Global warming triggers shrinking and thinning of glaciers worldwide,with potentially severe implications for human society.However,regional differences in glacier retreat and its relationship with climatic characteri...Global warming triggers shrinking and thinning of glaciers worldwide,with potentially severe implications for human society.However,regional differences in glacier retreat and its relationship with climatic characteristics have not been conclusively demonstrated.In this study,regional changes in global glaciers based on two primary features,area change and mass balance,were investigated on the basis of data collected from published research on glacier changes.Results show that during the period 1980—2015,the rate of global glacier area shrinkage was 0.18%per year and that of global glacier mass loss was 0.25 m w.e.per year.Retreat of glaciers located at low and middle latitudes was characterized by severe area shrinkage and mass loss.Correspondingly,in the Arctic,deglaciation was characterized by ice thinning due to a low area reduction but relatively high mass loss rate.However,glaciers in high southern latitudes were in a relatively stable status.High Mountain Asia exhibited the lowest rate of area shrinkage and mass loss among glaciers located at low and middle latitudes,and a slower rate of mass loss compared with the global average.Glaciers in the Tropical Andes exhibited the fastest rate of glacier area shrinkage(—1.6%per year),whereas Antarctic and Subantarctic glaciers showed the lowest rate(—0.11%per year).For mass balance,the most negative occurred at Southern Andes(—0.81 m w.e.per year),followed by Alaska(-0.74 m w.e.per year).Only the Antarctic and Subantarctic experienced small mass gain(0.04 m w.e.per year).High levels of correlation are found between the rates of glacier retreat and annual average temperature and annual total precipitation instead of their trends.The variability of the surface climate conditions in the glacier environment plays a key role in driving these regional differences in global glacier retreat.展开更多
A study has been carried out in part of Chenab basin,Himalaya to understand the relationship between glacio-morphological factors and change in glacial area. Initially change in areal extent of glaciers was derived fo...A study has been carried out in part of Chenab basin,Himalaya to understand the relationship between glacio-morphological factors and change in glacial area. Initially change in areal extent of glaciers was derived for two time frames(1962-2001/02 and 2001/02-2010/11). The study comprised of 324 glaciers for the monitoring period of 1962-2001/02 for,which 11% loss in glacial area was observed. Two hundred and thirty-eight glaciers were further monitored between 2001/02 and 2010/11. These glaciers showed an area loss of 1.1%. The annual deglaciation has been found to be higher during the period of 1962-2001/02 compared to 2001/02-2010/11. The spatial and temporal variability in deglaciation was also addressed usingglacio-morphic parameters. Area,length,percentage of debris cover,and various elevation parameters of glaciers were observed to have significant controls on relationships to the rate of glacial shrinkage. Largerarea and longer glaciers show a lower percentage of retreat than smaller and shorter ones. Moreover,glaciers located at lower altitudes and having gentle slopes show more area retreat. The results of area retreat in debris covered and debris free glaciers supports that the glaciers covered by debris retard ice melting at some extent. 158 glaciers were observed having no debris cover,and these exhibit 14% of loss in surface area. In glaciers having 40% debris cover,8% of deglaciation was observed. The glaciers located below equilibrium line altitude(ELA) have experienced 4.6% of deglaciation for the time frame 2001/02 – 2010/11 whereas it was found to be 1.1% for the glaciers occurring above ELA. However,theorientation of glaciers did not show any considerable influence on glacial change based on hypothesis.展开更多
The highest volcano in Mexico,at the same time the third largest mountain in North America(Citlaltépetl,5610 m a.s.l.),is home to the largest glacier in the country.Because of the extinction of the Popocatép...The highest volcano in Mexico,at the same time the third largest mountain in North America(Citlaltépetl,5610 m a.s.l.),is home to the largest glacier in the country.Because of the extinction of the Popocatépetl glacier(5500 m a.s.l.)caused by eruptive activity,and the almost disappearance of the Iztaccíhuatl glaciers(5220 m a.s.l.)due to the lower elevation of the mountain,the Glaciar Norte of Citlatépetl has been the only glacier that has shown a certain degree of stability as a response to the altitude in which it is located.However,as occurs in almost all glaciers on the planet,the retreat of its glacier terminus has been continuous.Furthermore,during the last years the thickness of its upper part began to decrease rapidly until its bedrock was exposed for the first time in 2019.Due to its ecosystem importance and because it is the main glacier in Mexico,as well as the only one in the world located at latitude 19°N,in this work its current dimensions are updated,as well as the local climatology that governs the current state of the glacier is pointed out.The study was based on the analysis of high-resolution Sentinel-2 optical images,as well as through Sentinel-1 SAR images,with the support of climatological information from the study area.Therefore,the outcropping of the bedrock in the accumulation zone and the consequent horizontal retreat of the upper part of the glacier are documented;at the same time,the decrease in the thickness of the ice along it is noted.The rocky outcrop in the accumulation zone suggests that the flow dynamics of the ice towards the ablation zone will be considerably less,accelerating the retreat of the glacier terminus.Finally,the ascent of the glacial front to 5102 m a.s.l.and the modelled altitude of the equilibrium line to 5276 m a.s.l.are reported as a warning signal in terms of snow catchment and mass balance;likewise,the decrease of 23%of its surface is also indicated regarding the surface reduction monitoring that has been done until 2017.These findings may indicate that the future of this glacier is related to its possible extinction sooner than previously thought,with severe environmental consequences,especially in terms of the provision of drinking water for thousands of inhabitants of the slopes of the volcano.This research is expected to help reflect on the impacts of current climate variability and at the same time serve as a reference for the tropical glaciers on the planet.展开更多
The Chenab basin is located in northwest India and eastern Pakistan.Glaciers in Chenab basin,as local freshwater resources,are very important to the regional ecological environment and development.At the same time,SBA...The Chenab basin is located in northwest India and eastern Pakistan.Glaciers in Chenab basin,as local freshwater resources,are very important to the regional ecological environment and development.At the same time,SBAS InSAR can monitor the deformation of the ground for a long time,the monitoring accuracy can reach mm level,and can obtain the time series change of deformation,whcih provides a new idea and method for glacier detection.In this study,the deformation from SBAS InSAR was combined with glacial area data to study the glacial changes in Chenab Basin.Sentinel-1 and Landsat series images were used to obtain the deformation and change in the area of glaciers by SBAS InSAR and the semi-automated method.The results showed that glaciers in the Chenab basin retreated rapidly,especially in the past ten years.The glacier area decreased by 88.05 km^(2)in 1990~2000 and 118.86 km^(2) in 2000~2010,and the glacier area decreased by 236.01 km^(2) in 2010~2020,which was the largest rate of change of 9.49%.Moreover,glacial deformation decreased in 2020,and the deformation rate ranged from-146.3mm/a to 119.52 mm/a.Most glaciers had deformation rates between-50 mm/a and 50 mm/a.Influenced by precipitation and temperature,glacial deformation in the Chenab basin started to change in August,the maximum accumulation was 6,828.43mm,and the minimum ablation was-20,656.41 mm.展开更多
The aim of the international project “Global Land Ice Measurements from Space (GLIMS)" headed by the US Geological Survey is to establish a world wide glacier inventory based on satellite imagery.This data set w...The aim of the international project “Global Land Ice Measurements from Space (GLIMS)" headed by the US Geological Survey is to establish a world wide glacier inventory based on satellite imagery.This data set will form a first digital baseline study for future glacier monitoring.The presented GIS_based glacier inventory for King George Island is a case study for the area of the Antarctic Peninsula.In the database of the glacier inventory topographic information,specific glaciological parameters as well as metadata will be included.The topographic data consists of drainage basin limits,basin areas,altitudinal ranges,perimeters and mean lengths.Glaciological data sets should comprise information on glacier retreat in different periods,glacier velocities,ice thickness and bedrock topography as well as derived parameters.Modelled and measured mass balance parameters could be included as additional data layers.In particular,these metadata records must comprise background information on data accuracy and data sources and should be compatible with a future data model for the King George Island GIS (KGIS).Three examples illustrate that the GLIMS database will not only contain information valuable for glaciological applications,but also other environmental studies on the island will benefit from this standardised remote sensing data sets.Therefore,a very close link between the data models of KGIS and GLIMS has to be established to enable these synergisms.Finally,better access to historic aerial photography would enable a continuous record of glacier retreat from the beginning of the 1950’s onward.展开更多
Topography plays an important role in determining the glacier changes.However,topography has often been oversimplified in the studies of the glacier changes.No systematic studies have been conducted to evaluate the re...Topography plays an important role in determining the glacier changes.However,topography has often been oversimplified in the studies of the glacier changes.No systematic studies have been conducted to evaluate the relationship between the glacier changes and topographic features.The present study provided a detailed insight into the changes in the two branches(east branch and west branch)of Urumqi Glacier No.1 in the Chinese Tianshan Mountains since 1993 and systematically discussed the effect of topography on the glacier parameters.This study analyzed comprehensive recently observed data(from 1992/1993 to 2018/2019),including mass balance,ice thickness,surface elevation,ice velocity,terminus,and area,and then determined the differences in the changes of the two branches and explored the effect of topography on the glacier changes.We also applied a topographic solar radiation model to analyze the influence of topography on the incoming shortwave radiation(SW_(in))across the entire glacier,focusing on the difference in the SW_(in) between the two branches.The glacier mass balance of the east branch was more negative than that of the west branch from 1992/1993 to 2018/2019,and this was mainly attributed to the lower average altitude of the east branch.Compared with the west branch,the decrease rate of the ice velocity was lower in the east branch owing to its relatively increased slope.The narrow shape of the west branch and its southeast aspect in the earlier period resulted in a larger glacier terminus retreat of the west branch.The spatial variability of the SW_(in) across the glacier surface became much larger as altitude increased.The SW_(in) received by the east branch was slightly larger than that received by the west branch,and the northern aspect could receive more SW_(in),leading to glacier melting.In the future,the difference of the glacier changes between the two branches will continue to exist due to their topographic differences.This work is fundamental to understanding how topographic features affect the glacier changes,and provides information for building different types of relationship between the glacier area and ice volume to promote further studies on the basin-scale glacier classification.展开更多
Mountains have been described as the water towers of the world. Almost all major rivers have their sources in mountains; glaciers are important water resources that contribute meltwater to river discharge. Glaciers pa...Mountains have been described as the water towers of the world. Almost all major rivers have their sources in mountains; glaciers are important water resources that contribute meltwater to river discharge. Glaciers participate in the global water cycle and, with their solid water storage, are an important component of the water balance. As solid reservoirs, glaciers continue to receive the mass nourishment of solid precipitation from the atmosphere, and their meltwater feed and regulate fiver discharge. Physical changes in glaciers are an indicator of climate change. Over the past half century, the global temperature has increased by 1-2 ℃, which emphasizes the urgent task of monitoring glaciers and predicting their trend. As an example, we have investigated, researched, and surveyed Glacier No. 1 in the Urumqi River source, Tianshan （abbr. Glacier No. 1 Tianshan or Glacier No.l） for half a century. We have found an increase by degrees of the glacial regression during the last 400 years and discovered a terminal moraine which is forming today. The global temperature is rising continually, while the local glacial temperature is 0.4 times that of the global temperature change. Thus, we forecast that Glacier No. 1 Tianshan will disappear during the late 21 st Century （2074-2100 A.D.）.展开更多
The areal extent of many Himalayan glaciers is decreasing where number of glaciers is increasing. This increasing number is subject to the fragmentation of limbs of main trunk glacier. However, disintegration of limbs...The areal extent of many Himalayan glaciers is decreasing where number of glaciers is increasing. This increasing number is subject to the fragmentation of limbs of main trunk glacier. However, disintegration of limbs is not observed in all the glacier system. This paper emphases the scenario of the fragmentation occurred in glaciers. Two glaciers from the two different basins have been taken into the consideration for this study. The peculiar characteristic of these glaciers is that, the tributary glaciers are showing less retreat in compare to main trunk glaciers. Due to this reason the rate of shift in snout is higher in main trunk glaciers than tributary glaciers. However, in recent data the tributary glaciers have experienced little higher loss in glacial ice than main glacier. But the shift of snout in main trunk glacier is no doubt surprising since past. Therefore, various parameters have been examined to identify the cause of such a behavior of glaciers. The common factors observed in both the glaciers are accumulation area ratio which is higher, snow line altitude which is lower in tributary glaciers for the period of 2005-2013. Another factor is the orientation as tributary glaciers are towards NE direction. In addition, slope of Dharlang glacier (main limb) is 4? where it is 18? in tributary glacier.展开更多
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA19070501)the National Natural Science Foundation of China(41730751&41671066)the International Partnership Program of Chinese Academy of Sciences(131C 11KYSB20160061,Y560L01001).
文摘Global warming triggers shrinking and thinning of glaciers worldwide,with potentially severe implications for human society.However,regional differences in glacier retreat and its relationship with climatic characteristics have not been conclusively demonstrated.In this study,regional changes in global glaciers based on two primary features,area change and mass balance,were investigated on the basis of data collected from published research on glacier changes.Results show that during the period 1980—2015,the rate of global glacier area shrinkage was 0.18%per year and that of global glacier mass loss was 0.25 m w.e.per year.Retreat of glaciers located at low and middle latitudes was characterized by severe area shrinkage and mass loss.Correspondingly,in the Arctic,deglaciation was characterized by ice thinning due to a low area reduction but relatively high mass loss rate.However,glaciers in high southern latitudes were in a relatively stable status.High Mountain Asia exhibited the lowest rate of area shrinkage and mass loss among glaciers located at low and middle latitudes,and a slower rate of mass loss compared with the global average.Glaciers in the Tropical Andes exhibited the fastest rate of glacier area shrinkage(—1.6%per year),whereas Antarctic and Subantarctic glaciers showed the lowest rate(—0.11%per year).For mass balance,the most negative occurred at Southern Andes(—0.81 m w.e.per year),followed by Alaska(-0.74 m w.e.per year).Only the Antarctic and Subantarctic experienced small mass gain(0.04 m w.e.per year).High levels of correlation are found between the rates of glacier retreat and annual average temperature and annual total precipitation instead of their trends.The variability of the surface climate conditions in the glacier environment plays a key role in driving these regional differences in global glacier retreat.
文摘A study has been carried out in part of Chenab basin,Himalaya to understand the relationship between glacio-morphological factors and change in glacial area. Initially change in areal extent of glaciers was derived for two time frames(1962-2001/02 and 2001/02-2010/11). The study comprised of 324 glaciers for the monitoring period of 1962-2001/02 for,which 11% loss in glacial area was observed. Two hundred and thirty-eight glaciers were further monitored between 2001/02 and 2010/11. These glaciers showed an area loss of 1.1%. The annual deglaciation has been found to be higher during the period of 1962-2001/02 compared to 2001/02-2010/11. The spatial and temporal variability in deglaciation was also addressed usingglacio-morphic parameters. Area,length,percentage of debris cover,and various elevation parameters of glaciers were observed to have significant controls on relationships to the rate of glacial shrinkage. Largerarea and longer glaciers show a lower percentage of retreat than smaller and shorter ones. Moreover,glaciers located at lower altitudes and having gentle slopes show more area retreat. The results of area retreat in debris covered and debris free glaciers supports that the glaciers covered by debris retard ice melting at some extent. 158 glaciers were observed having no debris cover,and these exhibit 14% of loss in surface area. In glaciers having 40% debris cover,8% of deglaciation was observed. The glaciers located below equilibrium line altitude(ELA) have experienced 4.6% of deglaciation for the time frame 2001/02 – 2010/11 whereas it was found to be 1.1% for the glaciers occurring above ELA. However,theorientation of glaciers did not show any considerable influence on glacial change based on hypothesis.
文摘The highest volcano in Mexico,at the same time the third largest mountain in North America(Citlaltépetl,5610 m a.s.l.),is home to the largest glacier in the country.Because of the extinction of the Popocatépetl glacier(5500 m a.s.l.)caused by eruptive activity,and the almost disappearance of the Iztaccíhuatl glaciers(5220 m a.s.l.)due to the lower elevation of the mountain,the Glaciar Norte of Citlatépetl has been the only glacier that has shown a certain degree of stability as a response to the altitude in which it is located.However,as occurs in almost all glaciers on the planet,the retreat of its glacier terminus has been continuous.Furthermore,during the last years the thickness of its upper part began to decrease rapidly until its bedrock was exposed for the first time in 2019.Due to its ecosystem importance and because it is the main glacier in Mexico,as well as the only one in the world located at latitude 19°N,in this work its current dimensions are updated,as well as the local climatology that governs the current state of the glacier is pointed out.The study was based on the analysis of high-resolution Sentinel-2 optical images,as well as through Sentinel-1 SAR images,with the support of climatological information from the study area.Therefore,the outcropping of the bedrock in the accumulation zone and the consequent horizontal retreat of the upper part of the glacier are documented;at the same time,the decrease in the thickness of the ice along it is noted.The rocky outcrop in the accumulation zone suggests that the flow dynamics of the ice towards the ablation zone will be considerably less,accelerating the retreat of the glacier terminus.Finally,the ascent of the glacial front to 5102 m a.s.l.and the modelled altitude of the equilibrium line to 5276 m a.s.l.are reported as a warning signal in terms of snow catchment and mass balance;likewise,the decrease of 23%of its surface is also indicated regarding the surface reduction monitoring that has been done until 2017.These findings may indicate that the future of this glacier is related to its possible extinction sooner than previously thought,with severe environmental consequences,especially in terms of the provision of drinking water for thousands of inhabitants of the slopes of the volcano.This research is expected to help reflect on the impacts of current climate variability and at the same time serve as a reference for the tropical glaciers on the planet.
基金funded by the National Natural Science Foundation of China(Grant Nos.41907396,42001388,42071277)Chongqing Research Program of Basic Research and Frontier Technology(No.cstc2019jcyj-msxmX0515)+3 种基金the Science and Technology Research Program of Chongqing Municipal Education Commission(Grant No.KJQN202200526)Preferential Funding Scheme for Ideological and Political Teachers and Counselors in Colleges and Universities(Grant No.FDYZY2020003)the Science Foundation of the Chongqing Normal University(22XLB002,22XLB003)Humanities and Social Sciences Research Program of Chongqing Education Commission(22SKSZ030)。
文摘The Chenab basin is located in northwest India and eastern Pakistan.Glaciers in Chenab basin,as local freshwater resources,are very important to the regional ecological environment and development.At the same time,SBAS InSAR can monitor the deformation of the ground for a long time,the monitoring accuracy can reach mm level,and can obtain the time series change of deformation,whcih provides a new idea and method for glacier detection.In this study,the deformation from SBAS InSAR was combined with glacial area data to study the glacial changes in Chenab Basin.Sentinel-1 and Landsat series images were used to obtain the deformation and change in the area of glaciers by SBAS InSAR and the semi-automated method.The results showed that glaciers in the Chenab basin retreated rapidly,especially in the past ten years.The glacier area decreased by 88.05 km^(2)in 1990~2000 and 118.86 km^(2) in 2000~2010,and the glacier area decreased by 236.01 km^(2) in 2010~2020,which was the largest rate of change of 9.49%.Moreover,glacial deformation decreased in 2020,and the deformation rate ranged from-146.3mm/a to 119.52 mm/a.Most glaciers had deformation rates between-50 mm/a and 50 mm/a.Influenced by precipitation and temperature,glacial deformation in the Chenab basin started to change in August,the maximum accumulation was 6,828.43mm,and the minimum ablation was-20,656.41 mm.
文摘The aim of the international project “Global Land Ice Measurements from Space (GLIMS)" headed by the US Geological Survey is to establish a world wide glacier inventory based on satellite imagery.This data set will form a first digital baseline study for future glacier monitoring.The presented GIS_based glacier inventory for King George Island is a case study for the area of the Antarctic Peninsula.In the database of the glacier inventory topographic information,specific glaciological parameters as well as metadata will be included.The topographic data consists of drainage basin limits,basin areas,altitudinal ranges,perimeters and mean lengths.Glaciological data sets should comprise information on glacier retreat in different periods,glacier velocities,ice thickness and bedrock topography as well as derived parameters.Modelled and measured mass balance parameters could be included as additional data layers.In particular,these metadata records must comprise background information on data accuracy and data sources and should be compatible with a future data model for the King George Island GIS (KGIS).Three examples illustrate that the GLIMS database will not only contain information valuable for glaciological applications,but also other environmental studies on the island will benefit from this standardised remote sensing data sets.Therefore,a very close link between the data models of KGIS and GLIMS has to be established to enable these synergisms.Finally,better access to historic aerial photography would enable a continuous record of glacier retreat from the beginning of the 1950’s onward.
基金jointly funded by the Third Xinjiang Scientific Expedition Program (2021xjkk0801)the Youth Innovation Promotion Association of Chinese Academy of Sciences (Y2021110)the State Key Laboratory of Cryospheric Science (SKLCS-ZZ-2022)
文摘Topography plays an important role in determining the glacier changes.However,topography has often been oversimplified in the studies of the glacier changes.No systematic studies have been conducted to evaluate the relationship between the glacier changes and topographic features.The present study provided a detailed insight into the changes in the two branches(east branch and west branch)of Urumqi Glacier No.1 in the Chinese Tianshan Mountains since 1993 and systematically discussed the effect of topography on the glacier parameters.This study analyzed comprehensive recently observed data(from 1992/1993 to 2018/2019),including mass balance,ice thickness,surface elevation,ice velocity,terminus,and area,and then determined the differences in the changes of the two branches and explored the effect of topography on the glacier changes.We also applied a topographic solar radiation model to analyze the influence of topography on the incoming shortwave radiation(SW_(in))across the entire glacier,focusing on the difference in the SW_(in) between the two branches.The glacier mass balance of the east branch was more negative than that of the west branch from 1992/1993 to 2018/2019,and this was mainly attributed to the lower average altitude of the east branch.Compared with the west branch,the decrease rate of the ice velocity was lower in the east branch owing to its relatively increased slope.The narrow shape of the west branch and its southeast aspect in the earlier period resulted in a larger glacier terminus retreat of the west branch.The spatial variability of the SW_(in) across the glacier surface became much larger as altitude increased.The SW_(in) received by the east branch was slightly larger than that received by the west branch,and the northern aspect could receive more SW_(in),leading to glacier melting.In the future,the difference of the glacier changes between the two branches will continue to exist due to their topographic differences.This work is fundamental to understanding how topographic features affect the glacier changes,and provides information for building different types of relationship between the glacier area and ice volume to promote further studies on the basin-scale glacier classification.
基金supported by The State Key Science Research Programme for Global Change Research of China (Grant No.2010CB951402)State Key Laboratory of Cryospheric Sciences Fund (SKLCS 2010-04)+1 种基金the State Key Basic Research Development Program of China (973 Program)(Grant No.2007 CB411507)the National Natural Science Foundation of China (Grant No. 40771047)
文摘Mountains have been described as the water towers of the world. Almost all major rivers have their sources in mountains; glaciers are important water resources that contribute meltwater to river discharge. Glaciers participate in the global water cycle and, with their solid water storage, are an important component of the water balance. As solid reservoirs, glaciers continue to receive the mass nourishment of solid precipitation from the atmosphere, and their meltwater feed and regulate fiver discharge. Physical changes in glaciers are an indicator of climate change. Over the past half century, the global temperature has increased by 1-2 ℃, which emphasizes the urgent task of monitoring glaciers and predicting their trend. As an example, we have investigated, researched, and surveyed Glacier No. 1 in the Urumqi River source, Tianshan （abbr. Glacier No. 1 Tianshan or Glacier No.l） for half a century. We have found an increase by degrees of the glacial regression during the last 400 years and discovered a terminal moraine which is forming today. The global temperature is rising continually, while the local glacial temperature is 0.4 times that of the global temperature change. Thus, we forecast that Glacier No. 1 Tianshan will disappear during the late 21 st Century （2074-2100 A.D.）.
文摘The areal extent of many Himalayan glaciers is decreasing where number of glaciers is increasing. This increasing number is subject to the fragmentation of limbs of main trunk glacier. However, disintegration of limbs is not observed in all the glacier system. This paper emphases the scenario of the fragmentation occurred in glaciers. Two glaciers from the two different basins have been taken into the consideration for this study. The peculiar characteristic of these glaciers is that, the tributary glaciers are showing less retreat in compare to main trunk glaciers. Due to this reason the rate of shift in snout is higher in main trunk glaciers than tributary glaciers. However, in recent data the tributary glaciers have experienced little higher loss in glacial ice than main glacier. But the shift of snout in main trunk glacier is no doubt surprising since past. Therefore, various parameters have been examined to identify the cause of such a behavior of glaciers. The common factors observed in both the glaciers are accumulation area ratio which is higher, snow line altitude which is lower in tributary glaciers for the period of 2005-2013. Another factor is the orientation as tributary glaciers are towards NE direction. In addition, slope of Dharlang glacier (main limb) is 4? where it is 18? in tributary glacier.
