. We present a two-step technique that avoids this interference and thus imposes no constraints on object thickness. Our method first extracts an approximate surface crust and then iteratively refines the crust to yield the final surface mesh. To extract the crust, we use a novel observation-dependent kernel density estimation to robustly estimate the approximate surface location from the samples. Free space is similarly estimated from the samples' visibility information. In the following refinement, we determine the remaining error using a surface-based kernel interpolation that limits the samples' influence to nearby surface regions with similar orientation and iteratively move the surface towards its true location. We demonstrate our results on synthetic as well as real datasets reconstructed using multi-view stereo techniques or consumer depth sensors.

High-temperature annealing of macroporous silicon in an inert-gas flow

Interest in the sintering of macroporous silicon is due to the possibility of purposefully modifying its structure. The annealing of macroporous structures in an atmosphere of Ar, instead of H2, simplifies the requirements to equipment and safety engineering. The sintering of macroporous silicon as result of annealing at T = 1000–1280°C in a horizontal tube purged with high-purity gases: Ar or Ar + 3%H2 is examined. Experiments were conducted with layers having deep cylindrical macropores produced by the electrochemical etching of samples with seed pits on their surface (ordered pores) and without seeds (random pores). The morphology of the porous structure and the changes in this structure upon annealing are studied with electron and optical microscopes. It is shown that, depending on the pore diameter and treatment temperature, the following transformation occurs: the pore surface is smoothed, pores are closed and a surface crust is formed, cylindrical pores are spheroidized and decompose into isolated hollow spheres, and a fine structure and faceting are formed. It is shown that the (111) planes have the minimal surface energy. It is found that the annealing of macroporous silicon in an inert gas leads to strong thermal etching, which is manifested in the fact that the porosity increases or even the porous layer at the sample edge fully disappears. Moreover, an oxide layer appears as a film, beads, or long filaments forming a glass wool upon annealing, especially at low temperatures. These features can be attributed to the presence of trace amounts of an oxidizing agent in the inert gas, which causes the formation of highly volatile SiO and products formed in the reaction involving this compound.

Characteristic properties of macroporous silicon sintering in an argon atmosphere

The temperature and time dependences of the sintering of macroporous silicon in Ar or Ar + 3% H2 are studied. The contribution of various mechanisms governing this process is determined. The specific features of the sintering of macroporous silicon are examined by means of isochronous and isothermal annealing of the samples with ordered and random macropores in the temperature range 1000–1225°C. It is found that the sintering of macroporous silicon under atmospheric pressure in an inert gas flow containing 2 × 10–4% O2 is greatly affected by thermal etching. Thermal etching competes with the substance-transfer processes characteristic of sintering and hinders the formation of a defect-free surface crust. The reason for etching consists in that gaseous silicon monoxide is generated and then carried away by the gas flow. The etching effect is dominant in the low-temperature range and is independent of whether H2 is added. The values obtained for the activation energy of the silicon diffusion coefficient, E a = 2.57 eV, and for the exponent n = 3.31–3.74 in the time dependence of the pore radius, r ~ t 1/n are indicative of a mixed substance-transfer mechanism via the surface and volume diffusion of silicon atoms.

Zones of the origin of seismic centers in the Pamir–Tien Shan sector of High Asia

The zones of the origin of seismic centers within highly seismic areas of the Pamirs and Tien Shan are established. The majority of catastrophic earthquakes coincide with them in this part of High Asia. Their establishment is based on the distribution of the most intensive epicenters and the maximal volumes of the seismic energy together with its calculation and forecasting of the possible manifestations of high seismicity. The investigation of the deep structure of these zones allows us to determine the connection of the seismicity with geophysical field anomalies and some factors of the deep and near surface lithosphere and crust structure, which influence the present-day geodynamics. The results of our research enable us to appreciate the level of the seismic danger in different parts of the region investigated.