Pub Date : 2019-06-30DOI: 10.1080/04353676.2019.1622919
D. Evans, S. Guðmundsson, Jonathan L. Vautrey, Kate Fearnyough, W. G. Southworth
ABSTRACT Independent dating of closely-spaced moraines on the west Breiðamerkurjökull foreland is used to test the accuracy of the size frequency (SF) and largest lichen (5LL) lichenometric dating techniques. The 5LL technique derived the most accurate ages for three undated moraines within the dated sequence but growth rates and lag times produced by the two methods (5LL = 0.71 mm yr−1 and 11 years; SF = 0.64 mm yr−1 and 7 years) were not significantly different. We therefore reject previous conclusions that any one technique is demonstrably inferior to the other, at least for dating glacial landforms created over the last 130 years in SE Iceland. Comparisons of climate trends and recession rates indicate that air temperature anomalies, particularly those of the summer, are the strongest driver of glacier retreat. No clear relationship between NAO trends and glacier retreat were identified, although a positive and/or rising trend in NAO is associated with the slowing of ice retreat overall, and the marked readvances of the mid-1950s, mid-1970s and mid-1990s are all coincident with positive and/or rising NAO 5yr moving averages. Summer and annual temperature trends, not the NAO, clearly show that recent accelerated global warming is driving the marked recession of the period 1995–2015. Over the last 100 years temperature has been the major driver of glacier terminus oscillations at west Breiðamerkurjökull but it is clear that extreme decreases in winter precipitation (i.e. 1960–1973) have the potential to increase retreat rates significantly even during times of below average annual temperatures.
摘要利用Breiðamerkurjökull西部前陆紧密间隔冰碛的独立测年方法，验证了尺寸频率(SF)和最大地衣(5LL)测年技术的准确性。5LL技术在确定日期的序列中得到了三个未确定日期的冰碛最准确的年龄，但两种方法产生的生长速率和滞后时间(5LL = 0.71 mm yr - 1和11年;SF = 0.64 mm yr - 1和7年)无显著差异。因此，我们拒绝先前的结论，即任何一种技术明显不如另一种技术，至少对于冰岛东南部过去130年形成的冰川地貌定年而言。对气候趋势和衰退率的比较表明，气温异常，特别是夏季的气温异常，是冰川退缩的最大驱动力。NAO趋势与冰川退缩之间没有明确的关系，尽管NAO的积极和/或上升趋势与总体冰退缩的减缓有关，并且20世纪50年代中期、70年代中期和90年代中期的显著上升都与NAO的积极和/或上升的5年移动平均相一致。夏季和年度气温趋势，而不是国家气象组织，清楚地表明，最近加速的全球变暖正在推动1995-2015年期间的明显衰退。在过去的100年里，温度一直是西部Breiðamerkurjökull冰川末端振荡的主要驱动因素，但很明显，冬季降水的极端减少(即1960-1973年)即使在低于年平均气温的时期也有可能显著增加退缩率。
{"title":"Testing lichenometric techniques in the production of a new growth-rate (curve) for the Breiðamerkurjökull foreland, Iceland, and the analysis of potential climatic drivers of glacier recession","authors":"D. Evans, S. Guðmundsson, Jonathan L. Vautrey, Kate Fearnyough, W. G. Southworth","doi":"10.1080/04353676.2019.1622919","DOIUrl":"https://doi.org/10.1080/04353676.2019.1622919","url":null,"abstract":"ABSTRACT Independent dating of closely-spaced moraines on the west Breiðamerkurjökull foreland is used to test the accuracy of the size frequency (SF) and largest lichen (5LL) lichenometric dating techniques. The 5LL technique derived the most accurate ages for three undated moraines within the dated sequence but growth rates and lag times produced by the two methods (5LL = 0.71 mm yr−1 and 11 years; SF = 0.64 mm yr−1 and 7 years) were not significantly different. We therefore reject previous conclusions that any one technique is demonstrably inferior to the other, at least for dating glacial landforms created over the last 130 years in SE Iceland. Comparisons of climate trends and recession rates indicate that air temperature anomalies, particularly those of the summer, are the strongest driver of glacier retreat. No clear relationship between NAO trends and glacier retreat were identified, although a positive and/or rising trend in NAO is associated with the slowing of ice retreat overall, and the marked readvances of the mid-1950s, mid-1970s and mid-1990s are all coincident with positive and/or rising NAO 5yr moving averages. Summer and annual temperature trends, not the NAO, clearly show that recent accelerated global warming is driving the marked recession of the period 1995–2015. Over the last 100 years temperature has been the major driver of glacier terminus oscillations at west Breiðamerkurjökull but it is clear that extreme decreases in winter precipitation (i.e. 1960–1973) have the potential to increase retreat rates significantly even during times of below average annual temperatures.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"152 1","pages":"225 - 248"},"PeriodicalIF":1.5,"publicationDate":"2019-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85411529","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 : 2019-04-09DOI: 10.1080/04353676.2019.1591042
A. Pisabarro, Ramón Pellitero, E. Serrano, J. López‐Moreno
ABSTRACT The Atlantic mountains of Spain are suffering a strong landscape change due to a widespread and intensive emigration to urban areas since the 1950s. This process, representative of global developments in an imminent future, is dominated by urban societies and leads to deep landscape changes in which crop fields and grasslands are abandoned and progressively covered by forest and shrubs. These dynamics have caused in turn a decrease in the runoff and a general slowdown of geomorphological processes. The impacts of land cover change have been simultaneous to an irregularity in precipitation and a significant increase of temperatures. With this background, this paper assesses in detail the impact of landscape change occurred over the last decades (twentieth and twenty-first centuries) on the water and sediment yield in the Pisuerga catchment headwaters (Cantabrian Mountains, N Spain). We analyzed the different components of Global Change in a catchment of 233 km2 extent, that has passed from 15 to 2 habitants/km2, from multiple data sources. Evolution of land cover was reconstructed from aerial photographs, remote sensing and other resources. The climatic parameters have been studied through meteorological stations, and the hydrological and sedimentological responses over time are based on available runoff data and sedimentological analysis. Our results show a significant decrease in water and sediment transport mainly driven by vegetation increase occurred in a non-linear way, more intense immediately after abandonment. This fact opens the opportunity to control more accurately water resources in Mediterranean catchments through land use management.
{"title":"Impacts of land abandonment and climate variability on runoff generation and sediment transport in the Pisuerga headwaters (Cantabrian Mountains, Spain)","authors":"A. Pisabarro, Ramón Pellitero, E. Serrano, J. López‐Moreno","doi":"10.1080/04353676.2019.1591042","DOIUrl":"https://doi.org/10.1080/04353676.2019.1591042","url":null,"abstract":"ABSTRACT The Atlantic mountains of Spain are suffering a strong landscape change due to a widespread and intensive emigration to urban areas since the 1950s. This process, representative of global developments in an imminent future, is dominated by urban societies and leads to deep landscape changes in which crop fields and grasslands are abandoned and progressively covered by forest and shrubs. These dynamics have caused in turn a decrease in the runoff and a general slowdown of geomorphological processes. The impacts of land cover change have been simultaneous to an irregularity in precipitation and a significant increase of temperatures. With this background, this paper assesses in detail the impact of landscape change occurred over the last decades (twentieth and twenty-first centuries) on the water and sediment yield in the Pisuerga catchment headwaters (Cantabrian Mountains, N Spain). We analyzed the different components of Global Change in a catchment of 233 km2 extent, that has passed from 15 to 2 habitants/km2, from multiple data sources. Evolution of land cover was reconstructed from aerial photographs, remote sensing and other resources. The climatic parameters have been studied through meteorological stations, and the hydrological and sedimentological responses over time are based on available runoff data and sedimentological analysis. Our results show a significant decrease in water and sediment transport mainly driven by vegetation increase occurred in a non-linear way, more intense immediately after abandonment. This fact opens the opportunity to control more accurately water resources in Mediterranean catchments through land use management.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"19 1","pages":"211 - 224"},"PeriodicalIF":1.5,"publicationDate":"2019-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87730504","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 : 2019-03-26DOI: 10.1080/04353676.2019.1588543
E. S. Holmlund, P. Holmlund
ABSTRACT Geodetic volume estimates of Storglaciären in Sweden suggest a 28% loss in total ice mass between 1910 and 2015. Terrestrial photographs from 1910 of Tarfala valley, where Storglaciären is situated, allow for an accurate reconstruction of the glacier's surface using Structure-from-Motion photogrammetry, which we used for past volume and mass estimations. The glacier's yearly mass balance gradient and net mass balance was also estimated back to 1880 using weather data from Karesuando, 170 km north-east of Storglaciären, through neural network regression. These combined reconstructions provide a continuous mass change series between the end of the Little Ice Age and 1946, when field data become available. The resultant reconstruction suggests a state close to equilibrium between 1880 and the 1910s, followed by drastic melt until the 1970s, constituting 76% of the 1910–2015 ice loss. More favourable conditions subsequently stabilized the mass balance until the late 1990s, after which Storglaciären started losing mass again. The 1910 reconstruction allows for a more accurate mass change series than previous estimates, and the methodology can be used on other glaciers where early photographic material exists.
{"title":"Constraining 135 years of mass balance with historic structure-from-motion photogrammetry on Storglaciären, Sweden","authors":"E. S. Holmlund, P. Holmlund","doi":"10.1080/04353676.2019.1588543","DOIUrl":"https://doi.org/10.1080/04353676.2019.1588543","url":null,"abstract":"ABSTRACT Geodetic volume estimates of Storglaciären in Sweden suggest a 28% loss in total ice mass between 1910 and 2015. Terrestrial photographs from 1910 of Tarfala valley, where Storglaciären is situated, allow for an accurate reconstruction of the glacier's surface using Structure-from-Motion photogrammetry, which we used for past volume and mass estimations. The glacier's yearly mass balance gradient and net mass balance was also estimated back to 1880 using weather data from Karesuando, 170 km north-east of Storglaciären, through neural network regression. These combined reconstructions provide a continuous mass change series between the end of the Little Ice Age and 1946, when field data become available. The resultant reconstruction suggests a state close to equilibrium between 1880 and the 1910s, followed by drastic melt until the 1970s, constituting 76% of the 1910–2015 ice loss. More favourable conditions subsequently stabilized the mass balance until the late 1990s, after which Storglaciären started losing mass again. The 1910 reconstruction allows for a more accurate mass change series than previous estimates, and the methodology can be used on other glaciers where early photographic material exists.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"1 1","pages":"195 - 210"},"PeriodicalIF":1.5,"publicationDate":"2019-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89748329","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 : 2019-02-27DOI: 10.1080/04353676.2019.1583498
Munkhdavaa Munkhjargal, L. Menzel
ABSTRACT Net radiation is a key component of surface radiation balance and has a strong influence on hydrological processes via evapotranspiration. In this study, daily average net radiation (Rnmean) for all-sky conditions was investigated as a function of the estimated daily average global radiation (GRmean) during the summers of 2011 and 2012 (128 days total) in the Sugnugur Valley of Northern Mongolia. We present a simple alternative remote sensing approach that considers factors such as topography, cloud fraction, cloud optical thickness and surface albedo. First, a geometric model for the simulation of daily average global radiation (GRCS:mean) for clear-sky conditions was applied on a daily basis. It considers topographical effects, such as slope, azimuth and elevation. GRmean was then derived for all-sky conditions by coupling the averaged atmospheric products of MODIS. Finally, Rnmean was obtained as a function of the simulated GRmean using the linear regression parameters found at a permanent observation site. The results were validated with the data from a nearby temporary observation site. The root mean square errors (RMSE) were 44 and 52 Wm−2 for GRmean and 18 and 25 Wm−2 for Rnmean at the two different sites. This methodology requires few observations and offers a simple means for estimating GRmean with high spatial (30 m) and temporal (daily) resolution under any sky conditions in the absence of ground measurements. Furthermore, Rnmean can be modeled from the simulated GRmean at regional or watershed scales where ground observations exist at one site at least.
{"title":"Estimating daily average net radiation in Northern Mongolia","authors":"Munkhdavaa Munkhjargal, L. Menzel","doi":"10.1080/04353676.2019.1583498","DOIUrl":"https://doi.org/10.1080/04353676.2019.1583498","url":null,"abstract":"ABSTRACT Net radiation is a key component of surface radiation balance and has a strong influence on hydrological processes via evapotranspiration. In this study, daily average net radiation (Rnmean) for all-sky conditions was investigated as a function of the estimated daily average global radiation (GRmean) during the summers of 2011 and 2012 (128 days total) in the Sugnugur Valley of Northern Mongolia. We present a simple alternative remote sensing approach that considers factors such as topography, cloud fraction, cloud optical thickness and surface albedo. First, a geometric model for the simulation of daily average global radiation (GRCS:mean) for clear-sky conditions was applied on a daily basis. It considers topographical effects, such as slope, azimuth and elevation. GRmean was then derived for all-sky conditions by coupling the averaged atmospheric products of MODIS. Finally, Rnmean was obtained as a function of the simulated GRmean using the linear regression parameters found at a permanent observation site. The results were validated with the data from a nearby temporary observation site. The root mean square errors (RMSE) were 44 and 52 Wm−2 for GRmean and 18 and 25 Wm−2 for Rnmean at the two different sites. This methodology requires few observations and offers a simple means for estimating GRmean with high spatial (30 m) and temporal (daily) resolution under any sky conditions in the absence of ground measurements. Furthermore, Rnmean can be modeled from the simulated GRmean at regional or watershed scales where ground observations exist at one site at least.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"17 1","pages":"177 - 194"},"PeriodicalIF":1.5,"publicationDate":"2019-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76130749","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 : 2019-02-10DOI: 10.1080/04353676.2019.1574209
A. Maaß, H. Schüttrumpf
ABSTRACT An often underrated but historically long-lasting human impact on river-floodplain systems is that of the presence of water mills. The objective of this study is to determine how the construction and later removal of water mills influence the longitudinal bed profile of a river and its floodplain sedimentation. The effects of a river-mill system were analyzed using physically-based equations of backwater effects and sediment mobility in combination with field measurements of channel slope and floodplain development pre- and postdating water mills in the Wurm River (Germany) and the Geul River (Netherlands). The results show that the construction and removal of water mills likely resulted in a net incision of the riverbed into the valley bottom to a level below the original bed, with reduced floodplain inundation rates and, consequently, reduced floodplain sedimentation.
{"title":"Elevated floodplains and net channel incision as a result of the construction and removal of water mills","authors":"A. Maaß, H. Schüttrumpf","doi":"10.1080/04353676.2019.1574209","DOIUrl":"https://doi.org/10.1080/04353676.2019.1574209","url":null,"abstract":"ABSTRACT An often underrated but historically long-lasting human impact on river-floodplain systems is that of the presence of water mills. The objective of this study is to determine how the construction and later removal of water mills influence the longitudinal bed profile of a river and its floodplain sedimentation. The effects of a river-mill system were analyzed using physically-based equations of backwater effects and sediment mobility in combination with field measurements of channel slope and floodplain development pre- and postdating water mills in the Wurm River (Germany) and the Geul River (Netherlands). The results show that the construction and removal of water mills likely resulted in a net incision of the riverbed into the valley bottom to a level below the original bed, with reduced floodplain inundation rates and, consequently, reduced floodplain sedimentation.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"38 1","pages":"157 - 176"},"PeriodicalIF":1.5,"publicationDate":"2019-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76589549","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 : 2019-02-10DOI: 10.1080/04353676.2019.1572973
Natalia Pilguj, Leszek Kolendowicz, M. Kryza, K. Migała, B. Czernecki
ABSTRACT This paper presents trends in wind speed and wind direction indices at selected stations in Svalbard (Bjørnøya, Hopen and Ny-Ålesund) and in the NCEP/NCAR and ERA-Interim reanalysis for the period 1986–2015. The analysed wind indices include the sum of days (annual or seasonal) with the daily range wind speed or wind direction. Using the Mann-Kendall trend test, we look for temporal trends in these indices, compare the results for the measured and gridded datasets, and then analyse the spatial variability in those trends. For the stations, statistically significant decreasing trends are detected for the frequency of days with very low wind speed (≤2 m s−1) and for days with strong wind (>10 m s−1). From the reanalysis data, indices with wind speed of up to 5 m s−1 were characterized by decreasing trends, while indices with wind speed above the mentioned threshold show increasing trends. Wind direction indices are characterized by different tendencies in the Ny-Ålesund station, where local elements modify the dominant directions of the air mass advection. The trends vary in space for the given region. Reanalysis data show the biggest positive trend for the occurrence of northerly winds over the Greenland Sea and Arctic Ocean, which cannot be confirmed by measurements (no stations available). The trends in wind speed and direction indices may partly be explained by changes in the frequency of circulation patterns.
本文介绍了1986-2015年斯瓦尔巴群岛(Bjørnøya, Hopen和Ny-Ålesund)选定站点的风速和风向指数的变化趋势，以及NCEP/NCAR和ERA-Interim再分析。分析的风指数包括日数(年或季)和风速或风向的日变化范围。使用Mann-Kendall趋势检验，我们寻找这些指数的时间趋势，比较测量数据集和网格数据集的结果，然后分析这些趋势的空间变异性。风速极低日(≤2 m s - 1)和强风日(>10 m s - 1)的频率均有显著的减少趋势。从再分析数据来看，风速在5 m s−1以下的指数呈下降趋势，风速在5 m s−1以上的指数呈上升趋势。Ny-Ålesund站的风向指数表现出不同的趋势，局地因素改变了气团平流的主导方向。这一趋势在给定区域的空间上有所不同。再分析数据显示，格陵兰海和北冰洋出现北风的趋势最大，这一点无法通过测量得到证实(没有可用的台站)。风速和风向指数的变化趋势可以部分地用环流型频率的变化来解释。
{"title":"Temporal changes in wind conditions at Svalbard for the years 1986–2015","authors":"Natalia Pilguj, Leszek Kolendowicz, M. Kryza, K. Migała, B. Czernecki","doi":"10.1080/04353676.2019.1572973","DOIUrl":"https://doi.org/10.1080/04353676.2019.1572973","url":null,"abstract":"ABSTRACT This paper presents trends in wind speed and wind direction indices at selected stations in Svalbard (Bjørnøya, Hopen and Ny-Ålesund) and in the NCEP/NCAR and ERA-Interim reanalysis for the period 1986–2015. The analysed wind indices include the sum of days (annual or seasonal) with the daily range wind speed or wind direction. Using the Mann-Kendall trend test, we look for temporal trends in these indices, compare the results for the measured and gridded datasets, and then analyse the spatial variability in those trends. For the stations, statistically significant decreasing trends are detected for the frequency of days with very low wind speed (≤2 m s−1) and for days with strong wind (>10 m s−1). From the reanalysis data, indices with wind speed of up to 5 m s−1 were characterized by decreasing trends, while indices with wind speed above the mentioned threshold show increasing trends. Wind direction indices are characterized by different tendencies in the Ny-Ålesund station, where local elements modify the dominant directions of the air mass advection. The trends vary in space for the given region. Reanalysis data show the biggest positive trend for the occurrence of northerly winds over the Greenland Sea and Arctic Ocean, which cannot be confirmed by measurements (no stations available). The trends in wind speed and direction indices may partly be explained by changes in the frequency of circulation patterns.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"4 1","pages":"136 - 156"},"PeriodicalIF":1.5,"publicationDate":"2019-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80863889","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 : 2018-11-29DOI: 10.1080/04353676.2018.1549945
Jayne E. Kamintzis, T. Irvine‐Fynn, Tom O. Holt, John P. P. Jones, Stephen Tooth, Hywel Griffiths, Bryn Hubbard
ABSTRACT Despite numerous studies of knickpoints in bedrock and alluvial channels, no detailed description of knickpoint change on ice has been reported to date. This paper presents the first investigation of knickpoint evolution within a supraglacial stream. Repeat longitudinal profile surveys of a knickpoint on Vadrec del Forno, Switzerland reveal a step height increase of 115 mm and upstream migration of 0.26 m over three days during the 2017 ablation season. Rates and magnitudes of erosion vary spatially across the knickpoint in relation to differing discharge regimes. At high discharges (∼0.013 m3 s−1), erosion is focused at the step base; at low discharges (∼0.003 m3 s−1), erosion is focused on the reach upstream of the knickpoint, at the step lip and the step-riser face. This results in replacement of knickpoint morphology, driven by frictional thermal erosion and hydraulic action. Pool formation further influences step morphology, inducing secondary circulation and increased melt at the base of the step-riser, causing steepening. Results highlight the complexities of water flow over knickpoints, demonstrating that the stream power law does not accurately characterise changing knickpoint morphology or predict retreat rates. Although morphological similarities have been reported between supraglacial and bedrock/alluvial channels, knickpoints in non-ice-walled channels will not necessarily respond to discharge similarly to those on ice due to the different erosional processes involved.
尽管对基岩和冲积河道中的裂缝点进行了大量研究，但迄今为止还没有关于冰上裂缝点变化的详细描述。本文首次研究了冰上河流中裂缝点的演化。在2017年消融季节，瑞士Vadrec del Forno的裂口点在3天内台阶高度增加了115毫米，上游迁移了0.26米。在不同的排放制度下，侵蚀的速率和幅度在空间上不同。在高流量(~ 0.013 m3 s−1)时，侵蚀集中在台阶底部;在低流量(~ 0.003 m3 s−1)时，侵蚀主要集中在裂缝点上游、台阶边缘和台阶提升面。这导致了由摩擦热侵蚀和水力作用驱动的缺口点形态的替换。池的形成进一步影响台阶形态，在台阶立管底部诱发二次循环和熔体增加，造成陡化。结果强调了裂缝点上水流的复杂性，表明水流幂律不能准确地表征裂缝点形态的变化或预测退缩率。尽管冰川上河道和基岩/冲积河道在形态上有相似之处，但由于涉及的侵蚀过程不同，非冰壁河道中的裂缝点对流量的反应不一定与冰上的相似。
{"title":"Knickpoint evolution in a supraglacial stream","authors":"Jayne E. Kamintzis, T. Irvine‐Fynn, Tom O. Holt, John P. P. Jones, Stephen Tooth, Hywel Griffiths, Bryn Hubbard","doi":"10.1080/04353676.2018.1549945","DOIUrl":"https://doi.org/10.1080/04353676.2018.1549945","url":null,"abstract":"ABSTRACT Despite numerous studies of knickpoints in bedrock and alluvial channels, no detailed description of knickpoint change on ice has been reported to date. This paper presents the first investigation of knickpoint evolution within a supraglacial stream. Repeat longitudinal profile surveys of a knickpoint on Vadrec del Forno, Switzerland reveal a step height increase of 115 mm and upstream migration of 0.26 m over three days during the 2017 ablation season. Rates and magnitudes of erosion vary spatially across the knickpoint in relation to differing discharge regimes. At high discharges (∼0.013 m3 s−1), erosion is focused at the step base; at low discharges (∼0.003 m3 s−1), erosion is focused on the reach upstream of the knickpoint, at the step lip and the step-riser face. This results in replacement of knickpoint morphology, driven by frictional thermal erosion and hydraulic action. Pool formation further influences step morphology, inducing secondary circulation and increased melt at the base of the step-riser, causing steepening. Results highlight the complexities of water flow over knickpoints, demonstrating that the stream power law does not accurately characterise changing knickpoint morphology or predict retreat rates. Although morphological similarities have been reported between supraglacial and bedrock/alluvial channels, knickpoints in non-ice-walled channels will not necessarily respond to discharge similarly to those on ice due to the different erosional processes involved.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"32 1","pages":"118 - 135"},"PeriodicalIF":1.5,"publicationDate":"2018-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80766842","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 : 2018-11-22DOI: 10.1080/04353676.2018.1539829
D. Sugden, A. Hall, W. Phillips, M. Stewart
ABSTRACT Concentrations of boulders are a common feature of landscapes modified by former mid-latitude ice sheets. In many cases, the origin of the boulders can be traced in the up-ice direction to a cliff only tens to hundreds of metres distant. The implication is that a pulse of plucking and short boulder transport occurred beneath thin ice at the end of the last glacial cycle. Here we use a case study in granite bedrock in the Dee Valley, Scotland, to constrain theory and explore the factors involved in such a late phase of plucking. Plucking is influenced by ice velocity, hydrology, effective ice pressure, the extent of subglacial cavities and bedrock characteristics. The balance between these factors favours block removal beneath thin ice near a glacier margin. At Ripe Hill in the Dee Valley, a mean exposure age of 14.2 ka on blocks supports the view that the boulder train formed at the end of ice sheet glaciation. The late pulse of plucking was further enhanced by ice flowing obliquely across vertical joints and by fluctuations in sub-marginal meltwater conditions. An implication of the study is that there is the potential for a wave of ice-marginal plucking to sweep across a landscape as an ice sheet retreats.
{"title":"Plucking enhanced beneath ice sheet margins: evidence from the Grampian Mountains, Scotland","authors":"D. Sugden, A. Hall, W. Phillips, M. Stewart","doi":"10.1080/04353676.2018.1539829","DOIUrl":"https://doi.org/10.1080/04353676.2018.1539829","url":null,"abstract":"ABSTRACT Concentrations of boulders are a common feature of landscapes modified by former mid-latitude ice sheets. In many cases, the origin of the boulders can be traced in the up-ice direction to a cliff only tens to hundreds of metres distant. The implication is that a pulse of plucking and short boulder transport occurred beneath thin ice at the end of the last glacial cycle. Here we use a case study in granite bedrock in the Dee Valley, Scotland, to constrain theory and explore the factors involved in such a late phase of plucking. Plucking is influenced by ice velocity, hydrology, effective ice pressure, the extent of subglacial cavities and bedrock characteristics. The balance between these factors favours block removal beneath thin ice near a glacier margin. At Ripe Hill in the Dee Valley, a mean exposure age of 14.2 ka on blocks supports the view that the boulder train formed at the end of ice sheet glaciation. The late pulse of plucking was further enhanced by ice flowing obliquely across vertical joints and by fluctuations in sub-marginal meltwater conditions. An implication of the study is that there is the potential for a wave of ice-marginal plucking to sweep across a landscape as an ice sheet retreats.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"100 1","pages":"34 - 44"},"PeriodicalIF":1.5,"publicationDate":"2018-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79342520","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 : 2018-11-22DOI: 10.1080/04353676.2018.1542202
Małgorzata Kijowska-Strugała, Ł. Wiejaczka, Jarosław Cebulski, Krzysztof Kiszka, M. Maślanka, Daria Maria Kramkowska
ABSTRACT Evolution of the bluffs within the shore zone of a reservoir is dependent on many environmental factors. In this study, a characterization of bluffs was presented with reference to the entire shore zone of a mountain reservoir. The research was conducted on the Czorsztyn reservoir – one of the largest functioning reservoirs within the Polish Carpathians (created in 1997). The analysis was based on a study conducted in 2015 and 2016 with the use of a Terrestrial Scanning Laser (TLS) and Airborne Laser Scanning (ALS), (data from 2013). The objectives are to identify the bluffs’ height on the mountain reservoir shoreline and assess the impact of various environmental factors (geological basement, slope exposure and gradient, bluff position in a different part of the reservoir, water level, wave height and the presence of landslides) on bluff development. Environmental factors were assessed using statistical methods, Beta factor and Principal Component Analysis. After 18 years of operation, bluffs on the reservoir covered 89% of the shoreline. The maximum height reaches about 10.00 m, and most often does not exceed 2.00 m. The most developed bluffs (height) are found in the south-western and western exposures of the shoreline. Amongst the analyzed factors affecting the bluff development on the Czorsztyn reservoir, the wave height, water level, the position of bluffs within the shoreline, slope gradient and exposure were identified as the dominant factors based on statistical analysis. Due to the fact that multiple factors are acting together, the distinction of the dominant factor affecting bluff development is difficult.
{"title":"Factors affecting bluff development around a mountain reservoir: a case study in the Polish Carpathians","authors":"Małgorzata Kijowska-Strugała, Ł. Wiejaczka, Jarosław Cebulski, Krzysztof Kiszka, M. Maślanka, Daria Maria Kramkowska","doi":"10.1080/04353676.2018.1542202","DOIUrl":"https://doi.org/10.1080/04353676.2018.1542202","url":null,"abstract":"ABSTRACT Evolution of the bluffs within the shore zone of a reservoir is dependent on many environmental factors. In this study, a characterization of bluffs was presented with reference to the entire shore zone of a mountain reservoir. The research was conducted on the Czorsztyn reservoir – one of the largest functioning reservoirs within the Polish Carpathians (created in 1997). The analysis was based on a study conducted in 2015 and 2016 with the use of a Terrestrial Scanning Laser (TLS) and Airborne Laser Scanning (ALS), (data from 2013). The objectives are to identify the bluffs’ height on the mountain reservoir shoreline and assess the impact of various environmental factors (geological basement, slope exposure and gradient, bluff position in a different part of the reservoir, water level, wave height and the presence of landslides) on bluff development. Environmental factors were assessed using statistical methods, Beta factor and Principal Component Analysis. After 18 years of operation, bluffs on the reservoir covered 89% of the shoreline. The maximum height reaches about 10.00 m, and most often does not exceed 2.00 m. The most developed bluffs (height) are found in the south-western and western exposures of the shoreline. Amongst the analyzed factors affecting the bluff development on the Czorsztyn reservoir, the wave height, water level, the position of bluffs within the shoreline, slope gradient and exposure were identified as the dominant factors based on statistical analysis. Due to the fact that multiple factors are acting together, the distinction of the dominant factor affecting bluff development is difficult.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"52 1","pages":"79 - 93"},"PeriodicalIF":1.5,"publicationDate":"2018-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83608504","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 : 2018-11-19DOI: 10.1080/04353676.2018.1545120
M. Temminghoff, M. Temminghoff, D. Benn, D. Benn, Jason Gulley, Heïdi Sevestre
ABSTRACT This paper presents new data obtained by speleological surveys and ground-penetrating radar (GPR) on a cut-and-closure conduit in Scott Turnerbreen, a small cold glacier in Svalbard, Norwegian Arctic. We use these data to propose criteria for the identification of cut-and-closure conduits from GPR data. In addition, we describe subglacial and englacial structures exposed in the conduit, which shed light on the former dynamic behaviour of the glacier. The glacier bed consists of a thick layer of subglacial traction till, from which till-filled fractures extend upward into the ice. These observations show that Scott Turnerbreen was formerly warm-based, and are consistent with a surge or surge-like behaviour. The channel system was also imaged using GPR. Varying channel morphologies have distinctive signatures on GPR profiles, allowing the identification and mapping of englacial drainage systems in situations where direct access is impossible.
{"title":"Characterization of the englacial and subglacial drainage system in a high Arctic cold glacier by speleological mapping and ground-penetrating radar","authors":"M. Temminghoff, M. Temminghoff, D. Benn, D. Benn, Jason Gulley, Heïdi Sevestre","doi":"10.1080/04353676.2018.1545120","DOIUrl":"https://doi.org/10.1080/04353676.2018.1545120","url":null,"abstract":"ABSTRACT This paper presents new data obtained by speleological surveys and ground-penetrating radar (GPR) on a cut-and-closure conduit in Scott Turnerbreen, a small cold glacier in Svalbard, Norwegian Arctic. We use these data to propose criteria for the identification of cut-and-closure conduits from GPR data. In addition, we describe subglacial and englacial structures exposed in the conduit, which shed light on the former dynamic behaviour of the glacier. The glacier bed consists of a thick layer of subglacial traction till, from which till-filled fractures extend upward into the ice. These observations show that Scott Turnerbreen was formerly warm-based, and are consistent with a surge or surge-like behaviour. The channel system was also imaged using GPR. Varying channel morphologies have distinctive signatures on GPR profiles, allowing the identification and mapping of englacial drainage systems in situations where direct access is impossible.","PeriodicalId":55112,"journal":{"name":"Geografiska Annaler Series A-Physical Geography","volume":"3 1","pages":"117 - 98"},"PeriodicalIF":1.5,"publicationDate":"2018-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89081904","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}
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