Iceberg Calving and Meltwater Drainage at the Ice-Cliff Terminus of Helheim Glacier, Greenland
Open Access
- Author:
- Melton, Sierra
- Graduate Program:
- Geosciences
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- October 19, 2020
- Committee Members:
- Sridhar Anandakrishnan, Thesis Advisor/Co-Advisor
Richard B Alley, Thesis Advisor/Co-Advisor
Byron Richard Parizek, Thesis Advisor/Co-Advisor
Mark E Patzkowsky, Program Head/Chair - Keywords:
- Greenland
Glaciology
Iceberg
Glacier
Meltwater
Glacial Hydrology
Remote Sensing
Satellite Imagery
Climate Change
Iceberg Calving
Helheim Glacier - Abstract:
- Ice-cliff failure through calving of large icebergs may cause rapid retreat of outlet glaciers and destabilization of inland ice sheets. An improved understanding of calving and other failure processes at ice cliffs is of critical importance to better constrain ice-sheet models and sea-level projections. Helheim Glacier, a tidewater glacier on Greenland’s eastern coast, terminates in an ice cliff ~100-m-tall behind a fjord choked with ice mélange. Icebergs calved at Helheim’s lightly grounded terminus are primarily nontabular bergs that rotate during calving, yet some wider tabular icebergs also calve and remain floating upright. Calving behavior is influenced by basal coupling and may be related to meltwater drainage processes. We utilize high-resolution satellite and time-lapse imagery to observe temporal variability in calving, terminus position, supraglacial meltwater pooling, and the surface expression of a buoyant meltwater plume at Helheim’s terminus from 2011-2019. The terminus position was relatively stable through 2016 despite seasonal advances and retreats, but in 2017 and 2019 Helheim retreated ~1.5 km beyond the most retreated positions of previous years. A surface meltwater lake filled and drained in most summers, typically followed by meltwater filling of down-glacier crevasses and the appearance of a buoyant plume in the mélange. We observed 200 calving episodes, 85% of which were nontabular. Of the 23 well-imaged plumes, only the April 2017 plume also coincided with a calving episode, when a tabular berg broke from the northern part of the terminus, well removed from the plume. Otherwise, calving generally ceased during plume surfacing despite crevassing and apparent slumping at the terminus. This observation and the generally consistent plume location from 2012-2019 suggest that the plume discharges from a well-established channelized drainage system and that plume appearance indicates a grounded glacial front. As the terminus becomes ungrounded, calving resumes and the plume disappears. Our results provide insight into a connection between meltwater drainage and full-thickness calving, and this relationship may exist at other lightly grounded outlet glaciers with significant surface melt. Helheim’s terminus behavior may also serve as an analogue to future processes at glacial margins currently buttressed by floating ice shelves, where warming ocean waters may lead to ice-shelf collapse and expose unstable ice cliffs.