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Iceberg Calving and Meltwater Drainage at the Ice-Cliff Terminus of Helheim Glacier, Greenland
Photo: NASA
Sierra MeltonRichard Alley
Sridhar AnandakrishnanByron Parizek
Penn State Geosciences
Introduction Methods Results Discussion Conclusion
Helheim
NASA JPL
2
Introduction Methods Results Discussion Conclusion
Marine-terminating glaciers
Glacier
Fjord
Image: NASA
3
Introduction Methods Results Discussion Conclusion
Marine-terminating glaciers lose ice through…
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Iceberg calving Melting
Modified from www.AntarcticGlaciers.org, Jacob BendleModified from Parizek et al., 2019
Introduction Methods Results Discussion Conclusion
Calving: Not all icebergs are created equal
NontabularIcebergs
Tabular Icebergs
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Sentinel-2, 7 May 2016, Helheim
Introduction Methods Results Discussion Conclusion
Nontabular iceberg calving at Helheim Glacier
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Time-lapse footage, James et al., 12 July 2010
icebergs
fjord
Modified from www.AntarcticGlaciers.org, Jacob Bendle
glacier
Meltwater: Glacial hydrology
surface meltwater lake
7Introduction Methods Results Discussion Conclusion
Subglacial hydrologyHigh water supply: Channelized network(Röthlisberger, 1972)
Surface meltwater drains to bed
fjord
Modified from www.AntarcticGlaciers.org, Jacob Bendle
glacier
8Introduction Methods Results Discussion Conclusion
Meltwater: Glacial hydrology
icebergs
surface meltwater lake
Surface meltwater drains to bed
fjord
Modified from www.AntarcticGlaciers.org, Jacob Bendle
glacier
9Introduction Methods Results Discussion Conclusion
Meltwater: Glacial hydrology
icebergs
surface meltwater lake
Meltwater plumeBuoyant freshwater rises toward surface, stopping after reaching neutral density
Subglacial hydrologyHigh water supply: Channelized network(Röthlisberger, 1972)
Hypothesis: Plume appearance indicates that the subglacial water system is channelized to a grounded glacial front
Introduction Methods Results Discussion Conclusion
Drone footage from Sridhar Anandakrishnan, summer 2019
Buoyant meltwater plume at Helheim Glacier
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Introduction Methods Results Discussion Conclusion
Greenland’s 5th largest glacier (Enderlin et al., 2014)
Flows up to >25 m/day: Fastest-flowing glacier in East Greenland (Rignot et al., 2004)
Helheim Glacier, Greenland
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Introduction Methods Results Discussion Conclusion
What is Helheim’s calving behavior?
How does meltwater drain?
How are calving and meltwater drainage related?
Satellite Imagery Time-Lapse Imagery
Extreme Ice Survey
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2011-2019
Introduction Methods Results Discussion Conclusion
Satellite Imagery
1NIR: Near-Infrared 2SWIR: Short-wave Infrared3CAVIS: Clouds, Aerosols, Water Vapor, Ice, & Snow
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Meltwater plume observationIntroduction Methods Results Discussion Conclusion
07-18-2017 06:00
Plume at center terminusFractures south of plume
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Introduction Methods Results Discussion Conclusion
07-18-2017 09:00
Plume disappeared
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Introduction Methods Results Discussion Conclusion
07-18-2017 12:00
Large nontabular calving a few hours after plume disappeared
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Introduction Methods Results Discussion Conclusion 17
Plume consistently appeared at central terminus
WorldView-1 (©2012 Maxar Technologies, Inc.), 24 June 2012
Introduction Methods Results Discussion Conclusion 18
Sentinel-2 band 2, 8 September 2019
Digitized terminus positions from satellite imagery
Introduction Methods Results Discussion Conclusion
Meltwater pooling on glacier surface
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QuickBird (© 2011 MaxarTechnologies, inc.), 24 Aug 2011
Introduction Methods Results Discussion Conclusion
Calculated water surface area with NDWIice
NDWIice method developed by Yang & Smith (2013)
𝑁𝐷𝑊𝐼𝑖𝑐𝑒 =𝐵𝐿𝑈𝐸 − 𝑅𝐸𝐷
𝐵𝐿𝑈𝐸 + 𝑅𝐸𝐷True-color Sentinel-2
imagery from 23 July 2017
Normalized Difference Water Index for Ice
Classified into “water” and “no water” pixels
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Introduction Methods Results Discussion Conclusion 21
Time-series: Plume
Introduction Methods Results Discussion Conclusion 22
Time-series: Plume, calving
Introduction Methods Results Discussion Conclusion
Time-series: Plume, calving, terminus position
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Introduction Methods Results Discussion Conclusion
Time-series: Plume, calving, terminus position, & surface water
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Introduction Methods Results Discussion Conclusion
Terminus position: Advance and retreat
Most advanced – 10 Mar 2011 (defined as zero)Most retreated – 8 Sep 2019 (5.6 km behind)
Relatively stable terminus position 2011-2016 despite ~3-4 km seasonal fluctuations
Retreated ~1.5 km beyond previous retreats in 2017 & 2019
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Introduction Methods Results Discussion Conclusion 26
Calving and plumes
Introduction Methods Results Discussion Conclusion
Ceased calving when plume was visible
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One exception: 16 April 2017
Introduction Methods Results Discussion Conclusion
Ceased calving when plume was visible, except…
16 April 2017
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WV-2 (©2017 Maxar Technologies, Inc.)
Landsat-8
Tabular iceberg
Plume
Introduction Methods Results Discussion Conclusion
Why did calving (generally) not occur while a plume was visible?
Supports our hypothesis thatplume appearance indicates a grounded glacial front and channelized subglacial water system
Basal crevasses could be unable to form at a completely grounded glacial front, inhibiting full-thickness calving
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Modified from Murray et al. (2015)
Introduction Methods Results Discussion Conclusion 30
Sentinel-2, 7 May 2016
Subglacial flow pathways coincide with plume locations
Meltwater drainage: Subglacial flow pathways
Meltwater drainage: Timing
Lake & crevasses: Downglacier filling & drainage progression
Plumes:Appear after subglacial system reconfigures into channelized network
Visible while surface crevasses are filled
Introduction Methods Results Discussion Conclusion 31
Introduction Methods Results Discussion Conclusion
Seasonal sequence driven by evolving hydrology
Lake drainage & large release of meltwater into the subglacial system
Channelized subglacial drainage system
Buoyant plume discharges from grounded terminus Calving ceases
Ungrounding of terminus:Plume dispersion and disappearance
Calving resumes
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Introduction Methods Results Discussion Conclusion
Background Image: NASA
33
Link between meltwater drainage and iceberg calving, the two major ways in which marine-terminating glaciers lose ice
• Huge thank you to my advisors/committee: Sridhar Anandakrishnan, Richard Alley, and Byron Parizek
• Funding from a National Science Foundation Graduate Research Fellowship and the Heising-Simons Foundation
• Michael Shahin, Leigh Stearns, the Cold Regions Research and Engineering Laboratory (CRREL), Laura Kehrl, and Ian Joughin
• Cathleen Torres Parisian and the Polar Geospatial Center
• Nouf Waleed Alsaad, Luke Trusel, the Penn State Ice and Climate Exploration research team, and the Penn State Geosciences Department
Acknowledgements
Background Image: NASA 34
Thank you!
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@SierraMelting