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Moraines
Kinds of Moraines Terms modified by Moraines Selected AbstractsCosmogenic 10BE Age Constraints for The Wester Ross Readvance Moraine: Insights Into British Ice-Sheet BehaviourGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2006Jeremy D. Everest This study presents the first absoluteage constraints from a palaeo-ice-sheet margin in western Scotland. Cosmogenic 10Be from four Lewisian gneiss boulders on the Gairloch Moraine in NW Scotland have yielded reliable exposure ages. Three of these dates, taken from a single moraine ridge, cluster around c. 15.5,18 ka BP, with a weighted mean of 16.3 ± 1.6 ka BP. These findings indicate that the last British Ice Sheet had retreated to the present-day coastline in NW Scotland by this time. It is suggested that the Wester Ross Readvance represents an ice-sheet oscillation during, or in the immediate aftermath of, Heinrich Event 1 (c. 17,18 ka BP). [source] 40Ar- 39Ar age determinations of lunar basalt meteorites Asuka 881757, Yamato 793169, Miller Range 05035, La Paz Icefield 02205, Northwest Africa 479, and basaltic breccia Elephant Moraine 96008METEORITICS & PLANETARY SCIENCE, Issue 6 2009Vera A. FERNANDES Stepped heating 40Ar- 39Ar analyses of several bulk fragments of related meteorites A-881757, Y-793169 and MIL 05035 give crystallization ages of 3.763 ± 0.046 Ga, 3.811 ± 0.098 Ga and 3.845 ± 0.014 Ga, which are comparable with previous age determinations by Sm-Nd, U-Pb Th-Pb, Pb-Pb, and Rb-Sr methods. These three meteorites differ in the degree of secondary 40Ar loss with Y-793169 showing relatively high Ar loss probably during an impact event ,200 Ma ago, lower Ar loss in MIL 05035 and no loss in A-881757. Bulk and impact melt glass-bearing samples of LAP 02205 gave similar ages (2.985 ± 0.016 Ga and 2.874 ± 0.056 Ga) and are consistent with ages previously determined using other isotope pairs. The basaltic portion of EET 96008 gives an age of 2.650 ± 0.086 Ga which is considered to be the crystallization age of the basalt in this meteorite. The Ar release for fragmental basaltic breccia EET 96008 shows evidence of an impact event at 631 ± 20 Ma. The crystallization age of 2.721 ± 0.040 Ga determined for NWA 479 is indistinguishable from the weighted mean age obtained from three samples of NWA 032 supporting the proposal that these meteorites are paired. The similarity of 40Ar- 39Ar ages with ages determined by other isotopic systems for multiple meteorites suggests that the K-Ar isotopic system is robust for meteorites that have experienced a significant shock event and not a prolonged heating regime. [source] Molecular and isotopic indicators of alteration in CR chondritesMETEORITICS & PLANETARY SCIENCE, Issue 9 2006V. K. Pearson However, in contrast to other chondrite groups, the CR organic fraction is poorly characterized. The carbonaceous chondrite literature shows that relatively anhydrous thermal processing results in a condensed, poorly alkylated, O-poor macromolecular material, while for aqueous processing the converse is true. Such characteristics can be used to discern the alteration histories of the carbonaceous chondrites. We have performed bulk elemental and isotopic analysis and flash pyrolysis on four CR chondrites (Renazzo, Al Rais, Elephant Moraine [EET] 87770, and Yamato [Y-] 790112) to determine the nature of their organic component. Renazzo, Al Rais, and Y-790112 release qualitatively similar pyrolysis products, although there are some variations. Al Rais' macromolecular structure contains substantially higher relative abundances of alkylated and oxidized species and relatively lighter ,15N, suggesting that it has endured more extensive aqueous processing than the other CR chondrites. Renazzo appears relatively unprocessed, with a low degree of alkylation, a lack of detectable nitrogen-bearing components, and low methylnaphthalene ratio. EET 87770's low abundance of alkylated species suggests its macromolecular structure may be relatively condensed, with condensation potentially assisted by a period of mild thermal alteration. [source] Ice dynamics of the Allan Hills meteorite concentration sites revealed by satellite aperture radar interferometryMETEORITICS & PLANETARY SCIENCE, Issue 9 2003F. COREN The area includes a number of meteorite concentration sites, in particular the Allan Hills ice fields. Regional ice flow velocities around the Midwestern and Near-western ice fields and the Allan Hills main ice field are shown to be ,2.5 m yr,1. These sites are located on a horseshoe-shaped area that bounds an area characterized by higher ice flow velocities of up to 5 m yr,1. Meteorite find locations on the Elephant Moraine are located in this "high ice flow" area. The SAR derived digital elevation model (DEM) shows atypical low surface slopes for Antarctic conditions, which are the cause for the slow ice movements. Numerous ice rises in the area are interpreted to cap sub-ice obstacles, which were formed by tectonic processes in the past. The ice rises are considered to represent temporary features, which develop only during warm stages when the regional ice stand is lowered. Ice depressions, which develop in warm stages on the lee side of ice rises, may act as the sites of temporary build-up of meteorite concentrations, which turn inoperative during cold stages when the regional ice level rises and the ice rises disappear. Based on a simplified ice flow model, we argue that the regional ice flow in cold stages is reduced by a factor of at least 3. [source] Thermoluminescence sensitivity and thermal history of type 3 ordinary chondrites: Eleven new type 3.0,3.1 chondrites and possible explanations for differences among H, L, and LL chondritesMETEORITICS & PLANETARY SCIENCE, Issue 6 2002P. H. Benoit We have identified 11 UOCs of petrologic types 3.0,3.1: Adrar 003, Elephant Moraine (EET) 90066, EET 90161, Grosvenor Mountains (GRO) 95502, Lewis Cliff (LEW) 88477, Meteorite Hills (MET) 96503, Yamato (Y)-790787, Y-791324, Y-791558, Y-793565, and Y-793596. These samples represent an important new resource for researchers interested in the nature of primitive solar system materials. Previously reported trends in which TL sensitivity increases with TL peak temperature and TL peak width, which we interpret in terms of crystallization of feldspar in the ordered or disordered forms during metamorphism, are confirmed by the new data. Importantly, the present data strengthen the trend described earlier in which the mean level of metamorphism experienced by UOCs increases along the series LL, L and H. This suggests either different burial depths for the UOCs from each class, or formation at similar depths in regoliths of different thickness. [source] Petrology and chemistry of the new shergottite Dar al Gani 476METEORITICS & PLANETARY SCIENCE, Issue 1 2000J. ZIPFEL The meteorite is classified as a basaltic shergottite and is only the 13th martian meteorite known to date. It has a porphyritic texture consisting of a fine-grained groundmass and larger olivines. The groundmass consists of pyroxene and feldspathic glass. Minor phases are oxides and sulfides as well as phosphates. The presence of olivine, orthopyroxene, and chromite is a feature that DaG 476 has in common with lithology A of Elephant Moraine (EET) A79001. However, in DaG 476, these phases appear to be early phenocrysts rather than xenocrysts. Shock features, such as twinning, mosaicism, and impact-melt pockets, are ubiquitous. Terrestrial weathering was severe and led to formation of carbonate veins following grain boundaries and cracks. With a molar MgO/(MgO + FeO) of 0.68, DaG 476 is the most magnesian member among the basaltic shergottites. Compositions of augite and pigeonite and some of the bulk element concentrations are intermediate between those of lherzolitic and basaltic shergottites. However, major elements, such as Fe and Ti, as well as LREE concentrations are considerably lower than in other shergottites. Noble gas concentrations are low and dominated by the mantle component previously found in Chassigny. A component, similar to that representing martian atmosphere, is virtually absent. The ejection age of 1.35 ± 0.10 Ma is older than that of EETA79001 and could possibly mark a distinct ejection. Dar al Gani 476 is classified as a basaltic shergottite based on its mineralogy. It has a fine-grained groundmass consisting of clinopyroxene, pigeonite and augite, feldspathic glass and chromite, Ti-chromite, ilmenite, sulfides, and whitlockite. Isolated olivine and single chromite grains occur in the groundmass. Orthopyroxene forms cores of some pigeonite grains. Shock-features, such as shock-twinning, mosaicism, cracks, and impact-melt pockets, are abundant. Severe weathering in the Sahara led to significant formation of carbonate veins crosscutting the entire meteorite. Dar al Gani 476 is distinct from other known shergottites. Chemically, it is the most magnesian member among known basaltic shergottites and intermediate in composition for most trace and major elements between Iherzolitic and basaltic shergottites. Unique are the very low bulk REE element abundances. The CI-normalized abundances of LREEs are even lower than those of Iherzolitic shergottites. The overall abundance pattern, however, is similar to that of QUE 94201. Textural evidence indicates that orthopyroxene, as well as olivine and chromite, crystallized as phenocrysts from a magma similar in composition to that of bulk DaG 476. Whether such a magma composition can be a shergottite parent melt or was formed by impact melting needs to be explored further. At this time, it cannot entirely be ruled out that these phases represent relics of disaggregated xenoliths that were incorporated and partially assimilated by a basaltic melt, although the texture does not support this possibility. Trapped noble gas concentrations are low and dominated by a Chassigny-like mantle component. Virtually no martian atmosphere was trapped in DaG 476 whole-rock splits. The exposure age of 1.26 ± 0.09 Ma is younger than that of most shergottites and closer to that of EETA79001. The ejection age of 1.35 ± 0.1 Ma could mark another distinct impact event. [source] The Late-Devensian proglacial Lake Humber: new evidence from littoral deposits at Ferrybridge, Yorkshire, EnglandBOREAS, Issue 2 2008MARK D. BATEMAN Proglacial Lake Humber is of UK national significance in terms of landscape drainage and development of the British Ice Sheet (BIS) during Marine Isotope Stage 2 (MIS 2), yet it is poorly understood in terms of its dynamics and timing. Sands and gravels exposed at Ferrybridge, West Yorkshire, UK, are interpreted as part of the Upper Littoral sands and gravels related to a high-level Lake Humber, which inundated the Humber Basin to ,30 m OD during MIS 2. Excavations exposed well-rounded gravels of local origin extending downslope from the 27.5 m OD contour and interbedded sands and fine gravels, which are interpreted as the coarse littoral deposits and nearshore associated deposits. A sample from the distal sands returned an Optically Stimulated Luminescence age of 16.6±1.2 kyr, providing the first direct age for the high-level lake and for when North Sea Basin ice must have blocked the Humber Gap. An underlying sequence included a diamicton dated to after 23.3 ±1.5 kyr and before 20.5±1.2 kyr, indicating that the Late Devensian ice reached at least 15 km south of the Escrick Moraine prior to the high-level lake. Previous to both the high-level lake and this ice advance, loess found at the two sites investigated indicates a long period of loess deposition earlier in MIS 2. These new data for the history of Lake Humber are discussed in the context of ice-marginal oscillations in both the Vale of York and the North Sea Basin. [source] A New Method to Identify Quaternary Moraine: Acoustic Emission Stress MeasurementACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2006ZHAO Zhizhong Abstract: How to effectively identify glacial sediments, especially Quaternary moraine, has been in dispute for decades. The traditional methods, e.g., sedimentary and geomorphologic ones, are facing challenge in eastern China where controversial moraine deposits are dominatingly distributed. Here, for the first time, we introduce the acoustic emission (AE) stress measurement, a kind of historical stress measurement, to identify Quaternary moraine. The results demonstrate that it can be employed to reconstruct stress information of glaciation remaining in gravels, and may shed light on the identification of Quaternary moraine in eastern China. First, we measured the AE stress of gravels of glacial origin that are underlying the Xidatan Glacier, eastern Kunlun Mountains in western China. Second, we calculated the stress according to the actual thickness of the glacier. The almost identical stress values suggest that the glacial gravels can memorize and preserve the overlying glacier-derived aplomb stress. And then we introduce this new approach to the controversial moraine in Mount Lushan, eastern China. The results indicate that the stress is attributed to the Quaternary glacier, and the muddy gravels in the controversial moraine in Mount Lushan are moraine deposits but not others. [source] Impact of a rock avalanche on a moraine-dammed proglacial lake: Laguna Safuna Alta, Cordillera Blanca, PeruEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2005Bryn Hubbard Abstract Moraines that dam proglacial lakes pose an increasing hazard to communities in the Andes and other mountain ranges. The moraines are prone to failure through collapse, overtopping by lake waters or the effect of displacement waves resulting from ice and rock avalanches. Resulting floods have led to the loss of thousands of lives in the Cordillera Blanca mountains of Peru alone in the last 100 years. On 22 April 2002 a rock avalanche occurred immediately to the south-west of Laguna Safuna Alta, in the Cordillera Blanca. The geomorphic evidence for the nature, magnitude and consequences of this event was investigated in August 2002. Field mapping indicated that the avalanche deposited 8,20 × 106 m3 of rock into the lake and onto the surface of the frontal region of Glaciar Pucajirca, which flows into the lake. Repeated bathymetric surveying indicated that ,5 × 106 m3 of this material was deposited directly into the lake. The immediate effect of this event was to create a displacement wave that gained in height as it travelled along the lake basin, overtopping the impounding moraine at the lake's northern end. To achieve overtopping, the maximum wave height must have been greater than 100 m. This, and subsequent seiche waves, caused extensive erosion of both the proximal and distal faces of the impounding terminal moraine. Further deep gullying of the distal face of this moraine resulted from the supply of pressurized water to the face via a relief overflow tunnel constructed in 1978. Two-dimensional, steady-state analysis of the stability of the post-avalanche moraine rampart indicates that its proximal face remains susceptible to major large-scale rotational failure. Copyright © 2005 John Wiley & Sons, Ltd. [source] Re-Dating the Moraines at Skálafellsjökull and Heinabergsjökull using different Lichenometric Methods: Implications for the Timing of the Icelandic Little Ice Age MaximumGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2004Krista M. Mckinzey Abstract 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. [source] Glacier response in the European Alps to Heinrich Event 1 cooling: the Gschnitz stadial,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2006Susan Ivy-Ochs Abstract The Gschnitz stadial was a period of regionally extensive glacier advance in the European Alps that lies temporally between the breakdown of the Last Glacial Maximum piedmont lobes and the beginning of the Bølling warm interval. Moraines of the Gschnitz stadial are found in medium to small catchments, are steep-walled and blocky, and reflect a snowline lowering of 650,700,m in comparison to the Little Ice Age reference snowline. 10Be surface exposure dating of boulders from the moraine at the type locality at Trins (Gschnitz valley, Tyrol, Austria) shows that it stabilised no later than 15,400,±,1400,yr ago. The overall morphological situation and the long reaction time of the glacier suggest that the climatic downturn lasted about 500,±,300,yr, indicating that the Gschnitz cold period began approximately 15,900,±,1400,yr ago, if not somewhat earlier. This is consistent with published radiocarbon dates that imply that the stadial occurred sometime between 15,400 14C,yr BP (18,020,19,100,cal.,yr) and 13,250 14C,yr BP (15,360,16,015,cal.,yr). A palaeoclimatic interpretation of the Gschnitz glacier based on a simple glacier flow model and statistical glacier-climate models shows that precipitation was about one-third of modern-day precipitation and summer temperatures were about 10,K lower than today. In comparison, during the Younger Dryas, precipitation in this area was only about 10% less and Ts (summer temperature) was only 3.5,4,K lower than modern values. Based on the age of the moraine and the cold and dry climate at that time, we suggest that the Gschnitz stadial was the response of Alpine glaciers to cooling of the North Atlantic Ocean associated with Heinrich Event 1. Copyright © 2005 John Wiley & Sons, Ltd. [source] Edge-roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering ratesBOREAS, Issue 2 2010MARTIN P. KIRKBRIDE Kirkbride, M.P. & Bell, C.M. 2009: Edge-roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering rates. Boreas, 10.1111/j. 1502-3885.2009.00131.x. ISSN 0300-9483. The relative ages of late Quaternary morainic and rock avalanche deposits on Late Precambrian Torridonian Sandstone are determined from the characteristic edge-roundness of constituent boulders. Because weathering of sandstone is manifest as edge-rounding by granular disintegration, a relative chronology can be derived by measuring the effective radii of curvature of a sample of boulder edges. Thirteen samples totalling 597 individual boulder edges fall into two statistically distinct groups. Moraines of inferred Younger Dryas age (12.9,11.5 kyr BP) are distinguished from moraines of the Wester Ross Re-advance (,14.0 kyr BP). One moraine previously assumed to be of Younger Dryas age is reassigned to the older group. The method allows spatial extrapolation of deposit ages from dated sites where lithological and sampling criteria are met. Calculated rates of edge-rounding imply that granular disintegration was several times more rapid during cold stadial climates than during the Holocene. Used as a proxy for boulder ,erosion rate', this indicates that surface loss of grains in glacial climates exceeds that during interglacials by a factor of 2,5, with implications for the calculation of exposure ages from cosmogenic nuclides. [source] Impact of a rock avalanche on a moraine-dammed proglacial lake: Laguna Safuna Alta, Cordillera Blanca, PeruEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2005Bryn Hubbard Abstract Moraines that dam proglacial lakes pose an increasing hazard to communities in the Andes and other mountain ranges. The moraines are prone to failure through collapse, overtopping by lake waters or the effect of displacement waves resulting from ice and rock avalanches. Resulting floods have led to the loss of thousands of lives in the Cordillera Blanca mountains of Peru alone in the last 100 years. On 22 April 2002 a rock avalanche occurred immediately to the south-west of Laguna Safuna Alta, in the Cordillera Blanca. The geomorphic evidence for the nature, magnitude and consequences of this event was investigated in August 2002. Field mapping indicated that the avalanche deposited 8,20 × 106 m3 of rock into the lake and onto the surface of the frontal region of Glaciar Pucajirca, which flows into the lake. Repeated bathymetric surveying indicated that ,5 × 106 m3 of this material was deposited directly into the lake. The immediate effect of this event was to create a displacement wave that gained in height as it travelled along the lake basin, overtopping the impounding moraine at the lake's northern end. To achieve overtopping, the maximum wave height must have been greater than 100 m. This, and subsequent seiche waves, caused extensive erosion of both the proximal and distal faces of the impounding terminal moraine. Further deep gullying of the distal face of this moraine resulted from the supply of pressurized water to the face via a relief overflow tunnel constructed in 1978. Two-dimensional, steady-state analysis of the stability of the post-avalanche moraine rampart indicates that its proximal face remains susceptible to major large-scale rotational failure. Copyright © 2005 John Wiley & Sons, Ltd. [source] Geomorphic and sedimentological signature of a two-phase outburst ,ood from moraine-dammed Queen Bess Lake, British Columbia, CanadaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2005Jane A. Kershaw Abstract On 12 August 1997, the lower part of Diadem Glacier in the southern Coast Mountains of British Columbia fell into Queen Bess Lake and produced a train of large waves. The waves overtopped the broad end moraine at the east end of the lake and ,ooded the valley of the west fork of Nostetuko River. The displacement waves also incised the out,ow channel across the moraine. Stratigraphic and sedimentologic evidence supports the conclusion that the ,ood had two phases, one related to wave overtopping and a second to breach formation. Empirical equations were used to calculate the peak discharge of the ,ood at various points along the west fork of the Nostetuko valley and to describe the attenuation of the ,ood wave. The velocity of the ,ood was also calculated to determine the time it took for the ,ood to reach the main fork of Nostetuko River. The highest peak discharges were achieved in the upper reach of the valley during the displacement phase of the ,ood. Peak discharge declined rapidly just below the moraine dam, with little change thereafter for approximately 7 km. Empirical formulae and boulder measurements indicate a rise in peak discharge in the lower part of the west fork valley. We suggest that ,ow in the upper part of the valley records the passage of two separate ,ood peaks and that the rise in discharge in the lower part of the valley is due to amalgamation of the wave and breach peaks. Hydraulic ponding in con,ned reaches of the valley extended the duration of the ,ood. In addition, erosion of vegetation and sediment in the channel and valley sides may also have exerted an in,uence on the duration and nature of ,ooding. Sediments were deposited both upstream and downstream of channel constrictions and on a large fan extending out into the trunk Nostetuko River valley. This study extends our understanding of the variety and complexity of outburst ,oods from naturally dammed lakes. It also shows that simple empirical and other models for estimating peak discharges of outburst ,oods are likely to yield erroneous results. Copyright © 2005 John Wiley & Sons, Ltd. [source] Rock weathering creates oases of life in a High Arctic desertENVIRONMENTAL MICROBIOLOGY, Issue 2 2010Sara Borin Summary During primary colonization of rock substrates by plants, mineral weathering is strongly accelerated under plant roots, but little is known on how it affects soil ecosystem development before plant establishment. Here we show that rock mineral weathering mediated by chemolithoautotrophic bacteria is associated to plant community formation in sites recently released by permanent glacier ice cover in the Midtre Lovénbreen glacier moraine (78°53,N), Svalbard. Increased soil fertility fosters growth of prokaryotes and plants at the boundary between sites of intense bacterial mediated chemolithotrophic iron-sulfur oxidation and pH decrease, and the common moraine substrate where carbon and nitrogen are fixed by cyanobacteria. Microbial iron oxidizing activity determines acidity and corresponding fertility gradients, where water retention, cation exchange capacity and nutrient availability are increased. This fertilization is enabled by abundant mineral nutrients and reduced forms of iron and sulfur in pyrite minerals within a conglomerate type of moraine rock. Such an interaction between microorganisms and moraine minerals determines a peculiar, not yet described model for soil genesis and plant ecosystem formation with potential past and present analogues in other harsh environments with similar geochemical settings. [source] RESPONSE OF A MONTENEGRO GLACIER TO EXTREME SUMMER HEATWAVES IN 2003 AND 2007GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2008PHILIP. ABSTRACT. 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. [source] A Polygenetic Landform At Stígá, Öræfajökull, Southern IcelandGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2004Tim Harris Abstract Recent research has identified problems inherent in the identification and description of landforms. Morphologically similar small-scale glacial and periglacial landforms can be misinterpreted, thus hindering environmental reconstruction. This study reveals that a landform resembling a moraine at Stígárjökull, southern Iceland, is the product of both glacial deposition and mass movement. The landform has two distinct morphological and sedimentological components: a basal, lithologically diverse component, and an upper, lithologically homogenous component. Clast lithological analysis, particle shape and particle size measurements demonstrate that the basal component of the landform consists of sediment whose characteristics match nearby moraines. In contrast, the source of the upper component is a narrow outcrop of rock above the valley floor. Evidence suggests that frost-shattered material was transported across a perennial snow patch to a small moraine, leading to growth of the ,moraine'. This combination of processes is unlikely to be unique, but the geological peculiarities of the field site permitted their identification. It is possible that many similar ,moraines' could be enlarged by subaerial feeding, leading to false reconstruction of glacier form and/or associated rates of erosion and sedimentation. Such polygenetic landform genesis therefore has implications for environmental reconstruction. [source] Using DC resistivity tomography to detect and characterize mountain permafrostGEOPHYSICAL PROSPECTING, Issue 4 2003Christian Hauck ABSTRACT Direct-current (DC) resistivity tomography has been applied to different mountain permafrost regions. Despite problems with the very high resistivities of the frozen material, plausible results were obtained. Inversions with synthetic data revealed that an appropriate choice of regularization constraints was important, and that a joint analysis of several tomograms computed with different constraints was required to judge the reliability of individual features. The theoretical results were verified with three field experiments conducted in the Swiss and the Italian Alps. At the first site, near Zermatt, Switzerland, the location and the approximate lateral and vertical extent of an ice core within a moraine could be delineated. On the Murtel rock glacier, eastern Swiss Alps, a steeply dipping boundary at its frontal part was observed, and extremely high resistivities of several M, indicated a high ice content. The base of the rock glacier remained unresolved by the DC resistivity measurements, but it could be constrained with transient EM soundings. On another rock glacier near the Stelvio Pass, eastern Italian Alps, DC resistivity tomography allowed delineation of the rock glacier base, and the only moderately high resistivities within the rock glacier body indicated that the ice content must be lower compared with the Murtel rock glacier. [source] Late Pleistocene and Holocene glaciation of the Fish Lake valley, northeastern Alaska Range, Alaska,JOURNAL OF QUATERNARY SCIENCE, Issue 7 2009Nicolás E. Young Abstract We reconstructed a chronology of glaciation spanning from the Late Pleistocene through the late Holocene for Fish Lake valley in the north-eastern Alaska Range using 10Be surface exposure dating and lichenometry. After it attained its maximum late Wisconsin extent, the Fish Lake valley glacier began to retreat ca. 16.5,ka, and then experienced a readvance or standstill at 11.6,±,0.3,ka. Evidence of the earliest Holocene glacial activity in the valley is a moraine immediately in front of Little Ice Age (LIA) moraines and is dated to 3.3,3.0,ka. A subsequent advance culminated at ca. AD 610,900 and several LIA moraine crests date to AD 1290, 1640, 1860 and 1910. Our results indicate that 10Be dating from high-elevation sites can be used to help constrain late Holocene glacial histories in Alaska, even when other dating techniques are unavailable. Close agreement between 10Be and lichenometric ages reveal that 10Be ages on late Holocene moraines may be as accurate as other dating methods. Copyright © 2009 John Wiley & Sons, Ltd. [source] Seafloor glacial features reveal the extent and decay of the last British Ice Sheet, east of Scotland,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2009Alastair G. C. Graham Abstract Three-dimensional (3D) seismic datasets, 2D seismic reflection profiles and shallow cores provide insights into the geometry and composition of glacial features on the continental shelf, offshore eastern Scotland (58° N, 1,2° W). The relic features are related to the activity of the last British Ice Sheet (BIS) in the Outer Moray Firth. A landsystem assemblage consisting of four types of subglacial and ice marginal morphology is mapped at the seafloor. The assemblage comprises: (i) large seabed banks (interpreted as end moraines), coeval with the Bosies Bank moraine; (ii) morainic ridges (hummocky, push and end moraine) formed beneath, and at the margins of the ice sheet; (iii) an incised valley (a subglacial meltwater channel), recording meltwater drainage beneath former ice sheets; and (iv) elongate ridges and grooves (subglacial bedforms) overprinted by transverse ridges (grounding line moraines). The bedforms suggest that fast-flowing grounded ice advanced eastward of the previously proposed terminus of the offshore Late Weichselian BIS, increasing the size and extent of the ice sheet beyond traditional limits. Complex moraine formation at the margins of less active ice characterised subsequent retreat, with periodic stillstands and readvances. Observations are consistent with interpretations of a dynamic and oscillating ice margin during BIS deglaciation, and with an extensive ice sheet in the North Sea basin at the Last Glacial Maximum. Final ice margin retreat was rapid, manifested in stagnant ice topography, which aided preservation of the landsystem record. Copyright © 2008 John Wiley & Sons, Ltd. [source] Glacier response in the European Alps to Heinrich Event 1 cooling: the Gschnitz stadial,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2006Susan Ivy-Ochs Abstract The Gschnitz stadial was a period of regionally extensive glacier advance in the European Alps that lies temporally between the breakdown of the Last Glacial Maximum piedmont lobes and the beginning of the Bølling warm interval. Moraines of the Gschnitz stadial are found in medium to small catchments, are steep-walled and blocky, and reflect a snowline lowering of 650,700,m in comparison to the Little Ice Age reference snowline. 10Be surface exposure dating of boulders from the moraine at the type locality at Trins (Gschnitz valley, Tyrol, Austria) shows that it stabilised no later than 15,400,±,1400,yr ago. The overall morphological situation and the long reaction time of the glacier suggest that the climatic downturn lasted about 500,±,300,yr, indicating that the Gschnitz cold period began approximately 15,900,±,1400,yr ago, if not somewhat earlier. This is consistent with published radiocarbon dates that imply that the stadial occurred sometime between 15,400 14C,yr BP (18,020,19,100,cal.,yr) and 13,250 14C,yr BP (15,360,16,015,cal.,yr). A palaeoclimatic interpretation of the Gschnitz glacier based on a simple glacier flow model and statistical glacier-climate models shows that precipitation was about one-third of modern-day precipitation and summer temperatures were about 10,K lower than today. In comparison, during the Younger Dryas, precipitation in this area was only about 10% less and Ts (summer temperature) was only 3.5,4,K lower than modern values. Based on the age of the moraine and the cold and dry climate at that time, we suggest that the Gschnitz stadial was the response of Alpine glaciers to cooling of the North Atlantic Ocean associated with Heinrich Event 1. Copyright © 2005 John Wiley & Sons, Ltd. [source] Surface exposure dating of the Great Aletsch Glacier Egesen moraine system, western Swiss Alps, using the cosmogenic nuclide 10BeJOURNAL OF QUATERNARY SCIENCE, Issue 5 2004Meredith A. Kelly Abstract Egesen moraines throughout the Alps mark a glacial advance that has been correlated with the Younger Dryas cold period. Using the surface exposure dating method, in particular the measurement of the cosmogenic nuclide 10Be in rock surfaces, we attained four ages for boulders on a prominent Egesen moraine of Great Aletsch Glacier, in the western Swiss Alps. The 10Be dates range from 10,460±1100 to 9040±1020,yr ago. Three 10Be dates between 9630±810 and 9040±1020,yr ago are based upon samples from the surfaces of granite boulders. Two 10Be dates, 10,460±1100 and 9910±970,yr ago, are based upon a sample from a quartz vein at the surface of a schist boulder. In consideration of the numerous factors that can influence apparently young 10Be dates and the scatter within the data, we interpret the weighted mean of four boulder ages, 9640±430,yr (including the weighted mean of two 10Be dates of the quartz vein), as a minimum age of deposition of the moraine. All 10Be dates from the Great Aletsch Glacier Egesen moraine are consistent with radiocarbon dates of nearby bog-bottom organic sediments, which provide minimum ages of deglaciation from the moraine. The 10Be dates from boulders on the Great Aletsch Glacier Egesen moraine also are similar to 10Be dates from Egesen moraines of Vadret Lagrev Glacier on Julier Pass, in the eastern Swiss Alps. Both the morphology of the Great Aletsch Glacier Egesen moraine and the comparison with 10Be dates from the inner Vadret Lagrev Egesen moraine support the hypothesis that the climatic cooling that occurred during the Younger Dryas cold episode influenced the glacial advance that deposited the Great Aletsch Glacier Egesen moraine. Because of the large size and slow response time of Great Aletsch Glacier, we suggest that the Great Aletsch Glacier Egesen moraine was formed during the last glacial advance of the multiphased Egesen cold period, the Kromer stage, during the Preboreal chron. Copyright © 2004 John Wiley & Sons, Ltd. [source] Moraine development at a small High-Arctic valley glacier: Rieperbreen, SvalbardJOURNAL OF QUATERNARY SCIENCE, Issue 6 2001Astrid Lyså Abstract Ice-cored lateral and frontal moraine complexes, formed at the margin of the small, land-based Rieperbreen glacier, central Svalbard, have been investigated through field observations and interpretations of aerial photographs (1936, 1961 and 1990). The main focus has been on the stratigraphical and dynamic development of these moraines as well as the disintegration processes. The glacier has been wasting down since the ,Little Ice Age' (LIA) maximum, and between 1936 and 1990 the glacier surface was lowered by 50,60 m and the front retreated by approximately 900 m. As the glacier wasted, three moraine ridges developed at the front, mainly as melting out of sediments from debris-rich foliation and debris-bands formed when the glacier was polythermal, probably during the LIA maximum. The disintegration of the moraines is dominated by wastage of buried ice, sediment gravity-flows, meltwater activity and some frost weathering. A transverse glacier profile with a northward sloping surface has developed owing to the higher insolation along the south-facing ice margin. This asymmetric geometry also strongly affects the supraglacial drainage pattern. Lateral moraines have formed along both sides of the glacier, although the insolation aspect of the glacier has resulted in the development of a moraine 60 m high along its northern margin. Copyright © 2001 John Wiley & Sons, Ltd. [source] Edge-roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering ratesBOREAS, Issue 2 2010MARTIN P. KIRKBRIDE Kirkbride, M.P. & Bell, C.M. 2009: Edge-roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering rates. Boreas, 10.1111/j. 1502-3885.2009.00131.x. ISSN 0300-9483. The relative ages of late Quaternary morainic and rock avalanche deposits on Late Precambrian Torridonian Sandstone are determined from the characteristic edge-roundness of constituent boulders. Because weathering of sandstone is manifest as edge-rounding by granular disintegration, a relative chronology can be derived by measuring the effective radii of curvature of a sample of boulder edges. Thirteen samples totalling 597 individual boulder edges fall into two statistically distinct groups. Moraines of inferred Younger Dryas age (12.9,11.5 kyr BP) are distinguished from moraines of the Wester Ross Re-advance (,14.0 kyr BP). One moraine previously assumed to be of Younger Dryas age is reassigned to the older group. The method allows spatial extrapolation of deposit ages from dated sites where lithological and sampling criteria are met. Calculated rates of edge-rounding imply that granular disintegration was several times more rapid during cold stadial climates than during the Holocene. Used as a proxy for boulder ,erosion rate', this indicates that surface loss of grains in glacial climates exceeds that during interglacials by a factor of 2,5, with implications for the calculation of exposure ages from cosmogenic nuclides. [source] Formation of submarginal and proglacial end moraines: implications of ice-flow mechanism during the 1963,64 surge of Brúarjökull, IcelandBOREAS, Issue 3 2009ÍVAR ÖRN BENEDIKTSSON The morphology, sedimentology and architecture of an end moraine formed by a ,9 km surge of Brúarjökull in 1963,64 are described and related to ice-marginal conditions at surge termination. Field observations and accurate mapping using digital elevation models and high-resolution aerial photographs recorded at surge termination and after the surge show that commonly the surge end moraine was positioned underneath the glacier snout by the termination of the surge. Ground-penetrating radar profiles and sedimentological data reveal 4,5 m thick deformed sediments consisting of a top layer of till overlying gravel and fine-grained sediments, and structural geological investigations show that the end moraine is dominated by thrust sheets. A sequential model explaining the formation of submarginal end moraines is proposed. The hydraulic conductivity of the bed had a major influence on the subglacial drainage efficiency and associated porewater pressure at the end of the surge, thereby affecting the rates of subglacial deformation. High porewater pressure in the till decreased its shear strength and raised its strain rate, while low porewater pressure in the underlying gravel had the opposite effect, such that the gravel deformed more slowly than the till. The principal velocity component was therefore located within the till, allowing the glacier to override the gravel thrust sheets that constitute the end moraine. The model suggests that the processes responsible for the formation of submarginal end moraines are different from those operating during the formation of proglacial end moraines. [source] Structure and composition of a tidewater glacier push moraine, Svalbard, revealed by DC resistivity profilingBOREAS, Issue 1 2009LENE KRISTENSEN A push moraine deposited by the surging tidewater glacier Paulabreen (Svalbard) was investigated using 2D resistivity profiling. Six longitudinal and transverse profiles were obtained on the moraine and the resistivities were compared with data from three boreholes. Four profiles indicate that the inner part of the moraine is ice-cored and that the buried glacier ice is more than 30 m thick. A transverse profile shows evidence of basal crevasses near the former glacier margin. Three profiles cross the former glacier margin and onto a proglacial plain which dips slightly away from the former glacier margin. Low resistivities were encountered where borehole and field observations indicate that the plain consists of marine muds with a high salt content. This landform has previously been interpreted as a slab of seabed pushed up in front of the surging glacier, possibly facilitated by permafrost in the seabed. We suggest, alternatively, that the landform originated from sediments extruded from below (or pushed in front of) the glacier at the surge terminus and deposited as a debrisflow. Ground penetrating radar can reveal small-scale structures, but larger structures and overall composition are better imaged by resistivity measurements. [source] Towards a chronology of the Late Pleistocene in the northern Alpine ForelandBOREAS, Issue 3 2004FRANK PREUSSER Dating results from terrestrial records in the northern foreland of the Alps have been compiled in order to establish an independent chronostratigraphy for the climate history of this region. U/Th dates of peat deposited during the final phase of the Last Interglacial indicate that it lasted until at least c. 115 000 yr ago. The Early Würmian started with a period of severe cold climate causing a substitution of forest by tundra-like vegetation. It is assumed that during this period glaciers advanced to the margin of the foreland of at least the Western Alps. Sediments attributed to this glaciation are dated to about 103 000 yr. Three subsequent interstadials, all characterized by coniferous forest, were interrupted by cold stadials with steppe to tundra-like vegetation. The first interstadial is dated to about 95 000 yr. There is evidence for an interstadial with open coniferous woodland and three phases of steppe vegetation during the Middle Würmian, between c. 50000 and 30 000 yr ago. The last glaciation of the Alpine Foreland reached its maximum extension between 24 000 and 21 500 yr and glaciers rapidly collapsed before ,17 500 yr ago. A series of minor re-advances during the Lateglacial is reported from within the Alps, but the glaciers barely reached the main Alpine valleys during this time. The last of these advances formed the Egesen moraine and occurred at about 11 800 yr ago during the Younger Dryas. [source] Lateglacial landform associations at Jæren (SW Norway) and their glaci-dynamic implicationsBOREAS, Issue 3 2003STÅLE RAUNHOLM The Jæren lowland is located on the southwestern coast of Norway between a mountainous region in the east and the offshore Norwegian Channel in the west. During the Last Glacial Maximum, Jæren was in an intermediate position between an ice stream following the Norwegian Channel northwards, and westward flowing inland ice. The dynamic behaviour of the inland ice and the interaction with the ice stream are examined by means of geomorphological analysis of digital terrain models and sedimentological investigations. SW-trending drumlins were formed at Jæren below tributary ice from the inland, feeding into the Norwegian Channel Ice Stream. The presence of Rogen moraine in the central part of Jæren indicates a frozen substratum prior to their formation, and this suggests a transition to cold-based ice between the tributaries. The deglaciation of the Norwegian Channel at about 15 ka BP resulted in an unstable ice front for the inland ice sheet. The formation of Rogen moraine may be explained by a dynamic advance resulting in extensional flow and fracturing of the frozen substratum between the tributaries. The dynamic advance was followed by an early deglaciation of the coastal areas as evidenced by shallow marine sediments. Deformation of the shallow marine sand indicates a glacial readvance through the valleys formerly acting as tributaries to the ice stream. [source] A New Method to Identify Quaternary Moraine: Acoustic Emission Stress MeasurementACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2006ZHAO Zhizhong Abstract: How to effectively identify glacial sediments, especially Quaternary moraine, has been in dispute for decades. The traditional methods, e.g., sedimentary and geomorphologic ones, are facing challenge in eastern China where controversial moraine deposits are dominatingly distributed. Here, for the first time, we introduce the acoustic emission (AE) stress measurement, a kind of historical stress measurement, to identify Quaternary moraine. The results demonstrate that it can be employed to reconstruct stress information of glaciation remaining in gravels, and may shed light on the identification of Quaternary moraine in eastern China. First, we measured the AE stress of gravels of glacial origin that are underlying the Xidatan Glacier, eastern Kunlun Mountains in western China. Second, we calculated the stress according to the actual thickness of the glacier. The almost identical stress values suggest that the glacial gravels can memorize and preserve the overlying glacier-derived aplomb stress. And then we introduce this new approach to the controversial moraine in Mount Lushan, eastern China. The results indicate that the stress is attributed to the Quaternary glacier, and the muddy gravels in the controversial moraine in Mount Lushan are moraine deposits but not others. [source] A Polygenetic Landform At Stígá, Öræfajökull, Southern IcelandGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2004Tim Harris Abstract Recent research has identified problems inherent in the identification and description of landforms. Morphologically similar small-scale glacial and periglacial landforms can be misinterpreted, thus hindering environmental reconstruction. This study reveals that a landform resembling a moraine at Stígárjökull, southern Iceland, is the product of both glacial deposition and mass movement. The landform has two distinct morphological and sedimentological components: a basal, lithologically diverse component, and an upper, lithologically homogenous component. Clast lithological analysis, particle shape and particle size measurements demonstrate that the basal component of the landform consists of sediment whose characteristics match nearby moraines. In contrast, the source of the upper component is a narrow outcrop of rock above the valley floor. Evidence suggests that frost-shattered material was transported across a perennial snow patch to a small moraine, leading to growth of the ,moraine'. This combination of processes is unlikely to be unique, but the geological peculiarities of the field site permitted their identification. It is possible that many similar ,moraines' could be enlarged by subaerial feeding, leading to false reconstruction of glacier form and/or associated rates of erosion and sedimentation. Such polygenetic landform genesis therefore has implications for environmental reconstruction. [source] | |||||||||||||||||||