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Calving retreat and proglacial lake growth at Hooker Glacier, Southern Alps, New Zealand
Abstract
Hooker Glacier in the central Southern Alps of New Zealand has undergone significant downwasting and recession (∼2.14km) during the last two centuries. High retreat rates (51ma-1 1986-2001, 43ma-1 2001-2011) have produced a large (1.22km2) proglacial lake. We present a retreat scenario for Hooker Glacier. A retreat scenario predicts that the glacier terminus will stabilise >3km up-valley of the current lake outlet after 2028 when ice velocity equals calving rate. © 2013 The Authors. New Zealand Geographer
... The five lake-terminating glaciers shown in Fig. 4 have experienced substantial terminal zone thinning (shown here and in Bolch et al., 2011;Nuimura et al., 2012), flow acceleration (Fig. 4) and increased longitudinal strain (Table 1), and sustained or accelerating ice front retreat rates over the last 26 years (Fig. 6). We therefore suggest that the set of processes incorporated into the model of Benn et al. (2007) are in operation on some Himalayan lake-terminating glaciers, as has been inferred on laketerminating glaciers in other glacierised regions (Muto and Furaya, 2013;Robertson et al., 2013;Sakakibara and Sugiyama, 2014;Chernos et al., 2016). The variability in cumulative glacier front retreat and glacier front retreat rates we show in Fig. 6, and the broad range of mass balance estimates generated for lake-terminating glaciers by King et al. (2017), likely reflects the variable response of glaciers depending on their topographic setting (i.e. ...
The impact of glacial lake development on the evolution of glaciers in the Himalaya is poorly quantified, despite the increasing prevalence of supraglacial and proglacial water bodies throughout the region. In this study we examine changes in the geometry, velocity and surface elevation of nine lake-terminating and nine land-terminating glaciers in the Everest region of the central Himalaya over the time period 2000 to 2015. The land-terminating glaciers we examined all decelerated (mean velocity change of −0.16 to −5.60 m a‾¹ for different glaciers), thinned most in their middle reaches, and developed a more gently sloping surface (−0.02 to −0.37° change) down-glacier over the period 2000–2015. The lake-terminating glaciers we examined all retreated (0.46 to 1.42 km), became steeper (0.04 to 8.68° change), and showed maximum thinning towards their termini, but differed in terms of their dynamics, with one group of glaciers accelerating (mean speed-up of 0.18 to 8.04 m a‾¹) and the other decelerating (mean slow-down of −0.36 m a−1 to −8.68 m a‾¹). We suggest that these two scenarios of glacier evolution each represent a different phase of glacial lake expansion; one that is accompanied by increasingly dynamic glacier behaviour and retreat, and a phase where glacial lakes have little impact on glacier behaviour that may precede or follow the phase of active retreat. Our observations are important because they quantify the interaction of glacial lake expansion with glacier ice mass loss, and show that increased glacier recession should be expected where a glacial lake has begun to develop.
... Hooker Lake had a greater than predicted volume in 1995 and 2002 but not in 2009. Comparison of glacier terminus position and bathymetric maps in Robertson et al. (2013) indicates that in 1995, the glacier terminus was retreating out of a deep basin. By 2002, the glacier had retreated to the position of a deep notch in the bed profile. ...
Supraglacial, moraine-dammed and ice-dammed lakes represent a potential glacial lake outburst
flood (GLOF) threat to downstream communities in many mountain regions. This has motivated the development of empirical relationships to predict lake volume given a measurement of lake surface area obtained from satellite imagery. Such relationships are based on the notion that lake depth, area and volume scale predictably. We critically evaluate the performance of these existing empirical relationships by examining a global database of glacial lake depths, areas and volumes. Results show that lake area and depth are not always well correlated (r2 = 0.38)and that although lake volume and area are well correlated (r2 = 0.91), and indeed are auto-correlated, there are distinct outliers in the data set. These outliers represent situations where it may not be appropriate to apply existing empirical relationships to predict lake volume and include growing supraglacial lakes, glaciers that recede into basins with complex overdeepened morphologies or that have been deepened by intense erosion and lakes formed where glaciers advance across and block a main trunk valley. We use the compiled data set to develop a conceptual model of how the volumes of supraglacial ponds and lakes, moraine-dammed lakes and ice-dammed lakes should be expected to evolve with increasing area. Although a large amount of bathymetric data exist for moraine-dammed and ice-dammed lakes, we suggest that further measurements of growing supraglacial ponds
and lakes are needed to better understand their development.
... Hooker Lake had a greater than predicted volume in 1995 and 2002, but not in 2009. Comparison of 5 glacier terminus position and bathymetric maps in Robertson et al. (2013) indicates that in 1995, the glacier terminus was retreating out of a deep basin. By 2002, the glacier had retreated to the position of a deep notch in the bed profile. ...
Supraglacial, moraine-dammed and ice-dammed lakes represent a potential glacial lake outburst flood (GLOF) threat to downstream communities in many mountain regions. This has motivated the development of empirical relationships to predict lake volume given a measurement of lake surface area obtained from satellite imagery. Such relationships are based on the notion that lake depth, area and volume scale predictably. We critically evaluate the performance of these existing empirical relationships by examining a global database of measured glacial lake depths, areas and volumes. Results show that lake area and depth are not always well correlated (r2 = 0.38), and that although lake volume and area are well correlated (r2 = 0.91), there are distinct outliers in the dataset. These outliers represent situations where it may not be appropriate to apply existing empirical relationships to predict lake volume, and include growing supraglacial lakes, glaciers that recede into basins with complex overdeepened morphologies or that have been deepened by intense erosion, and lakes formed where glaciers advance across and block a main trunk valley. We use the compiled dataset to develop a conceptual model of how the volumes of supraglacial ponds and lakes, moraine-dammed lakes and ice-dammed lakes should be expected to evolve with increasing area. Although a large amount of bathymetric data exist for moraine-dammed and ice-dammed lakes, we suggest that further measurements of growing supraglacial ponds and lakes are needed to better understand their development.
Links between proglacial lakes and glacier dynamics are poorly understood but are necessary to predict how mountain glaciers will react to a warmer, wetter climate, where such lakes are expected to increase both in number and volume. Here, we examine a long-term (~120 year) record of terminus retreat, thinning and surface velocities from in-situ and remote sensing observations at the terminus of Kaskawulsh Glacier, Yukon, Canada, and determine the impact of a local proglacial hydrological reorganisation on glacier dynamics. After an initial deceleration during the late 1990s, terminus velocities increased at a rate of 3 m a ⁻² from 2000–12, while proglacial Slims Lake area increased simultaneously. The rapid drainage of the lake in May 2016 substantially altered the velocity profile, decreasing annual velocities by 48% within 3 km of the terminus between 2015 and 2021, at an average rate of ~ 12.5 m a ⁻² . A key cause of the rapid drop in glacier motion was a reduction in flotation of the lower part of the glacier terminus after lake drainage. This has important implications for glacier dynamics and provides one of the first assessments of the impacts of a rapid proglacial lake drainage event on local terminus velocities.
The objective of
this project is to establish an updated glacier inventory for New Zealand. We have used Landsat 8 OLI satellite imagery from February and March 2016 for delineating clean glaciers using a semiautomatic band ratio method and debris-covered glaciers using a maximum likelihood classification. The outlines have been checked against Sentinel-2 MSI data, which have a higher resolution. Manual post processing was necessary due to misclassifications (e.g. lakes, clouds), mapping in shadowed areas, and combining the clean and debris-covered parts into single glaciers. New Zealand glaciers cover an area of 794 ± 34 km2 in 2016 with a debris-covered area of 10%. Of
the 2918 glaciers, seven glaciers are >10 km2 while 71% is <0.1 km2. The debris cover on those largest glaciers is >40%. Only 15 glaciers are located on the North Island. For a selection of glaciers, we were able to calculate the area reduction between the 1978 and 2016 inventories.
The Southern Alps of New Zealand are host to over 3000 glaciers that owe their existence to high amounts of precipitation ranging from 3 to 10m. Lake Tekapo and Lake Pukaki are both utilized for hydropower. The reduction of glacier area in the region will reduce summer runoff into Lake Pukaki and this hydropower system. Mueller Glacier drains the eastern side of Mount Sefton, Mount Thompson, and Mount Isabel. Hooker Glacier is a low-gradient glacier, which helps reduce its overall velocity and a debris-covered ablation zone reducing ablation, both factors increasing response time to climate change. Murchison Glacier drains south in the next valley east of Tasman Glacier and terminates in a lake that is rapidly developing as the glacier retreats. The Douglas Neve flows down the steep side of Mount Scott and Seddon Peak. Fox Glacier is well known for its rapid response to climate changes leading to substantial advances within limited time periods.
Glaciers and ice sheets are important constituents of the Earth's land surface. Current worldwide retreat of glaciers has implications for the environment and for civilisation. There are a range of geomorphic changes occurring in cold environments and it is anticipated that these will be accentuated as a consequence of climate change. In particular, the number and size of proglacial lakes is currently increasing as a result of deglaciation and their significance for the physical environment and for society is becoming increasingly apparent. This article provides an overview of the major interdependent relationships between climate change, glaciers and proglacial lake development. In particular, it describes the key processes and impacts associated with proglacial lake evolution with reference to examples drawn from the European Alps, North America, the Himalayas, the Andes, Greenland, New Zealand and Iceland.
Flood and debris-flow hazards at Grubengletscher near Saas Balen in the Saas Valley, Valais, Swiss Alps, result from the formation and growth of several lakes at the glacier margin and within the surrounding permafrost. In order to prevent damage related to such hazards, systematic investigations were carried out and practical measures taken. The evolution of the polythermal glacier, the creeping permafrost within the large adjacent rock glacier and the development of the various periglacial lakes were monitored and documented for the last 25 years by photogrammetric analysis of annually flown high-resolution aerial photographs. Seismic refraction, d.c. resistivity and gravimetry soundings were performed together with hydrological tracer experiments to determine the structure and stability of a moraine dam at a proglacial lake. The results indicate a maximum moraine thickness of > 100 m; extremely high porosity and even ground caverns near the surface may have resulted from degradation of sub- and periglacial permafrost following 19th/20thcentury retreat of the partially cold glacier tongue. The safety and retention capacity of the proglacial lake were enhanced by deepening and reinforcing the outlet structure on top of the moraine complex. The water level of an ice-dammed lake was lowered and a thermokarst lake artficially drained.
The onset of rapid calving in the early 1980s initiated retreat at ≤440 m a-1. The 1992-93 calving rate (vc) is estimated to be 60 m a-1 in a mean water depth (hw) of 67 m. A vc/hw relationship for fresh water based on 14 sites around the world, including seven deep-water sites, confirms both the linear dependency of vc on hw and the contrast between calving rates in tide water and fresh water. As yet, no physical explanation for this contrast exists, but differences in subaqueous melt rates, longitudinal strain rates and crevassing may provide a partial explanation. -Authors
Tasman Glacier is the largest glacier in the New Zealand Southern Alps. Despite a century of warming and down-wastage, the glacier remained at its Little Ice Age terminus until the late 20th century. Since then, a proglacial lake formed, and comparatively rapid calving retreat has been initiated. In this paper we use sequential satellite imagery to document terminus retreat, growth of supraglacial ponds, and expansion of the proglacial Tasman Lake. Between 2000 and 2008, the glacier terminus receded a maximum of c. 3.7 km on the western margin, and the ice-contact Tasman Lake expanded concomitantly. This northward expansion of Tasman Lake up-valley proceeded at a mean annual rate of 0.34 x 10(6) m(2) a(-1) 2000-2008, attaining a surface area of 5.96 x 10(6) m(2) in May 2008, with a maximum depth of c. 240 m. Terminus retreat rates (U(r)) vary in both space and time, with two distinct periods of calving retreat identified during the study period: 2000-2006 (mean U(r) = 54 m a(-1)) and 2007-2008 (mean U(r) = 144 m a-1). Terminus retreat can also be categorized into two distinct zones of activity: (1) the main ice cliff (MIC), and (2) the eastern embayment ice cliff (EEIC). During the period 2000-2006, and between 2006 and 2008 for the EEIC, the controlling process of ice loss at the terminus was iceberg calving resulting from thermal undercutting. In contrast, the retreat of the MIC between 2006 and 2008 was controlled by buoyancy-driven iceberg calving caused by decreasing overburden pressure as a result of supraglacial pond growth, increased water depth, and rainfall. The presence of a >130-m-long subaqueous ice ramp projecting from the terminal ice cliff into the lake suggests complex interactions between the glacier and ice-contact lake during the 8-10 km of possible future calving retreat.
The subaqueous margins of calving glaciers have the potential to make significant contributions to glacier mass loss. However, to date, very little is known about the morphology and development of subaqueous margins. A unique combination of sub-bottom profile and bathymetric data collected between 2008 and 2010 in proglacial lakes at Mueller, Hooker and Tasman glaciers in New Zealand's Southern Alps reveal subaqueous ice ramps extending up to 510 m from the terminus of each glacier. Ice ramp surfaces are undulating and covered with a thick layer (up to 10 m) of unsorted sediment derived from supraglacial and englacial debris, lateral moraines and deltaic deposits. A cyclic calving pattern, relatively stable lake level and the debris cover appear to control the development and maintenance of these ice ramps. High subaerial retreat rates generally correspond to high subaqueous calving rates, although the highest subaerial retreat rates are not associated with the largest ice ramp. Debris mantling the subaqueous ice ramp surfaces insulates the ice from melting and also reduces buoyant forces acting on the terminus. Comparisons with previous studies show that the ice ramps evolve over time with changes in glacier dynamics and water-body properties.
Coverage of ice velocities in the central part of the Southern Alps, New Zealand, is obtained from feature tracking using repeat optical imagery in 2002 and 2006. Precise orthorectification, co-registration and correlation is carried out using the freely available software COSI-Corr. This analysis, combined with short times between image acquisitions, has enabled velocities to be captured even in the accumulation areas, where velocities are lowest and surface features ephemeral. The results indicate large velocities for mountain glaciers (i.e. up to ~5 m d–1) as well as dynamic changes in some glaciers that have occurred between 2002 and 2006. For the steep and more responsive Fox and Franz Josef Glaciers the speed increased at the glacier snout during the advance period, while the low-angled and debris-covered Tasman Glacier showed no measurable velocity change. Velocity increases on the steeper glaciers are the result of an observed thickening and steepening of the glacier tongues as they moved from a retreat phase in 2002 to an advance phase in 2006. This contrasting behaviour is consistent with historic terminus position changes. The steeper glaciers have undergone several advance/retreat cycles during the observation period (1894 to present), while the low-angled glacier showed little terminus response until retreat resulting from the accelerating growth of a proglacial lake commenced in 1983.
Glacier lakes are a common phenomenon in high mountain areas. Outbursts from glacier lakes have repeatedly caused the loss of human lives as well as severe damage to local infrastructure. In several high mountain ranges around the world, a grave uncertainty about the hazard potential of glacier lakes still exists, especially with respect to the effects of accelerating rates of glacier retreat as a consequence of atmospheric warming. Area-wide detection and modeling of glacier lake hazard potentials is, therefore, a major challenge. In this study, an approach integrating three scale levels allows for the progressive focus on critical glacier lakes. Remote sensing methods for application in glacier lake hazard assessment are presented, and include channel indexing, data fusion, and change detection. Each method matches the requirements of a certain scale level. For estimating potential disaster amplitudes, assessments must be made of maximum discharge and runout distance of outbursts floods and debris flows. Existing empirical relations are evaluated and complementary ones as derived from available data are proposed. Tests with observations from a recent outburst event from a moraine-dammed lake in the Swiss Alps show the basic applicability of the proposed techniques and the usefulness of empirical relations for first hazard assessments. In particular, the observed runout distance of the debris flow resulting from the outburst does not exceed the empirically estimated maximum runout distance. A list of decision criteria and related remote sensing techniques are discussed in conclusion. Such a list is an essential tool for evaluating the hazard potential of a lake. A systematic application of remote sensing based methods for glacier lake hazard assessment is recommended.
Seasonal variations in ablation and surface velocity were investigated on the lower part of Fox Glacier, South Westland, New Zealand. A large variation between summer and winter ablation was recorded, with daily averages of 129 mm d21 and 22 mm d21, respectively. Variations in measured climatic variables were found to account for ,90% of variation in ablation during both summer and winter seasons, with significant increases in ablation occurring in conjunction with heavy rainfall events. Surface velocity also showed seasonality, averaging 0.87 m d21 during summer and 0.64 m d21 in winter, a reduction of ,26%. It is thought that the general reduction in velocity during winter can be attributed to a decrease in the supply of surface meltwater to the subglacial zone. Short-term velocity peaks appeared to coincide with heavy rainfall events, with surface velocity responses typically occurring within 24 hours of each rainfall event. During winter, moderate rainfall events (#100 mm over 24 hours) created a surface velocity response up to 44% greater than the prevailing velocity. Though difficult to deconvolve, magnitudes of surface velocity response to rainfall inputs appear linked to time lags between rainfall events and subglacial drainage efficiency and water storage. The longer-term dynamics of Fox Glacier appear linked to fluctuations in the Southern Oscillation Index (SOI), with positive mass balances of Southern Alps' glaciers appearing to mirror negative SOI (El Nino) conditions. Given the calculated response time of ,9.1 years for Fox Glacier, the current terminus advance may be linked to mass gains reported in the mid-1990s, with current mass balance gains perhaps leading to terminus advances ,9 years hence.
The steep outlet glaciers of Jostedalsbreen, western Norway, are good examples of sensitively reacting maritime mountain glaciers. Their changes in length, frontal position and lower tongue's morphology during the past 20 years have been well documented. At first they experienced a strong frontal advance. After AD 2000 glacier behaviour was dominated by a strong frontal retreat, in some cases causing a separation of the lowermost glacier tongue. In this paper, the glacier length changes are presented both visually and numerically, supplemented by mass balance and meteorological data. The glacier behaviour is interpreted and its causes are discussed. Whereas the factors controlling the advance during the 1990s seem clear, the interpretation of the most recent retreat still leaves some uncertainties. The actual glacier front behaviour cannot fully be related to the mass balance data. Terminus response times and relations between individual mass balance and meteorological parameters have changed. Some hypotheses are given, including disturbance of the `normal' mass transfer and dynamical response of the glacier front because of excessive ablation on the lowermost glacier tongues and summer back melting. These findings underline the sensitivity of maritime glaciers to climate changes. The empirical findings need to be taken into account in the interpretation of recent glacier length changes and their future modelling.
The spatial characteristics for all glaciers in the North Cascades National Park Complex, USA, were estimated in 1958 and again in 1998. The total glacier area in 1958 was 117.3 ± 1.1 km2; by 1998 the glacier area had decreased to 109.1 ± 1.1 km2, a reduction of 8.2 ± 0.1 km2 (7%). Estimated volume loss during the 40 year period was 0.8 ± 0.1 km3 of ice. This volume loss contributes up to 6% of the August-September stream-flow and equals 16% of the August-September precipitation. No significant correlations were found between magnitude of glacier shrinkage and topographic characteristics of elevation, aspect or slope. However, the smaller glaciers lost proportionally more area than the larger glaciers and had a greater variability in fractional change than larger glaciers. Most of the well-studied alpine glaciers are much larger than the population median, so global estimates of glacier shrinkage, based on these well-studied glaciers, probably underestimate the true magnitude of regional glacier change.
A marginal ice-contact lake at Miage glacier, Mont Blanc, Italian Alps, has been studied to reconstruct changes in lake area. Historical sources, comprising sketches, maps, photographs and scientific surveys, have been supplemented by recent field surveys. These include surveys of glacier surface velocity (which varied along the glacier tongue from 70 m a−1 in the upper part to about 6 m a−1 close to the snout, consistent with data in the literature, showing that velocity rates have remained constant during the last 40 years), volumetric ice-cliff loss (−92 000 ± 180 m3 in 2002-03), lake temperature and bathymetry, and qualitative observation of calving events, crevassing, and meltwater production. Results indicate that the lake has been stable for the last half-century following a period of enlargement due to ice-marginal retreat. The lake hydrology is complex, with possible reversals of englacial water flow causing infrequent emptying episodes. The debris cover on the glacier and ice-cliff surfaces seems to have played an important role in the ice-cliff evolution and the calving phenomena; calving is driven by undercutting at the water-line aided by the opening of water- and debris-filled crevasses in the glacier surface.
Flood and debris-flow hazards at Grubengletscher near Saas Balen in the Saas Valley, Valais, Swiss Alps, result from the formation and growth of several lakes at the glacier margin and within the surrounding permafrost. In order to prevent damage related to such hazards, systematic investigations were carried out and practical measures taken. The evolution of the polythermal glacier, the creeping permafrost within the large adjacent rock glacier and the development of the various periglacial lakes were monitored and documented for the last 25 years by photogrammetric analysis of annually flown high-resolution aerial photographs. Seismic refraction, d.c. resistivity and gravimetry soundings were performed together with hydrological tracer experiments to determine the structure and stability of a moraine dam at a proglacial lake. The results indicate a maximum moraine thickness of > 100 m; extremely high porosity and even ground caverns near the surface may have resulted from degradation of sub- and periglacial permafrost following 19th/20thcentury retreat of the partially cold glacier tongue. The safety and retention capacity of the proglacial lake were enhanced by deepening and reinforcing the outlet structure on top of the moraine complex. The water level of an ice-dammed lake was lowered and a thermokarst lake artficially drained.
Glaciar Nef, a 164 km2eastern outlet of Hielo Patagónico Norte (the northern Patagonia icefield), terminates in a proglacial lake that has formed in conjunction with 20th-century glacier retreat. The terminus is inferred to be transiently afloat. A hinge-calving mechanism is proposed in which buoyant forces impose a torque on the glacier tongue, resulting in the release of coherent sections of the glacier tongue as "tabular" ice-bergs. A simple model shows how torque and tensile stress reach a maximum at the up-glacier limit of the buoyant zone, and that glacier thinning causes this point to migrate up-glacier. Empirical evidence supporting this model includes elevated thermo-erosional notches ≤6.5 m above lake level, and the ubiquitous presence since 1975 of "tabular" ice- bergs with surface areas ≤0.3 km2. Flow speeds of 1.2−1.3 m d−1 were measured near the terminus in February 1998. Extrapolations from these short-term data yield a calvingrate of 785−835 m a−1 and a calvingflux of 232 × 106 m3 a−1 or 0.2 km3 a−1. The calculated mean water depth at the terminus is 190 m. This calvingrate is higher than at grounded temperate glaciers calving in fresh water, but is nevertheless almost an order of magnitude less than calvingrates at both grounded and floatingtidewater glaciers.
The Imja Glacier Lake (Imja Tsho) (1.03 km2 in 2007) is repeatedly cited as one of the most dangerous glacial lakes in the Himalaya with a glacial lake outburst flood (GLOF) claimed to be imminent. Knowledge of lake development and its dynamics, however, is limited and forecasts of a possible outburst are not scientifically based. Nevertheless, prospects for such a catastrophe are repeatedly exaggerated, attracting alarmist mass media coverage. The paper provides an assessment of the lake expansion rates from 1956 to 2007. Stage 1 (1956–1975), slowest: coalescence of several small supra-glacial ponds; Stage 2 (1975–1978), a short period of most rapid expansion; Stage 3 (1978–1997), slow: gradual expansion of single lake; and Stage 4 (1997–2007), renewed acceleration: mainly eastward expansion into the glacier surface. The lake's water level has fallen from 5041 m to 5004 m (1964–2006). The results show that there is no immediate danger of catastrophic outburst although the dynamics of up-glacier and down-valley lake expansion, fluctuation of lake water level, and dead-ice morphology changes should be continuously and comprehensively monitored. Alarmist prognostications based solely upon rapid areal expansion are counterproductive.
The sum of winter accumulation and summer losses of mass from glaciers and ice sheets (net surface mass balance) varies with changing climate. In the Arctic, glaciers and ice caps, excluding the Greenland Ice Sheet, cover about 275,000 km2of both the widely glacierized archipelagos of the Canadian, Norwegian, and Russian High Arctic and the area north of about 60°N in Alaska, Iceland, and Scandinavia. Since the 1940s, surface mass balance time-series of varying length have been acquired from more than 40 Arctic ice caps and glaciers. Most Arctic glaciers have experienced predominantly negative net surface mass balance over the past few decades. There is no uniform recent trend in mass balance for the entire Arctic, although some regional trends occur. Examples are the increasingly negative mass balances for northern Alaska, due to higher summer temperatures, and increasingly positive mass balances for maritime Scandinavia and Iceland, due to increased winter precipitation. The negative mass balance of most Arctic glaciers may be a response to a step-like warming in the early twentieth century at the termination of the cold Little Ice Age. Arctic ice masses outside Greenland are at present contributing about 0.13 mm yr−1to global sea-level rise.
Calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world. Calving rates can increase dramatically in response to increases in velocity and/or retreat of the glacier margin, with important implications for sea level change. Despite their importance, calving and related dynamic processes are poorly represented in the current generation of ice sheet models. This is largely because understanding the ‘calving problem’ involves several other long-standing problems in glaciology, combined with the difficulties and dangers of field data collection. In this paper, we systematically review different aspects of the calving problem, and outline a new framework for representing calving processes in ice sheet models. We define a hierarchy of calving processes, to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events. The first-order control on calving is the strain rate arising from spatial variations in velocity (particularly sliding speed), which determines the location and depth of surface crevasses. Superimposed on this first-order process are second-order processes that can further erode the ice margin. These include: fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front; undercutting of the glacier terminus by melting at or below the waterline; and bending at the junction between grounded and buoyant parts of an ice tongue. Calving of projecting, submerged ‘ice feet’ can be regarded as a third-order process, because it is paced by first- or second-order calving above the waterline.
This study uses the database from national glacier inventories in the European Alps and the Southern Alps of New Zealand (hereinafter called the New Zealand Alps), which contain for the time of the mid-1970s a total of 5154 and 3132 perennial surface ice bodies, covering 2909 km2 and 1139 km2 respectively, and applies to the mid-1970s. Only 1763 (35%) for the European Alps and 702 (22%) for the New Zealand Alps, of these are ice bodies larger than 0.2 km2, covering 2533 km2 (88%) and 979 km2 (86%) of the total surface area, respectively containing useful information on surface area, total length, and maximum and minimum altitude. A parameterisation scheme using these four variables to estimate specific mean mass balance and glacier volumes in the mid-1970s and in the ‘1850 extent’ applied to the samples with surface areas greater than 0.2 km2, yielded a total volume of 126 km3 for the European Alps and 67 km3 for the Southern Alps of New Zealand. The calculated area change since the ‘1850 extent’ is − 49% for the New Zealand Alps and − 35% for the European Alps, with a corresponding volume loss of − 61% and − 48%, respectively. From cumulative measured length change data an average mass balance for the investigated period could be determined at − 0.33 m water equivalent (we) per year for the European Alps and − 1.25 m we for the ‘wet’ and − 0.54 m we per year for the ‘dry’ glaciers of the New Zealand Alps. However, there is some uncertainty in several unknown factors, such as the values used in the parameterisation scheme of mass balance gradients, which, in New Zealand vary between 5 and 25 mm m− 1.
An open access copy of this article is available from the publishers website. A 3 km long section of the Hooker Glacier near its terminus was studied in 1996 using GPS, tacheometric, and bathymetric surveys, as well as ground penetrating radar and gravity surveys. With reference to sparse surface levels and oblique photos dating back to 1889, the studies indicate that between c. 1915 and 1964 downwasting of an axial strip along the terminal section occurred at a rate of c. 0.7 m/yr. Between 1964 and 1986 the rate increased to 1.0 m/yr. Marginal segments of the glacier near the terminus experienced positive buoyancy from 1982 onwards, which promoted rapid melting. Apparent subaqueous melting rates of c.9 m/yr occurred between 1986 and 1996 over large stretches of the downmelting terminal area. By 1996, a 1.4 km long sector of the glacier had melted down forming a melt lake (Hooker Lake) with a volume of c. 40 x 106 m3 covering an area of 0.78 x 106 m2. A maximum water depth of 135 m was measured near the retreating glacier front where the ice wall descends as a vertical cliff to the lake bottom and temperatures of 0.5ﾰC prevail. Ice thickness measurements by radar surveys along profiles 1.7 and 3.0 km upstream from the terminus indicate a maximum thickness of 165 and 260 m, respectively; the results have been confirmed by the interpretation of residual gravity anomalies. The lake level is controlled by the outlet level (875 m a.s.l.) of the Hooker River, which has remained almost constant since 1889. Melting of the glacier front at a rate of c. 40 m/yr will cause the glacier to retreat at a rather uniform rate. The lake will continue to grow until it reaches the glacier bed c. 5 km upstream from the terminus.
Vive La Différence
How closely do climate changes in the Northern and Southern Hemispheres resemble each other? Much discussion has concentrated on the Holocene, the warm period of the past 11,500 years in which we now live, which represents a baseline to which contemporary climate change can be compared. Schaefer et al. (p. 622 ; see the Perspective by Balco ) present a chronology of glacial movement over the last 7000 years in New Zealand, which they compare to similar records from the Northern Hemisphere. Clear differences are observed between the histories of glaciers in the opposing hemispheres, which may be owing to regional controls. Thus, neither of two popular arguments—that the hemispheres change in-phase or that they change in an anti-phased manner—appear to be correct.
The calving rates and calving styles of temperate glaciers that calve into fresh water are distinctively different from those of temperate tide-water glaciers. These contrasts are important for interpreting and predicting the response of ice masses to climate change. Glaciar Upsala is a large calving outlet of Hielo Patagónico Sur (southern Patagonia ice field). Its twentieth-century retreat has been climate-driven but significantly modulated by calving dynamics and by the transition from melting to calving at its eastern terminus. Here, the onset of rapid calving in the early 1980s initiated retreat at ≤440 m a−1. The 1992–93 calving rate (v c) is estimated to be 60 m a−1 in a mean water depth (h w) of 67 m. A v c/h w relationship for fresh water based on 14 sites around the world, including seven deep-water sites, confirms both the linear dependency of v c on h w and the contrast between calving rates in tide water and fresh water. As yet, no physical explanation for this contrast exists, but differences in subaqueous melt rates, longitudinal strain rates and crevassing may provide a partial explanation.
In order to improve their hydro-electric power production in the Grimsel area, Kraftwerke Oberhasli (KWO) plan to construct a new reservoir with a storage level about 110 m higher than the existing Grimselsee. This paper deals with the expected changes of Unteraargletscher after periodical contact with the resulting water body. Upon initial flooding, the lowermost section of Unteraargletscher, about 800 m long, will float, drift away, and melt. A rough estimate of the heat balance shows that the energy input into the lake would be sufficient to melt this ice within 2–3 years, so that calving and melting will continue at a frontal ice cliff. The main effort of the study was aimed at forecasting this retreat. A pre-existing seismic survey was supplemented by new soundings by radar and seismic reflection, resulting in reliable cross-sections and information about the sub-bottom material. The forecast is based on the existing mass flux and an empirical calving rate relationship with water depth and predicts an equilibrium position of the terminus some 3–4 km further back than today, and a gain of water storage volume of 50 × 106 m3 after 10 years.
Between October 1998 and October 1999, a supraglacial lake on the Ngozumpa Glacier, Khumbu Himal, Nepal, underwent rapid growth, mainly by a combination of calving retreat and basin flooding during the 1999 monsoon season. The lake in unlikely to develop into a large moraine-dammed lake, but while it persists, growth of the lake will probably continue to result in locally high rates of ablation, contributing to overall downwasting of the glacier surface.
Historical records, including maps, photographs, paintings and written accounts, are used to reconstruct the changing ice levels and terminal positions of the six main valley glaciers in Mt Cook National Park, New Zealand. The historical record, which began in 1862, is compared with the New Zealand climatic record for the same period. Patterns of glacial fluctuation are related to the general trends in climate. Between 1862 and 1888 there was locally important glacier recession. This was followed by a cooler period marked by glacier advance. A glacier stillstand is recorded during the first four decades of the present century and since 1940, a period of general temperature warming, the glaciers have all receded. Ice fronts have retreated up to 5 km from positions reached in 1862 and ice levels have dropped over 100 m.
Melt rates of the dead ice in front of "Imja Glacier Lake' varied between 0.1 and 2.7 m/yr during the period 1989-1994. A maximum in excess of 5.0 m/yr occurred where the ice surface had been submerged by lake water before 1994. The lake level fell from 5022 m asl in 1984 to about 5017 m in 1989, and to about 5007 m in 1994. This decrease is atributed to melt of dead ice along the outflow; thus there is less danger of collapse of the lateral moraines. Instead, the rapid melting is expected to cause the lake to expand westward, that is towards the terminal moraine. Maximum dimensions by the winter of 1992, is due to melting of the glacier at the east (upper) end of the lake. Nevertheless, if the melt rate is sustained the western shoreline could migrate to the edge of the terminal moraine in little more than seven years. Immediate action to lower the lake level below the level of the spillway is needed. -from Authors
Abstract The Tasman Glacier is the largest glacier in New Zealand. Although 20th century warming caused down-wastage, it remained at its Little Ice Age terminus until the late 20th century. Since then, rapid calving retreat (Ur) has occurred, allowing a large (5.96 × 106 m2) proglacial lake to form (maximum depth ∼240 m). From sequential satellite image analysis and echo sounding of Tasman Lake, we document (Ur) from 2000 to 2008. Ur varies temporally, with mean Ur of 54 m/a from 2000 to 2006 and a mean Ur of 144 m/a from 2007 to 2008. Consistent with global data sets, calving rate appears closely associated with lake depth at the calving terminus.
Blocks of ice with the proportions of tabular icebergs have been observed melting in water of different temperatures and salinities. The sub-surface shape adopted by the blocks melting in water of the same salinity as sea-water was typically a ‘bath-tub’ one. The basal and mean-side melt rates were of a similar value. The melt rates obtained in the laboratory for icebergs in water of a low temperature match those inferred from population studies of Antarctic icebergs. The melt rate is proportional to the water temperature above the onset of freezing raised to the power 1.5 and melt rates at 18°C are likely to be greater than one metre per day.
Upon initial flooding, the lowermost section of Unteraargletscher, about 800 m long, will float, drift away, and melt. A rough estimate of the heat balance shows that the energy input into the lake would be sufficient to melt this ice within 2-3 years, so that calving and melting will continue at a frontal ice cliff. The main effort of the study was aimed at forecasting this retreat. A pre-existing seismic survey was supplemented by new soundings by radar and seismic reflection, resulting in reliable cross-sections and information about the sub-bottom material. The forecast is based on the existing mass flux and an empirical calving rate relationship with water depth and predicts an equilibrium position of the terminus some 3-4 km further back than today, and a gain of water storage volume of 50 × 106 m3 after 10 years. -from Authors
Moraine-dammed glacial lakes are becoming increasingly common in the Himalaya as a result of glacier mass loss, causing concern about glacier lake outburst flood risk. In addition to extant lakes, the potential exists for many more to form, as more glaciers ablate down to the level of potential moraine dams. In this paper, we document the recent rapid growth of, a moraine-dammed lake on Ngozumpa Glacier, Nepal. Using a combination of ground-based mapping and sonar surveys, aerial photographs (<1 m resolution), and ASTER imagery (15 m resolution), processes and rates of lake expansion have been determined. The lake first formed between 1984 and 1992 when collapse of an englacial conduit allowed water to accumulate at the level of a gap in the lateral moraine, similar to km from the glacier terminus. Lake growth was initially slow, but since 2001 it has undergone exponential growth at an average rate of 10%y(-1). In 2009, the lake area was 300,000 m(2), and its volume was at least 2.2 million m(3). Calving, subaqueous melting, and melting of subaerial ice faces all contribute to the expansion of the lake; but large-scale, full-height slab calving is now the dominant contributor to growth. Comparison with other lakes in the region indicate that lake growth will likely continue unchecked whilst the spillway remains at its current level and may attain a volume of hundreds of millions of cubic metres within the next few decades.
Termini of valley glaciers in the central Southern Alps are undergoing a three-phase sequence of retreat that began in the 1950s. An initial phase of melting and slow downwasting under thickening supraglacial debris mantles is associated with stationary or slowly retreating termini. This is followed by a transitional phase of disruption of insulating debris mantles allowing the rapid growth of shallow thermokarst lakes, the shape and location of which vary according to glacier gradient and marginal topography. A third phase of rapid calving retreat of ice cliffs into deepening proglacial lakes develops from the transitional phase. At no stage are terminal responses simply related to climate. Present transitions to calving retreat are related to the morphology of glacier termini, particularly to large outwash heads. Landform evidence indicates that similar calving phases do not appear to have occurred since Late Pleistocene deglaciation, so that present changes to glacier termini are of great significance in the context of the whole Holocene. At millennial timescales, the melting-calving transition is effectively instantaneous and represents a sharp threshold heralding rapid deglaciation. The commencement of calving is imminent at the stationary terminus of Tasman Glacier which will soon retreat rapidly as a result.
Several ice‐contact lakes have formed in conjunction with twentieth century glacier retreat in Mt Cook National Park. They occupy overdeepened glacial valleys and are dammed by terminal moraines and/or outwash heads. During the autumns of 1994 and 1995, the temperature and bathymetry of “Maud lake”, “Godley lake”, and Hooker Lake were surveyed. The near‐glacier vertical water temperature profiles exhibited greater temperature variation than those at the distal ends of the lakes. Thermal stratification existed in Hooker Lake, whereas both Maud and Godley lakes were thoroughly mixed. Water temperatures in the latter were consistently between 3 and 4.5°C, but most parts of Hooker Lake were cooler than 2°C, with a minimum recorded temperature of 0.2°C. These contrasts are important because melting of submerged parts of glacier termini is significant for ablation rates and for the dynamics of calving termini. All the lakes are steep sided and deep. Maud and Godley lakes approach 100 m in depth, whereas Hooker Lake has a maximum recorded depth of 136 m. Extensive flat floors in Maud and Godley lakes probably reflect rapid sediment accumulation following glacier retreat. Water depth at the termini of iceberg‐calving glaciers is known to correlate strongly with rates of iceberg production and hence the rate of glacier retreat. However, given the substantial water depths through which these glaciers (and also the neighbouring Tasman Glacier) have retreated, they appear to be more stable than comparable glaciers in other countries. The subaqueous geometry of all the glacier termini comprises a projecting ramp of glacier ice. All the lakes are being enlarged by glacier retreat except Maud lake, which has been reduced in size since 1995 by the advance of Maud and Grey Glaciers.
An investigation of 127 glaciers of the New Zealand Southern Alps shows the losses that have occurred since the end of the Little Ice Age. On average they have shortened by 38% and lost 25% in area. The great variability within the measurements emphasises the need to consider response times and climate sensitivity when analysing glacier fluctuations. The upward shift of glacier mean elevation with this century of change is approximately equivalent to a temperature rise of 0.6°C. Extensive debris cover on many glaciers is significant in damping the climate signal, and proglacial lake formation may decouple a glacier from the climate signal.
Based on a review of observations on different types of calving glaciers, a simple calving model is proposed. Glaciers that exist in a sufficiently cold climate can form floating ice shelves and ice tongues that typically do not extend beyond confinements such as lateral fjord walls or mountains, and ice rises. If the local climate exceeds the thermal limit of ice shelf viability, as is the case for temperate glaciers, no floating tongue can be maintained and the position of the terminus is determined by the thickness in excess of flotation. If the snout is sufficiently thick, a stable terminus position at the mouth of the confining fjord - usually marked by a terminal shoal - can be maintained. Further advance is not possible because of increasing sea-floor depth and diverging flow resulting from lack of lateral constraints. If a mass balance deficiency causes the terminal region to thin, retreat is initiated with the calving front retreating to where the thickness is slightly in excess of flotation. In that case, the calving rate is determined by glacier speed and thickness change at the glacier snout. Advance or retreat of the calving front is not driven by changes in the calving rate, but by flow-induced changes in the geometry of the terminal region. This model is essentially different from prior suggestions in which some empirical relation - most commonly the water-depth model - is used to calculate calving, rate and the rate of retreat or advance of the terminus.
Ablation of debris-mantled glaciers in Nepal has resulted in the formation of several potentially unstable moraine-dammed lakes, some of which constitute serious hazards. Ngozumpa Glacier, Khumbu Himal, has undergone significant downwasting in recent decades, and is believed to lie close to the threshold for moraine-dammed lake formation. The debris-mantled ablation area of the glacier is studded with numerous supraglacial lakes, the majority of which occupy closed basins with no perennial connections to the englacial drainage system ("perched lakes''). Perched lakes can undergo rapid growth by subaerial and water-line melting of exposed ice faces, and calving. Subaerial and subaqueous melting beneath thick(>1m) debris mantles is comparatively insignificant. Although lake expansion can contribute substantially to ablation of the glacier, perched lakes cannot continue to grow indefinitely, but are subject to rapid drainage once a connection is made to englacial conduits. The level of one of the lakes on the Ngozumpa, however, is controlled by the altitude of a spillway through the lateral moraine of the glacier. This lake underwent only limited growth in the period 1998-2000, but is likely to experience monotonic growth if glacier mass balance continues to be negative.
Calving speeds and calving mechanisms in fresh water contrast with those in tidewater. We obtained calving speeds for six lake-calving glaciers in New Zealand's Southern Alps, and surveyed the depths and temperatures of their ice-contact lakes. The glaciers are temperate, grounded in shallow (≤20 m) water, and exhibit compressive flow at their termini. These data increase the global dataset of fresh-water calving statistics by 40%, bringing the total to 21glaciers. For this dataset, calving rates (uc) correlate positively with water depths (hw) (r2 = 0.83), the relationship being expressed by: uc = 17.4 + 2.3hw. This is an order of magnitude lower than values of uc at temperate tide-water glaciers. For a subset of 10 glaciers for which ice-proximal water temperature (tw) data are available, uc also correlates positively with tw, supporting a physical relation between calving and melting at and below the water-line. Fluctuations of New Zealand lake-calving glaciers in the period 1958-97 show that although the transition from non-calving to calving dramatically increases frontal retreat rates, the onset of calving does not isolate terminus change from climatic forcing. In terms of climatic sensitivity, lake-calving glaciers occupy an intermediate position between tidewater glaciers (least sensitive) and non-calving glaciers (most sensitive).
Controls on glacier calving rates are receiving increased scientific interest. At fresh-water-calving glaciers, limnological factors might be more important than glaciological ones. Measurements of thermo-erosional notch development at the calving ice cliff of Tasman Glacier, New Zealand, suggest that the calving rates at this glacier are directly controlled by the rate of thermal undercutting. Notch formation rates typically vary between 10 and 30 cm d−1 (maximum rate 65 cm d−1) in summer, corresponding to an average calving rate of 34 m a−1. Notch formation is slower than waterline melt and is controlled by water temperatures and circulation, cliff geometry, debris supply and water-level fluctuations. The latter shift the position of undercutting, resetting the level of the notch formation process and thereby slowing it. The geometry of the notch and the debris supply determine the extent of influence of the lake on notch water temperatures and circulation. Hence, water temperatures in the lake are not necessarily indicative of the rate of notch formation. The prediction of rate of notch formation from far-field variables is hampered by the complex interaction of the influencing factors. The significance of thermal undercutting as a calving rate-controlling process decreases with increasing ice velocities, calving rates and surface gradients.
Despite their relatively small total ice volume, mid-latitude valley glaciers are expected to make a significant contribution to global sea-level rise over the next century due to the sensitivity of their mass-balance systems to small changes in climate. Here we use a degree-day model to reconstruct the past century of mass-balance variation at 'Ka Roimata o Hine Hukatere' Franz Josef Glacier, New Zealand, and to predict how mass balance may change over the next century. Analysis of the relationship between temperature, precipitation and mass balance indicates that temperature is a stronger control than precipitation on the mass balance of Franz Josef Glacier. The glacier's mass balance, relative to its 1986 geometry, has decreased at a mean annual rate of 0.02 ma−1 w.e. between 1894 and 2005. We compare this reduction to observations of terminus advance and retreat, of which Franz Josef Glacier has the best record in the Southern Hemisphere. For the years 2000-05 the relative mass balance ranged from −0.75 to +1.50 ma−1 w.e., with 2000/01 the only year showing a negative mass balance. In a regionally downscaled Intergovernmental Panel on Climate Change mean warming scenario, the annual relative mass balance will continue to decrease at 0.02 ma−1 w.e. through the next century.
The rates and processes of freshwater calving at Miage Glacier (Mont Blanc Massif, Italy) are described. Calving at Miage Glacier has occurred for two centuries on its right-lateral side, into a small ice-marginal lake (Miage Lake). Field surveys identified the main processes leading to iceberg production and quantified the calving losses over a summer season. Calving losses were compared (1) with the surface ablation of the debris-covered tongue, evaluated through a simple model based on measured ablation rates at different altitudes and debris cover thicknesses, and (2) with other inputs to the lake (stream inflow discharge) and with the lake volume. Results show that thermal undercutting by warmer surface water plays an important role in driving ice-cliff evolution. Thermal notches grow at ∼30–35m year−1 and cause a similar amount of cliff retreat. Calving contributes ∼2% of the estimated summer runoff from the debris-covered part of the ablation zone, but this is equivalent to ∼38% of the lake volume, and is of the same magnitude as the mean discharge from the inflow streams. These data indicate that calving of the ice cliff is one of the main water sources for maintaining the lake at the maximum summer volume, with the surface at the level of the subaerial outlet stream. A survey of Italian calving glaciers shows that calving is becoming more widespread, and that debris covers are present at all calving ice margins. The lake–ice interactions described in this study can, therefore, be considered to have wider representativeness. Copyright © 2006 John Wiley & Sons, Ltd.
Mendenhall Glacier is a lake-calving glacier in southeastern Alaska, USA, that is experiencing substantial thinning and increasingly rapid recession. Long-term mass wastage linked to climatic trends is responsible for thinning of the lower glacier and leaving the terminus vulnerable to buoyancy-driven calving and accelerated retreat. Bedrock topography has played a major role in stabilizing the terminus between periods of rapid calving and retreat. Lake-terminating glaciers form a population distinct from both tidewater glaciers and polar ice tongues, with some similarities to both groups. Lacustrine termini experience fewer perturbations (e.g. tidal flexure, high subaqueous melt rates) and are therefore inherently more stable than tidewater termini. At Mendenhall, rapid thinning and simultaneous retreat into a deeper basin led to flotation conditions along approximately 50% of the calving front. This unstable terminus geometry lasted for approximately 2 years and culminated in large-scale calving and terminus collapse during summer 2004. Buoyancy-driven calving events and terminus break-up can result from small, rapidly applied perturbations in lake level.
The interpretation of climate change based on the behavior of small cirque glaciers is not always straightforward or unique. In this study of Sperry Glacier, Glacier National Park, Montana, we model future change of the glacier under 11 different warming scenarios. The scenarios vary from no warming from present conditions to warming at a linear rate of 10 °C/century. We assume constant precipitation and only consider change invoked by warming. Our cellular automata model is based on simple rules that account for mass balance gradient, aspect, avalanching, and the flow of ice to redistribute mass. We constrain the model with glaciological data including georadar-measured ice depth, field-measured surface mass balance, and field-mapped ice surface topography. Under the most probable temperature increase based on downscaled OA-GCM output for the IPCC A1B scenario, we conservatively estimate the glacier persisting through at least 2080. By comparing glacier volume responses to different warming scenarios we elucidate a relationship between the magnitude of temperature change and the sensitivity of the glacier to small variations in the temperature increase. We find that the greater the magnitude of the temperature increase, the less sensitive the glacier area and volume become to slight differences in the warming rate. If we generalize this relationship to the region, we expect that a small change in climate will produce varying responses for glaciers throughout the region, whereas the glacier response to a large change in climate will likely be very similar over the entire region.
Norway and New Zealand both experienced recent glacial advances, commencing in the early 1980s and ceasing around 2000, which were more extensive than any other since the end of the Little Ice Age. Common to both countries, the positive glacier balances are associated with an increase in the strength of westerly atmospheric circulation which brought increased precipitation. In Norway, the changes are also associated with lower ablation season temperatures. In New Zealand, where the positive balances were distributed uniformly throughout the Southern Alps, the period of increased mass balance was coincident with a change in the Interdecadal Pacific Oscillation and an associated increase in El Niño/Southern Oscillation events. In Norway, the positive balances occurred across a strong west-east gradient with no balance increases to the continental glaciers of Scandinavia. The Norwegian advances are linked to strongly positive North Atlantic Oscillation events which caused an overall increase of precipitation in the winter accumulation season and a general shift of maximum precipitation from autumn towards winter. These cases both show the influence of atmospheric circulation on maritime glaciers.
The nature and rate of the transition from a thinning, melting ablation zone to a retreating, calving terminus is examined at the debris-mantled Tasman Glacier. The debris mantle has existed since the earliest glaciological observations were made in 1863, indicating that debris cover is the normal glaciological state regardless of historic mass-balance change. The relationship between debris thickness and ablation rate has been derived from short-term heat flow calculations. Extrapolation over time and space indicate that the thermal effect of the debris mantle has resulted in a post-1890 reduction in glacier surface gradient which, through positive feedback involving ablation rate, ice velocity and particle emergence paths, has caused upglacier spread of supraglacial debris and upstream migration of the locus of maximum ablation. This has lead to the preservation of a long ice tongue at low gradient while preventing terminus retreat from the outwash head, and has made the glacier vulnerable to calving. Since the late 1970s, thermokarst melting has formed an ice-contact proglacial lake in which water depths now exceed ca. 130 m against the ice front. Since 1994, evidence of extending and accelerating flow may indicate the imminent onset of rapid calving. Predicted retreat scenarios suggest a rapid retreat of at least 10 km will probably cause major (possibly catastrophic) rock and debris avalanches into the enlarging proglacial lake as debuttressing of mountainsides progresses.
This paper presents data concerning recent (1990–2007) surface morphological and ice-dynamical changes on the Tasman Glacier, New Zealand. We use remote-sensing data to derive rates of lake growth, glacier velocities and rates of glacier surface lowering. Between 1990 and 2007, the glacier terminus receded ~ 3.5 km and a large ice-contact proglacial lake developed behind the outwash head. By 2007 the lake area was ~ 6 km2 and had replaced the majority of the lowermost 4 km of the glacier tongue. There is evidence that lake growth is proceeding at increasing rates — the lake area doubled between 2000 and 2007 alone. Measured horizontal glacier velocities decline from 150 m a− 1 in the upper glacier catchment to almost zero at the glacier terminus and there is a consequent down-glacier increase in surface debris cover. Surface debris mapping shows that a large catastrophic rockfall onto the glacier surface in 1991 is still evident as a series of arcuate debris ridges below the Hochstetter icefall. Calculated glacier surface lowering is most clearly pronounced around the terminal area of the glacier tongue, with down-wasting rates of 4.2 ± 1.4 m a− 1 in areas adjacent to the lateral moraine ridges outside of the current lake extent. Surface lowering rates of approximately 1.9 ± 1.4 m a− 1 are common in the upper areas of the glacier. Calculations of future lake expansion are dependent on accurate bathymetric and bed topography surveys, but published data indicate that a further 8–10 km of the glacier is susceptible to calving and further lake development in the future.
Oblique aerial photography of 111 glaciers during the past 2 decades has recorded a reversal of the past century glacier-recession trend. Cirque glaciers show little response to the recent mass balance increase; mountain glaciers show visible advances. Some valley glaciers have advanced, some have thickened in the upper trunk, and the larger ones and those with proglacial lakes continue to recede. The shift to advance is driven by an average lowering of snowlines of 67 m, equivalent to a cooling of 0.47°C if other factors are held constant.
After a long period of general retreat, the Franz Josef Glacier on the western flanks of the Southern Alps of New Zealand has undergone a major advance, beginning about 1982. Key climatic variables, atmospheric circulation patterns over the Southwest Pacific, and the Southern Oscillation Index (SOI), are compared for two 20-year periods that represent advance and retreat phases of the Franz Josef Glacier. The results show strong links between atmospheric circulation changes, climate variables and glacier behaviour. The retreat phase is characterised by slightly warmer temperatures and markedly lower precipitation in the ablation season, a high pressure anomaly over New Zealand, and a southward shift in the subtropical high pressure zone. In contrast, the advance phase is characterised by anomalous southwest airflow, especially during the ablation season, and higher precipitation. The high pressure anomaly is shifted westward by about 55° of longitude so as to lie south of Australia. The advance phase is also related to a higher frequency of El Niño events.
I constructed a temperature history for different parts of the world from 169 glacier length records. Using a first-order
theory of glacier dynamics, I related changes in glacier length to changes in temperature. The derived temperature histories
are fully independent of proxy and instrumental data used in earlier reconstructions. Moderate global warming started in the
middle of the 19th century. The reconstructed warming in the first half of the 20th century is 0.5 kelvin. This warming was
notably coherent over the globe. The warming signals from glaciers at low and high elevations appear to be very similar.
Glacier response to climate change
- J Salinger
- Tjh Chinn
- A Willsman
- B Fitzharris
Salinger J, Chinn TJH, Willsman A, Fitzharris B
(2008). Glacier response to climate change.
Water & Atmosphere 16, 16-7.
Columbia Glacier during rapid retreat: interactions between glacier flow and iceberg calving dynamics
- Mf Meier
Meier MF (1994). Columbia Glacier during rapid
retreat: interactions between glacier flow and
iceberg calving dynamics. In: Reeh N, ed. Workshop on the Calving Rate of West Greenland
Glaciers in Response to Climate Change. Danish
Polar Center Report, Copenhagen, p. 171.