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1.
Thaw modification is the general process whereby frost-fissure wedges are modified during thaw, and by which frost-fissure pseudomorphs may develop. Specific processes of thaw modification are inferred from ice-wedge pseudomorphs, composite-wedge pseudomorphs and deformed sand wedges in the Pleistocene Mackenzie Delta: i.e. thermal erosion, collapse, subsidence, refreezing, loading, buoyancy, spreading, folding and shearing. Thaw modification is believed to result in selective preservation of pseudomorphs and wedges. Sand wedges are more likely to be preserved than are ice-wedge pseudomorphs or compositewedge pseudomorphs, because only those sand wedges that penetrate massive ice or icy sediments are prone to thaw modification. Furthermore, whereas ice wedges preferentially develop in ice-rich, fine-grained sediments (thaw-sensitive), their pseudomorphs appear to be selectively preserved in ice-poor, coarse-grained sediments (thaw-stable). 相似文献
2.
A massive ground-ice body was found exposed in the headwall of a thaw flow developed within the Chapman Lake terminal moraine complex on the Blackstone Plateau (Ogilvie Mountains, central Yukon Territory), which is contemporaneous to the Reid glaciation. Based on visible cryostructures in the 4-m-high headwall, two units were identified: massive ground ice, overlain sharply by 2 m of icy diamicton. The nature and origin of the Chapman Lake massive ground ice was determined using cryostratigraphy, petrography, stable O-H isotopes and the molar concentration of occluded gases (CO2, O2, N2 and Ar) entrapped in the ice, a new technique in the field of periglacial geomorphology that allows to distinguish between glacial and non-glacial intrasedimental ice. Collectively, the results indicate that the Chapman Lake massive ground ice formed by firn densification with limited melting-refreezing and underwent deformation near its margin. Given that the massive ground-ice body consists of relict glacier ice, it suggests that permafrost persisted, at least locally, on plateau areas in the central Yukon Territory since the middle Pleistocene. In addition, the d value of Chapman Lake relict glacier ice suggests that the ice covering the area during the Reid glaciation originated from a local alpine glaciation in the Ogilvie Mountains. 相似文献
3.
Denis Lacelle Melanie St-Jean Bernard Lauriol Ian D. Clark Antoni Lewkowicz Duane G. Froese Stephen C. Kuehn Grant Zazula 《Quaternary Science Reviews》2009,28(27-28):3401-3413
This study describes the origin and age of a body of massive ground ice exposed in the headwall of a thaw slump in the Red Creek valley, central Yukon, Canada. The site is located beyond the limits of Pleistocene glaciation in central Yukon and within the southern limit of the modern continuous permafrost zone. The origin of the massive ground ice, which is preserved under a fine-grained diamicton containing thin layers of tephra, was determined through ice petrography, stable O-H isotope composition of the ice, and gas composition of occluded air entrapped in the ice. The age of the massive ground ice was established by identifying the overlying tephra and radiocarbon dating of a “muck” deposit preserved within the ice. Collectively, the results indicate that the massive ground ice formed by snow densification with limited melting-refreezing and is interpreted as being a buried perennial snowbank. The muck deposit within the ice, which yielded an age of 30,720 ± 340 14C a BP, and the Dawson tephra (25,300 14C a BP) overlying the perennial snowbank, indicates that the snowbank accumulated at roughly the transition between marine isotope stages 3 and 2. Dry climatic conditions at this time and possibly high winds enabled the snowbank to accumulate in the absence of extensive local valley glaciation as occurred in the mountains to the south. In addition to documenting the persistence of relict permafrost and ground ice to warming climate in regions where they are predicted to disappear by numerical models, this study presents evidence of an isotopic biosignature preserved in a body of massive ground ice. 相似文献
4.
Abstract: Permafrost (perennially frozen ground) appears widely in the Golmud-Lhasa section of the Qinghai-Tibet railway and is characterized by high ground temperature (≥ ?1°C) and massive ground ice. Under the scenarios of global warming and human activity, the permafrost under the railway will gradually thaw and the massive ground ice will slowly melt, resulting in some thaw settlement hazards, which mainly include longitudinal and lateral cracks, and slope failure. The crushed rock layer has a thermal semiconductor effect under the periodic fluctuation of natural air. It can be used to lower the temperature of the underlying permafrost along the Qinghai-Tibet railway, and mitigate the thaw settlement hazards of the subgrade. In the present paper, the daily and annual changes in the thermal characteristics of the embankment with crushed rock side slope (ECRSS) were quantitatively simulated using the numerical method to study the cooling effect of the crushed rock layer and its mitigative ability. The results showed that the ECRSS absorbed some heat in the daytime in summer, but part of it was released at night, which accounted for approximately 20% of that absorbed. Within a year, it removed more heat from the railway subgrade in winter than that absorbed in summer. It can store approximately 20% of the “cold” energy in subgrade. Therefore, ECRSS is a better measure to mitigate thaw settlement hazards to the railway. 相似文献
5.
为了研究高含冰量冻土路基的融化固结规律，在线性大变形融化固结理论的基础上引入非线性本构关系，并运用分段插值法实现了孔隙比与压缩模量之间的非线性关系，完善了三维大变形融化固结数值模拟方法。在此基础上结合青藏公路实测数据验证了其合理性。研究结果表明，采用非线性应力?应变关系的大变形融化固结理论能够显著提高高含冰量冻土路基的沉降计算精度，并能够进一步合理描述热学场和力学场的相互叠加影响。冻土融化固结度受有效融化固结时间以及特征排水长度等因素的影响呈现出完全不同于融土路基的发展规律，即在路基运营初期其融化固结度上升，随着时间发展，其固结度在达到峰值后持续降低，这主要是由于融化深度持续增大后所引起的特征排水长度的增加和有效融化固结时间的缩短所造成的。因此，在计算高含冰量冻土路基稳定性设计指标时，应采用非线性应力?应变关系来进一步提高融化深度、沉降以及固结度等指标的计算精度。 相似文献
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7.
Frost-cracking and ice-wedge growth are fundamental processes within the permafrost environment. Extensive areas of contemporary permafrost terrain are characterised by frost-fissure polygons, formed by repeated thermal contraction-cracking of the ground. The incremental growth of ice veins and wedges along the axes of contraction-cracks contributes significantly to the volume of ground ice in near-surface permafrost. In areas beyond the present limit of permafrost, the recognition of ice-wedge pseudomorphs provides one of the few unambiguous indications of the former existence of permafrost conditions. An understanding of the processes of ice-wedge growth and thaw transformation is essential if contemporary ice wedges are to be used as analogues for Pleistocene frost-fissure structures, in palaeoenvironmental reconstructions. 相似文献
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9.
Impacts of climate, lake size, and supra- and sub-permafrost groundwater flow on lake-talik evolution, Yukon Flats, Alaska (USA) 总被引：3，自引：2，他引：1
In cold regions, hydrologic systems possess seasonal and perennial ice-free zones (taliks) within areas of permafrost that control and are enhanced by groundwater flow. Simulation of talik development that follows lake formation in watersheds modeled after those in the Yukon Flats of interior Alaska (USA) provides insight on the coupled interaction between groundwater flow and ice distribution. The SUTRA groundwater simulator with freeze–thaw physics is used to examine the effect of climate, lake size, and lake–groundwater relations on talik formation. Considering a range of these factors, simulated times for a through-going sub-lake talik to form through 90 m of permafrost range from ～200 to >?1,000 years (vertical thaw rates <?0.1–0.5 m?yr?1). Seasonal temperature cycles along lake margins impact supra-permafrost flow and late-stage cryologic processes. Warmer climate accelerates complete permafrost thaw and enhances seasonal flow within the supra-permafrost layer. Prior to open talik formation, sub-lake permafrost thaw is dominated by heat conduction. When hydraulic conditions induce upward or downward flow between the lake and sub-permafrost aquifer, thaw rates are greatly increased. The complexity of ground-ice and water-flow interplay, together with anticipated warming in the arctic, underscores the utility of coupled groundwater-energy transport models in evaluating hydrologic systems impacted by permafrost. 相似文献
10.
Adriano Ribolini Alessandro Chelli Mauro Guglielmin Marta Pappalardo 《Quaternary Research》2007,68(3):353-363
In the Schiantala Valley of the Maritime Alps, the relationship between a till-like body and a contiguous rock glacier has been analyzed using geomorphologic, geoelectric and ice-petrographic methodologies. DC resistivity tomographies undertaken in the till and in the rock glacier show the presence of buried massive ice and ice-rich sediments, respectively. Ice samples from a massive ice outcrop show spherical gas inclusions and equidimensional ice crystals that are randomly orientated, confirming the typical petrographic characteristics of sedimentary ice. The rock glacier formation began after a phase of glacier expansion about 2550 ± 50 14C yr BP. Further ice advance during the Little Ice Age (LIA) overrode the rock glacier root and caused partial shrinkage of the pre-existing permafrost. Finally, during the 19th and 20th centuries, the glacial surface became totally debris covered. Geomorphological and geophysical methods combined with analyses of ice structure and fabric can effectively interpret the genesis of landforms in an environment where glaciers and permafrost interact. Ice petrography proved especially useful for differentiating ice of past glaciers versus ice formed under permafrost conditions. These two mechanisms of ice formation are common in the Maritime Alps where many sites of modern rock glaciers were formerly occupied by LIA glaciers. 相似文献
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13.
Marcel Elie Afonso C.R. Nogueira Anne Ndlec Ricardo I.F. Trindade Fabien Kenig 《地学学报》2007,19(5):303-308
Organic matter from the cap dolostones overlying the Marinoan‐age glacigenic diamictites of the Araras Group, Amazon craton, has been studied to reconstruct the post‐glacial ecosystem. Molecular fossils indicate that the post‐Marinoan ecosystem was marked by an apparent decline in marine algal diversity. The proliferation of red algae may be explained by environmental changes, such as a massive nutrient input accompanying continental weathering after the ice thaw and a dimer light penetrating sea water due to the drowning of the platform. In addition, the presence of green sulphur bacteria indicates that sea water was stratified with an anoxic (possibly euxinic, i.e. sulphidic) layer at the water–sediment interface. Sulphur cycling probably occurred at the redox boundary as suggested by the recognition of active sulphate reduction. This observation supports a microbially induced model for the formation of the cap dolostones. 相似文献
14.
Yu. K. Vasil’chuk A. C. Vasil’chuk N. A. Budantseva Ju. N. Chizhova W. Papesh Ye. Ye. Podborny L. D. Sulerzhitsky 《Doklady Earth Sciences》2009,429(1):1326-1332
The conditions and forming time of massive ice were specified (Bovanenkovo gas condensate field, Central Yamal). Here, massive
ice lies as stratums, laccoliths, stocks, and lenses. Three thousand boreholes 10–100 m in depth were analyzed. In 260 of
them massive ice was broached. The ice foot is situated from 1 to 57 m deep. The maximal thickness of ice broached with boreholes
came to 28.5 m; on average, it was about 8 m. The extension of massive ice is sometimes more than 2000 m, and its area is
quite often more than 10 km2. According to the radiocarbon method, loams of the third terrace, containing and overlapping ice deposits, were formed from
25 000 to 20 000 years ago or somewhat later. These strongly peat loams containing massive ice formed either in shallow sea
conditions or during periodical draining conditions of beaches or low laida, where organic matter appeared due to erosion
and deposition and accumulated during draining and overgrowing of drains. In more inclement conditions than at present, loam
deposits were frozen immediately, forming massive ice, which occupied the barely water-saturated layers. The oxygen isotope
composition (δ18O) of massive ice samples varied from −12.49‰ (here and further, relative to SMOW) to −22.95‰. The deuterium
concentration (δD) varied from −91.7 to −177.1‰. Deuterium kurtosis (d
exc) varied from 3.4 to 10.6‰. In one seam outcrop, the content of stable isotopes varied significantly. Here, at a depth of
0.2–0.8 m, the δ18O content varied by more than 10‰ (from −12.49 to −22.75), and the δD content, from −91.7 to −171.9‰. Such variations testify
about ice extraction upon freezing of water-saturated grounds in a closed system. According to palynological analysis of ice
stratums, numerous remains of unicellular green algae and diatoms were revealed. It is possible that this is evidence of the
existence of a fresh well, which was a source of water, feeding the layer. Most probably these were near-bottom silt waters
of a large lake or desalted bay, which were frozen syngenetically. This accentuates the new type of massive ice, syncriogenic
segregative ice, which probably formed 25 000–20 000 yr BP. 相似文献
15.
JULIAN B. MURTON 《Sedimentology》1996,43(4):737-760
Three stages of deposition are distinguished in thermokarst-lake-basin sequences in ice-rich permafrost of the Tuktoyaktuk Coastlands, western arctic Canada: (1) widespread retrogressive thaw slumping around lake margins that rapidly transports upland sediments into thermokarst lakes, forming a distinctive basal unit of impure sand and/or diamicton; (2) a reduction or cessation of slumping-because of the pinching out of adjacent ground ice, slump stabilization or climatic cooling, that reduces the input of clastic sediment, permitting reworking of sediment around lake margins and suspension settling, principally in basin centres; (3) lakes drain and deposition may continue by gelifluction and accumulation of in situ peat or aeolian sand. Radiocarbon dating of detrital peat and wood from a progradational sequence (basal unit) defines a lateral younging trend in the direction of progradation. A progradation rate is calculated to be ～ 4 cm yr?1, consistent with rapid deposition during stage (1) above. The nonuniform nature of the trend is attributed to episodic influxes of old organic material by slumping and reworking by waves and currents. In comparison with thermokarst-lake-basin sequences previously described in Alaska, Canada and Siberia, the middle unit of those in the Tuktoyaktuk Coastlands is similar, whereas the basal unit is generally thicker and, by contrast, often contains diamicton. These differences are attributed, respectively, to larger-scale resedimentation of upland sediments by retrogressive thaw slumping and debris-flow deposition in thermokarst lakes in the Tuktoyaktuk Coastlands. Compared with the sediments within supraglacial lakes in areas of moderate to high relief, the middle unit of thermokarst-lake-basin sequences in the Tuktoyaktuk Coastlands lacks clastic varves and the basal unit is much thinner and texturally less variable. These differences are attributed to higher relief and larger volumes of meltwater and glacigenic sediment in supraglacial lakes, which promote more suspension settling and resedimentation of glacigenic sediment than in thermokarst lakes in the Tuktoyaktuk Coastlands. It may be impossible to distinguish glacial and periglacial thermokarst-lake-basin sediments in permafrost areas of incomplete deglaciation. Not only is it often difficult to distinguish intrasedimental and buried glacier ice, but the depositional processes associated with thaw of both ice types are presumably the same and the host sediments very similar. 相似文献
16.
The Sandhills Moraine is a Late Wisconsinan lateral moraine complex on southwest Banks Island. The occurrence of ice-ablation landforms, ground ice slumps, kettle lakes and catastrophic lake drainage in winter suggests the presence of substantial bodies of massive ground ice. The distinctive hummocky topography of the Sandhills Moraine is thought to reflect partial melt-out of this ice. Stratigraphic observations indicate that the ice is overlain irregularly and unconformably by glacigenic sediments, notably pebbly clay (till) and/or sandy gravels (outwash), while the ice itself possesses numerous and variable mineral inclusions, faults and foliations. Petrofabric analyses indicate a strongly preferred orientation to the ice crystals. It is suggested that these characteristics are best explained if the ground ice is interpreted as relict glacier ice. 相似文献
17.
The active-layer hydrology of a peat plateau with thawing permafrost (Scotty Creek, Canada) 总被引：2，自引：0，他引：2
The southern margin of permafrost is experiencing unprecedented rates of thaw, yet the effect of this thaw on northern water resources is poorly understood. The hydrology of the active layer on a thawing peat plateau in the wetland-dominated zone of discontinuous permafrost was studied at Scotty Creek, Northwest Territories (Canada), from 2001 to 2010. Two distinct and seasonally characteristic levels of unfrozen moisture were evident in the 0.7-m active layer. Over-winter moisture migration produced a zone of high ice content near the ground surface. The runoff response of a plateau depends on which of the three distinct zones of hydraulic conductivity the water table is displaced into. The moisture and temperature of the active layer steadily rose with each year, with the largest increases close to the ground surface. Permafrost thaw reduced subsurface runoff by (1) lowering the hydraulic gradient, (2) thickening the active layer and, most importantly, (3) reducing the surface area of the plateau. By 2010, the cumulative permafrost thaw had reduced plateau runoff to 47 % of what it would have been had there been no change in hydraulic gradient, active layer thickness and plateau surface area over the decade. 相似文献
18.
Damages to natural building stones induced by the action of frost are considered to be of great importance. Commonly, the frost resistance of building stones is checked by standardised freeze–thaw tests before using. Corresponding tests normally involve 30–50 freeze–thaw action cycles. In order to verify the significance of such measurements, we performed long-term tests on four selected rocks over 1,400 freeze–thaw action cycles. Additionally, numerous petrophysical parameters were analysed to compare the behaviour of rocks in the weathering tests according to the current explanatory models of stress formation by growing ice crystals in the pore space. The long-term tests yield more information about the real frost sensibility of the rocks. A clear deterioration cannot be determined in most cases until 50 weathering cycles have been completed. In the freeze–thaw tests, the samples are also stressed by changing temperature and moisture, indicating that different decay mechanisms can interfere with each other. Thus, thermohygric and moisture expansion are important damage processes. 相似文献
19.
REIN VAIKMÄE FREDERICK A. MICHEL VLADIMIR I. SOLOMATIN 《Boreas: An International Journal of Quaternary Research》1993,22(3):205-213
Studies of the stratigraphy, sedimentology, structure and isotope composition of a buried massive ice body and its encompassing sediments at Ledyanaya Gora in northwestern Siberia demonstrate that the ice is relict glacier ice, probably emplaced during the Early Weichselian. Characteristics of this ice body should serve as a guide for the identification of other relict buried glacier ice bodies in permafrost regions. 相似文献
20.
气候变化条件下青藏铁路沿线多年冻土概率预报(Ⅱ):活动层厚度与沉降变形 总被引：2，自引：2，他引：0
利用土壤表层温度计算Stefan公式中融化指数,并结合铁路沿线地下冰和土体干密度分布特征,由Stefan公式集合预报未来100 a逐年最大季节融化深度;利用铁路沿线地下冰和干密度分布特征计算冻土融化时最大沉降量空间分布,与Stefan公式计算得到的活动层厚度变化数据叠加分析,得到未来100 a逐年的沉降量空间分布及其置... 相似文献