The path-independent M integral implies the creep closure of englacial and subglacial channels

Drainage channels are essential components of englacial and subglacial hydrologic systems. Here we use the M integral, a path-independent integral of the equations of continuum mechanics for a class of media, to unify descriptions of creep closure under a variety of stress states surrounding drainage channels. The advantage of this approach is that the M integral around the hydrologic channels is identical to same integral evaluated in the far-field. In this way, the creep closure on the channel wall can be determined as a function of the far-field loading, e.g. involving antiplane shear as well as overburden pressure. We start by analyzing the axisymmetric case and show that the Nye solution for the creep closure of the channels is implied by the path-independence of the M integral. We then examine the effects of superimposing antiplane shear. We show that the creep closure of the channels acts as a perturbation in the far-field, which we explore analytically and numerically. In this way, the creep closure of channels can be succinctly written in terms of the pathindependent M integral and understanding the variation with applied shear is useful for glacial hydrology models.