Small Cirque Research Articles

Glacial Sediment Production and Development of Hydro-Electric Power in Glacierized Areas

This paper discusses the results of a sediment-monitoring programme carried out in connection with hydro-electric power development plans in the river basins surrounding the Jostedalsbreen ice cap in Norway. Whereas the highest suspended-sediment transport rates occur during years with several flash-flood events, the bed load is more dependent upon the duration of large magnitude flood events. Bed-load transport has been obtained from annual measurements of deltaic growth in small lakes at the front of glaciers. During the years 1968–86, the mean ratio of bed load to total load amounted to 0.30–0.50% of the total load, but in years with large magnitude floods this ratio decreased. The mean annual suspended sediment yield of Norwegian glaciers ranges from 100 tonnes km2 a−1 to 1300 tonnes km2 a−1. Valley glaciers cause the highest erosion rates, with the exception of the small cirque glacier, Trollbergdalsbreen, which is thought to be a soft bed glacier. The investigation programme undertaken involved monitoring the volume of suspended sediments, together with the size distribution, mineralogy and shape of grains. In general, the valley glaciers supply more sand than the smaller cirque glaciers, whereas particles in the fine sand and silt-size ranges in almost all of the glaciers are angular in shape. Methods of comparing the abrasive capacity of the sediment load at various intakes in a power plant are discussed. Long-term sediment supply from the glaciers was investigated by studies of varves and rythmites in sediment cores from glacier-fed lakes.

Glacial Sediment Production and Development of Hydro-Electric Power in Glacierized Areas

This paper discusses the results of a sediment-monitoring programme carried out in connection with hydro-electric power development plans in the river basins surrounding the Jostedalsbreen ice cap in Norway. Whereas the highest suspended-sediment transport rates occur during years with several flash-flood events, the bed load is more dependent upon the duration of large magnitude flood events. Bed-load transport has been obtained from annual measurements of deltaic growth in small lakes at the front of glaciers. During the years 1968–86, the mean ratio of bed load to total load amounted to 0.30–0.50% of the total load, but in years with large magnitude floods this ratio decreased. The mean annual suspended sediment yield of Norwegian glaciers ranges from 100 tonnes km2 a−1 to 1300 tonnes km2 a−1. Valley glaciers cause the highest erosion rates, with the exception of the small cirque glacier, Trollbergdalsbreen, which is thought to be a soft bed glacier. The investigation programme undertaken involved monitoring the volume of suspended sediments, together with the size distribution, mineralogy and shape of grains. In general, the valley glaciers supply more sand than the smaller cirque glaciers, whereas particles in the fine sand and silt-size ranges in almost all of the glaciers are angular in shape. Methods of comparing the abrasive capacity of the sediment load at various intakes in a power plant are discussed. Long-term sediment supply from the glaciers was investigated by studies of varves and rythmites in sediment cores from glacier-fed lakes.

Forty Years of Mass-Balance Observations on Glacier de Sarennes, French Alps

Located south of Grenoble, in the French Alps, Glacier de Sarennes is a small cirque glacier whose mass balance has been measured since 1948.Field measurements are made after the accumulation period (from October to May) and during the ablation period (from June to September). The main variables for snow are depth, density, and water equivalent for accumulation, together with ice depth and water equivalent for ablation which are used to calculate mass balance and regime. We present an example of the data collected on the glacier during the 1986–87 season, the evolution of the mass balance during the summer of 1987, and the main variables followed during the 40 years of observation, 1948–88. Mass balance, accumulation, and ablation are directly related to precipitation and temperature. Glacier de Sarennes is a simple glacier which has no tongue and no ice movement, and is like a gigantic rain gauge. The evolution of its mass balance is simply related to the meteorological variables of the year. For more significant and complex glaciers, it is necessary to take account of past as well as present meteorological variables.

Single Folds at the Margins of Dry-Based Glaciers as Indicators of a Glacial Advance

Single folds which enclose the marginal “inner moraines” of the dry-based Jeremy Sykes and Alberich Glaciers, Dry Valleys area, Antarctica, are deduced to have formed during an advance of the margins of these glaciers where the thin, stiff marginal ice has obstructed glacier flow and expansion.It is suggested that the occurrence of this type of fold can be an indicator of an advance in many fully dry-based glaciers. On Alberich Glacier, the fold and associated margin forms suggest that a sequence of margin forms evolves when a small cirque glacier expands outward from a sloping ramp front to a tongue terminating in a calving ice cliff.

Forty Years of Mass-Balance Observations on Glacier de Sarennes, French Alps

Located south of Grenoble, in the French Alps, Glacier de Sarennes is a small cirque glacier whose mass balance has been measured since 1948. Field measurements are made after the accumulation period (from October to May) and during the ablation period (from June to September). The main variables for snow are depth, density, and water equivalent for accumulation, together with ice depth and water equivalent for ablation which are used to calculate mass balance and regime. We present an example of the data collected on the glacier during the 1986–87 season, the evolution of the mass balance during the summer of 1987, and the main variables followed during the 40 years of observation, 1948–88. Mass balance, accumulation, and ablation are directly related to precipitation and temperature. Glacier de Sarennes is a simple glacier which has no tongue and no ice movement, and is like a gigantic rain gauge. The evolution of its mass balance is simply related to the meteorological variables of the year. For more significant and complex glaciers, it is necessary to take account of past as well as present meteorological variables.

Mass Balance of Four Cirque Glaciers in the Torngat Mountains of Northern Labrador, Canada

AbstractThe net mass balance of four small cirque glaciers (0.7–1.4 km2) in the Torngat Mountains of northern Labrador was measured for 1981–84, allowing three complete mass-balance years to be calculated. The two largest glaciers experienced positive mass-balance conditions in 1982 while all the glaciers were negative in 1983. The temporal pattern relates directly to general climatic conditions, in particular winter snowfall. Spatial variations of mass balance on the glaciers are the result of several factors including altitude, extent of supraglacial debris cover, slope, proximity to side and backwalls of the enclosing cirque, and the height of the backwall above the ice surface. Abraham Glacier, the smallest studied and with consistently the largest negative mass balance (–1.28 m in 1983), re-advanced an average of 1.2 m each year between 1981 and 1984. Mean equilibrium-line altitude (ELA) for the four glaciers is 1050 m, varying substantially from one glacier to another (+240 to –140 m) and from year to year (+60 to –30 m).

Mass Balance of Four Cirque Glaciers in the Torngat Mountains of Northern Labrador, Canada

Abstract The net mass balance of four small cirque glaciers (0.7–1.4 km2) in the Torngat Mountains of northern Labrador was measured for 1981–84, allowing three complete mass-balance years to be calculated. The two largest glaciers experienced positive mass-balance conditions in 1982 while all the glaciers were negative in 1983. The temporal pattern relates directly to general climatic conditions, in particular winter snowfall. Spatial variations of mass balance on the glaciers are the result of several factors including altitude, extent of supraglacial debris cover, slope, proximity to side and backwalls of the enclosing cirque, and the height of the backwall above the ice surface. Abraham Glacier, the smallest studied and with consistently the largest negative mass balance (–1.28 m in 1983), re-advanced an average of 1.2 m each year between 1981 and 1984. Mean equilibrium-line altitude (ELA) for the four glaciers is 1050 m, varying substantially from one glacier to another (+240 to –140 m) and from year to year (+60 to –30 m).

Sediment production and transport in a proglacial stream: Hilda Glacier, Alberta, Canada

Hilda Glacier, a small cirque glacier in the Canadian Rocky Mountains, yields two principal types of sediment: ablation till, deficient in fine material and produced by rockfalls and avalanches falling on to the glacier surface, and basal lodgement till, rich in fines and formed mainly by subglacial erosion. Recent recession from its Neoglacial maximum has exposed large areas of basal till with thin veneers of ablation till which, when combined with present subglacial and supraglacial debris, provide abundant material for erosion and transport by the mcltwatcr stream. Sediment transport measurements over two summers (1977–1978) showed that bed load and suspended load occur in approximately equal proportions and that dissolved loads are minor. Local source variations, especially bank slumps, are a major cause of scatter in sediment rating curves. Suspended‐sediment concentrations are greater early in the melt season due to availability of loose sediment produced by freezing and thawing. Other contributors to scatter in suspended‐sediment rating curves include rain showers and diurnal hysteretic effects. Although the distinction between bed load and suspended load is never sharp, available data suggest that the sand/ gravel grain‐size boundary (‐1ø) approximates the suspendcd‐load/bed‐load division for characteristic Hilda flows transporting gravel. This approximation, combined with till grain‐size analyses, suspended‐sediment measurements, and spatial distributions of till types, leads to the following computations of fluvial sediment sources: for suspended load ‐ 6% supraglacial, 47% subglacial, 47% channel banks; for bed load ‐ 46% supraglacial, 27% each subglacial and channel banks. Supraglacial debris provides only about one‐fourth of all fluvial sediment, but nearly half of the bed load.

Geometry of Former Subglacial Water Channels and Cavities

AbstractThe spatial pattern of the formerly active processes of water flow, cavitation, abrasion, dissolution, and precipitation at the base of a small cirque glacier has been reconstructed by detailed mapping of surficial features on recently deglaciated limestone bedrock near the glacier terminus. Our interpretation of these features, which reflect basal conditions averaged over a period of several or several tens of years, leads us to the following conclusions:1.A nearly continuous, non-arborescent network of cavities and incised channels existed and probably acted as the primary drainage of melt waters. This network evolved through time as many channels were filled, perhaps intermittently, by basal ice.2.At least 20% of the glacier sole was separated from the bed by water-filled cavities. The rest of the glacier–rock interface characteristically comprises a very thin water film.3.Abrasion was locally intensified, relative to chemical alteration, in 5–10 m wide zones paralleling the ice-flow direction, perhaps as a result of locally enhanced sheet flow of subglacial water.

Geometry of Former Subglacial Water Channels and Cavities

AbstractThe spatial pattern of the formerly active processes of water flow, cavitation, abrasion, dissolution, and precipitation at the base of a small cirque glacier has been reconstructed by detailed mapping of surficial features on recently deglaciated limestone bedrock near the glacier terminus. Our interpretation of these features, which reflect basal conditions averaged over a period of several or several tens of years, leads us to the following conclusions: 1.A nearly continuous, non-arborescent network of cavities and incised channels existed and probably acted as the primary drainage of melt waters. This network evolved through time as many channels were filled, perhaps intermittently, by basal ice.2.At least 20% of the glacier sole was separated from the bed by water-filled cavities. The rest of the glacier–rock interface characteristically comprises a very thin water film.3.Abrasion was locally intensified, relative to chemical alteration, in 5–10 m wide zones paralleling the ice-flow direction, perhaps as a result of locally enhanced sheet flow of subglacial water.

Ivory Glacier, New Zealand, an I.H.D. Representative Basin Study

AbstractMass, water, and energy balances were measured lit the Ivory Glacier, South Island, New Zealand from 1969 to 1975 as part of an I.H.D. programme of representative basin studies. Ivory Glacier is a small cirque glacier within the high-precipitation maritime environment of Westland and was chosen initially for convenience of study rather than representativeness. Mass-balance investigations included a detailed study of the sampling efficiency of a pole network. Annual mass balance was consistently negative during the study period. The run-off pattern was dominated by rain. The estimated annual mean precipitation is 9630 mm for 1971-75. Snow represents about 25% of annual precipitation. Melt contributed 21% of run-off including 9% contributed by melt of perennial snow and ice. The relative contributions of different fluxes to the energy balance during summer are: net radiation 52%, sensible heat 29%, and latent heat 17%. Heat content of precipitation contributes significantly to the energy balance during individual rain-storms and is probably significant during periods of high precipitation in spring and autumn. Climatic characteristics and behaviour of Ivory Glacier appear to follow regional trends in the Southern Alps and the glacier is considered to be reasonably representative.

Source, Transportation and Deposition of Debris on Arapaho Glacier, Front Range, Colorado, U.S.A.

This study was undertaken to determine the sources of debris and methods of transportation and deposition in and on a small cirque glacier. Data were collected on the amount of debris, stone roundness, the presence of striations and polish, and till fabric. Lichenometry gave relative ages of the tills, and suggests that the Gannett Peak till is of at least three ages and probably overlies Audubon till.Debris originating from subglacial erosion can be differentiated from that from rockfall or avalanches on stone roundness, polish and striations. A maximum of 70% of the present glacial load derives from subglacial erosion, as compared to 88% during the Gannett Peak stade. Rockfall rates are 35-50 m3/year at present and were 290–485 m3/year during the Gannett Peak stade. Data on present-day processes and on the volume and age of Gannett Peak moraines can be used to make comparisons on present and past rates of denudation. The denudation rate in the cirque at present is 95–165 mm/1 000 year; in the past it was 4 920-8 160 mm/ 1 000 year. The denudation rate and the glacial effects on debris are comparable to rates from other glacial areas and effects on debris carried by valley glaciers and continental ice sheets.

Source, Transportation and Deposition of Debris on Arapaho Glacier, Front Range, Colorado, U.S.A.

This study was undertaken to determine the sources of debris and methods of transportation and deposition in and on a small cirque glacier. Data were collected on the amount of debris, stone roundness, the presence of striations and polish, and till fabric. Lichenometry gave relative ages of the tills, and suggests that the Gannett Peak till is of at least three ages and probably overlies Audubon till.Debris originating from subglacial erosion can be differentiated from that from rockfall or avalanches on stone roundness, polish and striations. A maximum of 70% of the present glacial load derives from subglacial erosion, as compared to 88% during the Gannett Peak stade. Rockfall rates are 35-50 m3/year at present and were 290–485 m3/year during the Gannett Peak stade. Data on present-day processes and on the volume and age of Gannett Peak moraines can be used to make comparisons on present and past rates of denudation. The denudation rate in the cirque at present is 95–165 mm/1 000 year; in the past it was 4 920-8 160 mm/ 1 000 year. The denudation rate and the glacial effects on debris are comparable to rates from other glacial areas and effects on debris carried by valley glaciers and continental ice sheets.

Traces d'activité glaciaire dans les montagnes de Grèce centrale

Abstract. — Some small cirques were carved in the moutains of Central Greece (38°40'N) during the late quaternary periods. They are generally oriented north-eastwards and their lower altitudinal limit during Würm varies between 1 700 and 2 200 m from west to east on a distance of 32 km ; the only exception is introduced by one rock glacier developed in Mount Parnassus.

Trend Surface Mapping of Cirque Floor Levels

THE spatial distribution of the height of cirques might be regarded as indicating areal variations in the climatic conditions required for their formation1. Contemporary cirques, especially small cirques peripheral to glaciated areas, have been observed close to the level of the snowline2, but the level of cirque excavation in any one area is related more to a composite Pleistocene regional snowline than to a snowline at any specific glacial age3–5. Thus although the altitude of cirque floors is governed broadly by the height of the regional or climatic snowline, controlled entirely by the climatic gradient6,7, local variations in altitude will reflect other locally operative factors favouring enlargement, survival or destruction of cirques.

Further Observations on the Glaciers of the Ruwenzori

Intermittent observations on the behaviour of 4 of the main glaciers on the Uganda slopes of the Ruwenzori are reported. While this does not represent a large sample of the 37 glaciers of the massif, it probably shows clearly the pattern of change at least on the eastern slopes. The glaciers examined were relatively active valley tongues whereas many of the so-called glaciers of the range are either summit icecaps or small cirque glaciers. Due to the smallness and steepness of the glaciers examined, they probably react rapidly to mass- budget changes. Such a supposition finds confirmation in the similarity of their behaviour. Over the period of observations rapid retreat is evident; this has been neither constant nor continuous. Speculations con- cerning the significance of these variations are offered.

Further Observations on the Glaciers of the Ruwenzori

Intermittent observations on the behaviour of 4 of the main glaciers on the Uganda slopes of the Ruwenzori are reported. While this does not represent a large sample of the 37 glaciers of the massif, it probably shows clearly the pattern of change at least on the eastern slopes. The glaciers examined were relatively active valley tongues whereas many of the so-called glaciers of the range are either summit icecaps or small cirque glaciers. Due to the smallness and steepness of the glaciers examined, they probably react rapidly to mass-budget changes. Such a supposition finds confirmation in the similarity of their behaviour. Over the period of observations rapid retreat is evident; this has been neither constant nor continuous. Speculations concerning the significance of these variations are offered.

Quaternary deposits in the Frederikshåb district, South-West Greenland

The Quaternary geology of an area of approximately 3000 km2 in the vicinity of Frederikshåb has been mapped during the summers 1964-1966. In this part of Greenland the unglaciated land between the outer coast and the margin of the Inland Ice is 40-70 km wide. The ice-free area is mostly a plateau at about 1000 m with isolated tops reaching 1600 m, and is deeply dissected by fjords some of which reach the ice margin. Small cirque glaciers occur in the higher parts of the plateau.

Snow Action on Mount Twynam, Snowy Mountains, Australia

Abstract A commonly accepted distinction between snow-patches and glaciers is the slow mass movement of the latter with consequent abrasion of stones and rock surfaces. However, the observations of some workers do not support this distinction. The present study, in a snow-patch area on Mount Twynam in the Snowy Mountains (Australia), presents positive evidence of slow mass sliding of snow, causing transport, abrasion and detachment of stones and abrasion of the bedrock surface. Consequently, no sharp separation is possible between the erosional effects of snow-patches and small cirque glaciers. In areas such as the Snowy Mountains the relative importance of glacial and nivational processes becomes more difficult to evaluate.

Snow Action on Mount Twynam, Snowy Mountains, Australia

AbstractA commonly accepted distinction between snow-patches and glaciers is the slow mass movement of the latter with consequent abrasion of stones and rock surfaces. However, the observations of some workers do not support this distinction. The present study, in a snow-patch area on Mount Twynam in the Snowy Mountains (Australia), presents positive evidence of slow mass sliding of snow, causing transport, abrasion and detachment of stones and abrasion of the bedrock surface. Consequently, no sharp separation is possible between the erosional effects of snow-patches and small cirque glaciers. In areas such as the Snowy Mountains the relative importance of glacial and nivational processes becomes more difficult to evaluate.