Petermann is having an exceptional meltwater year and calving events, large and small, would come as no surprise. However it's been incorrectluy stated up-forum and elsewhere that the new central crack is an unprecedented crevasse and likely to lead to a massive tabular iceberg.
Actually there is no stress on the ice shelf here, either horizontally or from local buoyancy forces; the alignment angle cuts across meltwater drainages, and there's been no distortion of features on either side. It appeared last year in early July but has largely been stable since (2nd image, 01 Jun 17). This has nothing in common with the physics of hydro-fracturing of Antarctic glaciers at their grounded calving fronts.
The Petermann ice shelf has all sorts of deeply channeled bottom topography as seen by ice-penetrating radar; one of these has merely been eroded up to the surface and re-frozen at the waterline (~30m below ice shelf surface). There's another much older example of this below the eastern calving front that's been dormant for a decade or more.
The animation looks at TorB's terminal pair of cracks over the last 12 months. The first two frames are co-registered to sidewall rocks, ie as provided straight off the Sentinel-1AB site (best by whole-window screenshots). The third frame has the June 2016 ice advanced ~1200m so fixed features west (left) of the drainage channel co-register with the June 2017.
The fourth frame shows by differencing that that the left-central half of the ice sheet indeed moves as a rigid block. Geometric changes on the west side, largely induced by the ongoing collision with the incoming tributary glacier, are then effectively displayed relative to this moving lagrangian reference frame.
What happens next? Last year, after the annual ice in the upper fjord went away, a small piece in the NW corner broke off. There is a similar piece developing this year right at the junction of main ice shelf with tributary ice from much further south (2nd frame); that crack extends into the annual ice.
Alternatively, the much larger piece that Tor has highlighted could come apart, though the lower crack seems to have over-shot the vertical one instead of joining it.
At least 3 other 'traditional' cracks have developed over the last 12 months as the ice shelf has moved past stress-inducing shore features (that induce bends in the channel). These relieve stress on older fractures. Thus a big tabular event may happen at one of these, rather than rapid propagation at a now-dormant feature. The 2nd animation shows changes mid-sheet; note the much slower moving tributary ice along the shore.
While the main fracture is still growing, the direction of propagation is up-glacier rather than than across-glacier. Yet this can literally change overnight.
Whatever, big tabular bergs from floating ice shelves do not raise sea level and, unlike in Antarctica, will not significantly un-buttress Petermann nor speed up discharge of grounded glacier ice from the mainland.
