Debris entrainment by basal freeze‐on and thrusting during the 1995–1998 surge of Kuannersuit Glacier on Disko Island,west Greenland

Kuannersuit Glacier, a valley glacier on Disko Island in west Greenland, experienced a major surge from 1995 to 1998 where the glacier advanced 10·5 km and produced a ～65 m thick stacked sequence of debris‐rich basal ice and meteoric glacier ice. The aim of this study is to describe the tectonic evolution of large englacial thrusts and the processes of basal ice formation using a multiproxy approach including structural glaciology, stable isotope composition (δ¹⁸O and δD), sedimentology and ground‐penetrating radar. We argue that the major debris layers that can be traced in the terminal zone represent englacial thrusts that were formed early during the surge. Thrust overthrow was at least 200–300 m and this lead to a 30 m thick repetition of basal ice at the ice margin. It is assumed that the englacial thrusting was initiated at the transition between warm ice from the interior and the cold snout. The basal debris‐rich ice was mainly formed after the thrusting phase. Two sub‐facies of stratified basal ice have been identified; a lower massive ice facies (S_M) composed of frozen diamict enriched with heavy stable isotopes overlain by laminated ice facies (S_L) consisting of millimetre thick lamina of alternating debris‐poor and debris‐rich ice. We interpret the stratified basal ice as a continuum formed mainly by freeze‐on processes and localized regelation. First laminated basal ice is formed and as meltwater is depleted more sediment is entrained and finally the glacier freezes to the base and massive diamict is frozen‐on. The increased ability to entrain sediments may partly be associated with higher basal freezing rates enhanced by loss of frictional heat from cessation of fast flow and conductive cooling through a thin heavily crevassed ice during the final phase of the glacier surge. The dispersed basal ice facies (D) was mainly formed by secondary processes where fine‐grained sediment is mobilized in the vein system of ice. Our results have important implications for understanding the significance of basal ice formation and englacial thrusting beneath fast‐flowing glaciers and it provides new information about the development of landforms during a glacier surge. Copyright © 2010 John Wiley & Sons, Ltd.     

Rock glacier dynamics in marginal periglacial environments

Vertical electric sounding, bottom temperature of winter snowcover (BTS) and ground thermal measurement, debris surface analysis and a differential global positioning system (DGPS) survey were performed on the Posets rock glacier (Pyrenees) between 2001 and 2008. High precision records of horizontal and vertical movements of the rock glacier were measured using a DGPS on ten steel rods. Total and annual average displacements and thickness changes for each control point were derived from the field survey. Horizontal and vertical displacement rates in different sectors of the rock glacier were compared, and these compared with thermal, structural and morphological maps. The inferred surface deformation was characterized by extensional and compressive flows in which two dynamic types were found. The first type of movement is defined by the slide and flows related to the existence of an ice body over the frost body. The second dynamic type involved the displacement generated by deformation of the frozen body. The study attempts to understand the surface movement and dynamics of rock glaciers in marginal cold environments and their usefulness as environmental geoindicators. Copyright © 2010 John Wiley & Sons, Ltd.     

THE CLIMATIC CONDITIONS OF POLAR-TYPE GLACIERS DEVELOPMENT IN CHINA

ＴＨＥＣＬＩＭＡＴＩＣＣＯＮＤＩＴＩＯＮＳＯＦＰＯＬＡＲ－ＴＹＰＥＧＬＡＣＩＥＲＳＤＥＶＥＬＯＰＭＥＮＴＩＮＣＨＩＮＡ￥ＨｕａｎｇＭａｏｈｕａｎ（黄茂桓）（ＬａｎｚｈｏｕＩｎｓｔｉｔｕｔｅｏｆＧｌａｃｉｏｌｏｇｙａｎｄＧｅｏｃｒｙｏｌｏｇｙ，ｔｈｅＣ...     

Arctic-alpine brown soils as a source of palaeoenvironmental information: Further 14C dating and palynological evidence from Vestre Memurubreen,Jotunheimen, Norway

¹⁴C dating and pollen analytical evidence is presented relating to the usefulness of arctic-alpine Brown Soils for palaeoenvironmental reconstruction. A present-day soil has been examined together with its continuation beneath the outermost ?Little Ice Age’? end moraine of the glacier Vestre Memurubreen at a location well above the tree-line in the mid-alpine belt of southern Norway. Fourteen ¹⁴C dates from chemically-fractionated soil samples, which range in age from 495 ± 55 ¹⁴C yr in the uppermost 1 cm to > 4000 ¹⁴C yr within 13 cm of the buried soil surface, demonstrate near-linear age/depth gradients in the palaeosol. Continuous development of the palaeosol over at least 5000 calendar yr prior to burial confirms that Vestre Memurubreen attained its Neoglacial maximum extent in the ?Little Ice Age’?. Pollen stratification in buried and unburied profiles indicates a single vegetation change from a low-alpine dwarf-shrub heath to a mid-alpine ?grass’? heath, reflecting an altitudinal lowering of vegetation belts and a possible climatic cooling of 2-4°C. Surface additions of allochthonous (aeolian) mineral particles appear to have contributed to soil development, whilst mixing processes have been relatively unimportant at this site. The immobilisation of resistant organic residues and the ineffectiveness of biological and chemical activity are major reasons for the preservation of a palaeoenvironmental record in these high altitude soils.     

Analysis of flute forming conditions using ice sheet reconstructions and field techniques

Basal shear stress and sediment strength associated with the development of glacial flutes exposed during the 20th century in the Saskatchewan Glacier Valley Alberta, Canada, were determined by comparing reconstructed ice thicknesses, basal shear stresses, and field properties of sediments with the morphologically similar Kiwa Glacier Valley, British Columbia, Canada, where flutes are absent. Reconstructed subglacial conditions in these two valleys were compared to understand why flutes were developed in the former and not the latter. Using an existing topographic map of each glacier, equations for a series of longitudinal profile lines were determined to represent the existing ice surface. A previous ice surface, identified by trimlines along the valley walls, was reconstructed by applying the equations of longitudinal profile lines from the existing ice surface to a previous terminus between 5 and 10 km downvalley. After subtracting the elevation of the land surface (determined from topographic maps) from the reconstructed glacier surface, and calculating former ice surface slope, ice thickness and basal shear stress distributions were determined. Sediment texture and the location of flutes on a morainal topographic high, downglacier from a proglacial lake basin, allowed high porewater pressures to develop as glaciers extended to terminus positions in the Saskatchewan Glacier Valley. Sediment strength was reduced sufficiently below values of reconstructed shear stress plots to allow deformation creating flutes. The absence of a similar topographic high and different sediment textural characteristics in the Kiwa Glacier Valley resulted in lower porewater pressures and consequently less reduction in sediment strength preventing the development of glacial flutes despite higher shear stress values here. Results indicate that the degree to which sediment characteristics and porewater pressure allow reduction of subglacial sediment strength relative to basal shear stress is important in determining conditions when flutes may develop.     

Recent behaviour of the Debeli Namet glacier,Durmitor, Montenegro

A small cirque glacier is present in a north‐east facing cirque on the mountain of ?ljeme (2455 m a.s.l.) in the Durmitor massif, Montenegro. Sediment ridges in front of this glacier are interpreted as moraines and can be attributed to recent glacier activity over the past 130 years. Lichenometry was applied to determine the relative ages of different moraines using Aspicilia calcarea agg. One set of moraines dates from about 1878 AD, whilst another set of inner moraines dates from about 1904 AD. The most recent moraines appear to have formed within the last 11 years in front of an active glacier margin. Copyright © 2007 John Wiley & Sons, Ltd.     

中国天山冰川变化脆弱性研究

冰川是重要的淡水资源,对社会经济发展和生态环境影响显著,而其变化的脆弱性也关乎区域生态服务和经济可持续发展。本文以中国天山为例,基于脆弱性的暴露度、敏感性、适应能力构建涵盖自然地理特征、人口状况、社会经济水平、农业发展和社会服务等因素的冰川变化脆弱性框架,并以此针对性构建评价指标体系,探析天山冰川变化脆弱性的空间特征,采用地理探测器模型探讨自然、社会、经济和人口等因素对冰川变化适应能力的影响及交互作用。结果表明：① 脆弱性等级由西部地区向东部地区呈降低趋势,且水平差异显著。天山东部地区脆弱性最低、中部地区次之、西部地区较高。② 暴露度、敏感性和适应能力在空间上分别存在明显正相关与负相关,表明区域范围内冰川变化具有高暴露、高敏感地区往往适应能力较低,进而导致脆弱性较高;反之,脆弱性较低。③ 天山应对冰川变化能力的空间异质性是自然、社会、经济和人口因素共同作用的结果。其中,第二、三产业产值、城镇人口数、城镇固定资产投资与年末单位从业人员等因素具有主导作用。     

基于无人机摄影测量的梅里雪山明永冰川末端表面高程动态监测

位于横断山区的梅里雪山地区,受地形与气候的影响,该地区光学遥感及微波遥感应用较为受限。论文基于大疆精灵4RTK无人机搭配中海达UBase,于2018年11月9日和2019年11月12日对梅里雪山地区明永冰川末端开展了2期摄影测量,估算冰川消融区表面高程变化,监测冰川动态变化。研究结果表明:冰川区表面形态在不同位置有显著差别,航测冰川区中下部大量表碛覆盖,有少量沿冰川主流线方向发育的裂隙;航测冰川区中上部表碛覆盖较少,大量横向裂隙发育。2018年11月至2019年11月,明永冰川末端表面高程平均变化-1.67 m。冰川表面高程变化空间分布差异显著,在航测冰川区上部高程差存在正负交替现象,航测冰川区中部以减薄为主,而航测冰川区下部以增厚为主。与高亚洲地区其他山系冰川变化对比,梅里雪山地区是冰川表面高程变化最显著的地区。     

Vulnerability of glacier change in the Tianshan Mountains region of China

The glacier is a crucial freshwater resource in arid and semiarid regions,and the vulnerability of the glacier change is intimately linked to regional ecological services and so-cio-economic sustainability.Taking the Tianshan Mountains region in China as an example,a basic framework for studying the vulnerability of glacier change was constructed so as to address factors such as physical geography,population status,socio-economic level,agri-cultural development,and social services.The framework was based on key dimensions,that is,exposure,sensitivity,and adaptability,and this constituted a targeted evaluation index system.We examined the spatial structure and spatial autocorrelation of the glacier change vulnerability using ArcGIS and GeoDa software.The influence and interaction of natural,so-cial,economic,population and other factors on glacier change adaptability was examined using the GeoDetector model.The results suggested the following:(1) The vulnerability level decreased from the western region to the eastern region with significant differences between the two regions.The eastern region had the lowest vulnerability,followed by the central re-gion,and then western region which had the highest vulnerability.(2) Significant positive and negative correlations were found between exposure,sensitivity,and adaptability,indicating that the areas with high exposure and high sensitivity to glacier change tended to have a low adaptive capacity,which led to high vulnerability,and vice versa.(3) The spatial heterogeneity regarding the ability to cope with glacier change reflected the combined effects of the natural,social,economic,and demographic factors.Among them,factors such as the production value of secondary and tertiary industries,the urban population,urban fixed-asset investment,and the number of employees played major roles regarding the spatial heterogeneity of glacier change.