The (mis)conception of an average Quaternary equilibrium line altitude

2020 ◽  
Author(s):  
Matteo Spagnolo ◽  
Brice Rea ◽  
Iestyn Barr
Keyword(s):  
Equilibrium Line ◽  
Glacial Cycle ◽  
Equilibrium Line Altitude ◽  
Glacier Surface ◽  
Quantitative Expression ◽  
Mountain Glaciers ◽  
The Past ◽  
The Relationship ◽  
Simple Definition ◽  
Do So

<p>The glacier equilibrium line altitude (ELA) represents the elevation on the glacier surface at which the amount of mass gained (via precipitation, avalanching and windblown snow, equals the amount of ice lost (via ablation and sublimation, over the mass balance year. The ELA can be measured on modern glaciers or calculated for reconstructed, former glaciers. Despite its simple definition, the ELA represents an incredibly powerful, quantitative expression of the relationship between glaciers and climate. As a glacier responds dynamically to climate, so does the ELA. Precipitation at the glacier ELA has been empirically linked to ablation season temperature. Thus, the reconstruction of former glacier geometries and their ELAs leads to the quantification of palaeoclimate.</p><p>In recent years, the concept of an “average Quaternary ELA” (or “mean Quaternary ELA”) has become popular because of the role it might play in relation to the glacial buzzsaw hypothesis, i.e. the idea that glacial erosion could offset mountain uplift and therefore control and limit the growth of mountains. Attempts to determine the average Quaternary ELA have been undertaken, leading to some interesting conclusions. For example, it has been argued that the floor altitudes of glacial cirques can be used as a measure of average Quaternary ELA, therefore implying that average Quaternary mountain glaciers expansion was confined to the topmost portion of alpine valleys.</p><p>Time has passed from these initial attempts to determine the average Quaternary ELA and more palaeoclimatic and palaeoglaciological data have become available, so it is appropriate to reconsider these calculations and perhaps question the validity of such a concept. To do so, we revisit how the idea of an average Quaternary ELA developed and what such a parameter would really mean. We do so in light of a new quantitative study on the average ELA relative to both a single glacial cycle and multiple glaciations experienced during the past   ̴2.6 million years, i.e. the Quaternary. Collectively, this new study presents a very different perspective than previously suggested.</p>

scholarly journals Modeling debris-covered glaciers: response to steady debris deposition

2016 ◽  
Vol 10 (3) ◽  
pp. 1105-1124 ◽  
Author(s):  
Leif S. Anderson ◽  
Robert S. Anderson
Keyword(s):  
Equilibrium Line ◽  
Surface Velocity ◽  
Equilibrium Line Altitude ◽  
Glacier Surface ◽  
Glacier Terminus ◽  
Ice Accumulation ◽  
Debris Cover ◽  
Long Valley ◽  
Glacier Length ◽  
The Relationship

Abstract. Debris-covered glaciers are common in rapidly eroding alpine landscapes. When thicker than a few centimeters, surface debris suppresses melt rates. If continuous debris cover is present, ablation rates can be significantly reduced leading to increases in glacier length. In order to quantify feedbacks in the debris–glacier–climate system, we developed a 2-D long-valley numerical glacier model that includes englacial and supraglacial debris advection. We ran 120 simulations on a linear bed profile in which a hypothetical steady state debris-free glacier responds to a step increase of surface debris deposition. Simulated glaciers advance to steady states in which ice accumulation equals ice ablation, and debris input equals debris loss from the glacier terminus. Our model and parameter selections can produce 2-fold increases in glacier length. Debris flux onto the glacier and the relationship between debris thickness and melt rate strongly control glacier length. Debris deposited near the equilibrium-line altitude, where ice discharge is high, results in the greatest glacier extension when other debris-related variables are held constant. Debris deposited near the equilibrium-line altitude re-emerges high in the ablation zone and therefore impacts melt rate over a greater fraction of the glacier surface. Continuous debris cover reduces ice discharge gradients, ice thickness gradients, and velocity gradients relative to initial debris-free glaciers. Debris-forced glacier extension decreases the ratio of accumulation zone to total glacier area (AAR). Our simulations reproduce the "general trends" between debris cover, AARs, and glacier surface velocity patterns from modern debris-covered glaciers. We provide a quantitative, theoretical foundation to interpret the effect of debris cover on the moraine record, and to assess the effects of climate change on debris-covered glaciers.

scholarly journals Mass Balance of “Vesper” Glacier, Washington, U.S.A.

1981 ◽  
Vol 27 (96) ◽  
pp. 271-282 ◽  
Author(s):  
David P. Dethier ◽  
Jan E. Frederick
Keyword(s):  
Nineteenth Century ◽  
Mass Balance ◽  
Cascade Range ◽  
Equilibrium Line ◽  
Equilibrium Line Altitude ◽  
Climatic Fluctuations ◽  
The North ◽  
Snow Line ◽  
The Relationship ◽  
Geologic Data

AbstractDuring 1974–75 glaciologic and geologic studies were conducted on a small (0.17 km2) avalanche-nourished glacier in the North Cascade Range of Washington. The approximate equilibrium-line altitude (ELA) for this ice body, informally called “Vesper” glacier, lies at 1475 m, some 300 m below the regional ELA value. Estimated annual accumulation was 6 100±675 mm during the two years of study; 15 to 30% of this flux resulted from avalanche and wind–transported snow. Average annual ablation during the period was 5 350 mm, giving a total net balance of + 1 600 mm for the two-year study period. “Vesper” glacier persists well below the regional snow-line because of excessive local precipitation, substantial avalanche contributions, and a favourable north-facing aspect.Neoglacial moraines indicate that maximum ELA lowering in this period was approximately 165 m and occurred prior to a.d. 1670. Minor re-advances occurred during the nineteenth century. These reconnaissance measurements are consistent with the sparse geologic data reported from other glaciers in the Cascade Range. While the relationship between regional lowering of snow-line and avalanche activity is uncertain at present, these data suggest that avalanche-nourished glaciers provide a useful record of climatic fluctuations.

scholarly journals Sensitivity of Rhonegletscher, Switzerland, to climate change: experiments with a one-dimensional flowline model

1998 ◽  
Vol 44 (147) ◽  
pp. 383-393 ◽  
Author(s):  
Jakob Wallinga ◽  
Roderik S.W. Van De Wal
Keyword(s):  
Climate Change ◽  
Statistical Correlation ◽  
Equilibrium Line ◽  
Climate Change Scenarios ◽  
Climate Data ◽  
Equilibrium Line Altitude ◽  
Glacier Surface ◽  
One Dimensional ◽  
Glacier Length ◽  
Warming Rate

AbstractA one-dimensional time-dependent flowline model of Rhonegletscher, Switzerland, has been used to test the glacier’s response to climatic warming. Mass-balance variations over the last 100 years are obtained from observations of the equilibrium-line altitude (ELA) and a reconstruction of the ELA based on a statistical correlation between temperature and ELA. For the period prior to AD 1882, for which no reliable climate data exist, we chose equilibrium-line altitudes that enabled us to simulate accurately the glacier length from AD 1602.The model simulates the historical glacier length almost perfectly and glacier geometry very well. It underestimates glacier-surface velocities by 1-18%. Following these reference experiments, we investigated the response of Rhonegletscher to a number of climate-change scenarios for the period AD 1990-2100. For a constant climate equal to the 1961-90 mean, the model predicts a 6% decrease in glacier volume by AD 2100. Rhonegletscher will retreat by almost 1 km over the next 100 years at this scenario. At a warming rate of 0.04 K a-1, only 4% of the glacier volume will be left by AD 2100.

scholarly journals From Doktor Kurowski's Schneegrenze to our modern glacier equilibrium line altitude (ELA)

2015 ◽  
Vol 9 (3) ◽  
pp. 3165-3204 ◽  
Author(s):  
R. J. Braithwaite
Keyword(s):  
Close Agreement ◽  
Equilibrium Line ◽  
Surface Mass Balance ◽  
Equilibrium Line Altitude ◽  
Surface Mass ◽  
Inappropriate Use ◽  
Mountain Glaciers ◽  
Precipitation Increase ◽  
The Mean ◽  
Balanced Budget

Abstract. Translated into modern terminology, Kurowski suggested in 1891 that the equilibrium line altitude (ELA) of a glacier is equal to the mean altitude of the glacier when the whole glacier is in balance between accumulation and ablation. Kurowski's method has been widely misunderstood, partly due to inappropriate use of statistical terminology by later workers, and has been little tested except by Braithwaite and Müller in a 1980 paper (for 32 glaciers). I now compare Kurowski's mean altitude with balanced-budget ELA calculated for 103 modern glaciers with measured surface mass balance data. Kurowski's mean altitude is significantly higher (at 95% level) than balanced-budget ELA for 19 outlet and 42 valley glaciers, but not significantly higher for 34 mountain glaciers. The error in Kurowski mean altitude as a predictor of balanced-budget ELA might be due to generally lower balance gradients in accumulation area compared with ablation areas for many glaciers, as suggested by several workers, but some glaciers have higher gradients, presumably due to precipitation increase with altitude. The relatively close agreement between balanced-budget ELA and mean altitude for mountain glaciers (mean error −8 m with standard deviation 59 m) may reflect smaller altitude ranges for these glaciers such that there is less room for effects of different balance gradients to manifest themselves.

scholarly journals Mass Balance of “Vesper” Glacier, Washington, U.S.A.

1981 ◽  
Vol 27 (96) ◽  
pp. 271-282
Author(s):  
David P. Dethier ◽  
Jan E. Frederick
Keyword(s):  
Nineteenth Century ◽  
Mass Balance ◽  
Cascade Range ◽  
Equilibrium Line ◽  
Equilibrium Line Altitude ◽  
Climatic Fluctuations ◽  
The North ◽  
Snow Line ◽  
The Relationship ◽  
Geologic Data

AbstractDuring 1974–75 glaciologic and geologic studies were conducted on a small (0.17 km2) avalanche-nourished glacier in the North Cascade Range of Washington. The approximate equilibrium-line altitude (ELA) for this ice body, informally called “Vesper” glacier, lies at 1475 m, some 300 m below the regional ELA value. Estimated annual accumulation was 6 100±675 mm during the two years of study; 15 to 30% of this flux resulted from avalanche and wind–transported snow. Average annual ablation during the period was 5 350 mm, giving a total net balance of + 1 600 mm for the two-year study period. “Vesper” glacier persists well below the regional snow-line because of excessive local precipitation, substantial avalanche contributions, and a favourable north-facing aspect.Neoglacial moraines indicate that maximum ELA lowering in this period was approximately 165 m and occurred prior to a.d. 1670. Minor re-advances occurred during the nineteenth century. These reconnaissance measurements are consistent with the sparse geologic data reported from other glaciers in the Cascade Range. While the relationship between regional lowering of snow-line and avalanche activity is uncertain at present, these data suggest that avalanche-nourished glaciers provide a useful record of climatic fluctuations.

scholarly journals Policy preferences in a post-war environment

2018 ◽  
Vol 5 (2) ◽  
pp. 205316801877993
Author(s):  
Dino Hadzic
Keyword(s):  
Policy Preferences ◽  
Future Research ◽  
Personal Safety ◽  
The Past ◽  
Large N ◽  
Nationally Representative ◽  
Post War ◽  
The Relationship ◽  
Do So

Can reminders of violence committed in the past influence citizens’ policy preferences in the present? Prior work has found that under the threat of violence individuals prioritize safety and adopt policy views aimed at reducing the threat. Elites can then strategically employ concerns over personal safety and security to shape the public’s preferences. I contribute to this literature by conducting an exploratory study of whether invocations of violence committed in the past shape preferences in the long-term, years after the actual violence has ended. To do so, I fielded an experiment on a large ( N = 1125) and nationally representative sample of respondents in Bosnia, the site of a major ethnic civil war in 1992–1995. I did not find evidence that reminders of wartime violence in and of themselves affect policy preferences. Ultimately, this study represents a first cut at a neglected question in the literature and has implications that could motivate future research on the relationship between violent conflict and policy preferences.

scholarly journals Experience – Information – Image: A Historiography of Unfolding. Arab Cinema as Example

1970 ◽  
Vol 14 (1) ◽  
Author(s):  
Laura U. Marks
Keyword(s):  
Information Age ◽  
Public Image ◽  
Economic Interests ◽  
The Past ◽  
Contemporary Politics ◽  
The Matrix ◽  
Information Image ◽  
The Relationship ◽  
Triadic Relationship ◽  
Do So

Why do certain images of history reach us, while others remain seemingly forgotten, in the infinite breadth of the past? Why do only certain events seem to matter? I suggest those experiences are not forgotten but enfolded. The contemporary politics of historiography can be conceptualized according to the relationship between Experience, Information, and Image; a triadic relationship I have proposed to understand the nature of the image in the information age. While Experience is infinite, the vast majority of experience lies latent. Few Images ever arise from it. In our age, those that do tend to be selected, or unfolded, by political and economic interests that deem them to be useful as Information. Nevertheless, anyone can unfold any aspect of Experience to become a public image, and artists (and others) do so in order to allow other aspects of Experience to circulate, before they enfold, back into the matrix of history. I will show an animated diagram that illustrates this concept of history as a flow of unfolding and enfolding, influenced by concepts from Charles Sanders Peirce and Gilles Deleuze. Many artworks can be illuminated by this process. My examples will be drawn from contemporary Arab cinema. In the heavily politicized Arab milieu, the Image world is constructed as a selective unfolding of only those aspects of Experience that are deemed to be useful or profitable. Some Arab filmmakers, rather than deconstruct the resulting ideological images, prefer to carry out their own unfoldings:  explicating hitherto latent events, knowledges, and sensations. Thus what official history deems merely personal, absurd, micro-events, or no events at all, becomes the stuff of a rich alternative historiography. This process characterizes the work of, among others, Joana Hadjithomas and Khalil Joreige, Nisrine Khodr, Mohammed Soueid, and Akram Zaatari (Lebanon), Azza El-Hassan, Elia Suleiman, and Sobhi Al-Zobaidi (Palestine), and Mohamad Khan (Egypt).

scholarly journals Relation between the Mass Balance of Western Canadian Mountain Glaciers and Meteorological Data

1988 ◽  
Vol 34 (116) ◽  
pp. 11-18 ◽  
Author(s):  
Anne Letréguilly
Keyword(s):  
Mass Balance ◽  
Meteorological Data ◽  
Winter Precipitation ◽  
Summer Temperature ◽  
Equilibrium Line ◽  
Regression Equations ◽  
Equilibrium Line Altitude ◽  
Mountain Glaciers

AbstractThe mass balance, summer balance, winter balance, and equilibrium-line altitude of three Canadian glaciers (Peyto, Place, and Sentinel Glaciers) are compared with the meteorological records of neighbouring stations for the period 1966—84. While Peyto Glacier’s mass balance is almost entirely related to summer temperature, Sentinel Glacier’s mass balance is mostly controlled by winter precipitation. Place Glacier is influenced by both elements. Statistical reconstructions are presented for the three glaciers, using the best regression equations with the meteorological records since 1938.

The Hangman's Noose and the Empty Box: Kyd's Use of Dramatic and Mythological Sources in The Spanish Tragedy (III.iv-vii)

1977 ◽  
Vol 30 (3) ◽  
pp. 334-340
Author(s):  
Frank Ardolino
Keyword(s):  
Intellectual History ◽  
The Past ◽  
Source Study ◽  
The Relationship ◽  
Do So

Source study has generally been discredited as a useful critical tool because of the past simplistic conception of the relationship between the source and its adapted context. Generally, source hunters emphasized parallel passages as the major proof of similarities between texts, merely listing the parallels without investigating more important critical implications. If we are to continue to consider source study a valuable scholarly tool—and there are good reasons to do so—we need to establish its interpretational relevance through a method which compares the conventional ideas and symbols of the source with the motifs and themes of the adapted context. Thus, the contextual method of ascription, as it shall be termed for purposes of discussion, will require an understanding of the interaction between the source's original context, including subsequent intellectual history, and the themes of the new context.

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