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.
This project examined the physical processes involved in the collapse of large ice shelves. Its major outcome was the determination that the energy used in their disintegration could be traced to capsizing of an ice block during its detachment from the larger ice structure; this work sheds light on the mechanism by which such processes can generate observable seismic waves, as well as hydrodynamic disturbances in the form of mini-tsunamis, which in turn can be used to detect cpasizing, and hence serve as harbingers of imminent disintegration. An additional important result was that ambient noise, as recorded by seismometers on a tabular iceberg in the absence of identifiable seismic sources such as earthquakes, could be used to study the structure (e.g., thickness) of the iceberg-water system. This technique thus offers a surface-based monitoring tool to investigate the evolution of that sturcture during the life of the iceberg, e.g., the thinning of the ice. Finally, we have studied the characteristics of acoustic waves generated inside icebergs and propagated to long distances in the oceanic water column, and shown tentatively that appopriate algorithms can be developed to effectively discriminate them from man-made explosions, a result of significance in the context of the verification of the Comprehensive Nuclear-Test Ban Treaty.
