The main force working on the glacier is the force of gravity (MG) on the flubber in the system.  The gravity forces the mass of flubber to flow downhill (down the plexiglass valley).  The opposing forces are that there is a resistance of the flubber on the plexiglass (Fp).  Then when the flubber reaches the water the friction at the base will lessen, and then as the flubber continues down the plexiglass and onto the base of the tub, there is additional friction (Ff) along the base of the glacier.  The other forces working on the system are the buoyancy force of the flubber (Fb) and the hydrostatic pressure (Hp) of the water keeping the flubber from expanding more than it has already.  This hydrostatic pressure is due to the displacement of the water by the flubber causing there to be a larger force due to the water because of the increase in the amount of flubber in the water. When running the model there is little vertical displacement of the water, but this is most likely due the fact that there is a large amount of salt water in the 80 x 45 x 12 cm container (36000 cubic cm of salt water) and not a significant amount of water is displaced.  This means that the hydrostatic pressure did not affect the flubber lobe until the lobe was significantly large.  Also the friction of the plexiglass changed as the flubber got to the water line where the flubber was then slowed down slightly even thought there was a decrease in the amount of friction at the base of the system.  Top

The cartoon on the left shows the velocity of the flubber at the boundary between the plexiglass and the free volume area.  In Time 1 there is a change in velocity as the depth of the flubber changes.  This leads to the top of the flubber column to move faster than the bottom and this is due to friction between the flubber and the plexiglass.  This leads to the shape of the flubber in the water to be curved as is seen in the cartoon.  The upward shaped curve is due to the buoyancy of the flubber in the salt water. Time 2 is right after the calving event.  When this happens there is a release of the hydrostatic pressure on the flubber.  In the system the velocity gradient becomes a strong factor on the system.  Because the top of the flubber is moving faster than the base the top of the flubber starts to over take the base of the flubber and it curves downward into the water.  Because of the velocity gradient there is a surge or acceleration of the flubber on the surface.  The side views of the fourth run from the fourth run are below.

This picture is taken from the final placement of the lobe in the second run of the flubber model.  This run did not have calving events.  This side view shows that the base of the flubber does not move as fast as the top.  This can be seen in the layered ellipsoids (same color layers) bending down into the water in the front part of the lobe that is produced by the flubber.  There is also a good view of the increase in the thickness of the flubber as the flubber goes down the plexiglass valley.  You can also see the affect of friction of the sides of the plexiglass on the flubber by the stretching of the flubber ellipsoid.

This picture is taken from the final placement of the lobe in the second run of the flubber model.  This run did not have caving events.  In this picture the change in the velocity gradient can be seen.  The blue layer of flubber at the plexiglass limit is not vertical like it should be if the flubber was moving at the same velocity.  The top of the blue column of flubber is further to the right than the rest of the column.  This is due to the top of the flubber column moving faster than the base of the column.  Top

Side view before first calving event	Side view after first calving event
In this picture the lobe of flubber is building in the typical shape with the flubber starting to float at the margin of the lobe.  The flubber is grounded at this stage with there being thickening of the flubber as it reaches the water.  In this picture the difference in the speed of the flubber from the top to the bottom can be seen by the change in the shape of the flubber as it goes further into the water.	In this picture the flubber has been cut at the edge of the plexiglass valley.  It can also be seen in this picture the uneven cutting of the flubber.  The top part of the freshly cut flubber lobe is already moving faster than the base of the flubber causing the top of the flubber to "fall" into the water and move downward and causing the flubber to thin vertically.
Side view before second calving event	Side view after second calving event
In this picture the flubber is completely grounded with little evidence for the change in the vertical velocity.  All of the flubber in this picture is grounded.	After the calving event there is an even stronger difference in the velocity due to the uneven shape of the flubber at the top of the flubber.
	This is the final side view of the flubber for this run.  In this picture the flubber shows that there was a change in the velocity gradient and that the buoyancy force was acting in this lobe.  The shape also shows that there was a thinning of the flubber as it went further into the water.  This shows evidence for the top of the flubber moving faster than the base of the flubber.  It can also be see by the bright pink flubber at the base of the lobe, where there was no pink flubber at the base of the flubber, because it was added later in the run at the top of the flubber glacier.  Top