A glaciação Plistocénica do Alto Vez (PNPG): morfometria dos circos e espessura da língua glaciária

No Noroeste da Península Ibérica, os estudos comprovam a presença de vestígios glaciares a baixas altitudes (Perez-Alberti et al., 1993). Assim, e tendo como ponto de partida os trabalhos realizados por outros investigadores (Coudé-Gaussen, 1981; Coudé et al., 1983; Moreira & Ramos, 1981, Pereira et al., 2009; Santos et al., 2013; entre outros), retoma-se o estudo da Glaciação Plistocénica no setor do Alto Vez (serras da Peneda-Soajo), numa área que abrange parte dos concelhos de Arcos de Valdevez, Melgaço e Monção. Foi a partir dos anos 70, com os trabalhos de Coudé-Gaussen (1981), que vários factos e testemunhos foram evidenciados sobre esta problemática, clarificando que efetivamente, durante o final do plistocénico, as Serras da Peneda e do Gerês apresentaram uma cobertura glaciária (Soares de Carvalho, 1981). Neste trabalho apresentam-se os resultados preliminares da investigação que decorre sobre a glaciação Plistocénica desta área, nomeadamente: a análise morfométrica dos circos glaciários existentes no maciço montanhoso Soajo-Peneda, o cálculo da espessura da língua glaciária do vale do Rio Vez aquando da sua máxima extensão e um esboço geomorfológico de pormenor para este setor. A morfometria dos circos glaciares no Alto Vez foi estudada a partir da metodologia seguida por Hughes et al. (2007) e aplicada nas montanhas do Mediterrânico (Bathrellos et al., 2014). A morfometria dos circos consistiu em medir os seguintes parâmetros: área dos circos; comprimento dos circos; largura dos circos; rácio do comprimento/largura dos circos; rácio da largura/amplitude dos circos; altitude do "ápex" de cada circo; altitude do "lip" de cada circo; amplitude entre a altitude máxima ("ápex") e a alitude mínima ("lip"); geologia de cada circo e orientação segundo os quadrantes em octantes de cada circo. Os parâmetros foram calculados através do software ArcGIS da ESRI e do Microsoft Excel. No Alto Vez foram identificados 26 circos (Tabela I), cuja área média ocupada é 39354,33m2, o comprimento médio é de 223,63m e a largura média é de 283,98m. Através do rácio largura-comprimento e do rácio largura-amplitude foi possível conhecer o alongamento dos circos e o seu grau de incisão. Assim, o circo mais alongado apresenta um rácio de 1,45m, numa média de 0,86m, e o circo com maior incisão apresenta um rácio de 1,81m, numa média de 29,04m. A amplitude média, isto é, a diferença média entre a altitude máxima do circo ("ápex") e a altitude mínima do circo ("lip"), é de 30,91m, variando entre os 0,60m e os 115,36m. Relativamente à orientação dos circos, verifica-se um domínio dos circos virados a leste. A geologia predominante nos circos é o granito de grão médio, de duas micas, com 20 circos. O cálculo da espessura máxima da língua glaciária com base nas evidências geomorfológicas foi executado segundo o método proposto por Benn & Hulton (2010). Desse modo, estima-se que a espessura máxima da língua glaciária atingiu cerca de 150 metros e que a altitude máxima da língua de gelo alcançaria os 1300m. O setor onde o gelo se acumulou com mais abundância corresponde a uma área aplanada que se desenvolve no alto vale do Rio Vez, entre os 1000 e os 1150m de altitude. Neste setor encontram-se igualmente inúmeras moreias laterais que podem representar as diferentes fases da glaciação. A cartografia geomorfológica já executada permite esboçar uma visão preliminar da área glaciada e o registo de mais elementos que comprovam a extensão da glaciação. O reconhecimento de campo mais detalhado de alguns setores permitirá afinar a modelação que se está a desenvolver sobre a área glaciada e caracterizar de forma mais assertiva as fases de avanço/retrocesso da glaciação

Glare, a GIS tool to reconstruct the 3D surface of palaeoglaciers

Acknowledgements This research has been supported by the Leverhulme Trust International Network Grant IN-2012-140. Processing and collecting of ground penetrating data in Forgefonna was part of Elend Førre's master's project that was completed in 2009 at the Department of Geography, University of Bergen. We also acknowledge Dr Andreas Bauder for providing the subglacial topography data for Griessgletscher and Simone Tarquini for granting access to the high resolution TIN of Italy, a cut of which is provided to the reader to practice the tools (see Appendix). Referees Dr. Iestyn Barr, Dr. Jeremy Ely and Dr. Marc Oliva are thanked for their constructive comments and tool testing, which significantly improved the final output.Peer reviewedPostprin

Pleistocenska poledenitev v Logarski dolini

Članek prinaša rezultate preučevanja ledeniških ostankov iz časa zadnjega poledenitvenega viška na območju Logarske doline v Kamniško-Savinjskih Alpah. Namen članka je reinterpretirati dosedanje ugotovitve in podati novo tolmačenje obsega viška zadnje poledenitve na tem območju. S pomočjo ugotovitev, pridobljenih s terenskim delom, so bile opravljene morfometrične analize, po katerih smo začrtali skrajno mejo poledenitvenega sunka in izdelali tridimenzionalno rekonstrukcijo topografije površja takratnega ledenika

Late Pleistocene glaciation in the headwaters of the Ceremuşul Alb valley (Maramureş Mountains, Romania)

The Late Pleistocene Jupania palaeoglacier (area 0.85 km2, 1.7 km long) was reconstructed in the headwaters of the Ceremuşul Alb/Bilyj Cheremosh valley (Maramureş Mountains). The study area represents one of the most inaccessible natural areas in the Romanian part of the Eastern Carpathians where the legacy of the Pleistocene glaciation has recently been discovered. Based on mapping of glacial landforms and deposits, we reconstruct glacier dimension and ice-surface geometry, as well as estimate equilibrium line altitude (ELA) during the maximal ice extent (MIE). Well-preserved terminal moraines mark the extent of glacier front at ~1400 m a.s.l. Sedimentological analysis documents that the lateral moraines are sometimes overbuilt by 1-1.5 m thick colluvial deposits. The ELA for the Jupania palaeoglacier calculated with the Area-Altitude- Balance-Ratio (AABR) 1.6 was 1630 m. However, the gentle-sloping mountain-top could serve as an important snow contribution area to glacier mass balance; therefore, the ELA could potentially exist even higher at 1676 m. The resulting climatic ELA (1630-1676 m) in the south-eastern part of the Maramureş Mountains fits well with the rising trend of ELA towards the southeast observed between Chornohora (ELA = 1516 m) and Rodna Mountains (ELA = 1697 m). The SE rising trend of the ELA corresponds well with the dominant palaeowind direction suggested in the Carpathian region and supports the prevalence of zonal circulation pattern in Central Eastern Europe during the culumination of the last glaciation

Glacial geomorphology and Pleistocene glacier reconstruction in the Demänovská Valley, Low Tatra Mountains, Slovakia

In the Western Carpathians, clear evidence of the Pleistocene glaciations only occurs in two mountain massifs – the Tatra and Low Tatra Mountains. The Low Tatra Mountains (2043 m a.s.l.), contrary to the higher and more strongly glaciated Tatra Mountains (2654 m a.s.l.), have previously been much less attractive for scientific research. Hence, in these mountains, both glacial landforms and chronology, together with a detailed reconstruction of glacier geometry and resulted equilibrium line altitude (ELA), are poorly documented. The aim of this paper is to characterize the glacial relief and reconstruction of geometry and ELA of the Zadná voda glacier in the Demänovská Valley system which belongs to the category of the largest Pleistocene glaciers on the northern slope of the Low Tatra Mountains. The mapping results show that a freshly shaped, massive terminal moraine of maximal ice extent (MIE, likely formed during the global Last Glacial Maximum – LGM) occurs 4.3 km distance down-valley from the glacial cirque backwalls. There is no evidence of deposits from older glaciations beyond the terminal moraine down the valley. The terminal zone of the MIE features a fresh morainic landscape with hummocky topography with kettle hollows and the only known morainic lake in the Low Tatra Mountains – Vrbické pleso. During the MIE, the Zadná voda glacier covered 7 km2 of the area and featured a mean thickness of 48 m. The ELA of this glacier was 1433 m, determined by the area-altitude balance ratio (AABR) 1.6 method, which is a similar value to the LGM ELA calculated in the Western Tatra Mountains. The recessional stages were only recognized in the cirques area, where one or two generations of debris-covered glaciers and rock glaciers mark the final deglaciation of the study area

Glacier Reconstruction

Glacier reconstruction typically aims to establish the former extent of ice masses at any given period. Such reconstructions are important because they provide crucial information about past (palaeo) glacier changes over much longer timescales than the observational record permits. Reconstructing the dimensions and dynamics of palaeo-ice masses enables equilibrium line altitudes, and temperature or precipitation to be calculated, making glaciers an important palaeo-climate proxy. Given this utility, geomorphologically-based glacier reconstructions have been generated for many regions globally, although the specific methods employed are rarely described formally. To address this shortcoming, this chapter describes some of the methods employed in generating geomorphologically-based reconstructions for ice sheets and mountain-scale glaciers (< ~1,000 km2)

Spatial and climatic characterization of three glacial stages in the Upper Krnica Valley, SE European Alps

The southeastern European Alps represent the spot where mean annual precipitation is at its highest in the entire Alpine chain. Accordingly, the glacial evolution here might have a different spatial and chronological pattern if compared with other alpine areas. This paper discusses geomorphological evidence of three glacial stages from the Krnica Valley in the Julian Alps of Slovenia, and is the first step towards a comprehensive palaeoglaciological studies in this alpine sector. Very well-preserved glacial landforms in the Upper Krnica Valley allowed the reconstruction of glacier surface topographies and corresponding equilibrium line altitudes (ELAs) by means of field-based geomorphological and sedimentological data and by using geospatial analysis. The uppermost frontal moraines belong to the Little Ice Age (LIA) and the corresponding ELA is estimated at 1973 m a.s.l. Other two stages with the ELA depressed by 50 m and 161 m compared to the LIA ELA, suggest early Holocene and Younger Dryas ages of the palaeoglaciers, respectively. This assumption ensues from absolute age datings and related ELA depressions observed elsewhere in the European Alps. The presence of buried ice under the debris in the Krnica cirque, imaged through geophysical investigations, point to peculiar microclimatic conditions able to preserve relict glacier ice. This is favoured by the recursive presence of snow on the ground caused by the extreme summer shading and the significant winter snow-recharge triggered by snowblow and avalanche feeding. The possible evolution of such relict ice under the ongoing climate warming is also discussed

Investigation of Glacier Dynamics During the Last Glacial Maximum at Tioga Pass, Yosemite National Park

Previous investigations of glacier dynamics at Tioga Pass during the Last Glacial Maximum (LGM) have produced different conclusions. A map of the LGM ice extent and flow direction (Alpha et al., 1987) illustrates a south-to-north direction of ice flow across the pass with little evidence to support this inference. Since the production of this map, unexpected glacial erratics of Cathedral Peak Granodiorite (CPG) have been noted in the vicinity of Tioga Pass, which are not consistent with the inferred flow direction. A comprehensive spatial data set of CPG erratics was collected. This data was collected between Tioga Lake and the southeastern boundary of the CPG bedrock, south of Tioga Pass. The erratics display trends of decreasing abundance from north to south, characteristic of boulder trains used to infer glacier flow patterns. Based on these trends, the erratics indicate a north-to-south flow across the pass, opposite to what Alpha et al. (1987) had inferred. This flow is determined to have originated from the eastern cirque of Mt. Conness, the northeastern boundary of the CPG bedrock. The Excel spreadsheet, “Profiler V. 2” (Benn and Hulton, 2009) was used to model the flows from Mt. Conness down the Lee Vining Canyon and the Grand Canyon of the Tuolumne River; these flows branched at Tioga Lake. The model provided insight into the ice dynamics in this region but was unable to provide insight into small flow reversals. Based on the distribution of CPG erratics, the “Profiler V. 2” analysis, past field research yielding evidence of other erratic boulder trains, a comprehensive set of striations and glacial landforms, and a plan-view map of ice coverage and flow direction at the peak of the LGM (Wahrhaftig et al., 2019), there is evidence to support the standing hypothesis that ice flowed south across Tioga Pass at the peak of the LGM, then became stagnant, with ice from Mt. Conness and Tioga pass eventually flowing into Lee Vining Canyon after peak LGM conditions receded