Glacier Reconstructions Research Articles

An ice cap landsystem for palaeoglaciological reconstructions: characterizing the Younger Dryas in western Scotland

This paper reviews the contrasting behaviours of ice caps and icefields, defines a generic landsystem model that can effectively discriminate between them, and applies the model to landform-sediment assemblages in an area of western Scotland. Such a model is necessary, since many palaeoenvironmental inferences from formerly glaciated terrains are based on the geometry, extent and dynamics of reconstructed ice masses. The validity of these glacier reconstructions is dependent on the accurate initial interpretation of relict landforms and sediments, and their inter-relationships. A new landsystems model is presented here, in which individual geological and geomorphological elements are checked against a set of eight theoretical diagnostic criteria that characterize the style of former glaciation. When applied to a 1200 km 2 area of the western Scottish Highlands, the landsystem tool predicts (1) an extensive Younger Dryas ice cap with a maximum surface elevation of 900 m above sea level, implying colder or wetter conditions than previously thought, and (2) the survival of an independent mountain icefield in part of the area during deglaciation. Glaciological theory, proxy palaeoenvironmental data and established glacier-climate-topography relationships support these predictions, thereby giving credibility to the landsystem methodology as a generic tool for palaeoglaciological reconstructions.

A glacial geological and geomorphological map of the far NW Highlands, Scotland. Part 1

Please click here to download the map associated with this article. The “Glacial geological and geomorphological map of the NW Highlands, Scotland” is the result of detailed aerial photograph interpretation and field mapping at a scale of 1: 25,000 and presents the distribution of glacial deposits and landforms in an area of ca. 1000 km2 in the far NW Scottish Highlands (58°5″N 4°58″W to 58°29″N 4°34″W; British National Grid: NC 250140 to NC 500 540). This area has never been mapped in detail before, and previous glacier reconstructions have solely been carried out from aerial photographs without much ground-truthing. The present mapping reveals that glacial landforms, most notably recessional “hummocky” moraines attributed to the Younger Dryas (ca. 12.7-11.5 ka BP), are more widely distributed throughout the study area than recognised on earlier overview maps. Detailed mapping enables the detailed reconstruction of part of a large mountain icefield of ca. 211 km2 which is significantly larger than the 36 km2 previously envisaged for the NW Highlands. These findings demonstrate that “traditional” mapping from aerial photographs and in the field can result in a high-resolution reconstruction of palaeo-glaciers from which palaeoclimatic variables can then be calculated. Such variables are crucial to validate and further constrain numerical models used to predict future climate change.

Climate during the last glacial maximum in the Wasatch and southern Uinta Mountains inferred from glacier modeling

Recent improvements in understanding glacial extents and chronologies in the Wasatch and Uinta Mountains and other mountain ranges in the western U.S. call for a more detailed approach to using glacier reconstructions to infer paleoclimates than commonly applied AAR-ELA-ÄT methods. A coupled 2-D mass balance and ice-flow numerical modeling approach developed by [Plummer, M.A., Phillips, F.M., 2003. A 2-D numerical model of snow/ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features. Quaternary Science Reviews 22, 1389–1406] allows exploration of the combined effects of temperature, precipitation, shortwave radiation and many secondary parameters on past ice extents in alpine settings. We apply this approach to the Little Cottonwood Canyon in the Wasatch Mountains and the Lake Fork and Yellowstone Canyons in the south-central Uinta Mountains. Results of modeling experiments indicate that the Little Cottonwood glacier required more precipitation during the local Last Glacial Maximum (LGM) than glaciers in the Uinta Mountains, assuming lapse rates were similar to modern. Model results suggest that if temperatures in the Wasatch Mountains and Uinta Mountains were ∼ 6 °C to 7 °C colder than modern, corresponding precipitation changes were ∼ 3 to 2× modern in Little Cottonwood Canyon and ∼ 2 to 1× modern in Lake Fork and Yellowstone Canyons. Greater amounts of precipitation in the Little Cottonwood Canyon likely reflect moisture derived from the surface of Lake Bonneville, and the lake may have also affected the mass balance of glaciers in the Uinta Mountains.

Reconstruction of glacier equilibrium‐line altitudes for the Last Glacial Maximum on the High Plain of Bogotá, Eastern Cordillera, Colombia: climatic and topographic implications

AbstractThe High Plain of Bogotá in the Andes of Colombia provides an exceptionally detailed record of glaciation. A two‐stage Last Glacial Maximum (LGM) is noted in Bogotá; the older stage (max) presents an opportunity to reconstruct individual valley glaciers and explore spatial patterns. Well‐mapped geomorphic features on topographic base maps permit the reconstruction of 23 palaeoglacier surfaces. Glacier extent varies across the region, with lower altitudes reached farther to the east. Equilibrium line altitudes (ELAs) are reconstructed using the area–altitude balance ratio (AABR) method, with BRs in three groups reflecting the W–E gradient in glacier extent and selected by minimising variation from group means. Average LGM ELA for all palaeoglaciers is 3488 m with a standard deviation of 182 m. The average lowering in ELA from LGM to modern of ca. 1300 m is best explained by a considerable drop in temperature. Significant intra‐regional variance in LGM ELA can be ascribed to topography and its influence on precipitation and/or glacier form, with lower headwall elevations being correlated to larger accumulation areas. Copyright © 2005 John Wiley & Sons, Ltd.

Evaluating Younger Dryas glacier reconstructions in part of the western Scottish Highlands: a combined empirical and theoretical approach

Current understanding of the Younger Dryas (Loch Lomond Stadial) ice cap in Scotland is dominated by reconstructions derived solely from field evidence. We use an area in the western Scottish Highlands to evaluate three examples of this approach by comparing the proposed glacier reconstructions with new empirical data and the predictions of a high‐resolution numerical model. Particular emphasis is placed on accurately determining the maximum surface altitude attained by the ice cap, dominant palaeo‐iceflow directions and the style of ice‐cap recession. By combining new geomorphological and sedimentological data with model predictions, we present a revised interpretation of the build‐up and decay of Loch Lomond Stadial ice in the study area—one that suggests a maximum ice‐surface altitude of c. 900 m a.s.l., east and southeastward iceflow and active recession of a dynamic margin. Good agreement between the new field‐based interpretation and the predictions of the numerical model validates the latter and by implication extends confidence in its veracity beyond the study area.

Evaluating Younger Dryas glacier reconstructions in part of the western Scottish Highlands: a combined empirical and theoretical approach

Evaluating Younger Dryas glacier reconstructions in part of the western Scottish Highlands: a combined empirical and theoretical approach

Identification of climate controls on the dynamic behaviour of the subarctic glacier salajekna, northern scandinavia

ABSTRACT. In this paper we describe the dynamic behaviour of Salajekna, a valley glacier, over the last 200 years using terrestrial observations, in situ measurements, remote sensing observations and glacier reconstructions. The response time of the glacier was calculated using analytical models and field measurements. We were subsequently able to attribute specific dynamic responses to climate trends in the available climate record. The glacier's historical maximum extension was reached around 1880–1910 and was the result of a more continental climate with multi‐modal airflows in the late 18th and early 19th centuries. A transition to more maritime conditions in the mid‐19th century resulted in a near‐continuous 20th century retreat before the glacier adjusted to a near‐steady state.

Utilizing physical sediment variability in glacier-fed lakes for continuous glacier reconstructions during the Holocene, northern Folgefonna, western Norway

The maritime plateau glacier of northern Folgefonna in western Norway has a short (subdecadal) response time to climatic shifts, and is therefore well suited for reconstructing high-resolution glacier fluctuations. The reconstruction presented here is based on physical parameters of glaciolacustrine sediments retrieved from two glacier-fed lakes and a peat bog north of the ice cap. Bulk density and modelled glacier net mass balance for the last 200 years show a remarkably similar pattern, where maximum sediment yield lags the glacier net mass balance by-10 years. The record of glacier variations has been transferred into an equilibrium-line altitude (ELA) variation curve. Glaciers respond primarily to changes in summer temperature and winter precipitation. At present there is a high correlation between the North Atlantic Oscillation (NAO) index and measured (since the early 1960s) net mass balance on maritime glaciers in western Norway (r=-0.8). Reconstructed glacier variations from maritime western Norway are therefore considered indicative of the strength of the westerly airflow associated with NAO during the Holocene. The early phase of mid-Holocene glacier growth (5200 cal. yr BP) was characterized by gradual glacier expansion culminating in the first Subatlantic glacial event at 2300 cal. yr BP The climate during the last 2200 years has favoured increased glacier activity at Folgefonna. High-amplitude shifts in ELA may be explained by unstable modes of the westerlies causing significant variability of winter precipitation. During the last 2000 years, Folgefonna expanded and decayed with significant decadal variability. During the latest period of the‘Mediaeval Warm Epoch’, Folgefonna advanced. The Neoglacial maximum, however, was reached during the‘Little Ice Age’ at AD 1750 and AD 1870. The northern Folgefonna glacial record is compared to other Holocene glacier records in Scandinavia.

Evidence for and Reconstruction of a Nahanagan Stade Glacier at Croloughan Lough, Derryveagh Mountains, Co. Donegal

Evidence for and Reconstruction of a Nahanagan Stade Glacier at Croloughan Lough, Derryveagh Mountains, Co. Donegal

The Loch Lomond Readvance on the Isle of Mull, Scotland: glacier reconstruction and palaeoclimatic implications

AbstractGeomorphological mapping of Mull provides evidence for an icefield 143 km2 in area flanked by six corrie glaciers with a total area of ca. 13 km2. The absence of Lateglacial periglacial features, shorelines and pollen sites from the area occupied by this readvance, together with radiocarbon dating of shell fragments, confirm that it occurred during the Loch Lomond (Younger Dryas) Stade. The thickness of glacigenic deposits within the area of the readvance is attributed to reworking of paraglacial sediments. Up‐valley continuity of recessional moraines indicates that the ice remained active and near to equilibrium during retreat, consistent with slow warming following the coldest part of the stade. Reconstructed equilibrium line altitudes (ELAs) imply vigorous snow‐blowing by westerly winds, and are consistent with a general southwestwards decline in ELAs across the Scottish Highlands. An ELA of 250 m was calculated for the Mull Icefield using an ablation:accumulation balance ratio (ABR) approach. Palaeotemperature and palaeoprecipitation estimates were derived by calculating a theoretical regional ELA from meteorological data and assuming that the combination of temperature and precipitation implied by the theoretical ELA approximates conditions at 250 m on Mull during the Loch Lomond Stade. The result indicates a mean July sea‐level temperature of 5.7 ± 0.5°C and a mean annual precipitation at 250 m of ca. 2700–3800 mm (best estimate 3200 mm), indicating higher precipitation totals than at present owing to more vigorous atmospheric circulation. Copyright © 2002 John Wiley & Sons, Ltd.

Late Quaternary Glacier response to humidity changes in the arid Andes of Chile (18–29°S)

Today, no glaciers exist between 18°30′S and 27°S, even on mountains much higher than 6000m. These dry high-mountain environments are very sensitive to changes in climatic boundary conditions, particularly humidity since temperatures are far below freezing. Here we present a reconstruction of climatic changes since the Last Glacial Maximum for the Chilean dry Andes of the southern hemisphere. We reconstructed regional equilibrium line altitudes (ELA) for three different moraine stages, representing extensive past glaciations in this currently unglaciated region. Comparison of the regional pattern of the ELA with modern climate conditions allows us to draw implications about the paleoclimatic conditions during the best preserved ‘moraine stage II’ glaciations in the northern as well as in the southern part of the research area. Our results suggest humid conditions in the northern part (18–24°S) during Late Glacial times, with strongly increased convective precipitation during austral summer. The temporal-coincidence of glaciers in the mountains and high lake levels on the Altiplano (Tauca Phase) is evident. To the south, no simple shift of the Westerlies is implied by our glacier reconstructions. The northern limit of effective moisture for glacier formation did not shift significantly, but stayed in the area of the present day northernmost glaciers of the Westerlies at about 27°S. But further south, precipitation increased significantly, accompanied by at least 2–3°C colder conditions. The age of this glaciation is uncertain, but probably of Late Glacial or Last Glacial Maximum (LGM) times. Overall, glaciers in the dry Andes of South America clearly responded to large changes in the humidity, not primarily the temperature regime, with all its consequences on the environment (hydrology, vegetation, etc.), illustrating the different regional responses to global climatic change.

Snowline depression in the tropics during the Last Glaciation

Five primary methods have been used to reconstruct Pleistocene snowlines or equilibrium-line altitudes (ELAs) in the tropics (23.5°N–23.5°S) during the last glaciation, but each has inherent errors that limit the accuracy of the results. Additional potential errors in determining ELA depression involve estimates of modern snowline altitude, dating resolution, topographic reconstruction of former glaciers, orographic effects, the presence of rockfall debris on glaciers, and calculation of regional ELA gradients. Eustatic sea-level lowering during the last glaciation is an additional factor influencing estimates of ELA depression (ΔELA). In cases where modern snowline lies above a mountain summit, only a minimum value for ΔELA can be obtained. At 12 tropical sites in Africa, the Americas (to 10°S latitude), and Pacific islands, estimates of average ΔELA range from 440 to 1400 m, but most fall in the range of 800–1000 m (mean ±1 σ=900±135 m). In a regional study of ELA depression in the southern tropical Andes (8–22°S), an average ΔELA of ca 920±250 m has been reported. Based on the assumption that glacier mass balance was controlled solely by ablation-season temperature, and assuming a full-glacial temperature lapse rate of −6°C/km, depression of mean annual temperature in glaciated alpine areas was ca 5.4±0.8°C. If adjusted for a sea-level fall of −120 m at the glacial maximum, this value is reduced to 4.7±0.8°C. The figure is based on the (unlikely) assumption that accumulation on alpine glaciers has been invariant; nevertheless, it is similar to values of temperature depresson (5–6.4°C) for the last glaciation obtained from various terrestrial sites, but contrasts with tropical sea-surface temperature estimates that are only 1–3°C cooler than present.

Further glacier and snowbed sites of inferred Loch Lomond Stadial age in the northern Lake District, England

Field mapping and evaluation of morphological and some sedimentological characteristics indicate that three debris accumulations in the hills centred on Knott in the northern Lake District result from glacial deposition. Another debris accumulation is interpreted as a pronival (protalus) rampart that developed at the downslope margin of a former snowbed. A Loch Lomond Stadial (LLS) age (11-10 k 14 C years bp ) is inferred for all the landforms and extends distribution of LLS glaciation into a new area of the Lake District. Reconstruction of the former glaciers reveals that two had larger surface areas than a substantial number of previously recognized LLS glaciers and estimated equilibrium line altitudes were lower than those for glaciers in the neighbouring Blencathra group hills. Glacier and snowbed development were favoured by site aspects, which provided protection from direct solar radiation, and occurrence of adjacent high ground, from which snow could be transferred by wind to contribute to glacier and snowbed mass. It is possible that other LLS glacier and snowbed sites in the Lake District remain to be discovered.

Late quaternary glacial stades in the Cordillera Central, Colombia, based on glacial geomorphology, tephra–soil stratigraphy, palynology, and radiocarbon dating

Using data from glacial geomorphology, tephra–soil stratigraphy and mineralogy, palynology, and radiocarbon dating, a sequence of glacial and bioclimatic stades and interstades has been identified for the last ca. 50000 yr in the Ruiz-Tolima massif, Cordillera Central, Colombia. Six Pleistocene cold stades separated by warmer interstades occurred: before 48000, between 48000 and 33000, between 28000 and 21000, from ≥16000 to ca. 14000, ca. 13000–12400, and ca. 11000–10000 yr BP. Although these radiocarbon ages are minimum-limiting ages obtained from tephra layers on top of tills, the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections. Two minor moraine stages likely reflect glacier standstill during cold intervals ca. 7400 yr BP and slightly earlier. Finally, glaciers readvanced between the seventeenth and nineteenth centuries. In contrast to the ice-clad volcanoes of the massif, ca. 34 km2 in area above an altitude of ca. 4800 m, the ice cover expanded to 1200 km2 during the Last Glacial Maximum (LGM) and was still 800 km2 during Late-glacial time (LGT). Glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude (ELA) by ca. 1100 m during the LGM and 500–600 m during LGT relative to the modern ELA, which lies at ca. 5100 m in the Cordillera Central. Glaciers in this region apparently reached their greatest extent when the climate was cold and wet, e.g. during stades corresponding to Oxygen Isotope Stage 3; glaciers were still expanding during the LGM ca. 28000–21000 yr BP, but they shrank considerably after 21000 yr BP because of greatly reduced precipitation. © 1997 John Wiley & Sons, Ltd.

Teaching geomorphology through spreadsheet modelling

Geomorphology, like most scientific disciplines, has evolved from a descriptive stage through quantification to modelling of processes and outcomes. Indeed, high-resolution modelling has been termed the “third branch of science” for its ability to generate high-quality hypotheses, testable in turn through field mapping and laboratory experimentation. I teach the principles and basic applications of modelling using microcomputer spreadsheets. These serve as “transparent boxes” in which graphical output is generated in response to numerical input, and more importantly, in which the modeler (student) can see the equations and order of steps (unlike traditional “black box” models). The technology is widely available and familiarity with it can be assumed, required, or taught at the undergraduate level. Modelling can be taught through a series of spreadsheet exercises in which students, while learning topical material in a traditional sequence, progress from a simple, “cookbook” exercise through more realistic, process-based exercises to the level of addressing a previously unstudied research question. At each step the model can be used to generate testable hypotheses. I have worked with scarp evolution, stream longitudinal profiles, and glacier reconstructions, and plan to include eolian, soil development, mass wasting, and coastal processes in additional exercises. The first year of use of this technique in a junior-level Geomorphology course clarified the strengths and weaknesses of the modelling approach. The strengths involve students learning the capabilities and flaws of modelling, a stronger understanding of causeeffect relationships, and the effects of time on landforms. The weaknesses involve time commitment, supervision in model implementation, and limitations to student ability to independently pursue openended research.

Paleoenvironmental Changes and Glacial Stades of the Last 50,000 Years in the Cordillera Central, Colombia

Using data from glacial geomorphology, tephra-soil stratigraphy and mineralogy, palynology, and radiocarbon dating, a sequence of glacial and bioclimatic stades and interstades has been identified for the past ca. 50,000 yr in the Ruı́z-Tolima massif, Cordillera Central. Six cold stades separated by warmer interstades occurred before 48,000, between 48,000 and 33,000, between 28,000 and 21,000, from ≥16,000 to ca. 14,000, ca. 13,000–12,400, and ca. 11,000–10,000 yr B.P. Although the radiocarbon ages are minimum-limiting ages obtained from tephra layers on top of tills, the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections. Two minor moraine stages likely reflect glacier pauses during cold intervals ca. 7400 yr B.P. and slightly earlier. Finally, glaciers readvanced between the 17th and 19th centuries. In contrast to the glacier cover (ca. 34 km2) on volcanoes of the massif during the last glacial maximum (LGM) the ice cover expanded to 1200 km2and was still 800 km2during late-glacial time (LGT). Glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude (ELA) by ca. 1100 m during the LGM and 500–600 m during LGT relative to the modern ELA which lies at ca. 5100 m in the Cordillera Central. Glaciers in this region apparently reached their greatest extent when the climate was cold and moist, e.g., during stades corresponding to marine isotope stage 3; glaciers were still expanding during the LGM ca. 28,000–21,000 yr B.P., but they shrank considerably after 21,000 yr B.P. because of greatly reduced precipitation.

Significance of snowblow in the generation of Loch Lomond Stadial (Younger Dryas) glaciers in the western Pennines, northern England

Geomorphological mapping has identified the former existence of five cirque glaciers that formed during the Loch Lomond Stadial in the western Pennines, northern England. Landforms in Mallerstang, which previously have been interpreted as moraine ridges, are shown to be better explained as large complex landslides. Reconstruction of these former glaciers has allowed the calculation of the former equilibrium line altitudes (ELA) by a number of different methods. Values for the ELA show a range across the area from 311 m to 608 m OD, but with low values (311 m and 428 m) for the two western glaciers. These are explained by the existence of large plateau areas adjacent to the former glaciers, which contributed additional mass to the glaciers by snowblow on to the glacier surfaces. Delimitation of the potential snowblow area for each glacier shows that it has a distinct orientation, with the western sector (225–315°) being statistically significant with the ELA indicating the importance of winds from this direction in determining the existence of these palaeoglaciers. The significance of snowblow for the generation of small glaciers in marginal areas means that such local factors must be investigated before regional firn line trends are determined in former glaciated areas.

Postglacial emergence and distribution of late Weichselian ice-sheet loads in the northern Barents and Kara seas, Russia

Reconstructions of late Weichselian glacier coverage on the continental shelves of the Russian Arctic range from a large ice sheet terminating in northern Siberia to isolated ice caps restricted to Arctic archipelagos. This disparity in glacier reconstructions reflects the lack of chronological control on glacial and deglacial landforms. We present new Holocene relative sea-level data from Franz Josef Land and northern Novaya Zemlya, Russia, that place the thickest glacier loads in the northern Barents Sea and not over Novaya Zemlya. Radiocarbon ages from shelf and terrestrial areas at the former ice-sheet margin support deglaciation of the northern Barents Sea between 13.0 and 10.3 ka, considerably later than inferred from isotopic records for the Arctic Ocean. This analysis indicates that the Barents Sea ice sheet was a dominant sea-level reservoir in northern Eurasia, and that glacier loading of Novaya Zemlya was comparatively limited during the last glaciation.

Glacial and volcanic geomorphology of the Chimborazo-Carihuairazo Massif, Ecuadorian Andes

ABSTRACTThe Chimborazo (6,310 m)–Carihuairazo (5,102 m) massif is one of the largest ice-capped central volcanic complexes in the northern Andes. Combined evidence from volcanic and glacial landforms and sediments suggests cyclical evolution during the Pleistocene. Effusive eruptions of mixed high-silica andesite (SiO2%wt c. 60) predominated and built the bulk of the edifice. Explosive activity developed as the parental magma evolved to dacite-rhyolite (SiO2%wt 64–74), culminating with cone collapse and large-scale debris avalanching. Post-collapse activity evolved from the production of high-silica andesite to terminate with monogenetic eruptions of basic andesite (SiO2%wt 54–56) from flank fissures. The last eruption occurred before 11,000 yBP.The interstratification of volcanic and glacial deposits shows that glaciers expanded and contracted several times during the later Pleistocene, while the volcanic edifices were evolving. Glaciers expanded to altitudinal limits of 3,400–3,600 m during the early last glaciation and reached similar limits sometime after 33,000 yBP; an intervening interstadial interval lasted for 10,000 y. By 20,000–18,000 yBP, glaciers receded slightly because of decreased precipitation, but later readvances culiminated at 12,000–10,000 yBP and during the last 5,000 y. Glacier reconstruction and estimation of former equilibrium line altitudes suggest that the mean annual temperatures during the full glacial, late-glacial and Neoglaciation intervals were lower than now by c. 5–6°C, 2–3°C and 1°C, respectively, but these may be underestimates because of the assumption that precipitation was constant.

Reconstructions of mountain glacier profiles, northeastern United States

Ice surface profiles are reconstructed for 37 proposed mountain glacier localities in the northeastern United States, including sites in the Catskill and Adirondack Mountains, New York; the Green Mountains, Vermont; the White Mountains, New Hampshire; and the Longfellow Mountains and Mount Katahdin, Maine. The reconstructions, determined numerically from the shear-stress equation ϒ = ρgh sin α, show estimated ice thickness as a function of valley position and slope. In general, ice thickness increases from zero at the position of the glacier terminus (terminal position is a required input to the model) to some equilibrium thickness in the upper valley, where the slab thickness is inversely proportional to valley slope. Glacier reconstructions support the empirical evidence for former local glaciation in the Catskill and White Mountains and in some localities in the Adirondack Mountains. In several proposed glacier locations in the Adirondack and Green Mountains (in very shallow basins and in very gently sloping valleys), however, estimated ice thicknesses exceed the depth of their respective valleys or the elevation of up-valley cols, suggesting a re-evaluation of these localities as sites of local confined ice flow. Confirmed localities of local glaciation are mostly in valleys with mean gradients greater than about 5° where reconstructed ice thicknesses are less than about 200 m.