Rock control on microweathering of bedrock surfaces in a periglacial environment

Microweathering of ice-smoothed bedrock surfaces was investigated in the Røldal area of Hardanger Plateau (60°), southern Norway. Postglacial rates of weathering were determined from surface lowering using quartz veins as reference surfaces. Weathering processes are inferred from assessment of weathering rind formation, surface hardness, and the preservation of small-scale glacial erosional features.Surface lowering rates for a range of metamorphic rocks vary from 0.05 to 2.20 mm ka^− 1 and are broadly comparable with those obtained from crystalline rocks in other periglacial environments. The mean rate of surface lowering at 0.55 mm ka^− 1 is low and demonstrates the relatively small impact of microweathering on postglacial landscape evolution. Variations in bedrock microweathering can be explained by lithological variation. Amphibolite and mica-rich bedrock surfaces experience greater denudation and weakening, least weathering rind formation, and abundant preservation of glacial striae, despite greater surface lowering. Conversely, quartz-rich bedrock surfaces are most resistant to denudation and weakening, but have greater weathering rind formation and fewer preserved striae. Postglacial microweathering is achieved primarily through granular disintegration involving detachment and removal of mineral grains and weakening from increased porosity. Granular decomposition is manifest in the formation of weathering rinds. Analysis of interactions between weathering indices indicates that rind accumulation is limited by microerosion.A conceptual model is proposed that illustrates the temporal interrelationships between in situ and erosional facets of microweathering in two contrasting mineral assemblages. The model proposes that cyclic processes of in situ disintegration, decomposition, and erosion are at work. The relative balance between these processes varies with lithology so that in more resistant quartz-rich rocks the net effect is minimal surface lowering and accumulation of weathering rind. In weaker, amphibolitic and micaceous rocks, the net effect is greater surface lowering and minimal accumulation of weathering rind. The results of the research demonstrate the important influence of rock properties, notably mineral composition, in postglacial microweathering of crystalline bedrock in a periglacial environment.     

Temporal distribution of suspended sediment transport in a humid Mediterranean badland area: The Araguás catchment, Central Pyrenees

This paper analyses the temporal patterns of suspended sediment yield in the Araguás catchment, Central Spanish Pyrenees, a small experimental catchment with extensive badlands. The catchment has been monitored since 2004 to study weathering, erosion, and hydrological and sediment responses to understand the superficial dynamics of a badland area in a relatively humid environment. The development of badlands in the Central Spanish Pyrenees is favoured by the presence of marls and a markedly seasonal climate. The continuous observation of selected physical parameters and environmental variables enables us to establish seasonal patterns of weathering processes and identify those factors that control regolith development. Freeze–thaw cycles in winter and wetting–drying in spring–summer are the main processes involved in regolith weathering, thereby controlling slope development in combination with rainfall-related erosion processes.The 64 floods recorded during the study period (December 2005 to January 2007) were used for a hydrosedimentological analysis. The main observed features indicate that the Araguás catchment reacts to all rainfall events, resulting in steep rising and recession limbs on the hydrograph and a very short time lag. Floods show high suspended sediment concentrations and a heterogeneous temporal distribution related to seasonal variations in surface runoff production. These differences increase the degree of complexity involved in studying sediment response. Suspended sediment concentration and transport mainly depend on rainfall volume, maximum rainfall intensity, peak flow, and runoff occurrence. Finally, the similarities among the obtained hydrographs, sedigraphs, and hyetographs, in combination with the rapid response of most of the floods, suggest a large contribution of overland flow, derived mainly from infiltration excess runoff upon badland areas. Accordingly, the significant correlations obtained between rainfall intensity and sediment concentration (mainly during the dry season), which suggest a single source area for both runoff and sediment, also support the hypothesis of Hortonian hydrological response within badland areas.     

粤北岩溶山地土壤垂直渗漏与粒度变化特征

选择广东粤北连南两个典型岩溶山地剖面,调查了剖面裂隙、漏斗等的垂直分布特征,采样分析了土壤粒度垂向变化。结果表明：碳酸盐岩的构造运动、差异风化和溶蚀等形成的裂隙、漏斗和孔穴在降水入渗、土壤自重力和溶蚀作用下成为土壤地下迁移的通道;漏斗、裂隙及孔穴主要分布在0-10 m的范围,根据横断面调查计算,漏斗土壤占整个断面面积的23.1%-28.1%,裂隙土占整个断面面积的5.3%-8.9%,孔穴土占0.16%,土壤面积占整个剖面面积的28.4%-37.16%。在漏斗和裂隙中土壤颗粒物以粗粉沙和砂粒为主,次为粘粒和细粉沙,随深度增加砂粒含量降低,粘粒含量总体呈增加趋势但其变化与漏斗和裂隙底部形态、角度、宽度等有关;土壤粒度分布特征证明岩溶山地土壤存在水平和垂直两个运移过程以及地表侵蚀、土壤细粒物质下渗和土壤细粒物质堆积三个迁移阶段。     

Geomorphology's role in the study of weathering of cultural stone

Great monumental places—Petra, Giza, Angkor, Stonehenge, Tikal, Macchu Picchu, Rapa Nui, to name a few—are links to our cultural past. They evoke a sense of wonderment for their aesthetic fascination if not for their seeming permanence over both cultural and physical landscapes. However, as with natural landforms, human constructs are subject to weathering and erosion. Indeed, many of our cultural resources suffer from serious deterioration, some natural, some enhanced by human impact. Groups from the United Nations to local civic and tourism assemblies are deeply interested in maintaining and preserving such cultural resources, from simple rock art to great temples. Geomorphologists trained in interacting systems, process and response to thresholds, rates of change over time, and spatial variation of weathering processes and effects are able to offer insight into how deterioration occurs and what can be done to ameliorate the impact.Review of recent literature and case studies presented here demonstrate methodological and theoretical advances that have resulted from the study of cultural stone weathering. Because the stone was carved at a known date to a “baseline” or zero-datum level, some of the simplest methods (e.g., assessing surface weathering features or measuring surface recession in the field) provide useful data on weathering rates and processes. Such data are difficult or impossible to obtain in “natural” settings. Cultural stone weathering studies demonstrate the importance of biotic and saline weathering agents and the significance of weathering factors such as exposure (microclimate) and human impact. More sophisticated methods confirm these observations, but also reveal discrepancies between field and laboratory studies. This brings up two important caveats for conservators and geomorphologists. For the conservator, are laboratory and natural setting studies really analogous and useful for assessing stone damage? For the geomorphologist, does cultural stone data have any real relevance to the natural environment? These are questions for future research and debate. In any event, cultural stone weathering studies have been productive for both geomorphologists and conservators. Continued collaboration and communication between the geomorphic, historic preservation, archaeological, and engineering research communities are encouraged.     

塔克拉玛干沙漠河湖相沉积平原风蚀地貌发育的外营力作用机制

 河湖相沉积是一种非固结沉积物,是风蚀地貌发育的一种重要地质基础。在塔克拉玛干沙漠中发育在这种沉积物上的风蚀地貌分布非常普遍,但相关研究较少,尚缺乏风蚀地貌发育过程方面的研究。基于野外调查信息和理论分析,结合相关文献,分析了塔克拉玛干沙漠河湖相平原风蚀地貌发育的外营力作用机制。研究结果表明：（1）风蚀地貌发育的外营力作用主要有：风化作用、流水作用、风蚀作用以及重力作用;（2）风蚀作用是风蚀地貌发育的主要外营力,但是风化作用、流水作用和重力作用也发挥着重要的作用,它们的关键作用是形成风蚀突破口,而重力作用和风化作用是促进风蚀地貌后期快速发展的重要作用;（3）各种外营力协同作用和互为条件,它们在风蚀地貌发育的各阶段的重要性不同;（4）沉积层特殊沉积构造和外营力作用共同造成了风蚀地貌形态特征。     

阿尔泰山晚新生代以来的古风化壳及其形成时代

阿尔泰山古风化壳研究结果表明，晚新生以来，至少存在两个风化期，形成了不同类型的风化壳，本文阐述这两个风化期的特征及相应形成的风化壳的类型及特点。     

Quaternary bedrock erosion and landscape evolution in the Sør Rondane Mountains, East Antarctica: Reevaluating rates and processes

Rates and processes of rock weathering, soil formation, and mountain erosion during the Quaternary were evaluated in an inland Antarctic cold desert. The fieldwork involved investigations of weathering features and soil profiles for different stages after deglaciation. Laboratory analyses addressed chemistry of rock coatings and soils, as well as ¹⁰Be and ²⁶Al exposure ages of the bedrock. Less resistant gneiss bedrock exposed over 1 Ma shows stone pavements underlain by in situ produced silty soils thinner than 40 cm and rich in sulfates, which reflect the active layer thickness, the absence of cryoturbation, and the predominance of salt weathering. During the same exposure period, more resistant granite bedrock has undergone long-lasting cavernous weathering that produces rootless mushroom-like boulders with a strongly Fe-oxidized coating. The red coating protects the upper surface from weathering while very slow microcracking progresses by the growth of sulfates. Geomorphological evidence and cosmogenic exposure ages combine to provide contrasting average erosion rates. No erosion during the Quaternary is suggested by a striated roche moutonnée exposed more than 2 Ma ago. Differential erosion between granite and gneiss suggests a significant lowering rate of desert pavements in excess of 10 m Ma^− 1. The landscape has been (on the whole) stable, but the erosion rate varies spatially according to microclimate, geology, and surface composition.     

Contrasting soils and landscapes of the Piedmont and Coastal Plain, eastern United States

The Piedmont and Coastal Plain physiographic provinces comprise 80 percent of the Atlantic Coastal states from New Jersey to Georgia. The provinces are climatically similar. The soil moisture regime is udic. The soil temperature regime is typically thermic from Virginia through Georgia, although it is mesic at altitudes above 400 m in Georgia and above 320 m in Virginia. The soil temperature regime is mesic for the Piedmont and Coastal Plain from Maryland through New Jersey. The tightly folded, structurally complex crystalline rocks of the Piedmont and the gently dipping “layer-cake” clastic sedimentary rocks and sediments of the Coastal Plain respond differently to weathering, pedogenesis, and erosion. The different responses result in two physiographically contrasting terrains; each has distinctive near-surface hydrology, regolith, drainage morphology, and morphometry.The Piedmont is predominantly an erosional terrain. Interfluves are as narrow as 0.5 to 2 km, and are convex upward. Valleys are as narrow as 0.1 to 0.5 km and generally V-shaped in cross section. Alluvial terraces are rare and discontinuous. Soils in the Piedmont are typically less than 1 m thick, have less sand and more clay than Coastal Plain soils, and generally have not developed sandy epipedons. Infiltration rates for Piedmont soils are low at 6–15 cm/h. The soil/saprolite, soil/rock, and saprolite/rock boundaries are distinct (can be placed within 10 cm) and are characterized by ponding and/or lateral movement of water. Water movement through soil into saprolite, and from saprolite into rock, is along joints, foliation, bedding planes and faults. Soils and isotopic data indicate residence times consistent with a Pleistocene age for most Piedmont soils.The Coastal Plain is both an erosional and a constructional terrain. Interfluves commonly are broader than 2 km and are flat. Valleys are commonly as wide as 1 km to greater than 10 km, and contain numerous alluvial and estuarine terrace sequences that can be correlated along valleys for tens of kilometers. Coastal Plain soils are typically as thick as 2 to 8 m, have high sand content throughout, and have sandy epipedons. These epipedons consist of both A and E horizons and are 1 to 4 m thick. In Coastal Plain soils, the boundaries are transitional between the solum and the underlying parent material and between weathered and unweathered parent material. Infiltration rates for Coastal Plain soils are typically higher at 13–28 cm/h, than are those for Piedmont soils. Indeed, for unconsolidated quartz sand, rates may exceed 50 cm/h. Water moves directly from the soil into the parent material through intergranularpores with only minor channelization along macropores, joints, and fractures. The comparatively high infiltration capacity results in relatively low surface runoff, and correspondingly less erosion than on the Piedmont uplands.Due to differences in Piedmont and Coastal Plain erosion rates, topographic inversion is common along the Fall Zone; surfaces on Cenozoic sedimentary deposits of the Coastal Plain are higher than erosional surfaces on regolith weathered from late Precambrian to early Paleozoic crystalline rocks of the Piedmont. Isotopic, paleontologic, and soil data indicate that Coastal Plain surficial deposits are post-middle Miocene to Holocene in age, but most are from 5 to 2 Ma. Thus, the relatively uneroded surfaces comprise a Pliocene landscape. In the eastern third of the Coastal Plain, deposits that are less than 3.5 Ma include alluvial terraces, marine terraces and barrier/back-barrier complexes as morphostratigraphic units that cover thousands of square kilometers. Isotopic and soil data indicate that eastern Piedmont soils range from late Pliocene to Pleistocene in age, but are predominantly less than 2 Ma old. Thus, the eroded uplands of the Piedmont “peneplain” comprise a Pleistocene landscape.     

Frost weathering and rockwall erosion in the southeastern Swiss Alps: Long-term (1994–2006) observations

Rates and processes of frost weathering in the Alps were investigated by visual observations of intensively shattered rocks, continuous monitoring of frost wedging and rock temperatures in bedrock and measurements of rockfall activity. Rapid frost weathering of hard-intact rocks occurs along lakes and streams where seasonal freezing promotes ice segregation in the rock. Otherwise, rocks require pre-existing weakness or a long exposure period for intensively shattered. Automated monitoring shows that crack opening occurs at three scales, including small opening accompanying short-term frost cycles, slightly larger movements during seasonal freezing and occasional large opening originating from refreezing of snow-melt water during seasonal thawing. The opening events require at least partial water saturation in the crack. The repetition of crack opening (frost wedging) results in permanent opening and finally debris dislocation. Debris collections below fractured rockwalls show that pebble falls occur at an average rate of about 0.1 mm a^− 1 with significant spatial and inter-annual variations. Occasional large boulder falls significantly raise the rockwall erosion rates, controlled by such factors as the joint distribution in the bedrock, repetition of annual freeze–thaw cycles and extraordinary summer thaw.     

Space–time variability of denudation rates at the catchment and hillslope scales on the Tyrrhenian side of Central Italy

Studies on denudation rates can provide insight into the influence of climate change, tectonics, and human activities on landscape evolution. Research performed in Central Italy has shown considerable spatial variability of denudation rates in the major river basins. These studies have focused mainly on the Tyrrhenian side of the Italian peninsula, where Plio-Pleistocene marine deposits filling NW–SE elongated sedimentary basins have been uplifted during the Quaternary up to several hundreds of meters above present sea level. Small sub-catchments developed on clays are affected by sharp- and/or rounded-edged badlands (i.e. calanchi and biancane), representing denudation “hot spots” in the present-day morphoclimatic framework.In this paper, we analyze the relationships between indirectly estimated denudation rates at the catchment scale and field monitoring data at the hillslope scale. We attempt to better understand and quantify all hillslope processes that contribute to seasonal variability of denudation, to help with predicting the net input from “hot spots” to the overall estimated sediment yield at the basin outlets. At the hillslope scale, we discuss, in particular, the variability of denudation rates at calanchi and biancane badlands as a function of their different morphoevolution.     

福建长乐屏山风化坑与河流壶穴的成因及其证据

风化坑和壶穴是一种常见的岩石坑穴地形,其形成原因和形态完全不同,但容易被误解和混淆.结合对福建长乐三溪河地区这两种坑穴地形的实地考察,本文从地貌学,沉积学,岩石化学和矿物学等各个方面对两者的形成过程、影响因素进行了论证和对比.研究表明：风化坑形成于岩石面积水的风化作用,壶穴则是由河流的旋转水流对河床产生的侵蚀作用形成;山顶风化坑的发育与河流流水作用没有关系,河流壶穴的形成与河谷的发育过程有关,河谷中的风化坑只能在河流深切后,流水不再作用到的河床部位发育;只要条件合适,风化坑或壶穴随时可以生成;风化坑与河流壶穴的形态,坑内沉积物的磨圆度、粒度特征等反映出各自不同的形成过程.风化坑内碎屑与周边岩石的化学蚀变指数CIA 值的差异反映了风化坑的化学风化成因;风化坑内碎屑与周边岩石石英长石比例的差异说明风化坑是矿物差异风化的结果;用CIA 值和英长比均无法区分河流壶穴和风化坑中的碎屑颗粒,但两者化学元素迁移特征的差别反映了风化坑的风化作用和河流壶穴的流水搬运作用的成因差别;风化坑的风化程度达不到当地风化壳的风化程度,但不同气候带风化坑碎屑的CIA 值能反映不同气候带风化作用的强度差异.     

Effectiveness of grade-control structures in reducing erosion along incised river channels: the case of Hotophia Creek, Mississippi

Herein, we undertake a geomorphological analysis in which spatial and temporal trends of bed and bank erosion along an 18-km length of Hotophia Creek, Mississippi, are estimated for the period between 1961 and 2050. The evaluation was undertaken for two scenarios of channel response to channelization during 1961–1963. One scenario represents the ‘actual’ response of the channel and includes the effects of installing a series of grade-control structures (GCS) between 1980 and 1996, while the other represents a hypothetical scenario in which the channel is left to adjust naturally. This allows the effectiveness of GCS in reducing in-channel erosion to be assessed. The analysis relies on the availability of channel survey data to develop empirical bed and bank response models for each adjustment scenario, supplemented by bank stability modelling to predict future rates of bank erosion. Results indicate that channel erosion rates decline nonlinearly with respect to time since 1961, for both adjustment scenarios. However, by the year 2050, the “with” GCS adjustment scenario results in the cumulative removal of some 663,000 (9%) extra tonnes of sediment relative to the “without” GCS scenario. Most (63%) of this excess is derived from enhanced bed erosion during 1976–1985 and 1985–1992, with the remainder derived from increased bank erosion during 1985–1992. Detailed analysis of the patterns of erosion and deposition, and their association with the GCS, provides evidence to support the view that GCS installed along Hotophia Creek have, for the most part, been ineffective in reducing channel erosion rates. This is because the GCS were installed too late to prevent bed degradation, caused by the 1961–1963 channelization, migrating upstream. In addition, some structures have disrupted the downstream transmission of bed material from eroded reaches upstream, exacerbating bed degradation and bank erosion in incised reaches downstream.     

Boulder weathering and erosion associated with a wildfire, Sierra Ancha Mountains, Arizona

An April–May 2000 “Coon Creek Fire” burned 37.5 km² of the Sierra Ancha Mountains, 32.3 km miles north of Globe, AZ—including 25 sandstone and 19 diorite boulders surveyed in 1989 and resurveyed after the burn, after the summer 2000 monsoon season, and after the winter 2001 season. When viewed from the perspective of cumulative eroded area, both sandstone and diorite displayed bimodal patterns with 79% of sandstone boulder area and 93% of diorite boulder area undergoing either no fire-induced erosion or fire-induced erosion >76 mm. When stretched over cumulative boulder areas, erosion due to the fire averaged >26 mm for sandstone and >42 mm for diorite. Post-fire erosion from thunderstorm summer rains averaged <1 mm for 5 diorite and 1 mm for 10 sandstone boulders. While only a single diorite boulder eroded an average of 1.2 mm after the winter, winter erosion removed an average of 5.5 mm from 14 sandstone boulders. Thus, fire appears to increase a rock's susceptibility to post-fire weathering and erosion processes, as predicted by Goudie et al. [Earth Surf. Process. Landf. 17 (1992) 605]. In contrast to experimental research indicating the importance of size in fire weathering, no statistically significant relationship exists between erosion and boulder height or boulder surface area—a result similar to Zimmerman et al. [Quat. Res. 42 (1994) 255]. These data exclude 12 original sites and 85 boulders at sites impacted by the fire that could not be relocated, with a reasonable cause for the lack of relocation being boulder obliteration by the fire. Given evidence from ¹⁰Be and ²⁶Al cosmogenic nuclides [Earth Planet. Sci. Lett. 186 (2001) 269] supporting the importance of boulders in controlling evolution of nonglaciated, bouldered landscapes [Geol. Soc. Amer. Bull. 76 (1965) 1165], fire obliteration of boulders could be an important process driving drainage evolution in nonglaciated mountains.     

The persistence of oil pollution on a rocky shore

Spots of oil thrown up on to a coastal rock platform just above high water mark protect the rock beneath from weathering. Differential weathering subsequently leads to the emergence of oil-capped pedestals. Measurement of the rate of bedrock lowering of the surrounding surface by micro-erosion meter (MEM) provides a method of estimating the age of the pedestals and consequently the duration of oil persistence on the shore. The maximum duration of oil is estimated at 17–18 years.     

Deep-seated failure propagation in a fractured rock slope over 10,000 years: The La Clapière slope, the south-eastern French Alps

The “La Clapière” area (Tinée valley, Alpes Maritimes, France) is a typical large, complex, unstable rock slope affected by Deep Seated Gravitational Slope Deformations (DGSD) with tension cracks, scarps, and a 60 × 10⁶ m³ rock slide at the slope foot that is currently active. The slope surface displacements since 10 ka were estimated from ¹⁰Be ages of slope gravitational features and from morpho-structural analyses. It appears that tensile cracks with a strike perpendicular to the main orientation of the slope were first triggered by the gravitational reactivation of pre-existing tectonic faults in the slope. A progressive shearing of the cracks then occurred until the failure of a large rock mass at the foot of the slope. By comparing apertures, variations and changes in direction between cracks of different ages, three phases of slope surface displacement were identified: 1) an initial slow slope deformation, spreading from the foot to the top, characterized by an average displacement rate of 4 mm yr^− 1, from 10–5.6 ka BP; 2) an increase in the average displacement rate from 13 to 30 mm yr^− 1 from the foot to the middle of the slope, until 3.6 ka BP; and 3) development of a large failure at the foot of the slope with fast displacement rates exceeding 80 mm yr^− 1 for the last 50 years. The main finding of this study is that such a large fractured slope destabilization had a very slow displacement rate for thousands of years but was followed by a recent acceleration. The results obtained agree with several previous studies, indicating that in-situ monitoring of creep of a fractured rock slope may be useful for predicting the time and place of a rapid failure.     

Influence of rock strength on the valley morphometry of Big Creek, central Idaho, USA

Analysis of valley morphometry and bedrock strength along Big Creek, central Idaho, shows that valley floor width is strongly controlled by bedrock. We performed statistical analysis of Schmidt hammer rock strength as a function of lithology and aspect and of valley morphometry as a function of rock strength. Rock strength is significantly greater on the south side of the valley and in Eocene granodiorites. Rock strength is weakest in Eocene volcanic tuffs. Valley floor width depends negatively on weakest valley-side rock strength, and hillslope gradient on the north side of the valley depends positively on rock strength. Stream gradient does not depend on rock strength. Valley floor width appears to be controlled by bedrock strength on the weaker side of the valley, which was generally the north (south-facing) side. We speculate that a higher degree of weathering via freeze–thaw cycles contributes to lower strength on the north side. The positive dependence of hillslope gradient on rock strength on the north side provides evidence that differential weathering across lithologies determines the gradient that can be maintained as lateral migration of the stream erodes valley walls. These results suggest that in situ rock strength exerts strong influences on some measures of valley morphometry by modulating hillslope mass wasting processes and limiting lateral erosion.     

Soil erosion at Albourne, West Sussex, England

Few measurements of the rate of soil erosion from agricultural land in Britain have been published. Loamy soils in England may be particularly vulnerable to erosion. Thus, in a field of strawberries near Albourne at least 181 t ha⁻¹ of fine loamy soil was eroded in a 9-month period; this is almost 100 times greater than a suggested ‘acceptable’ figure. Factors which have induced erosion at Albourne are: the removal of field boundaries; the choice of crop which left the ground bare for a prolonged period ; and the working of the land downslope. Other factors contributing to erosion are the low clay and organic matter content of the soil. The soil slakes and the resultant crust reduces the rate of infiltration of rainfall into the soil and this produces overland flow. Large amounts of rainfall are not necessary to cause erosion. Erosion in the Albourne area is probably a relatively recent phenomenon brought about by changes in land use.     

A frost “buzzsaw” mechanism for erosion of the eastern Southern Alps, New Zealand

In the Southern Alps, New Zealand, large gradients in precipitation (< 1 to 12 m year^− 1) and rock uplift (< 1 to 10 mm year^− 1) produce distinct post-glacial geomorphic domains in which landslide-driven sediment production dominates in the wet, rapid-uplift western region, and rockfall controls erosion in the drier, low-uplift eastern region. Because the western region accounts for < 25% of the active orogen, the dynamics of erosion in the extensive eastern region are of equal importance in estimating the relative balance of uplift and erosion across the Southern Alps. Here, we assess the efficacy of frost cracking as the primary rockfall mechanism in the eastern Southern Alps using air photo and topographic analysis of scree slopes, cosmogenic radionuclide dating of headwalls, paleo-climate data, and a numerical model of headwall temperature. Currently, active scree slopes occur at a relatively uniform mean elevation ( 1450 m) and their distribution is independent of hillslope aspect and rock type, consistent with the notion that frost cracking (which is maximized between − 3 and − 8 °C) may control rockfall erosion. Headwall erosion rates of 0.3 to 0.9 mm year^− 1, measured using in-situ ¹⁰Be and ²⁶Al in the Cragieburn Range, confirm that rockfall erosion is active in the late Holocene at rates that roughly balance rock uplift. Models of the predicted depth of frost activity are consistent with the scale of fractures and scree blocks in our field sites. Also, vegetated, paleo-scree slopes are ubiquitous at elevations lower than active scree slopes, consistent with the notion that lower temperatures during the last glacial advance induced pervasive rockfall erosion due to frost cracking. Our modeling suggests temporally-averaged peak frost cracking intensity occurs at 2300 m a.s.l., the approximate elevation of the highest peaks in the central Southern Alps, suggesting that the height of these peaks may be limited by a “frost buzzsaw.”     

Saprolite Remnants as Indicators of Pre-Glacial Landform Genesis in Southeast Sweden

Twenty‐six sites with remnants of gravelly saprolites (grus) have been located in southeast Sweden. Joint block hills (castle kopjes) and steep rock walls with weathered joints as well as rounded boulders are documented to have an origin in deep weathering and subsequent stripping of saprolites. The saprolite remnants and landforms result from the fragmentation of the re‐exposed sub‐Cambrian peneplain along fracture systems. Only shallow saprolites occur on the elevated intact parts of the sub‐Cambrian peneplain, while saprolites up to 20 m thick are encountered in areas where the sub‐Cambrian peneplain is fractured and dissected. Neogene uplift with reactivation of the weathering system is thought to be the main cause of saprolite formation. Deep weathering is thus judged to have been the major agent of landform formation in the study area, while glacial and glaciofluvial erosion has contributed mainly by stripping saprolites, detaching corestones, and plucking joint blocks along weathered joints.     

滇中红层含盐层水文地质特征

红层沉积环境多样,易溶盐会在一些区段富集形成含盐层。含盐层岩石矿物成分复杂,可溶岩和可溶性矿物含量较高,更易形成溶隙、溶孔,地下水类型以溶蚀裂隙孔隙水为主,水质复杂,水化学成分、含量与易溶矿物成分、含量关系密切。云南红层地下水勘查示范成果表明,滇中红层含盐层浅部全－强风化带含盐层容易淋滤沉着形成自封闭带,富水性较差,地下水位以下的中等－微风化带岩层透水性好,富水性强;含盐层区亦有可饮用淡水分布,补给、排泄条件好的裸露型含盐层中水质较好,循环条件差的埋藏型、覆盖型含盐层中水质较差;浅层地下水水质随深度的变化不明显。