Thank you for you astute questions, and while I may be assiduous, I am more of a student rather than an illuminator, of all matters Antarctic, but I will give the best responses that I can:
- First, I stated that Yuha's post was timely, because I believe that the warm CDW entering the PIG trough is actually protected by the presence of the sea ice; and the timing of the calving both confirms this (in my mind). Most researchers expect the rate of retreat of the PIG grounding line, GL, to slow as the GL approaches rougher bed conditions; however, if the buttressing action of the Pine Island Ice Shelf, PIIS, (part of which just calved) degrades fast enough, and if the advection of sufficiently warm CDW is strong enough then the GL will continue past the rough terrain that it is approaching.
- Second, I believe that the calving could have happened any time, but that it happened now because the advection of warm CDW cause: (a) sufficient basal ice melt of the local PIIS connecting to shore to weaken it so that; (b) hydrodynamic drag forces from the exiting current and tides, and internal ice stresses (thermal, flexural and shear) to exceed the crack propagation strength (and shear strength) of the local portion of the PIIS connection to the shore. You should realize that the PIIS is floating (except where it connects to the shore on one or typically both sides of the PIG trough). The grounded glacier is several kilometers upstream and thus while it continues to slide forward over bedrock and glacial till, its actions has little to do with the calving. Also, note that the velocity of the ice shelf is faster than the glacier's ice velocity, thus contributing to the thinning of the ice shelf from the GL out toward the face of the ice shelf. Let me know if you want more details on why the thin outer portion of the ice shelf calves when its internal strength (which weakens as it thins and warms from the CDW) is exceeded by the internal stresses on the ice shelf (significantly associated with the shear restraints from the shores while the center portion of the ice shelf is moving outward faster then the edges).
- Regarding the movement of the berg out of the bay, this is dependent on many factors, including: (a) the strength and directions of the currents (including advection from the salinity gradient of salty water flowing into the lower portion of the trough and fresher water flowing outward at the upper portion of the trough), eddies and tides; (b) storm-action, storm surge, winds and barometric pressure changes; (c) the presence and strength of adjoining sea ice; and (d) the nature of the grounding risks for the berg. If the berg does not clear the bay, then it may be possible for the PIIS to advance sufficiently to run into the grounded berg; which might temporarily slow the velocity of the ice shelf until the berg became un-grounded; but it is most likely that the berg will float out of the bay during the Austral Spring sea ice break-up.
You should also note that the Thwaites Ice Tongue surged in Sept. of 2012 (when there was still a lot of adjoining sea ice); and you may want to review some of my earlier posts in the "Surge" thread.
I hope that some of this is helpful. In any event it is a fascinating phenomenon to observe.