Relationship between tidewater glacier calving velocity and water depth at the calving front

An analysis of the relationship between iceberg calving rates and water depth has been completed for 22 tidewater glaciers. A linear relationship provides reasonable accuracy, with a correlation coefficient of 0.85, for all tidewater glaciers examined, whether they be polar or temperate. The polar glaciers have a slightly lower calving rate for a given water depth. This relationship indicates a lower calving rate for water depths over 50 m than determined by Brown and others (1982). It is based only on glaciers or ice streams and cannot be applied to ice shelves.

Download Full-text

Tidewater calving

Journal of Glaciology ◽

10.3189/s0022143000004226 ◽

1996 ◽

Vol 42 (141) ◽

pp. 375-385 ◽

Cited By ~ 14

Author(s):

С.J. Van Der Veen

Keyword(s):

Water Depth ◽

Fold Increase ◽

Actual Rate ◽

Tidewater Glaciers ◽

Glacier Terminus ◽

Tidewater Glacier ◽

Iceberg Calving ◽

Speed Up ◽

Calving Rate ◽

Subglacial Drainage

AbstractData from Columbia Glacier are used to identify processes that control calving from a temperate tidewater glacier and to re-evaluate models that have been proposed to describe iceberg calving. Since 1981, Columbia Glacier has been retreating rapidly, with an almost seven-fold increase in calving rate from the mid-1970s to 1993. At the same time, the speed of the glacier increased almost as much, so that the actual rate of retreat increased more slowly. According to the commonly accepted model, the calving rate is linearly related to the water depth at the terminus, with retreat of the glacier snout into deeper water, leading to larger calving rates and accelerated retreat. The Columbia Glacier data show that the calving rate is not simply linked to observed quantities such as water depth or stretching rate near the terminus. During the retreat, the thickness at the terminus appears to be linearly correlated with the water depth; at the terminus, the thickness in excess of flotation remained at about 50 m. This suggests that retreat may be initiated when the terminal thickness becomes too small, with the rate of retreat controlled by the rate at which the snout is thinning and by the basal slope. The implication is that the rapid retreat of Columbia Glacier (and other comparable tidewater glaciers) is not the result of an increase in calving as the glacier retreated into deeper water. Instead, the retreat was initiated and maintained by thinning of the glacier. For Columbia Glacier, the continued thinning is probably associated with the increase in glacier speed and retreat may be expected to continue as long as these large speeds are maintained. It is not clear what mechanism may be responsible for the speed-up but the most likely candidate is a change in basal conditions or subglacial drainage. Consequently, the behavior of tidewater glaciers may be controlled by processes acting at the glacier bed rather than by what happens at the glacier terminus.

Download Full-text

Tidewater calving

Journal of Glaciology ◽

10.1017/s0022143000004226 ◽

1996 ◽

Vol 42 (141) ◽

pp. 375-385 ◽

Cited By ~ 140

Author(s):

С.J. Van Der Veen

Keyword(s):

Water Depth ◽

Fold Increase ◽

Actual Rate ◽

Tidewater Glaciers ◽

Glacier Terminus ◽

Tidewater Glacier ◽

Iceberg Calving ◽

Speed Up ◽

Calving Rate ◽

Subglacial Drainage

AbstractData from Columbia Glacier are used to identify processes that control calving from a temperate tidewater glacier and to re-evaluate models that have been proposed to describe iceberg calving. Since 1981, Columbia Glacier has been retreating rapidly, with an almost seven-fold increase in calving rate from the mid-1970s to 1993. At the same time, the speed of the glacier increased almost as much, so that the actual rate of retreat increased more slowly. According to the commonly accepted model, the calving rate is linearly related to the water depth at the terminus, with retreat of the glacier snout into deeper water, leading to larger calving rates and accelerated retreat. The Columbia Glacier data show that the calving rate is not simply linked to observed quantities such as water depth or stretching rate near the terminus. During the retreat, the thickness at the terminus appears to be linearly correlated with the water depth; at the terminus, the thickness in excess of flotation remained at about 50 m. This suggests that retreat may be initiated when the terminal thickness becomes too small, with the rate of retreat controlled by the rate at which the snout is thinning and by the basal slope. The implication is that the rapid retreat of Columbia Glacier (and other comparable tidewater glaciers) is not the result of an increase in calving as the glacier retreated into deeper water. Instead, the retreat was initiated and maintained by thinning of the glacier. For Columbia Glacier, the continued thinning is probably associated with the increase in glacier speed and retreat may be expected to continue as long as these large speeds are maintained. It is not clear what mechanism may be responsible for the speed-up but the most likely candidate is a change in basal conditions or subglacial drainage. Consequently, the behavior of tidewater glaciers may be controlled by processes acting at the glacier bed rather than by what happens at the glacier terminus.

Download Full-text

Dynamics of tidewater glaciers: comparison of three models

Journal of Glaciology ◽

10.3189/172756506781828755 ◽

2006 ◽

Vol 52 (177) ◽

pp. 183-190 ◽

Cited By ~ 14

Author(s):

F.M. Nick ◽

J. Oerlemans

Keyword(s):

Water Depth ◽

Mass Conservation ◽

Equilibrium States ◽

The Other ◽

Tidewater Glaciers ◽

One Dimensional ◽

Glacier Terminus ◽

Tidewater Glacier ◽

Linear Behaviour ◽

Calving Rate

AbstractA minimal model of a tidewater glacier based solely on mass conservation is compared with two one-dimensional numerical flowline models, one with the calving rate proportional to water depth, and the other with the flotation criterion as a boundary condition at the glacier terminus. The models were run with two simplified bed geometries and two mass-balance formulations. The models simulate the full cycle of length variations and the equilibrium states for a tidewater glacier. This study shows that the branching of the equilibrium states depends significantly on the bed geometry. The similarity between the results of the three models indicates that if there is a submarine undulation at the terminus of a tidewater glacier, any model in which the frontal ice loss is related to the water depth yields qualitatively the same non-linear behaviour. For large glaciers extending into deep water, the flotation model causes unrealistic behaviour.

Download Full-text

‘Calving laws’, ‘sliding laws’ and the stability of tidewater glaciers

Annals of Glaciology ◽

10.3189/172756407782871161 ◽

2007 ◽

Vol 46 ◽

pp. 123-130 ◽

Cited By ~ 111

Author(s):

Douglas I. Benn ◽

Nicholas R.J. Hulton ◽

Ruth H. Mottram

Keyword(s):

Water Depth ◽

Ice Thickness ◽

Strain Rates ◽

Effective Pressure ◽

Ice Shelves ◽

Tidewater Glaciers ◽

Surface Gradient ◽

Ice Velocity ◽

Calving Rate ◽

The Stability

AbstractA new calving criterion is introduced, which predicts calving where the depth of surface crevasses equals ice height above sea level. Crevasse depth is calculated from strain rates, and terminus position and calving rate are therefore functions of ice velocity, strain rate, ice thickness and water depth. We couple the calving criterion with three ‘sliding laws’, in which velocity is controlled by (1) basal drag, (2) lateral drag and (3) a combination of the two. In model 1, velocities and strain rates are dependent on effective pressure, and hence ice thickness relative to water depth. Imposed thinning can lead to acceleration and terminus retreat, and ice shelves cannot form. In model 2, ice velocity is independent of changes in ice thickness unless accompanied by changes in surface gradient. Velocities are strongly dependent on channel width, and calving margins tend to stabilize at flow-unit widenings. Model 3 exhibits the combined characteristics of the other two models, and suggests that calving glaciers are sensitive to imposed thickness changes if basal drag provides most resistance to flow, but stable if most resistance is from lateral drag. Ice shelves can form if reduction of basal drag occurs over a sufficiently long spatial scale. In combination, the new calving criterion and the basal–lateral drag sliding function (model 3) can be used to simulate much of the observed spectrum of behaviour of calving glaciers, and present new opportunities to model ice-sheet response to climate change.

Download Full-text

The retreat of a tidewater glacier: observations and model calculations on Hansbreen, Spitsbergen

Journal of Glaciology ◽

10.3189/172756502781831089 ◽

2002 ◽

Vol 48 (163) ◽

pp. 592-600 ◽

Cited By ~ 81

Author(s):

Andreas Vieli ◽

Jacek Jania ◽

Lezek Kolondra

Keyword(s):

Direct Response ◽

Critical Height ◽

Time Step ◽

Model Calculations ◽

Tidewater Glaciers ◽

Water Line ◽

Glacier Terminus ◽

Front Position ◽

Tidewater Glacier ◽

Calving Rate

AbstractBased on observations and model calculations, the retreat over the last two decades of Hansbreen, a tidewater glacier in southern Spitsbergen, Svalbard, is investigated. The observations of the calving-front position between 1982 and 1998 show an abrupt retreat in 1990, which is suggested to be related to a depression in the glacier bed. The observed seasonal variations of the front position are mainly due to variations of the calving rate. The observations of Hansbreen further indicate that during periods of slow front-position changes, melting at the water-line may play an important role in triggering the process of calving. The evolution of Hansbreen between 1982 and 1998 is simulated with a numerical model for the dynamics of tidewater glaciers. Using a flotation criterion for calving in which for each time-step the part of the glacier terminus which is below a critical height above buoyancy is removed, we are able to reproduce the observed rapid retreat of Hansbreen through the depression in the glacier bed. From the observations and model calculations, we conclude that the rapid retreat is mainly an effect of basal topography in the terminus region and not a direct response to a change in mass balance.

Download Full-text

A minimal model of a tidewater glacier

Annals of Glaciology ◽

10.3189/172756405781813023 ◽

2005 ◽

Vol 42 ◽

pp. 1-6 ◽

Cited By ~ 23

Author(s):

J. Oerlemans ◽

F.M. Nick

Keyword(s):

Velocity Field ◽

Water Depth ◽

Ice Thickness ◽

Global Dynamics ◽

Equilibrium Line Altitude ◽

Glacier Terminus ◽

Tidewater Glacier ◽

Glacier Length ◽

Parameterized Model ◽

Calving Rate

AbstractWe propose a simple, highly parameterized model of a tidewater glacier. The mean ice thickness and the ice thickness at the glacier front are parameterized in terms of glacier length and, when the glacier is calving, water depth. We use a linear relation between calving rate and water depth. The change in glacier length is determined by the total change in the mass budget (surface balance and calving flux), but not by the details of the glacier profile and the related velocity field. We show that this may still yield relatively rapid rates of retreat for an idealized bed geometry with a smooth overdeepening. The model is able to simulate the full cycle of ice-free conditions, glacier terminus on land, tidewater glaciers terminus, and backwards. We study two cases: (i) a glacier with a specific balance (accumulation) that is spatially uniform, and (ii) a glacier in a warmer climate with the specific balance being a linear function of altitude. Equilibrium states exhibit a double branching with respect to the climatic forcing (equilibrium-line altitude). One bifurcation is related to the dependence of the calving process on the bed profile; the other bifurcation is due to the height–mass-balance feedback. We discuss the structure of the solution diagram for different values of the calving-rate parameter. The model results are similar to those of Vieli and others (2001), who combined a fairly sophisticated two-dimensional (vertical plane) numerical ice-flow model with the modified flotation criterion suggested by Van der Veen (1996). With regard to the global dynamics of a tidewater glacier, we conclude that the details of the glacier profile or velocity field are less significant than the bed profile and the relation between the water depth and the calving rate.

Download Full-text

Investigating calving front morphology as a precursor to dynamic behaviour at a large Greenlandic tidewater glacier

10.5194/egusphere-egu2020-16531 ◽

2020 ◽

Author(s):

Charlie Bunce ◽

Pete Nienow ◽

Noel Gourmelen ◽

Tom Cowton

Keyword(s):

Morphological Change ◽

Dynamic Models ◽

Greenland Ice Sheet ◽

Glacier Retreat ◽

Accurate Estimation ◽

Tidewater Glaciers ◽

Air Temperatures ◽

Glacier Dynamics ◽

Tidewater Glacier ◽

Iceberg Calving

<p>Successful prediction of the response of the Greenland Ice Sheet to climate warming requires accurate estimation of future ice loss from tidewater glaciers. Patterns of tidewater glacier retreat and advance have acted as an important proxy for understanding the processes associated with frontal ablation. It has not however been possible to effectively constrain commonality in these observed patterns that can then be directly linked to the influence of specific controls on ice loss. Here, we investigate planform changes in calving front morphology, an aspect of glacier dynamics that has received little prior attention; however, an improved understanding and quantification of the role of morphometric change in influencing glacier dynamics and iceberg calving may provide critical insights into tidewater glacier behaviour. We develop a buffer analysis method to quantify changes in calving front morphology at Narsap Sermia, a large tidewater glacier in southwest Greenland that has experienced substantial recent retreat. Our results reveal no distinct temporal or spatial patterns in the timing or magnitude of morphological change. Furthermore, we found no statistically significant relationships between morphological change and a range of forcing factors including air temperatures, modelled estimates of subglacial discharge and variations in glacier bed geometry. Our results therefore suggest that process driven morphological terminus change is not an effective predictor of terminus retreat and instead support the application of generalised parameterisations of tidewater glacier retreat within ice-dynamic models.</p>

Download Full-text

Calving speed and climatic sensitivity of New Zealand lake-calving glaciers

Annals of Glaciology ◽

10.3189/172756403781816446 ◽

2003 ◽

Vol 36 ◽

pp. 173-178 ◽

Cited By ~ 42

Author(s):

Charles R. Warren ◽

Martin P. Kirkbride

Keyword(s):

New Zealand ◽

Fresh Water ◽

Climatic Forcing ◽

Tidewater Glaciers ◽

Physical Relation ◽

Compressive Flow ◽

Climatic Sensitivity ◽

Order Of Magnitude ◽

The Relationship ◽

Water Depths

AbstractCalving 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 21 glaciers. For this dataset, calving rates (uc) correlate positively with water depths (hw) (r2 = 0.83), the relationship being expressed by: uc = 17.4 + 2.3 hw. This is an order of magnitude lower than values of uc at temperate tidewater 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).

Download Full-text

A 15-year circum-Antarctic iceberg calving dataset derived from continuous satellite observations

Earth System Science Data ◽

10.5194/essd-13-4583-2021 ◽

2021 ◽

Vol 13 (9) ◽

pp. 4583-4601

Author(s):

Mengzhen Qi ◽

Yan Liu ◽

Jiping Liu ◽

Xiao Cheng ◽

Yijing Lin ◽

...

Keyword(s):

Mass Loss ◽

Ice Sheet ◽

Satellite Observations ◽

Ice Shelf ◽

Time Intervals ◽

Antarctic Ice Sheet ◽

Ice Shelves ◽

Iceberg Calving ◽

Calving Rate ◽

The Antarctic

Abstract. Iceberg calving is the main process that facilitates the dynamic mass loss of ice sheets into the ocean, which accounts for approximately half of the mass loss of the Antarctic ice sheet. Fine-scale calving variability observations can help reveal the calving mechanisms and identify the principal processes that influence how the changing climate affects global sea level through the ice shelf buttressing effect on the Antarctic ice sheet. Iceberg calving from entire ice shelves for short time intervals or from specific ice shelves for long time intervals has been monitored before, but there is still a lack of consistent, long-term, and high-precision records on independent calving events for all of the Antarctic ice shelves. In this study, a 15-year annual iceberg calving product measuring every independent calving event larger than 1 km2 over all of the Antarctic ice shelves that occurred from August 2005 to August 2020 was developed based on 16 years of continuous satellite observations. First, the expansion of the ice shelf frontal coastline was simulated according to ice velocity; following this, the calved areas, which are considered to be the differences between the simulated coastline, were manually delineated, and the actual coastline was derived from the corresponding satellite imagery, based on multisource optical and synthetic aperture radar (SAR) images. The product provides detailed information on each calving event, including the associated year of occurrence, area, size, average thickness, mass, recurrence interval, and measurement uncertainties. A total of 1975 annual calving events larger than 1 km2 were detected on the Antarctic ice shelves from August 2005 to August 2020. The average annual calved area was measured as 3549.1 km2 with an uncertainty value of 14.3 km2, and the average calving rate was measured as 770.3 Gt yr−1 with an uncertainty value of 29.5 Gt yr−1. The number of calving events, calved area, and calved mass fluctuated moderately during the first decade, followed by a dramatic increase from 2015/2016 to 2019/2020. During the dataset period, large ice shelves, such as the Ronne–Filchner and Ross ice shelves, advanced with low calving frequency, whereas small- and medium-sized ice shelves retreated and calved more frequently. Iceberg calving of ice shelves is most prevalent in West Antarctica, followed by the Antarctic Peninsula and Wilkes Land in East Antarctica. The annual iceberg calving event dataset of Antarctic ice shelves provides consistent and precise calving observations with the longest time coverage. The dataset provides multidimensional variables for each independent calving event that can be used to study detailed spatial–temporal variations in Antarctic iceberg calving. The dataset can also be used to study ice sheet mass balance, calving mechanisms, and responses of iceberg calving to climate change. The dataset, entitled “Annual iceberg calving dataset of the Antarctic ice shelves (2005–2020)”, is shared via the National Tibetan Plateau Data Center: https://doi.org/10.11888/Glacio.tpdc.271250 (Qi et al., 2021). In addition, the average annual calving rate of 18.4±6.7 Gt yr−1 for calving events smaller than 1 km2 of the Antarctic ice shelves and the calving rate of 166.7±15.2 Gt yr−1 for the marine-terminating glaciers were estimated.

Download Full-text