No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Cirques in the Sierra de Guadarrama and Somosierra Mountains (Iberian Central System): Shape, size and controlling factors
Abstract
The Guadarrama and Somosierra mountain ranges form the eastern sector of the Iberian Central System and hosted numerous glaciers during the Late Pleistocene (MIS2). Glaciation was of low intensity with glaciers of small sizes, strongly controlled by the climatic context and the topography. This study analyses the shape, size, distribution and location of 96 cirques existing in these mountain ranges. In addition to the standard morphometric parameters and controlling factors (altitude, aspect and lithology) used in most studies, additional factors were considered here in relation to the pre-glacial relief and fracture network. The data were obtained and processed using ArcGIS 10.4 and relations between the parameters and controlling factors were evaluated using statistical methods. The results indicate that most are simple cirques, tending to isometry, with low vertical incision capacity, considerable variation in size and predominantly east-facing. In the context of the Iberian Peninsula and other European mountains, these cirques are among the most isometric, the lowest in height and present the least overdeepening. The development of these cirques has generally been the result of random combination of various factors. Thus: (i) the largest cirques are located at intermediate altitudes, with the headwall located on the main divides, at former torrential valley heads or at the headwalls of fracture corridor valleys, and are north-facing; (ii) the longest cirques are located at former torrential valley heads, on metamorphic bedrock (i.e. schists, slates) and on uniform slopes. Finally, the prevailing eastern aspects are explained by topoclimatic factors and are in agreement with previous studies, which have proposed a Circulation Weather Type (CWT) model throughout the Iberian Peninsula during the Last Glacial Period, similar to its current configuration.
... Huget del Villar, E., 1915 Range. The area affected by the glaciers during the LGM is delimited according to previous publications Pedraza et al., 2019). whose headwaters glacial cirques were formed during the Pleistocene (Fernández-Navarro, 1915;Sanz-Herráiz, 1988;Bullón, 2016;Pedraza et al., 2019). ...
... The area affected by the glaciers during the LGM is delimited according to previous publications Pedraza et al., 2019). whose headwaters glacial cirques were formed during the Pleistocene (Fernández-Navarro, 1915;Sanz-Herráiz, 1988;Bullón, 2016;Pedraza et al., 2019). The dominant lithologies in both mountains are crystalline rocks of the Paleozoic and pre-Paleozoic basements (GEODE, 2004). ...
The Sierra de Gredos forms the central sector of the Central Range and extends for 155 km between the Sierra de Guadarrama to the east and the Sierra de Gata-Peña de Francia to the west, its highest peak being the Pico Almanzor (2591 m, 40° 14′ 46″ N and 5° 17′ 51″ W). The bedrock is mostly made up of granite rocks. The Sierra de Gredos has a Mediterranean–continental climate, with a clear increase in rainfall to the west due to its proximity to the Atlantic. Its glacial landscapes present a great variety of landforms, from small cirques in the massifs of the smaller summits and southern slopes, to large glacial valleys of lengths exceeding 10 km and plateau glaciers in the highest and western-most summits. The glacial evolution during the Late Pleistocene, since the maximum extent occurred before the global Last Global Maximum until the definitive disappearance of the glaciers, just at the beginning of the Holocene, is well known. Phases of glacial advance have also been clearly detected during the Oldest Dryas and, to a much more limited extent, during the Younger Dryas.
... The faults and folding structures transversal to these blocks originated structural corridors that conditioned the development of a fluvial network, in Range. The area affected by the glaciers during the LGM is delimited according to previous publications (Palacios et al., 2012a;Carrasco et al., 2018;Pedraza et al., 2019). whose headwaters glacial cirques were formed during the Pleistocene (Fernández-Navarro, 1915;Sanz-Herráiz, 1988;Bullón, 2016;Pedraza et al., 2019). ...
... The area affected by the glaciers during the LGM is delimited according to previous publications (Palacios et al., 2012a;Carrasco et al., 2018;Pedraza et al., 2019). whose headwaters glacial cirques were formed during the Pleistocene (Fernández-Navarro, 1915;Sanz-Herráiz, 1988;Bullón, 2016;Pedraza et al., 2019). The dominant lithologies in both mountains are crystalline rocks of the Paleozoic and pre-Paleozoic basements (GEODE, 2004). ...
The Sierras de Guadarrama and Somosierra are located at the eastern end of the Central Range, in the center of the Iberian Peninsula, culminating in the Pico de Peñalara (2428 m, 40° 51′ 01″ N and 3° 57′ 17″ W). There are landforms from 79 palaeoglaciers in the Sierra de Guadarrama and 18 in the Sierra de Somosierra. The majority of these palaeoglaciers were cirque and slope glaciers. Plateau and alpine glaciers only appeared in two areas. The moderate altitude of theses Sierras and their continental climate were determining factors that limited the glacial development. However, they house a great variety of landforms that retain most of the chronological information of the complex process that represents the last major deglaciation in Europe. All their glacial landforms come from the Last Glacial Cycle. The most important impact was the LGM, when the largest moraine formations were formed, although some cirques showed earlier major advances. The massive deglaciation started by 19 ka BP, although the recessional moraines in many valleys indicate the existence of advances between 17.5 and 14.6 ka. Later advances during the Younger Dryas are also possible. The glaciers disappeared immediately at the beginning of the Holocene. Some areas of the Peñalara Massif, including important glacial landforms, have been restored recently and are now part of the Guadarrama National Park, the most visited on the Iberian Peninsula.
... Huget del Villar, E., 1915 Range. The area affected by the glaciers during the LGM is delimited according to previous publications Pedraza et al., 2019). whose headwaters glacial cirques were formed during the Pleistocene (Fernández-Navarro, 1915;Sanz-Herráiz, 1988;Bullón, 2016;Pedraza et al., 2019). ...
... The area affected by the glaciers during the LGM is delimited according to previous publications Pedraza et al., 2019). whose headwaters glacial cirques were formed during the Pleistocene (Fernández-Navarro, 1915;Sanz-Herráiz, 1988;Bullón, 2016;Pedraza et al., 2019). The dominant lithologies in both mountains are crystalline rocks of the Paleozoic and pre-Paleozoic basements (GEODE, 2004). ...
The Iberian Range is home to various preserved glacial landforms and deposits inherited from the cold Quaternary periods. However, they are small in size due to the moderate altitudes of the peaks, located at heights slightly higher than 2000 m above sea level. A total of 108 Pleistocene glaciers have been identified, of which 62 are located in the Sierra de la Demanda, 19 in the Sierra de Cebollera, 16 in the Sierra de Urbión, 7 in the Sierra de Neila, 3 in the Sierra del Moncayo, and 1 in the Sierra de Albarracín. The lithological and structural diversity explains the varied types of landforms found here as well as the dimensions of the glaciers. Thus, the Demanda and Moncayo mountain ranges developed smaller glaciers on very resistant Paleozoic materials, which exceptionally allowed the formation of glacial tongues. On the other hand, the Neila, Urbión, and Cebollera mountain ranges, which are marked by slightly deformed Mesozoic materials, favored the development of large cirques with abrupt walls that gave rise to glacial tongues exceeding lengths of 2 km and were accompanied by numerous moraine deposits. The available data indicate that the outermost moraines were formed during the global Last Glacial Maximum, that is, around 20 ka, with frequent later advances between 17 and 140 ka. Several rock glaciers and debris-covered glaciers were formed at the end of the 18.9–14.6 ka period and the transition to the Bølling–Allerød, in some cases with activity up to the Early Holocene.
... This requires three inputs: cirque outlines (polygons), threshold midpoints, and a DEM. This toolbox has been used to extract cirque metrics and infer palaeoclimate conditions in various settings worldwide, including Britain and Ireland (Barr et al., , 2019, the Guadarrama and Somosierra mountains in Spain (Pedraza et al., 2019), the Faeroe Islands (Wallick and Principato, 2020), High Mountain Asia (Zhang et al., 2020(Zhang et al., , 2021Li et al., 2023), and Antarctica (Barr et al., 2022(Barr et al., , 2023. Use of DEMs allowed ACME to calculate new descriptors such as hypsometric integral, mean slope and 3D area. ...
... The altitudinal factor was favourable in most of the sectors of the Spanish ICS, since their summits are 300e500 m higher than the maximum altitude of the Serra da Estrela (Torre, 1993 m asl). As for the terrain morphology factor, as explicitly pointed out in several works (Vidal-Box, 1948; Martínez de Pis on and Muñoz-Jim enez, 1972;Sanz-Donaire, 1979; Martínez de Pis on and Palacios, 1997;Pedraza and Carrasco, 2006;Pedraza et al., 2019;Carrasco et al., 2022aCarrasco et al., , 2022b, numerous geomorphological indicators allow us to establish that the presence of pre-glacial valleys and fluvial catchments determined the development of glaciers in the Spanish ICS. As the sedimentary sequences show, one of the most critical stages for the consolidation of the modern drainage network in the fluvial basins of the Iberian plateau (Meseta) happened during the last interglacial (Eemian; MIS 5e) (Santisteban and Schulte, 2007;P erez-Gonz alez et al., 2008;Silva et al., 2012Silva et al., , 2017. ...
The area of Prados del Cervunal (PC) is an intra-morainic topographic depression located at 1800 m asl in the divide or interfluve between Garganta de Gredos and Garganta del Pinar valleys (Central Gredos; Iberian Central System, ICS). Both valleys, along with the adjacent Hoya Nevada, were occupied by glaciers during the Upper Pleistocene, leading to the development of the Prados del Cervunal moraine complexes studied in this work. Using cartographic methods and morphostratigraphic analysis, the three main glacial formations established in the Regional Chrono-Evolutionary Pattern for the ICS, PeripheralDeposits (PD), Principal Moraine (PM) and Internal Deposits (ID), have been identified and mapped in this area. The chronology of these formations has been implemented by Cosmic Ray Exposure (CRE)techniques using 10Be (new data) and 26Cl (previous data, recalculated in this work) in samples frommorainic boulders. With these data, the following chrono-evolutionary sequence has been established:(stage 1) local-Maximum Ice Extent (MIE), dated in 25.0 ± 1.4 ka and corresponding to the maximum age obtained in these paleoglaciers; (stage 2) period of oscillations around the MIE, corresponding to the development of the PD Formation between ~25 ka and ~21 ka; (stage 3) period of readvance and stabilisation, dated after ~21 ka (average age obtained for the PD moraines attached to PM moraines) and previous to ~18 (minimum age obtained for a main crest of the PM formation); and (stage 4) onset of deglaciation dated around to ~18 ka (average of ages obtained for the first main crest of the ID formation). During the stages of maximum ice expansion, these three glaciers formed an Ice field whose tongues were interconnected on the PC flat by an ice transfluence system (stages 1 and 2, Plateau GlacierPeriod). In later stages, the ice masses were partitioned, giving rise to valley glaciers and large moraines forming morainic complexes like those of PC (stages 2, 3 and 4, Valley Glaciers Period). The local MIE and onset of deglaciation stages in this area show a good fit with the ages stablished to global level for the global Last Glacial Maximum (LGM) and the onset of the Last Glacial Termination (Termination I). They also show good correlation at local (with other areas of the ICS), peninsular (with other Iberian mountains) and continental (some areas of the Alps and mountains of Central Europe) level.
... The altitudinal factor was favourable in most of the sectors of the Spanish ICS, since their summits are 300e500 m higher than the maximum altitude of the Serra da Estrela (Torre, 1993 m asl). As for the terrain morphology factor, as explicitly pointed out in several works (Vidal-Box, 1948; Martínez de Pis on and Muñoz-Jim enez, 1972;Sanz-Donaire, 1979; Martínez de Pis on and Palacios, 1997;Pedraza and Carrasco, 2006;Pedraza et al., 2019;Carrasco et al., 2022aCarrasco et al., , 2022b, numerous geomorphological indicators allow us to establish that the presence of pre-glacial valleys and fluvial catchments determined the development of glaciers in the Spanish ICS. As the sedimentary sequences show, one of the most critical stages for the consolidation of the modern drainage network in the fluvial basins of the Iberian plateau (Meseta) happened during the last interglacial (Eemian; MIS 5e) (Santisteban and Schulte, 2007;P erez-Gonz alez et al., 2008;Silva et al., 2012Silva et al., , 2017. ...
An MIS 2 glaciation type is asserted in the central Iberian Peninsula (W Europe) in which a competition to enlarge their glacier tongues produced the built-up a middle-moraine complex, suited for cosmogenic dating. The glacial evolution of Gredos and Pinar glacier is in this paper exposed and provide the fundamentals for further research in the region.
... En la Sierra de Guadarrama se ha comprobado en el control de la estabilidad de las vertientes y en el desarrollo de los procesos nivales (PALACIOS & SÁNCHEZ-COLOMER, 1997). Especialmente notorias son las vertientes de derrubios (canchales o pedreras) en las laderas norte de los macizos de Peñalara, Mujer Muerta y Cabezas de Hierro que, como se ha comprobado, aparecen enmascarando las antiguas morfologías glaciares (SANZ-HERRÁIZ, 1988;BULLÓN, 2016;PEDRAZA et al., 2019). Notorias también son las coladas solifluidales y los flujos de derrubios (debris flow) localizados en valles y circos de los antiguos glaciares. ...
RESUMEN El presente trabajo se localiza en el sector central de la Sierra de Guadarrama, coincidiendo con las delimitaciones del Parque Nacional. El objetivo es realizar el inventario, cartografía, cronología e interpretación de la secuencia crono-evolutiva de sus paleoglaciares. La Sierra de Guadarrama es una montaña media mediterránea, estructurada en bloques de falla, en la que predomina las litologías cristalinas del sustrato (granitos y, fundamentalmente, gneises) y cuyas cimas presentan una altura media en torno a los 2100 m, estando cubiertas por la nieve durante gran parte de periodo invernal. Las aportaciones más relevantes de esta investigación se resumen en: (1) la cartografía y descripción de un total de 79 glaciares desarrollados entre los 2413 m s.n.m. (cota máxima de un circo) y los 1490 m s.n.m. (cota mínima de un frente glaciar); (2) junto a los glaciares de circo, ladera y valle, por primera vez se describe en esta sierra un glaciar de meseta localizado en la altiplanicie de Los Pelados-El Nevero; (3) la reconstrucción de este glaciar durante su etapa de máxima extensión (Máximo Glaciar) indica que tenía un superficie de hielo de ~ 13 km 2 , un espesor máximo de ~ 120 m y un flujo centrífugo pero más incisivo hacia el NE; (4) la ELA estimada durante esa etapa fue de 1926 m, lo que significa una depresión de 1.000-1.200 m respecto a la ELA actual estimada; (5) los datos obtenidos mediante datación absoluta 10 Be-CRE, en el paleoglaciar de Hoyo Grande muestran una secuencia cronológica de ~26 ka (Máximo Glaciar sincrónico con el máximo global o LGM), ~15,6 ka (final de la etapa de reavance y estabilización), ~15 ka (inicios de la etapa de deglaciación) y ~4,6 ka (evento frío post glaciar Holoceno); (6) a partir de esta secuencia y la del Macizo de Peñalara se ha podido elaborar un modelo
... Cirques are present almost ubiquitously in formerly glaciated regions. They have been studied throughout the world [1][2][3][4][5][6][7], and these studies have shown that cirque morphology is linked to the paleoclimate. For example, a large cirque size indicates that former glaciers were dynamic or long-lasting; the cirque floor altitude (CFA) is an indicator of the former glacial equilibrium line altitude (ELA) and reflects information about the former moisture and wind directions; and the cirque aspect indicates information about the solar radiation, wind direction, and glacial extensions [2]. ...
Cirque morphology is used to reflect the patterns of paleoclimate, paleoglaciation, and landscape evolution. Cirque study has been conducted in the Gangdise Mountains of the southern Tibetan Plateau (TP) and the central TP (dominated by a weak Indian summer monsoon (ISM) or a continental climate). This study focused on the cirques in the southeastern TP, which is dominated by a strong ISM, to analyse the controlling factors on cirque morphology. A total of 361 cirques were mapped in the Taniantaweng Range of the southeastern TP, and their metrics were calculated. The results showed that the cirque sizes increased with temperature and decreased with precipitation, which may be due to the development of valley-type glaciers and the effect of non-climatic factors. The cirques tended to face NE, implying that they prefer leeward slopes, and they were under the ‘morning–afternoon’ effect. With altitude, the tendency of the cirque aspect shifted from N to SE, and the cirque size decreased. The former may indicate the ability of the high altitude to support cirque development on climatically unfavourable slopes; the latter may be due to the development of valley-type glaciers or insufficient space for cirque development. The cirque size and shape did not show statistical differences between aspects. The cirques on soft bedrocks had larger heights than those on hard bedrocks, indicating that soft bedrocks promote subglacial erosion. A comparison with the results of the western, central, and eastern sectors of the Gangdise Mountains and the central TP reveals that the strength of the ISM did not necessarily increase the cirque density but limited the cirque size on a regional scale. The CFA did not show a reverse relationship with precipitation, but it showed a positive correlation with the cirque Zmean, which implies that the CFA was greatly affected by altitude, and its distribution does not always reflect paleoclimatic patterns.
... Instead of small glaciers, the mean cirque sizes in the study area (average: 564 m long, 564 m wide; Table 1) are comparable with those in Svydovets (average: 530 m long, 593 m wide; Kłapyta et al., 2021b), Maramureş Mountains (average: 504 m long, 548 m wide; Mîndrescu and Evans, 2014) and Călimani Mountains (average: 486 m long and 556 m wide; Kłapyta et al., 2022), where larger Pleistocene glaciers occurred. The average ratio of length to height range in Polonyna Rivna and Borzhava (2.11 and 2.0, respectively), is similar to those in the Romanian Carpathians (2.10) (Mîndrescu and Evans, 2014), which may be related to effective glacial erosion in relatively low competent sandstone-mudstone bedrock (Mîndrescu and Evans, 2014;Pedraza et al., 2019;Evans, 2021). ...
The Polonyna Rivna (1480 m asl) and Borzhava (1682 m asl) ranges represent medium-high mountain massifs located in the north-western part of the Ukrainian Carpathians, where the legacy of the Pleistocene glaciation has long been unexplored. Based on the first detailed mapping of glacial landforms and sedimentological analysis, we document the presence of freshly-shaped outer moraines and glacial cirques and reconstruct the extent and ice-surface geometry of the six very small (0.09–0.78 km² area) palaeoglaciers. The specific feature of the area is the presence of extensive mountain-top plateaus that play an important role as additional areas for snowblow accumulation. The equilibrium line altitudes (ELAs) calculated from hypsometry of reconstructed local Last Glacial Maximum (LLGM) using the area x altitude balance ratio (AABR) 1.6 method is exceptionally low at 1138 m asl in the Polonyna Rivna and 1230 m asl in the Borzhava range. Excluding the topographic effect produced by additional snow accumulation the ELA shift upwards between 120 and 180 m which corresponds to 25–53% of the glacier elevation range. The resulted climatic ELA (1282–1352 m asl) together with the mean cirque floor altitude (1194 m asl) and mean elevation of the glacier fronts (994 m asl) represent the lowest values in the entire Carpathian arc. Our data indicate glacier-friendly conditions in the mountain massifs exceeding 1400 m asl in the windward NW part of the Ukrainian Carpathians where due to relatively cold air temperatures and orographic induced precipitation local topolimatic factors dictated the development of marginal glaciation.
... Instead of small glaciers, the mean cirque sizes in the study area (average: 564 m long, 564 m wide; Table 1) are comparable with those in Svydovets (average: 530 m long, 593 m wide; Kłapyta et al., 2021b), Maramureş Mountains (average: 504 m long, 548 m wide; Mîndrescu and Evans, 2014) and Călimani Mountains (average: 486 m long and 556 m wide; Kłapyta et al., 2022), where larger Pleistocene glaciers occurred. The average ratio of length to height range in Polonyna Rivna and Borzhava (2.11 and 2.0, respectively), is similar to those in the Romanian Carpathians (2.10) (Mîndrescu and Evans, 2014), which may be related to effective glacial erosion in relatively low competent sandstone-mudstone bedrock (Mîndrescu and Evans, 2014;Pedraza et al., 2019;Evans, 2021). ...
... Cirques have been studied throughout the world (e.g., Barr et al., 2019;Spagnolo, 2015a, 2015b;Evans, 2021;Ipsen et al., 2018;Oliva et al., 2020;Pedraza et al., 2019;Wallick and Principato, 2020), including the Gangdise Mountains in the southern Tibetan Plateau (TP) (Zhang et al., 2020). The climatic domains of the TP can be categorised into a zone dominated by the Indian summer monsoon (ISM) in the south, a Westerlies dominated zone in the north, and a transitional zone between these ( Fig. 1) (Thompson et al., 2018). ...
Cirque morphology represents the characteristics of palaeoglaciations and palaeoclimate. This study mapped and analysed 70 cirques in the central Tibetan Plateau (TP) with dominant continental climate. The results show that from northwest to southeast, cirque dimensions (i.e., length, width, and area) increase, while cirque floor altitudes decrease. A likely reason is the high precipitation rate caused by the Indian summer monsoon in the southeastern part. The diversity of cirque aspect values indicates weak or inconsistent prevailing winds during cirque development. Cirques enlarge with altitude, which might imply that cirques at high altitudes developed early and thus increased in size. Cirque aspect diversity increases with altitude from 5100 to 5600 m above sea level (asl), which indicates the capacity of high altitudes to support cirques at less favourable slopes. If altitude increases above 5600 m asl, the diversity of cirque aspect first increases and then decreases, which may be because of local topography. Mountain orientation and lithology had an effect on cirque aspect/size. Cirque numbers and sizes were compared between western, central, and eastern sectors of the Gangdise Mountains in the southern TP with those in the central TP. This comparison showed that a strengthening Indian summer monsoon can raise the value of ‘cirque density’ (i.e., cirque number per unit area), promote glacier development into valley-type, and limit cirque enlargement.
... Haag et al. (2019) applied GIS approach in order to build the catalog of monogenetic volcanoes in the southern Puna Plateau (Argentina) and explored their evolution and relationship with geotectonic events by combining spatial analysis with morphometric measurements. Moreover, morphometric analyses of isolated PFs such as glacial and periglacial landforms have been used to make deductions regarding the associations between their form and aspect, as well as the natural processes responsible for their formation (Johnsson et al., 2012;Dowling et al., 2015;Wang et al., 2017;Pedraza et al., 2019). ...
This paper introduces a free and open-source geographic information system (GIS) plug-in, named PolyMorph-2D, for morphometric analysis of vector-based polygon features (PFs) in OpenJUMP. Written in Java™ programming language, the plug-in allows researchers from various earth and spatial science-related disciplines to compute morphometric parameters of 2D input vector features forming a polygon (i.e., a closed curve) which may represent outer boundaries or contours of various natural and/or man-made entities that differ in size, shape, complexity and drawing scale (e.g., craters, sinkholes, cirques, drainage basins, land parcels, buildings, lakes, ponds, peaks, pits, playas, pockmarks, coral mounds, seamounts, landslides, drumlins, islands, atolls, granular materials, mineral crystals, fossils, etc.). Using this plug-in, a number of basic tasks (e.g., calculations related to location, length, width, perimeter, radius, area, and orientation) can be performed and derived parameters (i.e., shape and size measures) of PFs (e.g., axis ratios, ellipticity, circularity, compactness, dispersion, complexity, elongation, regularity, convexity, concavity, solidity, rectangularity, roundness, and sphericity) are computed and written to input polygon layer’s attribute table, through a simple point-and-click interface. The derived parameters calculated by the plug-in are invariant to the PF's location, scale (size), and rotation. The plug-in is also capable of performing aforementioned morphometric calculations on overlapping PFs with or without holes, provided they are topologically correct. The extensive data matrix (consisting of 39 parameters) obtained from this route can be further subjected to a number of multivariate statistical analysis methods to decipher underlying processes and/or environmental factors responsible for formation of these shapes and to classify them into homogeneous subtypes or typologies featuring similar characteristics.
... The Sierra Cebollera cirques, and specifically the Peña Negra glacial cirque, originated from small glaciers that were characterized by relatively short (or no) ice tongues and moderate capacity to erode the slopes around the main divides. The cirques are not particularly small (average width 600 m and length 532 m) compared with those in other Iberian mountains, and are similar in size to those of the Central Range (529 m wide and 556 m long; Pedraza et al., 2019) for elevations slightly higher than those of Sierra Cebollera. In the Cantabrian Mountains, northwest Iberian Peninsula, reported cirque sizes in the Alto Sil area vary between 707 m and 605 m (width and length) (Gómez-Villar et al., 2015), and 594 m and 486 m (Ruiz-Fernández et al., 2009). ...
The objective of this study was to assess whether it is possible to obtain a comprehensive record of the last deglaciation from the small Peña Negra glacial cirque in a marginal mountain range in the Iberian Range (northern Iberian Peninsula). The cirque is located in Sierra Cebollera, at an elevation slightly over 2000 m a.s.l. in the divide, and has relatively low elevational difference between its uppermost and lowest parts. The Peña Negra glacial cirque was selected because of the presence of several lateral moraines indicating the occurrence of a glacial tongue of 1.8 km length and a small rock glacier, enabling identification of the main glacial stages that affected the paleo-evolution of the glacier. Using cosmogenic exposure dating techniques and geomorphological mapping it was possible to reconstruct the historical Peña Negra glacier and to distinguish: (i) the maximum ice extent (MIE) at approximately 18–20 ka, coinciding with the Global Last Glacial Maximum (GLGM), although the occurrence of a previous stage was not ruled out; (ii) a stage of glacial re-advance at 16–17 ka, coinciding with the Oldest Dryas, followed by rapid ice melting; (iii) the development of a rock glacier in a minor structural cirque near the headwall at 14–15 ka, when paraglacial processes were probably dominant; and (iv) evidence of ice melting in the uppermost cirque at 13.5 ka. Study of the Peña Negra glacier revealed the history of a minor valley glacier affected by distinct stages, including the formation of a small rock glacier in the final phases of deglaciation. No evidence of a Younger Dryas re-advance was found.
La dinámica geomorfológica glaciar y periglaciar modeló intensamente el relieve de las montañas de las sierras de Guadarrama y Gredos durante el Pleistoceno, dando lugar a los principales sistemas lagunares de alta montaña del sistema Central ibérico en España. Aunque estas lagunas comparten un origen glaciar común, presentan características morfogenéticas diferentes en función de la acción de los hielos y su edad de deglaciación. En este trabajo se realiza por primera vez una clasificación tipológica individualizada de la morfogénesis glaciar de las cubetas de los sistemas lacustres del sistema Central ibérico. Para la caracterización y definición de los tipos se han utilizado variables morfométricas de las cubetas lacustres y topográficas del entorno, datos geomorfológicos de trabajos previos de otros autores y clasificaciones tipológicas de lagos de origen glaciar establecidas en otros ámbitos con diferentes escalas geográficas. Sobre un conjunto de 26 lagunas, en su mayoría con superficies > 0,5 ha y profundidades máximas > 0,5 m, repartidas en la sierra de Guadarrama (macizo de Peñalara) y en la sierra de Gredos (macizo Central de Gredos, sierra del Barco y sierra de Béjar) se han definido 9 tipos morfogenéticos que representan la diversidad geomorfológica de su origen glaciar. Se han clasificado en dos grupos genéticos por su origen común: de hoya, generados por la acción directa de sobreexcavación de los hielos, y morrénicas, formados por el represamiento de las aguas producido por los materiales erosionados, transportados y depositados por los glaciares. El primero comprende 7 tipos: hoya-circo sensu estricto (s.s.), hoya-circo con morrena, hoya-valle s.s., hoya-valle en rosario, hoya-valle lateral, hoya-ombligo y hoya-fluvial. El segundo incluye 2 tipos: morrénica s.s. e intermorrénica. La ubicación en nichos colgados o circos en las cabeceras, zonas bajas, depresiones laterales o ejes fluviales de los valles, la presencia de umbrales y estrechamientos rocosos del terreno, las pendientes y orientaciones del entorno, o la existencia de cordones morrénicos únicos o múltiples, son algunas de las variables principales que diferencian los tipos establecidos. Algunas lagunas han perdido su condición natural al haber sido represadas para usos hidroeléctricos y de regadío, en especial, las de tipología genética de hoya-valle.
The objective of the work is to calibrate the Schmidt hammer exposure dating (SHD) method in the Sierra de Guadarrama National Park in correlation with the dates previously obtained by Cosmogenic Radiation Exposure (CRE) dating methods. The dates were recalculated according to the new production models of 36Cl and 10Be cosmogenic isotopes. For this purpose, three glacial cirques were selected (Dos Hermanas, Laguna and Pepe Hernando), located on the eastern slope of Peñalara Peak, Spain (40°51'N, 3°57'O; 2428 m), the highest altitude of this mountain range. The application of the SHD method seems to be influenced neither by the different altitude of the samples nor by their height with respect to the current ground level. The degree of roughness of the rock surfaces (gneiss) has a slight influence, but does not change the actual volume of the results. The results of this work show a clear relationship between the CRE ages and the SHD R-values. The oldest landforms (31–19 ka) give mean values R < 50, both for moraine boulders and polished bedrock. The boulders of a rock glacier (16–15 ka) and the boulders of the innermost moraine yielded higher values: R-value >50. The youngest polished bedrock surface, located under the Peñalara Peak (12–11 ka), yielded R-value >60.
Cirques are typical erosional landforms of glaciers and have been used as bases for paleoclimate and paleoenvironment reconstruction and for understanding the interactions between glacial erosion, climate, and topography. The availability of high-resolution digital elevation models (DEMs) provides the opportunity to map large populations of cirques for regional and global scale analysis. However, cirque outlines are still mainly determined based on manual digitization, which is time consuming and labor intensive. This paper introduces an automated method to recognize and delineate cirques using DEMs based on a series of hydrological and morphological analyses, including delineating stream network, filtering streams, determining potential cirque threshold points, and delineating cirque outlines. A semi-automated tool is also developed based on user-specified threshold points or cross sections. The related tools are coded in python and imported into ArcGIS as a toolbox, AutoCirque, with user friendly interfaces. Comparison in a test area of the eastern Tian Shan, China, indicated that the population statistics are relatively consistent between manually digitized and auto-delineated cirques. Detailed comparisons for 11 selected cirques indicated that the AutoCirque-delineated and manually digitized cirque outlines are similar in shape with an average boundary offset of approximately one DEM cell size (30 m) and a 70–90% overlap-fit percentage. The derived cirque metrics are also similar, especially for elevation, slope, and aspect related metrics. This toolbox can significantly speed up the analytical processes, remove the subjectivity in delineating cirque outlines, and allow for the comparison of cirque morphology and metrics at regional and global scales.
The chronology of the maximum ice extent during the Last Glacial Cycle has been a subject of intense debate within the Iberian glacial geomorphologists community. Until the last decades of the 20th century, the use of radiocarbon dating suggested that the Local Last Glacial Maximum (LLGM) occurred in Iberian Mountains at c. 50–40 cal ka BP, or before. More recently, the chronology of the LLGM has been reconsidered thanks to the widespread use of other dating techniques, namely, optically stimulated luminescence and cosmic-ray exposure dating. In most massifs the LLGM took place during the Global Last Glacial Maximum (GLGM), and in others LLGM glaciers were only slightly larger than the GLGM expansion and left smaller moraine complexes than the larger GLGM moraines.
We present a detailed geomorphological map of the landform assemblages originated by the two major paleoglaciers of the Sierra de Gredos mountain range in the Spanish Iberian Central System. Based on previous works, our map focused on the features formed by Gredos and Pinar paleoglaciers during the last glaciation and subsequent glacial events. Based on a remote sensing analysis and exhaustive field surveys, we identified with great accuracy the local distribution of glacial, periglacial, mass movement, structural, fluvial, and lacustrine features. We recognized three main glacial geomorphological formations representing: (i) the maximum glacial extension reached (peripheral deposits); (ii) the culmination of glacial conditions (principal moraines) and (iii) the local glacial withdrawal (internal deposits). Our map offers a renewed spatial framework on which to conduct higher-resolution glacial chronologies, especially of Late Glacial and Holocene glacial activity, providing key information for performing future paleoclimatic reconstructions of the northern hemisphere mid-latitudes. ARTICLE HISTORY
It has been proposed that most cirques are source-area depressions of large, deep-seated rock slope failures. Yet the close relation between cirques and climate is convincing evidence of the dominance of glacial erosion, rather than rock slope failure, in mountain cirque development and distribution. Cirque floor altitudes have a lower limit that varies with snowfall by 1000 m or more between windward and leeward sides of mountain systems. Glaciation Levels and Equilibrium Line Altitudes implied by cirques vary in parallel with those for modern glaciers. Cirques are often found mainly on the poleward or leeward slopes of individual mountain ranges, as are modern small glaciers (because of solar radiation and wind effects on ablation and accumulation).
Most rock-slope failures (RSFs: rock slides, rock avalanches and gravitational deformations) do not involve the deep-seated rotational movement that would produce a cirque form. Although some deep-seated RSFs with arcuate head scars may be confused with cirques, identification as a glacial cirque is more confident as the floor is longer, wider and more gently-sloping. Some scars from major RSFs may resemble poor or moderately developed cirques, but tend to have steeper floors, to be more scattered and closely related to geology, whereas glacial cirques develop on all rock types. Deep-seated RSFs high on slopes can be associated with seismic shaking, but cirques develop without relation to seismicity. Degree of cirque development can be related to duration of exposure to glaciation. Often RSFs are found adjacent to cirques, or in glacial transfluences; only a proportion are well situated to develop into glacial cirques. Valley-head cirques are continued down-valley by glacial troughs. The ‘overdeepening’ (rock basins with reversed slopes) found in a large minority of cirques is not due to rock avalanching, fluvial or periglacial erosion.
The RSF proposal should therefore be rejected in favour of the traditional glacial explanation, without any nivation stage being necessary. Rock slope failure is one of several possible ways of initiating hollows for glacier accumulation, as well as an ancillary process of cirque extension or widening through collapse of glacially-oversteepened slopes.
Headward extension of adjacent cirques on a ridge leads to displacement of the divide, sometimes by 2 km or more, lowering ridge and summit altitudes and producing the ‘glacial buzzsaw’ effect. Where a relatively lower snowline has led to cirque erosion on all sides of a mountain, cirque intersection lowers summits further. The buzzsaw hypothesis is not applicable, however, where remnants of a preglacial summit surface survive.
http://dx.doi.org/10.1002/esp.4810
The Sierra Baguales Mountain Range, forming the eastern foothills of the Southern Patagonian Andes, has well-developed alpine-glaciated landforms which present an ideal opportunity to study climatic and non-climatic factors that control cirque development and morphology. One hundred and forty-three glacial cirques were studied with reference to 14 morphometric attributes which were analyzed using statistical analysis and GIS methodologies. The cirques were classified into two types using cluster analysis complimented with a composite map based on the attributes, the latter technique that is applied to glacial cirque analysis for the first time. Type 1 cirques are associated with glacial processes isolated from the Southern Patagonian Ice Field (SPIF), developed under locally cold and dry climatic conditions. Type 2 glacial cirques are associated with older, more extensive glacial processes controlled by regional-scale climate variables and the presence of the Pleistocene Ice Sheet. The results show that the development of most of the glacial cirques has been controlled mainly by their aspect, exposure to solar radiation, Southern Hemisphere Westerly winds, and cirque floor slope. Finally, we concluded that our analyses show the evolution of cirques in the Sierra Baguales Mountain Range was not uniform. Cirque glaciers that developed to the west, close to the Southern Patagonian Ice field, have been more dynamic, and therefore their cirques experienced more erosion than those located to the east.
The European Alps, the cradle of pioneering glacial studies, are one of the regions where geological markers of past glaciations are most abundant and well-studied. Such conditions make the region ideal for testing numerical glacier models based on simplified ice flow physics against field-based reconstructions and vice versa.
Here, we use the Parallel Ice Sheet Model (PISM) to model the entire last glacial cycle (120–0ka) in the Alps, using horizontal resolutions of 2 and 1km. Climate forcing is derived using two sources: present-day climate data from WorldClim and the ERA-Interim reanalysis; time-dependent temperature offsets from multiple palaeo-climate proxies. Among the latter, only the European Project for Ice Coring in Antarctica (EPICA) ice core record yields glaciation during marine oxygen isotope stages 4 (69–62ka) and 2 (34–18ka). This is spatially and temporally consistent with the geological reconstructions, while the other records used result in excessive early glacial cycle ice cover and a late Last Glacial Maximum. Despite the low variability of this Antarctic-based climate forcing, our simulation depicts a highly dynamic ice sheet, showing that Alpine glaciers may have advanced many times over the foreland during the last glacial cycle. Ice flow patterns during peak glaciation are largely governed by subglacial topography but include occasional transfluences through the mountain passes. Modelled maximum ice surface is on average 861m higher than observed trimline elevations in the upper Rhône Valley, yet our simulation predicts little erosion at high elevation due to cold-based ice. Finally, despite the uniform climate forcing, differences in glacier catchment hypsometry produce a time-transgressive Last Glacial Maximum advance, with some glaciers reaching their modelled maximum extent as early as 27ka and others as late as 21ka.
Glacial cirques are typical landscape features of mid-latitude mountain environments like the Central Pyrenees. Their morphology as well as their spatial distribution provides insights about past glaciers and climates. In this study, we examine the distribution, morphometrical and topographical characteristics of glacial cirques in two U-shaped glacial valleys located in the Central Pyrenees-the Aran and the Boí valleys. They are located in different aspects of this mountain range (north vs south) under different climatic influences that promoted distinct glaciation patterns during the late Pleistocene. The spatial mapping of these landforms was carried out using high-resolution imagery and field observations. We analysed the data of the morphometrical and topographical variables of the glacial cirques by using different statistical and geospatial methods in order to unveil the factors controlling their formation and development. A total of 186 glacial cirques were mapped in the study area, including 119 in the Aran and 67 in the Boí valleys. The local topography and microclimate conditions lead to substantial differences in both areas in terms of the morphology and dimensions of the cirques. Glacial cirques in Boí are distributed at slightly higher elevations than in Aran and they are also larger, though their dimensions decrease with elevation in both valleys. Aran cirques are mostly oriented NE, while Boí landforms do not show any prevailing aspect. Even though lithology does not control the distribution of the glacial cirques, some specific lithological settings may favour the development of larger cirques. In general, glacial cirques in the Aran and the Boí valleys show morphometrical properties similar to those reported in other mid-latitude mountain ranges.
The spatial distribution and dating of archaeological sites suggest a poor occupation of southern Iberia by hunter-gatherers after the Last Glacial Maximum (LGM) and during Heinrich event 1 (H1) compared to Northern Iberia. The H1 was a period of cold and arid climate conditions and is suspected to have played an important role in the population dynamics in Europe at the end of the Pleistocene. In this study, the potential influence of climate change on the human settlement patterns in Iberia is analysed based on regional palaeoclimate modelling. Here, the WRF model is used to simulate continuous time slices of 30 years of climate conditions representative for both the LGM and H1 at high spatial resolution. The model results indicate that, apart from a general decrease in temperature, a considerable decrease in precipitation over southern Iberia occurred during the H1, that agrees with the available climate proxy data. The analysis of ombrotypes unveils extremely arid conditions, particularly over southern Iberia and during the growing season (summer), which could have constrained the availability of food and water to the inhabitants. The total area in Iberia that can be characterized as ultrahyperarid in summer enlarged from 2% (13 K km2) during the LGM to 22% (148 K km2) during the H1. Likewise, the reconstruction of vegetation types shows an increase of non-arboreal (open shrubland, grassland) types at the expense of arboreal types in southern Iberia for H1. Thus, the different climate conditions and changes in palaeovegetation between the LGM and H1 probably played a major role in the decrease of the hunter-gatherer populations in southern Iberia.
This work describes a mountain meteorological network that was in operation from 1999 to 2014 in a mountain range with elevations ranging from 1104 to 2428 m in Central Spain. Additionally, some technical details of the network are described, as well as variables measured and some meta information presented, which is expected to be useful for future users of the observational database. A strong emphasis is made on showing the observational methods and protocols evolution, as it will help researchers to understand the sources of errors, data gaps and the final stage of the network. This paper summarizes mostly the common sources of errors when designing and operating a small network of this kind, so it can be useful for individual researchers and small size groups that undertake a similar task on their own. Strengths and weaknesses of some of the variables measured are discussed and some basic calculations are made in order to show the potential of the database and to anticipate future deeper climatological analyses over the area. Finally, the configuration of an automatic mountain meteorology station is suggested as a result of the lessons learned and the the common state of the art automatic measuring techniques.
Passglaciären is a small cirque glacier in the Kebnekaise massif, northern Sweden. It is frozen to its bed over more than 70% of its area, and under present climatic conditions has little effect on cirque formation. More favourable conditions for cirque glacier erosion during the Holocene are of short duration. Assuming similar conditions during previous interglacials, it is suggested that forms such as the Passglaciären cirque developed mainly during the initial phases of glacials when they were part of networks of large valley glaciers or of a small warm-based mountain-centred ice sheet. Passglaciären has been examined in order to evaluate its erosive capacity and its association with the subglacial cirque morphology. The methods used are radar surveys and direct ice-temperature measurements. Erosion is restricted to a small section of the glacier bed, at present resulting in only partial deepening of the cirque and erosion of the backwall. In cold, arid regions with extensive permafrost, small cirque glaciers are largely frozen to the bed, and therefore cannot contribute significantly to cirque formation. In such regions glacial erosion by larger temperate glaciers is more likely to be the major cause of cirque excavation.
We map glacial cirques, and analyse spatial variability in their altitude and aspect to derive a long-term, time-integrated, perspective on climate patterns during former periods of mountain glaciation (likely spanning multiple Quaternary glaciations) in Britain and Ireland. The data reveal that, although air temperatures were important, exposure to moisture-bearing air masses was the key factor in regulating sites of former mountain glacier formation, and indicate that during such periods, moisture supply was largely controlled by North Atlantic westerlies, with notable inland precipitation gradients (precipitation decreasing inland), similar to present day. In places, trends in cirque altitude may also reflect regional differences in the extent of cirque deepening, controlled by the dimensions and dynamics of the glaciers that came to occupy them. Specifically, comparatively deep cirques in coastal locations may reflect the former presence of dynamic (fed by moisture from the North Atlantic), but comparatively small, glaciers (largely confined to their cirques). By contrast, decreasing cirque depth further inland, may reflect the former presence of larger and/or less dynamic ice masses, occupying comparatively continental climatic conditions.
Resumen: Los datos disponibles sobre la morfología glaciar de Somosierra lo describen como un glaciarismo de menor incidencia con el desarrollo de algunos glaciares de circo muy localizados. Tanto por sus dimensiones, como por su localización geográfica y altitud, las condiciones presentes en Somosierra para la instalación de los glaciares, en principio deben considerarse menos adecuadas que en los otros sectores del Sistema Central Ibérico donde se localizaron estos procesos a lo largo del Pleistoceno. Sin embargo, esos datos son muy escasos y poco actualizados, por lo cual su valor es limitado. En este trabajo se presentan los resultados de una serie de estudios recientes que modifican las interpretaciones precedentes sobre la dimensión de algunos paleoglaciares y aporta la primera cartografía y análisis morfométrico de la morfología glaciar de este sector del Sistema Central Ibérico. Palabras clave: glaciarismo, Pleistoceno Superior, cartografía, Somosierra, Sistema Central Ibérico. Abstract: According to available data, the development of glacial processes on Somosierra Mountain would have been minor and there was only some cirque glaciers in very specific locations. Both for its extension and its geographical location and altitude, the conditions present in Somosierra for installation of glaciers in principle should be considered less suitable than the other sectors of the Central System Iberian where also they are located these processes along the Pleistocene. However, such available data are very sparse and outdated, so its value is limited. In this work presents the results of a series of recent studies that modify previous interpretations about the dimension of some paleo-glaciers and for the first time provides a detailed cartography and a morphometric analysis of glacial morphology of this sector of the Iberian Central System.
The present paper provides new information on Pleistocene glacial activity in a mountainous area of the Iberian Central System. A sediment analysis associated with Pleistocene modelling was carried out using: (1) granulometric and morphometric procedures, (2) quartz grain microtexture techniques (SEM) to discriminate between glacial and no glacial origins of sediments, (3) clay X-ray diffraction study to determine intra-Pleistocene climate variability, and (4) optically stimulated luminescence (OSL) absolute dating. The results show that the sediments were formed in two different phases associated with glacial dynamics, one of them was 35–30 ky BP and another was 25–20 ky BP, separated by a short intermediate warm-wet period. Identification of glacial phenomena is new for the northern slopes of the Guadarrama Mountains (facing the north Meseta, Duero basin), although they are not unusual within the general context of the Iberian Central System. From the data provided, we deduce that glaciation in these mountains was much more intense and widespread than had previously been thought because, on the northern slopes, glaciers occupied large areas reaching the base of the mountains. The evidence favours new interpretations of Pleistocene morphology in the centre of the Iberian Peninsula and, by extension, on the southwestern edge of Europe; it also highlights the sensitivity of mountainous areas with regard to Quaternary climate changes.
The Last Glacial Maximum (LGM) exhibits different large-scale atmospheric conditions compared to present-day climate due to altered boundary conditions. The regional atmospheric circulation and associated precipitation patterns over Europe are characterized for the first time with a weather typing approach (circulation weather types, CWT) for LGM paleoclimate simulations. The CWT approach is applied to four representative regions across Europe. While the CWTs over Western Europe are prevailing westerly for both present-day and LGM conditions, considerable differences are identified elsewhere: Southern Europe experienced more frequent westerly and cyclonic CWTs under LGM conditions, while Central and Eastern Europe was predominantly affected by southerly and easterly flow patterns. Under LGM conditions, rainfall is enhanced over Western Europe but is reduced over most of Central and Eastern Europe. These differences are explained by changing CWT frequencies and evaporation patterns over the North Atlantic Ocean. The regional differences of the CWTs and precipitation patterns are linked to the North Atlantic storm track, which was stronger over Europe in all considered models during the LGM, explaining the overall increase of the cyclonic CWT. Enhanced evaporation over the North Atlantic lead to higher moisture availability over the ocean. Despite the overall cooling during the LGM, this explains the enhanced precipitation over southwestern Europe, particularly Iberia. This study links large scale atmospheric dynamics to the regional circulation and associated precipitation patterns and provides an improved regional assessment of the European climate under LGM conditions.
The occurrence of periglacial landforms in the most elevated part of the Karkonosze has been recognized within glacial cirques and on slopes of residual hills. Some of these landforms have not been previously documented. The inventory of periglacial landforms includes protalus ramparts, rock glaciers, nivation hollows, cryoplanation terraces and solifluction lobes. Their position in relation to other landscape facets, and to cirques and moraine ridges in particular, allows one to identify phases of geomorphic development at the turn of the Pleistocene and to correlate these tentatively with stratigraphic units of the late Pleistocene. The presented hypothesis of landscape evolution calls for detailed geomorphological research, in which quantitative techniques, GIS-based modelling and dating would be widely implemented.
The surface geometry of the accumulation area and flow patterns of the ice at the Last Glacial Maximum (LGM) have been reconstructed in the Central Swiss Alps, where the ice surface formed two individual ice domes. One of them was located in the headwaters of the Rhein river and attained a minimum altitude of 2700 m. The second dome culminated at about 2900 m in the Upper Rhone valley. According to 174 trimline data, the ice surface gradients were steeper towards the south and north than to the southwest and northeast. Flowlines are perpendicular to ice-surface contours and underline the presence of a dome-type glaciation with radial outflow. The ice-flow pattern indicates drainage through the large longitudinal valleys and ice-transfluences over all major passes and lower cols to the north and south. Modelling of the LGM surface configuration by means of a Geographical Information System (GIS) likewise displays a surface geometry consisting of multiple domes with the ice divides located overhead the Rhone- and Rhein valleys, respectively. This configuration was then used to reconstruct the prevalent precipitation pattern and as the main atmospheric paleocirculation for the Alps. The position of both ice domes to the south of the Alpine main weather divide indicates that the atmospheric pressure system during the last glaciation was markedly different from today's, with prevailing southerly instead of westerly circulation. This is correlated with the southward displacement of the atmospheric Polar Front in the North Atlantic to the latitude of 40-50°due to the advancing sea ice cover. This caused the related storm tracks to move to the south of the Alps across the Mediterranean, resulting in increased rainfall in the Southern Alps and in notably reduced precipitation to the north of the Alps where dry katabatic winds promoted permafrost conditions.
Glaciers produce cirques by scouring their beds and sapping their headwalls, but evidence to constrain models of these processes has been elusive. We report a suite of environmental measurements from three cirque glacier bergschrunds, including the first temperature series recorded at depth throughout most of an annual cycle. Compared to the ambient air, the bergschrunds were colder in summer and warmer in winter. Freeze-thaw cycles were rare, and relatively stable subfreezing temperatures persisted from November until May. Using a model for rock fracturing driven by ice segregation, we demonstrate that favorable conditions for fracturing occur not only on the headwall above the glacier, but also within the bergschrund, where periglacial weathering and glacial transport can act together to drive cirque headwall retreat. A small (similar to 3 degrees C) year-round decrease in temperatures to conditions more typical of the Pleistocene would likely intensify the weathering process. Though so far ignored in all glacial landscape evolution models, the bergschrund likely plays an essential role in the sculpting of alpine landscapes.
This paper attempts to reinterpret the scenery of the Cairngorm mountains; in particular, it suggests that there is little evidence for the view that the mountains escaped a cover of ice during the Pleistocene. Following discussion of the problems of interpretation, the two major elements in the landscape of the mountains are examined in turn. The first, comprising the subdued, rolling slopes with associated fluvial forms, conformable pseudobedding, tors and rotted granite exposures, is held to reflect the detailed form of the massif in pre-glacial times. Precipitous valleys and ice-moulded forms form the second major element of the landscape and, with the exception of forms of local glaciation, reflect the passage north-eastward across the mountains of a major Scottish ice sheet. Using examples from East Greenland, it is suggested that watershed breaching occurred beneath such an ice sheet rather than as a result of valley-glacier action. The distribution of the landforms of glacial erosion can be related to a large extent to the pre-glacial topography. Troughs appear to have been excavated along the lines of pre-glacial river valleys suitably orientated for the discharge of Scottish ice, while pre-glacial valleys at right angles to the main direction of ice flow have frequently retained their original fluvial form. Apparently, new troughs, such as the Lairig Ghru, have been created where no suitable pre-glacial valley existed. The clarity of the junction between the two associations of landforms and the survival since pre-glacial times of such relatively fragile forms as tors is a remarkable tribute to the selectivity with which the overriding ice sheet eroded.
The only glaciers existing today in the Iberian Peninsula are small features located in the Pyrenees, though their number and extension has undergone significant changes over the Late Quaternary. The wide range of glacial landforms and deposits distributed across different Iberian ranges suggests the occurrence of several past periods with larger glacial systems. The objective of this research is to summarize the current knowledge on the spatial and temporal patterns of glacial activity in the Iberian mountains during the Late Quaternary. To this purpose, the chronological framework was divided in six periods: glaciations prior to the Last Glacial Cycle (Middle Pleistocene), Last Glacial Cycle (Late Pleistocene), Termination-1, Holocene, Little Ice Age (LIA) and present-day. The data were geographically divided considering the mountain systems where glacial evidence exists: Pyrenees, Cantabrian Range, NW ranges, Central Range, Iberian Range and Sierra Nevada. During Quaternary cold stages, ice accumulated in the head valleys of these mountain ranges and glaciers flowed down-valleys. In all cases, glaciers remained confined within the mountain systems and did not reach the surrounding lowlands. Depending on the combination of temperatures and moisture conditions, more or less ice was stored. In some ranges, there is evidence of Middle Pleistocene glaciations, one potentially correlating with marine isotope stage (MIS) 12 and another correlating with MIS 6 with glaciation dated to ca. 130-170 ka. However, most of the glacial records correspond to the Last Glacial Cycle and subsequent Termination. The maximum glacial expansion of this last Pleistocene glaciation stage occurred well before the global Last Glacial Maximum (LGM) between 30 and 60 ka in the Cantabrian Mountains and Pyrenees, at ca. 30 ka in Sierra Nevada and NW ranges, and (almost) synchronously to the LGM in the Central Range and Iberian Range. A massive glacial retreat occurred in all ranges at 19-20 ka, but the long-term deglaciation process was interrupted by cold intervals, such as the Oldest and Younger Dryas, which favoured glacial expansion in the highest mountains. Temperature increase recorded during the Holocene conditioned the melting of glaciers, which only reappeared in the highest massifs during the coldest periods, such as the LIA. However, post-LIA warming led to glacier disappearance in the Cantabrian Mountains, Sierra Nevada and most massifs of the Pyrenees, together with an accelerated shrinkage of the small glaciers still existing in this range at elevations near 3000 m.
The formation of loess deposits strongly depends on the availability of deflatable dust‐sized material. Identification of source areas and mechanisms of dust production is essential for an appropriate characterization of related palaeoenvironmental conditions. So far, little research has been done on loess deposits in the Mediterranean region and information about mechanisms of dust production is very rare. In this context, it is not clear from where the loess deposits from the upper Tagus Basin in central Spain originated. The main objective of this study was to find out whether these loess deposits were formed primarily by mountain processes and fluvial comminution, or whether they have their origin in the weathering of Tertiary marls in the centre of the Madrid Basin. A further concern was to link the determined source areas with loess formation mechanisms and concomitant environmental contexts. Following a comprehensive approach using heavy minerals and grain‐size data, together with information on stratigraphic features and geomorphic positions, different local loess sources could be identified. This study shows that during the last 35 ka a major proportion of the Tagus loess deposits was deflated from river floodplains, while the mountain region of the Iberian Range was identified as a significant source of respective floodplain sediments. Based on heavy mineral compositions and dating results, it was found that during Heinrich Stadial 3, sediment supply from the Iberian Range strongly increased, suggesting an environmental shift from initially warmer towards colder temperatures in late Marine Isotope Stage 3. Furthermore, it was found that grain‐size patterns clearly indicate maximum wind strengths during Heinrich Stadial 3, followed by Heinrich Stadial 2 and Heinrich Stadial 1. These results demonstrate that the formation of dust‐sized particles in this part of the Mediterranean operated similar to many other places in temperate and continental regions, and that weathering processes linked to hot and dry environments were only of minor importance. This article is protected by copyright. All rights reserved.
Results of measurements of cirque size, shape, site and aspect are presented for the Kintail-Affric-Cannich area of northwest Scotland and are compared with those derived for cirques elsewhere. The correlation structure of the descriptors suggests that as cirgue size increases, the degree of cirque enclosure increases in both plan and profile dimensions, and overall cirque gradient decreases. As size increases, length also tends to increase slightly relative to cirque amplitude, but length to breadth ratio remains relatively constant. The assumption of a space-time transformation leads to the hypotheses that cirque headwall retreat proceeds slightly faster than downcutting and that semicircular equilibrium forms are not developed in this area.
Variations in cirque morphometry and location are largely the function of local-scale, rather than macro-scale factors, in particular the maximum altitude of the area draining into each cirque.
Corries are taken as an example of a glaciated landform. The preliminary aim is to find a simple curve to describe the general shape of the corrie longitudinal profile. These curves are useful to separate true corries from other mountain hollows. Types of deviations from the ideal curves can be pinpointed and analysed. Several types of curve are investigated. The previously used arc of a circle is generally unsatisfactory. A logarithmic curve which fits 81% of the corrie sample is a simpler means of comparison. The great similarity between corries must be due to the effect of glacial flow patterns, but variations within the prescribed morphological limitations are clearly related to structure. Its influence on the backwall foot area and the floor is discussed. In both, glacial processes and structure are linked in a complex manner. Reverse slopes are developed only where rock structures permit. ‘Schrundline’ corries also appear to be related to a special combination of joints. This particular type of corrie is comparatively rare, as are many text-book land-forms.
During 1959–63 cirque forms in Swedish Lapland were inventoried by air photo interpretation in combination with field checks. Some field work was also performed during 1970–71.
The concepts of glacial cirque and nivation cirque are briefly discussed as well as some systems to classify cirque forms. The author also presents a classification system of his own.
On the enclosed point map the regional distribution of quite 2000 cirque forms can be studied. About half of them are regarded as glacial cirques. Some characteristics in their regional distribution are pointed out, e.g. mountains rich in cirque forms in relation to mountains with few forms. Formations, supposed to be cirque stairways, are mentioned.
The vertical distribution of the cirque forms is described and discussed with regard to cirque type as well as to variations within the investigated area—particularly from east to west but even from north to south. In this connection special attention is paid to the lowest cirque forms and their importance as indicators of lower glaciation levels.
The orientation (aspect) of these Laplandish cirque forms is studied too, e.g. with regard to cirque type and regional variation. An attempt is made to analyse such factors that are thought to be determinative for the cirque aspect. Thus the author discusses prevailing winds and general topography, exposure to sunlight and rock type/rock tectonics. As a link in these analyses the attitude of about 6000 joints and cleavage planes were measured and plotted on fabric diagrams—some of them are presented in this paper. A few concluding remarks on the age of the cirque forms are made too.
The paper is illustrated by photos, maps, sketches, diagrams, tables, and plates.
An analysis of 320 cirques with similar lithology indicates that the depth of cirque erosion varies systematically in relation to the topoclimatic factors, altitude and aspect. Altitude and aspect presumably exert direct control over glacier mass balance thereby affecting variations in the degree of cirque floor lowering. Within the Sierra Nevada Mountains of central California altitude and aspect exert independent effects as well as an interaction effect upon the depth of cirque erosion.
Three ice-drainage basins on western Vatnajökull have been delineated with the aid of the first available, accurate ice-surface maps. These basins drain ice towards the major river systems: Tungnaá, Sylgja, and Kaldakvísl, There seems to be an important difference in the location of ice-drainage basins and melt water-drainage basins for the rivers Tungnaá and Sylgja. This is due to the influence of the bedrock topography on the flow of basal water.
El presente trabajo se localiza en el Macizo de Los Pelados-El Nevero y tiene como objetivos el inventario, car-tografía, cronología e interpretación de la secuencia evolutiva de sus paleoglaciares. La altura media de este macizo es de 2100 m (Pico del Nevero, 2209 m) y su litología (orto, para y leuco-gneises) y ambiente climático (mediterráneo de montaña continentalizado) son los propios del Guadarrama Central. En el contexto fisiográfico, este macizo destaca por su trazado casi E-W frente a la dirección general NE-SW del conjunto de los Montes Carpetanos y por su mor-foestructura de bloque disimétrico basculado (laderas meridionales escarpadas-laderas septentrionales tendidas). Esa dismetría, junto a los escalones oriental y occidental debidos a sistemas de fallas de tendencia N-S (los de los puertos de Navafría y Malagosto), dieron origen a una pequeña meseta topográfica en la planicie de cumbres que posibilitó el desarrollo de un glaciarismo distintivo en estas áreas, caracterizados por: una tendencia centrífuga de las lenguas glaciares a partir de las cimas; una relativa abundancia de glaciares con localización septentrional y la presencia de un pequeño glaciar de meseta. Los datos obtenidos mediante datación absoluta 10 Be-TCN en el paleoglaciar de Hoyo Grande, muestran que la MIE local (~26 ka BP; MIS2) ocurrió sincrónicamente con el LGM.
When comparably defined, cirque size and shape vary moderately but significantly between regions. For nine spatial divisions in three countries, differences in vertical dimensions (height range, amplitude, wall height) are greater than those in horizontal dimensions. Problems of data quality, especially contour interval and reliability, affect mainly comparisons of slope gradients between countries. Problems are more apparent from graphical displays of complete distributions than from means and extremes. A broader set of data from several authors shows greater variability, especially in mean values, for which there are several possible explanations.
“As maps and air photos of glaciated areas become increasingly available it should be possible to develop glacial morphometry to provide many valuable data in studying the processes that created the forms of both glacial erosion and glacial deposition.” C.A.M. King 1974, p. 162.
Regional scale studies of glacial cirque metrics provide key insights on the (palaeo) environment related to the formation of these erosional landforms. The growing availability of high resolution terrain models means that more glacial cirques can be identified and mapped in the future. However, the extraction of their metrics still largely relies on time consuming manual techniques or the combination of, more or less obsolete, GIS tools. In this paper, a newly coded toolbox is provided for the automated, and comparatively quick, extraction of 16 key glacial cirque metrics; including length, width, circularity, planar and 3D area, elevation, slope, aspect, plan closure and hypsometry. The set of tools, named ACME (Automated Cirque Metric Extraction), is coded in Python, runs in one of the most commonly used GIS packages (ArcGIS) and has a user friendly interface. A polygon layer of mapped cirques is required for all metrics, while a Digital Terrain Model and a point layer of cirque threshold midpoints are needed to run some of the tools. Results from ACME are comparable to those from other techniques and can be obtained rapidly, allowing large cirque datasets to be analysed and potentially important regional trends highlighted.
La presente investigación constituye un estudio de Geomorfología glaciar y periglaciar del Alto Sil, un territorio montañoso, con altitudes de entre 750 y 2100 m,caracterizado por una compleja orografía y unos notables valores ambientales, situado en la Cordillera Cantábrica, al noroeste de la provincia de León (España).El trabajo se divide en dos partes fundamentales. En la primera, se analizan en detalle las formas glaciares tanto erosivas como deposicionales. Se hace especial hincapié en la descripción e interpretación de diversos depósitos, así como en otros restos glaciares significativos, como las estrías y los bloques erráticos. Se estudian también las acumulaciones fluvioglaciares y glaciolacustres, y la dinámica paraglaciar, que supuso una importante transformación del relieve tras la deglaciación. Todo ello ha servido para reconstruir la dinámica glaciar de la cuenca alta del Sil, estableciéndose tres fases principales. En la de máximo avance, el complejo glaciar del Sil era el de mayor dimensión de toda la Cordillera Cantábrica y similar a los más extensos del Pirineo.La segunda parte se centra en los procesos periglaciares actuales y heredados. En primer lugar se analiza el régimen térmico del suelo de la alta montaña, obteniendo datos de la importancia real del hielo en él. Posteriormente, se lleva a cabo un análisis detallado de las características y distribución de todas las formas periglaciares presentes,distinguiendo entre las que se desarrollaron en presencia de permafrost, las derivadas dela congelación estacional del suelo, las generadas por la acción de las heladas, las que se producen como consecuencia de la crioclastia y, por último, los procesos relacionados con la acción nival en la actualidad. Todo ello ha permitido conocer no sólo las características de estos elementos, sino también los factores que explican su distribución y génesis. En conjunto, el estudio supone una importante aportación al conocimiento de la dinámica climática y geomorfológica actual y pleistocena. También constituye una importante base para la protección del patrimonio geomorfológico del Alto Sil, que sólo recientemente se ha comenzado a poner en valor.
La cuenca de drenaje del Rio Lozoya (Comunidad de Madrid) es una depresion tectonica ubicada en la parte oriental del Sistema Central Espanol. Esta area esta caracterizada por una litologia muy heterogenea y una historia estructural muy compleja. Durante el Cuaternario, en este sector, se genero una extensa secuencia de terrazas rocosas que demuestra la enrevesada evolucion de relieve en la cuenca del Rio Lozoya. La ausencia de depositos sedimentarios hace muy dificil obtener informacion numerica a partir de este tipo de morfologias. Para poder superar esta problematica se ha empleado el metodo de datacion por exposicion de una superficie erosiva por isotopos cosmogenicos mediante una modelizacion inversa de chi-cuadrado para ajustar los valores medidos de 10Be y 26Al en modelos de perfiles de profundidad en dos niveles de la secuencia regional de terrazas rocosas: TE15 (+62-64m) y TE17 (+42-46m). En ambos casos, los ratios de concentracion 26Al/10Be en las muestras medidas es muy parecido al ratio de produccion superficial (~6,75), lo que indica una constante exposicion. Usando la modelizacion inversa, se han calculado edades minimas de>232 ka y ratios de erosion 18-19 mm/ka para TE15 y >140 ka y 7-8 mm/ka para TE17.
This book provides a broad account of glacial geology which is particularly suited to students at undergraduate level. Following an introductory chapter the book is organised as follows: chapter two introduces the history of ice on Earth underlining the causes of ice ages; chapters three and four detail the mechanisms of the glacial system; chapters five and six continue with the processes of glacial erosion and consider the landforms they create; chapters seven to eleven tackle the processes of glacial sedimentation and landform development; and finally chapter 12 interprets how large scale patterns of glacial erosion are reflected in the landscape.
Flash floods are a common natural hazard in Mediterranean mountain environments and responsible for serious economic and human disasters. The study of flash flood dynamics and their triggers is a key issue; however, the retrieval of historical data is often limited in mountain regions as a result of short time series and the systematic lack of historical data. In this study, we attempt to overcome data deficiency by supplementing existing records with dendrogeomorphic techniques which were employed in seven mountain streams along the northern slopes of the Guadarrama Mountain range. Here we present results derived from the tree-ring analysis of 117 samples from 63 Pinus sylvestris L. trees injured by flash floods, to complement existing flash flood records covering the last ~ 200 years and comment on their hydro-meteorological triggers. To understand the varying number of reconstructed flash flood events in each of the catchments, we also performed a comparative analysis of geomorphic catchment characteristics, land use evolution and forest management. Furthermore, we discuss the limitations of dendrogeomorphic techniques applied in managed forests.
The Cuerpo de Hombre paleoglacier occupies the upper sector of the Cuerpo de Hombre river basin, located on the northwest slope of the Sierra de B�ejar Mountains (Iberian Central System). At the stage of the maximum ice extent during the last glacial cycle, this paleoglacier was one of the longest tongues emerging from the Sierra de B�ejar plateau glacier. The study of the morphostratigraphic succession and the geometric and genetic relations between the geomorphological indicators of this paleoglacier has revealed its evolutionary sequence during the last glacial cycle. The comparison between this sequence
and the one previously established by a regional evolutionary pattern shows that although they both coincide in general terms, some stages/substages of this pattern must be corrected or more clearly defined. The absolute chronology of the different stages was obtained using terrestrial cosmogenic nuclides (10Be). The maximum ice extent of Cuerpo de Hombre paleoglacier has been dated to ~25.0 ka (MIS2 and concurrent with the LGM). This chronology coincides with date obtained for other paleoglaciers in the Iberian Central System, but is slightly more modern than the regional chronology estimated as most likely for the maximum ice extent in these areas. Subsequent to reaching the maximum extent, the glacier had a retreat (minimum age ~20.6 ka), followed by another stage of expansion or readvance, after which it stabilised until the start of the deglaciation stage (~17.8 ka). In all previous work, the deglaciation stages in the Iberian Central System have been described as one continuous recession process. However, in the Cuerpo de Hombre paleoglacier, all the data point to stabilisations of considerable magnitude, and particularly to another stage of readvance of the glacier. Based on its chronology (minimum age ~11.1 ka) and its evolutionary significance, this new readvance has been correlated with the Older Dryas stadial. Finally, the evolutionary context marked by the indicators and its chronology confirm that the whole of the Late Glacial sequence identified in Cuerpo de Hombre can be correlated with the traditionally established in northern Europe (climatic periods or stadials and interstadials): Oldest Dryas-Bølling-Older Dryas-Allerød-Younger Dryas. The minimum ages obtained for the cold periods (stadials) in this sequence in the Cuerpo de Hombre paleoglacier are (respectively): ~17.5 ka, ~13.9 ka and ~11.1 ka. This complete sequence of the Late Glacial Period, including the stadials Older and Younger Dryas, had not been previously identified in any of the paleoglaciers in the Iberian Central System.
Allometry, scaling and scale-specificity are general concepts useful in a broad range of sub-disciplines of geomorphology, and thus provide some common ground at a time of increasing specialisation. The specific geomorphometry of some very different landforms- cirques, landslides, volcanoes and mobile bedforms- shows scalespecificity (modal sizes, limits, thresholds, break-points) as well as scaling behaviour. Scaling is generally accompanied by size limits or breaks: 'scale invariance' has been used too loosely. Scaling is often confined to one or two decimal orders of magnitude, and is allometric rather than isometric: shape changes with size. This is demonstrated by comparing confidence intervals on allometric exponents for large populations of glacial cirques in many regions in Europe and British Columbia. Whether power or geometric mean regression is used, vertical dimensions are seen to increase with overall size more slowly than do length and width. Drumlins and other glacial bedforms show both scale-specificity and static allometry. Landslide frequency distributions exhibit a 'rollover' effect which cannot generally be attributed to omission of small features.
The main aims of the investigation were, first, to establish whether there are significant differences of form between Austrian and British cirques, and secondly, to discover what factors control differences of morphometry either in the cirque population as a whole or within individual groups. For 302 cirques three form indices were measured (length-height ratio, angle between backwall and cirque floor, and cirque closure), together with four other variables (orientation, cirque-floor, height, lithology and relief amplitude) that were considered to have a possible influence on cirque form. Explanations for the relationships are discussed, together with the possible influences of two factors that cannot be precisely quantified, namely, the duration of glaciation and glacier thermal regime. -after Authors
Glacial cirques are armchair-shaped erosional hollows, typified by steep headwalls and, often, overdeepened floors. They reflect former regions of glacier initiation, and their distribution is, therefore, linked to palaeoclimate. Because of this association, cirques can be analysed for the information they provide about past environments, an approach that has a strong heritage, and has seen resurgence over recent years. This paper provides a critical assessment of what cirques can tell us about past environments, and considers their reliability as palaeoenvironmental proxies. Specific focus is placed on information that can be obtained from consideration of cirque distribution, aspect, altitude, and morphometry. The paper highlights the fact that cirques potentially provide information about the style, duration and intensity of former glaciation, as well as information about past temperatures, precipitation gradients, cloud-cover and wind directions. In all, cirques are considered a valuable source of palaeoenvironmental information (if used judiciously), particularly as they are ubiquitous within formerly glaciated mountain ranges globally, thus making regional or even global scale studies possible. Furthermore, cirques often occupy remote and inaccessible regions where other palaeoenvironmental proxies may be limited or lacking.
The direct comparison between marine and terrestrial data from the NW Iberian margin, core MD03-2697, allows us to accurately evaluate, without chronological ambiguity, the vegetation response to North Atlantic climate events across the last deglaciation. Comparison of MD03-2697 data with other marine and terrestrial records from a vast area stretching from the Azores to western (W) France, Iberia and its margin, the W Mediterranean and NW Africa reveals the importance of enhanced winter North Atlantic westerlies episodes in driving a heterogeneous regional climatic signal during particular events of the last deglaciation. Heinrich Stadial 1 (HS1)/Oldest Dryas is a complex event marked by three synchronous main phases (a: extremely cold/relatively wet; b: cool/dry; c: relatively warmer/increasing moisture availability) in regions directly influenced by the North Atlantic while it is characterized by a single phase (cold and dry) in most inland and high altitude areas. Changes in the strength and position of North Atlantic westerlies could explain the variability in moisture during HS1 from W Pyrenees to W Mediterranean. The Bølling-Allerød (B-A) event is marked by a synchronous progressive increase of ocean and atmospheric temperatures and precipitation from the Bølling to the Allerød in W Iberia and W Pyrenees contrasting with the Greenland temperature pattern. Mid-to high latitudes thermal contrast and the gradual strengthening of the Atlantic Meridional Overturning Circulation (AMOC) triggered the continuing enhancement of westerlies, and moisture, along this period.
A streamlined computer-based method for morphometric analysis of cirques is presented. Application to the complete population of 158 cirques in the Lake District demonstrates that: 1) Cirque size is unimodal. 2) Larger cirques are better developed. 3) Although altitude, aspect, position nd relief control cirque distribution, they account for only a little of the variability in form within the Lake district. Mapped geology likewise has limited effect. 4) Better-developed cirques have greater plan closure, higher maximum gradient and lower minimum gradient. -from Authors
A total of 156 glacial cirques located on two different areas in the Cantabrian Mountains (NW Spain) were identified and measured in order to continue and expand the study of these large-scale erosional forms in European mountains. Environmental variables that may explain cirque distribution (altitude, aspect and lithology), and their most important morphometric features (area, length (L), width (W), headwall height (H), and L/W, L/H and W/H indices), are analysed. Statistical analysis has been applied as indicators of contrast (ANOVA) and association (correlation and regression). Conglomerate analysis (CLUSTER) has been used to discriminate cirque groups based on their morphometric variables. Results show that cirques occur at lower altitudes in the Upper Sil River basin area than in the Montaña Central area due to a lower former equilibrium line altitude (ELA) position. In the Upper Sil River basin, environmental variables appear to have had a strong influence on the location and size of cirques: the largest cirques are located in quartzite rocks at elevations above 2000 m and face N or NE. In Montaña Central, the influence of these factors was more limited as a consequence of higher geological structure control. Cirque sizes generally are modest compared with cirques present in other mountain ranges globally, most likely due to shorter glacial occupancy in the Cantabrian Mountains.
During 1959--63 cirque forms in Swedish Lapland were inventoried by air photo interpretation in combination with field checks. Some field work was also performed during 1970--71. The concepts of glacial cirque and nivation cirque are briefly discussed as well as some systems to classify cirque forms. The author also presents a classification system of his own. On the enclosed point map the regional distribution of quite 2000 cirque forms can be studied. About half of them are regarded as glacial cirques. Some characteristics in their regional distribution are pointed out, e.g. mountains rich in cirque forms in relation to mountains with few forms. Formations, supposed to be cirque stairways, are mentioned. The vertical distribution of the cirque forms is described and discussed with regard to cirque type as well as to variations within the investigated area--particularly from east to west but even from north to south. In this connection special attention is paid to the lowest cirque forms and their importance as indicators of lower glaciation levels. The orientation (aspect) of these Laplandish cirque forms is studied too, e.g. with regard to cirque type and regional variation. An attempt is made to analyse such factors that are thought to be determinative for the cirque aspect. Thus the author discusses prevailing winds and general topography, exposure to sunlight and rock type/rock tectonics. As a link in these analyses the attitude of about 6000 joints and cleavage planes were measured and plotted on fabric diagrams--some of them are presented in this paper. A few concluding remarks on the age of the cirque forms are made too. The paper is illustrated by photos, maps, sketches, diagrams, tables, and plates.
Topoclimatic effects on glacier balance encourage shade, lee and east-facing glaciers in varying combination in different regional climates and at different altitudes. Present-day glaciers usually face slightly east of poleward on average: in Scandinavia and the Urals, consistent westerly winds strengthen the lee tendency, especially where gentle summits favour drifting of snow. Eastward cirque aspects are found in the Falkland Islands, New Hampshire and Central Spain, east-northeast aspects in the American Rockies, the Faeroes, Central Europe, Japan and Tasmania. In Scandinavia, the British Isles and the Carpathians, northeastward resultants are most common, showing a lee effect tempered with a shade effect. Elsewhere (in the Canadian Arctic, Alaska, British Columbia, western U.S.A., central Chile, the Alps, southwest and central Asia, the Altai and even Papua--New Guinea), both cirque and glacier aspect resultants are poleward or within 30° further east. This situation reflects differential ablation from direct solar radiation as a more important factor than wind. Cirque aspects provide a constraint on palaeoclimatic reconstructions but cannot provide precise information on palaeowind directions. The degree of asymmetry (vector strength) varies more locally and is usually greater in ranges which were only just high enough to nourish glaciers. For a temporal comparison of glaciers with cirques, this observation may be formalised as a "law of decreasing glacial asymmetry with increasing glacier cover".
Corries are taken as an example of a glaciated landform. The preliminary aim is to find a simple curve to describe the general shape of the corrie longitudinal profile. These curves are useful to separate true corries from other mountain hollows. Types of deviations from the ideal curves can be pinpointed and analysed. Several types of curve are investigated. The previously used arc of a circle is generally unsatisfactory. A logarithmic curve which fits 81% of the corrie sample is a simpler means of comparison. The great similarity between corries must be due to the effect of glacial flow patterns, but variations within the prescribed morphological limitations are clearly related to structure. Its influence on the backwall foot area and the floor is discussed. In both, glacial processes and structure are linked in a complex manner. Reverse slopes are developed only where rock structures permit. 'Schrundline' corries also appear to be related to a special combination of joints. This particular type of corrie is comparatively rare, as are many text-book landforms.