UC San Diego

Iceberg calving accounts for two thirds of the mass discharged from the cryosphere to the ocean. Despite the prominent role that iceberg calving plays in the mass balance of ice sheets and glaciers, it remains one of the most poorly understood glaciological processes. Iceberg calving is preceded by the formation and propagation of fractures that sever the entire ice thickness. These fractures, known as rifts, can propagate for decades before an iceberg detaches. This dissertation presents results from three targeted field campaigns of geodetic and seismic measurements around the tip of a propagating rift on the Amery Ice Shelf, East Antarctica in 2002-03, 2004-05 and 2005-06. These observations are the first in situ measurements of rift propagation on an ice shelf. Chapter 1 provides the motivation and background that inspired a detailed study of ice shelf rifting. Chapter 2 presents results from the first field season where it was shown that rift propagation is episodic. In Chapter 3 the detailed seismic network that was installed over the following two field seasons was exploited to accurately map the spatial and temporal trends in seismicity. In Chapter 4 data from automatic weather stations were used in combination with field measurements to show that neither winds, ocean currents nor tides trigger rift propagation. In Chapter 5 we look at vertical deformation around the rift using data from both our global positioning system receivers and elevation profiles across the rift obtained from a satellite laser altimeter (ICESat). Using these two data sources, we show that the pattern of deformation along the rift walls is consistent with normal faulting. In Chapter 6 we derive an empirical non-dimensional stability parameter that predicts when unstable retreat of tidewater glaciers and ice shelves will occur. The stability parameter is validated using data from several Alaskan tidewater glaciers, two Greenland glaciers and three Antarctic ice shelves. Chapter 7 summarizes the work done and suggests directions for future research