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1.
Eruption records in the terrestrial stratigraphy are often incomplete due to erosion after tephra deposition, limited exposure and lack of precise dating owing to discontinuity of strata. A lake system and sequence adjacent to active volcanoes can record various volcanic events such as explosive eruptions and subaqueous density flows being extensions of eruption triggered and secondary triggered lahars. A lacustrine environment can constrain precise ages of such events because of constant and continuous background sedimentation. A total of 71 subaqueous density flow deposits in a 28 m long core from Lake Inawashiro‐ko reveals missing terrestrial volcanic activity at Adatara and Bandai volcanoes during the past 50 kyr. Sedimentary facies, colour, grain size, petrography, clay mineralogy, micro X‐ray fluorescence analysis and chemistry of included glass shards characterize the flow event deposits and clarify their origin: (i) clay‐rich grey hyperpycnites, extended from subaerial cohesive lahars at Adatara volcano, with sulphide/sulphate minerals and high sulphur content which point to a source from hydrothermally altered material ejected by phreatic eruptions; and (ii) clay‐rich brown density flow deposits, induced by magmatic hydrothermal eruptions and associated edifice collapse at Bandai volcano, with the common presence of fresh juvenile glass shards and low‐grade hydrothermally altered minerals; whereas (iii) non‐volcanic turbidites are limited to the oldest large slope failure and the 2011 Tohoku‐oki earthquake events. The high‐resolution chronology of volcanic activity during the last 50 kyr expressed by lacustrine event deposits shows that phreatic eruption frequency at Adatara has roughly tripled and explosive eruptions at Bandai have increased by ca 50%. These results challenge hikers, ski‐fields and downstream communities to re‐evaluate the increased volcanic risks from more frequent eruptions and far‐reaching lahars, and demonstrate the utility of lahar and lacustrine volcanic density flow deposits to unravel missing terrestrial eruption records, otherwise the recurrence rate may be underestimated at many volcanoes.  相似文献   

2.
Perennially ice‐covered lakes can have significantly different facies than open‐water lakes because sediment is transported onto the ice, where it accumulates, and sand grains preferentially melt through to be deposited on the lake floor. To characterize the facies in these lakes, sedimentary deposits from five Antarctic perennially ice‐covered lakes were described using lake‐bottom observations, underwater video and images, and sediment cores. One lake was dominated by laminated microbial mats and mud (derived from an abutting glacier), with disseminated sand and rare gravel. The other four lakes were dominated by laminated microbial mats and moderately well to moderately sorted medium to very coarse sand with sparse granules and pebbles; they contained minor interstitial or laminated mud (derived from streams and abutting glaciers). The sand was disseminated or localized in mounds and 1 m to more than 10 m long elongate ridges. Mounds were centimetres to metres in diameter; conical, elongate or round in shape; and isolated or deposited near or on top of one another. Sand layers in the mounds had normal, inverse, or no grading. Nine mixed mud and sand facies were defined for perennially ice‐covered lakes based on the relative proportion of mud to sand and the style of sand deposition. While perennially ice‐covered lake facies overlap with other ice‐influenced lakes and glaciomarine facies, they are characterized by a paucity of grains coarser than granules, a narrow range in sand grain sizes, and inverse grading in the sand mounds. These facies can be used to infer changes in ice cover through time and to identify perennially ice‐covered lakes in the rock record. Ancient perennially ice‐covered lakes are expected on Earth and Mars, and their characterization will provide new insights into past climatic conditions and habitability.  相似文献   

3.
2008年夏季北冰洋海冰表面积雪特征初步分析   总被引：1，自引：0，他引：1  
运用中国第三次北极考察期间观测的积雪资料, 分析了夏季北冰洋中心海域海冰表面积雪的空间分布特征. 结果表明: 积雪在垂直分布上呈现6种粒雪状态, 表层到底层依次为新降雪、风板、冰片、深霜、冻结状粗雪和渗浸冻结冰层, 积雪表面常被新降雪或厚度为2～3 cm的风板所覆盖. 考察区域积雪的平均密度为(304.01±29.00)kg·m-3, 表层密度略低于次表层, 遵循雪的密实化原理. 积雪厚度, 雪水当量和新降雪皆具有由南向北递减的空间分布特征, 表明在海冰消融末期, 积雪的气候态分布主要是由降水量的多少决定的, 积雪的消融和蒸发并非海冰表面积雪评估需考虑的首要因素. 雪温随深度的增加而增加, 具有明显的垂直梯度, 观测区积雪表面的平均温度为(-2.01～±0.96)℃, 比海冰/积雪界面的温度高得多.  相似文献   

4.
受全球气候变暖对高海拔山地区气温放大效应影响,冰雪型地质灾害趋于增多,且普遍呈现链式发育特征,具有灾害类型动态转化、影响范围大、破坏程度高等特点,严重威胁区域内重大工程建设安全。基于实地考察与文献调研方式,将高寒山地区常见冰雪型地质灾害凝练为:冰岩崩、雪岩崩、冰雪型碎屑流、冰碛物堆积滑坡、冰湖溃决、冰川型泥石流6类,并分别剖析各自典型的发育特征;而后,对冰雪型地质灾害3种典型链式组合关系予以剖析,发现:冰雪型地质灾害链普遍存在“高位萌生→动力溃散→物相转化”动态演化过程;据此,对冰雪型地质灾害高位萌生、动力溃散及物相转化三阶段特征及内在机制进行分析,明确了冰雪型地质灾害的“高位萌生→位能转化→侵蚀铲刮→滑移堆积”累积链生放大机理。最后,对冰雪型地质灾害链各演化阶段进行评价模型梳理,认为:新型破碎-扩散模型、Flores接触力模型可用于评价冰雪型地质灾害高位萌生向动力溃散过程;犁切模型可较好描述其侵蚀铲刮与体积放大过程;颗粒流模型、空气润滑模型、超孔隙水压力模型可用于揭示后续的高速滑移堆积特征;而Voellmy流变模型、Bingham流体渗流模型可较好解释其灾害链条的物相转化特征。研究对于科学评价冰雪型地质灾害链动态演化过程具有基础参考价值。  相似文献   

5.
Reconstructing ice‐lake histories is of considerable importance for understanding deglacial meltwater budgets and the role of meltwater reservoirs for sea‐level rise in response to climate warming. We used the latest data on chronology and ice‐sheet extents combined with an isostatically adjusted digital elevation model to reconstruct the development of proglacial lakes in the area of the Karelian ice stream complex of the Late Weichselian Scandinavian Ice Sheet on the East European Plain. We derived the deglacial ice lake development in seven time‐slices from 19 to 13.8 ka, assuming the individual ice‐marginal positions to be isochronous throughout the studied domain. Modelling is based on mapping of critical drainage thresholds and filling the depressions that are potentially able to hold meltwater. Such an approach underestimates the real dimensions of the ice lakes, because the role of erosion at the thresholds is not considered. Our modelling approach is sensitive to the (local) ice‐margin location. Our results prove the southward drainage of meltwater during the glacier extent maxima and at the beginning of deglaciation whereas rerouting to the west had taken place already around 17.5 ka, which is some 1.5 ka earlier than hitherto supposed. The total ice‐lake volume in the study area was lowest (~300 km3) during the maximum glacier extent and highest (~2000 km3) during the highstand of the Privalday Lake at c. 14.6 ka. At 14.6–14.4 ka, the Privalday Lake drained to the early Baltic Ice Lake. The released ~1500 km3 of water approximately corresponds to 20% of the early Baltic Ice Lake water volume and therefore it is unlikely that it was accommodated there. Thus, we argue that the additional meltwater drained through the Öresund threshold area between the early Baltic Ice Lake and the sea, becoming a part of the Scandinavian Ice Sheet's contribution to the Meltwater Pulse 1A event.  相似文献   

6.
The macro‐ and micro‐sedimentology of a supraglacial melt‐out till forming at the Matanuska Glacier was examined in relationship to the properties of the stratified basal zone ice and debris from which it is originating. In situ melting of the basal ice has produced a laminated to bedded diamicton consisting mainly of silt. Macroscopic properties include: discontinuous laminae and beds; lenses of sand, silt aggregates and open‐work gravel; deformed and elongate clasts of clay; widely dispersed pebbles and cobbles, those that are prolate usually with their long axes subparallel to parallel to the bedding. Evidence for deformation is absent except for localized bending of beds over or under rock clasts. Microscopic properties are a unique element of this work and include: discontinuous lineations; silt to granule size laminae; prolate coarse sand and rock fragments commonly with their long axis subparallel to bedding; subangular to subrounded irregular shaped clay clasts often appearing as bands; sorted and unsorted silt to granule size horizons, sometimes disrupted by pore‐water pathways. Limited deformation occurs around rock clasts and thicker parts of lamina. This study shows that in situ melting of debris‐rich basal ice can produce a laminated and bedded diamicton that inherits and thereby preserves stratified basal ice properties. Production and preservation of supraglacial melt‐out till require in situ melting of a stagnant, debris‐rich basal ice source with a low relief surface that becomes buried by a thick, stable, insulating cover of ice‐marginal sediment. Also required are a slow melt rate and adequate drainage to minimize pore‐water pressures in the till and overlying sediment cover to maintain stability and uninterrupted deposition. Many modern and ancient hummocky moraines down glacier of subglacial overdeepenings probably meet these process criteria and their common occurrence suggests that both modern and pre‐modern supraglacial melt‐out tills may be more common than previously thought.  相似文献   

7.
Concentrations of lead have been measured by ultraclean Isotope Dilution Mass Spectrometry in snow cores covering the last two centuries collected at an inland site in East Antarctica using an ultra clean all plastic hand operated auger and in a prehistoric blue ice block collected at an Antarctic coastal site. Lead contamination of 16 to 200 pg Pb/g existed on the outside of the snow cores, but the measured concentrations decreased more or less abruptly along a radius from the outside to the centers of the snow cores, establishing interior values in the 1 to 5 pg Pb/g range. Some of these interior values are however possibly still slightly affected by lead contamination which could have intruded to the center of the cores because of slight melting of some of the snow cores before laboratory analysis. The interior of the blue ice block appears not to have been significantly contaminated, and contains about 1.7 pg Pb/g.These new data show that most previously published data on lead in Antarctic snow and ice were in high positive error because of contamination during field sampling, laboratory analysis or both. They show that lead concentrations could not have increased in Antarctic snows or ice from prehistoric times to present more than 2 to 3 fold, confirming that the remote polar areas of the Southern Hemisphere are still little affected by industrial lead pollution. Prehistoric Antarctic ice is shown to contain about 1 pg Pb/g natural excess lead above silicate dust lead; this excess cannot be entirely accounted for by volcanoes or sea spray, which suggests the possible existence of some other unknown natural source of prehistoric excess lead. Present day mean eolian fallout flux of lead in Antarctica is estimated to be about 0.07 ng Pb cm?2 yr?1, which stands in about the same proportion to that in the South Pacific Westerlies (about 1:30) as the flux in Greenland is observed to stand to those in the North Pacific and North Atlantic Westerlies.  相似文献   

8.
Aguilera  E.  Pareschi  M. T.  Rosi  M.  Zanchetta  G. 《Natural Hazards》2004,33(2):161-189
Cotopaxi volcano (Ecuador) is famous for production of large-scale laharsthrough melting of ice and snow on its summit glacier. The lahar hazard inthe northern valleys of the volcano is assessed through numerical simulationof a maximum expected event. Considerations of past activity suggest that anevent like that of the 1877 eruption is the maximum expected lahar event.Review of the historical records reveals that northerly flowing lahars initiallyfollowed the Rio Pita and Rio Salto; at ``La Caldera', owing to a sharp bendin the channel, the lahar partly overflowed into Rio Santa Clara. The laharsalong Rio Pita and Rio Santa Clara were conveyed to the Los Chillos valley.The simulation, using an initial flow volume of 60 × 106 m3reproduces the maximum heights reached by the 1877 lahar along the northernvalley. The volume of lahar triggered by an eruption similar to that of 1877 isestimated to have a volume about 2/3 of that of 1877. This hypothesized reductionof volume is attributed to shrinkage of the summit glacier over the past century.However, dramatic population growth along valleys exposed to lahar hazard overthe past 100 years makes the present risk from lahars higher than in the past. Thesharp bend of ``La Caldera' represents a crucial site controlling lahar propagation:should a lahar overflow into the Santa Clara valley the risk increases considerablydue to the much higher concentration of human settlements along the valley. Resultsof a lahar simulation in which the entire flow is artificially forced into Rio Pita suggestthat construction of a dyke at ``La Caldera' to prevent overflow would substantiallyreduce the general risk in the area.  相似文献   

9.
Glaciers in the southern province of the Southern Volcanic Zone (SVZ) of Chile (37–46°S) have experienced significant frontal retreats and area losses in recent decades which have been primarily triggered by tropospheric warming and precipitation decrease. The resulting altitudinal increase of the Equilibrium Line Altitude or ELA of glaciers has lead to varied responses to climate, although the predominant volcanic stratocone morphologies prevent drastic changes in their Accumulation Area Ratios or AAR. Superimposed on climate changes however, glacier variations have been influenced by frequent eruptive activity. Explosive eruptions of ice capped volcanoes have the strongest potential to destroy glaciers, with the most intense activity in historical times being recorded at Nevados de Chillán, Villarrica and Hudson. The total glacier area located on top of the 26 active volcanoes in the study area is ca. 500 km2. Glacier areal reductions ranged from a minimum of −0.07 km2 a −1 at Mentolat, a volcano with one of the smallest ice caps, up to a maximum of −1.16 km2 a −1 at Volcán Hudson. Extreme and contrasting glacier–volcano interactions are summarised with the cases ranging from the abnormal ice frontal advances at Michinmahuida, following the Chaitén eruption in 2008, to the rapid melting of the Hudson intracaldera ice following its plinian eruption of 1991. The net effect of climate changes and volcanic activity are negative mass balances, ice thinning and glacier area shrinkage. This paper summarizes the glacier changes on selected volcanoes within the region, and discusses climatic versus volcanic induced changes. This is crucial in a volcanic country like Chile due to the hazards imposed by lahars and other volcanic processes.  相似文献   

10.
We present a new time‐slice reconstruction of the Eurasian ice sheets (British–Irish, Svalbard–Barents–Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 ka, and at four selected time periods back to 40 ka. The time‐slice maps of ice‐sheet extent are based on a new Geographical Information System (GIS) database, where we have collected published numerical dates constraining the timing of ice‐sheet advance and retreat, and additionally geomorphological and geological evidence contained within the existing literature. We integrate all uncertainty estimates into three ice‐margin lines for each time‐slice; a most‐credible line, derived from our assessment of all available evidence, with bounding maximum and minimum limits allowed by existing data. This approach was motivated by the demands of glaciological, isostatic and climate modelling and to clearly display limitations in knowledge. The timing of advance and retreat were both remarkably spatially variable across the ice‐sheet area. According to our compilation the westernmost limit along the British–Irish and Norwegian continental shelf was reached up to 7000 years earlier (at c. 27–26 ka) than the eastern limit on the Russian Plain (at c. 20–19 ka). The Eurasian ice sheet complex as a whole attained its maximum extent (5.5 Mkm2) and volume (~24 m Sea Level Equivalent) at c. 21 ka. Our continental‐scale approach highlights instances of conflicting evidence and gaps in the ice‐sheet chronology where uncertainties remain large and should be a focus for future research. Largest uncertainties coincide with locations presently below sea level and where contradicting evidence exists. This first version of the database and time‐slices (DATED‐1) has a census date of 1 January 2013 and both are available to download via the Bjerknes Climate Data Centre and PANGAEA ( www.bcdc.no ; http://doi.pangaea.de/10.1594/PANGAEA.848117 ).  相似文献   

11.
利用模拟软件LAHARZ,基于长白山天池火山1/25万数字地形图,对二道白河、松花江、鸭绿江以及图们江4条泥石流易发河道进行了火山泥石流的数值模拟。模拟中依据历史喷发柱高度和地形平均坡度设定能量锥最佳阈值为0.07;通过实际河流与计算所得河流的对比匹配,设定河流最佳阈值为5 000;根据历史上长白山地区火山泥石流的爆发规模,设定了108 m3,109 m3,1010 m3和1011 m3 4个体积阈值。通过模拟计算发现,不同河道设定不同阈值流动影响范围有所不同,其灾害规模也相应变化,且模拟所得灾害分布范围与长白山地区的历史火山泥石流分布范围相似。依据模拟计算结果,将长白山火山泥石流灾害区划为4级,其对应的覆盖半径分别约为40 km,70 km,80 km和100 km,该结果可为长白山地区的建设规划提供参考。另外,该模型与灾害区划的方法也可为其它火山区的火山泥石流灾害区划提供借鉴。  相似文献   

12.
Inactive ice wedges are still present today at Yituli'he in the middle Da Xing'anling (Greater Hinggan) Mountains in northeastern China, which is the southernmost known site (50°37′N) with ice wedges in the Northern Hemisphere. However, it is uncertain whether the ice‐wedge isotope composition, characterized by low δ18O, δD and low deuterium excess values, is representative of the isotope signature of a broader region. In this paper, the ice‐wedge isotope compositions were examined in the context of the stable isotopes of precipitation from the nearby Global Network of Isotopes in Precipitation (GNIP) stations. In addition, the pollen spectra from the host sediments were analysed to provide additional information on local vegetation in order to better understand the climate conditions favouring ice‐wedge formation. The pollen spectra suggest that the Yituli'he ice wedges developed during the colder and wetter period after 6000 cal. a BP. The isotopes in the Yituli'he ice wedges are consistent with the isotope background recorded in atmospheric precipitation collected at the nearby GNIP stations. When the snow‐melt froze into ice veinlets, the isotope signals did not change substantially because of the strong, cold, continental anticyclones in winter as well as a strong temperature inversion that prevail in the Da Xing'anling Mountains. As the climate pattern did not change substantially, the neoglacial cold period is unlikely to have allowed for strong secondary fractionation of isotope records during ice‐wedge formation. Thus, the annual isotope signature can be interpreted as a valid archive of climate data.  相似文献   

13.
Lusardi, B. A., Jennings, C. E. & Harris, K. L. 2011: Provenance of Des Moines lobe till records ice‐stream catchment evolution during Laurentide deglaciation. Boreas, 10.1111/j.1502‐3885.2011.00208.x. ISSN 0300‐9483. Mapping and analysis of deposits of the Des Moines lobe of the Laurentide Ice Sheet, active after the Last Glacial Maximum (LGM), reveal several texturally and lithologically distinct tills within what had been considered to be a homogeneous deposit. Although the differences between tills are subtle, minor distinctions are predictable and mappable, and till sheets within the area covered by the lobe can be correlated for hundreds of kilometres parallel to ice flow. Lateral till‐sheet contacts are abrupt or overlap in a narrow zone, coincident with a geomorphic discontinuity interpreted to be a shear margin. Till sheets 10 to 20 m thick show mixing in their lower 2 to 3 m. We suggest that: (i) lithologically distinct till sheets correspond to unique ice‐stream source areas; (ii) the sequence of tills deposited by the Des Moines lobe was the result of the evolution and varying dominance of nearby and competing ice streams and their tributaries; and (iii) in at least one instance, more than one ice stream simultaneously contributed to the lobe. Therefore the complex sequence of tills of subtly different provenances, and the unconformities between them record the evolution of an ice‐catchment area during Laurentide Ice Sheet drawdown. Till provenance data suggest that, after till is created in the ice‐stream source area, the subglacial conditions required for transporting till decline and incorporation of new material is limited.  相似文献   

14.
The spatial extent and volume of global snow and ice cover at present and during glacial conditions are reviewed for each of the principal components (snow cover, land ice, sea ice and permafrost). The state of global monitoring of snow and ice conditions is shown to be adequate for some variables, but unsatisfactory for others. Recent trends are reported and expected changes projected for increasing concentrations of greenhouse gases are examined.  相似文献   

15.
Artificial ground freezing (AGF) is a commonly used technique in geotechnical engineering for ground improvement such as ground water control and temporary excavation support during tunnel construction in soft soils. The main potential problem connected with this technique is that it may produce heave and settlement at the ground surface, which may cause damage to the surface infrastructure. Additionally, the freezing process and the energy needed to obtain a stable frozen ground may be significantly influenced by seepage flow. Evidently, safe design and execution of AGF require a reliable prediction of the coupled thermo‐hydro‐mechanical behavior of freezing soils. With the theory of poromechanics, a three‐phase finite element soil model is proposed, considering solid particles, liquid water, and crystal ice as separate phases and mixture temperature, liquid pressure, and solid displacement as the primary field variables. In addition to the volume expansion of water transforming into ice, the contribution of the micro‐cryo‐suction mechanism to the frost heave phenomenon is described in the model using the theory of premelting dynamics. Through fundamental physical laws and corresponding state relations, the model captures various couplings among the phase transition, the liquid transport within the pore space, and the accompanying mechanical deformation. The verification and validation of the model are accomplished by means of selected analyses. An application example is related to AGF during tunnel excavation, investigating the influence of seepage flow on the freezing process and the time required to establish a closed supporting frozen arch. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

16.
Turbid meltwater plumes and ice‐proximal fans occur where subglacial streams reach the grounded marine margins of modern and ancient tidewater glaciers. However, the spacing and temporal stability of these subglacial channels is poorly understood. This has significant implications for understanding the geometry and distribution of Quaternary and ancient ice‐proximal fans that can form important aquifers and hydrocarbon reservoirs. Remote‐sensing and numerical‐modelling techniques are applied to the 200 km long marine margin of a Svalbard ice cap, Austfonna, to quantify turbid meltwater‐plume distribution and predict its temporal stability. Results are combined with observations from geophysical data close to the modern ice front to refine existing depositional models for ice‐proximal fans. Plumes are spaced ca 3 km apart and their distribution along the ice front is stable over decades. Numerical modelling also predicts the drainage pattern and meltwater discharge beneath the ice cap; modelled water‐routing patterns are in reasonable agreement with satellite‐mapped plume locations. However, glacial retreat of several kilometres over the past 40 years has limited build‐up of significant ice‐proximal fans. A single fan and moraine ridge is noted from marine‐geophysical surveys. Closer to the ice front there are smaller recessional moraines and polygonal sediment lobes but no identifiable fans. Schematic models of ice‐proximal deposits represent varying glacier‐terminus stability: (i) stable terminus where meltwater sedimentation produces an ice‐proximal fan; (ii) quasi‐stable terminus, where glacier readvance pushes or thrusts up ice‐proximal deposits into a morainal bank; and (iii) retreating terminus, with short still‐stands, allowing only small sediment lobes to build up at melt‐stream portals. These modern investigations are complemented with outcrop and subsurface observations and numerical modelling of an ancient, Ordovician glacial system. Thick turbidite successions and large fans in the Late Ordovician suggest either high‐magnitude events or sustained high discharge, consistent with a relatively mild palaeo‐glacial setting for the former North African ice sheet.  相似文献   

17.
北极海冰消融初期,上覆积雪急剧消融,融池开始形成,海冰表面物理特征异常复杂。由于观测资料缺乏,对这一时期海冰变化的研究仍存在较大不确定性。利用2015年5月份在巴罗Elson Lagoon海域观测的海冰表面物理特征和光谱反射率数据,分析了巴罗地区海冰消融初期表面积雪、裸冰和融池反射率特性及其影响因素。结果表明：消融初期,海冰表面异质性强,积雪、裸冰和融池相间分布。在积雪覆盖的区域,积雪对海冰光谱反射率起决定性作用,观测到不同雪深（3~23 cm）的反射率变化在0.53~0.85之间,平均反射率为0.76且反射率与雪深呈正相关。在表面积雪厚度相同的情况下,积雪底层含水量越大,表层反射率越小。观测还显示,在融池形成的区域,海冰的反射率急剧降低,融池初形成时反射率为0.206,略低于裸冰（0.216）。随着融池的发展,当其深度达到10 cm时,反射率仅为0.04,与开阔海域海水接近。  相似文献   

18.
A prominent thrust‐moraine system formed in the inner van Mijenfjorden, Svalbard, during a surge event in a tributary fjord, creating a large temporary lake. Based on geomorphological, sedimentological, stratigraphical and chronological data, the lake began to form shortly after 648–551 cal. a BP. At its maximum, the lake covered an estimated area of 77 km2 with a water volume of 1.2 km3. Lake sediment up to 80 cm thick was rapidly deposited on top of terrestrial and marine sediments. At its maximum extent, the short‐lived lake was the largest of any known Holocene lake in Svalbard. Modern river discharge would fill the lake to its highest shoreline at 23 m a.s.l. in only one season. Drainage was stepwise, as evidenced by four shorelines and abandoned drainage channels. This study has taken advantage of a unique suite of data available for such an ice‐dammed lake. The results demonstrate the power of a multidisciplinary approach for recognizing lake events in the geological record, which is essential given the low preservation potential of such sediments.  相似文献   

19.
Lyså, A., Jensen, M. A., Larsen, E., Fredin, O. & Demidov, I. N.* 2010: Ice‐distal landscape and sediment signatures evidencing damming and drainage of large pro‐glacial lakes, northwest Russia. Boreas, Vol. 40, pp. 481–497. 10.1111/j.1502‐3885.2010.00197.x. ISSN 0300‐9483. Sediments from river sections and the morphology of the upper reaches of Severnaya Dvina and Vychegda in northwest Russia show evidence of the existence of large ice‐dammed lakes in the area twice during the Weichselian. During the Late Weichselian, three separate ice‐dammed lakes (LGM lake(s)) existed, the largest one at about 135 m a.s.l. having a volume of about 1510 km3. Stepwise and rapid lake drainage is suggested to have taken place within less than 1000 years. The locations of various passpoints controlled the drainage, and when the lake was at its maximum level water spilled southeastwards into the Volga basin. Later, but before the lake water finally drained into the White Sea, water was routed northeastwards into the southeastern part of the Barents Sea. The oldest lake, the White Sea lake, existed around 67–57 ka ago, slightly in conflict with earlier palaeogeographic reconstructions regarding the chronology. The extent of the lake was constrained by, in addition to the Barents Sea ice‐sheet margin in the north, thresholds in the drainage basin. Later, one threshold was eroded and lowered during the LGM lake drainage. Given a lake level of about 115 m a.s.l., a lake area of about 2.5 × 104 km3 and a water volume of about 4800 km3, the lake drainage northwards and into the ocean probably impacted the ocean circulation.  相似文献   

20.
冰川/积雪-大气相互作用研究进展   总被引：10，自引：9，他引：1  
杨兴国  秦大河  秦翔 《冰川冻土》2012,34(2):392-402
冰川和积雪是冰冻圈的重要组成部分,在全球或区域气候系统中起着极其重要的作用.开展冰川/积雪-大气相互作用研究,是研究冰冻圈物理过程及其对气候系统反馈作用的必然需求,也是研究冰川/积雪对气候变化响应的有效手段,同时还可为全球(区域)气候和水文模式提供冰川/积雪面的地表特征参数.近一个世纪以来,在冰川/积雪面辐射特征、能量通量计算方法和平衡特征等方面开展了许多观测试验和理论研究,并取得了卓有成效的研究结果.但是在准确获取辐射通量、研发普适性较强的反照率参数化方案、复杂地形条件下能量通量的计算,以及发展分布式能量平衡模式等方面尚存在许多不确定性,仍面临许多技术难点,也是未来的研究重点.  相似文献   

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