| 1. |
- De Angelis, Hernán, 1974-
(författare)
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El Manto de Hielo Antártico: estructura interna, dinámica y estabilidad
- 2009. - 1
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Ingår i: El agua en el norte de la Península Antártica. - Buenos Aires : Fundación de Historia Natural Félix de Azara. - 9789872212186 ; , s. 105-130
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- El Manto de Hielo Antártico, la cubierta glaciaria del Continente Antártico, es la mayor extensión de hielo actual de nuestro planeta y la mayor reserva de agua potable. En este capítulo se describen sus características glaciológicas principales y la de los elementos que la integran de acuerdo a los estudios y compilaciones más recientes. Se ha puesto énfasis en los aspectos dinámicos de cada uno de los componentes y en sus interrelaciones dentro del manto de hielo en su conjunto. Por último, se presenta el paradigma de la inestabilidad del Manto de Hielo Antártico Occidental y se discute la potencial evolución futura a la luz de los últimos hallazgos en la materia.
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| 2. |
- De Angelis, Hernán
(författare)
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Glacial geomorphology of the east-central Canadian Arctic
- 2007
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Ingår i: Journal of Maps. - 1744-5647. ; v2007, s. 323-341
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Tidskriftsartikel (refereegranskat)abstract
- This article describes palaeoglaciological mapping of the portion of the Canadian Arctic formerly covered by north-easternmost Laurentide Ice Sheet. The mapped area stretches between the meridians 106°W and 61°W, and the parallels 60°N and 75°N, embracing an area of 3.19 x 10^6 km^2. The work was focused on determining the location of landforms that are required as input for a glaciological inversion model, i.e. glacial lineations, eskers, moraine ridges, ribbed moraine and De Geer moraines; and forms the basis of a reconstruction of the geometry and evolution of palaeo-ice streams in this portion of the Laurentide Ice Sheet. Emerged areas were mapped through the geomorphological interpretation of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) satellite images. Information on striae and other minor indicators of glacial activity were extracted from maps and reports by the Geological Survey of Canada, published articles and, on a few locations, by the author's own observations. Information on landforms located on some submerged areas where extracted from publicly available sonar surveys. All data were digitally processed within a Geographical Information System and stored in a spatially enabled database. The results are presented as a printable map at 1:2,400,000 scale.
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| 3. |
- De Angelis, Hernán, 1974-
(författare)
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Hypsometry and sensitivity of the mass balance to changes in equilibrium-line altitude : the case of the Southern Patagonia Icefield
- 2014
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 60:219, s. 14-28
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Tidskriftsartikel (refereegranskat)abstract
- We study the relation between glacier hypsometry and sensitivity of mass-balance rate to changes in equilibrium line altitude (ELA). Our aim is to assess whether hypsometry can be reliably used as an estimator of the sensitivity of unmeasured glaciers to changes in ELA. We express the sensitivity of mass-balance rate to ELA, \(d\dot{B}/dELA\), as a function of accumulation-area ratio (AAR), its derivative against altitude, \(dAAR/dELA\), and mass-balance functions of ELA. We then apply the concept to 139 glaciers in the Southern Patagonia Icefield for which we derive hypsometry and AAR, and analyze the influence of hypsometry on their mass-balance rate sensitivity. We confirm that glaciers where the bulk of area is located above the ELA are the least sensitive, whereas those where the bulk of area is located below the ELA are the most sensitive. Glaciers with unimodal hypsometric curves where the peak of area fraction is around the present ELA, and glaciers with bi- or multimodal area distributions, with the ELA located approximately between the bulges, have intermediate sensitivities. We conclude that hypsometry can be used as a first order estimator of the mass-balance rate sensitivity to ELA change.
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| 4. |
- De Angelis, Hernán
(författare)
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Larsen Ice Shelf
- 2007
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 5. |
- De Angelis, Hernán, et al.
(författare)
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Palaeo-ice stream onsets: examples from the north-eastern Laurentide Ice Sheet
- 2008
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Ingår i: Earth Surface Processes and Landforms. - : Wiley. - 0197-9337 .- 1096-9837. ; 33:4, s. 560-572
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report on observations of glacial landscapes at the head of geomorphologically interpreted palaeo-ice streams, i.e. palaeo-ice-stream onsets. Our work is based on the results of systematic palaeoglaciological mapping of the portion of north-eastern Canada formerly covered by the Laurentide Ice Sheet. Four different cases are considered and analysed in detail: one is the Dubawnt Lake Ice Stream and the others are smaller (<70 km long) palaeo-ice streams. We found that in this region onset zones are generally characterized by a heterogeneous landform record and are more easily recognized when landscapes typical of partially frozen beds are present. Based on publicly available topographical and geological data as well as theoretical developments, we discuss the conditions and controls on the location of these onset zones and their potential stability. Except for the Dubawnt Lake Ice Stream, we found that, although topography and geology are important conditioning factors, the geomorphological imprint of palaeo-ice-stream onsets cannot be explained without invoking the role of the basal thermal boundary between cold- and warm-based ice. Finally, we observed that, except for the Dubawnt Lake Ice Stream, the onset zones of large ice streams are rarely preserved, and we suggest two possible explanations for this. We conclude that although the same qualitative processes are present under the majority of ice streams, conditions for the preservation of the onset zones are more likely to be met in the case of relatively small ice streams because these are more rapidly deglaciated.
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| 6. |
- De Angelis, Hernán, et al.
(författare)
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Palaeo-ice streams in the Foxe/Baffin sector of the Laurentide Ice Sheet
- 2007
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26:9-10, s. 1313-1331
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we describe mapping of palaeo-ice streams in the Foxe/Baffin sector of the Laurentide Ice Sheet by means of geomorphological interpretation of high-resolution satellite images. Our interpretations were guided by a glaciological inversion scheme, aided by digital elevation models, publicly available sonar surveys and field studies. As a result, we produced a map depicting the location, geometry and relative temporal changes of palaeo-ice streams and analysed their palaeoglaciological implications for the Foxe/Baffin sector. We conclude that in the period between the Last Glacial Maximum and approximately 7.0 kyr BP, the Foxe/Baffin sector was largely drained by topographically controlled outlet glaciers and ice streams, which were organized in a relatively stable pattern. During this time, large areas of Melville Peninsula and central Baffin Island were subject to cold-based conditions. Between 7.0 and 6.0 kyr BP, the Foxe/Baffin sector collapsed catastrophically in the Foxe Basin, after which its remnant portion became confined to Baffin Island. During this collapse, rapid successions of small transient ice streams occurred along wide, loosely defined topographical corridors in two sectors of Baffin Island. The presently available landform archive on emerged land is not sufficient to conclusively support the existence of fully scaled ice streams along the whole length of Hudson Strait. As an alternative solution, we propose that topographically controlled ice streams might have occurred along the deepest parts of Hudson Strait, with attendant cold-based ice zones on marginal areas and islands at the head of the strait.
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| 7. |
- De Angelis, Hernán, 1974-
(författare)
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Palaeo-ice streams in the north-eastern Laurentide Ice Sheet
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a palaeoglaciological study aimed to determine the location, geometry and temporal evolution of palaeo-ice streams of the north-easternmost Laurentide Ice Sheet. The work was accomplished through the geomorphological interpretation of satellite imagery over 3.19 x 106 km2 of the Canadian Arctic, using a glaciological inversion scheme. Ice streams were active in this region during most of the time between the Last Glacial Maximum and the last deglaciation. A web of ice streams and inter-ice stream areas existed. Three major ice stream networks are identified: the M'Clintock Channel, Gulf of Boothia – Lancaster Sound and Hudson Strait. The M'Clintock Channel bears the most complex landform record, comprising three generations of palaeo-ice streams. Their location was weakly controlled by the subglacial topography and their geometry was determined by frozen-bed portions of the ice sheet, thus providing evidence for pure ice streams in the Laurentide Ice Sheet. In contrast, the more pronounced relief of the Gulf of Boothia – Lancaster Sound corridor supported topographically controlled ice streams. The landform record on emerged land along Hudson Strait is insufficient to support the existence of ice streams. It is therefore proposed that ice streams were constrained within the deep parts of the strait while flanked by cold-based zones on the margins. Small transient ice streams on Baffin and Prince of Wales islands drained local remnant ice caps during the collapse of the ice sheet. Analysis of the controls on the location and flow of palaeo-ice streams suggests that the interaction between the subglacial topography and thermal state of the substrate plays a more fundamental role than the geology. It is concluded that the behaviour of ice streams cannot be explained in terms of environmental controls alone, but the complex dynamics of ice stream shear margins and onset zones must be considered.
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| 8. |
- De Angelis, Hernán, et al.
(författare)
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Palaeo-ice streams in the northern Keewatin sector of the Laurentide Ice Sheet
- 2005
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Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 42, s. 135-144
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Tidskriftsartikel (refereegranskat)abstract
- Evidence for ice streams in the Laurentide ice sheet is widespread. In the region of northern Keewatin and the Boothia Peninsula, Nunavut, Canada, palaeo-ice streams have been recognized, but their location, size and potential role in ice-sheet dynamics are poorly constrained. Based on the interpretation of satellite imagery, we produce a palaeo-ice-stream map of this region. Glacial directional landforms, eskers and moraines were mapped and integrated into landform assemblages using a glacial geological inversion model. Palaeo-frozen bed areas were also identified. Relative age of the geomorphic swarms was assessed by cross-cutting relationships and radiocarbon ages where available. Using this information we obtained a glaciologically plausible picture of ice-stream evolution within the northernmost Laurentide ice sheet. On the M'Clintock Channel corridor, three generations of pure ice streams are found. On Baffin Island and the Gulf of Boothia, glaciation was dominated by frozen-bed zones located on high plateaus and ice streams running along the troughs, i.e. topographic ice streams. A massive convergent pattern at the head of Committee Bay drained ice from both the Keewatin and Foxe sectors and was probably one of the main deglaciation channels of the Laurentide ice sheet. Finally, our results indicate that streaming flow was present in the deep interior of the Laurentide ice sheet, as recently shown for the Greenland and Antarctic ice sheets.
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| 9. |
- De Angelis, Hernán, et al.
(författare)
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Snow zonation on Hielo Patagónico Sur, Southern Patagonia, derived from Landsat 5 TM data
- 2007
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181. ; 59, s. 149-158
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Tidskriftsartikel (refereegranskat)abstract
- Hielo Patagónico Sur (HPS), an icefield in Southern Patagonia, is the largest temperate ice mass in the southern hemisphere. Despite continued research efforts during the last decade many glaciological variables, especially mass balance, are still poorly known. This is partly because access to the icefield is difficult due to remoteness and persistent harsh weather conditions. Therefore, remote sensing appears to be a more suitable tool for the acquisition of data. In this work we present a remote sensing study of snow zonation on HPS using Landsat 5 Thematic Mapper data acquired on 12March 2001. By using image processing and classification techniques, proved to be useful in other glaciated regions, we map for the first time the extent and occurrence of major snow zones on the whole HPS. We separate between two classes of ice and three classes of snow. Ice facies are classified as bare or debris (i.e. dirt) covered ice, covering 2454 km2 and 777 km2 respectively, or 18.4% and 5.8% of the icefield on the day of image acquisition. Snow types are classifiedaccording to spectral differences in the images, following the glacier facies concept. Two of the three snow cover types are interpreted to represent differences in snow grain size within a fairly homogeneous snowpack whereas the third one is interpreted to represent the slush zone. A first order altitudinal control on the distribution of these snow facies is evident. In addition, our results show that snow accumulation on HPS is markedly controlled by the interaction of strong west–northwest snow-bearing winds and the roughmountainous terrain. In order of decreasing altitude we find that the two snow facies and the slush facies occupy 3819 km2, 3292km2 and2295 km2 respectively, or 28.6%, 24.6%and 17.2%of the icefield, on the day of image acquisition. Estimates of equilibrium line altitude using our results yield values of 800–900 m above sea level for the western side and 1500–1600 m above sea level for the eastern side, with an accumulation area ratio of 0.74.
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| 10. |
- Glasser, Neil F., et al.
(författare)
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Cosmogenic nuclide exposure ages for moraines in the Lago San Martin Valley, Argentina
- 2011
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Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; 75:3, s. 636-646
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Tidskriftsartikel (refereegranskat)abstract
- At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49 degrees S, 72 degrees W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide ((10)Be) exposure ages (n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 +/- 1.7 ka, 22.4 +/- 2.3 ka, 34.4 +/- 3.4 ka to 37.6 +/- 3.4 ka (and possibly 60 +/- 3.5 ka), and 99 +/- 11 ka (1 sigma). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on (14)C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought.
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| 11. |
- Kleman, Johan, et al.
(författare)
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North American Ice Sheet build-up during the last glacial cycle, 115-21 kyr
- 2010
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Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 29:17-18, s. 2036-2051
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Tidskriftsartikel (refereegranskat)abstract
- The last glacial maximum (LGM) outline and subsequent retreat pattern (21e7 kyr) of North Americanice sheets are reasonably well established. However, the evolution of the ice sheets during their build-upphase towards the LGM between 115 and 21 kyr has remained elusive, making it difficult to verifynumerical ice sheet models for this important time interval. In this paper we outline the pre-LGM icesheet evolution of the Laurentide and Cordilleran ice sheets by using glacial geological and geomorphologicalrecords to make a first-order reconstruction of ice sheet extent and flow pattern. We mappedthe entire area covered by the Laurentide and Cordilleran ice sheets in Landsat MSS images andapproximately 40% of this area in higher resolution Landsat ETMþ images. Mapping in aerial photographsadded further detail primarily in Quebec-Labrador, the Cordilleran region, and on Baffin Island.Our analysis includes the recognition of approximately 500 relative-age relationships from crosscuttinglineations. Together with previously published striae and till fabric data, these are used as the basis forrelative-age assignments of regional flow patterns. For the reconstruction of the most probable ice sheetevolution sequence we employ a stepwise inversion scheme with a clearly defined strategy for delineatingcoherent landforms swarms (reflecting flow direction and configuration), and linking these topreviously published constraints on relative and absolute chronology. Our results reveal that icedispersalcentres in Keewatin and Quebec were dynamically independent for most of pre-LGM time andthat a massive Quebec dispersal centre, rivalling the LGM in extent, existed at times when the SW sectorof the ice sheet had not yet developed. The oldest flow system in eastern Quebec-Labrador (Atlanticswarm had an ice divide closer to the Labrador coast than later configurations). A northern Keewatin-Central Arctic Ice Sheet existed prior to the LGM, but is poorly chronologically constrained. There is alsoevidence for older and more easterly Cordilleran Ice Sheet divide locations than those that prevailedduring the Late Wisconsinan. In terms of ice sheet build-up dynamics, it appears that “residual” ice capsafter warming phases may have played an important role. In particular, the location and size of remnantice masses at the end of major interstadials, i.e. OIS 5c and 5a, must have been critical for subsequentbuild-up patterns, because such remnant “uplands” may have fostered much more rapid ice sheetgrowth than what would have occurred on a fully deglaciated terrain. The ice-sheet configuration duringstadials would also be governed largely by the additional topography that such “residual” ice constitutesbecause of inherent mass balance-topography feedbacks.
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| 12. |
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