Thermal Regime of Rock and its Relation to Snow Cover in Steep Alpine Rock Walls: Gemsstock,Central Swiss Alps

Snow cover influences the thermal regime and stability of frozen rock walls. In this study, we investigate and model the impact of the spatially variable snow cover on the thermal regime of steep permafrost rock walls. This is necessary for a more detailed understanding of the thermal and mechanical processes causing changes in rock temperature and in the ice and water contents of frozen rock, which possibly lead to rock wall instability. To assess the temporal and spatial evolution and influence of the snow, detailed measurements have been carried out at two selected points in steep north‐ and south‐facing rock walls since 2012. In parallel, the one‐dimensional energy balance model SNOWPACK is used to simulate the effects of snow cover on the thermal regime of the rock walls. For this, a multi‐method approach with high temporal resolution is applied, combining meteorological, borehole rock temperature and terrain parameter measurements. To validate the results obtained for the ground thermal regime and the seasonally varying snowpack, the model output is compared with near‐surface rock temperature measurements and remote snow cover observations. No decrease of snow depth at slope angles up to 70° was observed in rough terrain due to micro‐topographic structures. Strong contrasts in rock temperatures between north‐ and south‐facing slopes are due to differences in solar radiation, slope angle and the timing and depth of the snow cover. SNOWPACK proved to be useful for modelling snow cover–rock interactions in smooth, homogenous rock slopes.     

FINE SCALE VARIABILITY IN SOIL FROST DYNAMICS SURROUNDING CUSHIONS OF THE DOMINANT VASCULAR PLANT SPECIES (AZORELLA SELAGO) ON SUB‐ANTARCTIC MARION ISLAND

Through changing soil thermal regimes, soil moisture and affecting weathering and erosion processes plants can have an important effect on the physical properties and structure of soils. Such physical soil changes can in turn lead to biological facilitation, such as vegetation‐banked terrace formation or differential seedling establishment. We studied the fine scale variability in soil temperature and moisture parameters, specifically focusing on frost cycle characteristics around cushions of the dominant, vascular plant species, Azorella selago, on sub‐Antarctic Marion Island. The frost season was characterised by numerous low intensity and very shallow frost cycles. Soils on eastern cushion sides were found to have lower mean and maximum temperatures in winterthan soils on western cushion sides. In addition, lower variability in temperature was found on eastern cushion sides in winterthan on western cushion sides, probably as a result of higher wind speeds on western cushion sides and/or eastern, lee‐side snow accumulation. Despite the mild frost climate, extensive frost heave occurred in the study area, indicating that needle ice forms at temperatures above ?2°C. Our results demonstrate the effectiveness of frost pull as a heave mechanism under shallow frost conditions. The results highlight the importance of Azorella cushions in modifying site microclimates and of understanding the consequences of these modifications, such as potentially providing microhabitats. Such potential microhabitats are particularly important in light of current climate change trends on the island, as continued warming and drying will undoubtedly increase the need for thermal and moisture refugia.     

RAINFALL AND TEMPERATURE ATTRIBUTES ON THE LESOTHO–DRAKENSBERG ESCARPMENT EDGE, SOUTHERN AFRICA

Located near the southeastern limit of Africa, the Lesotho‐Drakensberg and associated escarpment is the highest range of African mountains south of the massifs in Tanzania. At the escarpment summit and on the adjacent high peaks, the climate is generally interpreted as marginal periglacial yet few data, specifically rainfall and temperature, exist on record at these altitudes. Climatic data from two temporary field stations on the escarpment edge, one of which is the highest rainfall station yet on record in southern Africa, provide contemporary surface‐climate conditions. Mean annual rainfall recorded between 2001 and 2005 averages 767.8 mm at Sani Pass summit (three complete years), and 753.2 mm on Sentinel Peak (two complete years); these values are less than those recorded for the same period in the mountain foothills. Even though rainfall is slightly below long‐term rainfall averages for the area due to a marginally dry spell, the data show that earlier estimates of between 1000 mm and 2000 mm rainfall per annum on the escarpment are too high. A measured mean air temperature of 5.8°C at Sani Pass, however, falls within the range estimated for the escarpment summit. Frost cycles in air and at the soil surface are frequent in winter, but absent in soil for summer, and no long‐duration surface‐soil freeze was measured. Temperatures thus confirm the marginal periglacial nature as postulated for previously, but precipitation data indicate a dryer environment than anticipated. Palaeoenvironmental scenarios, notably arguments for former glaciation based on extrapolations from somewhat exaggerated contemporary precipitation values, thus require re‐consideration.     

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.     

THE EFFECT OF SYNOPTIC SCALE WEATHER SYSTEMS ON SUB‐SURFACE SOIL TEMPERATURES IN A DIURNAL FROST ENVIRONMENT: PRELIMINARY OBSERVATIONS FROM SUB‐ANTARCTIC MARION ISLAND

Marion Island in the South Indian Ocean has a maritime climate dominated by diurnal frost processes in the landscape. We test the hypothesis that synoptic time‐scale measurements are essential in understanding the drivers of diurnal frost processes. Preliminary results from automated microclimate measurements in a polar desert habitat show that diurnal soil surface temperatures on Marion Island are influenced by a complex interaction of radiation balance, air mass circulation, cloud cover and snow. The passage of synoptic scale weather systems influences soil thermal characteristics through changes in dominance of the radiation budget. Soil frost on Marion appears to be dependent on clear skies, while synoptic weather systems affect the duration and intensity of soil frost processes and non‐radiative heat fluxes. Air circulation patterns at Marion Island influence diurnal scale temperature fluctuations and its direct and indirect interactions with ecosystem processes. The data suggest that in a maritime sub‐Antarctic environment the climatic drivers of soil frost occur at a finertemporal resolution than for seasonal and permafrost environments and needs to be measured at a diurnal time‐scale to be meaningful.     

Effects of direct and indirect heating on the validity of rock weathering simulation studies and durability tests

Rock surface and subsurface temperature responses in samples exposed to direct heating (insolation) under natural hot desert conditions reveal considerable variability between lithologies related to differences in thermal properties, especially albedo and thermal conductivity. However, when the same samples are heated indirectly by air in an oven-based environmental cabinet, lithological differences in temperature response disappear and all samples attain temperatures similar to the air temperature within the cabinet. Rates and patterns of rock decay produced in such environmental cabinets may not, therefore, reflect those encountered under natural conditions, where breakdown is related to micro-environmental conditions at the rock/air interface and where rock temperature is one of the most important controlling factors. In addition to implications for assessment of weathering effectiveness, use of only indirect forms of heating affects the determination of comparative rock durability because all rock types are cycled through the same temperature regimes. Because temperature exerts such a major control on rock breakdown through its control on physical and chemical weathering processes, all significant factors influencing it must be included in the design of weathering simulations and durability tests.     

WEATHERING OF PALEOZOIC MARBLES IN THE INDEPENDENCE HILLS AND PATRIOT HILLS,ELLSWORTH MOUNTAINS,ANTARCTICA

Weathering processes in the Ellsworth Mountains of Antarctica are dominated by frost action. These processes were observed to be different on the same group of marbles under different slope conditions. North- and south-facing walls of the bedrock showed the same shattering rate in the summer of 1992–1993. Frost shattering of rocks is controlled by surface temperature, moisture, and the physical properties of the rock. The most important control on frost shattering in this area was moisture availability, given the same bedrock and freeze-thaw cycle. Snow particles are moved by katabatic winds, bringing moisture to the rock. Moisture is collected mainly in lower cliffs and cols. [Key words: weathering, marble, moisture conditions, Antarctica.]     

Ground Thermal Profiles from Mount Kenya, East Africa

This paper presents and compares ground thermal regimes at 4200 and 4800 m a.s.l. on Mount Kenya's southern aspect. Temperatures were recorded using Tinytalk? data loggers, installed at the ground surface and at depths of 1 cm, 5 cm, 10 cm and 50 cm. Temperatures were logged at 2‐hour intervals over a period of 12 months (August 1998 to July 1999). The study is designed to demonstrate near‐surface freeze conditions, which would have implications for contemporary periglacial landform production. Although ground freeze at 4200 m a.s.l. occurs during most nights (c. 70% at 1 cm depth), freeze penetration is restricted to the top 2 to 3 cm, such that no freeze was recorded at 5 cm depth. At 4800 m a.s.l., the diurnal frost frequency at the surface is 365 days (100%), whilst that at 10 cm depth is 165 days (45%). The paper demonstrates that a greater longevity of contemporary thin snow cover at 4800 m a.s.l. permits progressive sub‐surface cooling with depth. However, the near‐surface ground temperature profiles suggest that conditions are not conducive to permafrost development at the sites.     

ESSAY PAPER The interaction between geological structure and global tectonics in multistoreyed landscape development: a denudation chronology of the South Indian shield

This study constitutes a comprehensive attempt to interpret the multistoreyed benchland scenery of the South Indian shield. In South India, two rifted margins (and now competing base levels), a low-elevation margin facing the Bay of Bengal, in existence since ≈130  Ma, and a younger (65  Ma) high-elevation margin facing the Arabian Sea, together with a high-standing backbone of extremely resistant granulitic rocks known as charnockites, have influenced the long-term erosional response to rock uplift and to the eustatic shift of shorelines in a complex way.
Several tiers of flat-lying, denudational topographic surfaces, which are indifferent to stratification, schistosity or foliation and highlighted by a characteristic weathering mantle, are identified and the conditions of their genesis discussed. General definitions and assumptions concerning the evolution of planation surfaces are presented. A major key issue is the nature of crustal uplift in cratonic regions: its relation to global tectonics, its role in the redistribution in time and space of available relief and in the deformation of pre-existing planation surfaces, and its bearing on denudational signals which may be recorded both by isotopic measurement techniques and offshore sedimentary sequences. The proposed denudation chronology considers all these aspects, and the analysis sets out to establish a thread of geodynamic events that can account for the observed morphology. Drainage, weathering and crustal uplift patterns, geological structures and chronostratigraphic data are examined in relation to their possible connections with the migration of drainage divides and surface lowering patterns. The high number of degrees of freedom involved when considering the long-term interplay between gravity-driven and radiation-driven denudation systems is one of the many problems facing this analysis, and is extensively addressed in the discussion.     

THERMALLY DRIVEN SORPTION,DESORPTION, AND MOISTURE MIGRATION IN THE ACTIVE LAYER IN CENTRAL ALASKA

Combined observations of hourly soil temperature and electric potential, the latter converted to a relative index of soil-water solute concentration, yield information on the physical chemistry of near-surface frost effects. Solute concentration near the descending 0° C isotherm in the refreezing active layer above permafrost is divided into three distinct zones: (1) an ion-enriched zone in the unfrozen active layer that precedes the penetrating freezing front; (2) an ion-purified desorbed zone at the freezing front that is the source region of the downward-expelled ions and water; and (3) a hydrologically isolated subfreezing zone of enhanced solute concentration located above the freezing isotherm. High-frequency fluctuations superimposed on these general patterns are traceable to vapor migration driven by surface thermal fluctuations. These effects diminish at temperatures below about -0.4° C, as permeability decreases with soil-ice formation. The combined temperature-solute concentration time series is used to develop sorption curves for the frozen organic and mineral soils, and indicates that approximately half of the pore water present in the mineral soil at -0.4° C had not been converted to ice at -6° C. Gradual soil desiccation over winter appears to result from outward vapor diffusion, possibly through soil cracks. [Key words: Alaska, active layer, frozen ground, soil temperature, soil water, permafrost.]     

Influence of temperature variations during a cold period on the conditions of life of the population in East Siberia

On the territory of East Siberia, the positive deviations of mean monthly air temperatures from long-term annual mean air temperatures for the past 30 years (1981–2010) were caused by the shortening of the low-temperature periods. The largest decrease of the number of days with a daily mean temperature below ?25 °C is recorded in the southern and middle parts of the macroregion under conditions of a moderate, strong and very strong discomfort. On the other hand, the resulting range of variation in the number of days with a mean daily temperature below ?25 °C and the duration of the heating period remain within the long-term values. A slight rise in mean temperature for the heating period entails a marked reduction in degree-days.     

Controls on basalt terrace formation in the eastern Lesotho highlands

The objective of this study is to ascertain the relative importance of lithological controls and geomorphological processes in the development of Drakensberg basalt terraces. Various hypotheses for terrace formation are considered, including geological controls, macroscale geomorphology, and climatic–geomorphological controls. The variations in strength and relative age differences for scarp surface exposures on two slopes of varying aspect are determined, so that a comparison can be made between various scarp outcrops and relative rates of weathering. Scarp outcrops were measured for their rock mass strength, rock surface roughness, and percentage lichen cover. The ethylene glycol test was performed on prepared rock samples to determine susceptibility to tensional breakup. A satellite image depicting the distribution of late-lying contemporary snow was used to assist in the construction of topo-climatic linkages with scarp terrace localities. Findings show that terraces are most common on southeast-facing aspects, and coincide with the major joint strike direction. Lithological factors are thus considered the primary control to such terrace development. It is suggested that a different set of geomorphological processes operates on various slope-altitudinal and slope-orientational positions at any given time.     

ENDOLITHIC LICHENS,RAPID BIOLOGICAL WEATHERING AND SCHMIDT HAMMER R‐VALUES ON RECENTLY EXPOSED ROCK SURFACES: STORBREEN GLACIER FORELAND,JOTUNHEIMEN, NORWAY

The endolithic lichen Lecidea auriculata is known to enhance rock surface weathering on the Little Ice Age moraines of the glacier Storbreen in Jotunheimen, central southern Norway. This study demonstrates the reduction in Schmidt hammer Rvalues that followed the rapid colonization by this lichen of pyroxene‐granulite boulders on terrain deglaciated over the last 88 years. In the absence of this lichen, the characteristic mean R‐value of boulder surfaces is 61.0 ± 0.3; where this lichen is present, R‐values are lower by at least 20 units on surfaces exposed for 30–40 years. A similar reduction in rock hardness on rock surfaces without a lichen cover requires about 10 ka. The rapid initial weakening of the rock surfaces is indicative of rates of biological weathering by endolithic lichens that may be two orders of magnitude (200–300 times) faster than rates of physico‐chemical weathering alone. If not avoided, the effects of this type of lichen are likely to negate the effectiveness of the Schmidt hammer and other methods for exposure‐age dating, including cosmogenic‐nuclide dating, in severe alpine and polar periglacial environments. The results also suggest a new method for dating rock surfaces exposed for <50 years.     

Constraining basin thermal history and petroleum generation using palaeoclimate data in the Piceance Basin,Colorado

Careful assessment of basin thermal history is critical to modelling petroleum generation in sedimentary basins. In this paper, we propose a novel approach to constraining basin thermal history using palaeoclimate temperature reconstructions and study its impact on estimating source rock maturation and hydrocarbon generation in a terrestrial sedimentary basin. We compile mean annual temperature (MAT) estimates from macroflora assemblage data to capture past surface temperature variation for the Piceance Basin, a high‐elevation, intermontane, sedimentary basin in Colorado, USA. We use macroflora assemblage data to constrain the temporal evolution of the upper thermal boundary condition and to capture the temperature change with basin uplift. We compare these results with the case where the upper thermal boundary condition is based solely upon a simplified latitudinal temperature estimate with no elevation effect. For illustrative purposes, 2 one‐dimensional (1‐D) basin models are constructed using these two different upper thermal boundary condition scenarios and additional geological and geochemical input data in order to investigate the impact of the upper thermal boundary condition on petroleum source rock maturation and kerogen transformation processes. The basin model predictions indicate that the source rock maturation is very sensitive to the upper thermal boundary condition for terrestrial basins with variable elevation histories. The models show substantial differences in source rock maturation histories and kerogen transformation ratio over geologic time. Vitrinite reflectance decreases by 0.21%Ro, source rock transformation ratio decreases 10.5% and hydrocarbon mass generation decreases by 16% using the macroflora assemblage data. In addition, we find that by using the macroflora assemblage data, the modelled depth profiles of vitrinite reflectance better matches present‐day measurements. These differences demonstrate the importance of constraining thermal boundary conditions, which can be addressed by palaeotemperature reconstructions from palaeoclimate and palaeo‐elevation data for many terrestrial basins. Although the palaeotemperature reconstruction compiled for this study is region specific, the approach presented here is generally applicable for other terrestrial basin settings, particularly basins which have undergone substantial subaerial elevation change over time.     

Rock Weathering Processes in Antarctica: A Comparison of Some Recent Studies with Those from the Northern Hemisphere

A review of some recent studies on rock weathering in Antarctica has revealed that Antarctic weathering research has a significant contribution to make to the ongoing debate about rock weathering in cold climates. Largely conducted in the field rather than the laboratory as in the Northern Hemisphere, it demonstrates that whilst all weathering processes can occur in Antarctica this is highly localised and dependent on the particular micro‐environment. Freeze‐thaw, for example, is not the most dominant process in many parts of Antarctica. The right combination of rock temperature and moisture can mean that salt, insolation, hydration or even chemical weathering can predominate.     

High-frequency rock temperature data from hyper-arid desert environments in the Atacama and the Antarctic Dry Valleys and implications for rock weathering

In desert environments with low water and salt contents, rapid thermal variations may be an important source of rock weathering. We have obtained temperature measurements of the surface of rocks in hyper-arid hot and cold desert environments at a rate of 1/s over several days. The values of temperature change over 1-second intervals were similar in hot and cold deserts despite a 30 °C difference in absolute rock surface temperature. The average percentage of the time dT/dt > 2 °C/min was ~ 8 ± 3%, > 4 °C/min was 1 ± 0.9%, and > 8 °C/min was 0.02 ± 0.03%. The maximum change over a 1-second interval was ~ 10 °C/min. When sampled to simulate data taken over intervals longer than 1 s, we found a reduction in time spent above the 2 °C/min temperature gradient threshold. For 1-minute samples, the time spent above any given threshold was about two orders of magnitude lower than the corresponding value for 1-second sampling. We suggest that a rough measure of efficacy of weathering as a function of frequency is the product of the percentage of time spent above a given threshold value multiplied by the damping depth for the corresponding frequency. This product has a broad maximum for periods between 3 and 10 s.     

Rates Of Postglacial rock weathering on glacially scoured outcrops (Abisko–Riksgränsen area, 68°N)

Ice–polished quartz veins, feldspar phenocrysts and quartzite layers were used as reference surfaces to assess the impact of Postglacial rock weathering in Lapland (68°N). Over 3200 measurements were carried out on roches moutonées and glaciofluvially scoured outcrops distributed within three study areas covering 8 km². Inferred weathering rates demonstrate that 10,000 years of Holocene weathering did not significantly modify the geometry of Weichselian rock surfaces. However, rates of general surface lowering range from 1 to 25, depending on the rock type, with average values at 0.2 mm ka⁻¹ for homogeneous crystalline rocks (irrespective of their acidity and grain size), 1 mm ka⁻¹ for biotite–rich crystalline rocks, and 5 mm ka⁻¹ for carbonate sedimentary rocks. Accelerated rates were recorded in weathering pits and along joints with values up to ten times higher than on the rest of the rock surface. Comparisons with cold and temperate areas suggest that solution rates of carbonate rocks are highly dependent on climate conditions, whilst granular disintegration of crystalline rocks operates at the same rate whatever the environment. It probably means that microgelivation is not efficient on ice–polished crystalline outcrops even under harsh climate conditions, and that granular disintegration proceeds under various climates from the same ubiquitous combination of biochemical processes. Last, the weathering state of Late–Weichselian roches moutonées can be usefully compared to that of Preglacial tors of the nearby Kiruna area.     

Rates Of Postglacial rock weathering on glacially scoured outcrops (Abisko–Riksgränsen area, 68°N)

Ice–polished quartz veins, feldspar phenocrysts and quartzite layers were used as reference surfaces to assess the impact of Postglacial rock weathering in Lapland (68°N). Over 3200 measurements were carried out on roches moutonées and glaciofluvially scoured outcrops distributed within three study areas covering 8 km². Inferred weathering rates demonstrate that 10,000 years of Holocene weathering did not significantly modify the geometry of Weichselian rock surfaces. However, rates of general surface lowering range from 1 to 25, depending on the rock type, with average values at 0.2 mm ka⁻¹ for homogeneous crystalline rocks (irrespective of their acidity and grain size), 1 mm ka⁻¹ for biotite–rich crystalline rocks, and 5 mm ka⁻¹ for carbonate sedimentary rocks. Accelerated rates were recorded in weathering pits and along joints with values up to ten times higher than on the rest of the rock surface. Comparisons with cold and temperate areas suggest that solution rates of carbonate rocks are highly dependent on climate conditions, whilst granular disintegration of crystalline rocks operates at the same rate whatever the environment. It probably means that microgelivation is not efficient on ice–polished crystalline outcrops even under harsh climate conditions, and that granular disintegration proceeds under various climates from the same ubiquitous combination of biochemical processes. Last, the weathering state of Late–Weichselian roches moutonées can be usefully compared to that of Preglacial tors of the nearby Kiruna area.     

Fluid inclusions as constraints in a three‐dimensional hydro‐thermo‐mechanical model of the Paris basin,France

Fluid inclusion homogenization temperatures and three‐dimensional hydro‐thermo‐mechanical modelling were combined to constrain fluid flow, solute and heat transport in the Paris basin, France, focusing on the two main petroleum reservoirs i.e. the Dogger and the Triassic (Keuper) formations. The average homogenization temperatures of two‐phase aqueous inclusions in different samples range from 66 °C to 88 °C in the Dogger calcite cement, from 106 °C to 118 °C in the Keuper dolomite cement and from 89 °C to 126 °C in the Keuper quartz and K‐feldspar cements. The maximum homogenization temperatures for inclusions in the Keuper quartz and K‐feldspar cements were 17–47 °C higher than present‐day temperatures in the boreholes at similar depths. Processes that might explain higher temperatures in the past were examined through numerical simulations and sensitivity tests. A warmer climate in the Late Cretaceous–Early Tertiary resulted in a temperature rise of only 8 °C. Late Cretaceous chalk had a thermal blanketing effect that resulted in simulated temperatures as high as 15–20 °C above the present day ones. An additional 300 m deposition and subsequent erosion of chalk, not taken into account so far, has to be considered to simulate the high palaeo‐temperatures recorded by fluid inclusions in both reservoirs. In view of the simulated thermal history of the basin, in the Keuper, an age of about 85 Ma is consistent with quartz/K‐feldspar temperatures and an age of about 65 Ma is in agreement with the precipitation temperature of the dolomite cement. Our models suggest an age of about 50 Ma for the Dogger calcite cementation.     

THE FROST PHISICAL WEATHERING IN THE GREAT WALL STATION AREA, ANTARCTICA

Some weathering observation sites were set up at different height and face in Great Wall Station area of King Geroge Island, Antarctica, since 1989. Baced on the data series obtained from 1987-1991, the relationship between physical weathering of rock and season, height, face are discussed in this paper. We also compare the results to that of other periglacial area in the world in order to know the special features of King George Island in physical weathering of rock. The rock weathering in south-east face of sea stack is higher than that of north-west face in same environment. Get rid of influence of elevation, rock type, weathering time and organisms, the main reason which caused physical weathering of this area is climate and orientation of rock. The King George Island of Antarctica belong to high latitude area. The temperature time of below zero is 6-8 months in a year, so the process of freeze-thow is restricted. Compared with other periglacial area in the world, the weathering rate of rock is midd