Pub Date : 2022-06-27DOI: 10.1080/04353676.2022.2084591
J. Sutherland, D. Evans, J. Carrivick, J. Shulmeister, H. Rother
ABSTRACT The extent of the Southern Alps icefield in New Zealand is well-constrained chronologically for the last glacial cycle. The sediment-landform imprint of this glacial system, however, offers insight into ice-marginal processes that chronological control cannot. We present the first detailed investigation of sediments along the southwestern shores of Lake Tekapo, South Island. We identify seven lithofacies, from which a five-stage palaeoglaciological reconstruction of depositional and glaciotectonic events is proposed: (i) ice-marginal advance and deposition of outwash gravels in lithofacies (LF) 1; (ii) ice-marginal recession and the development of an ice-contact lake, manifest in rhythmite deposition and iceberg rafting of dropstones (LF 2), followed by a depositional hiatus; (iii) ice-marginal recession recorded in ice-proximal aggradation of glaciofluvial hyperconcentrated flows (LFs 3, 4); (iv) ice-marginal advance documented by glaciotectonic disturbance and localized hydrofracturing, coeval with the deposition of delta foresets and a subglacial diamicton/till (LFs 5, 6); (v) final stages of ice-marginal recession and deposition of outwash gravels in LF 7. Two infrared stimulated luminescence ages were obtained from the glaciolacustrine sediments and, whilst the dating has some limitations, the sediments pre-date both the global and local Last Glacial Maximum. Overall, this sequence, consistent with sediment fills recorded elsewhere across South Island, suggests recurrence of processes from different glacial advances and the role of topographic constraints on maintaining lake positions.
{"title":"A model of ice-marginal sediment-landform development at Lake Tekapo, Southern Alps, New Zealand","authors":"J. Sutherland, D. Evans, J. Carrivick, J. Shulmeister, H. Rother","doi":"10.1080/04353676.2022.2084591","DOIUrl":"https://doi.org/10.1080/04353676.2022.2084591","url":null,"abstract":"ABSTRACT The extent of the Southern Alps icefield in New Zealand is well-constrained chronologically for the last glacial cycle. The sediment-landform imprint of this glacial system, however, offers insight into ice-marginal processes that chronological control cannot. We present the first detailed investigation of sediments along the southwestern shores of Lake Tekapo, South Island. We identify seven lithofacies, from which a five-stage palaeoglaciological reconstruction of depositional and glaciotectonic events is proposed: (i) ice-marginal advance and deposition of outwash gravels in lithofacies (LF) 1; (ii) ice-marginal recession and the development of an ice-contact lake, manifest in rhythmite deposition and iceberg rafting of dropstones (LF 2), followed by a depositional hiatus; (iii) ice-marginal recession recorded in ice-proximal aggradation of glaciofluvial hyperconcentrated flows (LFs 3, 4); (iv) ice-marginal advance documented by glaciotectonic disturbance and localized hydrofracturing, coeval with the deposition of delta foresets and a subglacial diamicton/till (LFs 5, 6); (v) final stages of ice-marginal recession and deposition of outwash gravels in LF 7. Two infrared stimulated luminescence ages were obtained from the glaciolacustrine sediments and, whilst the dating has some limitations, the sediments pre-date both the global and local Last Glacial Maximum. Overall, this sequence, consistent with sediment fills recorded elsewhere across South Island, suggests recurrence of processes from different glacial advances and the role of topographic constraints on maintaining lake positions.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"81 1","pages":"151 - 182"},"PeriodicalIF":1.5,"publicationDate":"2022-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88444626","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.1080/04353676.2022.2054146
Javier de Marcos, J. Úbeda, N. Andrés, D. Palacios
ABSTRACT 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.
{"title":"A combination of cosmogenic and Schmidt hammer exposure dating in the study of the deglaciation timing of Sierra de Guadarrama National Park (Spain)","authors":"Javier de Marcos, J. Úbeda, N. Andrés, D. Palacios","doi":"10.1080/04353676.2022.2054146","DOIUrl":"https://doi.org/10.1080/04353676.2022.2054146","url":null,"abstract":"ABSTRACT\u0000 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.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"46 1","pages":"70 - 89"},"PeriodicalIF":1.5,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87507131","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.1080/04353676.2022.2064651
Jacques Mourey, L. Ravanel, C. Lambiel
ABSTRACT Climate change leads to deep modifications of high Alpine environments. Those modifications have significant consequences on mountaineering itineraries and make them technically more difficult and more dangerous. Although a growing number of studies have recently documented this issue, they only list the processes affecting the itineraries and do not document their characteristics. Therefore, the acquired data lack relevance to be spread and for prevention making among climbers. In the present study, on the basis of the processes identified in previous studies in the Mont Blanc massif, we developed a legend in order to map the processes related to climate change that affect the itineraries and modify their climbing parameters. Following the UNIL geomorphological legend and using the same color code, 21 symbols were defined to map 23 processes. In order to evaluate the applicability and interest of the legend proposed, we present a first application in the Valais Alps (Switzerland), based on 21 semi-structured interviews with local Alpine guides and hut keepers. The map then allowed to list the processes affecting each of the 36 itineraries studied. On average, an itinerary is affected by 9 different processes and 25% of the itineraries have greatly evolved, which means their ascent in summer cannot be recommended anymore because of climate change. More generally, this legend would provide a common methodological basis, destined to be completed within future studies and to be relevant beyond the European Alps. This basis would also ease the comparability and compilation of results from different future studies.
{"title":"Climate change related processes affecting mountaineering itineraries, mapping and application to the Valais Alps (Switzerland)","authors":"Jacques Mourey, L. Ravanel, C. Lambiel","doi":"10.1080/04353676.2022.2064651","DOIUrl":"https://doi.org/10.1080/04353676.2022.2064651","url":null,"abstract":"ABSTRACT Climate change leads to deep modifications of high Alpine environments. Those modifications have significant consequences on mountaineering itineraries and make them technically more difficult and more dangerous. Although a growing number of studies have recently documented this issue, they only list the processes affecting the itineraries and do not document their characteristics. Therefore, the acquired data lack relevance to be spread and for prevention making among climbers. In the present study, on the basis of the processes identified in previous studies in the Mont Blanc massif, we developed a legend in order to map the processes related to climate change that affect the itineraries and modify their climbing parameters. Following the UNIL geomorphological legend and using the same color code, 21 symbols were defined to map 23 processes. In order to evaluate the applicability and interest of the legend proposed, we present a first application in the Valais Alps (Switzerland), based on 21 semi-structured interviews with local Alpine guides and hut keepers. The map then allowed to list the processes affecting each of the 36 itineraries studied. On average, an itinerary is affected by 9 different processes and 25% of the itineraries have greatly evolved, which means their ascent in summer cannot be recommended anymore because of climate change. More generally, this legend would provide a common methodological basis, destined to be completed within future studies and to be relevant beyond the European Alps. This basis would also ease the comparability and compilation of results from different future studies.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"37 1","pages":"109 - 126"},"PeriodicalIF":1.5,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79930151","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.1080/04353676.2022.2070158
Ø. Rudjord, R. Solberg, G. Spreen, S. Gerland
ABSTRACT Information about the state of the Arctic sea ice is becoming increasingly important. This paper describes an approach for automatic retrieval of daily thin sea ice thickness maps around Svalbard. The algorithm uses thermal satellite imagery from MODIS to estimate the surface temperature of the ice and further uses a thermal model of the ice surface to estimate the thickness of the sea ice. The approach is usable for thin sea ice, up to ca. 50 cm thick, during cold weather (freezing) conditions and without cloud cover present. The algorithm is compared with helicopter-borne electromagnetic ice thickness measurements. The comparison yields increasing root-mean-square deviation (RMSD) for thicker ice. The lowest RMSD found is 8.7 cm for ice thickness in the range 10 cm < hi ≤ 20 cm. The highest RMSD found is 25.2 cm for ice thickness in the range 30 cm < hi ≤ 40 cm. The bias shows no such trend, and the overall bias is found to be −5.5 cm. The results show that this is a promising approach, allowing monitoring of thin sea ice thickness at relatively higher spatial resolution.
关于北极海冰状况的信息变得越来越重要。本文介绍了一种自动检索斯瓦尔巴群岛周边海冰薄厚度图的方法。该算法利用MODIS卫星热像图估算海冰表面温度，并利用海冰表面热模型估算海冰厚度。这种方法适用于在寒冷天气(冰冻)和没有云层覆盖的情况下，厚度约为50厘米的薄海冰。将该算法与直升机机载电磁测冰厚度进行了比较。比较结果表明，冰越厚，均方根偏差(RMSD)越大。在10 cm < hi≤20 cm范围内，冰厚RMSD最小值为8.7 cm。在30 cm < hi≤40 cm范围内，冰厚RMSD最大值为25.2 cm。偏置没有这种趋势，总体偏置为−5.5 cm。结果表明，这是一种很有前途的方法，可以以相对较高的空间分辨率监测薄海冰厚度。
{"title":"Estimating thin ice thickness around Svalbard using MODIS satellite imagery","authors":"Ø. Rudjord, R. Solberg, G. Spreen, S. Gerland","doi":"10.1080/04353676.2022.2070158","DOIUrl":"https://doi.org/10.1080/04353676.2022.2070158","url":null,"abstract":"ABSTRACT Information about the state of the Arctic sea ice is becoming increasingly important. This paper describes an approach for automatic retrieval of daily thin sea ice thickness maps around Svalbard. The algorithm uses thermal satellite imagery from MODIS to estimate the surface temperature of the ice and further uses a thermal model of the ice surface to estimate the thickness of the sea ice. The approach is usable for thin sea ice, up to ca. 50 cm thick, during cold weather (freezing) conditions and without cloud cover present. The algorithm is compared with helicopter-borne electromagnetic ice thickness measurements. The comparison yields increasing root-mean-square deviation (RMSD) for thicker ice. The lowest RMSD found is 8.7 cm for ice thickness in the range 10 cm < hi ≤ 20 cm. The highest RMSD found is 25.2 cm for ice thickness in the range 30 cm < hi ≤ 40 cm. The bias shows no such trend, and the overall bias is found to be −5.5 cm. The results show that this is a promising approach, allowing monitoring of thin sea ice thickness at relatively higher spatial resolution.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"4 1","pages":"127 - 149"},"PeriodicalIF":1.5,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78530214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-04-03DOI: 10.1080/04353676.2022.2054147
Jasmine Byrne, H. Renssen, D. Bui, A. Odland
ABSTRACT Treelines driven by climatic conditions are characteristic of alpine areas. This study assesses the degree of accuracy with which the TREELIM model predicts present treeline elevation along a regional continentality-maritimity gradient in southwest Norway. The study area consists of 15 sites chosen along this gradient, wherein observed treelines range from nearly sea level to over 1200 m a.s.l. The TREELIM model calculates treeline position based solely on meteorological parameters obtained from gridded climate datasets. The model assumes that tree growth occurs if the length of the growing season (LGS) exceeds a minimum duration and the seasonal mean temperature (SMT) does not fall below a certain value. Six different scenarios were developed in order to determine the effects of changing precipitation and drought within TREELIM. Within these scenarios, three different SMTs were used in order to model the treeline position. Model performance was evaluated by comparing resultant treeline elevation with observed values. Results of experiments using lapse rate-based temperature input data were compared to those using the gridded climate data. Statistical analysis determined that the lapse rate-based temperature scenario removing drought constraints and using a SMT of 6.4°C gave the most accurate prediction of treeline position, and a relatively uniform growing season ranging from 110 to 128 days. Precipitation and snow cover do not significantly affect treeline elevation. The results suggest that TREELIM accurately predicts the treeline in most cases, but is less suited in areas with steeply varying topography.
{"title":"Assessment of the TREELIM model in predicting present treeline along a longitudinal continentality-maritimity gradient in south-western Norway","authors":"Jasmine Byrne, H. Renssen, D. Bui, A. Odland","doi":"10.1080/04353676.2022.2054147","DOIUrl":"https://doi.org/10.1080/04353676.2022.2054147","url":null,"abstract":"ABSTRACT Treelines driven by climatic conditions are characteristic of alpine areas. This study assesses the degree of accuracy with which the TREELIM model predicts present treeline elevation along a regional continentality-maritimity gradient in southwest Norway. The study area consists of 15 sites chosen along this gradient, wherein observed treelines range from nearly sea level to over 1200 m a.s.l. The TREELIM model calculates treeline position based solely on meteorological parameters obtained from gridded climate datasets. The model assumes that tree growth occurs if the length of the growing season (LGS) exceeds a minimum duration and the seasonal mean temperature (SMT) does not fall below a certain value. Six different scenarios were developed in order to determine the effects of changing precipitation and drought within TREELIM. Within these scenarios, three different SMTs were used in order to model the treeline position. Model performance was evaluated by comparing resultant treeline elevation with observed values. Results of experiments using lapse rate-based temperature input data were compared to those using the gridded climate data. Statistical analysis determined that the lapse rate-based temperature scenario removing drought constraints and using a SMT of 6.4°C gave the most accurate prediction of treeline position, and a relatively uniform growing season ranging from 110 to 128 days. Precipitation and snow cover do not significantly affect treeline elevation. The results suggest that TREELIM accurately predicts the treeline in most cases, but is less suited in areas with steeply varying topography.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"87 1","pages":"90 - 108"},"PeriodicalIF":1.5,"publicationDate":"2022-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73504094","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-03-16DOI: 10.1080/04353676.2022.2049098
S. Harrison, A. Rowan, Adrian R. Dye, M. Plummer, K. Anderson
ABSTRACT In this paper we use a numerical glacier-climate model, a detailed photogrammetric survey and lichenometry to reconstruct small palaeoglaciers on Ben Nevis and surrounding mountains in western Scotland. These glaciers would have been sustained under a climate where the mean annual air temperature was –1.0°C to –2.0°C compared to present-day values either with or without a decrease in precipitation amount of 10–30%. Historical meteorological data show that these air temperatures were reached on Ben Nevis in the latter part of the 19th century. Although we have no data on the age of these small glaciers, palaeoclimate reconstructions suggest that such conditions almost certainly existed several times during the Holocene in Scotland; the last time being the Little Ice Age of the 16th to 19th Centuries. We argue from this that small Scottish glaciers may have been able to develop in high sheltered cirques at many times during the Holocene and that the glacial history of Scotland therefore requires revision.
{"title":"Late Holocene glaciers in western Scotland?","authors":"S. Harrison, A. Rowan, Adrian R. Dye, M. Plummer, K. Anderson","doi":"10.1080/04353676.2022.2049098","DOIUrl":"https://doi.org/10.1080/04353676.2022.2049098","url":null,"abstract":"ABSTRACT\u0000 In this paper we use a numerical glacier-climate model, a detailed photogrammetric survey and lichenometry to reconstruct small palaeoglaciers on Ben Nevis and surrounding mountains in western Scotland. These glaciers would have been sustained under a climate where the mean annual air temperature was –1.0°C to –2.0°C compared to present-day values either with or without a decrease in precipitation amount of 10–30%. Historical meteorological data show that these air temperatures were reached on Ben Nevis in the latter part of the 19th century. Although we have no data on the age of these small glaciers, palaeoclimate reconstructions suggest that such conditions almost certainly existed several times during the Holocene in Scotland; the last time being the Little Ice Age of the 16th to 19th Centuries. We argue from this that small Scottish glaciers may have been able to develop in high sheltered cirques at many times during the Holocene and that the glacial history of Scotland therefore requires revision.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"1 1","pages":"57 - 69"},"PeriodicalIF":1.5,"publicationDate":"2022-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83169158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-02-11DOI: 10.1080/04353676.2022.2136454
M. Ogurtsov
ABSTRACT Prognosis of temperature changes in the Northern Hemisphere for the period 1980–2020 was made using seven temperature paleoreconstructions covering the last 1–2 millennia and ending 1979–2016. Forecasts were made using the analogue nonlinear prediction method. A part of paleodata before 1800 (prior to the beginning of anthropogenic impact) was used as an information bank. In all seven cases, the forecast gave either a decrease or a very slight increase in temperature during 1980–2020. Statistical experiments performed with using prediction errors based on a conservative estimation of reconstruction uncertainties showed that a temperature increase of 0.25°C in the specified epoch is not excluded, but its probability is low (P < 0.20). This means that if the climate in the 20th - early 21st century was controlled by the same dynamic system as before 1800, the noticeable warming of the Northern Hemisphere in 1980–2020 should not be observed. Thus, it was shown that the data of modern paleoclimatology confirm that the climate of the Northern Hemisphere in the last 40–50 years was significantly influensed by an additional factor that did not act in the previous 1–2 millennia. It was also shown that if the actual uncertainties are significantly higher than the conservative estimates used, a warming of 0.5 degrees between 1980 and 2020 due to internal climate variability becomes possible.
{"title":"New paleoclimatic evidence of an extraordinary rise in temperature in the Northern Hemisphere in the last 3–4 decades","authors":"M. Ogurtsov","doi":"10.1080/04353676.2022.2136454","DOIUrl":"https://doi.org/10.1080/04353676.2022.2136454","url":null,"abstract":"ABSTRACT Prognosis of temperature changes in the Northern Hemisphere for the period 1980–2020 was made using seven temperature paleoreconstructions covering the last 1–2 millennia and ending 1979–2016. Forecasts were made using the analogue nonlinear prediction method. A part of paleodata before 1800 (prior to the beginning of anthropogenic impact) was used as an information bank. In all seven cases, the forecast gave either a decrease or a very slight increase in temperature during 1980–2020. Statistical experiments performed with using prediction errors based on a conservative estimation of reconstruction uncertainties showed that a temperature increase of 0.25°C in the specified epoch is not excluded, but its probability is low (P < 0.20). This means that if the climate in the 20th - early 21st century was controlled by the same dynamic system as before 1800, the noticeable warming of the Northern Hemisphere in 1980–2020 should not be observed. Thus, it was shown that the data of modern paleoclimatology confirm that the climate of the Northern Hemisphere in the last 40–50 years was significantly influensed by an additional factor that did not act in the previous 1–2 millennia. It was also shown that if the actual uncertainties are significantly higher than the conservative estimates used, a warming of 0.5 degrees between 1980 and 2020 due to internal climate variability becomes possible.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"72 1","pages":"288 - 297"},"PeriodicalIF":1.5,"publicationDate":"2022-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89206348","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-02DOI: 10.1080/04353676.2021.2022356
M. Krabbendam, A. Hall, R. M. Palamakumbura, A. Finlayson
ABSTRACT Roches moutonnées are typical landforms of glacial erosion developed in hard rocks, with an asymmetric profile caused by abrasion and lee-side plucking. In eastern Sweden, some roches moutonnées show extensive damage, including open fractures, disintegration into blocks, fracture caves and short boulder trains. Disintegration increases along ice-flow directions during deglaciation of the last Weichselian Fennoscandian Ice Sheet, indicating a subglacial origin: limited edge rounding can be explained by a combination of hard rock, slow abrasion rates and disintegration just prior to deglaciation. The roches moutonnées initially developed in kernels of gneissic rocks with a wide fracture spacing (large block size) and interlocking fracture pattern, and hence high overall rock mass strength. Dilated fractures and ‘fracture caves’ occur up to 15 m below the ice-bed interface. It is proposed that hydraulic jacking by overpressured water opened up the rock mass along pre-existing fractures. Jacking reduced rock mass strength, allowing glaciotectonic deformation of the roches moutonnées. Uneven hydraulic jacking led to uplift of individual fracture-bound blocks above the pre-existing smooth, abraded surface of the roches moutonnées, creating blunt, step-like edges. These edges allowed high ice pushing forces to act on large blocks: where blocks extend into the deeper rock mass, they further aided the disintegration of the rock mass. The disintegrated roches moutonnées can be regarded as transient features between intact bedrock and complete disintegration into boulders. The jacking-disintegration-transport sequence is characteristic of glacial ripping and very different from classic lee-side plucking.
{"title":"Glaciotectonic disintegration of roches moutonnées during glacial ripping in east Sweden","authors":"M. Krabbendam, A. Hall, R. M. Palamakumbura, A. Finlayson","doi":"10.1080/04353676.2021.2022356","DOIUrl":"https://doi.org/10.1080/04353676.2021.2022356","url":null,"abstract":"ABSTRACT Roches moutonnées are typical landforms of glacial erosion developed in hard rocks, with an asymmetric profile caused by abrasion and lee-side plucking. In eastern Sweden, some roches moutonnées show extensive damage, including open fractures, disintegration into blocks, fracture caves and short boulder trains. Disintegration increases along ice-flow directions during deglaciation of the last Weichselian Fennoscandian Ice Sheet, indicating a subglacial origin: limited edge rounding can be explained by a combination of hard rock, slow abrasion rates and disintegration just prior to deglaciation. The roches moutonnées initially developed in kernels of gneissic rocks with a wide fracture spacing (large block size) and interlocking fracture pattern, and hence high overall rock mass strength. Dilated fractures and ‘fracture caves’ occur up to 15 m below the ice-bed interface. It is proposed that hydraulic jacking by overpressured water opened up the rock mass along pre-existing fractures. Jacking reduced rock mass strength, allowing glaciotectonic deformation of the roches moutonnées. Uneven hydraulic jacking led to uplift of individual fracture-bound blocks above the pre-existing smooth, abraded surface of the roches moutonnées, creating blunt, step-like edges. These edges allowed high ice pushing forces to act on large blocks: where blocks extend into the deeper rock mass, they further aided the disintegration of the rock mass. The disintegrated roches moutonnées can be regarded as transient features between intact bedrock and complete disintegration into boulders. The jacking-disintegration-transport sequence is characteristic of glacial ripping and very different from classic lee-side plucking.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"1 1","pages":"35 - 56"},"PeriodicalIF":1.5,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88150960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-30DOI: 10.1080/04353676.2021.2022355
Suresh Das, M. Sharma, K. Miles
ABSTRACT Spatiotemporal surface velocity measurements of the alpine valley type debris-covered Miyar Glacier of the Chandrabhaga (Chenab) basin, western Himalaya, were assessed based on the cross-correlation of Landsat images spanning nearly three decades (1992-2019). Long-term (1950-2015) temperature and precipitation trends were evaluated using Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation (APHRODITE) datasets. The mean velocity (1992-2019) of the Miyar Glacier is ∼29 m/yr, with spatial patterns revealing that the debris-covered tongue is nearly stagnant (∼5 m/yr) compared to the debris-free up-glacier zone (∼35 m/yr). The transition zone from clean to debris-covered ice in the mid-ablation area shows the highest long-term mean velocities of ∼60 m/yr during the observation period, likely resulting from a steep surface gradient and greater ice thickness than the other regions of this glacier. The slow-moving and nearly stagnant debris-covered area reveals the highest amount of surface lowering due to the expansion of supraglacial ponds. Miyar Glacier experiences summer speed-up of ∼67–80% in seasonal velocity compared to winter, interpreted as a result from enhanced basal sliding during summer months due to warmer temperatures inputting more meltwater into the subsurface drainage system. Inter-annual velocity variations are greatest in the upper glacier, with higher velocities observed more frequently in recent decades. Future work should aim to elucidate the causes of this pattern, considering the overall rising air temperature trend in the western Himalaya.
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Pub Date : 2021-12-01DOI: 10.1080/04353676.2021.2010401
J. Kavan
ABSTRACT With the ongoing climate change and the prolongation of the summer melting season and increasing air temperature that this entails, fluvial transport is likely to become a more important process shaping the deglaciated areas of Antarctica. Quantification of suspended sediment transport in the deglaciated catchment of the Bohemian Stream is presented in this study. It was shown that a large amount of fine-grained material is being transported even in the relatively small catchment during the short period of the Antarctic summer. The average calculated suspended sediment concentration during the 2018 austral summer reached 274.6 mg l−1, which corresponded to an average suspended sediment load of 3662 kg day−1 and suspended sediment yield of 68 t km−2 year−1 when considering the flow season to be approximately 4 months per year. Such values are considerably higher than those reported from continental Antarctica; however, they are lower compared to most of the Arctic catchments.
随着气候的持续变化和夏季融化季节的延长以及随之而来的气温的升高，河流运输可能成为塑造南极洲冰川消融地区的一个更重要的过程。本文对波希米亚河消冰流域的悬沙输运进行了定量研究。结果表明，在南极夏季的短时间内，即使在相对较小的集水区，也有大量细粒物质被输送。2018年南方夏季平均悬沙浓度为274.6 mg l−1，考虑每年约4个月的流季，平均悬沙负荷为3662 kg d−1，悬沙产出量为68 t km−2 year−1。这些数值远高于南极洲大陆报告的数值;然而，与大多数北极集水区相比，它们的水位较低。
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