Over time, this thickening must have resulted in the relatively elevated topography. This correlation strongly suggests that the present topography at the head of ice stream C was formed subsequent to shut-down of the ice stream trunk. The hydraulic potential gradient depends largely on surface slope, a quantity that is known to change over various time scales. Analysis of the hydraulic potential gradient is then relevant only to the time of surface slope measurement. C's stagnation were similar to those observed today.
Several observations made here argue against that assumption.
Such a trough would focus basal water along the ice stream rather than divert it to the sides. Second, when taking such a trough into account along with the estimated date of stagnation and the calculated thickening rate, the current surface topography at the head of ice stream C can be accounted for. Third, the observed correlation between ice speed and surface elevation is most easily explained by simple arguments of continuity. Tributaries C1 and C2 have continued to flow into the head of ice stream C despite stagnation of the ice stream trunk. The result has been thickening over time and the formation of a non-steady bulge in the surface topography.