Iceberg Calving and Meltwater Drainage at the Ice-Cliff Terminus of Helheim Glacier, Greenland

Home , Meltwater

Sierra Melton Richard Alley Sridhar Anandakrishnan Byron Parizek

Penn State Photo: NASA Geosciences Helheim

NASA JPL

Introduction Methods Results Discussion Conclusion 2 Marine-terminating glaciers

Glacier

Fjord

Image: NASA

Introduction Methods Results Discussion Conclusion 3 Marine-terminating glaciers lose ice through…

Iceberg calving Melting

Modified from Parizek et al., 2019 Modified from www.AntarcticGlaciers.org, Jacob Bendle

Introduction Methods Results Discussion Conclusion 4 Calving: Not all icebergs are created equal

Nontabular Icebergs

Tabular Icebergs

Sentinel-2, 7 May 2016, Helheim

Introduction Methods Results Discussion Conclusion 5 Nontabular iceberg calving at Helheim Glacier

Time-lapse footage, James et al., 12 July 2010

Introduction Methods Results Discussion Conclusion 6 Meltwater: Glacial hydrology

surface meltwater lake

icebergs

glacier fjord

Modified from Introduction Methods Results Discussion Conclusion www.AntarcticGlaciers.org, Jacob Bendle 7 Meltwater: Glacial hydrology

surface meltwater lake

Surface meltwater icebergs drains to bed

glacier fjord Subglacial hydrology High water supply: Channelized network (Röthlisberger, 1972)

Modified from Introduction Methods Results Discussion Conclusion www.AntarcticGlaciers.org, Jacob Bendle 8 Meltwater: Glacial hydrology

surface meltwater lake

Surface meltwater icebergs drains to bed

glacier fjord Subglacial hydrology Meltwater plume High water supply: Channelized network (Röthlisberger, 1972) Buoyant freshwater rises toward surface, stopping after reaching neutral density Hypothesis: Plume appearance indicates that the subglacial water system is channelized to a grounded glacial front

Modified from Introduction Methods Results Discussion Conclusion www.AntarcticGlaciers.org, Jacob Bendle 9 Buoyant meltwater plume at Helheim Glacier

Drone footage from Sridhar Anandakrishnan, summer 2019

Introduction Methods Results Discussion Conclusion 10 Helheim Glacier, Greenland

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)

Introduction Methods Results Discussion Conclusion 11 What is Helheim’s calving behavior? How does meltwater drain? How are calving and meltwater drainage related?

Satellite Imagery Time-Lapse Imagery

2011-2019

Extreme Ice Survey

Introduction Methods Results Discussion Conclusion 12 Satellite Imagery

1NIR: Near-Infrared 2SWIR: Short-wave Infrared 3CAVIS: Clouds, Aerosols, Water Vapor, Ice, & Snow

Introduction Methods Results Discussion Conclusion 13 07-18-2017 06:00

Plume at center terminus Fractures south of plume

Meltwater plume observation

Introduction Methods Results Discussion Conclusion 14 07-18-2017 09:00

Plume disappeared

Introduction Methods Results Discussion Conclusion 15 07-18-2017 12:00

Large nontabular calving a few hours after plume disappeared

Introduction Methods Results Discussion Conclusion 16 Plume consistently appeared at central terminus

Introduction Methods Results Discussion Conclusion 17 Digitized terminus positions from satellite imagery

Sentinel-2 band 2, 8 September 2019

Introduction Methods Results Discussion Conclusion 18 Meltwater pooling on glacier surface

Introduction Methods Results Discussion Conclusion 19 Calculated water surface area with NDWIice Normalized Difference Water Index for Ice 퐵퐿푈퐸 − 푅퐸퐷 True-color Sentinel-2 푁퐷푊퐼푖푐푒 = Classified into “water” and imagery from 23 July 2017 퐵퐿푈퐸 + 푅퐸퐷 “no water” pixels

NDWIice method developed by Yang & Smith (2013)

Introduction Methods Results Discussion Conclusion 20 Time-series: Plume

Introduction Methods Results Discussion Conclusion 21 Time-series: Plume, calving

Introduction Methods Results Discussion Conclusion 22 Time-series: Plume, calving, terminus position

Introduction Methods Results Discussion Conclusion 23 Time-series: Plume, calving, terminus position, & surface water

Introduction Methods Results Discussion Conclusion 24 Terminus position: Advance and retreat

Relatively stable terminus position 2011-2016 Retreated ~1.5 km beyond despite ~3-4 km seasonal fluctuations previous retreats in 2017 & 2019

Most advanced – 10 Mar 2011 (defined as zero) Most retreated – 8 Sep 2019 (5.6 km behind)

Introduction Methods Results Discussion Conclusion 25 Calving and plumes

Introduction Methods Results Discussion Conclusion 26 Ceased calving when plume was visible

One exception: 16 April 2017

Introduction Methods Results Discussion Conclusion 27 Ceased calving when plume was visible, except…

16 April 2017

Tabular iceberg

Plume

Landsat-8

Introduction Methods Results Discussion Conclusion 28 Why did calving (generally) not occur while a plume was visible?

Basal crevasses could be unable to Supports our hypothesis that form at a completely grounded glacial plume appearance indicates a grounded glacial front, inhibiting full-thickness calving front and channelized subglacial water system

Modified from Murray et al. (2015)

Introduction Methods Results Discussion Conclusion 29 Meltwater drainage: Subglacial flow pathways

Subglacial flow pathways coincide with plume locations

Sentinel-2, 7 May 2016

Introduction Methods Results Discussion Conclusion 30 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 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

Introduction Methods Results Discussion Conclusion 32 Link between meltwater drainage and iceberg calving, the two major ways in which marine-terminating glaciers lose ice

Background Image: NASA

Introduction Methods Results Discussion Conclusion 33 Acknowledgements

• 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

Background Image: NASA 34 Thank you!

@SierraMelting