Rifting and Calving Event in 2015 at Pine Island Glacier, West Antarctica, Associated with Frontal and Basal processes

Abstract:

Calving is a process that glacier loses its mass by full-thickness penetration of crevasses (i.e. rifting), followed by separation of iceberg from the terminus. Pine Island Glacier (PIG) in West Antarctica has undergone several major calving events including those in 2001, 2007 and 2013. All of them have started from rifting at its shear margin, growing toward the center of the ice shelf, and finally reaching the margin at the other end.

However, recent observation of PIG from remote sensing data affirms unprecedented pattern of rifting, that the rifts start to grow at the center of the ice shelf and expanding to the each ends of the shear margin. Moreover, this evolution was accompanied with incessant disintegration of ice melange (mixture of small icebergs and sea ice) filling the shear margin around the terminus. We found from Landsat 8 images that those rifts start from the troughs transverse to the ice shelf, which are surface features of basal crevasses (i.e. cracks at the bottom of ice shelf). We also analyzed velocity fields of PIG’s flow and confirmed that its change is consistent with the rifting and melange loss. We postulate this rifting event attributes to the associated effects of reduced resistant force by melange disintegration, and expedited erosion of basal crevasses that causes the tensile stress to concentrate. As both of them are closely related to ocean forcing, we also hypothesize that warmer ocean current under the ice shelf has triggered this new mode of rifting and calving event.