Oceanography The Official Magazine of
The Oceanography Society
Volume 29 Issue 04

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Volume 29, No. 4
Pages 46 - 61

An Intensive Observation of Calving at Helheim Glacier, East Greenland

David M. Holland Denis VoytenkoKnut ChristiansonTimothy H. DixonM. Jeffrey MeiByron R. ParizekIrena Vaňková Ryan T. WalkerJacob I. WalterKeith NichollsDenise Holland
Article Abstract

Calving of glacial ice into the ocean from the Greenland Ice Sheet is an important component of global sea level rise. The calving process itself is relatively poorly observed, understood, and modeled; as such, it represents a bottleneck in improving future global sea level estimates in climate models. We organized a pilot project to observe the calving process at Helheim Glacier in East Greenland in an effort to better understand it. During an intensive one-week survey, we deployed a suite of instrumentation including a terrestrial radar interferometer, GPS receivers, seismometers, tsunameters, and an automated weather station. This effort captured a calving process and measured various glaciological, oceanographic, and atmospheric parameters before, during, and after the event. One outcome of our observations is evidence that the calving process actually consists of a number of discrete events, spread out over time, in this instance over at least two days. This time span has implications for models of the process. Realistic projections of future global sea level will depend on accurate parametrization of calving, which will require more sustained observations.


Holland, D.M., D. Voytenko, K. Christianson, T.H. Dixon, M.J. Mei, B.R. Parizek, I. Vaňková, R.T. Walker, J.I. Walter, K. Nicholls, and D. Holland. 2016. An intensive observation of calving at Helheim Glacier, East Greenland. Oceanography 29(4):46–61, https://doi.org/10.5670/oceanog.2016.98.

Supplementary Materials

SUPPLEMENTAL FIGURE S1. Feature-tracking results showing glacier ice surface velocity vectors over a two-day period (August 13 00:10–August 15 00:10, 2014) overlain on a terrestrial radar interferometry (TRI)-derived digital elevation map (DEM) from August 11 01:00. Speeds are of order 20 m d–1 and the velocity vectors were determined by using two TRI intensity images and the OpenPIV software (Taylor et al., 2010). The tracking was performed on imagery with 15 m spacing, with a 16-pixel window size and an overlap of 8 pixels. Each velocity component was filtered with a 2-sigma filter and later a 3 × 3 median filter and (for plotting purposes) downsampled by a factor of 10. These results show two-dimensional velocity vectors obtained over a multihour-scale time period. However, TRI results typically rely on interferometry and provide single-component velocity measurements (toward the radar) but over minute-scale time steps. White indicates areas of no data. (324 KB jpg)

SUPPLEMENTAL FIGURE S2. Time series of displacement and velocity of a pixel observed by terrestrial radar interferometry (TRI) near the Helheim Glacier terminus in August 2014. (top) Line-of-sight displacement of a pixel as recorded by the TRI. Black solid vertical lines show the timing of the primary (left side) and secondary (right side) calving events. (middle) Detrended version of the top panel showing displacement “anomaly” over time and also some semidiurnal tidal variability. Despite the presence of the primary calving event, the displacement rate remained relatively constant. (bottom). The derived velocity time series illustrates calving-driven variations and tidal variations, along with instrument-related phase unwrapping errors (spikes). The red line shows the velocity as derived from a nearby GPS receiver (HEL0 in Figure 7 in the main article). Note the good agreement between the TRI and GPS velocities and that the TRI velocity is lower than the GPS velocity (within the noise level). This is because TRI measures a projection of the true velocity vector onto the TRI look vector (line-of-sight). (251 KB png)

SUPPLEMENTAL FIGURE S3. Animated sequence of glacier front position at Helheim Glacier from terrestrial radar interferometry (TRI) during deployment in August 2014, spanning the primary (August 12) and secondary (August 13) calving events. The animation is based on three TRI intensity images (August 12, 05:46 UTC; August 12 07:46 UTC; August 13, 11:40 UTC) overlain on top of a Landsat 8 image. First frame shows the pre-calving terminus during the primary event. Second frame shows the terminus after the primary calving event. Third frame shows the terminus after a smaller secondary calving event that affected only the southern trunk of the glacier, and was likely a continuation of the primary event. (6.3 MB gif)

SUPPLEMENTAL FIGURE S4. Animated sequence of glacier front position at Helheim Glacier from terrestrial radar interferometry (TRI) during deployment in August 2014, spanning the primary (August 12) and secondary (August 13) calving events. The glacier is flowing from top right toward lower left. Background color indicates coherence of radar return with yellow indicating high-coherence thus slow moving glacier; pink color indicates low-coherence thus fast moving glacier. A time index is shown in the lower right.  (14.4 MB gif)

SUPPLEMENTAL FIGURE S5. Profiles of strain rate and surface elevation before (red), during (black), and after (blue) the primary calving event in the vicinity of the profile shown in Figure 6 in the main article. Strain rate (top curves) is given as a function of distance near the glacier front. Glacier front elevations (bottom curves) are obtained from hourly averages. The dashed line (top curves) shows transition from extension (positive strain rate, above) to compression (negative strain rate, below). Strain rates increase as the slope of the front becomes more pronounced. In all times, the mélange is under compression. (245 KB png)

SUPPLEMENTAL FIGURE S6. Animation of the elevation changes around the ~1 hour period associated with the primary calving event (~6:37 on August 12, 2014) on the northern trunk of Helheim Glacier. Each frame represents two minutes. Ice cliff elevations before calving are approximately 100 m. Note how the block of ice rotates during calving. (5.7 MB gif)

SUPPLEMENTAL FIGURE S7. A precursory seismic event detected at approximately 05:46 UTC on August 12, 2014, almost one hour prior to the primary calving event. The plots show the seismic energy as a function of time at (a) the on-land seismometer located on the south side of the fjord, (b) the on-land, north-side seismometer, and (c) the on-glacier, seismometer located near the calving front. Locations of the stations are seen in Figures 7 and 9 in the main article. (80 KB png)

SUPPLEMENTAL FIGURE S8. Animated one-year-long sequence of glacier front position at Helheim Glacier from an on-land automated weather station during the year preceding our pilot field campaign of August 2014. The winter calving advance and summer retreat as well as the aperiodic nature of calving is apparent. (7.9 MB gif)

SUPPLEMENTAL FIGURE S9. Simulation of elastic stresses in a two-dimensional (vertical slice) along-flow-line glacier model (glacier flow is from left to right). The stresses are generated by ocean tidal forcing at the glacier front, on the far right. (a) Tidal anomaly in front of Helheim Glacier from a seafloor Tsunameter pressure sensor. (b) Magnitude of deflection of the equilibrium glacier bed associated with a ~1.1 m low tide indicated by the red circle in (a), assuming a partially supported beam with Young’s Modulus of 4.8 GPa and Poisson ratio of 0.4. (c) Longitudinal deviatoric stress field within ~6.75 km of the glacier front due to the deflection in (b) (positive for tension and negative for compression). The glacier front is located at approximately position 41.5 km, at the far right. (459 KB jpg)


Alley, R.B., H.J. Horgan, I. Joughin, K.M. Cuffey, T.K. Dupont, B.R. Parizek, S. Anandakrishnan, and J. Bassis. 2008. A simple law for ice-shelf calving. Science 322(5906):1,344, https://doi.org/10.1126/science.1162543.

Amundson, J.M., J.F. Clinton, M. Fahnestock, M. Truffer, M.P. Lüthi, and R.J. Motyka. 2012. Observing calving-generated ocean waves with coastal broadband seismometers, Jakobshavn Isbræ, Greenland. Annals of Glaciology 53(60):79–84, https://doi.org/​10.3189/2012/AoG60A200.

Amundson, J.M., M. Fahnestock, M. Truffer, J. Brown, M.P. Luthi, and R.J. Motyka. 2010. Ice mélange dynamics and implications for terminus stability, Jakobshavn Isbræ, Greenland. Journal of Geophysical Research 115, F01005, https://doi.org/10.1029/2009JF001405.

Amundson, J.M., and M. Truffer. 2010. A unifying framework for iceberg-calving models. Journal of Glaciology 56(199):822–830, https://doi.org/​10.3189/002214310794457173.

Amundson, J.M., M. Truffer, M.P. Lüthi, M. Fahnestock, M. West, and R.J. Motyka. 2008. Glacier, fjord, and seismic response to recent large calving events, Jakobshavn Isbræ, Greenland. Geophysical Research Letters 35, L22501, https://doi.org/​10.1029/2008GL035281.

Bartholomaus, T.C., J.M. Amundson, J.I. Walter, S. O’Neel, M.E. West, and C.F. Larsen. 2015. Subglacial discharge at tidewater glaciers revealed by seismic tremor. Geophysical Research Letters 42(15):6,391–6,398, https://doi.org/10.1002/2015GL064590.

Bassis, J.N. 2011. The statistical physics of iceberg calving and the emergence of universal calving laws. Journal of Glaciology 57(201):3–16, https://doi.org/10.3189/002214311795306745.

Bassis, J.N., and C.C. Walker. 2011. Upper and lower limits on the stability of calving glaciers from the yield strength envelope of ice. Proceedings of the Royal Society A, https://doi.org/10.1098/rspa.2011.0422.

Benn, D.I., C.R. Warren, and R.H Mottram. 2007. Calving processes and the dynamics of calving glaciers. Earth-Science Reviews 82:143–179, https://doi.org/10.1016/j.earscirev.2007.02.002.

Böning, C.W., E. Behrens, A. Biastoch, K. Getzlaff, and J.L. Bamber. 2016. Emerging impact of Greenland meltwater on deepwater formation in the North Atlantic Ocean. Nature Geoscience 9:523–527, https://doi.org/10.1038/ngeo2740.

Bromirski, P.D., O.V. Sergienko, and D.R. MacAyeal. 2010. Transoceanic infragravity waves impacting Antarctic ice shelves. Geophysical Research Letters 37, L02502, https://doi.org/​10.1029/2009GL041488.

Brown, C.S., M.F. Meier, and A. Post. 1982. Calving Speed of Alaska Tidewater Glaciers with Applications to the Columbia Glacier, Alaska. US Geological Survey Professional Paper 1258-C, 13 pp.

Caduff, R., F. Schlunegger, A. Kos, and A. Wiesmann. 2015. A review of terrestrial radar interferometry for measuring surface change in the geosciences. Earth Surface Processes and Landforms 40(2):208–228, https://doi.org/10.1002/esp.3656.

Chen, G. 1998. GPS Kinematics Positioning for Airborne Laser Altimetry at Long Valley, California. PhD thesis, Massachusetts Institute of Technology, Cambridge, MA, USA.

Colgan, W., H. Rajaram, W. Abdalati, C. McCutchan, R. Mottram, M. Moussavi, and S. Grigsby. 2016. Glacier crevasses: Observations, models and mass balance implications. Reviews of Geophysics 54:119–161, https://doi.org/​10.1002/​2015RG000504.

De Angelis, H., and P. Skvarca. 2003. Glacier surge after ice shelf collapse. Science 299(5612):1,560–1,562, https://doi.org/10.1126/science.1077987

DeConto, R.M., and D. Pollard. 2016. Contribution of Antarctica to past and future sea-level rise. Nature 531(7596):591–597, https://doi.org/10.1038/nature17145.

Goldstein, R.M., H. Engelhardt, W.B. Kamb, and R.M. Frohlich. 1993. Satellite radar interferometry for monitoring ice sheet motion: Application to an Antarctic ice stream. Science 262:1,525–1,530, https://doi.org/10.1126/science.262.5139.1525.

Glen, J.W. 1958. The flow law of ice: A discussion of the assumptions made in glacier theory, their experimental foundations and consequences. International Association of Hydrological Sciences Publishing 47:171–183.

Hibler, W.D. 1979. A dynamic thermodynamic sea ice model. Journal of Physical Oceanography 9(4):815–846, https://doi.org/​10.1175/1520-0485(1979)009<0815:ADTSIM>​2.0.CO;2.

Holland, D.M., R.H. Thomas, B. DeYoung, M.H. Ribergaard, and B. Lyberth. 2008. Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters. Nature Geoscience 1:659–664, https://doi.org/10.1038/ngeo316.

Howat, I.M., I. Joughin, S. Tulaczyk, and S. Gogineni. 2005. Rapid retreat and acceleration of Helheim glacier, east Greenland. Geophysical Research Letters 32, L22502, https://doi.org/​10.1029/2005GL024737.

Howat, I.M., A. Negrete, and B.E. Smith. 2014. The Greenland Ice Mapping Project (GIMP) land classification and surface elevation datasets. The Cryosphere 8:1,509–1,518, https://doi.org/10.5194/tc-8-1509-2014.

IPCC (Intergovernmental Panel on Climate Change). 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller, eds, Cambridge University Press, Cambridge, United Kingdom, and New York, NY, USA, 996 pp.

IPCC. 2013. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. T.F. Stocker, D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex, and P.M. Midgley, eds, Cambridge University Press, Cambridge, United Kingdom, and New York, NY, USA, 1,535 pp. 

ISP/DIFF/LAT. 2016. GAMMA Processing Software: Interferometric SAR Processor (ISP), Differential Interferometry and Geocoding package (DIFF), and Land Application Tools (LAT), http://www.gamma-rs.ch/no_cache/software.html.

James, T.D., T. Murray, N. Selmes, K. Scharrer, and M. O’Leary. 2014. Buoyant flexure and basal crevassing in dynamic mass loss at Helheim Glacier. Nature Geoscience 7(8):593–596, https://doi.org/​10.1038/ngeo2204.

Joughin, I., W. Abdalati, and M. Fahnestock. 2004. Large fluctuations in speed on Greenland’s Jakobshavn Isbrae glacier. Nature 432:608–610, https://doi.org/10.1038/nature03130.

Joughin, I., R.B. Alley, and D.M. Holland. 2012. Ice sheet response to oceanic forcing. Science 338(6111):1,172–1,176, https://doi.org/10.1126/science.1226481.

Joughin, I., L. Gray, R. Bindschadler, S. Price, D. Morse, C. Hulbe, K. Mattar, and C. Werner. 1999. Tributaries of West Antarctic ice streams revealed by RADARSAT interferometry. Science 286:283–286, https://doi.org/10.1126/science.286.5438.283.

Joughin, I., I.M. Howat, R.B. Alley, G. Ekstrom, M. Fahnestock, T. Moon, M. Nettles, M. Truffer, and V.C. Tsai. 2008. Ice-front variation and tidewater behavior on Helheim and Kangerdlugssuaq Glaciers, Greenland. Journal of Geophysical Research 113, F01004, https://doi.org/10.1029/2007JF000837.

Krug, J., J. Weiss, O. Gagliardini, and G. Durand. 2014. Combining damage and fracture mechanics to model calving. The Cryosphere 8(6):2,101–2,117, https://doi.org/10.5194/tc-8-2101-2014.

Leuschen, C., and C. Allen. 2013. IceBridge MCoRDS L3 Gridded Ice Thickness, Surface, and Bottom, Version 2, Helheim_2008_2012_Composite. NASA DAAC at the National Snow and Ice Data Center. Boulder, Colorado, http://nsidc.org/data/docs/daac/icebridge/irmcr3.

Levermann, A., T. Albrecht, R. Winkelmann, M.A. Martin, M. Haseloff, and I. Joughin. 2012. Kinematic first-order calving law implies potential for abrupt ice-shelf retreat. The Cryosphere 6(2):273–286, https://doi.org/10.5194/tc-6-273-2012.

Luckman, A., T. Murray, R. de Lange, and E. Hanna. 2006. Rapid and synchronous ice-dynamic changes in East Greenland. Geophysical Research Letters 33, L03503, https://doi.org/​10.1029/2005GL025428.

MacAyeal, D.R., E.A. Okal, R.C. Aster, and J.N. Bassis. 2009. Seismic observations of glaciogenic waves (micro-tsunamis) on icebergs and ice shelves. Journal of Glaciology 55(190):193–206, https://doi.org/10.3189/002214309788608679.

Mei, M.J., D.M. Holland, S. Anandakrishnan, and T. Zheng. 2016. A two-station seismic method to localize glacier calving. The Cryosphere Discussion, https://doi.org/10.5194/tc-2016-85.

Meier, M.F., and A. Post. 1987. Fast tidewater glaciers. Journal of Geophysical Research 92(B9):9,051–9,058, https://doi.org/​10.1029/JB092iB09p09051.

Murray, T., N. Selmes, T.D. James, S. Edwards, I. Martin, T. O’Farrell, R. Aspey, I. Rutt, M. Nettles, and T. Baugé. 2015. Dynamics of glacier calving at the ungrounded margin of Helheim Glacier, southeast Greenland. Journal of Geophysical Research 120(6):964–982, https://doi.org/​10.1002/2015JF003531.

Moon, T., and I. Joughin. 2008. Changes in ice front position on Greenland’s outlet glaciers from 1992 to 2007. Journal of Geophysical Research 113, F02022, https://doi.org/10.1029/2007JF000927.

Nettles, M., T. Larsen, P. Elósegui, G. Hamilton, L. Stearns, A. Ahlstrøm, J. Davis, M. Andersen, J. de Juan, and S. Khan. 2008. Step-wise changes in glacier flow speed coincide with calving and glacial earthquakes at Helheim Glacier, Greenland. Geophysical Research Letters 35, L24503, https://doi.org/10.1029/2008GL036127.

Nick, F.M., A. Vieli, I.M. Howat, and I. Joughin. 2009. Large-scale changes in Greenland outlet glacier dynamics triggered at the terminus. Nature Geoscience 2:110–114, https://doi.org/10.1038/ngeo394.

Nick, F.M., C.J. Van der Veen, A. Vieli, and D.I. Benn. 2010. A physically based calving model applied to marine outlet glaciers and implications for the glacier dynamics. Journal of Glaciology 56(199):781–794, https://doi.org/​10.3189/002214310794457344.

O’Leary, M., and P. Christoffersen. 2013. Calving on tidewater glaciers amplified by submarine frontal melting. The Cryosphere 7(1):119–128, https://doi.org/10.5194/tc-7-119-2013.

Otero, J., F.J. Navarro, C. Martin, M.L. Cuadrado, and M.I. Corcuera. 2010. A three-dimensional calving model: Numerical experiments on Johnsons Glacier, Livingston Island, Antarctica. Journal of Glaciology 56(196):200–214, https://doi.org/​10.3189/002214310791968539.

Parizek, B.R., K. Christianson, S. Anandakrishnan, R.B. Alley, R.T. Walker, R.A. Edwards, D.S. Wolfe, G.T. Bertini, S.K. Rinehart, R.A. Bindschadler, and S.M.J. Nowicki. 2013. Dynamic (in)stability of Thwaites Glacier, West Antarctica. Journal of Geophysical Research 118:638–655, https://doi.org/10.1002/jgrf.20044.

Peters, I.R., J.M. Amundson, R. Cassotto, M. Fahnestock, K.N. Darnell, M. Truffer, and W.W. Zhang. 2015. Dynamic jamming of iceberg-choked fjords. Geophysical Research Letters 42(4):1,122–1,129, https://doi.org/​10.1002/2014GL062715.

Pralong, A., and M. Funk. 2005. Dynamic damage model of crevasse opening and application to glacier calving. Journal of Geophysical Research 110, B01309, https://doi.org/10.1029/2004JB003104.

Riesen, P., T. Strozzi, A. Bauder, A. Wiesmann, and M. Funk. 2011. Short-term surface ice motion variations measured with a ground-based portable real aperture radar interferometer. Journal of Glaciology 57(201):53–60, https://doi.org/​10.3189/002214311795306718.

Rignot, E. 1998. Fast recession of a West Antarctic glacier. Science 281(5376):549–551, https://doi.org/10.1126/science.281.5376.549.

Rignot, E., and P. Kanagaratnam. 2006. Changes in the velocity structure of the Greenland Ice Sheet. Science 311:986–990, https://doi.org/10.1126/science.1121381.

Rodriguez, E., and J.M. Martin. 1992. Theory and design of interferometric synthetic aperture radars. IEE Proceedings F (Radar and Signal Processing) 139(2):147–159, https://doi.org/10.1049/ip-f-2.1992.0018.

Scambos, T., H.A. Fricker, C.C. Liu, J. Bohlander, J. Fastook, A. Sargent, R. Masson, and A.-M. Wu. 2009. Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups. Earth and Planetary Science Letters 280(1):51–60, https://doi.org/10.1016/j.epsl.2008.12.027.

Schjøth, F., C.S. Andresen, F. Straneo, T. Murray, K. Scharrer, and A. Korablev. 2012. Campaign to map the bathymetry of a major Greenland fjord. Eos, Transactions American Geophysical Union 93(14):141–142, https://doi.org/​10.1029/2012EO140001.

Schoof, C. 2007. Ice sheet grounding line dynamics: Steady states, stability, and hysteresis. Journal of Geophysical Research 112, F03S28, https://doi.org/10.1029/2006JF000664.

Sergeant, A., A. Mangeney, E. Stutzmann, J.P. Montagner, F. Walter, L. Moretti, O. Castelnau. 2016. Complex force history of a calving-​generated glacial earthquake derived from broadband seismic inversion. Geophysical Research Letters 43:1,055–1,065, https://doi.org/​10.1002/2015GL066785.

Shepherd, A., A. Hubbard, P. Nienow, M. King, M. McMillan, and I. Joughin. 2009. Greenland ice sheet daily motion coupled with daily melting in late summer. Geophysical Research Letters 36, L01501, https://doi.org/10.1029/2008GL035758.

Strozzi, T., C. Werner, A. Wiesmann, and U. Wegmuller. 2012. Topography mapping with a portable real-​aperture radar interferometer. IEEE Geoscience and Remote Sensing Letters 9(2):277–281, https://doi.org/10.1109/LGRS.2011.2166751.

Taylor, Z.J., R. Gurka, G.A. Kopp, and A. Liberzon. 2010. Long-duration time-​resolved PIV to study unsteady aerodynamics. IEEE Transactions on Instrumentation and Measurement 59(12):3,262–3,269.

Timoshenko, S.P., and J.N. Goodier. 1970. Theory of Elasticity, 3rd ed. McGraw-Hill, New York, 567 pp.

Truffer, M., and R. Motyka. 2016. Where glaciers meet water: Subaqueous melt and its relevance to glaciers in various settings. Reviews of Geophysics 54:220–239, https://doi.org/​10.1002/2015RG000494.

Van der Veen, C.J. 1998. Fracture mechanics approach to penetration of surface crevasses on glaciers. Cold Regions Science and Technology 27:31–47, https://doi.org/10.1016/S0165-232X(97)00022-0.

Van der Veen, C.J. 2002. Calving glaciers. Progress in Physical Geography 26:96–122, https://doi.org/​10.1191/0309133302pp327ra.

Vaňková, I., and D.M. Holland. 2016. Calving signature in ocean waves at Helheim Glacier and Sermilik Fjord, East Greenland. Journal of Physical Oceanography 46(10):2,925–2,941, https://doi.org/​10.1175/JPO-D-15-0236.1.

Vaughan, D.G., and R. Arthern. 2007. Why is it hard to predict the future of ice sheets? Science 315:1,503–1,504, https://doi.org/10.1126/science.1141111.

Vieli, A., and F.M. Nick. 2011. Understanding and modelling rapid dynamic changes of tidewater outlet glaciers: Issues and implications. Surveys in Geophysics 32(4–5):437–458, https://doi.org/​10.1007/s10712-011-9132-4.

Voytenko, D., T.H. Dixon, I.M. Howat, N. Gourmelen, C. Lembke, C.L. Werner, S. De La Peña, and B. Oddsson. 2015a. Multi-year observations of Breiðamerkurjökull, a marine-terminating glacier in southeastern Iceland, using terrestrial radar interferometry. Journal of Glaciology 61(225):42–54, https://doi.org/10.3189/2015JoG14J099.

Voytenko, D., A. Stern, D.M. Holland, T.H. Dixon, K. Christianson, and R.T. Walker. 2015b. Tidally driven ice speed variation at Helheim Glacier, Greenland, observed with terrestrial radar interferometry. Journal of Glaciology 61(226):301–308, https://doi.org/10.3189/2015JoG14J173.

Walker, C.C., J.N. Bassis, H.A. Fricker, and R.J. Czerwinski. 2015. Observations in the interannual and spatial variability in rift propagation in the Amery Ice Shelf, Antarctica 2002–2014. Journal of Glaciology 1(226):243–252, https://doi.org/10.3189/2015JoG14J151.

Walter, J.I., J.E. Box, S. Tulaczyk, E.E. Brodsky, I.M. Howat, Y. Ahn, and A. Brown. 2012. Oceanic mechanical forcing of a marine-​terminating Greenland glacier. Annals of Glaciology 53(60):181–192, https://doi.org/​10.3189/2012AoG60A083.

Weijer, W., M.E. Maltrud, M.W. Hecht, H.A. Dijkstra, and M.A. Kliphuis. 2012. Response of the Atlantic Ocean circulation to Greenland Ice Sheet melting in a strongly-eddying ocean model. Geophysical Research Letters 39, L09606, https://doi.org/​10.1029/2012GL051611.

Werner, C., T. Strozzi, A. Wiesmann, and U. Wegmuller. 2008. A real-aperture radar for ground-based differential interferometry. Paper presented at the International IEEE Geoscience and Remote Sensing Symposium, July 7–11, 2008, https://doi.org/10.1109/IGARSS.2008.4779320.

Xie, S., T. Dixon, D. Voytenko, D.M. Holland, D. Holland, and T. Zheng. 2016. Precursor motion to iceberg calving at Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry. Journal of Glaciology 62(236):1,134–1,142, https://doi.org/10.1017/jog.2016.104.