Boulder Content Research Articles

Deposit comminution in a weak variably-cemented breccia rock avalanche

Rock avalanches display a distinct and complicated behavior that is not yet completely understood. Analyzing the deposit characteristics is crucial for studying the comminution mechanism during its emplacement. Combining field investigation, image processing, and numerical modeling, we explore the deposit characteristics and comminution process of the Wangjiapo rock avalanche triggered by the Mw6.2 Ludian earthquake. First, we use UAV photogrammetry to obtain a three-dimensional point cloud model and a digital orthophoto, from which we semi-automatically extract the geometry and position of 80,602 blocks by adopting a new block photo-analytical procedure, in addition to a further 4388 coarse blocks that were mapped from manual procedure. We analyze the longitudinal and transversal variation of the block distribution within the deposit. Large boulder content was more abundant in the middle part, while the fine blocks were distributed more evenly. Blocks were prevalently equant-sphere (ES) shaped with no dependence on volume and location, but the roundness increased significantly with runout. Additionally, we find fractal dimensions ranging from 1.42 to 1.83, lower with respect to other rock avalanches, probably due to the high weakness of materials. Furthermore, we propose two comminution models based on the significant differences observed between the eastern deposit II and western deposit III, which were caused by variably-cemented breccias. Finally, numerical modeling indicates that the large amount of fine material damped the grain-grain velocity during runout, leading to a limited spread of the rock avalanche and so explaining the short displacement of the front observed.

Logging Mats and Logging Residue as Ground Protection during Forwarder Traffic along Till Hillslopes

Forest soils in Northern Europe are generally trafficked by forest machinery on several occasions during a forest rotation. This may create ruts (wheel tracks), which could increase sediment transport to nearby surface water, reduce recreational value, and affect tree growth. It is therefore important to reduce soil disturbance during off-road forest transportation. In this study, rut depth was measured following forwarder traffic on study plots located along four harvested till hillslopes in Northern Sweden with drier soil conditions uphill and wet conditions downhill. The treatments included driving 1) using no ground protection, 2) on logging residue (on average, 38–50 kg m–2) and 3) on logging mats measuring 5×1×0.2 m. The hillslopes contain areas with a high content of boulders, stones, and gravel as well as areas with a significant content of silt. Six passes with a laden forwarder with four bogie tracks were performed. On the plots with ground protection, the application of logging residue and the application and removal of logging mats necessitated additional passes. Rut depth was measured using two methods: 1) as the difference in elevation between the interpolated original soil surface and the surface of the rut using GNSS positioning (Global Navigation Satellite Systems), and 2) manually with a folding rule from an aluminium profile, placed across the rut, to the bottom of the rut. The two methods generally gave similar results. Driving without ground protection in the upper part of the hillslopes generated ruts with depths <0.2 m. Here, the rut depth was probably modified by the high content of boulders and stones in the upper soil and drier soil conditions. In the lower part of the hillslopes, the mean rut depth ranged from 0.21 to 0.34 m. With a few exceptions, driving on logging residue or logging mats prevented exposure of mineral soil along the entire hillslope. Soil disturbance can thus be reduced by acknowledging the onsite variability in ground conditions and considering the need for ground protection when planning forest operations.

Літологічна характеристика алювію руслової фації ранньоплейстоценової тераси пра-Стрию в розрізі Болехів

The article highlighted main lithologic characteristics of channel facies alluvium, which is the most ancient within Morshynska hill of pra-Stryi terrace. Upper and central layers of alluvium section are found to have lenticular structure fixing lines of shallow (up to 1.0–1.2 m) palaeochannels 4–5 wide. Granulometric composition of alluvium of channel facies varies little up the incision. Its main component is the pebble and its content except the first one exceeds 50%. The content of other less spread components of the alluvial layer remains almost unchanged. The fact that there are no vivid changes in the granulometric composition of alluvium testifies the stability of conditions of accumulation of sediments in the bed course of palaeoflow. Petrographic composition of coarse fraction appeared to be immensely homogeneous due to the dominance of Carpathian sandstones. In particular, all boulders are composed of light-to-dark, fine-to-medium grained sandstones. Siltstones and silicites appear in the composition of pebble and gravel only, their content is insignificant and ranges from 1 to 6 %. Siltstones are yellowish-white and yellowish-brown, and silicites are dark grey and almost black. Analysis of roundness of coarse fraction alluvium has shown the predominance of fine-to-medium rounded grains in its content that, in its turn, testifies to long-distance transportation of fragmental matter. Besides, better roundness of clast is traced up the section. In particular, the number of poorly rounded clast in the boulders is decreasing and even well-rounded grains are appearing; the content of pebbles shows the decrease of poorly rounded clast and gradual increase of well-rounded pebbles. The samples of disc-like shape prevail in sampling material. Only boulders of sample 3 do not contain them at all. Samples of other shapes are less spread; first of all, it is spheroid and roller fragments. The lower part of the alluvium thickness contains the smallest amount of them. The content of blade fragments is the most consistent. Measurements of the imbrication of fragments testified them to have moved in the lower part of the alluvium thickness from northwest to the southeast that coincides with hypothetic flow of palaeo-Stryi during the formation of the terrace under investigation. The predominant direction of the palaeoflow in the upper part of alluvium accumulations has changed; there dominates the direction from southwest to northeast, which is closer to the direction of palaeo-Sukil flow. Taking into account relatively coarse content of alluvium, particularly, significant content of boulders and big pebbles and predominance of well-rounded fragments practically in all samples, it can be assumed that alluvium deposited in the bed of the pra-Stryi river, that flowed along the Carpathian escarpment to the southeast to the Svicha river during the formation of the terrace. Change in the direction of palaeoflow in the upper part of alluvium stratum may point out a local change in the direction of this river flow. Key words: terrace, pra-Stryi, alluvium, granulometric composition, petrographic composition, roundness, shape of fragments, Carpathian material.

Palaeogeographical conditions of the formation of the channel alluvium of the high (Susidovychi) terrace of the Dnister River in the Kulakivtsi section (Podillia-Dnister region)

The main lithological characteristics of the channel facies of the Susidovychi terrace, which correspond to the high (situated over the canyon) groups of Dnister terraces, were given. The investigations in the gravel pit at Kulakivtsi proved that the alluvium of the terrace has been formed in two stages. During the first stage, the lower 1.5 thick bed of the alluvium was deposited. The upper one, nearly 4 m thick alluvium bed was formed in the next, second one depositional stage. The stages of the alluvium formation were recorded in the changes of the granulometric and petrographical composition of the alluvium, and of the roundness of the coarse-grained clasts. The transition between these two alluvial beds is outlined by the voluminous intercalations of the sand lenses, and also by a change in the colour of the alluvial deposits. Granulometric composition of the alluvium of the channel facies, in general, changes little in the section. Only in the transition zone from the lower to the upper part of the alluvial deposits, there is a sharp, abrupt increase in the content of gravels and a sharp reduction in the content of boulders. Generally, in the composition of the alluvium two dominant and two subordinate components are clearly identified. The pebble grains and the sandy-clay matrix are the dominant components, whereas the gravel grains and the boulders are less common. Petrographic composition of the coarse-grained fraction of the terrace alluvium proved to be the richest of all the so far investigated sections of the high (situated over the canyon) terraces of the Dnister River (at Kunysivtsi, Ivane-Puste, Repuzhyntsi, and Lysychnyky). The pebbles 40–100 mm in diameter show particularly diverse petrographic composition which includes fragments of nine types of rocks: the four of the Carpathian provenance (sandstone, aleurite, cherts, and quartzite), and the five of the Podillian provenance (red-coloured Devonian sandstone, Albian cherts and sandstone, and lithothamnian and cryptocrystalline chemogenic limestone). More precisely, the richest is the lower part of the alluvial deposits where the fragments of all the nine rock types occur. The upper part of the alluvium is markedly poorer because only the five rock types occur there. Diversity of the petrographic composition of the alluvium decreased by reducing the local Podillian types of rocks, which are represented only by the red-coloured Devonian sandstones. The composition of the Carpathian types of rocks remained unchanged. The detected changes in the granulometric and petrographic composition of the alluvium of the investigated terrace permitted to show that the principal providers of the local (Podillian) debris of rocks was played by the Podillian tributaries of the Dnister River. The Dnister alone transported mainly the Carpathian material and only the small volume of Podillian rocks represented by the debris of the red-coloured Devonian sandstones. It was also found that the accumulation of the alluvial deposits of the Susidovychi terrace in the Kulakivtsi section took place in the conditions of restructuring of the Dnister palaeodrainage system. In the initial stages of this terrace formation, the palaeo-Dnister was directed from the village Dobryvliany further north than today, and it entered into the present-day Tupa River valley at environs of the village Bedrykivtsi. In the vicinity of the village Bedrykivtsi, the palaeo-Dnister was turning sharply eastward and proceeded along the present-day river valleys of Tupa and Seret. In the later stages of the Susidovychi terrace formation, the palaeo-Dnister left the portion of its valley stretching between the villages Bedrykivtsi and Schytivtsi, and it shifted several hundred meters to the south and has stopped practically within its current canyon valley. The desolate portion of its palaeo-valley located between the villages Bedrykivtsy and Kasperivtsi has been inherited by the Tupa River and the lower portion of this palaeo-valley located between the villages Kasperivtsi and Schytivtsi – by the Seret River. Key words: palaeo-Dnister, over the canyon terraces, Susidovychi terrace, alluvium, granulometric composition, petrographical composition, roundness, Carpathian material, Podillian material.

Geomorphological and sedimentological indicators of land degradation (Meghalaya Plateau, NE India)

AbstractReplacement of forests by cultivation in hilly regions can dramatically increase overland flow and soil erosion, frequently resulting in land degradation. This study aimed to determine the impact of long‐term human activity and natural geomorphic processes in land degradation of 2 catchments located in the Meghalaya Plateau in northeast India. Both catchments are built by deeply weathered granites with hilly topography but have contrasting land uses. Forested catchment (1.5 ha) is covered by natural deciduous forest, whereas deforested catchment (3.5 ha) is affected by slash and burn cultivation and boulder extraction. Detailed geomorphological mapping and sediment pattern analysis revealed a complex anthropogenic role in land degradation. Human activity contributes directly to the creation of new landforms in the deforested catchment and indirectly by influencing the course and intensity of geomorphological processes, masking the pre‐existing natural relief. Discontinuous agricultural terraces, zero‐order valleys, and furrows created coexisting cascade system and direct connectivity of water and sediment transport within the same slope. Higher content of fine‐grained material and lower content of boulders in the deforested catchment reflect overlapping of 2 traditional occupations of the local population: agriculture and selective boulders extraction, respectively. Human activity combined with accelerated erosion of abundant weathered material led to the transformation of incised valley bottom into flat accumulation plain as well as the extension and aggradation of the alluvial fan. This process increased the proportion of flat landforms favourable for cultivating the deforested catchment under growing population pressure.

Transformation models for effective friction angle and relative density calibrated based on generic database of coarse-grained soils

This study compiles a generic database of seven parameters, including relative density and friction angle, for coarse-grained soils from 176 studies, covering a wide range of reconstituted and in situ coarse-grained soils. This database, labeled as “SAND/7/2794”, is dominated by data from laboratory reconstituted soils such as Erksak, Hokksund, Monterey, Ottawa, Sacramento River, Ticino, and Tonegawa sands. About 15% of the data points in the database are in situ samples obtained from tube sampling, block sampling, or ground freezing techniques. The correlation behavior among some parameters in the database is consistent with existing transformation models in the literature. Mine tailings, volcanic soils, railroad ballast, gravelly soils with significant cobble or boulder content, and soils with high fines contents are removed from the database because they exhibit inconsistent behavior. Soils subjected to very high effective stresses are also removed from the database. The generic database is adopted to calibrate the bias and variability of existing transformation models. Transformation uncertainties are characterized based on their bias, variability, and the range of applicability.

Glacial geomorphology of the tableland east of the Andes between the Coyle and Gallegos river valleys, Patagonia, Argentina

ABSTRACTWe report the results of geomorphological mapping of the high tablelands of Patagonia east of the Andes and between the Coyle and Gallegos river valleys. The map covers a low-relief area of about 3400 km2 at a scale of 1:85,000. It contributes to knowledge of a landscape shaped by lobes of the Patagonian ice sheet and can be used as a tool for further Quaternary studies. The map was built from remote-sensing data, compiled, and analyzed in geographical information system packages and supported by fieldwork. It features glacial landforms including moraine ridges and belts, ground moraine, outwash plains, outwash fans, meltwater channels, traces of glacial lakes, and erratic boulders. Fluvial, aeolian, and volcanic landforms and structural features were also mapped to provide a complete understanding of the landscape. We define three glacial units that record the frontal positions of former piedmont glaciers. The criteria used to define these units are the morphology, maximum relief, boulder content of moraine ridges, and crosscutting relations.

Simulated productivity of one- and two-armed tree planting machines

To increase mechanized planting, planting machine productivity must increase in order to improve cost-efficiency. To determine if excavators with two crane arms could potentially help to increase planting machine productivity under Nordic clearcut conditions, we modelled one-armed and semi-automated two-armed excavators with one- and two-headed planting devices. Using a recently developed tool for discrete-event simulation, these machine models then mounded and planted seedlings on terrain models with moraine soil having various frequencies of obstacles (stumps, roots and stones). Compared to if the two heads were mounted pairwise on only one arm, the results showed that productivity did not increase if two planting heads were attached individually to two separate crane arms. But productivity did increase if the planting machine had four planting heads mounted pairwise on two separate arms. However, despite assuming automated mounding and crane motion between planting spots, the two-armed, four-headed model never achieved high enough productivity levels to make it more cost-efficient than one-armed machines. The simulations illustrate that our terrain models generate realistic root architecture and boulder content distributions in moraine soil, while our machine models functionally describe mechanized planting work. Based on our assumptions, we conclude that further development work on two-armed excavator-based planting machines for Nordic clearcut conditions is not warranted. Our simulations reveal that increasing the number of planting heads per crane arm rather than number of crane arms per base machine offers the greatest potential to raise the productivity of intermittently advancing planting machines.

The stone and boulder content of Swedish forest soils

Abstract Stone and boulder content has a strong influence on many soil processes and is a crucial factor to take into account when estimating element pools. In this paper we present the results of a large scale inventory of the stone and boulder content of forest soils, which employed a surface penetration method (Viro's method) in 1943 plots across Sweden. The volume of stones and boulders was 43.4%, on average, although it was 47.6% for the most common soil type on glacial till parent material. The variation was spatially correlated and there were regional patterns, which were related to bedrock composition and Quaternary development. A stoniness function was developed for the upper 30 cm of the mineral soil and this was used to translate the penetration depths into stone and boulder content. The function was based on a reference data set of 200 soil pits. A relationship was found between stone and boulder content and surface boulder frequency, but the strength of the relationship varied regionally. In some regions surface boulders may provide an indicator of stone and boulder content in the soil.

Electrical resistivity imaging of the architecture of substream sediments

The modeling of fluvial systems is constrained by a lack of spatial information about the continuity and structure of streambed sediments. There are few methods for noninvasive characterization of streambeds. Invasive methods using wells and cores fail to provide detailed spatial information on the prevailing architecture and its continuity. Geophysical techniques play a pivotal role in providing spatial information on subsurface properties and processes across many other environments, and we have applied the use of one of those techniques to streambeds. We demonstrate, through two examples, how electrical resistivity imaging can be utilized for characterization of subchannel architecture. In the first example, electrodes installed in riparian boreholes and on the streambed are used for imaging, under the river bed, the thickness and continuity of a highly permeable alluvial gravel layer overlying chalk. In the second example, electrical resistivity images, determined from data collected using electrodes installed on the river bed, provide a constrained estimate of the sediment volume behind a log jam, vital to modeling biogeochemical exchange, which had eluded measurement using conventional drilling methods owing to the boulder content of the stream. The two examples show that noninvasive electrical resistivity imaging is possible in complex stream environments and provides valuable information about the subsurface architecture beneath the stream channels.

Estimating stone and boulder content in forest soils — evaluating the potential of surface penetration methods

Given the amount and variation of stones and boulders in forest soils, it is remarkable that little attention has been paid to this property in the analysis and modelling of soil processes. This study aims (a) to investigate the stoniness (relative volume of stones and boulders) of representative forest soils in central Sweden, (b) to evaluate the possibilities to predict soil stoniness with non-destructive surface penetration methods, particularly the rod penetration method suggested by Viro in 1952. The content of stones and boulders down to 0.4 m depth in forest till were quantified in 200 systematically distributed pits. The mean content of stones and boulders was 0.50 with a range of 0.14-0.78. Penetration depths were useful as predictors only for cases of stoniness below 0.50 where 75% of the variation could be explained. The general evaluation of surface penetration methods revealed that large errors in very stony soils cannot be avoided. The major source of error is inherent in the method and not caused by sampling. This conclusion may lower expectations that ground-penetrating radar systems will become useful for predicting stoniness.

Characteristics of dams constructed with moraine soils at the hydroelectric developments of the Kovda cascade

The construction of 19 reservoirs with moraine soil under different geological conditions and with soils having different compositions has contributed to knowledge in hydraulic engineering practice, by making possible the development of the following design and construction techniques. 1. Moraine soil low in fine particles (30–35%) was successfully used as underlying material for stone protections. 2. Moraine soil high in content of boulders (40% and higher) was used instead of riprap on the upstream slopes; a boulder shield was formed after the fine particles were washed out by wave action. The thickness of the moraine layer placed was about 1 m. 3. New methods for placement of moraine fill in the pond-forming dikes were developed (dumping over previous deposits); the soil was pushed into the ponds by a bulldozer, and thus exfoliation of the soil was precluded. 4. On the riverbed portions of the dam foundations the boulder mantle was left unremoved, since eventually penetration of moraine soil placed in the water under a head [5], along with clay soil, would occur. 5. During construction of the dams, the possibility of placing moraine soil in the water, under winter conditions, became apparent; the beginning of the winter period was defined as corresponding to temperatures of − 3 to − 5°C.

The Formation and Shape of Drumlins and their Distribution and Orientation in Drumlin Fields

Abstract If glacial till contains more than a certain minimum boulder content, it is dilatant and requires a much larger stress to initiate shear deformation than to sustain it. If the stress level at the glacier–terrain interface drops below a certain critical level, or the till reaches its critical boulder-content density, then the till beneath the glacier packs into stable obstructions. These are shaped into streamlined forms by the glacier and are found distributed at random in drumlin fields. Due to drumlin coalescence there is a normal distribution of drumlin axes about the direction of ice movement.

The Formation and Shape of Drumlins and their Distribution and Orientation in Drumlin Fields

AbstractIf glacial till contains more than a certain minimum boulder content, it is dilatant and requires a much larger stress to initiate shear deformation than to sustain it. If the stress level at the glacier–terrain interface drops below a certain critical level, or the till reaches its critical boulder-content density, then the till beneath the glacier packs into stable obstructions. These are shaped into streamlined forms by the glacier and are found distributed at random in drumlin fields. Due to drumlin coalescence there is a normal distribution of drumlin axes about the direction of ice movement.

Indicator stones from the drift of south Midlothian and Peebles

The following communication describes some work on the glacial drift of the area lying at the south-western end of the Pentland Hills and extending north-east into Midlothian. Previous opinions on the drift of the area are numerous and somewhat contradictory as to its origin. Two main views have been advanced:— 1. That Highland ice advancing southward united with ice moving northward from the Southern Uplands, somewhere to the westward of the Pentlands, and thereafter the two bodies moved eastward as a confluent stream (Peach, 1908; Horne and others, 1910; Wright, 1937). 2. That the area was overwhelmed by ice from the Highlands, and after a partial retreat of that ice, was subjected to a readvance from the same quarter (Charlesworth, 1926). These views of the glaciation of the region obviously embody a considerable divergence of opinion on the question; and thus an investigation of the boulder content of the drift deposits was undertaken, in the hope that an accurate knowledge of the source of the boulders would enable the direction of the ice-movement to be more accurately plotted, and so shed a clearer light on its source or sources. The boulder content at any given place consists mainly of local rocks. Only the accessory constituents which have travelled considerable distances are of much value as indicators. Geological maps of adjoining areas were therefore inspected for rocks, which, by virtue of their extensive crops, their position relative to the area under consideration, and their readily recognisable nature in the drift, might serve as