Frost action and hydration as rock weathering mechanisms on schist: A laboratory study

Recently it has been proposed that stress generated by the adsorption of water to clay surfaces in argillaceous rocks may be an important agent of mechanical weathering in polar and alpine environments, implying that long-held views on the status of frost action in these areas may be in need of revision. This study documents the response, under controlled experimental conditions, of aggregates of fresh and partlyweathered schist and fresh pre-cut schist blocks to 500 accelerated (12 hour) freeze-thaw and hydration-dehydration cycles. Aggregate samples subjected to freezing cycles produced the largest amounts of material in the less than 2 mm size range (an average of 8 per cent and 16 per cent for the fresh and partly-weathered aggregates respectively), whereas humidity cycles above and below freezing yielded lesser amounts (3 per cent and 4 per cent respectively). The fresh schist blocks were found to be highly resistant to both mechanisms; only those experiencing freeze-thaw oscillations produced measurable amounts of detritus. Although hydration effects were not as effective as frost action in causing particle size reduction in aggregates, the two mechanisms may well reinforce one another in periglacial environments, enhancing the ability of these areas to serve as source regions for loess.     

‘frost and salt’ weathering: Further experimental results

A laboratory experiment has been conducted to examine the effects of ‘frost and salt’ weathering (i.e. physical breakdown by the freezing of salt solutions) on a limestone. Results show that the presence of certain salts in solution can inhibit frost damage. These findings are in direct conflict with those presented by Goudie (1974) and, more recently, Williams and Robinson (1981). Comparison of the experimental methods used in each of these three studies suggests that opposing results can be explained in terms of the different experimental procedures which were employed. If salt supply is frequent and plentiful then it seems likely that rock breakdown will be enhanced-this is the case represented by the experiment of Williams and Robinson. Conversely if the salt supply is limited and the amounts of salt remain more or less constant then rock breakdown will be inhibited-the case of the present experimental study. Caution is therefore advocated when attempting to extrapolate laboratory-derived results to infer on the behaviour of rocks under natural conditions. Several environmental situations in which ‘frost and salt’ weathering may be a possibility are dsiscussed, but it is concluded that further field data, especially concerning temperature regimes and salt availability at and below rock surfaces in cold regions, would be necessary before more definite statements could be made about the efficacy of this process.     

The rate of bedrock weathering by frost action: Field measurements and a predictive model

Shattering rate, surface temperature, moisture content, and the physical and strength properties of bedrock were measured in four rockwall sites of the Japanese Alps. Five-year observations revealed that the bedrock shattering rate was usually much higher in the freeze-thaw period from October to next May than in the frost-free period from June to September. This indicates that frost action is the most important shattering process, although unusual heavy rainstorms in summer are also responsible for the shattering. A combination of some empirical relationships derived from recent laboratory experiments leads to a predictive model of the frost shattering rate. This model shows that the annual shattering rate is dependent on the annual freeze-thaw frequency on the rock surface, and the degree of saturation and tensile strength of the rock masses. The coefficients involved in the model were determined using the field data.     

Application of rock creep experiment in calculating the viscoelastic parameters of earth medium

The viscosity of earth medium can explain many geophysical phenomena. The uplifting velocity of Ti- betan Plateau may be caused by extrusion of the low viscosity channel in middle and lower crust[1]. The post-deformation after earthquake also relates to the rheology of earth medium[2]. The aftershock sequence is considered a process of strain release after stress dropped[3]. There are two kinds of models in the study of rheological character of crustal medium, elastoplas- only when the forced…     

Some results of modeling D-D seismogenic pattern by the fracture model experiment of large-scale rock samples (I)

Using the natural limestone samples taken from the field with dimension of 500 mm×500 mm×1 000 mm, the D-D (dilatancy-diffusion) seismogeny pattern was modeled under the condition of water injection, which observes the time-space evolutionary features about the relative physics fields of the loaded samples from deformation, formation of microcracks to the occurrence of main rupture. The results of observed apparent resistivity show: 1 The process of the deformation from microcrack to main rupture on the loaded rock sample could be characterized by the precursory spatial-temporal changes in the observation of apparent resistivity; 2 The precursory temporal changes of observation in apparent resistivity could be divided into several stages, and its spatial distribution shows the difference in different parts of the rock sample; 3 Before the main rupture of the rock sample the obvious “tendency anomaly” and “short-term anomaly” were observed, and some of them could be likely considered as the “impending earthquake” anomaly precursor of apparent resistivity. The changes and distribution features of apparent resistivity show that they are intrinsically related to the dilatancy phenomenon of the loaded rock sample. Finally, this paper discusses the mechanism of resistivity change of loaded rock sample theoretically. This subject is supported by the key project during the 8-th “Five Year Plan” from the State Science and Technology Commission of China (85-04-04).     

Some results of modeling D-D seismogenic pattern by the fracture model experiment of large-scale rock samples(I)

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Experimental frost and salt weathering of chalk—II

Experiments are described in which chalk cubes were soaked in solutions of either sodium chloride, sodium sulphate, or magnesium sulphate at concentrations of 5·5 per cent and 12·5 per cent, or in a mixed solution of sodium chloride and sodium sulphate or in distilled water. After removal of excess liquid, the cubes were subjected to six freeze–thaw cycles with temperatures ranging from either +15 to ?10°C or +15 to ?30°C. The results confirm that frost weathering can be enhanced by the presence of certain salts, but the extent of weathering was much less than that previously reported for samples frozen totally immersed in the same liquids. Evidence is presented which suggests that salt crystallization is the major weathering process operative when non–immersed samples are frozen but a combination of frost and salt weathering operates when fully immersed samples are frozen.     

Measuring ignitability for in situ burning of oil spills weathered under Arctic conditions: from laboratory studies to large-scale field experiments

This paper compares the ignitability of Troll B crude oil weathered under simulated Arctic conditions (0%, 50% and 90% ice cover). The experiments were performed in different scales at SINTEF’s laboratories in Trondheim, field research station on Svalbard and in broken ice (70-90% ice cover) in the Barents Sea. Samples from the weathering experiments were tested for ignitability using the same laboratory burning cell. The measured ignitability from the experiments in these different scales showed a good agreement for samples with similar weathering. The ice conditions clearly affected the weathering process, and 70% ice or more reduces the weathering and allows a longer time window for in situ burning. The results from the Barents Sea revealed that weathering and ignitability can vary within an oil slick. This field use of the burning cell demonstrated that it can be used as an operational tool to monitor the ignitability of oil spills.     

Electrical triggering of earthquakes: results of laboratory experiments at spring-block models

Recently published results of field and laboratory experiments on the seismic/acoustic response to injection of direct current(DC) pulses into the Earth crust or stressed rock samples raised a question on a possibility of electrical earthquake triggering. A physical mechanism of the considered phenomenon is not clear yet in view of the very low current density(10~(-7)–10~(-8) A/m~2) generated by the pulsed power systems at the epicenter depth(5–10 km) of local earthquakes occurred just after the current injection. The paper describes results of laboratory‘‘earthquake' triggering by DC pulses under conditions of a spring-block model simulated the seismogenic fault. It is experimentally shown that the electric triggering of the laboratory ‘‘earthquake'(sharp slip of a movable block of the spring-block system) is possible only within a range of subcritical state of the system, when the shear stress between the movable and fixed blocks obtains 0.98–0.99 of its critical value. The threshold of electric triggering action is about 20 A/m~2 that is 7–8 orders of magnitude higher than estimated electric current density for Bishkek test site(Northern Tien Shan, Kirghizia) where the seismic response to the man-made electric action was observed. In this connection, the electric triggering phenomena may be explained by contraction of electric current in the narrow conductive areas of the faults and the corresponding increase in current density or by involving the secondary triggering mechanisms like electromagnetic stimulation of conductive fluid migration into the fault area resulted in decrease in the fault strength properties.     

Burial and turbulent transport by bioturbation: a 27‐year experiment in southeast Australia

In order to assess the net effect and relative importance of geomorphic processes at two natural woodland sites in southeast Australia, 100 small tiles were placed on the soil surface in 1979 and their movement was monitored over the course of nearly three decades. Rates of tile burial and other tile displacement were considerable but also markedly random, being largely inconsistent with expected patterns of displacement by orthodox creep and rainwash processes. This included substantial upslope displacement and burial depths that ranged from zero to 5 cm. We suggest that such turbulent transport in the topsoil has mostly been caused by the direct and indirect transfer of soil and clasts by animals and plants (i.e. bioturbation). In addition to direct evidence of biota interacting with tiles, the effectiveness of bioturbation at our sites has been well established and the overall tile burial rate of 0·25 to 0·4 mm yr^?1 is comparable to rates of surface mounding. Patterns of tile movement are generally consistent with soils‐geomorphic theory regarding the biomantle and bioturbation‐driven stonelayer formation, and provide further evidence that soil transfer and slope movement, in many situations, are markedly random and complex processes. Copyright © 2010 John Wiley & Sons, Ltd.     

The role of urban surfaces (permeable pavements) in regulating drainage and evaporation: development of a laboratory simulation experiment

Permeable pavements and similar stormwater control devices have not been exploited in the UK, in part because their adoption has been hindered by a lack of detailed knowledge of their hydrological performance. This paper describes a research programme that produced detailed information on the hydrological behaviour of a car park surface. The study involved the construction of full‐scale permeable pavement model car park structures and a rainfall simulator for use in the laboratory. A monitoring procedure was developed in order to measure inputs and changes in drainage, storage and evaporation over short and long time‐scales (2 hours to 3 months). A range of simulated rainfalls, which varied in intensity and duration, was applied to the model car park surfaces. Hydrological processes were monitored over an 18‐month period. Results demonstrated that evaporation, drainage and retention in the structures were strongly influenced by the particle size distribution of the bedding material and by water retention in the surface blocks. In general, an average of 55% of a one‐hour duration, 15 mm h⁻¹ rainfall event could be retained by an initially air‐dry structure. Subsequent simulations demonstrated that 30% of a one‐hour duration, 15 mm h⁻¹ rainfall event could be stored by an initially wet structure (with a minimum time interval between rainfall applications of 72 hours). Copyright © 1999 John Wiley & Sons, Ltd.     

Quantification of permafrost creep provides kinematic evidence for classifying a puzzling periglacial landform

Mechanical processes operating on the slope surface or at depth control the dynamics of alpine landforms and hold critical information of their geomorphological characteristics, yet they often lack systematic quantification and in-depth interpretation. This study aims to address a long-standing issue concerning geomorphological classification from a kinematic perspective. A group of periglacial landforms consisting of several lobes were discovered in the East Kunlun Mountains of China 30 years ago but were ambiguously classified as rock glaciers and later as gelifluction deposits. Here, we use satellite Interferometric Synthetic Aperture Radar to quantitatively characterize the spatial and temporal changes of the surface movement of these landforms. We observe that: (1) its 17 lobes show a pattern of landform-scale and uniform surface movement, especially during May to October; (2) the lobes move at a spatial mean downslope velocity of 10 to 60 cm/yr and a maximum velocity as high as 100 cm/yr in summer; (3) the landforms are nearly inactive from winter to late spring. Based on these observations, we postulate that the movement of the lobes are driven by deep-seated permafrost creep which typically occurs in rock glaciers. The debris of Lobe No.4 is composed of both boulders and pebbles supported by fine-grained matrix generated from the in situ weathering process. It develops a talus-like oversteepened front around 40° and a convex transverse profile perpendicular to the creep direction, which are also characteristic features of a rock glacier. Piecing these observations together, we identify Lobe No.4 as a debris-mantled-slope-connected rock glacier, with the gelifluction process occurring on the surface as small-scale and discrete events. © 2020 John Wiley & Sons, Ltd.     

Detecting underground cavities using microtremor data: physical modelling and field experiment

In this paper, we study the possibilities of the use of microtremor records in the detection and delineation of near‐surface underground cavities. Three‐dimensional physical modelling data showed that the averaging amplitude spectra of a large number of microtremor records makes it possible to evaluate the frequencies and amplitudes of compressional standing waves generated by microtremor in the space between the ground surface and underground cavities. We illustrate how these parameters can be used to estimate the shape of the underground cavity horizontal projection. If the compressional wave velocity in the enclosing rock is known, it is possible to evaluate the depth to the cavity top using the frequencies of the standing waves. The results of the field experiment confirmed the possibility of underground cavities detection using microtremor data.     

Laboratory frost sorting by needle ice: a pilot experiment on the effects of stone size and extent of surface stone cover

Sorted patterned ground is ubiquitous where gravelly fine soil experiences freeze–thaw cycles, but experimental studies have rarely been successful in reproducing such patterns. This article reports an attempt to reproduce miniature sorted patterns by repeating needle‐ice formation, which simulates frost sorting in regions dominated by diurnal freeze–thaw cycles. Six full‐scale laboratory models were tested. They consisted of near‐saturated volcanic fine soil topped by small stones of uniform size; the models explored a range of stone size (~6, ~12, ~17 and ~22 mm) and surface abundance (20, 40 and 60% cover). The stones were placed in a grid on the surface. These models were subjected to 20–30 temperature excursions between 10 °C and ?5 °C in 12 hours. The evolution of surface patterns were visually traced by photogrammetry. A data logging system continuously monitored vertical soil displacements, soil temperatures and moistures at different depths. All experimental runs displayed needle‐ice formation (2–3 cm in height) and resulting displacement of stones. The soil domains tended to heave faster and higher than the stones, leading to outward movement of the former and concentration of the stones. In plan view, smaller stones showed relatively fast and long‐lasting movements, while larger stones stabilized after the first five cycles. The 20% stone cover produced stone islands, whereas the 40% cover resulted in sorted labyrinths (a circle‐island complex) that may represent incipient sorted circles. The average diameter or spacing of these forms are 12–13 cm, being comparable to those in the field. The experiments imply that needle‐ice activity promotes rapid formation of sorted patterns, although the formation of well‐defined sorted circles may require hundreds of diurnal frost heave cycles. Copyright © 2014 John Wiley & Sons, Ltd.     

Continental subduction and exhumation of high-pressure rocks: insights from thermo-mechanical laboratory modelling

Thermo-mechanical physical modelling of continental subduction is performed to investigate the exhumation of deeply subducted continental crust. The model consists of two lithospheric plates made of new temperature sensitive analogue materials. The lithosphere is underlain by liquid asthenosphere. The continental lithosphere contains three layers: the weak sedimentary layer, the crust made of a stronger material, and of a still stronger lithospheric mantle. The whole model is subjected to a constant vertical thermal gradient, causing the strength reduction with depth in each lithospheric layer. Subduction is driven by both push force and pull force. During subduction, the subducting lithosphere is heating and the strength of its layers reduces. The weakening continental crust reaches maximal depth of about 120 km and cannot subduct deeper because its frontal part starts to flow up. The subducted crust undergoes complex deformation, including indicated upward ductile flow of the most deeply subducted portions and localised failure of the subducted upper crust at about 50-km depth. This failure results in the formation of the first crustal slice which rises up between the plates under the buoyancy force. This process is accompanied by the delamination of the crustal and mantle layers of the subducting lithosphere. The delamination front propagates upwards into the interplate zone resulting in the formation of two other crustal slices that also rise up between the plates. Average equivalent exhumation rate of the crustal material during delamination is about 1 cm/year. The crust-asthenosphere boundary near the interplate zone is uplifted. The subducted mantle layer then breaks off, removing the pull force and thereby stopping the delamination and increasing horizontal compression of the lithosphere. The latter produces shortening of the formed orogen and the growth of relief. The modelling reveals an interesting burial/exhumation evolution of the sedimentary cover. During initial stages of continental subduction the sediments of the continental margin are dragged to the overriding plate base and are partially accreted at the deep part of the interplate zone (at 60-70 km-depth). These sediments remain there until the beginning of delamination during which the pressure between the subducted crust and the overriding plate increases. This results in squeezing the underplated sediments out. Part of them is extruded upwards along the interplate zone to about 30-km depth at an equivalent rate of 5-10 cm/year.     

Frost sorting on slopes by needle ice: A laboratory simulation on the effect of slope gradient

Following a previous attempt to reproduce miniature sorted patterns on a level surface, we report the results of a full‐scale laboratory simulation on frost sorting produced by needle ice activity on inclined surfaces. Four models, with different slope gradients (5°, 7°, 9°, 11°), were designed. Stones 6 mm in diameter placed in a grid covered 20% of the surface of frost‐susceptible water‐saturated soil. These models were subjected to 20–40 freeze–thaw cycles between 10°C and ?5°C in 12 hours. The evolution of surface patterns was visually traced by photogrammetry. Needle ice growth and collapse induced downslope movement and concentrations of stones. A model produced incipient sorted circles on a 5° slope, whereas it resulted in three distinct sorted stripes on a 7° slope. The average diameter or spacing of these forms is 9.7–19.4 cm, comparable to those in the field dominated by diurnal freeze–thaw cycles. Surface parallel displacements of stone markers were traced with motion analysis software. The observed downslope stone displacements agree with those expected assuming that surface soil and stones move by repeated heaving perpendicular to the surface and vertical settlement due to gravity, although the growth of curved needle adds complexity to the overall displacements. Copyright © 2017 John Wiley & Sons, Ltd.     

Responses of benthic foraminifera to changes of temperature and salinity: Results from a laboratory culture experiment

The effects of temperature and salinity on intertidal foraminiferal community under laboratory conditions are poorly understood. We designed a two-factor crossed experiment in which foraminiferal communities were cultured at different temperatures (6, 12, and 18℃) and salinities (15, 20, 25, and 30 psu) for 10 weeks. In total, 2616 living (stained) specimens were obtained and analyzed. Foraminiferal abundance ranged from 9 to 202 individuals/10 g wet weight of sediment. The highest abundance was obtained at 12℃, 25 psu and the lowest at 6℃, 15 psu. Statistical results demonstrated that temperature affected foraminiferal community more significantly than salinity. Most foraminiferal community parameters (abundance, species richness, Margalef index, and Shannon-Wiener diversity) were significantly positively correlated to temperature, but not to salinity, whereas Pielou's evenness was significantly negatively correlated to both temperature and salinity. The interactive effect of temperature and salinity on foraminiferal abundance was significant. In addition, with increasing temperature, the species composition shifted from hyaline Rotaliida to porcellaneous Miliolida. The abundance of dominant species (e.g., Ammonia aomoriensis, A. beccarii, and Quinqueloculina seminula) showed significant positive correlations to temperature. Our study indicated that the intertidal foraminiferal community responds sensitively and rapidly to the changes of salinity and, especially,temperature by shifting foraminiferal species composition and altering the community parameters.     

Assessment of sacrificial anode impact by aluminum accumulation in mussel Mytilus edulis: a large-scale laboratory test

Since the early 1960s, the application of aluminum alloy sacrificial anodes to mitigate marine corrosion has been well known. The aim of this work was to study aluminum bioconcentration in Mytilus edulis by an in vitro test performed in two tanks: the first containing non-contaminated water (NCW) and the second containing aluminum-contaminated water (CW) (530 μg L⁻¹) released by sacrificial anode. The mussels were collected and examined over a period of 8 weeks. A comparison between the aluminum concentrations in the digestive glands of mussels from the CW and NCW tanks shows that the highest value (1700 mg/kg d.w.) was found in the CW mussels collected after 13 days. In NCW, the mean aluminum concentration in digestive glands during the test was 281 mg/kg d.w. The rapid concentration decrease in digestive glands is probably due to the inhibition of filtering activity due to valve closure at the high concentration as well as the induction of the detoxification response.     

Physical and chemical variability of the Baltic Sea: a joint experiment in the Gotland Basin

An area of 25 × 30 nmi with a subarea of 20 × 20 nmi in the Baltic Sea Gotland Basin was surveyed for about one month by vertical CTD and fluorometric chlorophyll a casts, and by towed profiles with a chemical profiler (nutrients, CTD, O₂, pH) and an undulating CTD. Autonomous current meter data were available for the same period.Five CTD surveys with a 5-mile spacing showed the existence of synoptic eddies and several other perturbations. A first mode eddy (with all the isopycnals lifted within the halocline) had reduced salinities in the upper layer and chlorophyll concentrations were reduced by 2 to 3-fold. A second mode eddy (with the isopycnals lifted in the top of the halocline and lowered in the bottom layers) with a diameter of 20 km was under prolonged observation. Anticyclonic currents at 96-m depth were up to 25 cm s^?1. Along the section across the eddy at 80-m depth, the mean nitrate concentration dropped from about 7 to 8 to 5 μmol dm^?3 while other chemical parameters lacked intense variations. An increased activity of the intrusive fine-structure was detected in the eddy center. The Baltic eddies are essentially non-linear, and transport water in their ‘nuclei’. An internal front, separating waters with different T,S composition, was discovered in the upper layers.The observations are discussed with respect to discovering long-term trends while monitoring the Baltic environment.