A parameterization for the closure rate of canals incised in subglacial till

Many of Antarctica’s ice streams reside on deformable beds. The description of their basal
conditions is a major source of uncertainty in modeling studies attempting to predict their
response to a changing climate. The mechanics at the glacier bed, often divided into glacier
sliding and deformation of the subglacial sediments (so-called till), depend on the subglacial
water pressure and thus on the subglacial drainage. To understand the drainage system at
the ice-till interface, past works modeled the stability of channels incised in the till (so-called
canals). Such canals open due to erosion by water flow and close due to till creep and fluvial
deposition. Till rheology is a central point of discussion in these models.
The original description by Walder and Fowler (1994) of canals assumed a viscous rheology of
the subglacial till. Lab and field experiments show the subglacial till to be better described by
a plastic rheology. A recent study by one of the co-authors of this contribution implemented a
plastic rheology and showed that this leads to plastic behaviour of the canals’ closure, such as
rapid canal collapse when their size is too large for prevailing effective pressure.
In this contribution, we extend this latter model to parameterize the effect of till deformation
induced by glacier sliding on canal dynamics. Our results show the glacier sliding to drive
canal closure at all effective pressures. We describe this process with a closure rate that scales
linearly with the basal sliding velocity and is increasing non-linearly with both the effective
pressure and the canals size.
By controlling the canals’ closure, basal sliding thus impacts the drainage capacity, and in
turn, the subglacial water pressure. Thus the positive relation between the basal sliding speed
and canal closure could potentially be a mechanism leading to high sliding speeds, such as
found in ice streams.