Study of thermal properties of supraglacial debris and degree-day factors on Lirung Glacier,Nepal

The extensive debris that covers glaciers in the ablation zone of the Himalayan region plays an important part in regulating ablation rates and water availability for the downstream region. The melt rate of ice is determined by the amount of heat conducted through debris material lying over the ice. This study presents the vertical temperature gradients, thermal properties in terms of thermal diffusivity and thermal conductivity, and positive degree-day factors for the debris-covered portion of Lirung Glacier in Langtang Valley, Nepal Himalaya using field-based measurements from three different seasons.Field measurements include debris temperatures at different debris thicknesses, air temperature, and ice melt during the monsoon(2013), winter(2013), and pre-monsoon(2014) seasons. We used a thermal equation to estimate thermal diffusivity and thermal conductivity, and degree-day factors(DDF) were calculated from cumulative positive temperature and ice melt of the measurement period. Our analysis of debris temperature profiles at different depths of debris show the daily linear gradients of-20.81 °C/m, 4.05 °C/m, and-7.79 °C/m in the monsoon, winter, and pre-monsoon seasons, respectively. The values of thermal diffusivity and thermal conductivity in the monsoon season were 10 times greater than in the winter season. The large difference in these values is attributed to surface temperature and moisture content within the debris. Similarly, we found higher values of DDFs at thinner debris for the pre-monsoon season than in the monsoon season although we observed less melting during the pre-monsoon season. This is attributed to higher cumulative temperature during the monsoon season than in the pre-monsoon season. Our study advances our understanding of heat conductivity through debris material in different seasons, which supports estimating ice melt and discharge from glacierized river basins with debris-covered glaciers in the Himalayan region.     

Estimate of Ablation Rate of Glacier Ice under a Supraglacial Debris Layer

The ablation rate under a debris layer is very difficult to measure directly at debris-covered glaciers, because the surface is highly heterogeneous, and the ablation rate varies tremendously from place to place. Heat budget considerations with a debris layer on top of glacier ice suggested that 'thermal resistance' of the debris layer could be estimated from surface temperature and the heat fluxes at the debris surface, and the ablation rate of the underlying glacier ice from the thermal resistance and meteorological data. The method was tested at the Lirung Glacier in Langtang Valley, Nepal Himalayas, using the thermal band of LANDSAT satellite for estimating surface temperature distribution of the debris top surface. The amount of melt water thus estimated was compatible with the observed discharge data from the glacier basin for periods of the monsoon season in 1985 and the pre-monsoon to the monsoon season in 1996. The investigation also revealed that the amount of discharge was much larger than the amount of precipitation over the basin, and it was suggested that the melt water from the debris-covered glacier contributes significantly to the river flow as a result of the shrinkage of the glacier.     

Spatial distribution of supraglacial debris thickness on glaciers of the China-Pakistan Economic Corridor and surroundings

Debris-covered glaciers, characterized by the presence of supraglacial debris mantles in their ablation zones, are widespread in the China-Pakistan Economic Corridor (CPEC) and surroundings. For these glaciers, thin debris layers accelerate the melting of underlying ice compared to that of bare ice, while thick debris layers retard ice melting, called debris-cover effect. Knowledge about the thickness and thermal properties of debris cover on CPEC glaciers is still unclear, making it difficult to assess the regional debris-cover effect. In this study, thermal resistance of the debris layer estimated from remotely sensed data reveals that about 54.0% of CPEC glaciers are debris-covered glaciers, on which the total debris-covered area is about 5,072 km², accounting for 14.0% of the total glacier area of the study region. We find that marked difference in the extent and thickness of debris cover is apparent from region to region, as well as the debris-cover effect. 53.3% of the total debris-covered area of the study region is concentrated in Karakoram, followed by Pamir with 30.2% of the total debris-covered area. As revealed by the thermal resistance, the debris thickness is thick in Hindu Kush on average, with the mean thermal resistance of 7.0×10^-2 ((m²?K)/W), followed by Karakoram, while the thickness in western Himalaya is thin with the mean value of 2.0×10^-2 ((m²?K)/W). Our findings provide a basis for better assessments of changes in debris-covered glaciers and their associated hydrological impacts in the CPEC and surroundings.     

中国冰川区表碛厚度估算及其影响研究进展

表碛覆盖型冰川是中国西部分布较为广泛的冰川类型,其典型特征是冰川消融区部分或全部覆盖了一层厚度不一的表碛。与裸冰或雪相比,表碛覆盖层下冰的融化过程有独特性,表碛厚度空间分布对一条冰川的消融、物质平衡和径流过程的影响有别于无表碛覆盖型冰川。本文回顾了近年来表碛厚度分布及其影响的研究,通过对这些进展进行总结以进一步明晰表碛影响研究的方向;同时着重介绍了近期发展的基于遥感影像热红外波段和可见光近红外波段、大气—表碛层—冰川界面能量平衡过程的表碛厚度估算方法和表碛覆盖综合评估模型,结合地面观测,分析了以遥感反演的表碛层热阻系数表征表碛厚度的精度,介绍了这类模型在表碛覆盖型冰川物质平衡和径流研究中的应用效果,以及在综合评估流域/区域尺度表碛影响的应用情况,并分析了该模型存在的不足及进一步改进的研究方向,为实现中国西部区域表碛影响的系统评估奠定基础,从而提升对区域水资源和冰川灾害的模拟和预测能力。     

SUB-DEBRIS MELT RATES ON SOUTHERN INYLCHEK GLACIER, CENTRAL TIAN SHAN

Melt rates of glacier surfaces are strongly influenced by the existence of a debris cover. Dependent on thickness and other physical parameters, the debris layer can enhance or reduce ablation as compared to bare ice conditions. Supraglacial moraines appear very frequently on Central Asian glaciers, greatly affecting water yield from these high mountain regions. In summer 2005, a network of 22 ablation stakes was drilled into locations with varying debris thicknesses on southern Inylchek Glacier in the central Tian Shan. Mean ablation rates varied from 2.8 to 6.7 cm/day, strongly correlated with moraine thickness. Parallel observation of air temperature allowed the application of a simple degree‐day approach and the calculation of ablation rates. Efforts to improve calculations of melt rates by incorporating relative air humidity to account for latent heat fluxes failed. This proves that air temperature is already a very good melt indicator. Ice albedo measurements show that reflectivity might be controlled by the occurrence of evaporation or condensation, but this topic needs further investigation.     

1990-2019年贡嘎山地区典型冰川表碛覆盖变化及其空间差异

表碛覆盖型冰川是中国西部较为常见的冰川类型。表碛层存在于大气—冰川冰界面,强烈影响大气圈与冰冻圈之间的热交换。表碛厚度的空间异质性可极大地改变冰川的消融率和物质平衡过程,进而影响冰川径流过程和下游水资源。基于Landsat TM/TIRS数据,运用能量平衡方程反演了贡嘎山地区冰川表碛厚度,研究了贡嘎山地区冰川在1990—2019年间表碛覆盖范围及厚度变化情况,同时对比了东西坡差异。结果表明：① 贡嘎山地区冰川表碛扩张总面积达43.824 km²。其中,海螺沟冰川扩张2.606 km²、磨子沟冰川1.959 km²、燕子沟冰川1.243 km²、大贡巴冰川0.896 km²、小贡巴冰川0.509 km²、南门关沟冰川2.264 km²,年均扩张率分别为3.2%、11.1%、1.5%、0.9%、1.0%和6.5%;② 海螺沟冰川、磨子沟冰川、燕子沟冰川、大贡巴冰川、小贡巴冰川、南门关沟冰川表碛平均增厚分别为5.2 cm、3.1 cm、3.7 cm、6.8 cm、7.3 cm和13.1 cm;③ 西坡冰川表碛覆盖度高,表碛覆盖年均扩张率低,冰川末端退缩量小;东坡冰川表碛覆盖年均扩张率高,但表碛覆盖度总体低于西坡,冰川末端退缩量大。     

ABLATION OF ICE‐CORED MORAINE IN A HUMID,MARITIME CLIMATE: FOX GLACIER,NEW ZEALAND

Depending on thickness, debris‐cover can enhance or reduce ablation, compared to bare‐ice conditions. In the geological record, hummocky moraines often represent the final product of the melt‐out of ice‐cored moraines, and the presence or absence of such moraine deposits can have paleoclimatic implications. To evaluate the effects of varying debris‐cover and climate on ice‐melt in a maritime mid‐latitude setting, an 11‐day ablation stake study was undertaken on ice‐cored moraine at Fox Glacier, on the western flank of the New Zealand Southern Alps. Ablation rates varied from 1.3 to 6.7 cm d^?1, with enhancement of melt‐rate under thin debris‐covers. Highest melt‐rates (effective thickness) occurred under debris‐cover of c. 2 cm, with ～3 cm being the debris thickness at which melt‐rates are equal to adjacent bare‐ice (critical thickness). Air temperature from nearby Franz Josef Glacier allowed for a simple degree‐day approach to ablation calculations, with regression relationships indicating air temperature is the key climatic control on melt. Digital elevation models produced from topographic surveys of the ice‐cored moraine over the following 19 months indicated that ablation rates progressively decreased over time, probably due to melt‐out of englacial debris increasing debris‐cover thickness. The morphology of the sandur appears to be strongly determined by episodic high‐magnitude fluvial flows (jökulhlaups), in conjunction with surface melt. Thus, ‘hummocky’ moraine appears to be a transient landform in this climatic setting.     

THE RESPONSE OF PARTIALLY DEBRIS‐COVERED VALLEY GLACIERS TO CLIMATE CHANGE: THE EXAMPLE OF THE PASTERZE GLACIER (AUSTRIA) IN THE PERIOD 1964 TO 2006

Long‐term observations of partly debris‐covered glaciers have allowed us to assess the impact of supra‐glacial debris on volumetric changes. In this paper, the behaviour of the partially debris‐covered, 3.6 km² tongue of Pasterze Glacier (47°05′N, 12°44′E) was studied in the context of ongoing climate changes. The right part of the glacier tongue is covered by a continuous supra‐glacial debris mantle with variable thicknesses (a few centimetres to about 1 m). For the period 1964–2000 three digital elevation models (1964, 1981, 2000) and related debris‐cover distributions were analysed. These datasets were compared with long‐term series of glaciological field data (displacement, elevation change, glacier terminus behaviour) from the 1960s to 2006. Differences between the debriscovered and the clean ice parts were emphasised. Results show that volumetric losses increased by 2.3 times between the periods 1964–1981 and 1981–2000 with significant regional variations at the glacier tongue. Such variations are controlled by the glacier emergence velocity pattern, existence and thickness of supra‐glacial debris, direct solar radiation, counter‐radiation from the valley sides and their changes over time. The downward‐increasing debris thickness is counteracting to a compensational stage against the common decrease of ablation with elevation. A continuous debris cover not less than 15 cm in thickness reduces ablation rates by 30–35%. No relationship exists between glacier retreat rates and summer air temperatures. Substantial and varying differences of the two different terminus parts occurred. Our findings clearly underline the importance of supra‐glacial debris on mass balance and glacier tongue morphology.     

泥石流预报中前期有效降水量的确定

前期有效降水量是泥石流预报的重要参数之一,对不同类型泥石流的形成有不同的影响形式,对土力类泥石流的形成主要是影响泥石流形成区土体的土壤含水量.在每次前期降水增加的土壤含水量和其有效降水量遵循相同衰减规律,以及每次前期降水的有效降水量和其增加的土壤含水量衰减过程都是相互独立的假设条件下,通过分析土壤含水量随时间的变化关系,可以得到前期有效降水量与前期降水量随时间的变化关系,从而可以确定前期有效降水量.通过对云南蒋家沟降水和土壤含水量的实际观测,对这个关系进行了分析研究,并利用最小二乘法得出了前期有效降水量的计算公式.     

Snow-avalanche impact landforms, deposits and effects at Urdvatnet, southern Norway: implications for avalanche style and process

An unusual assemblage of landforms and deposits is described from upper Norangsdalen, Sunnmøre region, southern Norway, and interpreted as the product of snow‐avalanche events that vary in magnitude, frequency and debris content. An avalanche impact plunge pool, proximal scar and distal mound are associated with a coarse gravel deposit covering part of the valley floor. Landforms in this debris spread include gravel ridges, boulder lines, beaded ridges, fine sediment banked against and covering large boulders, and gravel clumps. Many of these landforms are aligned, indicating across‐valley transport radiating from the plunge pool. Features were mapped in the field and samples analysed for grain size and heavy‐mineral content. The debris spread is attributed to deposition by high‐energy, debris‐rich snow‐avalanche events that collect debris from large areas of the valley side, lower slopes and plunge pool. Aligned landforms develop through sediment transport in a basal shear zone, and randomly distributed gravel clumps represent melt pits following debris transport in the avalanche body. Air displacement ahead of larger avalanches is thought to have felled and tilted trees on the lower slopes of the distal valley side. Approximate ages of damaged trees allowed estimation of the frequency of snow‐avalanche events: (1) small, frequent events (several per annum) carry debris to the lower valley slopes and the plunge pool; (2) moderate events with an annual to decadal frequency maintain the pool–scar–mound complex; and (3) large, debris‐rich events with a decadal to centennial frequency add material to the debris spread.     

泥石流颗粒组成的分形特征

1 IntroductionD ebris flow s in certain sense are a process of m ass interchanges through erosion and depositionbetw een the fluid and the sedim ent; and the interchange of m aterial caused change in thestructure of the flow s that can be ultim ately redu…     

Physical properties and stratigraphy of surface snow in western Dronning Maud Land, Antarctica

Information about the spatial variations of snow properties and of annual accumulation on ice sheets is important if we are to understand the results obtained from ice cores, satellite remote sensing data and changes in climate patterns. The layer structure and spatial variations of physical properties of surface snow in western Dronning Maud Land were analysed during the austral summers 1999/2000, 2000/01 and 2003/04 in five different snow zones. The measurements were performed in shallow (1–2 m) snow pits along a transect extending 350 km from the seaward edge of the ice shelf to the polar plateau. These pits covered at least the last annual accumulation and ranged in elevation from near sea level to 2500 m a.s.l. The ع⁸O values and accumulation rates had a good linear correlation with the distance from the coast. The mean accumulation on the ice shelf was 312±28 mm water equivalent (w.e.); in the coastal region it was 215±43 mm w.e. and on the polar plateau it was 92±25 mm w.e. The mean annual conductivity and grain size values decreased exponentially with increasing distance from the ice edge, by 48%/100 km and 18%/100 km respectively. The mean grain size varied between 1.5 and 1.8 mm. Depth hoar layers were a common phenomenon, especially under thin ice crusts, and were associated with low dielectric constant values.     

INFLUENCE OF SUPRAGLACIAL DEBRIS ON SUMMER ABLATION AND MASS BALANCE IN THE 24K GLACIER,SOUTHEAST TIBETAN PLATEAU

Many temperate glaciers in the southeast Tibetan Plateau are covered by supraglacial debris in the ablation area. To evaluate the effect of such debris on summer ablation and mass balance, the surface ablation on the 24K Glacier was measured in the summer of 2008. Mean ablation rates varied from 10 to 52 mm/day, strongly correlated to debris thickness. Synchronous observations of air temperature allowed application of a simple degree‐day model to calculate ablation rates. Maximum values of both ablation rate and degree‐day factors appeared in the middle area of the glacier where the debris layer thickness was about 1 cm. The simulated daily ablation obtained from the degree‐day approach showed that the debris layers significantly affected the total summer ablation. The calculated ablation would be increased by 36% of the total ablation with the actual surface debris cover if glacier surface had been assumed to be entirely debris free. If completely covered by 65 cm thick debris in the ablation area, the glacier would experience a 59% decrease in summer ablation. The presence of a debris cover also leads to a change in the ablation gradient in the ablation zone.     

泥石流颗粒组成的分形特征

泥石流是主动的流域物质输移形式,土体的颗粒组成决定了泥石流的活动。不同地区、不同流域、不同密度的泥石流样本分析表明,高密度(如籽s>2g/cm3)泥石流的颗粒分布曲线总体上具有指数形式,指数呈现出显著的区域性差异。泥石流多发生在一定的指数区间;颗粒组成具有良好的分形特征,不同密度泥石流颗粒的分形区间不同,这个区间可以认为是形成泥石流结构的颗粒区间,从而也确定了泥石流基质的颗粒界限;颗粒的分维随密度变化,密度越大(大颗粒含量越多),分维越大。颗粒的分形结构也是颗粒孔隙的分形结构,它决定了土体的液化,因而也决定了泥石流所表现的特征。     

高位滑坡的运动转化形式

高位滑坡剪出口高于坡脚,它一旦滑离滑坡发生区,运动可能转化成四种形式:1.崩塌:由滑体经分级解体滑过剪出口处依次向前倾倒而成;2.碎屑流动或3.碎屑滑动:由滑动块体经碎屑化而成;4.泥石流:在适当的细粒物质量和水体条件下生成的碎屑流动。     

粘性泥石流阻力规律初探

用曼宁公式分析泥石流阻力时,不同地区和不同流域之是的糙率ｎ值相差很大,即是同一条沟的ｎ值也很分散,若考虑单宽固体物质重量和粗、细颗粒含量之比沿垂线分布的不均习性之后,则使单沟的ｎ值点群分布趋于集中,且能将不同泥石流相差数倍数的ｎ值用统一的表达式加以描述。     

2013-2014年夏季南极普里兹湾海面反照率走航观测研究

在 2013—2014年南半球夏季时对南极普里兹湾海区的反照率进行了走航观测。利用安装于破冰船船头的高光谱辐照度计测量入射和反射的350—920 nm的太阳短波辐射, 基于此观测数据, 经计算得到了反照率。分析比较不同下垫面的反照率, 通过比较不同航段的观测结果, 得到了反照率的空间变化以及从海冰融化期至冻结初期的变化。不同下垫面的反照率差异较大, 有积雪覆盖的固定冰反照率最大, 有积雪覆盖的浮冰其次, 而积雪融化的浮冰则反照率有所降低。新冰的反照率较低, 有积雪覆盖的新冰反照率迅速增加。比较不同波段的反照率, 发现融化期由于积雪含水量较大, 增加了对近红外辐射的吸收, 降低了该波段的反照率。结合卫星遥感(AMSR-2)和人工观测的海冰密集度, 发现区域平均的反照率主要取决于海冰密集度, 然而也受下垫面物理特征影响, 例如2月底至3月初形成的新冰, 反照率只有老冰的1/3— 1/2。新冰形成, 会直接增加海冰密集度, 但由于其反照率较低, 对空间平均反照率的贡献较小。因此, 若要建立合理的冰水混合区的反照率参数化方案, 必须充分考虑海冰类型和冰面积雪的物理状态, 并考虑反照率的波长依赖性。     

Radiometric investigation of different snow covers in Svalbard

This paper examines the relationship between reflectance and physical characteristics of the snow cover in the Arctic. Field data were acquired for different snow and ice surfaces during a survey carried out at Ny-Ålesund, Svalbard, in spring 1998. In each measurement reflectance in the spectral range 350 - 2500 nm, snow data (including temperature, grain size and shape, density and water content), surface layer morphology, and vertical profile of the snow pack were recorded detailed analysis of reflectance based on the physical was performed. Field reflectance data were also re-sampled at the spectral intervals of Landsat TM to compare the ability of identifying different snow targets at discrete wavelength intervals. This analysis shows that reliable data on snow structure and thickness are necessary to understand albedo changes of the snow surfaces.     

Sedimentological and stratigraphic investigations of a sequence of 106 varves from glacial Lake Assiniboine,Saskatchewan

Sediments retrieved from a long core on the floor of glacial Lake Assiniboine, Saskatchewan, expose 106 couplets, consisting of thick, light coloured, silt-rich beds and thin, dark, clay-rich beds. The couplets contain sharp lower and upper contacts of the silt bed, silty and clayey laminations within both the silt and clay beds, and ice-rafted debris in the silt beds, which are features characteristic of glacial varves.Seasonal variations in runoff are reflected in grain size profiles of individual silt beds in the varves. Mean grain size maxima in the lower portion of the silt bed suggest that snow accumulation during the previous winter had been substantial and that a warm spring combined with a rapid melting rate generated significant volumes of nival meltwater runoff. Coarse laminae higher in the silty part of the couplet imply that substantial meltwater inflow was produced by summer melting of glacier ice.Vertical trends in clay bed thicknesses, silt bed thicknesses, and total couplet thicknesses were strongly influenced by the proximity of meltwater inflow channels and lake depth. These interpretations, and correlation of the core to varve exposures at the surface, formed the framework for a paleohydrological reconstruction. Close to 11,000 BP, ice dammed the outlet of glacial Lake Assiniboine and the water depth rose about 2 m yr^–1. Eventually the lake became deep enough for couplets to form. Varve years 1–40 contain thick clay beds, silt beds, and couplets as a result of the proximal inflow of meltwater. A decline in silt bed and couplet thicknesses from varve years 41–85 occurred in response to ice retreat and more distal inflow. Varve deposition ceased in the shallow part of the basin probably because underflow currents from the distal source were redirected. Varve years 86–106 are distinguished by an increase in silt bed and couplet thicknesses and a decrease in clay bed thickness caused by a reduction in water depth and a return to proximal inflow. Varved sedimentation terminated when Lake Assiniboine drained through the Assiniboine valley to Lake Agassiz.     

泥石流地声参数传播特征值的测试与分析

应用新的地声参数测试仪,在现场采集了多阵泥石流地声信号,并对数据进行了初步分析处理,提出泥石流地声参数值的大小与检测距离有关,地声波的衰减系数与埋设传感器地点的岩体质地有关,利用泥石流地声随距离变化的衰减系数,从而建立泥石流怕报警门槛值。