I continue to read such claims, without supporting evidence for the assertion. If the floating ice were providing significant impediment to the forward motion of the glacier, one would expect to observe compression features such as ridges or stacking of over-riding ice, as occurs in the Arctic from the wind blowing ice floes against the shore. Instead, one observes tension cracks, which usually facilitate calving. The upstream ice has significant ice-bedrock friction, and often undulating sub-ice topography that forces the ice to shear over obstructions. There is no question that the floating ice has significantly less friction than the land-based ice! At the speeds that a glacier moves, friction with water is negligible. Inertia is the primary characteristic. The ice has a momentum inherited from its down-slope travel. Once it begins floating, it no longer has any basal friction, which explains why tension cracks form. Newton’s First Law of Motion (modified slightly for this situation) states: “A body remains … in motion at a constant speed in a straight line, except insofar as it is acted upon by a force.” When a glacier leaves bedrock, the acceleration from gravity decreases, but the retarding force of friction also decreases. Therefore, the system that was formerly in balance now only has the forward momentum of the mass. Whereas, the glacial ice upstream is still under the influence of gravity, basal friction, and the force of the flowing ice at higher elevations.

I think that a thorough analysis of the glacier system will lead one to conclude that the claim of floating ice providing any buttressing effect is, if you will pardon the pun, without support.