Block Streams Research Articles

Morphometric characteristics of block streams: A case study of the Vladayska River basin, Vitosha Mountain (Bulgaria)

Block streams, also known as stone rivers, are common periglacial landforms in the alpine and subalpine zone of the Balkan Peninsula. These features are especially widely spread in the valleys, slopes and summit of Vitosha Mountain. The presented research aims to estimate the total area of block streams and perform morphometric analysis of these landforms within the basin of Vladayska River. Block streams are digitized man-ually from orthophotographs and topographic maps using GIS software. Morphometric parameters such as area, length, width, elongation ratio and mean elevation are calcu-lated or extracted from a digital elevation model for each polygon. A linear regression test was conducted to evaluate the relationship between morphometric properties. Results indicate a significant correlation between the area and perimeter (R2 = 0.93) and between the length and width (R2 = 0.94) of the block streams. Block streams are present in the elevation range between 1177 and 2244 m, covering a total area of 169.7 ha. The largest ones occupy the area of Zlatnite Mostove and Yurushki Most, as well as the vicinity of Cherni Vrah Peak. Their length varies from 5–6 m up to 2.2 km, while their width changes from a few meters up to 0.6–0.7 km. Comparisons between block streams from different sites within the catchment area yield new insights into the diver-sity of these landforms. Their dimensions and spatial distribution are key to understand-ing the processes of their formation and evolution.

풍혈, 얼음골, 암괴류 사면의 라돈 발생에 관한 시론적 연구

Radon gas is one of the natural radioactive substances that appear in nature and known to cause lung cancer. Granite is widely distributed in Korea and a relatively high radon content has been detected through groundwater inspection. Previous studies have found that the radon content in the wind-hole area were higher than the safety level suggested as international safety standards. In this study, radon content of granite in Mt. Geumjeongsan and coastal areas comparatively investigated with the Mt. Jangsan area in Busan, where underground cold springs and rhyolite block streams are distributed. Radon contents in Mt. Jangsan are over 1,000Bq/m3, while those of Mt. Geumjeongsan and Seaside are lower than 200Bq/m3. Sedimentary rocks with high carbonate content showed low radon content. In particular, the radon content measured in two places in Jeongseon-gun, where ice is formed even in mid-summer was very low, confirming that the area with sedimentary rock high in carbonate content exhibited low radioactivity level.

Data parallel processing in block streams for analysis of long-term series of ozone content in ground atmosphere

The article describes a new approach to the processing of long series of ozone monitoring data in the surface atmosphere called the Data Parallel Processing in Block Streams. The proposed method is based on splitting of a sequential series of initial data into blocks filled with surface ozone monitoring data for one day. Further, a chain is formed from such blocks, the length of which is determined by the total length of the monitoring process. Along this chain of blocks, parallel processing of the initial data is carried out, aimed at smoothing out fast fluctuations. The smoothed data is then used to determine the daily production of ozone due to photochemical reactions, its minimum nighttime levels, as well as the magnitude of nighttime maxima. The possibilities of the proposed approach are demonstrated using the analysis of surface ozone monitoring data in Moscow, Russia, in 2020. The prospects for further application of the developed method are discussed.

고성 운봉산 암괴지형 분포와 형태적 특성

Unbongsan Mountain is a volcanic edifice with a unique landscape, which is located alone between granite mountains in Goseong-gun, Gangwon-do. The slopes of the mountain are partially covered with talus and block streams consisting of large basalt bouders. The geological features of this mountain have been investigated in detail. However, their overall distribution patterns and development processes are not well known. This study aims to classify these bouldery landforms through mapping the location of basalt blocks, the analysis of the morphological characteristics of the slope, and field surveys on the large boulders. The exposed boulders are concentrated in the western valleys of the mountains and are rarely found in the eastern slopes. Field data show that all the boulders are composed of basalt rocks with columnar joints, and that there is a long-axis isotropy related to the elevation and gradient of slope. In addition, the result of TPI and slope analysis for DEM indicate that block stream was mainly distributed along the valley, and the talus appeared in the steep ridge and the lower part of the cliffs. The slope classification indicates that flat mountain tops, basalt cliffs, talus, and block streams develop in sequence, as the distance from the center of the mountain increases. The bouldery landforms of Unbongsan Mountain illustrate the process of slope change that appears as a slope retreat in a volcanic edifice.

Block fields and block streams deposits in the Pirin Mountains

The block fields and block streams are widespread in the Pirin Mountains. They are significant in size and are distributed on both relatively flat and sloping surfaces. Their origin is associated with frost weathering, which can subsequently be supplemented by other processes related to the destruction of the material – chemical weathering, fluvial, cryogenic processes, etc. The main aim of the study is to analyze the block field and block stream deposits which will give us a better understanding of their origin and evolution.

Block stream characteristics in Southern Carpathians (Romania)

Block streams, as common features in the Southern Carpathians, are essential for understanding the evolution of alpine environments. Despite their widespread occurrence, they have frequently been omitted from previous inventories of periglacial landforms and from the general understanding of landscape development. This study evaluated the environmental controls on spatial distribution and dimensions of 2056 block streams for a better understanding of their evolution and climatic significance. Different lithology classes and topographic characteristics were assessed using standard least-square linear regression and one-way analysis of variance (ANOVA). The majority of the block streams belong to the linear morphological type, but six other types of morphologies were found (e.g. sinuous, curved, and braided). Bivariate and multivariate statistical analysis revealed a high density of landforms on southern slopes (59%), granite terrains (47%), and above 1750 m. Large features occur mainly on southern slopes and in areas with granites. Landform dimensions and spatial distribution are influenced to a certain degree by lithology, slope aspect, and elevation, making it difficult to identify a dominant factor. Block streams developed extensively at the end of the Pleistocene under permafrost conditions. Today, these features suggest inactivity, but during the cool episodes of the Holocene (e.g. Little Ice Age - LIA), the formation of block streams above 2100 m was re-initiated. Future absolute dating and monitoring of landform dynamics will support these findings.

Influence of mountain geomorphology on alpine ecosystems in the Drakensberg Alpine Centre, Southern Africa

ABSTRACTIn the Drakensberg Range of eastern Lesotho, periglacial sorted circles, stone-banked and turf-banked lobes, blockfields, block streams and wetland thúfur (earth hummocks) are present. These features are of varying ages (likely from Last Glacial Maximum to contemporary) and have been disturbed by soil formation and vegetation growth. This study uses a mixed methodology to investigate relationships between periglacial landforms, slope aspect and their associated ecosystems, and the relative age relationships of these components at Mafadi Peak on the Lesotho–South Africa border. A distinctive alpine flora, belonging to the Drakensberg Alpine Centre of the wider Afromontane phytochorion, is found in association with different periglacial landforms. Vegetation quadrat analysis shows that slope and aspect have no significant effect on vegetation cover, plant species abundance and bare ground cover. The most likely microscale relationships are with surface geomorphic features. The relative surface hardness and thus age of clasts within and outside of the stone/turf-banked lobes show that even within single landforms, variations in weathering exist, likely related to episodic and seasonal alpine cryoturbation. Major soil physical properties (grain size, organic and C/N content) and soil depth were measured. Weathering and soil development, influenced by climate, provide a substrate for a nutrient-deficient, sparse alpine flora and vegetation assemblage. The relationships between periglacial geomorphology and alpine ecosystems are not well understood from southern African high mountain regions, but are important with respect to ecosystem responses to ongoing climate change.

Bouldery slope landforms on Mt. Biseul, Korea, and implications for paleoclimate and slope evolution

AbstractIdentification of bouldery landforms in mountains and correctly understanding their formative processes play an important role in reconstructing the geomorphic history of a region. We propose that blocks were liberated by frost cracking and wedging of cliff walls during the last glacial period. However, we further suggest and test four hypotheses comprising different scenarios for preconditioning by chemical weathering and subsequent block transport using terrain analysis, characterization of boulders, and10Be exposure dating. Frost shattering from the backing cliff produced the boulders since the beginning of the last glacial period (~80 ka), and gelifluction transported them downslope throughout the last glacial period. Their activity then entered a dormant phase at the beginning of the Holocene. Distribution patterns of exposure ages of tors and block streams are similar to those of previous studies, implying that bouldery landscapes in the southern Korean Peninsula were likely to be formed by similar processes under periglacial conditions. The timing of active periods in transport of block streams corresponds well with the cold periods identified in regional and global climate proxy records. Interestingly, the activity of block streams in the study area reached a maximum during Marine Oxygen Isotope Stage 3 to 2 when the growth rate of nearby speleothems was lowest.

Identification, characteristics and classification of cryogenic block streams

Cryogenic block streams consist of a stream of rocks superficially resembling a stream deposit but lacking a matrix, usually occurring on a valley or gully floor or on slopes that are less steep than the maximum angle of repose of coarse sediments. They are usually formed on perennially frozen ground, but can also occur as relict landforms. There are three main active kinds forming today, viz ., Siberian and Tibetan dynamic rock streams and lag block streams. During their formation, the blocks in the active Siberian and Tibetan dynamic block streams move downslope at up to 1 m/a. They are forming today on the Tibetan Plateau and in the more arid parts of south-central Siberia, although the processes involved in the movement are different. In the case of the Tibetan type, individual blocks slide downslope over the substrate in winter on an icy coating in areas of minimal winter precipitation. The Siberian type develops in areas of 15–80 cm of winter snow cover and an MAAT (mean annual air temperature) of ?4 ℃ to ?17 ℃. The movement is due to creep of snow and ice and collapse of the blocks downslope during thawing. Lag block streams are formed by meltwater flowing over the surface of sediment consisting primarily of larger blocks with a limited amount of interstitial sediment. The erosion of the matrix is primarily in the spring in areas of higher winter precipitation on 10°–30° slopes. The blocks remain stationary, but the interstitial sediment is washed out by strong seasonal flows of meltwater or rain to form an alluvial fan. The boulders undergo weathering and become more rounded in the process. Lag block streams can also develop without the presence of permafrost in areas with cold climates or glaciers. Block streams also occur as relict deposits in older deposits under various climatic regimes that are unsuitable for their formation today. An example of relict lag block streams with subangular to subrounded blocks occurs in gullies on the forested mountainsides at Felsen in Germany, and is the original 'felsenmeer'. Similar examples occur near Vitosha Mountain in Bulgaria. The 'stone runs' in the Falkland Islands are examples of the more angular relict lag block streams. In both Tasmania and the Falkland Islands, they mask a more complex history, the underlying soils indicating periods of tropical and temperate soil formation resulting from weathering during and since the Tertiary Period. Block streams have also been reported from beneath cold-based glaciers in Sweden, and below till in Canada, and when exhumed, can continue to develop.

The Rogowiec Landslide Complex (Central Sudetes, SW Poland) – a case of a collapsed mountain

The paper focuses on a large relict landslide complex in the northeastern part of the Kamienne Mts. (Sudetes, SW Poland) developed on Carboniferous and Permian volcanic and clastic sedimentary rocks. Whilst the presence of mass movements around Mt. Rogowiec has long been known, no attempts have yet been made to offer a comprehensive analysis. This study is based on recognition of geomorphic features from LiDAR-derived DTM, geomorphometric analysis, field geomorphological mapping, joint measurements at representative exposures, and electrical resistivity tomography. The total area affected by gravitational slope deformation exceeds 40 ha and consists of a few smaller units that show distinctive patterns of displacement. The eastern slopes of the Mt. Rogowiec ridge have been reshaped by large slides involving rigid blocks of trachyandesite in the upper part and deformed sedimentary successions in the middle and lower part. The central part of the area has experienced lateral spreading which resulted in complete disintegration of the volcanic cap. Fresh-looking ridge-top trenches indicate that this process is ongoing. Subsequent movements included flows into pre-existing valleys and rock wall collapses to produce spectacular block streams. The scale and variety of deformation structures at Mt. Rogowiec make this locality unique in the Sudetes.

Spatial and temporal variability of periglaciation of the Iberian Peninsula

Active periglacial processes are currently marginal in the Iberian Peninsula, spatially limited to the highest mountain ranges. However, a wide variety of periglacial deposits and landforms are distributed in low and mid-altitude environments, which shows evidence of past periods of enhanced periglacial activity. The purpose of this paper is to summarize the present knowledge of past periglacial activity in the Iberian Peninsula. The chronological framework takes four main stages into account: the last glaciation, deglaciation, Holocene and present-day processes. This study focuses on the highest massifs (Pyrenees, Cantabrian Range, NW ranges, Central Range, Iberian Range, Sierra Nevada) as well as other lower elevation environments, namely the central Iberian Meseta. During the last glaciation the periglacial belt extended to much lower altitudes than today, reaching current sea level in the NW corner of the Iberian Peninsula. A wide range of geomorphological landforms and sedimentary records is indicative of very active periglacial processes during that phase, in some cases related to permafrost conditions (i.e., block streams, rock glaciers). Most of the inactive landforms and deposits in low and mid-elevations in Iberia are also related to this phase. The massive deglaciation of the Iberian massifs was caused by a gradual increase in temperatures. The deglaciation phase was only interrupted by a short period with colder conditions (the Younger Dryas) that reactivated periglacial processes in the formerly glaciated cirques of the highest lands, specifically with the widespread development of rock glaciers. During the Holocene, periglacial processes have been only active in the highest ranges, shifting in altitude according to temperature regimes and moisture conditions. The Little Ice Age saw the reactivation of periglacial activity in lower elevations than today. Currently, periglacial processes are only active in elevations exceeding 2500 m in the southern ranges and above 2000–2200 m in the northern massifs, higher in Sierra Nevada, in the south of Iberian Peninsula.

Glaciarismo en la divisoria cantábrica: La evolución del glaciarismo Cuaternario en la Sierra de Cebolleda (León)

The Sierra de Cebolleda (Leon province, Castilla y Leon) is a 10 km length part of tha Cantabrian Divide, located to the South of Picos de Europa, the highest massif in the Cantabrian Mountain. The high lithological diversity and monocline structure have addressed the Quaternay glaciation. The paper studies the glacial evolution by mean of the glacial features and the objective is to know the temporal evolution and extent of Quaternary glaciers and to establish as accurate as possible correlations with the other Cantabrian massifs. A geomorphological map to scale 1/25,000, ELA calculation of each glacier and glacial period, and a morphostrtigraphical analysis, including aspect, front altitudes, glaciers lenght and ELA have been made. Eleven glaciers systems have been reconstructed, defining in the North side tongues longer than 5 km and a medium altitude of fronts of 1120 m a.s.l. The moraine complex point to between one and four glacial stages in each valley. Four glacial stages have been establish: two of alike extent (F1 and F2), a retreated and equilibrium stage (F3) and a marginal glacial stage defined by small cirque glacier (F4) and extreme periglacial processes (rock glaciers, block slopes, block streams and stratified debris). Finally, the glacial stages have been correlated with known absolute dating of other massif of the Cantabrian Mountain.

Freeze–thaw cycles on rock surfaces below the timberline in a montane zone: Field measurements in Kobugahara, Northern Ashio Mountains, Central Japan

Abstract Rock-surface temperatures were measured on a tor and a large block located below the timberline in the Kobugahara Highlands, an upland plateau composed of granodiorite in central Japan (36°N, E139°, 1300 m a.s.l.). Many blocks in the region originate from core stones distributed on the plateau, and there are several block streams in the valley bottoms. The tor is situated at the upper end of one of these block streams. The large block appears to have detached from another tor. The mean air temperature of the coldest month is − 4 °C. Rock-surface temperatures were recorded continually every 30 min from December 1, 2002 through December 13, 2004 by thermistor probes connected to miniature data loggers. The diurnal and the annual freeze–thaw cycles and effective freeze–thaw cycles were recorded at each site. The freezing index of rock-surface temperature showed a marked variability from year to year. In addition, differences in local conditions at observation sites within a given area greatly affected the rock-surface temperature. These are important considerations in relation to local weathering below the timberline.

Stone run (block stream) formation in the Falkland Islands over several cold stages, deduced from cosmogenic isotope (10Be and 26Al) surface exposure dating

AbstractCosmogenic isotope (10Be and 26Al) surface exposure dating has been applied to valley‐axis and hillslope stone runs (relict periglacial block streams) and their source outcrops in the Falkland Islands, South Atlantic. The data indicate that stone runs are considerably older landforms than previously envisaged and afford no evidence that they are a product of the Last Glacial Maximum; the samples range in apparent 10Be age from 42k to 731k yr BP, but some of these are minima. The results indicate that valley‐axis stone runs may be up to 700–800k yr old, have simple exposure histories and are composite landforms that developed over several cold stages. Analyses of some hillslope and outcrop samples also demonstrate simple exposure histories with 10Be ages from 42k to 658k yr BP. In contrast, isotopic ratios from other hillslope and outcrop samples reveal they have had a complex exposure history involving periods of burial or shielding; the samples range in 10Be age from 59k to 569k yr BP and these are regarded as minimum age estimates. Larger stone runs may be older than smaller runs and there is a possibility that stone runs older than 800k yr exist in other parts of the Falklands. The assertion that glaciation in the Falklands was restricted to the highest uplands is supported by the data, and the potential for age determination of other boulder‐strewn and bedrock landforms, using cosmogenic isotope analysis, in order to extend the geochronology of Quaternary events and processes is noted. Copyright © 2008 John Wiley & Sons, Ltd.

Relict blockfields in the Ligurian Alps (Mount Beigua, Italy)

AbstractThe area around Monte Beigua is characterized by accumulations of large blocks. Survey indicates the occurrence of flow structures on the surfaces of the blockfields, and a pattern of long axis orientation aligned in the same direction as the local gradient. Blocks are often imbricated upslope at the front. The formation of block streams is tentatively attributed to cold‐climate conditions during the Pleistocene. Copyright © 2006 John Wiley & Sons, Ltd.

Upper slope landforms and age of bedrock exposures in the St. Francois Mountains, Missouri: A comparison to relict periglacial features in the Appalachian Plateau of West Virginia

We observed upper slope landforms in the St. Francois Mountains of Missouri and compared them to relict periglacial landforms in the Appalachian Plateau of West Virginia in order to determine if periglacial conditions existed in southeastern Missouri. The St. Francois Mountains are the exposed igneous core of the Ozark Plateaus and are about 50 km from the Illinoian glacial boundary in southern Illinois and 75 km from the pre-Illinoian glacial boundary in east central Missouri. Summits of rhyolitic knobs have the appearance of cryoplanation summits but are structurally controlled, stratified pyroclastics with no evidence of periglacial features. Most rhyolite summits have a discontinuous mantle of 30–70 cm of loess. No patterned ground was observed in the St. Francois Mountains, but was observed at a summit in West Virginia. Block fields and block streams in Missouri are forested matrix-supported diamictons of large blocks partially buried in loess fines. Appalachian block fields and block streams largely consist of contiguous blocks with little or no fines and no vegetation. We measured length, width, aspect, slope, and size of the largest blocks along the axis of the Missouri block streams and block fields and on two typical West Virginia block streams (one 36Cl dated 143 ka, late Illinoian). The Missouri block accumulations show no size distribution patterns, are generally steeper and closer to the block source outcrop than the West Virginia block streams, and do not have the morphology of Appalachian relict periglacial landforms. Bedrock exposures in the St. Francois Mountains are old enough to have been exposed to any periglacial environments during the Pleistocene. One rhyolite summit has a 36Cl age of 536 ka (pre-Illinoian) at zero erosion. A granite summit has a 36Cl age of 333 ka (pre-Illinoian) at zero erosion.

Effects of late Pleistocene permafrost on the landscape of Wisconsin, USA

Pleistocene permafrost had a major but generally unappreciated effect on the landscape of Wisconsin, second only to glaciation. Evidence for continuous permafrost during the last part of the Wisconsin Glaciation includes ice‐wedge casts seen both in outcrop (generally in gravel pits) and as polygonal networks (on aerial photographs). Other important evidence includes fossil tundra organisms. Other features that are probably the result of permafrost in Wisconsin include talus cones, block streams, solifluction rubble at the base of most hillslopes, fluvial cobble gravel, gullies that are today inactive, lake‐ice collapse trenches, and ice‐walled‐lake plains. Permafrost caused accelerated regional erosion of the landscape; most topographic features formed before the last permafrost melted have been highly modified or even destroyed, whereas those formed after are much better preserved. In addition, the presence of permafrost influenced many glacial processes and land‐forms. Permafrost was present until about 14000 yr BP in the southern part of the state to about 10000 yr BP in the northern part.

Nature and dynamics of an active block stream, kunlun pass, qinghai province, people's republic of china

Active block streams are common on the slopes of mountains on the northern, drier portion of the Qinghai‐Xizang (Tibetan) Plateau. Between 1990 and 1995, the authors studied a block stream northeast of the crest of the Kunlun Pass at latitude 35°50’N, longitude 94°05’ E. It occurs on a 31° slope facing southwest at 4800 m altitude and consists of a 15 cm layer of blocks moving downslope over a sandy loam of lacustrine origin. The blocks are derived from both frost shattering of exposed bedrock and by ejection of blocks from the till capping the hill. No water flows in the block stream and its surface is level with the surrounding slope. Mean annual air temperature is –6°C and mean annual precipitation is about 320 mm. The few plants growing between the blocks exhibit elongated stems and/or roots, indicating movement of the upper layers of blocks relative to the underlying materials. Average mean annual downslope movement of the surface blocks ranges up to 95 cm but varies both across the block stream and also along its long axis. The blocks are gradually extending further downslope. Comparison of movement of lines painted on stones in summer and winter shows that most of the movement occurs in winter. The stones usually rotate randomly as they move, probably by sliding on ice. There is no obvious sorting or rounding of the blocks during movement downslope. The deposits produced differ from talus/scree sediments as they have a dip of less than the maximum angle of rest of dry sediment (c. 33°) and also show no sorting downslope. The movement of material takes place predominantly in winter, rather than in summer and the deposits occur in areas of negligible snow cover. Ground temperatures suggest exceptionally rapid temperature changes under the blocks, indicating air exchange in the voids. Mean ground temperatures in the loams beneath the blocks are about 7°C colder than in the adjacent soils. Winter snow covers are noticeably absent, and summer precipitation is often in the form of snow, which soon melts. Permafrost is present beneath the block stream but is absent in the sandy loam soils. The ground is also moister beneath the blocks. It appears that the surface blocks tend to slide downslope on the icy surface of the underlying blocks, perhaps aided by water from melting snow. This and the lack of sorting by clast size clearly differentiates them from talus slopes or avalanche deposits.

Climatic Zonality of Periglacial Landforms in Mountain Areas

The alpine periglacial areas of the world can be divided into three distinctive landscape types dominated by one of the following: active rock glaciers, active block streams, or gelifluction landforms. These also correspond to distinct climates, the active rock glaciers occurring under cold, humid conditions; the active block streams in cold, dry climates; and gelifluction-dominated landforms occurring in warmer areas. These have distinct ranges of mean annual temperature and precipitation, which can be used in interpreting climatic changes based on distribution of fossil landforms. Key words: alpine permafrost, block streams, rock glaciers, gelifluction

Block streams in the Southern part of the Kanto Mountains, Yamanashi Perfecture, Central Japan

Block streams in the Southern part of the Kanto Mountains, Yamanashi Perfecture, Central Japan