iceberg calving and meltwater drainage at the ice-cliff

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

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Introduction Methods Results Discussion Conclusion

Marine-terminating glaciers

Glacier

Fjord

Image: NASA

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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

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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