scholarly journals Equilibrium-Line Altitudes and Paleoenvironment in the Merchants Bay Area, Baffin Island, N.W.T., Canada

1985 ◽  
Vol 31 (109) ◽  
pp. 205-213 ◽  
Author(s):  
Fred F. Hawkins
Keyword(s):  
Area Ratio ◽  
Equilibrium Line ◽  
Storm Tracks ◽  
Lateral Moraine ◽  
Baffin Island ◽  
Statistical Comparison ◽  
Bay Area ◽  
The North ◽  
Simple Geometry ◽  
Accumulation Area Ratio

AbstractThe fiordlands south of Merchants Bay contain an extensive, well-preserved moraine record of a late Foxe advance of local valley glaciers. This has allowed accurate reconstruction of former glacier margins and computation of former equilibrium-line altitudes (ELAs) by a variety of methods. Statistical comparison of three methods (maximum lateral-moraine elevation, median elevation, and accumulation area ratio (AAR)) shows that different techniques can give different results for the same glaciers. Lateral moraines gave estimates that were too low, probably due to post-glacial erosion or to non-deposition. Median elevations and the AAR method produced statistically similar results but only for glaciers of simple geometry. The median-elevation method fails to take into account variations in valley morphology and glaciological parameters, and so is not reliable in all situations. The AAR method is supported by empirical evidence and is the best of the three methods for estimating former ELAs.Analysis of trend surfaces of present and late Foxe ELAs shows changes in elevation and orientation through time due to changing environmental factors. Present ELAs are strongly influenced by local factors, southerly storm tracks, and warm maritime conditions. Paleo-ELAs do not show this influence, suggesting that Davis Strait may have been ice-covered during the late Foxe stade and that storm tracks were from the north.

scholarly journals Equilibrium-Line Altitudes and Paleoenvironment in the Merchants Bay Area, Baffin Island, N.W.T., Canada

1985 ◽  
Vol 31 (109) ◽  
pp. 205-213 ◽  
Author(s):  
Fred F. Hawkins
Keyword(s):  
Area Ratio ◽  
Equilibrium Line ◽  
Storm Tracks ◽  
Lateral Moraine ◽  
Baffin Island ◽  
Statistical Comparison ◽  
Bay Area ◽  
The North ◽  
Simple Geometry ◽  
Accumulation Area Ratio

AbstractThe fiordlands south of Merchants Bay contain an extensive, well-preserved moraine record of a late Foxe advance of local valley glaciers. This has allowed accurate reconstruction of former glacier margins and computation of former equilibrium-line altitudes (ELAs) by a variety of methods. Statistical comparison of three methods (maximum lateral-moraine elevation, median elevation, and accumulation area ratio (AAR)) shows that different techniques can give different results for the same glaciers. Lateral moraines gave estimates that were too low, probably due to post-glacial erosion or to non-deposition. Median elevations and the AAR method produced statistically similar results but only for glaciers of simple geometry. The median-elevation method fails to take into account variations in valley morphology and glaciological parameters, and so is not reliable in all situations. The AAR method is supported by empirical evidence and is the best of the three methods for estimating former ELAs.Analysis of trend surfaces of present and late Foxe ELAs shows changes in elevation and orientation through time due to changing environmental factors. Present ELAs are strongly influenced by local factors, southerly storm tracks, and warm maritime conditions. Paleo-ELAs do not show this influence, suggesting that Davis Strait may have been ice-covered during the late Foxe stade and that storm tracks were from the north.

The Annual Balance of North Cascade Glaciers, Washington, U.S.A., Measured and Predicted Using An Activity-Index Method

1988 ◽  
Vol 34 (117) ◽  
pp. 194-199 ◽  
Author(s):  
Mauri S. Pelto
Keyword(s):  
Mass Balance ◽  
Activity Index ◽  
Prediction Method ◽  
Climatic Conditions ◽  
Area Ratio ◽  
Index Method ◽  
The North ◽  
Snow Line ◽  
Accumulation Area Ratio ◽  
Annual Balance

AbstractThe annual balance has been measured for ten North Cascade glaciers in 1983–84, 1984–85, 1985–86, and 1986–87 (1984, 1985, 1986, and 1987). Based on these data, an annual balance prediction method was designed and tested. Comparison of measured versus predicted annual balances indicates an accuracy of ±0.22–0.30 m. The method is based on annual measurement of the accumulation area ratio (AAR), and determination of the perennially constant activity index and area-altitude distribution on each glacier. The accumulation area ratio is determined from aerial and ground photographs at the end of the ablation season. The activity index is identified from observation of the rise of the snow line with time, compared to measured snow depths above the snow line. The AAR-activity index method was used to calculate the annual balance of 47 North Cascade glaciers in 1984, 1985, 1986, and 1987. The mean balance during the 4 year period was —0.33 m.From the mass-balance records, it is apparent that North Cascade glaciers can be divided into six climatic sensitivity groups. Each glacier type responds differently to specific climatic conditions. The mass-balance variation for glaciers of the same type is small.Since 1977, warmer, drier climatic conditions have prevailed in the North Cascades, resulting in the retreat of 42 of the 47 glaciers examined.

scholarly journals Forecasting temperate alpine glacier survival from accumulation zone observations

2010 ◽  
Vol 4 (1) ◽  
pp. 67-75 ◽  
Author(s):  
M. S. Pelto
Keyword(s):  
Mass Balance ◽  
Area Ratio ◽  
Surface Elevation ◽  
North Cascades ◽  
Rock Outcrops ◽  
Alpine Glacier ◽  
Accumulation Zone ◽  
The North ◽  
Cumulative Mass ◽  
Accumulation Area Ratio

Abstract. Temperate alpine glacier survival is dependent on the consistent presence of an accumulation zone. Frequent low accumulation area ratio values, below 30%, indicate the lack of a consistent accumulation zone, which leads to substantial thinning of the glacier in the accumulation zone. This thinning is often evident from substantial marginal recession, emergence of new rock outcrops and surface elevation decline in the accumulation zone. In the North Cascades 9 of the 12 examined glaciers exhibit characteristics of substantial accumulation zone thinning; marginal recession or emergent bedrock areas in the accumulation zone. The longitudinal profile thinning factor, f, which is a measure of the ratio of thinning in the accumulation zone to that at the terminus, is above 0.6 for all glaciers exhibiting accumulation zone thinning characteristics. The ratio of accumulation zone thinning to cumulative mass balance is above 0.5 for glacier experiencing substantial accumulation zone thinning. Without a consistent accumulation zone these glaciers are forecast not to survive the current climate or future additional warming. The results vary considerably with adjacent glaciers having a different survival forecast. This emphasizes the danger of extrapolating survival from one glacier to the next.

scholarly journals The Grinnell and Terra Nivea Ice Caps, Baffin Island

1956 ◽  
Vol 2 (19) ◽  
pp. 653-656 ◽  
Author(s):  
J. H. Mercer
Keyword(s):  
North America ◽  
Equilibrium Line ◽  
Eastern North America ◽  
General Tendency ◽  
Baffin Island ◽  
Ice Caps ◽  
Ice Cap ◽  
The North

AbstractThe Grinnell and Terra Nivea Ice Caps are the southernmost in eastern North America. The Grinnell Ice Cap reaches an altitude of 870 m. (2854 ft.). The general tendency is for slight retreat, but one large glacier is advancing. The equilibrium line is considerably lower than on the Penny Ice Cap to the north. Both firn and superimposed ice are important in the economy.

scholarly journals The Annual Balance of North Cascade Glaciers, Washington, U.S.A., Measured and Predicted Using An Activity-Index Method

1988 ◽  
Vol 34 (117) ◽  
pp. 194-199 ◽  
Author(s):  
Mauri S. Pelto
Keyword(s):  
Mass Balance ◽  
Activity Index ◽  
Prediction Method ◽  
Climatic Conditions ◽  
Area Ratio ◽  
Index Method ◽  
The North ◽  
Snow Line ◽  
Accumulation Area Ratio ◽  
Annual Balance

AbstractThe annual balance has been measured for ten North Cascade glaciers in 1983–84, 1984–85, 1985–86, and 1986–87 (1984, 1985, 1986, and 1987). Based on these data, an annual balance prediction method was designed and tested. Comparison of measured versus predicted annual balances indicates an accuracy of ±0.22–0.30 m. The method is based on annual measurement of the accumulation area ratio (AAR), and determination of the perennially constant activity index and area-altitude distribution on each glacier. The accumulation area ratio is determined from aerial and ground photographs at the end of the ablation season. The activity index is identified from observation of the rise of the snow line with time, compared to measured snow depths above the snow line. The AAR-activity index method was used to calculate the annual balance of 47 North Cascade glaciers in 1984, 1985, 1986, and 1987. The mean balance during the 4 year period was —0.33 m.From the mass-balance records, it is apparent that North Cascade glaciers can be divided into six climatic sensitivity groups. Each glacier type responds differently to specific climatic conditions. The mass-balance variation for glaciers of the same type is small.Since 1977, warmer, drier climatic conditions have prevailed in the North Cascades, resulting in the retreat of 42 of the 47 glaciers examined.

scholarly journals Testing the area–altitude balance ratio (AABR) and accumulation–area ratio (AAR) methods of calculating glacier equilibrium-line altitudes

2021 ◽  
pp. 1-12
Author(s):  
Rachel P. Oien ◽  
Brice R. Rea ◽  
Matteo Spagnolo ◽  
Iestyn D. Barr ◽  
Robert G. Bingham
Keyword(s):  
Time Series ◽  
Mass Balance ◽  
Area Ratio ◽  
Summer Temperature ◽  
Equilibrium Line ◽  
Field Observations ◽  
Median Difference ◽  
Accumulation Area Ratio

Abstract In this study, we compare equilibrium-line altitudes (ELAs) calculated using the area–altitude balance ratio (AABR) and the accumulation–area ratio (AAR) methods, with measured ELAs derived from direct field observations. We utilise a GIS toolbox to calculate the ELA for 64 extant glaciers by applying the AABR and AAR methods to DEMs and polygons of their geometry. The calculated ELAs (c-ELAs) are then compared to measured zero-net balance ELAs (znb-ELAs) obtained from mass-balance time series held by the WGMS for the same glaciers. The correlation between znb-ELAs and AABR (1.56)/AAR (0.58) c-ELAs is very strong, with an r2 = 0.99. The smallest median difference between znb-ELAs and c-ELAs (i.e. 65.5 m) is obtained when a globally representative AABR of 1.56 is used. When applied to palaeoglacier-climate applications, this difference translates to ~0.42°C, well within the uncertainty of palaeotemperature proxies used to determine mean summer temperature at the ELA. The more widely used mean AABR of 1.75 is shown to be statistically invalid due to the skewness of the dataset. On this basis, when calculating glacier ELAs, we recommend the use of a global AABR value of 1.56.

scholarly journals Altitudinal variations of temperature, equilibrium line altitude, and accumulation-area ratio in Upper Indus Basin

2016 ◽  
Vol 48 (1) ◽  
pp. 214-230 ◽  
Author(s):  
Biswajit Mukhopadhyay ◽  
Asif Khan
Keyword(s):  
Hydrological Modeling ◽  
Area Ratio ◽  
Temperature Data ◽  
Equilibrium Line ◽  
Indus Basin ◽  
Lapse Rate ◽  
Equilibrium Line Altitude ◽  
Upper Indus Basin ◽  
Temperature Equilibrium ◽  
Accumulation Area Ratio

Quantitative measures of adiabatic lapse rate, equilibrium line altitude (ELA), and accumulation-area ratio (AAR) are important to understand the hydrological processes and conduct hydrological modeling in a highly glaciated watershed. We present a detailed analysis of temperature data from 21 climatic stations, hypsometric analyses of glacier distributions, and a method to analyze ablation gradients and runoff curves concurrently to quantify these parameters for the watersheds of the Upper Indus Basin (UIB), with 15,062 km2 of glacierized area and an elevation range of 361–8,611 m. We show that the ELA varies considerably from one watershed to another, implying a highly variable upper elevation limit up to which melting of snows and glaciers takes place throughout the basin. This is in sharp contrast to the assertions made by previous researchers. We show that the ELA is as low as 4,840 m in Astore watershed and it is as high as 6,200 m in Shyok watershed. In accordance with the variation of ELA, the AAR also varies considerably from one watershed to another. It is as low as 0.10 in Gilgit and as high as 0.65 in Zanskar watersheds. We ascribe 15–20% uncertainty to these estimates of ELA and AAR in UIB.

scholarly journals Hypsometry and sensitivity of the mass balance to changes in equilibrium-line altitude: the case of the Southern Patagonia Icefield

2014 ◽  
Vol 60 (219) ◽  
pp. 14-28 ◽  
Author(s):  
Hernán De Angelis
Keyword(s):  
Mass Balance ◽  
Rate Sensitivity ◽  
Area Ratio ◽  
Area Fraction ◽  
Equilibrium Line ◽  
Equilibrium Line Altitude ◽  
First Order ◽  
Southern Patagonia ◽  
Accumulation Area Ratio ◽  
Balance Functions

AbstractWe study the relation between glacier hypsometry and sensitivity of mass-balance rate to changes in equilibrium-line altitude (ELA) to assess whether hypsometry can reliably be used to estimate the sensitivity of unmeasured glaciers to changes in ELA. We express the sensitivity of mass-balance rate to ELA, dḂ/ dELA, as a function of accumulation–area ratio (AAR), its derivative against altitude, dAAR/dELA, and mass-balance functions of ELA. We then apply the concept to 139 glaciers in the Southern Patagonia Icefield for which we derive hypsometry and AAR, and analyze the influence of hypsometry on their mass-balance rate sensitivity. We confirm that glaciers where the bulk of area is located above (below) the ELA are the least (most) sensitive. Glaciers with unimodal hypsometric curves where the peak of area fraction is around the present ELA, and glaciers with bi-or multimodal area distributions, with the ELA located approximately between the bulges, have intermediate sensitivities. We conclude that hypsometry can be used as a first-order estimator of mass-balance rate sensitivity to ELA change.

Equilibrium-line Altitudes of Late Quaternary Glaciers in the Southern Alps, New Zealand

1975 ◽  
Vol 5 (1) ◽  
pp. 27-47 ◽  
Author(s):  
Stephen C. Porter
Keyword(s):  
Late Holocene ◽  
Drainage Basin ◽  
Late Quaternary ◽  
Active Faults ◽  
Vertical Movement ◽  
Area Ratio ◽  
Southern Alps ◽  
Equilibrium Line ◽  
Accumulation Area Ratio ◽  
Geologic Data

AbstractEquilibrium-line altitudes (ELA's) of former glaciers in the Tasman River-Lake Pukaki drainage basin of the Southern Alps were reconstructed from glacial-geologic data on former ice limits by using an assumed accumulation-area ratio of 0.6 ± 0.05. Late Holocene (Neoglacial) ELA's were depressed 140 m below present levels, whereas those of four late Pleistocene ice advances were depressed 500 m (Birch Hill), 750 m (Tekapo), 875 m (Mt. John), and 1050 m (Balmoral). Reconstructed ELA gradients are approximately parallel to one another and range from 19 to 23 m km−1. Although vertical movement on active faults and isostatic tilting due to deglaciation have both contributed to modification of reconstructed ELA gradients from their original values, the maximum resulting effect probably amounts to less than 2.0 m km−1 and is undetectable from present data.

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