Palaeoglaciation of Parque Natural Lago de Sanabria, northwest Spain

Detailed geomorphological mapping provides evidence for at least three phases of glaciation in the Parque Natural Lago de Sanabria, in northwest Spain. The most extensive glaciation was characterised by a large plateau ice cap. A combination of geomorphological evidence and glacier modelling indicates that this ice cap covered an area of more than 440 km², with a maximum ice thickness of c. 300 m and outlet glaciers reaching as low as 1000 m. This represents the largest ice mass in Iberia outside the Pyrenees and one of the largest in the mountains of southern Europe and the Mediterranean region. Radiocarbon dates from the base of lacustrine sequences appear to suggest that the most extensive phase of ice-cap glaciation occurred during the last cold stage (Weichselian) with deglaciation occurring before 14–15 ka ¹⁴C BP. A second phase of glaciation is recorded by the moraines of valley glaciers, which may have drained small plateau ice caps; whilst a final phase of glaciation is recorded by moraines in the highest cirques.     

THE LAST GLACIATION OF SHETLAND, NORTH ATLANTIC

Evidence relating to the extent, dynamics, and relative chronology of the last glaciation of the Shetland Islands, North Atlantic, is presented here, in an attempt to better illuminate some of the controversies that still surround the glacial history of the archipelago. We appraise previous interpretations and compare these earlier results with new evidence gleaned from the interpretation of a high resolution digital terrain model and from field reconnaissance. By employing a landsystems approach, we identify and describe three quite different assemblages of landscape features across the main islands of Mainland, Yell and Unst. Using the spatial interrelationship of these landsystems, an assessment of their constituent elements, and comparisons with similar features in other glaciated environments, we propose a simple model for the last glaciation of Shetland. During an early glacial phase, a coalescent British and Scandinavian ice sheet flowed approximately east to west across Shetland. The terrestrial land‐forms created by this ice sheet in the north of Shetland suggest that it had corridors of relatively fast‐flowing ice that were partially directed by bed topography, and that subsequent deglaciation was interrupted by at least one major stillstand. Evidence in the south of Shetland indicates the growth of a local ice cap of restricted extent that fed numerous radial outlet glaciers during, or after, ice‐sheet deglaciation. Whilst the absolute age of these three landsystems remains uncertain, these new geo‐morphological and palaeoglaciological insights reconcile many of the ideas of earlier workers, and allow wider speculation regarding the dynamics of the former British ice sheet.     

Comments on Jansson, K.N. and Glasser, N.F. (2008) “Modification of peripheral mountain ranges by former ice sheets: The Brecon Beacons, southern UK,” Geomorphology 97, 178–189

Jansson and Glasser (Jansson, K.N., Glasser, N.F., 2008. Modification of peripheral mountain ranges by former ice sheets: the Brecon Beacons, southern UK. Geomorphology 97, 178–189.) have recently provided unconventional interpretations of selected glacial erosional and depositional landforms in the Brecon Beacons, UK, based on remotely sensed imagery. These new interpretations contradict well-established and reliable evidence for the origins and ages of certain glacial landforms of this upland area and elsewhere. They suggest that during a post-Last Glacial Maximum (LGM) ice-sheet event ice flowed up supposed, essentially “fluvial” valleys producing “glacial lineations” and depositing marginal moraines at the valley heads and on cirque floors. We argue that their interpretations of some key landforms are incorrect and that they have ignored much of the previous dating and field geomorphological evidence. Sedimentary and morphological evidence (e.g., lack of erratic content; convex planform with respect to the headwall; relatively large height range of moraines; and close association with headwall extent, height, and steepness) all indicate that higher level cirque-floor and valley-head moraines in the Brecon Beacons (> c. 400 m) were formed by cirque glaciers. Available dating evidence indicates a Younger Dryas age. We demonstrate that the supposed “fluvial” valleys, comprising trough heads with steep headwalls, have more nearly parabolic than V-shaped cross profiles indicating substantial glacial modification. Field evidence shows that proposed key exemplar post-LGM glacial lineations are in fact debris flow deposits. We conclude that whilst the adoption of a macroscale approach can shed new light on large-scale, ice-sheet movements, this approach should not be undertaken without consideration of the associated field evidence.     

LANDSLIDE‐GLACIER INTERACTION IN A NEOPARAGLACIAL SETTING AT TVERRBYTNEDE,JOTUNHEIMEN, SOUTHERN NORWAY

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.     

Development of tongue-shaped and multilobate rock glaciers in alpine environments – Interpretations from ground penetrating radar surveys

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

Drumlin Formation Time: Evidence from Northern and Central Sweden

Large‐scale drumlins occur abundantly throughout central and northern Sweden. Whereas many drumlins in the north are an integral part of a relict glacial landscape >100,000 years old, those to the south are generally interpreted as of last deglaciation age. Typically, the latter ones have not been overprinted by younger glacial landforms. Despite this apparent difference in formation history, drumlins in both regions have similar directional and morphological characteristics. A systematic analysis of >3000 drumlins in (i) areas within relict landscapes, (ii) areas with an ambiguous deglaciation age assignment, and (iii) areas within deglacial landscapes, indicates that these latter deglaciation drumlins differ clearly in both shape and size from drumlins in the other two types of landscapes. In addition, numerical modelling indicates that basal melting conditions, a prerequisite for drumlin formation, prevailed only for a very limited time over much of northern Sweden during the last deglaciation, but lasted for longer periods of time during earlier stages of the Weichselian. A reconnaissance radionuclide bedrock exposure date from the crag of a large drumlin in the relict landscape indicates that glacial erosion, and presumably drumlin formation, at this location predated Marine Isotope Stage 7. We conclude, therefore, that the large‐scale drumlins of central and northern Sweden did not form during the last deglaciation, or during any other specific ice flow event. Instead, we suggest that they were formed by successive phases of erosion and deposition by ice sheets of similar magnitude and configuration.     

Glacierkarst phenomena in Spitsbergen

Glacierkarst is a common phenomenon on Spitsbergen. The Spitsbergen glaciers circulate large amounts of liquid water, even during the polar winter. Investigations have revealed two types of drainage systems: marginal drainage canals and central drainage canals. Marginal drainage canals are located within the medial moraines or between the glacier margin and the unglaciated valley slope. Lengths up to 1 km and diameters of 10 m are known. The marginal drainage canals are often founded on solid bedrock. The central drainage systems are less well understood, but are located within the glacier mass, founded on ice. The two types of drainage canal systems contain many features associated with classic calcareous karst, such as phreatic tubes, vadose canyons, dripstones (in ice), multilevel development and integrated drainage. Surface analogs such as dry valleys, uvalas, ponors and poljes also exist. Conduits are found as much as 40 m below the ice surface.     

Reconstruction and Regional Significance of the Coire Breac Palaeoglacier,Glen Esk,Eastern Grampian Highlands,Scotland

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

POST‐LITTLE ICE AGE PATTERNED GROUND DEVELOPMENT ON TWO PYRENEAN PROGLACIAL AREAS: FROM DEGLACIATION TO PERIGLACIATION

This study aims to observe post‐Little Ice Age glacier retreat and the constitutive patterned ground development at two French Pyrenean glacier forelands (Taillon Glacier and Pays Baché Glacier). Periglacial feature observations are associated with periods of deglaciation using aerial photos and archive files. Four conclusions are drawn. (1) The two glaciers have lost respectively 68% and 92% of their surface since 1850, which corroborates observations on other Pyrenean glaciers. (2) Patterned ground can develop very rapidly, sometimes only 10 years after deglaciation. (3) Patterned ground size does not systematically increase as a function of the time elapsed since deglaciation. (4) All the forms, even those developing near the Little Ice Age moraines, are active. We propose that the location, activity and size of patterned ground are more probably linked to drift characteristics and local wetness conditions than to the time elapsed since deglaciation.     

Improving local estimations and regional trends of glacier equilibrium line altitudes

Abstract Small glaciers have short response times to climate change and therefore offer a powerful means of climate monitoring. Glacier responses to climate, or their mass change, may be suggested by a change in the Equilibrium Line Altitude (ELA). However, regional climatic reconstructions have repeatedly neglected the importance of local variations in ELAs in preference for regional trends. For small glaciers close to the glaciation level, ignoring the importance of local topographic components in mass balance estimates may lead to erroneous climatic reconstructions. Of 510 small valley and cirque glaciers digitised across northern Scandinavia, 284 were objectively deemed suitable for inferring an ELA. The inferred ELA was derived from the median elevation and several local topographic variables using regression analysis. The glacier elevation, area, slope and aspect parameters were found to be the best predictors of the local ELA. ELA estimations improved from 77% up to 94% accuracy when topographic parameters for every grid‐cell within rasters representing glacier surfaces were computed rather than using subjective measurements from topographic maps. Regional ELA trend surfaces, interpolated between the local ELA values, differed in effectively representing the local variability, depending upon the distribution and accuracy of the local ELA values. A second‐order polynomial trend surface most accurately represented ELA variations across the study area, within the initial local measurement accuracy of ±100 m. It is concluded that current subjective topographic map‐based analyses are unlikely to be sufficiently accurate for predicting the regional ELA of small, sensitive and marginal glaciers, unless CIS‐based spatial analyses are made at a reasonable resolution.     

EVIDENCE FOR EXPANDED MIDDLE AND LATE PLEISTOCENE GLACIER EXTENT IN NORTHWEST NELSON,NEW ZEALAND

The extent of Late Quaternary glaciation in the northwest Nelson region of New Zealand has traditionally been regarded as minor, with small‐scale valley glaciation in confined upland reaches. New geomorphological evidence, including moraines, kame terraces, till‐mantled bedrock and outwash terraces, indicate that greatly expanded valley glaciers flowed into the lowland valley system at the mouths of the Cobb‐Takaka and Anatoki drainages. The timing for this ice advance into lowland valleys is constrained by lowland landform characteristics and a single cosmogenic exposure age, suggesting Late and Middle Pleistocene ice expansion, respectively. Evidence for expanded upland ice on the Mount Arthur Tableland and adjacent areas includes trimlines, boulder trains and roche moutonées. Two cosmogenic exposure ages on upland bedrock surfaces suggest that major ice expansion occurred during MIS 3 and/or 4, while previously published exposure dating from Cobb Valley suggests large MIS 2 ice expansion as well. The inferred, markedly expanded ice left little or no clear geomorphic imprint on the Cobb–Takaka Gorge, and required temperature depression of 4–6°C with near‐modern precipitation levels.     

Former glacial lakes of the Bunger Hills,Antarctica

The Bunger Hills in East Antarctica occupy a land area of approximately 400 km². They have been exposed by Holocene retreat of the Antarctic ice sheet and its outlet glaciers. The accompanying sea level rise flooded the marine inlets that now separate the northern islands and peninsulas from the major part of the hills. During deglaciation the continental ice sheet margin retreated south‐eastwards with several temporary halts, during which ice‐dammed lakes were formed in some valleys. These lakes were maintained long enough to permit formation of beaches of sand and gravel, and for the erosion of shore platforms and low cliffs in bedrock. Around the western end of Fish Tail Bay impressive shoreline features 20 m above sea level define a former ice‐dammed lake that was 5.5 km long. A similar 7 km long former ice‐dammed lake was formed at Lake Dolgoe. The more extensive and deeper glacial lake is revealed by well‐developed and preserved shoreline features cut at 29 m which is 16 m above present lake level. In addition, several small ice‐dammed lakes existed temporarily near Lake Shchel and in the valley to the west. Lake Fish Tail existed more than 6,900 ¹⁴C years ago and Lake Shchel probably more than 6,680 ¹⁴C years ago. It is inferred that the shore platforms and beaches were formed by lake ice and wave action over considerable periods when the lakes were impounded by steep cold ice margins. There appears to have been a balance between meltwater input and evaporative loss from the lakes in the cold dry continental climate. There is no evidence for rapid lake level fluctuations, and there was very little input of clastic sediment. This resulted in poor development of deltaic and rhythmically laminated lake floor deposits. It is suggested that such deposits are more characteristic of ice‐dammed lakes formed in association with wet‐based temperate ice than those associated with dry‐based polar ice.     

Periglacial nivation cirques and local glaciations in the rock canyons of Söderåsen,Scania, Sweden. A discussion and new interpretation

Rapp, Anders: Periglacial nivation cirques and local glaciations in the rock canyons of Söderåsen, Scania, Sweden. A discussion and new interpretation. Geografisk Tidsskrift 82: 95–99, Copenhagen, October 15, 1982.

Present opinions about the genesis of the rock canyons OdensjOn, Skäralid and Klöva Hallar of Söderåsen, Sweden are reviewed, and a new theory is presented. It is proposed, that during periglacial tundra periods large amounts of drifting snow collected in valleys of north-south directions. Small glaciers were created, which caused local overdeepening and removal of loose material. These processes were active in tundra periods before and after the main Quaternary glaciations.

SUMMARY

Odensjön, Skäralid and Klöva Hallar are three valleys of canyon type, deeply cut (60–100 m) into the horst block of Söderåsen, of fractured Precambrian gneiss rock. It has been shown by other authors that the cold periods after the Weichselian deglaciation were characterized by permafrost and ice wedges on sandy plains in south Sweden. Strong winds caused widespread wind-polishing of stones and bedrock, predominantly from easterly and westerly directions. Based on this evidence, the author presents the theory that large deposits of wind-blown snow were trapped in the canyon valleys of Söderåsen, except for the valleys of east-west directions. The snow was metamorphosed to firn and local, small glaciers, which filled the valleys. The rims of the canyon valleys have in many cases well developed nivation hollows, either steep nivation funnels or gently sloping, semicircular nivation cirques. Odensjøn is a closed, semicircular rock basin, which has been much discussed by scientists earlier, and which seems to fit the theory of creation by nivation from mainly west, but also east, and a local cirque glacier flow northwards causing the overdeepening and removal of loose material. The three valleys mentioned were problably widened and deepened into a series of nivation basins in tundra periods before and after each major continental glaciation. The nivation hollows and the deep canyon valleys were not destroyed by glacial erosion during the Weichselian and earlier Quaternary major ice advances, because the valleys were filled with densely packed snow and ice from snow drifting before the main glacier front moved over them from NE directions. The theory will be further checked by a team of scientists from the Department of Physical Geography in Lund. A comparison is made with cirque forms in present-day mountain tundra conditions in the area of Kärkevagge in northern Lappland, investigated by the author during the 1950's and later.     

A MODELLING RECONSTRUCTION OF THE LAST GLACIAL MAXIMUM ICE SHEET AND ITS DEGLACIATION IN THE VICINITY OF THE NORTHERN PATAGONIAN ICEFIELD, SOUTH AMERICA

ABSTRACT. A time-dependent model is used to investigate the interaction between climate, extent and fluctuations of Patagonian ice sheet between 45° and 48°S during the last glacial maximum (LGM) and its subsequent deglaciation. The model is applied at 2 km resolution and enables ice thickness, lithospheric response and ice deformation and sliding to interact freely and is perturbed from present day by relative changes in sea level and equilibrium line altitude (ELA). Experiments implemented to identify an LGM configuration compatible with the available empirical record, indicate that a stepped ELA lowering of 750 to 950 m is required over 15000 years to bracket the Fenix I-V suite of moraines at Lago Buenos Aires. However, 900 m of ELA lowering yields an ice sheet which best matches the Fenix V moraine (c. 23000 a BP) and Caldenius' reconstructed LGM limit for the entire modelled area. This optimum LGM experiment yields a highly dynamic, low aspect ice sheet, with a mean ice thickness of c. 1130 m drained by numerous large ice streams to the western, seaward margin and two large, fast-flowing outlet lobes to the east. Forcing this scenario into deglaciation using a re-scaled Vostok ice core record results in an ice sheet that slowly shrinks by 25% to c. 14500 a bp , after which it experiences a rapid collapse, loosing some 85% of its volume in c. 800 years. Its margins stabilize during the Antarctic Cold Reversal after which it shrinks to near present-day limits by 11 000 a bp .     

GEOMORPHOLOGICAL CHARACTERISTICS AND SIGNIFICANCE OF LATE QUATERNARY PARAGLACIAL ROCK-SLOPE FAILURES ON SKIDDAW GROUP TERRAIN, LAKE DISTRICT, NORTHWEST ENGLAND

ABSTRACT. Eight relict rock-slope failures (RSFs) on Skiddaw Group terrain in the Lake District, northwest England, are described. Five of the failures are rockslides, one is a product of slope deformation, and two are compound features with evidence for sliding and deformation in different sectors. As none appears to have been overrun and modified by glacier ice it is concluded that they all post-date the Last Glacial Maximum (LGM ; c. 21 ± 3 cal. ka bp ). Slope stress readjustments resulting from glacial and deglacial influences are considered to have weakened the slopes, and application of the term paraglacial is appropriate. Permafrost aggradation and degradation, seismic activity and fluvial erosion are among processes that may have contributed to failure at certain sites. The failures are significant as potential debris sources during future ice advances, contributing to valley widening and cirque enlargement and, possibly, for acting as sites of cirque initiation. Previously, Skiddaw Group rocks have been regarded as homogeneous and of limited resistance to the weathering and erosion associated with Quaternary glacial, periglacial and fluvial processes. These characteristics and processes have been used to explain the steep smooth slopes and rounded hills that dominate Skiddaw Group terrain. Rock-slope failure has also helped shape this terrain and should be incorporated in future interpretations of landscape development.     

The geomorphic impact of glaciers as indicated by tors in North Sweden (Aurivaara, 68° N)

Geomorphological investigations carried out on 15 tor-like features located on the Aurivaara plateau (North Sweden, 68° N) provide new insights in the greatly debated age of these landforms. Erratics and till trapped deep in the tor joints support a pre-Weichselian age for tor formation. Moreover, the occurrence of various weathering stages in allochtonous material, the joint width up to 1.5 m (requiring long-term weathering), and the frequent association of tors with pediment-like forms, suggest pre-Quaternary tor formation. The juxtaposition of fresh erratics and in situ old weathering features (mushroom rocks, concentrically weathered well-rounded corestones, and grus) indicates a predominantly cold-based regime for the Scandinavian ice sheet, with erratics carried by the overlying moving ice being repeatedly deposited on tor summits during deglaciation phases. The relationships between tors and ice action indicated for the Aurivaara plateau result in the proposal of a morphodynamical succession of five tor subtypes ranging from the preservation of well-rounded corestones still embedded in grus (suggesting negligible glacial erosion) to the almost complete removal of tor features by ice scouring. A comparison with tors in similar geological and topographical contexts from the unglaciated Dartmoor area allows a tentative evaluation of an average overall glacial erosion of 0–10 m on the northern Sweden plateaus, in sharp contrast with the 190 m overdeepening of the nearby Torneträsk basin. Thus, this case study of Swedish tors provides additional support to the recent interpretations of relict landscapes in previously glaciated areas and is in accordance with the classical «model» of glacial selective erosion established in the Nordic and Arctic mountains.     

Past glaciation and sea levels on Bjørnøya, Svalbard

Bjørnøya has a very thin cover of unconsolidated Quaternary sediments. Glacial erratics of local origin are spread throughout the lowland areas, and glacial striae indicate glacial movement which was centred middle of the island. No traces of the Barents Sea ice sheet have been observed on Bjørnøya, nor has there been any postglacial emergence of the island. Lake cores date the deglaciation of the lowlands to ca 10,000 BP, and peat deposits on high mountains show that these were deglaciated before 8700 bp.     

Late Quaternary Lakes in the McMurdo Sound Region of Antarctica

Lake levels within the enclosed drainage basins of the Dry Valleys adjacent to McMurdo Sound have fluctuated widely during the Late Quaternary due to (a) local climate change and the consequent variation in the evaporation–precipitation regime, and (b) glacial fluctuations, resulting in changes in the catchment and meltwater drainage areas of the glaciers and, in some cases, in the volumes of the available lake basins. Three types of lakes can be distinguished on the basis of their water source: (1) lakes receiving the bulk of their water from melting of local alpine glaciers; (2) proglacial lakes associated with outlet glaciers from the East Antarctic Ice Sheet; (3) proglacial lakes associated with the marine oxygen-isotope stage 2 Ross Sea ice sheet and its precursors. The Dry Valleys contain an exceptionally long lacustrine record, extending back at least 300,000 years. Lacustrinesedimentation is cyclical, occurring over periods of about 100,000 years. During the last such cycle, relatively small lakes, both adjacent to East Antarctic outlet glaciers and fed by meltwater from alpine glaciers, existed during stage 5. However, these local lakes gave way to large proglacial lakes adjacent to the Ross Sea ice sheet in stage 2. The same relationship apparently occurred during the previous 100,000-year cycle. Dating of lacustrine sediments suggests that lakes proglacial to the Ross Sea ice sheet have existed during episodes of sea-level lowering during global glaciations. Lakes proglacial to outlet glaciers from the East Antarctic Ice Sheet have formed coincident with episodes of high eustatic sea level during interglacial periods.     

Internal Structure and Permafrost Characteristics of the Rock Glaciers of Southern Carpathians (Romania) Assessed by Geoelectrical Soundings and Thermal Monitoring

Six rock glaciers in the Southern Carpathians have been investigated by means of geoelectrical soundings in order to detect their internal stratigraphy and the existence of frozen sediments. In the case of three relict rock glaciers, the electrical resistivity measurements indicated a typical internal structure. Low resistivity values (<10 kΩm) which are typical of unfrozen fine‐grained materials were obtained, but high resistivity values (25–240 kΩm) measured in the Pietroasa, Ie?u and Pietrele rock glaciers denote the presence of sediments cemented by interstitial ice and ice lenses. Based on the moderate resistivity values, the ice content is probably low to medium in the upper portion of these rock glaciers, that is, above 2040 m. At two sites (Pietroasa and V?iuga rock glaciers), ground surface temperature (GST) evolution was monitored using digital dataloggers. Mean annual ground surface temperature and GST regime throughout the winter were extracted from the recordings and confirmed the probability of permafrost occurrence in Pietroasa rock glacier. In the Ie?u and Pietrele rock glaciers, measurements of bottom temperatures of the winter snow cover were performed in March 2012. Considering the thick active layer, the reduced ice content and the presence of scarce vegetation on their surface it could be assumed that the permafrost exists in marginal conditions in the Southern Carpathians. The ground ice in permafrost is produced by the groundwater freezing or by snow banks buried by coarse angular boulders following large rockfalls.