This award supports a project to examine and test a 3-step process model for explosive ice-shelf disintegration that emerged in the wake of the recent 2008 and 2009 events of the Wilkins Ice Shelf. The model is conditioned on Summer melt-driven increase in free-surface water coupled with surface and basal crevasse density growth necessary to satisfy an "enabling condition". Once met, the collapse proceeds through three steps: (Step 1), calving of a "leading phalanx" of tabular icebergs from the seaward ice front of the ice shelf which creates in its wake a region, called a "mosh pit" (located between the phalanx and the edge of the intact ice shelf), where ocean surface-gravity waves are trapped by reflection (a fast mechanically enabled process), (Step 2), and a rapid, runaway conversion of gravitational potential energy into ocean-wave energy by iceberg capsize and fragmentation within the "mosh pit" which leads to further wave-induced calving, capsize and fragmentation (Step 3). The project will be conducted by a multidisciplinary team and will focus on theoretical model development, numerical method development and application and new observations. The project will participate in both the Research Experience for Undergraduates program in the Physics Department and the Summer Research Early Identification Program (SR-EIP) that fosters participation in research by underrepresented minorities. The PIs, postdoctoral scholar, graduate students and unfunded participants will develop a graduate-level seminar/tutorial to introduce advanced computational methods to glaciology. A postdoctoral scholar and graduate student will be trained in new research techniques during the project.
The research project explored a phenomena that was not previously well understood, but which has a potential important impact on global sea level: explosive ice-shelf disintegration. In 2002, the Larsen B Ice Shelf literally exploded into 1000's of small pieces over the period of a few days. This disintegration caused glaciers that fed the ice shelf to speed up, thereby moving ice from land into the ocean and causing a minute amount of sea level rise. By figuring out the physics of the explosive disintegration, we can help to assess whether the process is possible in other ice shelves of the Antarctic. The work we conducted showed that the energy source for the explosive break up of the Larsen B was the capsize of icebergs. When an iceberg capsizes, it releases gravitational potential energy, because ice moves up and water moves down, on average. This energy tends to be rather large, in the kilotonnes of TNT equivalent. Our work was conducted using a variety of techiques; however, one novel technique which we found extremely useful was to re-create iceberg capsize in at a laboratory scale using plastic for the ice. Additional contributions of our research include examining conditions under which ocean waves can penetrate ice shelves and thereby break them up into sufficiently small pieces so as to stimulate the iceberg capsize mechanism of energy release. This allows us to potentially predict the environmental conditions that enable ice-shelf disintegration. Our work has an impact on the discipline of scientific assessment of climate change. In particular, the most recent IPCC working group reports (AR5) indicate that ice-shelf instability may be a wild-card in assessing the risk of sea-level changes that are higher than about 1 m by 2100. Our work helps to reduce the uncertainty associated with predicting the impact and likelihood of ice-shelf instability.
