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1.
Advance of part of the margin of the Greenland ice sheet across a proglacial moraine ridge between 1968 and 2002 caused progressive changes in moraine morphology, basal ice formation, debris release, ice‐marginal sediment storage, and sediment transfer to the distal proglacial zone. When the ice margin is behind the moraine, most of the sediment released from the glacier is stored close to the ice margin. As the margin advances across the moraine the potential for ice‐proximal sediment storage decreases and distal sediment flux is augmented by reactivation of moraine sediment. For six stages of advance associated with distinctive glacial and sedimentary processes we describe the ice margin, the debris‐rich basal ice, debris release from the glacier, sediment routing into the proglacial zone, and geomorphic processes on the moraine. The overtopping of a moraine ridge is a significant glaciological, geomorphological and sedimentological threshold in glacier advance, likely to cause a distinctive pulse in distal sediment accumulation rates that should be taken into account when glacial sediments are interpreted to reconstruct glacier fluctuations.  相似文献   

2.
Moraine morphology is a valuable indicator of climate change. The glacial deposits of ten valleys were selected in the Parlung Zangbo River Basin, southeastern Tibetan Plateau, to study the glacial characteristics of the Last Glaciation and the climate change processes as revealed by these moraines. Investigation revealed that a huge moraine ridge was formed by ancient glacier in the Marine Isotope Stage 2 （MIS2）, and this main moraine ridge indicates the longest sustained and stable climate. There are at least two smaller moraine ridges that are external extensions of or located at the bottom of the main moraine ridge, indicating that the climate of the glacial stage before MIS2 was severer but the duration was relatively shorter. This distribution may reflect the climate of MIS4 or MIS3b. The glacial valleys show multi-channel, small-scale moraine ridges between the contemporary glacial tongue and the main moraine ridge. Some of these multi-channel mo- raine ridges might be recessional moraine, indicating the significant glacial advance during the Younger Dryas or the Heinrich event. The moraine ridges of the Neoglaciation and the Little Ice Age are near the ends of the contemporary glaciers. Using high-precision system dating, we can fairly well reconstruct the pattern of climate change by studying the shape, extent, and scale characteristics of glacial deposits in southeastern Tibet. This is valuable research to understand the relationship between regional and global climate change.  相似文献   

3.
Large debris-flow units commonly occur on the distal sides of subaqueous end moraines deposited by surges of Svalbard tidewater glaciers, but have rarely been described in terrestrial settings. Some researchers have argued that these kinds of debris flows reflect processes unique to the subaqueous environment, such as the extrusion of subglacial deforming layers or extensive failure of oversteepened moraine fronts. In this paper, we describe terrestrial and subaqueous parts of a single late Holocene moraine system deposited by a major surge of the tidewater glacier Paulabreen in west Spitsbergen. The ice-marginal landforms on land closely resemble the corresponding landforms on the seabed as evidenced by geomorphic mapping and geophysical profiles from both environments. Both onland and offshore, extensive areas of hummocky moraine occur on the proximal side of the maximum glacier position, and large mud aprons (interpreted as debris flows) occur on the distal side. We show that the debris-flow sediments were pushed in front of the advancing glacier as a continuously failing, mobile push moraine. We propose that the mud aprons are end members of a proglacial landforms continuum that has thrust-block moraines as the opposite end member. Two clusters of dates (~ 8000 YBP and ~ 700 YBP) have previously been interpreted to indicate two separate surges responsible for the moraine formation. New dates suggest that the early cluster indicates a local extinction of the abounded species Chlamys islandica. Other changes corresponding to the widespread 8.2 ka event within the fjord, may suggest that the extinction of the C. islandica corresponds to that time.  相似文献   

4.
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   

5.
新疆阿尔泰山东段冰碛物光释光测年研究   总被引：3，自引：0，他引：3  
贾彬彬  周亚利  赵军 《地理学报》2018,73(5):957-972
冰川是塑造地表形态最积极的外营力之一,对冰川地貌的年代学研究是重建古冰川发展史的关键,也是研究气候变化的重要途径。冰碛物是冰川作用的直接产物,代表过去发生的冰川事件,对冰碛物进行准确测年能够为重建古冰川的进退、理解区域古气候变化提供年代学支撑。本文在新疆阿尔泰山东段采集了8个冰碛物样品以进行光释光测年,利用单片再生剂量法对90~125 μm的石英颗粒进行等效剂量的测定。通过等效剂量值频率分布特征及De（t）坪区图分析得出大部分冰碛物的光释光信号晒退不彻底,所以利用一阶动力学公式对持续激发的光释光信号晒退曲线（CW-OSL）进行多组分拟合拆分,得到快速、中速、慢速3种组分,依据分离出的快速组分确定等效剂量值。研究结果显示,距今32 ka以来阿尔泰山东段区域在MIS3阶段、MIS2阶段、8.2 ka左右、全新世大暖期及新冰期等5个时段有冰川发育,冰川发育与气候变化密切相关。  相似文献   

6.
ABSTRACT. The retreat of Nigardsbreen, an outlet glacier from the ice-cap Jostedalsbreen in south-central Norway, from its largest extent during the Little Ice Age, uncovered a proglacial lake during 1936–1967. This lake, Nigardsvatn, has been studied since 1968 in order to obtain data on solid material carried by the meltwater stream from the glacier, both in suspension and as bottom load. Between 70 and 85% of the suspended sediment has been deposited on the lake bottom, forming annual varves. The coarse material has been deposited in a delta, the formation of which started in 1968. Its growth, and hence the volume of total annual bottom load, has been surveyed annually for the past 36 years. In 1969 the entire bottom load was collected by building a fence-like net across the river. Material >3 cm was caught by this net, and formed approximately half the amount of suspended sediment transport during the same three-week period. Annual average deposition on the delta was 11800×103 kg for the period 1968–2003. This is almost the same amount as carried in suspension from the glacier on an annual mean basis for the 36-year period. If conditions remain constant, the lake will be completely filled in about 500 years. The glacier erosion is calculated to be 0.3 mm/a.  相似文献   

7.
Moraine ridges are commonly used to identify past glacier ice margins and so infer glacier mass balance changes in response to climatic variability. However, differences in the form of past ice margins and post-depositional modification of moraine surfaces can complicate these geomorphic records. As a result, simple relationships, such as distance from current ice margin, or linear alignments, may not necessarily indicate moraines deposited contemporaneously. These disturbances can also modify the size distribution of lichen populations, providing a distinctive signature for surfaces with similar histories and a means of identifying contemporaneous moraine surfaces. In this paper, statistical analysis of lichen size distributions is used to identify moraine surfaces with similar histories from complex suites of Little Ice Age moraine fragments in the proglacial areas of Skálafellsjökull (including Sultartungnajökull) and Heinabergsjökull, southeast Iceland. The analysis is based on a novel use of the goodness-of-fit statistic, Watson's U2 which provides a measure of 'closeness' between two sample distributions. Moraine fragments with similar histories are identified using cluster analysis of the U2 closeness values. The spatial pattern of the clustered moraines suggests three distinct phases of moraine deposition at Skálafellsjökull and Heinabergsjökull, four phases at Sultartungnajökull and a digitate planform margin at Heinabergsjökull. These spatial patterns are corroborated with tephrochronology. The success of the U2 statistical analysis in identifying surfaces with similar histories using lichen size distributions suggests that the technique may be useful in augmenting lichenometric surface dating as well as differentiating between other surfaces that support lichen populations, such as rock avalanche deposits.  相似文献   

8.
The Kanas River originates on the southern slope of Youyi Peak, the largest center of modern glaciers in Altai Mountains, China. Three sets of moraines and associated glacial sediments are well preserved near the Kanas Lake outlet, recording a complex history and landscape evolution during the Last Glacial. Dating the moraines allows the temporal and spatial glacier shift and climate during the Last Glacial to be determined, and then constrains when and how the Kanas Lake basin was formed. Dating of the glacial tills was undertaken by utilizing the optically stimulated luminescence (OSL) method. Results date four samples from the three sets of moraines to 28.0, 34.4, 38.1, and 49.9 ka and one sample from outwash sediment to 6.8 ka. The Kanas Lake basin is a downfaulted basin and was eroded by glacier before 28.0 ka, and the glacial moraines blocked the glacier-melt water after the glacier retreat, which made the present-day Kanas Lake eventually form at least before 6.8 ka BP. In Altai Mountains, the glacier advance was more extensive in Marine Isotope Stage (MIS) 3 than MIS 2, probably because the mid-latitude westerlies shifted northward and/or intensified during the MIS 3, resulting in a more positive glacier mass balance. Nevertheless, the Siberian High dominated the Altai Mountains in MIS 2, resulting in a relative decrease in precipitation.  相似文献   

9.
Samples taken from the top surfaces of boulders on the Lake Misery moraines at Arthur's Pass, in the Southern Alps of New Zealand, were analysed for 10Be by accelerator mass spectrometry. Exposure ages calculated with the currently accepted production rate, along with scaling corrections for sample latitude and elevation (42°50'S, 960 m), are: 9300 ± 990, 11,000 ± 1360, 11,410 ± 1030, 12,050 ± 960, and 12,410 ± 1180 years. We consider the date of 9300 years to be an outlier, not included in our mean exposure age of 11,720 ± 320 years for the Lake Misery moraines. Based on exposure ages and geomorphologic similarities, we compare the Lake Misery moraines with an Egesen moraine complex at Julier Pass in the Swiss Alps (46°30'N, 2200 m). Based on the 10Be, 26Al, and 36Cl exposure ages of three boulders, we calculate a mean exposure age of 11,750 ± 140 years for the outer Egesen moraine at Julier Pass. Based solely on 10Be measurements, we obtain a mean exposure age of 11,860 ± 210 years for this outer moraine. Egesen moraines in the Swiss Alps represent glacier readvance during the Younger Dryas cold reversal, based on regional correlations and on basal radiocarbon dates from bogs located up-valley of Egesen moraines. The exposure dates from Arthur's Pass and Julier Pass show synchronous glacier advances both in the Southern Alps and in the European Alps during the European Younger Dryas chronozone of Mangerud et al .  相似文献   

10.
Little Ice Age (LIA) moraines along the margins of Skálafellsjökull and Heinabergsjökull, two neighbouring outlet glaciers flowing from the Vatnajökull ice‐cap, have been re‐dated to test the reliability of different lichenometric approaches. During 2003, 12 000 lichens were measured on 40 moraine fragments at Skálafellsjökull and Heinabergsjökull to provide surface age proxies. The results are revealing. Depending on the chosen method of analysis, Skálafellsjökull either reached its LIA maximum in the early 19th century (population gradient) or the late 19th century (average of five largest lichens), whereas the LIA maximum of Heinabergsjökull occurred by the mid‐19th century (population gradient) or late‐19th century (average of 5 largest lichens). Discrepancies (c. 80 years for Skálafellsjökull and c. 40 years for Heinabergsjökull) suggest that the previously cited AD 1887 LIA maxima for both glaciers should be reassessed. Dates predicted by the lichen population gradient method appear to be the most appropriate, as mounting evidence from other geochronological reconstructions and sea‐ice records throughout Iceland tends to support an earlier LIA glacier maximum (late 18th to mid‐19th century) and probably reflects changes in the North Atlantic Oscillation. These revised chronologies shed further light on the precise timing of the Icelandic LIA glacier maximum, whilst improving our understanding of glacier‐climate interactions in the North Atlantic.  相似文献   

11.
ABSTRACT

The advance and retreat of glaciers, influenced by changes of local and regional climates, can result in dramatic landscape changes. The article, which follows up previous documentation of long-term studies at Svartisen, deals with changes of Flatisen: at the end of the 19th century, this was one of the largest glaciers of West Svartisen, and was supplied by accumulation areas that rose to > 1400 m a.s.l. It crossed the river Glomåga and ascended to 100 m above the valley floor. The river had a subglacial course until the 1920s. A proglacial lake, formed in front of the glacier in the 1930s and became larger throughout the rest of the 20th century. Changes of Flatisen between 1957 and 1990 were monitored during visits to the glacier. After the retreating front became inaccessible by land, photographs were taken. Early this century, the glacier retreated from the lake. A helicopter reconnaissance in July 2017 revealed that the surface was almost wholly below 1000 m a.s.l., the local equilibrium line altitude of recent years. Without a permanent accumulation zone, Flatisen is likely to disappear within the first half of the present century.  相似文献   

12.
ABSTRACT. Alpine glacier deposits in the McMurdo Dry Valleys of Antarctica have been interpreted to indicate that early Pliocene climate in that region was not warmer than it is today. Correlation of these alpine‐glacier till sheets to marine deposits that contain evidence consistent with warmer‐than‐present climate has been used to constrain the age of both deposits, preclude the warm interpretation of the marine evidence, and constrain mountain uplift as determined from the marine deposit. We tested the interpretation that, in the early Pliocene, the alpine glaciers in Wright Valley terminated in a fjord and, thereby, constrain the age, temperature, and depth of the fjord. We did this by mapping the surficial geology in this region using the newly available microtopography based on the light detection and ranging (LIDAR) technique. Stratigraphic issues like these need to be resolved in order to quantify early Pliocene climate in Antarctica and contribute to understanding warm global‐climate dynamics. We found that the Pliocene Alpine‐IIIA (A‐IIIA), A‐IIIB and A‐IV drift sheets were more likely deposited from terrestrial alpine‐glacier lobes than glaciers terminating either at tidewater or with a floating appendage. The principal evidence is the occurrence of moraine fragments well below the minimum elevation of the early Pliocene fjord surface, and moraine arrangement in arcs indicative of arcuate glacier fronts without flairing near the proposed shoreline. Our A‐IIIA till is more widespread in the proglacial areas of the five alpine glaciers examined than previously proposed. We propose that the existing distribution of A‐IIIB till reflects glaciers even less extensive than today rather than truncation at a hypothetical fjord surface. Additionally, the A‐IV moraine remnants outline glaciers that were significantly larger than those associated with A‐III moraines. If we are correct, the age of the A‐III till, 3.4 ± 0.1 Ma at maximum, does not constrain the age of the Prospect fjord episode which can be closer to 5.5 ± 0.4 Ma as previously inferred. Moreover, if the alpine tills are not as old as the Prospect fjord episode, the polar paleoclimatic interpretation from those tills does not preclude the high temperature (0–3°C) and reduced salinity previously inferred for the Prospect fjord. However, if alpine glacier extent was not limited by Prospect fjord surface elevation, then paleoclimate during the A‐IIIA, A‐IIIB, and A‐IV glacial episodes can be quantitatively reconstructed. The Prospect fjord might have been deep, not shallow, and, hence, mountain uplift might be greater than currently thought which would explain minimal alpine‐glacier erosion into the valley sides.  相似文献   

13.
The Aragón Valley glacier (Central Western Pyrenees) has been studied since the late nineteenth century and has become one of the best areas in the Pyrenees to study the occurrence of Pleistocene glaciations and the relationships between moraines and fluvial terraces. New morphological studies and absolute ages for moraines and fluvial terraces in the Aragón Valley allow a correlation with other Pyrenean glaciers and provide solid chronologies about the asynchroneity between global last glacial maximum (LGM) and the maximum ice extent (MIE). Six frontal arcs and three lateral morainic ridges were identified in the Villanúa basin terminal glacial complex. The main moraines (M1 and M2) correspond to two glacial stages (oxygen isotopic stages MIS 6 and MIS 4), dated at 171 ± 22 ka and 68 ± 7 ka, respectively. From a topographical point of view, moraine M1 appears to be linked to the 60 m fluvioglacial terrace, dated in a tributary of the Aragón River at 263 ± 21 ka. The difference in age between M1 moraine and the 60 m fluvioglacial terrace suggests that the latter belongs to an earlier glacial stage (MIS 8). Moraine M2 was clearly linked to the fluvioglacial 20 m terrace. Other minor internal moraines were related to the 7–8 m terrace. The dates obtained for the last glacial cycle (20–18 ka) are similar to other chronologies for Mediterranean mountains, and confirm the occurrence of an early MIE in the Central Pyrenees that does not coincide with the global LGM.  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.
The retreat of 293 glaciers in the Tien Shan Mountains (Kyrgyz Republic) from their maximum extent during the Little Ice Age (LIA) is estimated using aerial photographs from 1980 to 1985 and maps at a scale of 1:25000, constructed during period 1956–1990. Two indices of changes are used: the linear distance from the glacier terminus to its Little Ice Age moraine and the difference in absolute elevation of the terminus and the moraine. Historical information about the front positions of glaciers in the 1880s to the 1930s was used as an indirect control of remote sensing data. The age of moraines in key regions was estimated by lichenometry. On average, Tien Shan glaciers have retreated by 989 ± 540 m since the LIA maximum. Their front elevations (dh) rose by 151 ± 105 m. These changes are similar to changes observed in the Alps and western Norway, Pamir‐Alay and Koryak plateau, but greater than in east Siberia over the same interval. Differences between four regions in Tien Shan (northern, western, inner, central) are generally small, though in the northern Tien Shan the glacier retreat and frontal rise are more prominent (1065 ± 479 m and 215 ± 140 m, respectively).  相似文献   

16.
Terrace remnants close to the marine limit as well as two separate moraine ridges are observed in front of the glacier Albrechtbreen. The stacking of marine sediments from an original elevation of ca. 60–80 m a.s.l. into the Little Ice Age Moraine gives evidence for a considerably smaller glacier following the early Holocene deglaciation compared to that of the present. The outer moraine is composed of glacial diamicton. Radiocarbon datings of whale ribs, shell fragments and a log taken from sediment in front of Albrechtbreen indicate that the initial deglaciation occurred before 9, 400 B.P. and that the outer moraine was formed during a younger Holocene glacial advance. Lithological differences between the two moraine ridges suggest that the first ice advance occurred during a period with limited permafrost, whereas permafrost was more extensive during the Little Ice Age.  相似文献   

17.
The Debeli Namet glacier in the Durmitor massif, Montenegro, is one of the lowest altitude glaciers (2050–2300 m) at this latitude (42–44°N) in the northern hemisphere. The glacier survives well below the climatological equilibrium line altitude because of substantial inputs from avalanching and windblown snow. The glacier survived two of the hottest summers on record in 2003 and 2007, although it experienced significant retreat. However, during the intervening years (2004–2006) the glacier increased in size and advanced, forming a new frontal moraine. This rapid advance was primarily in response to much cooler summer temperatures, close to or cooler than average, and a marked increase in winter precipitation. The rapid growth and decay of the Debeli Namet glacier in response to inter‐annual climate variability highlights the sensitivity of small cirque glaciers to short‐term climate change.  相似文献   

18.
Mapping and laboratory analysis of the sediment—landform associations in the proglacial area of polythermal Storglaciären, Tarfala, northern Sweden, reveal six distinct lithofacies. Sandy gravel, silty gravel, massive sand and silty sand are interpreted as glaciofluvial in origin. A variable, pervasively deformed to massive clast‐rich sandy diamicton is interpreted as the product of an actively deforming subglacial till layer. Massive block gravels, comprising two distinctive moraine ridges, reflect supraglacial sedimentation and ice‐marginal and subglacial reworking of heterogeneous proglacial sediments during the Little Ice Age and an earlier more extensive advance. Visual estimation of the relative abundance of these lithofacies suggests that the sandy gravel lithofacies is of the most volumetric importance, followed by the diamicton and block gravels. Sedimentological analysis suggests that the role of a deforming basal till layer has been the dominant factor controlling glacier flow throughout the Little Ice Age, punctuated by shorter (warmer and wetter climatic) periods where high water pressures may have played a more important role. These results contribute to the database that facilitates discrimination of past glacier thermal regimes and dynamics in areas that are no longer glacierized, as well as older glaciations in the geological record.  相似文献   

19.
One of the largest outlet glaciers from the ice cap Jostedalsbreen has been studied by various scientists during the 19th and 20th centuries, and a detailed programme of mass balance investigations has been carried out in recent years. The paper summarizes results from earlier studies, even from observations since the large advance about 1740, and particularly recent data. Detailed mass balance studies since 1962 have shown that the glacier is growing in volume (more than 6 m of water equivalent from 1962 to 1975) but this has not yet resulted in any advance of the ice front. The maximum observed ice velocity is 1.4 m/day on the tongue, where the ice thickness is about 200 m in a surveyed profile located below the ice falls.  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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