Scottish landform examples 44: the Dirc Mhòr meltwater gorge

The Dirc Mhòr gorge in the central Grampian Highlands is 1.1 km long, ～250 m wide and up to 110 m deep, and is incised in granite bedrock. It is the largest of several bedrock gorges that are incised into spurs, cols or plateau margins in the area, and its present catchment area is negligible. The floor of the gorge is covered by coarse rockfall debris, and the sides of the gorge are mantled by talus accumulations; surface water flow is absent. The gorge is inferred to have evolved over several glacial-interglacial cycles, with subglacial meltwater erosion deepening the gorge under successive ice sheets, and paraglacial rockwall collapse widening the gorge during intervening interglacial periods. Subglacial erosion may also have contributed to gorge enlargement as it widened.     

The Changing Face of PEQ

Abstract

The spectacular relief of the sandstone inselbergs is maintained by an interplay of geological structure and weathering/erosion processes, in that vertical joints and faults provide the foci along which most weathering and erosion take place. There are three major varieties of sandstone breakdown; the first is failure of large rock masses along vertical joints, leading to rockfall. Associated with this process is the mechanical breaking of falling blocks upon impact, in some cases right down to the origjnal sand grains. Rockfall maintains vertical or steep slopes, provided basal talus is removed. The second variety is liberation of small blocks by weathering along closely-spaced joints and bedding planes. Rock prone to this style of erosion tends to be less steep and may have basal slopes buried by rubble. The third variety is grain by grain weathering by solution of cement. This process is the most fundamental, as it not only wears away the surfaces but attacks joints, leading to the processes described above. Grain by grain weathering is slowed or prevented on some surfaces by development of oxide rinds, particularly where run-off is concentrated.

These processes result in deposition of debris at slope bases, but in most cases the debris is quickly reduced to sand and removed by wind and water. Relatively clean slope bases allow slopes to retreat parallel to themselves. Where debris collects faster than it is reduced to sana, slope angles tend to decline until they reach the angle of repose of the debris.

Differences in structural expression of the various lithological units result in differing erosional characteristics. The Saleb Formation is typified by relatively gentle slopes littered with debris, due to thinly spaced joints. The Ishrin Formation, witll widely spaced vertical joints, is typified by rockfall of large masses. It is the major cliff-former. Grain by grain weathering, influenced by variations in varnish development, has produced spectacular tafoni on some Ishrin cliffs. The Disi Formation is extremely friable and although slopes are relatively gentle they are mostly rubble free. The Disi in many places forms rounded domelike shapes which may be due to exfoliation along pressure-relief joints. The Um Sahm Formation is highly fractured and similar in appearance to the Saleb.

Igneous rocks, where exposed below the sandstones, are undergoing chemical weathering, particularly along joints. The results are tors, tafoni, and large amounts of grüss.

The desert floor between inselbergs is in some places a bare bedrock surface with an integrated drainage network, and in other places a sand or playa surface. Running water seems to have been a major agent in shaping the floor, but is less important now than in the past. Transportation of sand by wind is common but there is no evidence for significant eolian aggradation or degradation at the present time.

A minimum rate of surface retreat by grain by grain weathering is 5 cm./1,000 years, based on weathering ofNabataean ruins. Overall slope retreat should be significantly greater, due to added effects of rockfall and removal of blocks by running water.     

Subglacial Meltwater Channels at Cape Jones,Obruchev Hills,Antarctica

Subglacial curved and winding meltwater channels, and Sichelwannen are recorded from Cape Jones in the Obruchev Hills. Such channels, sometimes referred to as P-forms, may have a variety of origins. After briefly considering the origins, it is deduced that those at Cape Jones were formed subglacially while the ice surface of the Denman Glacier became lower and bedrock was exposed The presence of water-laid glacial deposits on the summit of Cape Jones, and lakes on and adjacent to the eastern margin of the Denman Glacier suggests that the sudden release of impounded meltwater was important     

Late quaternary alluviation and soil formation in the southern Argolid: its history,causes and archaeological implications

In the context of an archaeological survey of the southern Argolid, Greece, studies have been carried out to elucidate the evolution of the landscape since its earliest known human occupation about 50,000 years ago. One of these studies was a detailed geological mapping of the late Quaternary alluvium and soils in the area. Dated by means of thorium-uranium disequilibria, archaeological finds, and historical information, seven periods of alluviation were identified, each of short duration relative to long intervening periods of stability and soil formation. The three earliest alluvial phases, falling before and during the last glacial interval, range from about 330,000 to 32,000 years in age. No alluviation accompanied the last glacial maximum around 20,000 years ago. In fact, a stable landscape persisted until about 4500 years ago, when debris flows and widespread aggradation in the valleys resulted from major slope destabilization and soil erosion, probably as a result of extensive land clearance in the Early Bronze Age. A subsequent stable period lasted through the many upheavals of the later Bronze Age, the Dark Ages, and the early historical period. It came to an end with a brief phase of alluviation between about 300 and 50 BC. Stability returned through the late Roman period, notwithstanding considerable expansion of the settled area. Another period of destabilization, this one marked by debris flows and hence major soil erosion, is poorly fixed in time, but probably coincides with expanded maquis clearance accompanying the resettlement of the area around AD 1000. Subsequent events of soil erosion and aggradation vary in nature and timing from one drainage to the next and, in some areas, continue today.Nature and chronology of the soil forming and alluviation events show that simple correlations with climatic events do not suffice to explain them. For the latter ones, past about 2500 BC, human activity seems to be the dominant cause, but once again the relation between cause and effect is not straightforward. Land clearing, or neglect of soil conservation efforts during economic downturns, appear to have a more devastating effect upon the landscape than do intensive land use or total land abandonment.     

Palaeontology of the Cerros Bayos section,Roca Formation (Danian), La Pampa Province,Argentina

Palynofloras from an outlier of Tertiary sediments in the One Tree Hill area north of Adelaide are nonmarine and correlate with similar assemblages from Middle Eocene North Maslin Sands from Maslin Bay and Golden Grove. Although there are similarities with time-equivalent Lower Nothofagidites asperus Zone palynofloras in the Gippsland Basin, a number of species in the South Australian palynofloras do not extend below the Late Eocene in the Gippsland sequences. This indicates earlier appearances for these species in southcentral Australia. The sediments overlie a highly weathered bedrock palaeosurface, indicating that a phase of significant weathering occurred prior to the Middle Eocene. A number of selected taxa are illustrated and their distribution in the palynofloras is discussed. Two new species, Proteacidites mildenhallii and Proteacidites parrawirrensis, are described and one species, Rhoipites byfieldensis, is emended.     

对大型土遗址的植物病害研究——以西安阿房宫遗址为例

在植物对土遗址作用的研究中,鲜有就真实的遗址来展开调查,以及讨论植物给土遗址带来的负作用及其机理。为此,本研究选取西安地区大型土遗址秦阿房宫为研究对象,利用现场调查结合样带法、图像分析法并采集土样,开展对遗址区植物分布、根系产生的裂隙和土壤环境的研究。结果表明:造成土遗址病害现象的主要原因为植物根系作用,加之雨蚀、风化作用及人为破坏的叠加作用,使遗址保存面临严重威胁;其中酸枣、臭椿等萌生树种所产生的根劈裂隙及植物根系对土壤环境的影响十分明显。现存土遗址由植物以及风雨作用而引发的主要病害,其类型包含了边缘夯土的基础掏蚀、洞穴遗存、开裂坍塌、冲沟发育、表面剥蚀,这些是阿房宫遗址面临的主要威胁,也是半干旱地区土遗址存在的特有问题。研究结果既有助于揭示植被对土遗址的作用机理,又能为土遗址保护的植物选择提供理论依据和技术支撑。     

Chemical Weathering of Detrital Sediments in the Taklamakan Desert,Northwestern China

Based on the analysis of major‐element compositions of detrital sediments from the Taklamakan Desert of northwestern China, this paper aims to study chemical weathering in a hyper‐arid desert environment. The major‐element compositions are basically similar to the Upper Continental Crust but show a clear enrichment of CaO and depletion of Na₂O and K₂O, indicating the enrichment of carbonates and the decomposition of sodium and potassium silicates. The indexes of chemical alteration are relatively low and correlate negatively with the content of Na₂O, implying that the degree of chemical weathering is weak and mainly controlled by the weathering of sodium feldspars. An A‐CN‐K model demonstrates that the detrital sediments from the Taklamakan Desert have a high homogeneity in the trend of chemical weathering. They are weathered less than sands and soil in many other Chinese deserts, and also less than similar detrital sediments in many other countries. This evidence suggests a low degree of mineralogical maturity in the Taklamakan Desert. The aeolian sediments of different ages have similar indexes of chemical weathering, suggesting that the degree of chemical weathering was consistent in the Taklamakan Desert throughout the period of aeolian deposition. The low degree of chemical weathering is caused principally by extreme aridity, rapid rejuvenation of detrital sediments associated with strong aeolian processes, and an intensive input of fluvial deposits, as well as a lack of vegetation. Due to the high concentration of erodible minerals, the desert is quite vulnerable to soil erosion and land degradation.     

3D Digital Documentation,Assessment, and Damage Quantifi cation of the Al-Deir Monument in the Ancient City of Petra,Jordan

Abstract

The rock-cut monuments in the ancient city of Petra in Jordan form an outstanding tangible heritage site. Unfortunately, this important part of the world's cultural heritage is gradually being diminished due to weathering and erosion problems. In this research, an approach combining in situ surveying and laboratory analysis is applied in order to provide sufficient and comprehensive data regarding the documentation and evaluation of the status of the Al-Deir monument in Petra. The purpose was not only to quantify the damage, but also to make a first step towards creating a 3D monitoring programme of the deterioration rate. The approach presents a correlation study between the environmental condition and the surface weathering damage, using 2D mapping of the weathering form and accurate 3D realistic modelling from laser scanning and digital photogrammetry. The 2D mapping provides detailed weathering damage information for the entire stone surface of the monument, whereas the 3D modelling provides information on the spatial distribution and texture of the damage. Additionally, the 3D digital model can provide reference data as an exact guide to the restoration needed. In order to support the visual presentation of 3D surface details, a hybrid approach combining data from laser scanning and digital imagery was developed.

Studies of stone texture and spatial distribution of soluble salts were carried out at the monument in order to explain the mechanism of the weathering problem. Relative humidity, temperature, and wind are the main factors in the salt damage process. In order to study the effect of these conditions in the salt crystallization process a series of fieldwork investigations and laboratory work were undertaken. The results show that visible zoning of weathering damage is correlated to different salt concentrations.     

Canadian Landform Examples

The flat topography of the Red River Valley reflects the morphology of underlying bedrock covered with late Quaternary glacial and glaciolacustrine sediments. The meandering Red River occupies a shallow stream‐cut valley that became incised into the Red River Valley plain following the final recession of glacial Lake Agassiz. Extreme flows carried by the river overtop the sides of the stream‐cut valley and spread laterally up to several tens of kilometres across the plain. An array of flood protection infrastructure has been constructed in the landscape to mitigate the flood hazard.     

基于定量分析的克孜尔尕哈烽燧遗址本体病害特征研究

克孜尔尕哈烽燧遗址本体发育主要病害为裂隙、掏蚀、冲沟、坍塌和片状剥蚀。为了确定病害是否危及遗址稳定,为保护工作提供有效数据支持,采用OKIO-Ⅱ光栅式三维扫描系统进行了14个月8期次的高精度病害变化特征监测。通过监测数据发现,遗址本体风化年缩进量比较大,北立面风化缩进量最大、风化最严重,西立面次之,南立面最小。冲沟侵蚀缩进量受水流作用的影响小于风化作用的影响,病害特征为:沿中心线侵蚀量大,冲沟两侧小;顶部侵蚀量大,底部小。掏蚀病害发展速率居首位,掏蚀区纵深缩进量两端变化较大,中间变化较小。裂隙病害扩张幅度较小,但绝大部分横向扩张,少数呈现横向收缩现象,整体趋势是扩张的。目前遗址发育的主要病害不影响遗址的整体稳定性,为遗址保护措施的选择提供了有效的数据支持。     

New Data on the Relief Development of the South Shetland Islands,Antarctica

Abstract

During several expeditions to the Antarctic Peninsula and the neighbouring islands, samples were collected from different sediments which contained datable materials or which were datable with new techniques. Thus it became possible to develop, together with our geomorphic field data, some new ideas on relief development at the rim of the Antarctic continent as well as on the glacial history of the area studied.

Planation surfaces in this area seem to be fairly old. For example, the prominent marine erosion surface on Fildes Peninsula, 35–45 m above mean sea level, is probably older than 85 000 years – older than the last interglacial period and the penultimate glaciation. All Holocene beaches, which are situated between 20 m and the present coastline, were formed during the last 6000 years.

Before 6000 BP the islands were still completely glaciated. The breakdown of the ice cover to nearly the present extent must have been extremely abrupt, taking no more than 1000 years (6000 to 5000 BP). Between 3000 and 1000 BP there were at least two re-advances. These advances were restricted to the prominent outlet glaciers, which followed pre-existing valleys.     

Pedogenetic dating of loess strata

Loess is an aeolian Pleistocene sediment of periglacial or arid origins, deposited without internal stratification in parcels representing geological periods. The contents of total as well as individual carbonates are comparatively uniform within a specific stratum, but the relative carbonate contents differ significantly between the various glacials as represented by loess facies. There is a consistent increase in the content of dolomite with decreasing age of stratigraphic units, which has traditionally been attributed to postdepositional alteration, notably the gradual removal of the calcite fraction by weathering. The explanation of pedogenetic enrichment in the course of aeolian recycling of glacial and glacio-fluvial deposits could convincingly account for the stepped profile of the dolomite's depth functions. The implication is that such recycled sediments can be attributed to specific cryocratic phases simply by their characteristic dolomite fraction, i.e. they can be dated. In order to test this hypothesis against the competing weathering hypothesis, strata of the Gudenus Cave in Lower Austria were subjected to carbonate differentiation analysis. The results are presented, analyzed and discussed. It is shown that the dolomite contents of the unweathered strata provide a clear trend that is even more pronounced than that found at open-air sites.     

Geomorphic reconstruction of formation and recession processes of waterfalls of the Kaminokawa river basin on Osumi Peninsula,southern Kyushu,Japan

To assess the geomorphological importance of waterfall recession in volcanic bedrock, we examined recession rates of six waterfalls in the lower reaches of Kaminokawa river basin on the Osumi Peninsula in southern Kyushu. The examination was performed with an empirical equation that uses a dimensionless parameter obtained by dimensional analysis of relevant measured factors, including erosive force, size of waterfall, and bedrock resistance. Welded Ata ignimbrite, formed at approximately 110 ka, may have played an initiating role to maintain such waterfalls because it resists weathering more than other local rocks. Estimated recession rates for the six waterfalls range from 0.2 to 3.0 cm/y, which compare with estimated rates for waterfalls in another region characterised by welded ignimbrite. Comparison of equation‐derived recession rates of waterfalls with actual recession distances from confluences supports the idea that an original waterfall will subsequently split into two distinct waterfalls when it recesses past an upstream junction of two channels. Our findings revealed that all six waterfalls likely would have been at almost the same point lower in the watershed in the past, marking the general site of the original waterfall. Moreover, the ancestral original waterfall is highly likely to have started from a point between the caldera rim and present river mouth. There, a knickpoint was likely caused by the river dropping into an inner part of the caldera, possibly just after the eruption of the Ata ignimbrite. The waterfall erodes upstream away from the caldera basin, and this happens to be to the east.     

Preliminary geochemical assessment of limestone resources and stone use at Maya sites in the Three Rivers Region,Belize

The carbonate bedrock of northwestern Belize is poorly understood from the standpoint of both geochemistry and the use of stone in prehispanic Maya sites for buildings and monuments. The friable nature of the rock in this topographically rugged area makes it especially difficult to distinguish monuments from bedrock spall, as little carving, if any, survives, and identification rests on location and positioning. The research presented here analyzed 63 limestone samples collected from two sites in the Three Rivers Region of Belize. ICP-MS and ICP-AES were used to characterize the major, minor, and trace element chemistry of the limestone bedrock of the region and determine the amount of geochemical variability. Another important objective was attempting to trace the movement of monument stone and determining whether it was imported from outside of the sites. Bedrock, quarries, and possible monuments were all sampled for these purposes. Bedrock proved to be similar across wide areas. However, at Chawak But'o'ob, along the flank of the Rio Bravo, changes downslope in Mg concentration suggest a leaching of the bedrock by meteoric waters based on differences in porosity. At Maax Na, a hilltop site, in contrast, such leaching is not as apparent. Many monuments at both sites were found to be composed of stone similar in chemistry to the local bedrock, including several of the identifiable stelae. However, our analyses also revealed that a few monuments at Maax Na were made of material with a different chemical composition, apparently from stone imported to the site. These results suggest that the Maya deliberately selected certain types of limestone for certain purposes, and may even have traded in non-local rock. Overall, the methods used in this pilot study indicate there is real potential in more intensive, regional assessments of the materials used at archaeological sites, even in areas where the local stone does not have a distinctive geochemical signature.     

The Sustainable Development of Kuwaiti Sabkhas

“Sabkha” is an Arabic term commonly used in foreign languages to denote a salt flat, a shallow depression. Sabkhas normally occur near sea level or at the underground water level. They usually are encrusted with a salt crust layer, the thickness of which depends on the location of the sabkhas and the evaporation rate. Sabkhas are one of the prominent surface topographical features in the Kuwaiti coastal zone, occupying an area of about 769.4 km², equivalent to 4.3 percent of the nation's total area. Due to their presence in the most important locations near the coastline, they are a most suitable setting for exploitative human activities. Sabkhas have attracted development proponents, particularly after the increased economic growth, and urgent need for homes and housing facilities. The most significant developments in the sabkha lands are urban development, agricultural forestation, and nature reserves. This study has revealed that there are environmental hazards related to the use of sabkha lands, including salt weathering, soil salinization, tree damage and depletion of natural reserves, the deterioration of nebakha (formation and growth around plants in the desert where groundwater is available for vegetation; the usual dune forms that occur in such instances are isolated mounds around individual plants) fields, and semikarstic (an area of irregular limestone in which erosion has produced fissures, sinkholes, underground streams, and caverns) solution holes. Therefore, use of such lands should take into account scientific investigation and selection among the different development fields. Such a fragile environment obliges us to consider nature conservation, a non‐disruption or depletion of sabkhas' limited natural resources, and their environmental components. The concept of the sustainable development should prevail in the use of such sabkhas.     

Soil erosion and flooding on the eastern South Downs, southern England, 1976–2001

The South Downs in southern England have been farmed for 5000 years: the initial loess cover is now a thin, stony remnant as a result of erosion. During the 1980s, field monitoring of erosion events in an area of 36 km² showed that average rates of erosion are low (0.5–5.0 m³ ha⁻¹ yr⁻¹), but that occasional storms result in losses of over 200 m³ ha⁻¹ yr⁻¹ on individual fields. On soils that are only 15 cm thick, such rates pose a threat to future farming. Almost all recent erosion has been on fields of winter cereals, which are bare in the wet autumn period. Of greater significance in the short term are the effects of soil-laden runoff (or muddy floods) on urban areas. Flood damage to property has been a regular event since the conversion of this area to winter cereals in the 1970s. Soil conservation measures have been negligible and flood protection has consisted mainly of engineering works and limited land-use change at sites where property damage has occurred. Conversion to grass under the Set Aside, and an Environmentally Sensitive Area (ESA) scheme, could be an effective soil conservation and flood protection approach. In the longer term, increasing stoniness of soils, the economic incentives for arable farming in marginal areas, and the success of legal proceedings relating to flood damage, will determine the future of erosion on the South Downs. Current farming systems clearly are unsustainable and would become more so under future climates without substantial site-targeted land use change.     

Weathering of Calcarenite Monuments at Roman and Byzantine Archaeological Sites at Sabratha,Northwestern Libya: A Pilot Study

The Roman and Byzantine monuments at Sabratha in northwest Libya represent cultural heritage of remarkable global significance. This report describes the weathering damage of calcarenites, the most dominant stone type used in the construction of monuments in the ancient city of Sabratha. Stone loss, particularly alveolar weathering, notching and breakout of compact stone fragments, dominates deterioration phenomena. Other weathering forms include stone detachment (granular disintegration into sand) and fractures. Most of the studied monuments are also severely affected by biodeterioration, due to microorganism colonization that appears as biofilm. Both the low durability of the calcarenites and the marine environment with characteristic humidity and salt-rich marine spray are the important factors contributing to stone weathering. The results obtained in this pilot study may be used as a guideline for future restoration works.     

Catastrophic Rock-Slope Failures in NW Scotland: Quantitative Analysis and Implications

126 postglacial catastrophic rock-slope failures (PRSFs) and 66 debris-free failure scarps (DFFSs) were identified using Google Earth? imagery on Lewisian Gneiss (LG), Torridon Sandstone (TS), Cambrian Quartzite (CQ) and Moine Schist (MS) terrains in NW Scotland. Normalisation of these data for area and gradient shows that RSF density on slopes ≥25° decreases in the sequence MS?>?LG?≈?CQ?>?TS. Most are apparently discordant with structure, suggesting that failure along slope-(sub)parallel joints was more common than failure along bedding or foliation planes. DFFSs represent failure scars from which runout debris has been removed by later glaciation. Eighteen were recorded outside the limits of the Loch Lomond Readvance, implying that they survived the last ice-sheet glaciation, and support the view that many steep upper rock slopes have been dominated by gravity-driven rock detachment rather than glacial erosion. We argue that many RSFs were probably triggered by Lateglacial earthquakes due to fault (re)activation by crustal rebound, as 74% of recorded PRSFs and DFFSs are located at or near slope crests. 44% of recorded PRSFs and DFFSs occur in cirques, suggesting that cirque enlargement during successive glacial-interglacial cycles involved deepening by glacial erosion, headwall retreat by rock-slope failure and removal of RSF debris during subsequent glaciation.     

Urban geoarchaeology and environmental history at the Lost City of the Pyramids,Giza: synthesis and review

Sediment accretion in ancient urban sites and tells records a combination of cultural and geomorphic processes. Urban geoarchaeology is focused on site accumulation, collapse, weathering and erosion, as constrained by architectural plans and structures. These may document settlement growth and decay, as well as environmental history, posing a multidisciplinary challenge of interactive and fluctuating processes.     

Geological controls on regional transmissivity anisotropy

A variety of data indicate that the Carbonate aquifer in southern Manitoba is a heterogeneous and anisotropic aquifer wherein groundwater flow follows preferred flow path networks. Specific capacity tests show that aquifer transmissivity can vary by up to four orders of magnitude within 1 km. Geostatistical analysis reveals a strong anisotropy in the transmissivity field, with better spatial continuity in NE–SW and NW–SE directions, coincident with the dominant orientations of fractures observed in bedrock exposures. However, discrepancies between the orientation of highest fracture density and best transmissivity continuity suggest that either additional geological factors control the preferred flow network or there is a biased representation of the fracture pattern because all direct fracture observations came from the northern part of the study area. In an effort to investigate whether the geographically biased fracture data set represents the fracture pattern for the whole region, Landsat images and digital elevation maps were processed to extract linear features that may indicate subsurface fracture zones in areas where bedrock is covered by glacial sediments. The results suggest a consistent fracture pattern throughout the study area, indicating that the two observed fracture groups might have gone through different processes in terms of permeability development. Alteration by mineral cementation and dissolution along fracture surfaces may have preferentially improved the fracture permeability in one orientation, while reducing it in the other. The in situ stress field is also believed to play a major role in the preferred regional flow network. This paper discusses the evidence for the preferred flow path network and possible geological factors controlling aquifer anisotropy in this region.