开河期冰盖纵向冰缝形成机理

春季河道武开河可能导致冰坝形成,至今仍缺乏以力学机制为基础的开河预测方法。春季河道径流增加导致与岸壁冻结的冰盖底部产生上举力,并引起纵向冰缝产生。利用力学分析中弹性基础上的梁理论对开河期冰盖纵向冰缝形成机理进行了研究,提出了纵向冰缝间距解析表达式,可用于开河期冰盖断裂预测。应用原型观测资料对提出的纵向冰缝间距理论表达式进行了验证分析。研究结果表明,开河期纵向冰缝间距计算值与实测值吻合较好。     

武开河的边壁阻力判别准则

春季河道武开河可能导致冰坝形成, 但至今仍缺乏以力学机制为基础上的开河预测方法. 根据水动力学及固体力学基本理论, 提出了以河道纵向冰缝处冰层残余抗剪强度为基础的边壁阻力判别准则, 可用于武开河的开河预测. 应用黄河河曲段1987年和1988年冬季原型观测资料对纵向冰缝处的残余抗剪强度进行了分析研究, 并进而提出了其临界值. 观测资料包括开河日期, 河道宽度, 流量及冰盖厚度. 结果表明, 初始开河期冰缝处的剪切应力年际变化不大.     

基于适体坐标变换的二维河冰模型

为精确模拟流动边界条件,克服边界形状复杂、长宽尺度相差悬殊及由于水位变化引起计算边界变化等困难,针对天然河道边界弯曲复杂等特点,应用水动力学和热力学等原理,建立了适体坐标下的二维河冰数值模型,模型主要包括流速场,水温沿河道变化,水内冰浓度分布,面冰输移,冰盖推进、稳定和消融,冰盖下冰的输移、堆积和冲蚀等,考虑了冰盖底部水中冰堆积和冰盖前沿形状对封冻过程的影响。采用MacCormack步进格式计算方法,并应用黄河河曲段实测资料对数值模拟结果进行了验证。验证结果表明,提出的数值模型能较好地体现河道的封冻过程。     

冰雷达探测研究南极冰盖的进展与展望

南极冰盖是地球上最大的陆缘冰体,其物质收支和稳定性对全球气候变化和海平面升高有重要的影响。冰雷达,或称无线电回波探测,是冰川学家调查南极冰盖冰下特征的主要方法。在过去的50年里,冰雷达被广泛用于测量冰盖厚度、内部构造和冰下地貌,这些参数是计算冰盖体积和物质平衡、重建过去冰雪积累和消融率以及冰盖动力和沉积过程的基础。现在,冰雷达测量覆盖了南极绝大部分区域,极大地提升了人们对南极冰盖和全球系统间相互作用的理解。首先,简要介绍了冰雷达及其技术发展,然后着重评述了冰雷达在探测研究南极冰盖厚度和冰下地形、内部反射层、冰下湖和冰下水系、冰床粗糙度以及冰晶组构上的进展。最后,对未来冰雷达探测研究南极冰盖的前景进行了展望,并给出我国的现状。


     

南大西洋渐新世初碳酸盐记录(ODP 1263站)

渐新世初期,南极大陆在短时间内出现永久性冰盖,地球由两极无冰进入到单极有冰的特殊时期。越来越多的研究表明,这一重大气候转型事件与大气CO2及大洋碳储库的变化密切相关。南大西洋ODP 1263站碳酸钙软泥的粒度分析揭示了在渐新世初期发生的强烈碳酸盐溶解事件,碳酸盐溶解超前于底栖有孔虫氧同位素重值约100 ka,显示碳酸盐溶解事件先于南极冰盖的形成。由于碳酸钙泵的作用,碳酸盐的溶解会消耗大量的大气CO2,从而可能驱动了气候的快速变冷,导致南极大陆永久性冰盖发育。     

湖北省宜昌县震旦系南沱组成因的新认识

在峡东王丰岗南沱组剖面上有一些杂砾岩透镜体和一些水道砂岩透镜体。这些是冰水环境的产物。在南沱组与莲沱组的界线上,见到了几个骑线砾石。这是冰陆环境的有力证据。由此可见,早期主要是冰陆环境,冰川刨蚀和剥蚀作用占主导,沉积作用是次要的。随着气温的回升,冰盖逐渐后退。当冰盖前沿退到研究区内,或刚退出本区时,就形成了本区冰期的主要沉积。因此,可以认为,本区南沱组杂砾岩主要是近源冰海相沉积。     

早更新世青藏大冰盖存在的证据

一、关于青藏大冰盖研究的简要历史及现状 青藏高原在整个第四纪地质发展过程中,是否曾形成统一的大冰盖(简称大冰盖,下同)?是一个自19世纪末叶以来,国内外地学界十分关心和长期存在争议的重大地学问题。一些研究者侧重于以现代地形、气候条件为依据,推测为无大冰盖形成(Sven Hedin,1907等);一些研究者则错误地把中晚更新世山谷、山麓冰川形成的冰     

青藏高原第四纪大陆冰盖形成的野外证据

青藏高原第四纪大陆冰盖形成的各种各样冰川遗迹,分布十分广泛。是重建和研究古大陆冰盖最有力的证据。目前发现和比较肯定的冰蚀遗迹有:冰蚀平原、冰蚀丘陵、U形谷、冰蚀洼地、冰盆、冰阶、冰笕、冰坡和基岩鼓丘等。冰碛遗迹主要有:块砾碛、鳍碛(新类型)、漂砾碛(新类型)、冰水砂砾岩、和冰碛丘陵、冰台及侧碛堤等。从大陆冰盖遗迹分布连续和普遍发育,证明青藏高原在第四纪时期曾形成连绵一片的统一的大陆冰盖。大陆冰盖形成的时期为早更新世,形成时的古雪线的海拔高度最多在2000m左右,冰川类型属于海洋性统一大陆冰川。     

冰盖下水流垂线流速分布规律研究

河道中冰盖显著改变了水流流动结构.采用k-ε紊流模型建立了冰盖下水流流动垂向二维数值模型;根据量纲分析理论提出了流速分布规律的影响因素;针对各种因素的不同组合进行了数值计算,并对其流动特性如最大流速点位置、冰区及床面区平均流速等进行了分析研究;对冬季封冻河道的二点测流法精度进行了理论分析.研究结果表明,冰盖下水流的纵向流速在流动核心区并不遵循对数分布规律,同时揭示了冰盖底部与河床的相对粗糙比、河床相对粗糙度及雷诺数对流速分布规律的影响.     

东南极冰盖上新世大规模退缩事件

笔者近年对东南极内陆格罗夫山(Grove Mountains)开展了上新世以来冰盖表面波动的综合研究,运用冰川地质、地貌、土壤、沉积岩、孢粉组合及宇宙核素等各种方法手段,提出东南极大冰盖形成以后并非稳定演化至今,而在上新世早期时发生过大规模退缩,其前缘至少曾经退缩到格罗夫山地区,距现今冰盖边缘约400 km。之后,冰盖又迅速膨胀,到距今2.3 Ma时,冰面至少超过现今高度约400 m。以后冰面缓慢平稳下降,至1.6 Ma时,东南极冰盖进入第四纪振荡期,但重新上升的冰面再也没有超过现今高度的100 m以上。东南极冰盖大规模消融事件在全球尺度上也有所响应,例如北半球大冰盖形成,青藏高原整体剧烈隆升,塔里木盆地黄土出现等。这类行星尺度的气候变化可能与直布罗陀海峡关闭与地中海盐化事件,巴拿马地峡关闭等大地构造事件有关。     

天山南坡科其喀尔冰川消融区运动特征分析

基于2009年5月至2011年10月科其喀尔冰川的花杆观测资料,对其消融区的表面运动特征进行分析. 结果表明：冰川消融区的年水平运动速度最大值为86.69 m·a^-1,年垂直运动速度最大值为15.34 m·a^-1,均出现在冰川海拔4 000~4 200 m的消融区上部;在靠近冰川末端的冰舌下部,受冰量补给减弱、厚层表碛覆盖等影响,冰川运动缓慢,年水平运动速度小于5 m·a^-1,而垂直运动速度值小于2 m·a^-1. 大多数横剖面的水平运动速度具有从中部向边缘逐渐减小的特征,而有的剖面却出现局部速度增大的区域. 整体而言,冰川水平及垂直运动速度随海拔降低而减小,符合冰川运动的一般规律,但主要受地形作用的影响,垂直运动速度随海拔的变化会出现波动. 消融期月水平运动速度与同期气温和降水的变化具有一定的相关性,可能反映出气候快速变化对冰川运动的影响.     

Sedimentation in ice-covered Lake Hoare, Antarctica

The sedimentation mechanisms that occur in ice-covered Lake Hoare, Antarctica are examined, to determine how sediment enters the lake, and how the sedimentation pattern affects blue-green algal growth at the lake bottom. The 3 m-thick ice cover contains pebbly sand as much as 2 m below the surface. Sediment with similar texture and mineralogy is found at the lake bottom. This evidence, together with the lack of sediment in the inflowing stream and the markedly different texture of sediment from the other terrains around the lake suggest that most of the sediment at the lake bottom comes in through the ice cover. Sand grains intermittently migrate through porous ice on the surface, water-filled vertical gas-channels penetrating two-thirds of the ice cover, and possibly through cracks in the ice that act as conduits. The algae at the lake bottom are able to survive in part because sediment that comes through the ice cover does not obliterate them.     

带分舱板海上风电筒型基础承载特性试验研究

为正确评估分舱对于海上风电筒型基础承载特性的影响,对有、无分舱板的相同钢筒进行室内模型对比试验,分别得出在水平荷载及弯矩共同作用下和竖直荷载作用下的荷载-位移曲线,及筒内外侧壁土压力及顶盖土压力的分布规律,同时进行有限元分析模拟。试验和计算结果表明：在竖向荷载作用下,分舱板使基础的极限承载力略有提高,分舱板分担了筒顶盖和筒壁的竖向承载,降低了顶盖的承载比例;在水平荷载和弯矩共同作用下,分舱板为筒型基础提供了较大的抗拔承载力,使筒型基础在水平和弯矩荷载作用下的极限承载力提高了20.2%,降低了极限状态下的水平位移和倾角。总之,分舱板不但可以提高海上风电基础施工浮运过程的稳定性,还可以提高基础运行时的极限承载力。     

水力与热力耦合的开河判别准则

寒带河流在春季往往会由于水力和热力因素的剧烈变化而引发冰盖溃决,国内俗称为"武开河"。这一现象会导致冰坝形成,造成巨大的自然灾害。通过冰盖断裂机理的力学分析,耦合热力对冰盖材料性质的影响,提出了一种开河判别方法。应用黄河河曲段实测原型资料进行验证分析,结果表明该准则判定结果与实际相符,是一种行之有效的判别准则。     

Development of low–centred ice–wedge polygons in the northernmost Ungava Peninsual, Queébec, Canada

Morphological and vegetation mapping and stratigraphic studies were carried out on a 60 by 250 m low–centered polygon field on a flood–plain of the Riviére Deception in the continuous permafrost zone of northernmost Ungava. Analyses of grain size, water and ice content, deformation structures, and macrorests were carried out on drill–core samples, up to a maximum depth of 3.19 m, and radiocarbon dates were obtained from several peat horizons. Five different vegetational habits were identified: uplifted banks, ice–wedge fissures, hummocky centres, wet polygon centres, and water ponds. The stratigraphic analyses revealed many sand layers and organic layers, alternating with a few layers of segregated ice. In the raises banks, brown fen peats represent former wet conditions prior to bank uplift. Total ice volumes of the core samples from polygon centres and banks averaged 60%, and were generally in the form of pore ice. Segregated ice was concentrated in ice wedges. The Low gradient of the polygon field and the shallow active layer are responsible for impded drainage. The origins of this isolated low–centred polygon field are discussed in terms of special local terrain conditions. River flooding since glacio–isostatic emergence at 6000 BP repeatedly spread alluvial sands onto the low flood–plain, which thus became progressively built up to its present elevation. Peat layers buried by these alluvial sands have permitted the changing local drainage conditions to be radiocarbon–dated for the last 2600 years for the core sites. Impeded drainage, low winter temperatures, probable thin snow cover, rapid sedimentation of flood–plain sands, and high volumetric ice contents have created the critical thermal regime necessary for repeated frost cracking in a polygonal pattern, with concomitant ice–wedge dev–elopment. Ice wedges developed at least as early as 2200 BP, causing the formation of low banks. Further growth of ice wedges deformed the peat and sand layers on the bank margins and led to the rise of the latter to heights of 0.5 to 1 m above the intervening low wet polygon centres. More water was then collected in the depressions, leading to a transformations of the vegetation cover from mossy heath to sphagnum bog, wet fen, sedge-covered ponds, and eventually in some cases to open-water pools. The stratigraphic evidence suggests that several generations of high banks formed and disappeared and that their position has changed. Deformation by continued ice–wedge growth has been insignificant since 1000 BP, However. A relatively thick surface peat layer also indicates that sand layers have not been contributed to the polygon field by flooding since ? 500 BP.     

土壤的冷生构造及其对阿拉斯加土地利用的意义

Cryogenic structure (patterns made by ice inclusions) in seasonally frozen and permafrost-af-fected soils result from ice formation during freezing. Analysis of cryogenic structures in soils is essential to our understanding of the cryogenic processes in soils and to formulating land use management interpretations. When soils freeze, the freezing front moves downward and attracts water moving upward resulting in mainly horizontal lenticular ice formation. Platy and lenticular soil structures form between ice lenses in upper active layer. The reticular soil structure usually forms above the permafrost table caused by freeze-back of the permafrost. The upward freeze-back resulted in platy soil structure and the volume changes following the annual freeze-thaw cycle resulted in vertical cracks. The combined result is an ice-net formation with mineral soils embedded in the ice net. The upper permafrost layer that used to be a part of the active layer has an ice content exceeding 50% due to repeated freeze-thaw cycles over time. The mineral soils appear in blocks embedded in an ice matrix. The permafrost layer that never experienced the freeze-thaw cycle often consists of alternate layers of thin ice lens and frozen soils with extreme hard consistence and has relatively lower ice content than the ice-rich layer of the upper permafrost. Ice contents and thaw settling potentials associated with each cryogenic structure should be considered in engineering and land use interpretations.     

印度查莫利“2·7”冰岩山崩堵江溃决洪水灾害链研究

2021年2月7日,印度查莫利北部里希恒河发生高位冰岩山崩堵江溃决洪水灾害链,造成下游20 km外的水电站和桥梁设施破坏,死亡、失踪人口近200人。文章运用多期高分辨率遥感影像,对比分析了印度查莫利里希恒河流域高位冰岩山崩灾害发生前后滑源区、堆积区变化特征,初步探讨了山崩的运动过程。结果显示:2013年以前,崩滑体蠕滑位移量较小,其表面冰雪覆盖层裂缝发育不明显;2013—2017年,崩滑体蠕滑位移量显著增加,冰雪覆盖层可见多达62处大小不一的冰裂缝,最长513 m;2021年2月5日卫星影像显示这些冰裂缝已发生连接、贯通,最大宽度为15 m,并于2月7日发生失稳、破坏。据滑后遥感影像,该崩滑体由4组不同方向的大型结构面切割而成,面积约0.32 km2,平均厚度约为70 m,体积约23×106 m3。崩滑体失稳、解体后以碎屑流沿沟谷向下高速运动,受地形拦挡,部分碎屑颗粒在地形急变带堆积且形成堰塞坝。堰塞坝体溃决后,形成山洪灾害。     

裂隙型单斜介质中弹性系数的计算及波的传播特性研究

根据Hudson等关于裂隙介质弹性系数计算的扰动理论及Bond变换矩阵原理，给出了各向同性介质中含多组垂直裂隙时等效弹性系数的计算方法。计算了含两组斜交的垂直裂隙形成的单斜各向异性介质中的等效弹性系数，并根据Christoffel方程推导、得出水平面内平面波传播的相速度和群速度随方位变化的特性。     

Stabilized equal low-order finite elements in ice sheet modeling – accuracy and robustness

We investigate the accuracy and robustness of one of the most common methods used in glaciology for finite element discretization of the ??-Stokes equations: linear equal order finite elements with Galerkin least-squares (GLS) stabilization on anisotropic meshes. Furthermore, we compare the results to other stabilized methods. We find that the vertical velocity component is more sensitive to the choice of GLS stabilization parameter than horizontal velocity. Additionally, the accuracy of the vertical velocity component is especially important since errors in this component can cause ice surface instabilities and propagate into future ice volume predictions. If the element cell size is set to the minimum edge length and the stabilization parameter is allowed to vary non-linearly with viscosity, the GLS stabilization parameter found in literature is a good choice on simple domains. However, near ice margins the standard parameter choice may result in significant oscillations in the vertical component of the surface velocity. For these reasons, other stabilization techniques, in particular the interior penalty method, result in better accuracy and are less sensitive to the choice of stabilization parameter. During this work, we also discovered that the manufactured solutions often used to evaluate errors in glaciology are not reliable due to high artificial surface forces at singularities. We perform our numerical experiments in both FEniCS and Elmer/Ice.     

An anisotropic elastic‐decohesive constitutive relation for sea ice

Thermodynamic growth or melt and mechanical redistribution due to lead opening or ridge formation shape the thickness distribution of the Arctic ice cover and impact the overall strength of pack ice. Specifically, the deformation and strength of ice are not isotropic but vary with the thickness and lead orientation. To reflect these facts, we develop an anisotropic, elastic‐decohesive constitutive model for sea ice together with a model to describe an oriented, ice thickness distribution. The tight connection between the mechanical response and the thickness distribution is an improvement over a previous model that only depended on the average ice thickness. The model describes mechanical responses anisotropically in both the elastic and failure regimes. In the elastic regime, the constitutive relation implicitly reflects strong and weak directions of the pack ice depending on the distribution of thin ice (including open water) and thicker ice (e.g., multi‐year ice or ridges). In the failure regime, the model predicts both failure initiation and the lead orientation. Evolution from initial failure to complete failure when traction‐free crack surfaces are formed is also modeled. Crack or lead width is determined during the evolution. Various examples of failure surfaces are presented to describe the behavior of modeled ice when the thickness distribution varies. The model predictions are also illustrated and compared with previous modeling efforts by examining regions of ice under idealized loading. Copyright © 2015 John Wiley & Sons, Ltd.