2015-2016 USAP Field Season
Impact of supraglacial lakes on ice-shelf stability
Dr. Douglas R MacAyeal
University of Chicago
Project Web Site:
Supporting Stations: McMurdo Station
Researchers on this project will work to establish a comprehensive theory of how ice shelves catastrophically disintegrate. The key research objectives are to characterize the energy balance and mechanical effects of natural meltwater lakes on the surface of the McMurdo Ice Shelf. The significance of the research is that it will attempt to experimentally verify a theory of ice-shelf instability recently proposed to explain the explosive break-up of Larsen B Ice Shelf in 2002. This theory holds that the filling and draining of supraglacial lakes on floating ice shelves induces sufficient flexure stress as to (a) induce upward/downward propagating fractures originating at the base/surface of the ice shelf that (b) can dissect the ice shelf into fragments of sufficiently small aspect ratio (horizontal to vertical scale ratio) as to promote extensive ice-shelf-fragment capsize during the break-up process (capsize releases gravitational potential energy and promotes explosiveness).
Field Season Overview
The first ("pilot") field season of activity is designed to objectively evaluate whether it is possible to build and maintain an artificial lake on the surface of the McMurdo Ice Shelf. If such a lake is found to be perennial, i.e., capable of surviving from year to year on its own, then its study will continue in future years as a means to observe processes of importance both to the future evolution of Antarctica's ice sheets in a cost-effective manner and to the technical aspects of maintaining runways at McMurdo Station.
A field team of 4 scientists will begin field activity by surveying the site proposed for building the artificial surface lake. The site survey will involve 3-5 days of optical and GPS surface topography measurements to develop a map of the ice-shelf surface elevation (and slope) within about a 1 km by 1 km area located somewhere NW of the Pegasus runway zone of exclusion. (It is necessary that our site, and roadways accessing our site not interfere with the regulations and mandates of the station's Pegasus Airfield.)
Following the site survey, the field team will assist and advise the USAP contractor to construct a 30 m by 30 m (by 2 m deep) surface basin using heavy machinery (e.g., earth moving machines). It is anticipated that this phase of field activity will last for 2-4 days (depending on preparation time). Lake construction will require keeping ice/snow removed to form the basin within a close proximity to the excavated basin (i.e., we envision the basin excavation to be done by "pushing" the loosened ice into a berm that forms the northern side of the basin). How this will be done will be developed by on-going consultations between the USAP contractor and the scientific team. One possible disposition of the snow and ice tailings will be to pile them into a berm that sits on the down-surface-gradient side of the artificial basin. We additionally desire shallow 2-3 m wide trenches to be dug (50 cm deep) on either side of the basin, extending some hundred to hundreds of meters form the basin, to present "catchment wings" that collect and channel any running surface water into the basin. Our goal is to fill the basin with running surface water that originates elsewhere to the south of the basin (e.g., runoff from the vicinity of Pegasus runway).
At the immediate conclusion of the basin construction phase, fresh water will be introduced into the basin. The goal of introducing water will be to flood the basin floor with between 50 cm and 100 cm of water. This water will "seed" the energy-balance characteristics of the basin so that it can continue to fill with meltwater due to solar loading.
Following the lake construction phase of the field activity. The field team will continue to conduct optical and GPS surveys through the approximately 1 km by 1 km region surrounding the basin, and will conduct preliminary electrical resistivity profiling to determine the response of the McM ice shelf to the lake. Additionally, a automatic weather station (AWS) will be placed within the lake on a tripod, mast or tower (potentially requiring some support from construction to optimize for a lake bottom footing) to monitor surface energy balance and weather conditions.
The field team anticipates remaining in the field after the lake is constructed for approximately 2-4 weeks while the summer melt season progresses. During this time, the field team expects to interact with the USAP engineers in their constant consideration of conditions on the Pegasus runway and surrounding infrastructure as a means of contributing to the USAP mission.
It is anticipated that the AWS will be left to winter over in the lake, and that it will be either removed (if the lake fails to re-open the following field season) or maintained after one full year of operation. At the conclusion of the winter-over period, the AWS units will either be maintained by the science team (e.g., should the "pilot study" be continued) or will be extracted by USAP station personnel in consultation with the science team (in the event that it does not deploy).
Deploying Team Members