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1.
Rock glaciers occur as lobate or tongue-shaped landforms composed of mixtures of poorly sorted, angular to blocky rock debris and ice. These landforms serve as primary sinks for ice and water storage in mountainous areas and represent transitional forms in the debris transport system, accounting for ~ 60% of all mass transport in some alpine regions. Observations of active (flowing) alpine rock glaciers indicate a common association between the debris that originates from cirque headwalls and the depositional lobes that comprise them. The delivery of this debris to the rock glacier is regulated primarily by the rate of headwall erosion and the point of origin of debris along the headwall. These factors control the relative movement of individual depositional lobes as well as the overall rate of propagation of a rock glacier. In recent geophysical studies, a number of alpine rock glaciers on Prins Karls Forland and Nordenskiöldland, Svalbard, Norway, and the San Juan Mountains of southwest Colorado, USA, have been imaged using ground penetrating radar (GPR) to determine if a relationship exists between the internal structure and surface morphology. Results indicate that the overall morphologic expression of alpine rock glaciers is related to lobate deposition during catastrophic episodes of rockfall that originated from associated cirque headwalls. Longitudinal GPR profiles from alpine rock glaciers examined in this study suggests that the difference in gross morphology between the lobate and tongue-shaped rock glaciers can be attributed primarily (but not exclusively) to cirque geometry, frequency and locations of debris discharge within the cirque, and the trend and magnitude of valley gradient in relation to cirque orientation. Collectively, these factors determine the manner in which high magnitude debris discharges, which seem to be the primary mechanism of formation, accumulate to form these rock glaciers.  相似文献   

2.
Uncertainty remains if ice–free marginal areas existed on the west coast of Svalbard during the Late Weichselian. Field mapping and correlation to well dated raised beach sequences on nearby Brøggerhalvøya reveal the existence of two generations of raised beach deposits on northern Prins Karls Forland. Distinct beach ridges rise up to the inferred Late Weichselian marine limit at 18 m a.s.l. Discontinuous pre–Late Weichselian beach deposits rise from the Late Weichselian marine limit up to approximately 60 m a.s.l. Expansion of local glaciers during the Late Weichselian is indicated by the limited distribution of a till that overlies parts of the older beach sequence. Stratigraphic data and chronological control indicate deposition in a shallow marine environment before 50 ka bp . Correlation to stratigraphic sites on western Svalbard suggests deposition at c . 70 ±10 ka. Glaciotectonic structures disclose expansion of local glaciers into the For–landsundet basin during stage 4 or late stage 5 high relative sea level. Palaeotemperature estimates derived from amino acid ratios indicate that during the time interval c . 70 to 10 ka the area was exposed to cold subaerial temperatures with low rates of racemization. Pedogenesis and frost–shattered clasts at the contact between c . 70 ka deposits and Holocene deposits further indicate a prolonged period of subaerial polar desert conditions during this time interval. The evidence suggests that the Barents Sea ice sheet did not extend across northern Prins Karls Forland during the Weichselian. It is inferred that during the Late Weichselian, ice was drained throughout the major fjords on the west coast of Svalbard and that relatively large marginal areas experienced polar desert conditions and minor expansions of local glaciers.  相似文献   

3.
Frich, Povl and Brandt, Erik: Holocene talus accumulation rates,—and their influence on rock glacier growth. A case study from Igpik, Disko—West Greenland. Geografisk Tidsskrift 85: 32–44 Copenhagen, October 1985.

The Igpik area is located ten km east of Godhavn on the south-coast of the island Disko. Geologically the area is dominated by Tertiary basalt formations.

A general geomorphological classification of this area, which covers approximately three square kms, has been made. Based on radiocarbon ages of former marine levels in the Disko Bugt area, the beginning of talus accumulation has been determined for two talus cones situated on raised beaches. They have ages of 5800 and 7900 14C y. B.P. Using theodolite readings, the volumes of three different talus cones have been determined and two average talus accumulation rates have been calculated for the cones located on raised beaches. These values are transformed into an average Holocene rockwall retreat rate of 0.0005 and 0.0015 m/year, respectively. The total volume of two lobate rock glaciers is calculated to be 2.2 mill, cu.m and as they are located inside 9000 years old local moraines, the average Holocene mass-transfer through the third talus cone has been estimated to 1.4 106 tons×m/sq.km/y. Finally the results are discussed, with reference to other areas, and as a possible threshhold for the initiation of rock glaciers.  相似文献   

4.
Modification of Lateglacial and Holocene talus sheets by debris flows and gully incision on Mynydd Du, Wales, has resulted in a convergence of upper slope form characterised by an upper rectilinear slope gradient of 36°±3° and a range of concavities of c. 0.1–0.2. In most cases, gully incision and accumulation of debris cones have led to an increase in slope concavity. Evidence for talus erosion, reworking and redeposition on the upper slope emphasises secondary reworking processes, as well as primary talus accumulation on the upper slope, and permits construction of a model of talus development at Mynydd Du. On the basis of talus volume, calculation of the first rockwall retreat data set for southern Britain suggests that c. 7.1 m (84%) of overall rockwall retreat (8.5 m) took place during the Lateglacial, and only c. 1.4 m (16%) occurred during the Holocene. These figures imply that Lateglacial retreat rates ranged from 1.01 to 2.44 m ka−1, with an overall mean rate of 1.23 m ka−1. In contrast, Holocene rockwall retreat rates range from 0.10 to 0.17 m ka−1, with a mean rate of 0.12 m ka−1. Approximately 27% of cliff retreat is attributed to microgelivation. While similar to Holocene and present-day alpine environments, these Lateglacial retreat rates are one order of magnitude higher than most equivalent values for arctic sites. This reflects both ‘alpine-style’ diurnal freeze–thaw activity on Mynydd Du during the Younger Dryas and paraglacial rock-mass instability following deglaciation. Assuming an exponential decline in rockwall sediment release, it is estimated that approximately half the talus had accumulated within c. 1 ka of deglaciation. At one site, paraglacial talus accumulation appears to have contributed significantly to the glacial sediment transport system of a subsequent ice advance. Present-day rates of rockwall retreat and talus accumulation by rockfall are estimated to be 0.014 and 0.022 mm yr−1 (m ka−1), respectively, similar to values for other British sites and markedly lower than Holocene rates of cliff recession due to microgelivation. By implication, the geomorphic significance of microgelivation may have been greatly underestimated in studies of inland rock-slope evolution in temperate, mid-latitude environments.  相似文献   

5.
The stratigraphic importance of fossils is never more apparent than in attempts to unravel the complexities of metamorphic terrains. The age and stratigraphic relationships of the thick metasedimentary and metavolcanic succession of Prins Karls Forland, western Svalbard, have been the subject of investigation and debate since the early part of this century (Hoel 1914; Craig 1916; Tyrrel 1924), and sharply different interpretations have been proposed (e.g. Harland et al. 1979; Hjelle et al. 1979). Until now, such interpretations have been unconstrained by palaeontological data, an understandable consequence of the metamorphic alteration undergone by these rocks. In this paper, we report the discovery of stratigraphically useful microfossils preserved in chert nodules from carbonaceous, dolomitic shales on northern Prins Karls Forland. These fossils have significant implications for the stratigraphic and structural interpretation of Forland metasediments, as well as for the more general problem of palaeontological prospecting in severely deformed and metamorphosed terrains, including those characteristic of the Archean Eon.  相似文献   

6.
Two raised marine sequences from Prins Karls Forland, western Svalbard, interpreted to have been deposited during part of isotope substage 5e (Eemian) and substage 5a, were studied for foraminifera content. Time constraints are given by 14C ages, infrared stimulated luminescence age estimates and amino acid ratios in subfossil marine molluscs. A diamicton (unit B) separates the two marine sequences and reflects an advancement of local glaciers sometime late in isotope stage 5. The two marine sequences contain diverse benthic foraminiferal faunas, indicating periods of a relatively warm and seasonally ice-free marine shelf environment. Compared to the lowermost sequence (unit A), the upper marine sequence (unit C) seems to reflect a more shallow environment that could have resulted from the global lowering of the sea level towards the end of isotope stage 5. Our results further emphasise the problem of biostratigraphic distinction between interglacial and interstadial deposits at high latitudes, with temperature conditions for substage 5a close to those of substage 5e and present conditions.  相似文献   

7.
Lichenometric measurements using Rhizocarpon ssp. were carried out on 20 talus slopes in the cirques of the Finstertal valley (Austria) at an elevation of 2300–3000 m a.s.l. The aim was to assess activity patterns on selected slopes and between the slopes of the study area, to find evidence of rockfall pulses in the last centuries and to calculate rockwall retreat rates. A calibration curve was derived from five sites of known age and adapted to the prevailing size of talus boulders. We measured the five largest lichens on more than 300 boulders and the percentage coverage of Rhizocarpon‐free clasts on more than 1000 test fields. Most of the investigated talus cones are characterized by moderate rockfall supply, with the apex being more active than the talus foot and moderate redistribution by avalanche and debris flows. Considerably enhanced activity was found under rockwalls influenced by permafrost, particularly on the north faces at an elevation of >2600 m a.s.l. At currently moderately active sites, boulder falls seem to have been slightly more frequent in the late nineteenth and first half of the twentieth century. In positions where permafrost is expected in the rockwalls, a weak maximum in the late nineteenth century and highly active present‐day conditions were found, the latter being assigned to current permafrost melt. Rockwall retreat rates derived from lichen coverage are between 400 and 1500 mm/ka which is in good concurrence with talus volume assessments, but higher than the rates derived from direct rockfall measurements. The rates derived from lichen coverage have to be taken with caution as the effects of debris redistribution are hard to quantify.  相似文献   

8.
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9.
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.  相似文献   

10.
This note reports the occurrence of two generations of 14C dated raised beach deposits at Pricepynten. southern Prins Karls Forland, western Svalbard, dated to < 12 Kya and >30 Kya. In addition two new 14C ages of ca. 9.2 and 1.8 Ky are presented from Myrilus eclulis and a buried peat deposit, respectively.  相似文献   

11.
A tongue‐like, boulder‐dominated deposit in Tverrbytnede, upper Visdalen, Jotunheimen, southern Norway, is interpreted as the product of a rock avalanche (landslide) due to its angular to subangular boulders, surface morphology with longitudinal ridges, down‐feature coarsening, and cross‐cutting relationship to ‘Little Ice Age’ moraines. The rock avalanche fell onto glacier ice, probably channelled along a furrow between two glaciers, and stopped on the glacier foreland, resulting in its elongated shape and long runout distance. Its distal margin may have become remobilized as a rock glacier, but a rock glacier origin for the entire landform is discounted due to lack of source debris, presence of matrix, lack of transverse ridges, and sparcity of melt‐out collapse pits. Lichenometric dating of the deposit indicates an approximate emplacement age of ad 1900. Analysis highlights the interaction of rock‐slope failures and glaciers during deglacierization in a neoparaglacial setting, with reduced slope stability due to debuttressing and permafrost degradation, and enhanced landslide mobility due to flow over a glacier and topographic channelling. Implications for the differentiation of relict landslides, moraines and rock glaciers are discussed and interrelationships between these landforms are considered in terms of an ice‐debris process continuum.  相似文献   

12.
冀琴  刘睿  杨太保 《地理研究》2020,39(10):2403-2414
基于Landsat系列遥感数据,运用比值阈值法（B3/B5）和目视解译,研究1990—2015年喜马拉雅山冰川面积的分布与变化特征。结果表明：25年间研究区冰川面积共减少2553.10 km2,年均退缩率为0.44%/a,研究时段冰川加速退缩。研究区冰川主要分布在西段地区,中段次之,东段最少,近25年来西段、东段和中段地区冰川均表现为退缩趋势,其中东段地区退缩最快,中段最慢。从地形分布和变化特征看,5°~25°范围内冰川的分布面积较多,近25年来各坡度等级冰川均在退缩,其中25°~30°之间冰川面积退缩较快,在极平缓/极陡峭地区退缩较慢。尽管8个坡向上冰川均表现为退缩趋势,但退缩幅度有所差异,北坡与西北坡冰川退缩较慢,其他坡向退缩较快。研究时段表碛物覆盖型与非表碛物覆盖型冰川均在退缩,但后者的退缩幅度较大,表明研究区表碛物在一定程度上抑制了冰川消融。  相似文献   

13.
We present a glaciological and climatic reconstruction of a former glacier in Coire Breac, an isolated cirque within the Eastern Grampian plateau of Scotland, 5 km from the Highland edge. Published glacier reconstructions of presumed Younger Dryas‐age glaciers in this area show that equilibrium line altitudes decreased steeply towards the east coast, implying a arctic maritime glacial environment. Extrapolation of the ELA trend surface implies that glaciers should have existed in suitable locations on the plateau, a landscape little modified by glaciation. In Coire Breac, a 0.35 km2 cirque glacier existed with an equilibrium line altitude of 487 ± 15 m above present sea level. The equilibrium line altitude matches closely the extrapolated regional equilibrium line altitude trend surface for Younger Dryas Stadial glaciers. The mean glacier thickness of 24 m gives an ice volume of 7.8 × 106 m3, and a maximum basal shear stress of c. 100 kPa?1. Ablation gradient was c. –0.0055 m m?1, with a mean July temperature at the equilibrium line altitude of c. 5.1°C. The reconstruction implies an arctic maritime climate of low precipitation with local accumulation enhanced by blown snow, which may explain the absence of other contemporary glaciers nearby. Reconstructed ice flow lines show zones of flow concentration around the lower ice margin which help to explain the distribution of depositional facies associated with a former debris cover which may have delayed eventual glacier retreat. No moraines in the area have been dated, so palaeoclimatic interpretations remain provisional, and a pre‐Lateglacial Interstadial age cannot be ruled out.  相似文献   

14.
The origin and mobilization of the extensive debris cover associated with the glaciers of the Nanga Parbat Himalaya is complex. In this paper we propose a mechanism by which glaciers can form rock glaciers through inefficiency of sediment transfer from glacier ice to meltwater. Inefficient transfer is caused by various processes that promote plentiful sediment supply and decrease sediment transfer potential. Most debris‐covered glaciers on Nanga Parbat with higher velocities of movement and/ or efficient debris transfer mechanisms do not form rock glaciers, perhaps because debris is mobilized quickly and removed from such glacier systems. Those whose ice movement activity is lower and those where inefficient sediment transfer mechanisms allow plentiful debris to accumulate, can form classic rock glaciers. We document here with maps, satellite images, and field observations the probable evolution of part of a slow and inefficient ice glacier into a rock glacier at the margins of Sachen Glacier in c. 50 years, as well as several other examples that formed in a longer period of time. Sachen Glacier receives all of its nourishment from ice and snow avalanches from surrounding areas of high relief, but has low ice velocities and no efficient system of debris removal. Consequently it has a pronounced digitate terminus with four lobes that have moved outward from the lateral moraines as rock glaciers with prounced transverse ridges and furrows and steep fronts at the angle of repose. Raikot Glacier has a velocity five times higher than Sachen Glacier and a thick cover of rock debris at its terminus that is efficienctly removed. During the advance stage of the glacier since 1994, ice cliffs were exposed at the terminus, and an outbreak flood swept away much debris from its margins and terminus. Like the Sachen Glacier that it resembles, Shaigiri Glacier receives all its nourishment from ice and snow avalanches and has an extensive debris cover with steep margins close to the angle of repose. It has a high velocity similar to Raikot Glacier and catastrophic breakout floods have removed debris from its terminus twice in the recent past. In addition, the Shaigiri terminus blocked the Rupal River during the Little Ice Age and is presently being undercut and steepened by the river. With higher velocities and more efficient sediment transfer systems, neither the Raikot nor the Shaigiri form classic rock‐glacier morphologies.  相似文献   

15.
Smaller glaciers (<0.5 km2) react quickly to environmental changes and typically show a large scatter in their individual response. Accounting for these ice bodies is essential for assessing regional glacier change, given their high number and contribution to the total loss of glacier area in mountain regions. However, studying small glaciers using traditional techniques may be difficult or not feasible, and assessing their current activity and dynamics may be problematic. In this paper, we present an integrated approach for characterizing the current behaviour of a small, avalanche‐fed glacier at low altitude in the Italian Alps, combining geomorphological, geophysical and high‐resolution geodetic surveying with a terrestrial laser scanner. The glacier is still active and shows a detectable mass transfer from the accumulation area to the lower ablation area, which is covered by a thick debris mantle. The glacier owes its existence to the local topo‐climatic conditions, ensured by high rock walls which enhance accumulation by delivering avalanche snow and reduce ablation by providing topographic shading and regulating the debris budget of the glacier catchment. In the last several years the glacier has displayed peculiar behaviour compared with most glaciers of the European Alps, being close to equilibrium conditions in spite of warm ablation seasons. Proportionally small relative changes have also occurred since the Little Ice Age maximum. Compared with the majority of other Alpine glaciers, we infer for this glacier a lower sensitivity to air temperature and a higher sensitivity to precipitation, associated with important feedback from increasing debris cover during unfavourable periods.  相似文献   

16.
1973-2010年阿尔金山冰川变化   总被引：3，自引：0，他引：3  
祝合勇  杨太保  田洪阵 《地理研究》2013,32(8):1430-1438
利用1973 年MSS、1999 年ETM+和2010 年TM遥感影像资料,通过遥感图像处理和GIS技术,提取了阿尔金山地区三个时期的冰川信息,同时结合周边气象资料进行分析。结果表明:① 1973-2010 年,研究区冰川面积从347.99 km2 减少到293.77 km2,退缩了54.22km2,占1973 年冰川总面积的15.58%,年均退缩速率为0.42%·a-1。近10 年来冰川退缩尤为剧烈,年均退缩速率达到0.58%·a-1;② 研究区东段冰川退缩速率快于中段和西段;③ 冰川规模越小,退缩越明显;④ 研究区东坡冰川的面积退缩率最大,北坡次之,东南坡最小;⑤ 气温升高和降水在波动中变化不大是造成研究区冰川退缩的主要原因;⑥ 通过分形理论对研究区冰川空间结构特征进行分析,预计研究区冰川今后的消融速率仍将处于较高状态。  相似文献   

17.
廖海军  刘巧  钟妍  鲁旭阳 《地理学报》2021,76(11):2647-2659
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。  相似文献   

18.
To simulate the landform evolution at the caldera wall of Mount St. Helens, USA, a mathematical model for talus development was applied to model the topographic change during the 11years from the volcanic eruption, i.e., from formation of the cliff. Simulated results show that the topographic change is predicted to be large for about 10years after the eruption and to decline thereafter. If snow accumulation in the talus slope deposits is negligible, the talus top will not reach the cliff top within 300years after the eruption. Talus growth in Mount St. Helens was much faster than that in the Chichibu Basin, Japan. This may indicate the low strength and/or high weathering rate of the rockwall of Mount St. Helens, resulting in rapid production of debris and rapid retreat of the cliff.  相似文献   

19.
The Heihe River Basin is the second largest inland river basin in Northwest China and it is also a hotspot in arid hydrology, water resources and other aspects of researches in cold regions. In addition, the Heihe River Basin has complete landscape, moderate watershed size, and typical social ecological environmental problems. So far, there has been no detailed assessment of glaciers change information of the whole river basin. 1：50,000 topographic map data, Landsat TM/ETM＋ remote sensing images and digital elevation model data were used in this research. Through integrated computer automatic interpretation and visual interpretation methods, the object-oriented image feature extraction method was applied to extract glacier outline information. Glaciers change data were derived from analysis, and the glacier variation and its response to climate change in the period 1956/1963–2007/ 2011 were also analyzed. The results show that：（1） In the period 1956/1963–2007/2011, the Heihe River Basin＇s glaciers had an evident retreat trend, the total area of glaciers decreased from 361.69 km2 to 231.17 km~2; shrinking at a rate of 36.08%, with average single glacier area decrease 0.14 km~2; the total number of the glaciers decreased from 967 to 800.（2） Glaciers in this basin are mainly distributed at elevations of 4300–4400 m, 4400–4500 m and 4500–4600 m; and there are significant regional differences in glaciers distribution and glaciers change.（3） Compared with other western mountain glaciers, glaciers retreat in the Heihe River Basin has a higher rate.（4） Analysis of the six meteorological stations＇ annual average temperature and precipitation data from 1960 to 2010 suggests that the mean annual temperature increased significantly and the annual precipitation also showed an increasing trend. It is concluded that glacier shrinkage is closely related with temperature rising, besides, glacier melting caused by rising temperatures greater than glacier mass supply by increased precipitation to  相似文献   

20.
ABSTRACT. We examine the deglaciation of the eastern flank of the North Patagonian Icefield between latitudes 46° and 48°S in an attempt to link the chronology of the Last Glacial Maximum moraines and those close to present-day outlet glaciers. The main features of the area are three shorelines created by ice-dammed lakes that drained eastwards to the Atlantic. On the basis of 16 14C and exposure age dates we conclude that there was rapid glacier retreat at 15–16 ka (calendar ages) that saw glaciers retreat 90–125 km to within 20 km of their present margins. There followed a phase of glacier and lake stability at 13.6–12.8 ka. The final stage of deglaciation occurred at c. 12.8 ka, a time when the lake suddenly drained, discharging nearly 2000 km3 to the Pacific Ocean. This latter event marks the final separation of the North and South Patagonian Icefields. The timing of the onset of deglaciation and its stepped nature are similar to elsewhere in Patagonia and the northern hemisphere. However, the phase of lake stability, coinciding with the Antarctic Cold Reversal and ending during the Younger Dryas interval, mirrors climatic trends as recorded in Antarctic ice cores. The implication is that late-glacial changes in southern Patagonia were under the influence of the Antarctic realm and out of phase with those of the northern hemisphere.  相似文献   

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