Lower Glacier Research Articles

Glacier distribution and direction in Svalbard, Axel Heiberg Island and throughout the Arctic: General northward tendencies

Glacier distribution and direction in Svalbard, Axel Heiberg Island and throughout the Arctic: General northward tendenciesArctic glaciers depend on supply of moisture, mostly from the Atlantic. The snowline is remarkably high in northeast Siberia, remote from this source. Because of differential solar radiation receipt, local glaciers have a northward-facing tendency throughout the Arctic. This is weaker than in dry mid-latitudes but low sun angles enhance the effects of shading, compensating for the broader range of aspects (i.e.slope directions) illuminated in summer. Statistics from the World Glacier Inventory and other sources show that mass balance differences between slopes of different aspects give both more glaciers, and lower glaciers, facing the favoured direction: usually North. This is clear, for example, for local glaciers (and for all small glaciers) in central Spitsbergen and in Axel Heiberg Island. Wind effects (drifting snow to leeward slopes) are much less important, except in northwest Europe from Norway to Novaya Zemlya which is under the strong influence of westerly winds, greatest in the Polar and Sub-polar Urals. A thorough analysis is provided of aspect data for local glaciers within and near the Arctic Circle, and of variation in glacier mid-altitude with aspect and position. There is consistency between mean glacier aspect (in terms of numbers) and aspect with lowest glaciers, everywhere except in Wrangel Island.

Response of glaciers in northwestern North America to future climate change: an atmosphere/glacier hierarchical modeling approach

AbstractThe response of glaciers to changing climate is explored with an atmosphere/glacier hierarchical modeling approach, in which global simulations are downscaled with an Arctic MM5 regional model which provides temperature and precipitation inputs to a glacier mass-balance model. The mass balances of Hubbard and Bering Glaciers, south-central Alaska, USA, are simulated for October 1994–September 2004. The comparisons of the mass-balance simulations using dynamically-downscaled vs observed temperature and precipitation data are in reasonably good agreement, when calibration is used to minimize systematic biases in the MM5 downscalings. The responses of the Hubbard (a large tidewater glacier) and Bering (a large surge-type glacier) mass balances to the future climate scenario CCSM3 A1B, a ‘middle-of-the-road’ future climate in which fossil and non-fossil fuels are assumed to be used in balance, are also investigated for the period October 2010–September 2018. Hubbard and Bering Glaciers are projected to have increased accumulation, particularly on the upper glaciers, and greater ablation, particularly on the lower glaciers. The annual net balance for the entire Bering Glacier is projected to be significantly more negative, on average (–2.0ma–1w.e., compared to –1.3ma–1w.e. during the hindcast), and for the entire Hubbard Glacier somewhat less positive (0.3ma–1w.e. compared to 0.4 ma–1w.e. during the hindcast). The Hubbard Glacier mass balances include an estimated iceberg calving flux of 6.5 km3 a–1, which is assumed to remain constant.

Local aspect asymmetry of mountain glaciation: A global survey of consistency of favoured directions for glacier numbers and altitudes

Understanding aspect effects on present-day glaciers provides essential background to the palaeoclimatic interpretation of reconstructed former glaciers or glacial cirques. Several factors influencing glacier mass balance vary with slope aspect: these give more glaciers, lower glaciers and possibly larger glaciers on favoured aspects. Their effects can be measured by either vector analysis of the number of glaciers with each aspect or Fourier regression of glacier altitude or size against aspect. Both approaches are applied here to large data sets from the World Glacier Inventory, for all available regions. Favoured aspect is measured by direction of the resultant vector mean and by the direction of minimum glacier altitude, for 51 regions with a total of 66,084 glaciers. The two directions are broadly consistent in mid-latitudes and in the tropics, but large differences occur in the Arctic and Nepal. Poleward aspects dominate, especially in mid-latitudes: radiation receipt is the major factor, with strong wind effects limited to areas with only moderate relief. Strength of asymmetry is measured by vector strength (from glacier numbers) or by a combination of first Fourier coefficients (from glacier altitudes). Measuring two different facets of degree of asymmetry, they are essentially unrelated. The Fourier measure is the best estimate of local climatic asymmetry, as vector strength is more influenced by topography.

Hydrological controls on diurnal ice flow variability in valley glaciers

This paper uses a combination of field data and three‐dimensional modeling to investigate the spatial variability in basal conditions required to induce observed fluctuations in diurnal ice velocity at Haut Glacier d'Arolla, Switzerland. A network of surface velocity markers was observed at intervals of as little as four hours over diurnal cycles in both winter and late summer. Winter motion showed limited diurnal variability, presumably due to the absence of supraglacial meltwater inputs. By contrast, diurnal fluctuations in ice motion were recorded in summer across the lower and upper glacier. In the lower glacier, surface velocities were intimately linked to hydrological forcing in the vicinity of a subglacial channel. Previously observed diurnal excursions of meltwater away from the channel should reduce areas of basal drag adjacent to the channel thereby impacting on ice dynamics. Using a first‐order ice flow approximation, we investigated the distribution of basal shear traction adjacent to the channel necessary to replicate the observed surface velocity field during periods of rapid ice motion. The modeling suggests that the observed variations in diurnal velocity will only occur with extensive reductions in basal drag across a transverse zone of up to 560 m across, well beyond the immediate vicinity and previously observed extent of diurnal excursions of meltwater away from the subglacial channel.

Twentieth century thinning of Mendenhall Glacier, Alaska, and its relationship to climate, lake calving, and glacier run-off

Mendenhall Glacier is a dynamic maritime glacier in southeast Alaska that is undergoing substantial recession and thinning. The terminus has retreated 3 km during the 20th century and the lower part of the glacier has thinned 200 m or more since 1909. Glacier-wide volume loss between 1948 and 2000 is estimated at 5.5 km 3. Wastage has been the strongest in the glacier's lower reaches, but the glacier has also thinned at higher elevations. The shrinkage of Mendenhall Glacier appears to be due primarily to surface melting and secondarily to lake calving. The change in the average rate of thinning on the lower glacier, <1 m a −1 between 1948 and 1982 and >2 m a −1 since 1982, agrees qualitatively with observed warming trends in the region. Mean annual temperatures in Juneau decreased slightly from 1947 to 1976; they then began to increase, leading to an overall warming of ∼1.6 °C since 1943. Lake calving losses have periodically been a small but significant fraction of glacier ablation. The portion of the terminus that ends in the lake is becoming increasingly vulnerable to calving because of a deep pro-glacial lake basin. If current climatic trends persist, the glacier will continue to shrink and the terminus will recede onto land at a position about 500 m inland within one to two decades. The glacier and the meltwaters that flow from it are integral components of the Mendenhall Valley hydrologic system. Approximately 13% of the recent average annual discharge of the Mendenhall River is attributable to glacier shrinkage. Glacier melt contributes 50% of the total river discharge in summer.

Processes and rates of ice loss at the terminus of Tasman Glacier, New Zealand

The Tasman Glacier is the largest glacier in the Southern Alps of New Zealand. Despite a century of climate warming, the glacier has until recently remained at its “Little Ice Age” terminus position, although there has been substantial downwasting. The lower glacier is covered by an extensive debris layer, which has redistributed ice losses in both space and time compared to the conventional glacier response to climate change. Ice is lost at the terminus through melt of bare ice slopes, melt under the debris layer, and calving of ice into a newly established pro-glacial lake. Over the past ten years, the glacier has evolved from an ablation regime of melt under the debris and around sinkholes, to one where calving into the lake is of greater importance. This study investigates the processes and rates of ice loss at the terminus during the summer of 1995. Melt rates of ice are greatest on bare ice slopes, averaging 96 mm day −1 of ice depth over the summer period. Melt under the debris averaged 7 mm day −1, and calving accounted for a specific ice loss of 125 mm day −1. Overall, calving is the dominant form of ice loss at the terminus, accounting for 73% of the total. Melt under the debris layer accounted for 26% of terminus ablation, and melt on bare ice slopes just 1%, due to the relatively small area covered by these. Ice loss at the terminus is therefore largely de-coupled from climatic influences, and due mainly to the effect of the pro-glacial lake. However, when water loss from the whole ablation zone of the glacier is considered, calving accounts for just 4% of ice loss, with the largest portion of ice loss (80%) coming from melt on bare ice upstream of the debris cover. A total amount of 21 million m 3 a −1 of water is estimated to be supplied to Tasman River due to ice loss from the lowest 4 km 2 of glacier. 135 million m 3 a −1 of water is estimated to be lost below Ball Hut (approximately 10 km up-glacier), with 20% of this being calved from the terminus. This proportion will increase as the glacier terminus retreats up the valley, but at present rates, it will take over a century for the glacier to retreat to Ball Hut. Water stored as ice and then released from Tasman Glacier is resulting in a mean annual flow into Lake Pukaki of 4.3 m 3 s −1. The water released from all glaciers in the region due to glacier ice loss is 6% of the annual inflow to Lake Pukaki.

Glacial deposition along an ice‐contact slope: an example from the southern lake district, chile

Glacially derived sediments and structures vary systematically with topographic position along ice‐contact slopes near the margin of former temperate piedmont glaciers in the southern Lake District, Chile. Features along lower positions of the slopes include glaciolacustrine sediments and large‐scalethrusting. Middle slope features include low‐angle subglacial thrusting of thin slices of lacustrine sediment. Upper slope features include high‐angle thrusting, and lodgement and flow till. Locally, the same ordering of these features occurs in vertical sequence.A common theme that unifies the processes represented by these features is the distribution of hydrostatic pressure. Thicker ice (producing higher glacier overburden pressures) and aquicludes of fine‐grained sediments toward the center of the basin result in high hydrostatic pressures, whereas thin ice and porous out‐wash reduce these pressures at the top of the ice‐contact slopes.However, such a distribution cannot completely explain the observed vertical sequences; hence, local variations in hydrostatic pressure because of lithologic contrasts probably play a role. Nowhere along the ice‐contact slope are pervasively deformed glacial sediments observed; therefore they cannot be invoked to explain the low glacier profiles of these piedmont glacier lobes.

Ice flow and mass continuity of Shumsky Glacier in the Djungarski Alatau Range of Kazakhstan, Central Asia

The glaciological monitoring program on the Shumsky Glacier in the Djungarski Alatau Range of southeastern Kazakhstan has included measurements of horizontal surface ice flow velocity, net balance, and emergence velocity at a network of more than 200 stakes during 1967–1991, as well as mappings of the ice surface topography by double‐theodolite triangulation and determination of ice thickness and of bedrock topography by radio echo sounding in 1984. These observations are here evaluated together to deduce the long‐term average dynamic behavior of Shumsky Glacier. The glacier extends between 3100 and 4400 m with a total area of 3 km2 and length of nearly 4 km. Maximum surface velocity is 20 m yr−1 and maximum volume flux 9 × 105 m3 yr−1, located near the equilibrium line altitude around 3680 m. The ice‐volume‐equivalent net balance is +0.5 m yr−1 in the average over the accumulation area, changing to about −1.5 m yr−1 near the terminus. The submergent flow in the accumulation area changes to emergence of 1 m yr−1 in the lower glacier. The rate of ice thinning is less than 0.1 m yr−1 in the middle glacier, increases to 2.5 m yr−1 near the terminus, and averages 0.12 m yr−1 for the glacier as whole. In fact, the Shumsky glacier differs little from equilibrium, being in a more favorable location that the other glaciers of the Djungarski Alatau. However, trends toward slower ice flow, more negative net balance, and faster rate of ice thinning indicate response to a progressively adverse climatic environment.

Ice-flow and mass changes of Lewis Glacier, Mount Kenya, East Africa, 1986–90: observations and modeling

AbstractThe long-term monitoring of Lewis Glacier on Mount Kenya serves as a basis for the study of glacier evolution in response to climatic forcing through modeling of its ice flow and mass budget. Following up on an earlier modeling and prediction study to 1990, this paper examines the ice-mass and flow changes in relation to the net-balance conditions over 1986–90. A model experiment using as climatic forcing the observed 1978–86 vertical net-balance profile yielded a volume loss and slow down of ice flow more drastic than observed during 1986–90. The causes of this discrepancy were examined in successive model experiments. Realistic simulations of mass-budget and thickness changes over 1986–90 are obtained using as input the net-balance forcing for the same period rather than for the preceding 1978–86 interval, and approximate flow velocities. With the same net-balance forcing and a completely stagnant Lewis Glacier, the elimination of mass redistribution by ice flow acts to mitigate the loss of volume and thickness in the upper glacier, and to accentuate it in the lower glacier. Accordingly, the observed 1986–90 net-balance profile along with the 1990 ice-flow velocities provide suitable input for the modeling of Lewis Glacier changes to 1994. Under continuation of the 1986–90 climatic forcing, ice thinning ranging from less than 1 m in the upper glacier to more than 7 m in the lower glacier, and a total volume loss of order 57 × 104m3, are anticipated over the 1990–94 time interval.

Ice-flow and mass changes of Lewis Glacier, Mount Kenya, East Africa, 1986–90: observations and modeling

AbstractThe long-term monitoring of Lewis Glacier on Mount Kenya serves as a basis for the study of glacier evolution in response to climatic forcing through modeling of its ice flow and mass budget. Following up on an earlier modeling and prediction study to 1990, this paper examines the ice-mass and flow changes in relation to the net-balance conditions over 1986–90. A model experiment using as climatic forcing the observed 1978–86 vertical net-balance profile yielded a volume loss and slow down of ice flow more drastic than observed during 1986–90. The causes of this discrepancy were examined in successive model experiments. Realistic simulations of mass-budget and thickness changes over 1986–90 are obtained using as input the net-balance forcing for the same period rather than for the preceding 1978–86 interval, and approximate flow velocities. With the same net-balance forcing and a completely stagnant Lewis Glacier, the elimination of mass redistribution by ice flow acts to mitigate the loss of volume and thickness in the upper glacier, and to accentuate it in the lower glacier. Accordingly, the observed 1986–90 net-balance profile along with the 1990 ice-flow velocities provide suitable input for the modeling of Lewis Glacier changes to 1994. Under continuation of the 1986–90 climatic forcing, ice thinning ranging from less than 1 m in the upper glacier to more than 7 m in the lower glacier, and a total volume loss of order 57 × 104 m3, are anticipated over the 1990–94 time interval.

On the Relation of Net Balance, Ice Flow, and Surface Lowering of Lewis Glacier, Mount Kenya, East Africa, 1982–86

AbstractThe second 4 year phase of a long-term observation program on Lewis Glacier, Mount Kenya, was completed in March 1986. As for the 1978–82 interval, net-balance results at a stake network and repeated mapping of the ice-surface topography allowed assessment of the mass economy by both “glaciological” and “geodetic” methods.The general findings from the 1978–82 observations are confirmed: the vertical flow component is directed downward in the upper glacier, and upward in the lower glacier; surface lowering and negative net balance increase down-glacier; ice flow mitigates surface lowering by the negative net balance in the lower glacier, but enhances it in the upper glacier. However, the major difference between the 1982–86 and 1978–82 periods is the progressive slow-down of ice flow. This entails a reduction of mass redistribution, in consequence of which the surface lowering becomes increasingly dependent on the in-situ net balance. It is expected that this circumstance will simplify any inference on future glacier behavior.

On the Relation of Net Balance, Ice Flow, and Surface Lowering of Lewis Glacier, Mount Kenya, East Africa, 1982–86

AbstractThe second 4 year phase of a long-term observation program on Lewis Glacier, Mount Kenya, was completed in March 1986. As for the 1978–82 interval, net-balance results at a stake network and repeated mapping of the ice-surface topography allowed assessment of the mass economy by both “glaciological” and “geodetic” methods.The general findings from the 1978–82 observations are confirmed: the vertical flow component is directed downward in the upper glacier, and upward in the lower glacier; surface lowering and negative net balance increase down-glacier; ice flow mitigates surface lowering by the negative net balance in the lower glacier, but enhances it in the upper glacier. However, the major difference between the 1982–86 and 1978–82 periods is the progressive slow-down of ice flow. This entails a reduction of mass redistribution, in consequence of which the surface lowering becomes increasingly dependent on thein-situnet balance. It is expected that this circumstance will simplify any inference on future glacier behavior.

Continued Decrease of Ice-Flow Velocity at Lewis Glacier, Mount Kenya, East Africa

AbstractOur earlier monitoring program on Lewis Glacier, Mount Kenya, indicated a slow-down of the ice flow to January 1982, while based on the numerical modeling of the ice dynamics a further drastic decrease of the ice flow was predicted from the 1978 to the 1985 datum. This paper presents velocity measurements over the years 1982–83, 1984, and 1985. Changes of ice-flow conditions from 1978 to the mid 1980s are characterized by a velocity decrease by nearly half; a decrease of the maximum mass flux by more than half; a flattening and up-glacier shift of the velocity and mass-flux maxima; an up-glacier displacement of the transition between prevailingly longitudinal crevasses in the lower glacier and transverse crevasses in the upper glacier; and a terminus retreat by about 50 m. In consequence of the very weak ice flow remaining in Lewis Glacier, thinning and terminus retreat of the glacier are now primarily controlled by thein-situnet balance.

Continued Decrease of Ice-Flow Velocity at Lewis Glacier, Mount Kenya, East Africa

AbstractOur earlier monitoring program on Lewis Glacier, Mount Kenya, indicated a slow-down of the ice flow to January 1982, while based on the numerical modeling of the ice dynamics a further drastic decrease of the ice flow was predicted from the 1978 to the 1985 datum. This paper presents velocity measurements over the years 1982–83, 1984, and 1985. Changes of ice-flow conditions from 1978 to the mid 1980s are characterized by a velocity decrease by nearly half; a decrease of the maximum mass flux by more than half; a flattening and up-glacier shift of the velocity and mass-flux maxima; an up-glacier displacement of the transition between prevailingly longitudinal crevasses in the lower glacier and transverse crevasses in the upper glacier; and a terminus retreat by about 50 m. In consequence of the very weak ice flow remaining in Lewis Glacier, thinning and terminus retreat of the glacier are now primarily controlled by the in-situ net balance.

Glaciological and climatological investigations at Qamanârssûp sermia, West Greenland

As part of the GGU programme of investigations in connection with hydropower in West Greenland, glaciological and dimatological measurements were continued at Qamanârssâp sermia (inventory number 1CH21002) in 1982. The station was first established in late summer 1979 so that records for three complete summers 1980-1982 are now available. Brief reports on the work have been given by Olesen (1981) and Olesen &amp; Braithwaite (1982) while a more detailed field report and data summary for 1979-1981 is given by Braithwaite &amp; Olesen (1982). A similar report for 1982 is now in preparation. The sketch map in figure 44 shows the lower glacier together with locations of stakes and survey points. It should be noted that the three highest stakes, numbered 013, 015 and 016, are located off the map to the north-east of Stake 012.

Net Balance, Surface Lowering, and Ice-Flow Pattern in the Interior of Lewis Glacier, Mount Kenya, Kenya

AbstractObservations obtained in a long-term monitoring program on Lewis Glacier, Mount Kenya, include measurements of net balance and velocity at a stake network over the period 1978–82, and airborne mapping of the glacier surface topography at the beginning and end of this interval. Horizontal and vertical flow components and mass continuity are evaluated along the longitudinal axis of the glacier.The largest horizontal velocity at the surface is about 5 m a−1, while the submergent vertical velocity at the surface in the upper, and the emergent component in the lower glacier are of the order of 1–2 m a−1. Horizontal and vertical flow components in the interior of the glacier are calculated from the surface observations under plausible assumptions. Isotachs and streamlines plotted in a longitudinal–vertical cross-section permit the estimation of representative residence times of ice within Lewis Glacier. The largest values for the longest trajectories with submergence at the surface in the uppermost area of the glacier and emergence near the snout are of the order of a few centuries. However, such estimates are compromised, in particular, by the continuing non-equilibrium conditions of Lewis Glacier.Mass continuity is directly related to the vertical motion field. In the upper area of the glacier the submergence velocity exceeds the rise of glacier surface observed with respect to the stake network, while in the lower glacier the emergent flow component falls short of the local negative net balance. This differing behavior of altitudinal zones is consistent with the fact that actual lowering of the glacier surface topography documented by the repeated airborne mappings is larger than expected from the stake network in the upper but less in the lower glacier. This differing behavior of altitude zones appears mitigated by the tendency for confluence in the upper and diffluence in the lower glacier.

Net Balance, Surface Lowering, and Ice-Flow Pattern in the Interior of Lewis Glacier, Mount Kenya, Kenya

AbstractObservations obtained in a long-term monitoring program on Lewis Glacier, Mount Kenya, include measurements of net balance and velocity at a stake network over the period 1978–82, and airborne mapping of the glacier surface topography at the beginning and end of this interval. Horizontal and vertical flow components and mass continuity are evaluated along the longitudinal axis of the glacier.The largest horizontal velocity at the surface is about 5 m a−1, while the submergent vertical velocity at the surface in the upper, and the emergent component in the lower glacier are of the order of 1–2 m a−1. Horizontal and vertical flow components in the interior of the glacier are calculated from the surface observations under plausible assumptions. Isotachs and streamlines plotted in a longitudinal–vertical cross-section permit the estimation of representative residence times of ice within Lewis Glacier. The largest values for the longest trajectories with submergence at the surface in the uppermost area of the glacier and emergence near the snout are of the order of a few centuries. However, such estimates are compromised, in particular, by the continuing non-equilibrium conditions of Lewis Glacier.Mass continuity is directly related to the vertical motion field. In the upper area of the glacier the submergence velocity exceeds the rise of glacier surface observed with respect to the stake network, while in the lower glacier the emergent flow component falls short of the local negative net balance. This differing behavior of altitudinal zones is consistent with the fact that actual lowering of the glacier surface topography documented by the repeated airborne mappings is larger than expected from the stake network in the upper but less in the lower glacier. This differing behavior of altitude zones appears mitigated by the tendency for confluence in the upper and diffluence in the lower glacier.

Genesis of Englacial Debris within the Lower Glacier de Tsidjiore Nouve, Valais, Switzerland, as Revealed by Scanning Electron Microscopy

Genesis of Englacial Debris within the Lower Glacier de Tsidjiore Nouve, Valais, Switzerland, as Revealed by Scanning Electron Microscopy

A Numerical Model of Temperate Glacier Flow Applied to the Quiescent Phase of a Surge-Type Glacier

AbstractA time-dependent numerical model of temperate glacier flow without sliding is developed and applied to the quiescent phase of surge-type Variegated Glacier, Alaska. The model is based on a one-dimensional continuity equation but the transverse channel shape is explicitly included allowing the complex geometries of real glaciers to be modelled. Velocities and volume fluxes are calculated from the glacier geometry. Transverse stress is taken into account by shape factors which are fitted to measurements of geometry and velocity and are chosen to be insensitive to changes in geometry. Longitudinal stress gradients are taken into account by use of a large-scale surface slope. A Crank-Nicholson finite-difference approximation is used and it is unconditionally stable when a small contribution from the local slope is added to the average slope.Model parameters are fitted to extensive data collected on Variegated Glacier in 1973 and 1974. Predictions of the model over a four year interval agree well with field measurements. Predictions of the current quiescent phase (1965–84) indicate depth increases in the upper glacier of more than 75 m with a twenty-fold increase in the volume flux. During this interval the base shear stress increases 40% in the upper glacier and decreases 20% in the lower glacier. During the mid to late quiescent phase, ice motion becomes more important than mass balance in the redistribution of mass over the central region of the glacier. If normal flow were to persist, the predicted steady-state profile would be an average of 100 m deeper and 41% more voluminous than in 1973.The predicted base shear-stress gradient is never negative enough to satisfy Robin and Weertman’s (1973) condition for blockage of subglacial water flow. The annual rate of water production by dissipation of mechanical straining at the bed remains two orders of magnitude below that produced by summer surface melt. The predicted fractional increase in base stress during the quiescent phase is a maximum in the region believed to be the trigger zone of the surges.

Radiometric Chronology of Neh–nar Glacier, Kashmir

AbstractSurface and core samples of Neh–nar Glacier in the Kashmir Valley have been analysed for the radionuclides 32Si. 210Pb, 40K, and 137Cs. The lateral and vertical profiles (at an altitude of about 4 140 m) reveal:(1)32Si activity decreasing slowly from the accumulation zone to 4 050 m altitude and then abruptly towards the snout.(2)Five zones of alternating high and low 210Pb activity in the surface samples.(3)An horizon at between 2 and 3 m depth containing 210Pb activity above natural levels. This horizon is also associated with 137Cs and a maximum in total ß activity.The ice samples have been dated on the basis of a simplified two–component model, the “fresh“contribution determined by 2l0Pb and the old component by 32Si. The following conclusions can be drawn from these observations:(1)The model age of the snout ice is c. 850 years.(2)The average rate of ice movement in the lower glacier is about 2 m/year, which compares well with the annual movement rate of 2.65 m/year observed since 1974.